Electric power converting device

Abstract

The present invention addresses the problem of stopping zero voltage soft switching without pulse width modulation of a second control signal to each of a plurality of switches for zero voltage soft switching. In a first control operation, a control system (50) causes at least a portion of a high-level period of a second control signal to a switch (8) to overlap a dead time period set between a high-level period of a first control signal to a first switching element (1) and a high-level period of the first control signal to a second switching element (2). In a second control operation, the control system (50) shifts the high-level period of the second control signal to cause at least a portion of the high-level period of the second control signal to overlap the high-level period of the first control signal to a target switching element such that the overlapping period between the high-level period of the second control signal to be provided to each of a plurality of the switches (8) and the dead time period is shorter than in the case of the first control operation.

Description

Power Conversion Device

[0001] The present disclosure relates to a power conversion device, and more particularly to a power conversion device capable of converting DC power into AC power.

[0002] Patent Document 1 discloses a power conversion system.

[0003] The power conversion system (power conversion device) disclosed in Patent Document 1 includes a main switching means (power conversion circuit), two capacitors, one coil (resonant inductor), multiple auxiliary switching elements, and a controller. The main switching means is composed of a pair of main switching elements connected in series between both terminals of a DC power supply, and a main switching circuit is provided for each phase of the multi-phase AC, with the interconnection point of the pair of main switching elements serving as the output point for each phase. The two capacitors divide the voltage of the DC power supply. One end of the coil is connected to the voltage division point between the two capacitors. The multiple auxiliary switching elements connect the other end of the coil to the output points for each phase. The controller generates a control signal (first control signal) for PWM control of each main switching element and outputs it to the gate of each main switching element. The controller also generates a control signal (second control signal) for controlling the on / off of each auxiliary switching element and outputs it to the gate of each auxiliary switching element. When the controller determines that multiple phase currents flow through the coil, it controls the multiple auxiliary switch elements so that the current flowing through at least one phase is smaller than a preset value.

[0004] For example, in the power conversion system (power conversion device) disclosed in Patent Document 1, if it is predicted that the operating times of the auxiliary switches of two phases will collide, the controller sets the on time of the auxiliary switch element of one of the phases to zero and does not perform soft switching of that phase.

[0005] In a power conversion device, it may be desirable to stop the zero voltage soft switching of a switching element that is a target for zero voltage soft switching without pulse width modulating a control signal (second control signal) to each of a plurality of switches for zero voltage soft switching.

[0006] JP 2010-233306 A

[0007] An object of the present disclosure is to provide a power conversion device that can stop zero voltage soft switching without pulse width modulating a second control signal to each of a plurality of switches for zero voltage soft switching.

[0008] A power conversion device according to one aspect of the present disclosure includes a first DC terminal and a second DC terminal, a power conversion circuit, multiple AC terminals, multiple switches, multiple resonant capacitors, at least one resonant inductor, a regenerative capacitor, and a control system. The power conversion circuit includes multiple first switching elements and multiple second switching elements. In the power conversion circuit, multiple switching circuits, each of which has the multiple first switching elements and the multiple second switching elements connected in series in a one-to-one relationship, are connected in parallel to each other. In the power conversion circuit, the multiple first switching elements are connected to the first DC terminal. In the power conversion circuit, the multiple second switching elements are connected to the second DC terminal. The multiple AC terminals correspond one-to-one to the multiple switching circuits. Each of the multiple AC terminals is connected to a connection point between the first switching element and the second switching element in a corresponding one of the multiple switching circuits, through which a load current flows. The multiple switches correspond one-to-one to the multiple switching circuits. A first end of each of the plurality of switches is connected to the connection point between the first switching element and the second switching element in a corresponding switching circuit among the plurality of switching circuits. The plurality of resonant capacitors correspond one-to-one to the plurality of switches. Each of the plurality of resonant capacitors is connected between the first end and the second DC terminal of a corresponding switch among the plurality of switches. The at least one resonant inductor has a third end and a fourth end. The third end of the at least one resonant inductor is connected to the second end of the corresponding switch among the plurality of switches. The regenerative capacitor has a fifth end and a sixth end. The fifth end of the regenerative capacitor is connected to the second DC terminal, and the sixth end is connected to the fourth end of the at least one resonant inductor.The control system provides a first control signal, the potential of which changes between a high level and a low level, to each of the plurality of first switching elements and the plurality of second switching elements, and a second control signal, the potential of which changes between a high level and a low level, to each of the plurality of switches. The control system is capable of executing a first control operation and a second control operation when changing the first control signal to a target switching element to be turned on, of the first switching element or the second switching element, from a low level to a high level in each of the plurality of switching circuits. In the first control operation, the control system causes at least a part of a high-level period of the second control signal to a switch of the plurality of switches corresponding to each of the plurality of switching circuits to overlap with a dead time period set for each of the plurality of switching circuits between a high-level period of the first control signal to the first switching element and a high-level period of the first control signal to the second switching element. In the second control operation, the control system shifts the high-level period of the second control signal so that the overlap period between the high-level period of the second control signal applied to each of the plurality of switches and the dead time period is shorter than in the first control operation, thereby making at least a part of the high-level period of the second control signal overlap with the high-level period of the first control signal to the target switching element.

[0009] FIG. 1 is a circuit diagram of a system including a power conversion device according to a first embodiment. FIG. 2 is a diagram illustrating time variations in duty and load current corresponding to voltage commands for each of three phases in an AC load connected to multiple AC terminals of the power conversion device. FIG. 3 is a timing chart illustrating the operation of the power conversion device according to the first embodiment. FIG. 4 is a timing chart illustrating the operation of a power conversion device according to a second embodiment. FIG. 5 is a circuit diagram of a system including a power conversion device according to a third embodiment. FIG. 6 is a circuit block diagram of a signal generating circuit in the power conversion device according to the first embodiment. FIG. 7 is a timing chart illustrating the operation of the power conversion device according to the third embodiment. FIG. 8 is an explanatory diagram illustrating the operation of the power conversion device according to the first embodiment during a first period. FIG. 9 is an explanatory diagram illustrating the operation of the power conversion device according to the second period. FIG. 10 is an explanatory diagram illustrating the operation of the power conversion device according to the third period. FIG. 11 is an explanatory diagram illustrating the operation of the power conversion device according to the first embodiment during a high load. FIG. 12 is an explanatory diagram illustrating the operation of the power conversion device according to the first embodiment during a low load. FIG. 13 is an explanatory diagram illustrating the operation of the power conversion device according to the first embodiment during no load. FIG. 14 is a timing chart illustrating another operation of the power conversion device of the same. FIG. 15 is a timing chart illustrating the operation of the power conversion device according to the fourth embodiment. FIG. 16 is an explanatory diagram of the operation of the power conversion device of the same. FIG. 17 is a circuit diagram of a system including the power conversion device of the fifth embodiment. FIG. 18 is a timing chart illustrating an example of a boundary condition between a case where currents flowing through the resonant inductors in the same power conversion device do not overlap (do not flow simultaneously) and a case where they overlap (flow simultaneously). FIG. 19 is a timing chart illustrating an example of a boundary condition between a case where the U-phase resonant current and the V-phase resonant current do not overlap (do not flow simultaneously) and a case where they overlap (flow simultaneously) in the same power conversion device. FIG. 20 is a timing chart illustrating the operation of the same power conversion device. FIG. 21 is a timing chart illustrating the operation of the power conversion device according to the sixth embodiment. FIG. 22 is a timing chart illustrating the operation of the power conversion device according to the seventh embodiment. FIG. 23 is a timing chart illustrating the operation of the power conversion device according to the eighth embodiment.FIG. 24 is a timing chart for explaining the operation of the power conversion apparatus according to the ninth embodiment. FIG. 25 is a timing chart for explaining the operation of the power conversion apparatus according to the ninth embodiment. FIG. 26 is a timing chart for explaining the operation of the power conversion apparatus according to the tenth embodiment. FIG. 27 is a timing chart for explaining the operation of the power conversion apparatus according to the tenth embodiment. FIG. 28 is a timing chart for explaining the operation of the power conversion apparatus according to the eleventh embodiment. FIG. 29 is a timing chart for explaining the operation of the power conversion apparatus according to the twelfth embodiment. FIG. 30 is a timing chart for explaining the operation of the power conversion apparatus according to the thirteenth embodiment. FIG. 31 is a timing chart for explaining the operation of the power conversion apparatus according to the fourteenth embodiment. FIG. 32 is a timing chart for explaining the operation of the power conversion apparatus according to the fifteenth embodiment. FIG. 33 is a timing chart for explaining the operation of the power conversion apparatus according to the eighteenth embodiment. FIG. 34 is a timing chart for explaining the operation of the power conversion apparatus according to the sixteenth embodiment. FIG. 35 is a timing chart for explaining the operation of the power conversion apparatus according to the seventeenth embodiment. FIG. 36 is a timing chart for explaining the operation of the power conversion apparatus according to the eighteenth embodiment. FIG. 37 is a timing chart for explaining the operation of the power conversion apparatus according to the nineteenth embodiment. FIG. 38 is a timing chart for explaining the operation of the power conversion apparatus according to the twentieth embodiment. FIG. 39 is a timing chart for explaining the operation of the power conversion apparatus according to the twenty-first embodiment. FIG. 40 is a timing chart for explaining the operation of the power conversion apparatus according to the twenty-second embodiment. FIG. 41 is a timing chart for explaining the operation of the power conversion apparatus according to the twenty-third embodiment. FIG. 42 is a circuit diagram of a system including the power conversion apparatus according to the twenty-fourth embodiment. FIG. 43 is a circuit diagram of a system including the power conversion apparatus according to the twenty-fifth embodiment. FIG. 44 is a circuit diagram of a system including the power conversion apparatus according to the twenty-sixth embodiment. FIG. 45 is a circuit diagram of a system including the power conversion apparatus according to the twenty-seventh embodiment. FIG. 46 is a circuit diagram of a system including the power conversion apparatus according to the twenty-eighth embodiment. FIG. 47 is a circuit diagram of a system including the power conversion apparatus according to the twenty-ninth embodiment.Fig. 48 is a circuit diagram of a system including a power conversion device according to embodiment 30. Fig. 49 is a circuit diagram of a system including a power conversion device according to embodiment 31.

[0010] First Embodiment A power conversion device 100 according to a first embodiment will be described below with reference to FIGS. 1 to 3. FIG.

[0011] (1) Overall Configuration of the Power Conversion Device As shown in FIG. 1 , the power conversion device 100 includes a first DC terminal 31, a second DC terminal 32, and multiple (e.g., three) AC terminals 41. A DC power source E1 is connected between the first DC terminal 31 and the second DC terminal 32, and an AC load RA1 is connected to the multiple AC terminals 41. The AC load RA1 is, for example, a three-phase servo motor. The power conversion device 100 converts DC output from the DC power source E1 into AC power and outputs it to the AC load RA1. The DC power source E1 includes, for example, a solar cell or a fuel cell. The DC power source E1 may also include a DC-DC converter. In the power conversion device 100, when the multiple AC terminals 41 are three AC terminals 41, the AC power is, for example, three-phase AC power having a U phase, a V phase, and a W phase.

[0012] The power conversion device 100 includes a power conversion circuit 11, a plurality of (e.g., three) switches 8, a plurality of (e.g., three) resonant capacitors 9, a plurality of (e.g., three) resonant inductors L1, a regenerative capacitor 15, and a control system 50. Each of the plurality of switches 8 is, for example, a bidirectional switch. The power conversion device 100 also includes a plurality of (e.g., three) first clamp diodes 13 and a plurality of (e.g., three) second clamp diodes 14.

[0013] The power conversion circuit 11 has a plurality of (e.g., three) first switching elements 1 and a plurality of (e.g., three) second switching elements 2. In the power conversion circuit 11, a plurality of (e.g., three) switching circuits 10, each having a plurality of first switching elements 1 and a plurality of second switching elements 2 connected in series in a one-to-one relationship, are connected in parallel to each other. In the power conversion circuit 11, the plurality of first switching elements 1 are connected to first DC terminals 31, and the plurality of second switching elements 2 are connected to second DC terminals 32.

[0014] The plurality of AC terminals 41 correspond one-to-one to the plurality of switching circuits 10. Each of the plurality of AC terminals 41 is connected to a connection point 3 of the first switching element 1 and the second switching element 2 in the corresponding switching circuit 10.

[0015] The multiple switches 8 correspond one-to-one to the multiple switching circuits 10. Each of the multiple switches 8 has a first end 81 and a second end 82. The first end 81 of each of the multiple switches 8 is connected to a connection point 3 between a first switching element 1 and a second switching element 2 in a corresponding one of the multiple switching circuits 10.

[0016] The plurality of resonance capacitors 9 correspond one-to-one to the plurality of switches 8. Each of the plurality of resonance capacitors 9 is connected between the first end 81 of the corresponding switch 8 among the plurality of switches 8 and the second DC terminal 32.

[0017] Each of the plurality of resonance inductors L1 has a third end and a fourth end. The third end of each of the plurality of resonance inductors L1 is connected to the second end 82 of a corresponding one of the plurality of switches 8.

[0018] The regenerative capacitor 15 has a fifth end 153 and a sixth end 154. In the regenerative capacitor 15, the fifth end 153 is connected to the second DC terminal 32, and the sixth end 154 is connected to the fourth end of each of the plurality of resonant inductors L1.

[0019] The control system 50 provides a first control signal to each of the plurality of first switching elements 1 and the plurality of second switching elements 2. The control system 50 also provides a second control signal to each of the plurality of switches 8.

[0020] (2) Details of the Power Conversion Device Hereinafter, for convenience of explanation, the switching circuits 10 corresponding to the U phase, V phase, and W phase of the multiple switching circuits 10 may be referred to as switching circuit 10U, switching circuit 10V, and switching circuit 10W, respectively. Hereinafter, the first switching element 1 and the second switching element 2 of switching circuit 10U may be referred to as first switching element 1U and second switching element 2U. Hereinafter, the first switching element 1 and the second switching element 2 of switching circuit 10V may be referred to as first switching element 1V and second switching element 2V. Hereinafter, the first switching element 1 and the second switching element 2 of switching circuit 10W may be referred to as first switching element 1W and second switching element 2W. In the following, the connection point 3 between the first switching element 1U and the second switching element 2U will be referred to as connection point 3U, the connection point 3 between the first switching element 1V and the second switching element 2V will be referred to as connection point 3V, and the connection point 3 between the first switching element 1W and the second switching element 2W will be referred to as connection point 3W. In the following, the AC terminal 41 connected to connection point 3U will be referred to as AC terminal 41U, the AC terminal 41 connected to connection point 3V will be referred to as AC terminal 41V, and the AC terminal 41 connected to connection point 3W will be referred to as AC terminal 41W. In the following, the resonant capacitor 9 connected in parallel to the second switching element 2U will be referred to as resonant capacitor 9U, the resonant capacitor 9 connected in parallel to the second switching element 2V will be referred to as resonant capacitor 9V, and the resonant capacitor 9 connected in parallel to the second switching element 2W will be referred to as resonant capacitor 9W. In the following, the switch 8 connected to connection point 3U may be referred to as switch 8U, the switch 8 connected to connection point 3V may be referred to as switch 8V, and the switch 8 connected to connection point 3W may be referred to as switch 8W.

[0021] In the power conversion device 100, for example, a high-potential output terminal (positive electrode) of the DC power supply E1 is connected to the first DC terminal 31, and a low-potential output terminal (negative electrode) of the DC power supply E1 is connected to the second DC terminal 32. In addition, in the power conversion device 100, for example, a U-phase terminal, a V-phase terminal, and a W-phase terminal of the AC load RA1 are connected to three AC terminals 41U, 41V, and 41W, respectively.

[0022] In the power conversion circuit 11, each of a plurality of (three in the example of FIG. 1 ) first switching elements 1 and a plurality of (three in the example of FIG. 1 ) second switching elements 2 has a control terminal, a first main terminal, and a second main terminal. The control terminals of the plurality of first switching elements 1 and the plurality of second switching elements 2 are connected to a control system 50. In each of the plurality of switching circuits 10 of the power conversion device 100, a first main terminal of the first switching element 1 is connected to a first DC terminal 31, a second main terminal of the first switching element 1 is connected to a first main terminal of the second switching element 2, and a second main terminal of the second switching element 2 is connected to a second DC terminal 32. In each of the plurality of switching circuits 10, the first switching element 1 is a high-side switching element (P-side switching element), and the second switching element 2 is a low-side switching element (N-side switching element). Each of the plurality of first switching elements 1 and the plurality of second switching elements 2 is, for example, an IGBT (Insulated Gate Bipolar Transistor). Therefore, the control terminal, the first main terminal and the second main terminal of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 are the gate terminal, the collector terminal and the emitter terminal, respectively.

[0023] The power conversion circuit 11 further includes a plurality of (three) first diodes 4 connected in anti-parallel to the plurality of (three) first switching elements 1 in a one-to-one relationship, and a plurality of (three) second diodes 5 connected in anti-parallel to the plurality of (three) second switching elements 2 in a one-to-one relationship. In each of the plurality of first diodes 4, the anode of the first diode 4 is connected to the second main terminal (emitter terminal) of the first switching element 1 corresponding to the first diode 4, and the cathode of the first diode 4 is connected to the first main terminal (collector terminal) of the first switching element 1 corresponding to the first diode 4. In each of the plurality of second diodes 5, the anode of the second diode 5 is connected to the second main terminal (emitter terminal) of the second switching element 2 corresponding to the second diode 5, and the cathode of the second diode 5 is connected to the first main terminal (collector terminal) of the second switching element 2 corresponding to the second diode 5.

[0024] A connection point 3U between the first switching element 1U and the second switching element 2U is connected to, for example, a U-phase terminal of an AC load RA1 via an AC terminal 41U. A connection point 3V between the first switching element 1V and the second switching element 2V is connected to, for example, a V-phase terminal of the AC load RA1 via an AC terminal 41V. A connection point 3W between the first switching element 1W and the second switching element 2W is connected to, for example, a W-phase terminal of the AC load RA1 via an AC terminal 41W.

[0025] The plurality of resonant capacitors 9 correspond one-to-one to the plurality of switches 8. Each of the plurality of resonant capacitors 9 is connected between the first end 81 and the second DC terminal 32 of the corresponding switch 8. The power conversion device 100 has a plurality of resonant circuits. Each of the plurality of resonant circuits includes a resonant capacitor 9 and a resonant inductor L1.

[0026] Each of the multiple switches 8 has a third switching element 6 and a fourth switching element 7. Each of the multiple (three in the example of FIG. 1 ) third switching elements 6 and the multiple (three in the example of FIG. 1 ) fourth switching elements 7 has a control terminal, a first main terminal, and a second main terminal. The control terminals of the multiple third switching elements 6 and the multiple fourth switching elements 7 are connected to the control system 50. Each of the multiple third switching elements 6 and the multiple fourth switching elements 7 is, for example, an IGBT. Therefore, the control terminal, the first main terminal, and the second main terminal of each of the multiple third switching elements 6 and the multiple fourth switching elements 7 are a gate terminal, a collector terminal, and an emitter terminal, respectively. In each of the multiple switches 8, the third switching element 6 and the fourth switching element 7 are connected in anti-series. In each of the multiple switches 8, the first main terminal (collector terminal) of the third switching element 6 and the first main terminal (collector terminal) of the fourth switching element 7 are connected. In each of the switches 8, the second main terminal (emitter terminal) of the third switching element 6 is connected to the connection point 3 of a corresponding one of the switching circuits 10, and the second main terminal (emitter terminal) of the fourth switching element 7 is connected to the resonance inductor L1. Each of the switches 8 further includes a diode 61 connected in anti-parallel to the third switching element 6 and a diode 71 connected in anti-parallel to the fourth switching element 7.

[0027] In the power conversion device 100, the switch 8U is connected to a connection point 3U between the first switching element 1U and the second switching element 2U. The switch 8V is connected to a connection point 3V between the first switching element 1V and the second switching element 2V. The switch 8W is connected to a connection point 3W between the first switching element 1W and the second switching element 2W. Hereinafter, for convenience of explanation, the third switching element 6 and the fourth switching element 7 of the switch 8U will be referred to as the third switching element 6U and the fourth switching element 7U, the third switching element 6 and the fourth switching element 7 of the switch 8V will be referred to as the third switching element 6V and the fourth switching element 7V, and the third switching element 6 and the fourth switching element 7 of the switch 8W will be referred to as the third switching element 6W and the fourth switching element 7W, respectively.

[0028] The multiple switches 8 are controlled by the control system 50. In other words, the third switching element 6U, the fourth switching element 7U, the third switching element 6V, the fourth switching element 7V, the third switching element 6W, and the fourth switching element 7W are controlled by the control system 50.

[0029] Each of the multiple resonant inductors L1 has a third end and a fourth end. The third end of the resonant inductor L1 is connected to the second ends 82 of the multiple switches 8. In the first embodiment, the third end of each of the multiple resonant inductors L1 is connected to the second end 82 of a corresponding one of the multiple switches 8. The fourth end of the resonant inductor L1 is connected to the sixth end 154 of the regenerative capacitor 15.

[0030] The regenerative capacitor 15 is connected between the fourth end of the resonance inductor L1 and the second DC terminal 32. The regenerative capacitor 15 is, for example, a film capacitor.

[0031] In this embodiment, the control system 50 includes a control device 51, a plurality (three) of first gate drive circuits (not shown), a plurality (three) of second gate drive circuits (not shown), a plurality of third gate drive circuits (not shown), and a plurality (three) of fourth gate drive circuits (not shown). The plurality of first gate drive circuits correspond one-to-one to the plurality of first switching elements 1. The plurality of second gate drive circuits correspond one-to-one to the plurality of second switching elements 2. The plurality of third gate drive circuits correspond one-to-one to the plurality of third switching elements 6. The plurality of fourth gate drive circuits correspond one-to-one to the plurality of fourth switching elements 7.

[0032] The first control signal SU1 output from the control device 51 is provided to the first switching element 1U via one of the plurality of first gate drive circuits that corresponds to the first switching element 1U. The first control signal SV1 output from the control device 51 is provided to the first switching element 1V via one of the plurality of first gate drive circuits that corresponds to the first switching element 1V. The first control signal SW1 output from the control device 51 is provided to the first switching element 1W via one of the plurality of first gate drive circuits that corresponds to the first switching element 1W.

[0033] The first control signal SU2 output from the control device 51 is provided to the second switching element 2U via one of the plurality of second gate drive circuits that corresponds to the second switching element 2U. The first control signal SV2 output from the control device 51 is provided to the second switching element 2V via one of the plurality of second gate drive circuits that corresponds to the second switching element 2V. The first control signal SW2 output from the control device 51 is provided to the second switching element 2W via one of the plurality of second gate drive circuits that corresponds to the second switching element 2W.

[0034] The second control signal SU6 output from the control device 51 is provided to the third switching element 6U via one of the plurality of third gate drive circuits that corresponds to the third switching element 6U. The second control signal SV6 output from the control device 51 is provided to the third switching element 6V via one of the plurality of third gate drive circuits that corresponds to the third switching element 6V. The second control signal SW6 output from the control device 51 is provided to the third switching element 6W via one of the plurality of third gate drive circuits that corresponds to the third switching element 6W.

[0035] The second control signal SU7 output from the control device 51 is provided to the fourth switching element 7U via one of the plurality of fourth gate drive circuits that corresponds to the fourth switching element 7U. The second control signal SV7 output from the control device 51 is provided to the fourth switching element 7V via one of the plurality of fourth gate drive circuits that corresponds to the fourth switching element 7V. The second control signal SW7 output from the control device 51 is provided to the fourth switching element 7W via one of the plurality of fourth gate drive circuits that corresponds to the fourth switching element 7W.

[0036] The control device 51 controls a plurality of first switching elements 1 and a plurality of second switching elements 2. The control device 51 includes a computer system. The computer system is primarily composed of a processor and a memory as hardware. The processor executes a program recorded in the memory of the computer system to realize the functions of the control device 51 in the present disclosure. The processor of the computer system is composed of one or more electronic circuits including a semiconductor integrated circuit (IC) or a large-scale integrated circuit (LSI). The integrated circuits, such as ICs and LSIs, are referred to by different names depending on the degree of integration, and include integrated circuits called system LSIs, very large-scale integrations (VLSIs), or ultra-large-scale integrations (ULSIs). Furthermore, field-programmable gate arrays (FPGAs), which are programmed after the LSI is manufactured, or logic devices that can reconfigure the connections within the LSI or reconfigure the circuit partitions within the LSI, can also be used as processors. The electronic circuits may be integrated into a single chip or distributed across multiple chips. The multiple chips may be integrated into one device or distributed across multiple devices. The computer system referred to here includes a microcontroller having one or more processors and one or more memories. Therefore, the microcontroller is also composed of one or more electronic circuits including semiconductor integrated circuits or large-scale integrated circuits.

[0037] The control device 51 outputs first control signals SU1, SV1, and SW1 that control the on / off states of the multiple first switching elements 1U, 1V, and 1W, respectively. Each of the first control signals SU1, SV1, and SW1 is, for example, a PWM (Pulse Width Modulation) signal whose potential level changes between a first potential level (hereinafter also referred to as a low level) and a second potential level (hereinafter also referred to as a high level) that is higher than the first potential level. The first switching elements 1U, 1V, and 1W are turned on when the first control signals SU1, SV1, and SW1 are at a high level, and turned off when the first control signals SU1, SV1, and SW1 are at a low level. The control device 51 also outputs first control signals SU2, SV2, and SW2 that control the on / off states of the multiple second switching elements 2U, 2V, and 2W, respectively. Each of the first control signals SU2, SV2, and SW2 is, for example, a PWM signal whose potential level changes between a first potential level (hereinafter also referred to as a low level) and a second potential level (hereinafter also referred to as a high level) that is higher than the first potential level. The second switching elements 2U, 2V, and 2W are turned on when the first control signals SU2, SV2, and SW2 are at a high level, and turned off when the first control signals SU2, SV2, and SW2 are at a low level.

[0038] The control device 51 uses a sawtooth-wave carrier signal to generate first control signals SU1, SV1, SW1 corresponding to the multiple first switching elements 1U, 1V, and 1W, respectively, and first control signals SU2, SV2, and SW2 corresponding to the multiple second switching elements 2U, 2V, and 2W, respectively. More specifically, the control device 51 generates the first control signals SU1 and SU2 to be applied to the first switching element 1U and the second switching element 2U, respectively, based on at least the carrier signal and a U-phase voltage command. The control device 51 also generates the first control signals SV1 and SV2 to be applied to the first switching element 1V and the second switching element 2V, respectively, based on at least the carrier signal and a V-phase voltage command. The control device 51 also generates the first control signals SW1 and SW2 to be applied to the first switching element 1W and the second switching element 2W, respectively, based on at least the carrier signal and a W-phase voltage command. The U-phase voltage command, V-phase voltage command, and W-phase voltage command are, for example, sinusoidal signals whose phases differ by 120°, and whose values ​​(voltage command values) change over time. Note that the waveform of the carrier signal is not limited to a sawtooth waveform and may be, for example, a triangular wave. The U-phase voltage command, V-phase voltage command, and W-phase voltage command each have the same length per cycle. The U-phase voltage command, V-phase voltage command, and W-phase voltage command each have a longer length per cycle than the carrier signal.

[0039] The duty of the first control signals SU1 and SU2 provided by the control device 51 to the first switching element 1U and the second switching element 2U, respectively, varies based on the U-phase voltage command. In FIG. 2, the duty of the first control signal SU1 is shown as the U-phase duty. The control device 51 (see FIG. 1) compares the U-phase voltage command with a carrier signal to generate the first control signal SU1 provided to the first switching element 1U. The control device 51 also inverts the first control signal SU1 provided to the first switching element 1U to generate the first control signal SU2 provided to the second switching element 2U. The control device 51 also sets a dead time period between the high-level period of the first control signal SU1 and the high-level period of the first control signal SU2 so that the on-periods of the first switching element 1U and the second switching element 2U do not overlap.

[0040] The duty of the first control signals SV1 and SV2 provided by the control device 51 to the first switching element 1V and the second switching element 2V, respectively, varies based on the V-phase voltage command. In FIG. 2, the duty of the first control signal SV1 is shown as the V-phase duty. The control device 51 (see FIG. 1) compares the V-phase voltage command with a carrier signal to generate the first control signal SV1 provided to the first switching element 1V. The control device 51 also inverts the first control signal SV1 provided to the first switching element 1V to generate the first control signal SV2 provided to the second switching element 2V. The control device 51 also sets a dead time period between the high-level period of the first control signal SV1 and the high-level period of the first control signal SV2 so that the on periods of the first switching element 1V and the second switching element 2V do not overlap.

[0041] The duties of the first control signals SW1 and SW2 provided by the control device 51 to the first switching element 1W and the second switching element 2W, respectively, vary based on the W-phase voltage command. In FIG. 2, the duty of the first control signal SW1 is shown as the W-phase duty. The control device 51 (see FIG. 1) compares the W-phase voltage command with a carrier signal to generate the first control signal SW1 to be provided to the first switching element 1W. The control device 51 also inverts the first control signal SW1 to be provided to the first switching element 1W to generate the first control signal SW2 to be provided to the second switching element 2W. The control device 51 also sets a dead time period between the high-level period of the first control signal SW1 and the high-level period of the first control signal SW2 so that the on periods of the first switching element 1W and the second switching element 2W do not overlap.

[0042] The U-phase voltage command, V-phase voltage command, and W-phase voltage command are, for example, sinusoidal signals whose phases are different from each other by 120°, and whose values ​​change over time. Therefore, the duty of the first control signal SU1 (U-phase duty), the duty of the first control signal SV1 (V-phase duty), and the duty of the first control signal SW1 (W-phase duty) change like sinusoidal waves whose phases are different from each other by 120°, as shown in FIG. 2 . Similarly, the duty of the first control signal SU2, the duty of the first control signal SV2, and the duty of the first control signal SW2 change like sinusoidal waves whose phases are different from each other by 120°.

[0043] The control device 51 generates the first control signals SU1, SU2, SV1, SV2, SW1, and SW2 based on the carrier signal, the voltage commands, and information about the state of the AC load RA1. For example, if the AC load RA1 is a three-phase servo motor, the information about the state of the AC load RA1 includes, for example, detection values ​​from a plurality of current sensors that detect output currents (hereinafter also referred to as load currents) iU, iV, and iW flowing through the U-phase, V-phase, and W-phase of the AC load RA1, respectively.

[0044] The plurality of switches 8, the resonant inductor L1, the plurality of resonant capacitors 9, and the regenerative capacitor 15 are provided to perform zero-voltage soft switching of the plurality of first switching elements 1 and the plurality of second switching elements 2.

[0045] When the third switching element 6U is in the ON state and the fourth switching element 7U is in the OFF state, the switch 8U allows a charging current to pass through the path of the regenerative capacitor 15-resonant inductor L1-switch 8U-resonant capacitor 9U. The charging current is a current that charges the resonant capacitor 9U. When the third switching element 6U is in the OFF state and the fourth switching element 7U is in the ON state, the switch 8U allows a discharging current to pass through the path of the resonant capacitor 9U-switch 8U-resonant inductor L1-regenerative capacitor 15. The discharging current is a current that discharges the charge in the resonant capacitor 9U.

[0046] When the third switching element 6V is in the ON state and the fourth switching element 7V is in the OFF state, the switch 8V allows a charging current to pass through the path of the regenerative capacitor 15-resonant inductor L1-switch 8V-resonant capacitor 9V. The charging current is a current that charges the resonant capacitor 9V. When the third switching element 6V is in the OFF state and the fourth switching element 7V is in the ON state, the switch 8V allows a discharging current to pass through the path of the resonant capacitor 9V-switch 8V-resonant inductor L1-regenerative capacitor 15. The discharging current is a current that discharges the charge of the resonant capacitor 9V.

[0047] When the third switching element 6W is in the ON state and the fourth switching element 7W is in the OFF state, the switch 8W allows a charging current to pass through the path of the regenerative capacitor 15 - resonant inductor L1 - switch 8W - resonant capacitor 9W. The charging current is a current that charges the resonant capacitor 9W. When the third switching element 6W is in the OFF state and the fourth switching element 7W is in the ON state, the switch 8W allows a discharging current to pass through the path of the resonant capacitor 9W - switch 8W - resonant inductor L1 - regenerative capacitor 15. The discharging current is a current that discharges the charge in the resonant capacitor 9W.

[0048] The dead time period is a period set between the high-level period of the first control signal to the first switching element 1 and the high-level period of the first control signal to the second switching element 2 for each of the multiple switching circuits 10. This period is a period during which both the first control signal to the first switching element 1 and the first control signal to the second switching element 2 are low so that the on-periods of the first switching element 1 and the second switching element 2 do not overlap (i.e., there is no period during which both the first switching element 1 and the second switching element 2 are on). In this embodiment, for example, the length of the resonant half cycle corresponding to each of the multiple switches 8 is designed according to the length of the dead time period of each of the multiple switching circuits 10. The resonant half cycle is half the resonant cycle, which is the reciprocal of the resonant frequency of the resonant circuit including one switch 8, one resonant inductor L1, and one resonant capacitor 9. Therefore, when the inductance of the resonant inductor L1 is L and the capacitance of the resonant capacitor 9 is C, the resonant half cycle is expressed as π×(L·C) １／２ The length of the resonance half cycle is set to be the same as the length of the dead time period, for example.

[0049] The length of the resonant half cycle of the resonant circuit including the resonant inductor L1 and the resonant capacitor 9U is set, for example, to the length of the dead time period set between the high-level period of the first control signal SU1 and the high-level period of the first control signal SU2. The length of the resonant half cycle of the resonant circuit including the resonant inductor L1 and the resonant capacitor 9V is set, for example, to the length of the dead time period set between the high-level period of the first control signal SV1 and the high-level period of the first control signal SV2. The length of the resonant half cycle of the resonant circuit including the resonant inductor L1 and the resonant capacitor 9W is set, for example, to the length of the dead time period set between the high-level period of the first control signal SW1 and the high-level period of the first control signal SW2.

[0050] If the resonant period is Tres, then Tres / 2, which is the resonant half period, is the length of the dead time period. The end of the resonant half period preferably coincides with the end of the dead time period for the switching circuit 10 corresponding to the switch 8.

[0051] The length of the above-mentioned resonance half cycle is an ideal design example, and may be 90% or more and 110% or less of the length of the dead time period. The resonance half cycle and the dead time period may have different lengths.

[0052] Each of the multiple first clamp diodes 13 corresponds one-to-one to the multiple resonance inductors L1. The anode of each first clamp diode 13 is connected to the third end of the corresponding resonance inductor L1, and the cathode is connected to the first DC terminal 31. Furthermore, each of the multiple second clamp diodes 14 corresponds one-to-one to the multiple resonance inductors L1. The cathode of each second clamp diode 14 is connected to the third end of the corresponding resonance inductor L1, and the anode is connected to the second DC terminal 32.

[0053] In the first embodiment, the length of the high level period of the second control signal to each of the multiple switches 8 is longer than the length of the dead time period.

[0054] (3) Operation of the Power Conversion Device In the following description, the polarity of current iL1 flowing through resonant inductor L1 will be defined as positive when flowing in the direction of the arrow in Fig. 1, and as negative when flowing in the direction opposite to the direction of the arrow in Fig. 1. Also, in the following description, the polarity of load currents iU, iV, and iW flowing through the U, V, and W phases of AC load RA1 will be defined as positive when flowing in the direction of the arrow in Fig. 1, and as negative when flowing in the direction opposite to the direction of the arrow in Fig. 1. Also, in the following description, the polarity of currents i9U, i9V, and i9W flowing through resonant capacitors 9U, 9V, and 9W will be defined as positive when flowing in the direction of the arrow in Fig. 1, and as negative when flowing in the direction opposite to the direction of the arrow in Fig. 1. Therefore, in the case of a discharge operation in which the resonant capacitors 9U, 9V, and 9W are discharged, the polarity of the currents i9U, i9V, and i9W is positive, and in the case of a charge operation in which the resonant capacitors 9U, 9V, and 9W are charged, the polarity of the currents i9U, i9V, and i9W is negative.

[0055] Hereinafter, the switching element to be turned on out of the first switching element 1 and the second switching element 2 in each of the plurality of switching circuits 10 will also be referred to as the target switching element.

[0056] The control system 50 is capable of executing a first control operation and a second control operation when changing a first control signal to a target switching element to be turned on, out of the first switching element 1 and the second switching element 2, in each of the multiple switching circuits 10, from a low level to a high level.

[0057] In the first control operation, the control system 50 overlaps at least a portion of the high-level period of the second control signal to one of the multiple switches 8 corresponding to each of the multiple switching circuits 10 with a dead time period set between the high-level period of the first control signal to the first switching element 1 and the high-level period of the first control signal to the second switching element 2 for each of the multiple switching circuits 10.

[0058] In the second control operation, the control system 50 shifts the high-level period of the second control signal so that the overlap period between the high-level period of the second control signal applied to each of the multiple switches 8 and the dead time period is shorter than in the first control operation, and causes part of the high-level period of the second control signal to overlap with part of the high-level period of the first control signal to the target switching element.

[0059] (3.1) First Control Operation (3.1.1) When the Target Switching Element is the First Switching Element In FIG. 3 , for any switching circuit 10 including the target switching element, the first control signal provided from the control system 50 to the first switching element 1 is illustrated as a first control signal S1, and the first control signal provided from the control system 50 to the second switching element 2 is illustrated as a first control signal S2. Also, in FIG. 3 , the dead time period set between the high-level period of the first control signal S1 provided from the control system 50 to the first switching element 1 and the high-level period of the first control signal S2 provided to the second switching element 2 is illustrated as a dead time period Td. Also, in FIG. 3 , for the switch 8 corresponding to the any switching circuit 10 including the target switching element, the second control signal provided from the control system 50 to the third switching element 6 is illustrated as a second control signal S6, and a current iL1 flowing through a resonant inductor L1 connected to the switch 8 is illustrated. Also, in FIG. 3 , the current flowing through an AC terminal 41 connected to the connection point 3 of the any switching circuit 10 including the target switching element is illustrated as a load current i. 3, the voltage across the first switching element 1 of any switching circuit 10 including the target switching element is shown as voltage V1. Also, in FIG. 3, the voltage value of the DC power supply E1 is shown as Vd. In the example of FIG. 3, the start and end points of the dead time period Td are time t1 and time t3, respectively. Note that FIG. 3 illustrates a timing chart for one cycle of the carrier signal.

[0060] In the example of FIG. 3, the polarity of the load current i flowing through the AC terminal 41 connected to the target switching element is positive.

[0061] In the first control operation, the control system 50 overlaps part of the high-level period of the second control signal S6 to the third switching element 6 with the dead time period Td.

[0062] When the target switching element is the target first switching element 1, the voltage V1 across the first switching element 1 becomes zero at time t3, which is the end time of the dead time period Td immediately before the high-level period of the first control signal S1. Therefore, when the first control signal S1 changes from low to high at time t3, the first switching element 1 undergoes zero-voltage soft switching. In the example of Fig. 3 , the current iL1 flowing through the resonant inductor L1 starts to flow at time t1, which is the start time of the high-level period of the second control signal S6. At time t2, when a first predetermined time Tad1 has elapsed since time t1, the current iL1 becomes the same as the load current i at time t3, when the dead time period Td ends. Finally, the current iL1 becomes zero at time t4, when a second predetermined time Tad2 having the same length as the first predetermined time Tad1 has elapsed since time t3. The first predetermined time Tad1 is calculated in the control system 50 by, for example, calculating Tad1 = i × (L / V15) using the load current i detected by a current sensor, its signal processing value, or an estimated value of the load current i, the pre-stored inductance L of the resonant inductor L1, and the detected voltage V15 of the regenerative capacitor 15 (the potential V15 at the fourth end of the regenerative capacitor 15). In the control system 50, the second control signal S6 changes from low to high at time t1 when the first control signal S2 changes from high to low. At time t4, when the total time of the dead time period Td and the second predetermined time Tad2 has elapsed, the second control signal S6 changes from high to low. The current iL1 flowing between time t2 and time t3 is a resonant current (charging current for the resonant capacitor 9U) flowing from the regenerative capacitor 15 via the resonant inductor L1 to the resonant capacitor 9U. With regard to the current iL1, as a result of iL1≧i from time t2, the current iL1 in the hatched region of the current waveform in the fourth row from the top in Fig. 3 flows into the resonant capacitor 9, causing LC resonance. After time t3 when the dead time period Td ends, the current iL1 is regenerated in the power conversion circuit 11 via the first clamp diode 13 directly connected to the resonant inductor L1.

[0063] In the first control operation, the control system 50 overlaps part of the high-level period of the second control signal S6 to the third switching element 6 with the dead time period Td. As a result, the third switching element 6 is turned on during the dead time period Td, resonance occurs between the resonant inductor L1 connected to the target first switching element 1 and the resonant capacitor 9, and the resonant capacitor 9 is charged from the regenerative capacitor 15, so that the voltage V1 across the target first switching element 1 becomes zero. As a result, the power conversion device 100 can achieve zero-voltage soft switching of the target first switching element 1.

[0064] (3.1.2) When the Target Switching Element is the Second Switching Element In the first control operation, the control system 50 overlaps part of the high-level period of the second control signal to the fourth switching element 7 with the dead time period Td. As a result, the fourth switching element 7 is turned on during the dead time period Td, resonance occurs between the resonant inductor L1 connected to the target second switching element 2 and the resonant capacitor 9, and the regenerative capacitor 15 is charged by discharging from the resonant capacitor 9, so that the voltage across the target second switching element 2 becomes zero. This enables the power conversion device 100 to achieve zero-voltage soft switching of the target second switching element 2. After the end of the dead time period Td, the current iL1 is regenerated in the power conversion circuit 11 via the second clamp diode 14 directly connected to the resonant inductor L1.

[0065] (3.2) Second Control Operation (3.2.1) When the Target Switching Element is the First Switching Element In the second control operation, the control system 50 shifts the high-level period of the second control signal S6 applied to the third switching element 6 so that the overlap period between the high-level period of the second control signal S6 and the dead time period Td is shorter than in the first control operation, thereby causing part of the high-level period of the second control signal S6 to overlap with part of the high-level period of the first control signal S1 applied to the target first switching element 1. In this way, the control system 50 stops the zero-voltage soft switching of the target first switching element 1. "Stopping the zero-voltage soft switching" means that the target first switching element 1 is switched (turned on) in a shorter time than the zero-voltage soft switching in the first control operation, without performing zero-voltage soft switching. In this embodiment, part of the high-level period of the shifted second control signal S6 overlaps with part of the high-level period of the first control signal S1 to the target first switching element 1, while the remainder of the high-level period of the shifted second control signal S6 overlaps with part of the dead time period Td, so that the voltage V1 across the target first switching element 1 when the target first switching element 1 is turned on is reduced below the voltage value Vd of the DC power supply E1.

[0066] (3.2.2) When the Target Switching Element is the Second Switching Element In the second control operation, the control system 50 shifts the overlap period between the high-level period of the second control signal applied to the fourth switching element 7 and the dead time period Td so that it is shorter than in the first control operation, causing part of the high-level period of the second control signal to overlap with part of the high-level period of the first control signal applied to the target second switching element 2. In this way, the control system 50 stops the zero-voltage soft switching of the target second switching element 2. "Stopping the zero-voltage soft switching" means that the target second switching element 2 is switched (turned on) in a shorter time than the zero-voltage soft switching in the first control operation, without performing zero-voltage soft switching. In this embodiment, part of the high-level period of the shifted second control signal overlaps with part of the high-level period of the first control signal to the target second switching element 2, while the remainder of the high-level period of the shifted second control signal overlaps with part of the dead time period Td, so that the voltage across the target second switching element 2 when the target second switching element 2 is turned on is reduced below the voltage value Vd of the DC power supply E1.

[0067] (4) Advantages In the power conversion device 100 according to the first embodiment, the control system 50 can execute a first control operation and a second control operation when changing the first control signal from low level to high level for a target switching element to be turned on, out of the first switching element 1 and the second switching element 2, in each of the multiple switching circuits 10. In the first control operation, the control system 50 overlaps at least a part of the high-level period of the second control signal for each of the multiple switches 8 corresponding to each of the multiple switching circuits 10 with a dead time period Td set for each of the multiple switching circuits 10 between a high-level period of the first control signal S1 for the first switching element 1 and a high-level period of the first control signal S2 for the second switching element 2. In the second control operation, the control system 50 shifts the high-level period of the second control signal so that the overlap period between the high-level period of the second control signal applied to each of the multiple switches 8 and the dead time period Td is shorter than in the first control operation, and at least a portion of the high-level period of the second control signal overlaps with a portion of the high-level period of the first control signal to the target switching element.

[0068] According to the above configuration, it is possible to stop the zero voltage soft switching without pulse width modulating the second control signal to each of the plurality of switches 8 for zero voltage soft switching.

[0069] In the power conversion device 100, for example, the control device 51 may be configured to have a function of detecting a failure in the power conversion circuit 11 and to stop the zero voltage soft switching when the failure is detected. Also, in the power conversion device 100, for example, the control device 51 may be configured to stop the zero voltage soft switching of at least one target switching element among the plurality of first switching elements 1 and the plurality of second switching elements 2 based on a command signal from an external device (host device). Also, the power conversion device 100 may be configured to perform a second control operation to improve efficiency.

[0070] Second Embodiment (1) Configuration The configuration of the power conversion device 100 according to the second embodiment is the same as the configuration of the power conversion device 100 according to the first embodiment (see FIG. 1), and therefore will not be illustrated or described again.

[0071] (2) Operation The operation of the power conversion device 100 according to the second embodiment is substantially the same as the operation of the power conversion device 100 according to the first embodiment, but differs in the second control operation of the control system 50 .

[0072] (2.1) First Control Operation The first control operation of the control system 50 (see, for example, FIG. 4) is the same as the first control operation of the control system 50 of the first embodiment (see, for example, FIG. 3).

[0073] (2.2) Second Control Operation In the second control operation, the control system 50 shifts the high-level period of the second control signal so that the overlap period between the high-level period of the second control signal applied to each of the multiple switches 8 and the dead time period is shorter than in the first control operation, and the entire high-level period of the second control signal overlaps with part of the high-level period of the first control signal to the target switching element.

[0074] (2.2.1) When the Target Switching Element is the First Switching Element In the second control operation, the control system 50 shifts the high-level period of the second control signal S6 applied to the third switching element 6 so that the overlap period between the high-level period of the second control signal S6 and the dead time period Td is shorter than in the first control operation, thereby causing the entire high-level period of the second control signal S6 to overlap with part of the high-level period of the first control signal S1 applied to the target first switching element 1. In this way, the control system 50 stops the zero-voltage soft switching of the target first switching element 1. "Stopping the zero-voltage soft switching of the target first switching element 1" means that the target first switching element 1 is switched (turned on) without zero-voltage soft switching when switching, but in a shorter time than the zero-voltage soft switching in the first control operation. In this embodiment, the entire high level period of the shifted second control signal S6 overlaps with part of the high level period of the first control signal S1 to the target first switching element 1, so no current iL1 flows through the resonance inductor L1 (the current value of the current iL1 is 0), the resonance capacitor 9 is not charged, and the target first switching element 1 is hard switched. In the example of Fig. 4, the start time of the high level period of the second control signal S6 is the same as time t3 when the high level period of the first control signal S1 starts, but it may be later than time t3.

[0075] (2.2.2) When the Target Switching Element is the Second Switching Element In the second control operation, the control system 50 shifts the high-level period of the second control signal so that the overlap period between the high-level period of the second control signal applied to the fourth switching element 7 and the dead time period Td is shorter than in the first control operation, causing the entire high-level period of the second control signal to overlap with part of the high-level period of the first control signal applied to the target second switching element 2. In this way, the control system 50 stops the zero-voltage soft switching of the target second switching element 2. "Stopping the zero-voltage soft switching" means that the target second switching element 2 is switched (turned on) in a shorter time than the zero-voltage soft switching in the first control operation, without performing zero-voltage soft switching. In this embodiment, the entire high-level period of the shifted second control signal overlaps with part of the high-level period of the first control signal to the target second switching element 2, so that no current iL1 flows through the resonant inductor L1 (the current value of the current iL1 is 0), the resonant capacitor 9 is not discharged, and the target second switching element 2 is hard-switched.

[0076] (3) Advantages In the power conversion device 100 according to the second embodiment, similarly to the power conversion device 100 according to the first embodiment, it is possible to stop the zero voltage soft switching without pulse width modulating the second control signal to each of the plurality of switches 8 for zero voltage soft switching.

[0077] (Embodiment 3) A power conversion device 100A according to embodiment 3 will be described with reference to Figures 5 to 14. Regarding the power conversion device 100A according to embodiment 3, components that are the same as those of the power conversion device 100 according to embodiment 1 (see Figure 1) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0078] (1) Configuration As shown in Fig. 5, the power conversion device 100A differs from the power conversion device 100 according to the first embodiment (see Fig. 1) in that the power conversion device 100A includes only one resonant inductor L1. That is, in the present embodiment, the resonant inductor L1 is shared among the three resonant circuits. In the present embodiment, the third end of the resonant inductor L1 is connected to the common connection point 25 to which the second ends 82 of the multiple switches 8 are connected.

[0079] Furthermore, the power conversion device 100A differs from the power conversion device 100 in that it includes a control system 50A instead of the control system 50 of the power conversion device 100 (see FIG. 1).

[0080] The control system 50A includes a control device 51A and a signal generating circuit 52. The control device 51A provides a first control signal to each of the plurality of first switching elements 1 and the plurality of second switching elements 2. The signal generating circuit 52 provides a second control signal to each of the plurality of switches 8.

[0081] In the power conversion device 100A, the plurality of first switching elements 1 and the plurality of second switching elements 2 are controlled by a control device 51A. Control terminals of the plurality of first switching elements 1 are connected to the control device 51A via corresponding first gate drive circuits. Control terminals of the plurality of second switching elements 2 are connected to the control device 51A via corresponding second gate drive circuits.

[0082] In the power conversion device 100A, the multiple switches 8 are controlled by the signal generation circuit 52. In other words, the third switching element 6U, the fourth switching element 7U, the third switching element 6V, the fourth switching element 7V, the third switching element 6W, and the fourth switching element 7W are controlled by the signal generation circuit 52. Control terminals of the multiple third switching elements 6 and the multiple fourth switching elements 7 are connected to the signal generation circuit 52 (see FIG. 6 ).

[0083] The control device 51A controls a plurality of first switching elements 1 and a plurality of second switching elements 2. The control device 51A includes a computer system. The computer system is primarily composed of a processor and memory as hardware. The processor executes a program recorded in the memory of the computer system to realize the functions of the control device 51A in the present disclosure. The processor of the computer system is composed of one or more electronic circuits including a semiconductor integrated circuit (IC) or a large-scale integrated circuit (LSI). The integrated circuits, such as ICs and LSIs, are referred to by different names depending on the degree of integration, and include integrated circuits called system LSIs, very large-scale integrations (VLSIs), or ultra-large-scale integrations (ULSIs). Furthermore, field-programmable gate arrays (FPGAs), which are programmed after the LSI is manufactured, or logic devices capable of reconfiguring the connections within the LSI or reconfiguring the circuit partitions within the LSI, can also be used as processors. The electronic circuits may be integrated into a single chip or distributed across multiple chips. The multiple chips may be integrated into one device or distributed across multiple devices. The computer system referred to here includes a microcontroller having one or more processors and one or more memories. Therefore, the microcontroller is also composed of one or more electronic circuits including semiconductor integrated circuits or large-scale integrated circuits.

[0084] In this embodiment, the control device 51A outputs first control signals SU1, SV1, SW1 that control the on / off of each of the plurality of first switching elements 1U, 1V, 1W. Also, in this embodiment, the control device 51A outputs first control signals SU2, SV2, SW2 that control the on / off of each of the plurality of second switching elements 2U, 2V, 2W.

[0085] The control device 51A uses a sawtooth-wave carrier signal to generate first control signals SU1, SV1, SW1 corresponding to the multiple first switching elements 1U, 1V, and 1W, respectively, and first control signals SU2, SV2, SW2 corresponding to the multiple second switching elements 2U, 2V, and 2W, respectively. More specifically, the control device 51A generates the first control signals SU1 and SU2 to be applied to the first switching element 1U and the second switching element 2U, respectively, based on at least the carrier signal and a U-phase voltage command. The control device 51A also generates the first control signals SV1 and SV2 to be applied to the first switching element 1V and the second switching element 2V, respectively, based on at least the carrier signal and a V-phase voltage command. The control device 51A also generates the first control signals SW1 and SW2 to be applied to the first switching element 1W and the second switching element 2W, respectively, based on at least the carrier signal and a W-phase voltage command. The U-phase voltage command, V-phase voltage command, and W-phase voltage command are, for example, sinusoidal signals whose phases differ by 120°, and whose values ​​(voltage command values) change over time. Note that the waveform of the carrier signal is not limited to a sawtooth waveform and may be, for example, a triangular wave. The U-phase voltage command, V-phase voltage command, and W-phase voltage command each have the same length per cycle. The U-phase voltage command, V-phase voltage command, and W-phase voltage command each have a longer length per cycle than the carrier signal.

[0086] The duties of the first control signals SU1 and SU2 provided by the control device 51A to the first switching element 1U and the second switching element 2U, respectively, vary based on a U-phase voltage command (in FIG. 2, the duty of the first control signal SU1 is shown as a U-phase duty). The control device 51A compares the U-phase voltage command with a carrier signal to generate the first control signal SU1 provided to the first switching element 1U. The control device 51A also inverts the first control signal SU1 provided to the first switching element 1U to generate the first control signal SU2 provided to the second switching element 2U. The control device 51A also sets a first dead time period Td1 (see FIG. 7) between the high-level period of the first control signal SU1 and the high-level period of the first control signal SU2 so that the on periods of the first switching element 1U and the second switching element 2U do not overlap.

[0087] The duties of the first control signals SV1 and SV2 provided by the control device 51A to the first switching element 1V and the second switching element 2V, respectively, vary based on a V-phase voltage command (in FIG. 2, the duty of the first control signal SV1 is shown as a V-phase duty). The control device 51A compares the V-phase voltage command with a carrier signal to generate the first control signal SV1 to be provided to the first switching element 1V. The control device 51A also inverts the first control signal SV1 to be provided to the first switching element 1V to generate the first control signal SV2 to be provided to the second switching element 2V. The control device 51A also sets a first dead time period Td1 (see FIG. 7) between the high-level period of the first control signal SV1 and the high-level period of the first control signal SV2 so that the on periods of the first switching element 1V and the second switching element 2V do not overlap.

[0088] The duties of the first control signals SW1 and SW2 provided by the control device 51A to the first switching element 1W and the second switching element 2W, respectively, vary based on a W-phase voltage command (in FIG. 2, the duty of the first control signal SW1 is shown as a W-phase duty). The control device 51A compares the W-phase voltage command with a carrier signal to generate the first control signal SW1 to be provided to the first switching element 1W. The control device 51A also inverts the first control signal SW1 to be provided to the first switching element 1W to generate the first control signal SW2 to be provided to the second switching element 2W. The control device 51A also sets a first dead time period Td1 (see FIG. 7) between the high-level period of the first control signal SW1 and the high-level period of the first control signal SW2 so that the on periods of the first switching element 1W and the second switching element 2W do not overlap.

[0089] The control device 51A generates the first control signals SU1, SU2, SV1, SV2, SW1, and SW2 based on the carrier signal, the voltage commands, and information about the state of the AC load RA1. For example, if the AC load RA1 is a three-phase servo motor, the information about the state of the AC load RA1 includes, for example, detection values ​​from a plurality of current sensors that detect output currents (hereinafter also referred to as load currents) iU, iV, and iW flowing through the U-phase, V-phase, and W-phase of the AC load RA1, respectively.

[0090] The plurality of switches 8, the resonant inductor L1, the plurality of resonant capacitors 9, and the regenerative capacitor 15 are provided to perform zero-voltage soft switching of the plurality of first switching elements 1 and the plurality of second switching elements 2.

[0091] When the third switching element 6U is in the ON state and the fourth switching element 7U is in the OFF state, the switch 8U allows a charging current to pass through the path of the regenerative capacitor 15-resonant inductor L1-switch 8U-resonant capacitor 9U. The charging current is a current that charges the resonant capacitor 9U. When the third switching element 6U is in the OFF state and the fourth switching element 7U is in the ON state, the switch 8U allows a discharging current to pass through the path of the resonant capacitor 9U-switch 8U-resonant inductor L1-regenerative capacitor 15. The discharging current is a current that discharges the charge in the resonant capacitor 9U.

[0092] When the third switching element 6V is in the ON state and the fourth switching element 7V is in the OFF state, the switch 8V allows a charging current to pass through the path of the regenerative capacitor 15-resonant inductor L1-switch 8V-resonant capacitor 9V. The charging current is a current that charges the resonant capacitor 9V. When the third switching element 6V is in the OFF state and the fourth switching element 7V is in the ON state, the switch 8V allows a discharging current to pass through the path of the resonant capacitor 9V-switch 8V-resonant inductor L1-regenerative capacitor 15. The discharging current is a current that discharges the charge of the resonant capacitor 9V.

[0093] When the third switching element 6W is in the ON state and the fourth switching element 7W is in the OFF state, the switch 8W allows a charging current to pass through the path of the regenerative capacitor 15 - resonant inductor L1 - switch 8W - resonant capacitor 9W. The charging current is a current that charges the resonant capacitor 9W. When the third switching element 6W is in the OFF state and the fourth switching element 7W is in the ON state, the switch 8W allows a discharging current to pass through the path of the resonant capacitor 9W - switch 8W - resonant inductor L1 - regenerative capacitor 15. The discharging current is a current that discharges the charge in the resonant capacitor 9W.

[0094] 7, for any switching circuit 10 including the target switching element, the first control signal provided from the control system 50A to the first switching element 1 is shown as the first control signal S1, and the first control signal provided from the control system 50A to the second switching element 2 is shown as the first control signal S2. Also, for the switch 8 corresponding to the switching circuit 10 including the target switching element, the second control signal provided from the control system 50 to the third switching element 6 is shown as the second control signal S6, and the current iL1 flowing through the resonant inductor L1 is also shown. Also, in FIG. 7, the current flowing through the AC terminal 41 connected to the connection point 3 of the switching circuit 10 including the target switching element is shown as the load current i. Also, in FIG. 7, the voltage across the first switching element 1 of the switching circuit 10 including the target switching element is shown as the voltage V1. Also, in FIG. 7, the voltage value of the DC power supply E1 is shown as Vd. Note that FIG. 7 also shows a timing chart for one cycle of the carrier signal.

[0095] In the example of FIG. 7, the polarity of the load current i flowing through the AC terminal 41 connected to the target switching element is positive.

[0096] As shown in FIG. 7 , for each of the multiple switching circuits 10, the control device 51A sets a second dead time period Td2 by adding a predetermined time (additional time Tad) to a predetermined first dead time period Td1 so that the on periods of the first switching element 1 and the second switching element 2 do not overlap. The second dead time period Td2 includes the first dead time period Td1. The second dead time period Td2 has a length equal to the length of the first dead time period Td1 plus a predetermined time (the total length of the first dead time period Td1 and the predetermined time). In other words, the control device 51A sets the second dead time period Td2, which is the first dead time period Td1 extended by a predetermined time, as the dead time period.

[0097] The first dead-time period Td1 is a period set for each of the multiple switching circuits 10 between a high-level period of the first control signal S1 to the first switching element 1 and a high-level period of the first control signal S2 to the second switching element 2. This period is a period during which both the first control signal S1 to the first switching element 1 and the first control signal S2 to the second switching element 2 are low so that the on-periods of the first switching element 1 and the second switching element 2 do not overlap (i.e., there is no period during which both the first switching element 1 and the second switching element 2 are on). In this embodiment, for example, the length of the resonant half cycle corresponding to each of the multiple switches 8 is designed according to the length of the first dead-time period Td1 of each of the multiple switching circuits 10. The resonant half cycle is half the resonant cycle, which is the reciprocal of the resonant frequency of the resonant circuit including the switch 8, the resonant inductor L1, and one resonant capacitor 9. Therefore, when the inductance of the resonant inductor L1 is L and the capacitance of the resonant capacitor 9 is C, the resonant half cycle is expressed as π × (L C) １／２ The length of the resonance half cycle is set to be the same as the length of the first dead time period Td1, for example.

[0098] The length of the resonant half cycle of the resonant circuit including the resonant inductor L1 and the resonant capacitor 9 is set to, for example, the length of the first dead time period Td1 set between the high-level period of the first control signal S1 and the high-level period of the first control signal S2. In this case, if the resonant cycle is Tres, then Tres / 2, which is the resonant half cycle, is the length of the first dead time period Td1. It is desirable that the end of the resonant half cycle coincide with the end of the first dead time period Td1 for the switching circuit 10 corresponding to the switch 8. In the example of FIG. 7 , the start and end of the first dead time period Td1 are time t1 and time t3, respectively.

[0099] The length of the resonant half cycle described above is an ideal design example, and may be 90% to 110% of the length of the first dead time period Td1. Note that the resonant half cycle and the first dead time period Td1 may have different lengths, and Fig. 7 shows an example in which the resonant half cycle and the first dead time period Td1 are designed to have different lengths.

[0100] The second dead time period Td2 is a period obtained by extending the first dead time period Td1 by a predetermined time. The predetermined time is, for example, an additional time Tad determined by the current value of the load current i, the inductance L of the resonant inductor L1, the voltage value of the regenerative capacitor 15, and the inductance L of the resonant inductor L1. The current value of the load current i is, for example, the load current detection result obtained by a current sensor, a signal-processed value thereof, or an estimated value of the load current iU. The load current detection result or signal-processed value thereof is a detected value in a carrier cycle in which the additional time Tad is added to the first dead time period Td1, or a value closest to that carrier cycle. The estimated value of the load current i is, for example, an estimated value of the load current i in a carrier cycle in which the additional time Tad is added to the first dead time period Td1. The inductance L of the resonant inductor L1 is a value pre-stored in the control device 51A. The voltage value of the regenerative capacitor 15 is a detected value of the voltage V15 of the regenerative capacitor 15 (the potential V15 at the sixth terminal 154 of the regenerative capacitor 15). In the example of Fig. 7, the additional time Tad is a value obtained by calculating Tad = i × (L / V15).

[0101] The length of the predetermined time is an ideal design example, and may be 90% or more and 110% or less of the additional time Tad.

[0102] In the power conversion device 100A, a signal generating circuit 52 separate from the control device 51A controls the multiple switches 8.

[0103] The signal generating circuit 52 generates second control signals SU6, SU7, SV6, SV7, SW6, and SW7 that control the on / off of the third switching element 6U, the fourth switching element 7U, the third switching element 6V, the fourth switching element 7V, the third switching element 6W, and the fourth switching element 7W, respectively, and outputs these signals to the gate terminals of the third switching element 6U, the fourth switching element 7U, the third switching element 6V, the fourth switching element 7V, the third switching element 6W, and the fourth switching element 7W, respectively.

[0104] The signal generating circuit 52 generates, for each of the multiple switches 8, a second control signal having a high-level period corresponding to the second dead-time period Td2 for the corresponding switching circuit 10 among the multiple switching circuits 10. The signal generating circuit 52 delays the start of the high-level period of the second control signal to each of the multiple switches 8 by a specified time T1 (see FIG. 7 ) from the start of the second dead-time period Td2, and delays the end of the high-level period of the second control signal to each of the multiple switches 8 from the end of the second dead-time period Td2. The length of the high-level period of the second control signal to each of the multiple switches 8 (fixed length T2) is longer than the length of the first dead-time period Td1.

[0105] The signal generation circuit 52 generates a second control signal for each of the multiple switches 8 using one of the first control signal to the first switching element 1 and the first control signal to the second switching element 2 of the corresponding switching circuit 10 among the multiple switching circuits 10. The signal generation circuit 52 sets the length of the high-level period of the second control signal generated for each of the multiple switches 8 to a fixed length T2, and causes the start timing of the high-level period of the fixed length T2 to follow the start timing of the second dead time period Td2 for the corresponding switching circuit 10 among the multiple switching circuits 10 for each of the multiple switches 8. In this embodiment, as shown in FIG. 6 , the signal generation circuit 52 has multiple (e.g., six) logic circuits 521-526 and multiple (e.g., six) gate drive circuits 531-536. In the signal generation circuit 52, the multiple logic circuits 521-526 correspond one-to-one to the multiple gate drive circuits 531-536.

[0106] The logic circuit 521 is configured to generate a second control signal SU6 using the first control signal SU2. The logic circuit 521 detects the falling edge of the first control signal SU2 to the second switching element 2U and generates a second control signal SU6 having a high-level period of a fixed length T2. The logic circuit 521 includes, for example, two series-connected multivibrators M11 and M12. Each of the two multivibrators M11 and M12 is an edge-triggered monostable multivibrator. In the logic circuit 521, the inverting output terminal (represented by an overlined Q in FIG. 6 ) of the first-stage multivibrator M11 is connected to the inverting trigger terminal of the second-stage multivibrator M12. In the logic circuit 521, the specified time T1 is the length of a CR time constant determined by the capacitance of the capacitor C11 connected to the first-stage multivibrator M11 and the resistance value of the resistor R11. In the logic circuit 521, the fixed length T2 is the length of a CR time constant determined by the capacitance of the capacitor C12 connected to the multivibrator M12 in the subsequent stage and the resistance value of the resistor R12. In the logic circuit 521, the first control signal SU2 output from the control device 51A is input to the inverting trigger terminal of the multivibrator M11 in the previous stage, and the second control signal SU6 is output from the output terminal Q of the multivibrator M12 in the subsequent stage. The second control signal SU6 is provided to the third switching element 6U via the gate drive circuit 531.

[0107] The logic circuit 522 is configured to generate a second control signal SU7 using the first control signal SU1. The logic circuit 522 detects the falling edge of the first control signal SU1 to the first switching element 1U and generates a second control signal SU7 having a high-level period of a fixed length T2. The logic circuit 522 includes, for example, two series-connected multivibrators M21 and M22. Each of the two multivibrators M21 and M22 is an edge-triggered monostable multivibrator. In the logic circuit 522, the inverting output terminal (represented by an overlined Q in FIG. 6 ) of the first-stage multivibrator M21 is connected to the inverting trigger terminal of the second-stage multivibrator M22. In the logic circuit 522, the specified time T1 is the length of a CR time constant determined by the capacitance of the capacitor C21 connected to the first-stage multivibrator M21 and the resistance value of the resistor R21. In the logic circuit 522, the fixed length T2 is the length of a CR time constant determined by the capacitance of the capacitor C22 connected to the multivibrator M22 in the subsequent stage and the resistance value of the resistor R22. The logic circuit 522 receives the first control signal SU1 output from the control device 51A as input to the inverting trigger terminal of the multivibrator M21 in the previous stage, and outputs a second control signal SU7 from the output terminal Q of the multivibrator M22 in the subsequent stage. The second control signal SU7 is provided to the fourth switching element 7U via the gate drive circuit 532.

[0108] The logic circuit 523 is configured to generate a second control signal SV6 using the first control signal SV2. The logic circuit 523 detects the falling edge of the first control signal SV2 to the second switching element 2V and generates the second control signal SV6 having a high-level period of a fixed length T2. The logic circuit 523 includes, for example, two series-connected multivibrators M31 and M32. Each of the two multivibrators M31 and M32 is an edge-triggered monostable multivibrator. In the logic circuit 523, the inverting output terminal (represented by an overlined Q in FIG. 6 ) of the first-stage multivibrator M31 is connected to the inverting trigger terminal of the second-stage multivibrator M32. In the logic circuit 523, the specified time T1 is the length of a CR time constant determined by the capacitance of the capacitor C31 connected to the first-stage multivibrator M31 and the resistance value of the resistor R31. In the logic circuit 523, the fixed length T2 is the length of a CR time constant determined by the capacitance of the capacitor C32 connected to the multivibrator M32 in the subsequent stage and the resistance value of the resistor R32. The logic circuit 523 receives the first control signal SV2 output from the control device 51A as input to the inverting trigger terminal of the multivibrator M31 in the previous stage, and outputs a second control signal SV6 from the output terminal Q of the multivibrator M32 in the subsequent stage. The second control signal SV6 is provided to the third switching element 6V via the gate drive circuit 533.

[0109] The logic circuit 524 is configured to generate a second control signal SV7 using the first control signal SV1. The logic circuit 524 detects the falling edge of the first control signal SV1 to the first switching element 1V and generates a second control signal SV7 having a high-level period of a fixed length T2. The logic circuit 524 includes, for example, two series-connected multivibrators M41 and M42. Each of the two multivibrators M41 and M42 is an edge-triggered monostable multivibrator. In the logic circuit 524, the inverting output terminal (represented by an overlined Q in FIG. 6 ) of the first-stage multivibrator M41 is connected to the inverting trigger terminal of the second-stage multivibrator M42. In the logic circuit 524, the specified time T1 is the length of a CR time constant determined by the capacitance of the capacitor C41 connected to the first-stage multivibrator M41 and the resistance value of the resistor R41. In the logic circuit 524, the fixed length T2 is the length of a CR time constant determined by the capacitance of the capacitor C42 connected to the multivibrator M42 in the subsequent stage and the resistance value of the resistor R42. The logic circuit 524 receives the first control signal SV1 output from the control device 51A as input to the inverting trigger terminal of the multivibrator M41 in the previous stage, and outputs a second control signal SV7 from the output terminal Q of the multivibrator M42 in the subsequent stage. The second control signal SV7 is provided to the fourth switching element 7V via the gate drive circuit 534.

[0110] The logic circuit 525 is configured to generate a second control signal SW6 using the first control signal SW2. The logic circuit 525 detects the falling edge of the first control signal SW2 to the second switching element 2W and generates the second control signal SW6 having a high-level period of a fixed length T2. The logic circuit 525 includes, for example, two series-connected multivibrators M51 and M52. Each of the two multivibrators M51 and M52 is an edge-triggered monostable multivibrator. In the logic circuit 525, the inverting output terminal (represented by an overlined Q in FIG. 6 ) of the first-stage multivibrator M51 is connected to the inverting trigger terminal of the second-stage multivibrator M52. In the logic circuit 525, the specified time T1 is the length of a CR time constant determined by the capacitance of the capacitor C51 connected to the first-stage multivibrator M51 and the resistance value of the resistor R51. In the logic circuit 525, the fixed length T2 is the length of a CR time constant determined by the capacitance of the capacitor C52 connected to the multivibrator M52 in the subsequent stage and the resistance value of the resistor R52. The logic circuit 525 receives the first control signal SW2 output from the control device 51A as input to the inverting trigger terminal of the multivibrator M51 in the previous stage, and outputs the second control signal SW6 from the output terminal of the multivibrator M52 in the subsequent stage. The second control signal SW6 is provided to the third switching element 6W via the gate drive circuit 535.

[0111] The logic circuit 526 is configured to generate a second control signal SW7 using the first control signal SW1. The logic circuit 526 detects the falling edge of the first control signal SW1 to the first switching element 1W and generates a second control signal SW7 having a high-level period of a fixed length T2. The logic circuit 526 includes, for example, two multivibrators M61 and M62 connected in series. Each of the two multivibrators M61 and M62 is an edge-triggered monostable multivibrator. In the logic circuit 526, the inverting output terminal (represented by an overlined Q in FIG. 6 ) of the first-stage multivibrator M61 is connected to the inverting trigger terminal of the second-stage multivibrator M62. In the logic circuit 526, the specified time T1 is the length of a CR time constant determined by the capacitance of the capacitor C61 connected to the first-stage multivibrator M61 and the resistance value of the resistor R61. In the logic circuit 526, the fixed length T2 is the length of a CR time constant determined by the capacitance of the capacitor C62 connected to the multivibrator M62 in the subsequent stage and the resistance value of the resistor R62. The logic circuit 526 receives the first control signal SW1 output from the control device 51A as an input to the inverting trigger terminal of the multivibrator M61 in the preceding stage, and outputs a second control signal SW7 from the inverting output terminal (indicated by an overlined Q in FIG. 6 ) of the multivibrator M62 in the subsequent stage. The second control signal SW7 is provided to the fourth switching element 7W via the gate drive circuit 536.

[0112] (2) Operation The operation of the power conversion device 100A according to the third embodiment is substantially the same as that of the power conversion device 100 according to the first embodiment, except for the operation of the control system 50A. The operation of the power conversion device 100A will be described below with reference to FIG. 7 . FIG. 7 illustrates the first control signals S1 and S2, the output signal from the inverting output terminal of the upstream multivibrator (represented by an overlined Q in FIG. 6 ), and the second control signal S6 when the target switching element is the first switching element 1. FIG. 7 also illustrates the current iL1 flowing through the resonant inductor L1, the load current i, and the voltage V1 across the first switching element 1. In FIG. 7 , the voltage value of the DC power supply E1 is indicated as Vd.

[0113] (2.1) First Control Operation (2.1.1) When the Target Switching Element is the First Switching Element In the first control operation, in FIG. 7, the first control signal S2 falls from high level to low level at time t0, the output signal from the inverting output terminal of the preceding multivibrator falls from high level to low level at time t1, the first control signal S1 changes from low level to high level at time t3, and the second control signal S6 changes from high level to low level at time t4.

[0114] In the switching circuit 10, when the target switching element is the first switching element 1, the voltage across the second switching element 2 becomes Vd at time t3, which is the end point of the second dead time period Td2 immediately before the high-level period of the first control signal S1, and the voltage across the first switching element 1 becomes zero at time t3, which is the end point of the second dead time period Td2 immediately before the high-level period of the first control signal S1. Therefore, when the first control signal S1 changes from low to high at time t3, the first switching element 1 is subjected to zero-voltage soft switching. In the example of FIG. 7 , the current iL1 flowing through the resonant inductor L1 starts flowing at time t1, when the high-level period of the second control signal S6 begins, becomes the same as the load current i at time t2, when the first predetermined time Tad1 has elapsed, becomes the same as the load current i at time t3, when the second dead time period Td2 has elapsed, and becomes zero at time t4, when the second predetermined time Tad2 has elapsed from time t3. In the signal generating circuit 52, the second control signal SU6 changes from low to high at time t1, which is a specified time T1 after time t0 when the first control signal S2 changes from high to low. The current iL1 flowing between time t2 and time t3 is a resonant current (charging current for the resonant capacitor 9) flowing from the regenerative capacitor 15 to the resonant capacitor 9 via the resonant inductor L1.

[0115] For example, if the target first switching element 1 is the first switching element 1U, during the first period T01 (see FIG. 11), the first switching element 1U, the second switching element 2U, and the fourth switching element 7U are all in the OFF state, and the third switching element 6U is in the ON state. During the first period T01, the current iL1 flows through a path that passes through the regenerative capacitor 15, the resonant inductor L1, the diode 71, the third switching element 6U, and the AC terminal 41U, as shown by the thick solid line in FIG. 8. Also, during the first period T01, the load current iU flows through a path that passes through the second diode 5 connected in anti-parallel to the second switching element 2U, the AC terminal 41U, and the AC load RA1, as shown by the thick dashed line in FIG.

[0116] During the second period T02 (see FIG. 11), the first switching element 1U, the second switching element 2U, and the fourth switching element 7U are each in an OFF state, and the third switching element 6U is in an ON state. During the second period T02, the current iL1 flows through a path passing through the regenerative capacitor 15, the resonant inductor L1, the diode 71, and the third switching element 6U, as shown by the thick solid line in FIG. 9, and is divided into a current flowing to the AC terminal 41U and a current flowing to the resonant capacitor 9U (resonant current). During the second period T02, the resonant capacitor 9U is charged by the current flowing through the resonant capacitor 9U.

[0117] During the third period T03 (see FIG. 11), the first switching element 1U and the third switching element 6U are each in an ON state, and the second switching element 2U and the fourth switching element 7U are each in an OFF state. During the third period T03, the current iL1 flows through a path that passes through the regenerative capacitor 15, the resonant inductor L1, the diode 71, the third switching element 6U, and the AC terminal 41U, as shown in FIG. 10. This reduces the current iL1 to zero. Furthermore, during the third period T03, the load current iU flows through a path that passes through the first DC terminal 31, the first switching element 1U, the AC terminal 41U, and the AC load RA1, as shown by the thick dashed line in FIG.

[0118] 11 to 13, similar to the upper part of Fig. 7, show the first control signals S1 and S2, the output signal from the inverting output terminal of the preceding multivibrator (represented by an overlined Q in Figs. 11 to 13), the second control signal S6, the current iL1 flowing through the resonant inductor L1, the load current i, and the voltage V1 across the first switching element 1U for the case where the target switching element is the first switching element 1. Also, in Figs. 11 to 13, the voltage value of the DC power supply E1 is shown as Vd.

[0119] 11 to 13 show different current values ​​of the load current iU. Fig. 11 shows the case where the load current i has a maximum current value at a high load, Fig. 12 shows the case where the load current i has a smaller current value than Fig. 11 at a low load, and Fig. 13 shows the case where the load current i has a zero current value at no load.

[0120] As shown in FIG. 11 , the fixed length T2 is the total length of the first period T01, the second period T02, and the third period T03 when the load current i is at its maximum under a high load. The length of the first period T01 is the length of the first predetermined time Tad1. The length of the second period T02 is half the length of the resonance period. The length of the third period T03 is the length of the second predetermined time Tad2. In FIGS. 11 to 13 , the lengths of the first period T01 are different from each other. In FIG. 13 , the length of the first period T01 is zero. In addition, in FIGS. 11 to 13 , the lengths of the second period T02 are the same from each other. In addition, in FIGS. 11 to 13 , the lengths of the third period T03 are different from each other. In FIG. 13 , the length of the third period T03 is zero.

[0121] (2.1.2) When the Target Switching Element is the Second Switching Element In the first control operation, in FIG. 14, the first control signal S1 falls from high level to low level at time t40, the output signal from the inverting output terminal of the preceding multivibrator falls from high level to low level at time t41, the first control signal S2 changes from low level to high level at time t43, and the second control signal S7 changes from high level to low level at time t44.

[0122] When the target switching element is the second switching element 2, in the switching circuit 10, the voltage V1 across the first switching element 1 becomes Vd at time t43, which is the end of the second dead time period Td2 immediately before the high-level period of the first control signal S2, and the voltage V2 across the second switching element 2 becomes zero at time t43, which is the end of the second dead time period Td2 immediately before the high-level period of the first control signal S2. Therefore, when the first control signal S2 changes from low to high at time t43, the second switching element 2 is subjected to zero-voltage soft switching. In the example of FIG. 14 , the current iL1 flowing through the resonant inductor L1 starts to flow at time t41, which is the start of the high-level period of the second control signal S7, and becomes the same value as the load current i at time t42, when the first predetermined time Tad1 has elapsed. Then, the current iL1 becomes the same value as the load current i at time t43, when the second dead time period Td2 has ended. Finally, the current iL1 becomes zero at time t44, when the second predetermined time Tad2 has elapsed from time t43. In the signal generating circuit 52, the second control signal S7 changes from low level to high level at time t41, which is a specified time T1 after time t40 when the first control signal S1 changes from high level to low level. The current iL1 flowing between time t42 and time t43 is a resonant current (discharge current of the resonant capacitor 9) flowing from the resonant capacitor 9 to the regenerative capacitor 15 via the resonant inductor L1.

[0123] 14, the first period T01 is the period from time t41 to time t42. During the first period T01, the first switching element 1, the second switching element 2, and the third switching element 6 are all in an OFF state, and the fourth switching element 7 is in an ON state. During the first period T01, the current iL1 flows through a path that passes through the AC terminal 41, the diode 61, the fourth switching element 7, the resonance inductor L1, and the regenerative capacitor 15. Also, during the first period T01, the load current i flows through a path that passes through the AC load RA1, the AC terminal 41, and the first diode 4 that is connected in anti-parallel to the first switching element 1.

[0124] 14, the second period T02 is the period from time t42 to time t43. During the second period T02, the first switching element 1, the second switching element 2, and the third switching element 6 are all in an OFF state, and the fourth switching element 7 is in an ON state. During the second period T02, the current iL1 flowing through the resonant inductor L1 is a combined current of a current flowing from the AC terminal 41 through the diode 61, the fourth switching element 7, the resonant inductor L1, and the regenerative capacitor 15, and a current (resonant current) flowing from the resonant capacitor 9 through the diode 61, the fourth switching element 7, the resonant inductor L1, and the regenerative capacitor 15. During the second period T02, the resonant capacitor 9 is discharged.

[0125] In FIG. 14, the third period T03 is the period from time t43 to time t44. During the third period T03, the second switching element 2U is in the ON state, the first switching element 1U and the third switching element 6U are in the OFF state, and the fourth switching element 7U is in the ON state. During the third period T03, the current iL1 flows through the AC terminal 41U, the diode 61, the fourth switching element 7U, the resonant inductor L1, and the regenerative capacitor 15. This reduces the absolute value of the current iL1 to zero. Furthermore, during the third period T03, the load current iU flows through the AC load RA1, the AC terminal 41U, the second switching element 2U, and the second DC terminal 32.

[0126] (2.2) Second Control Operation In the second control operation, the control system 50A shifts the high-level period of the second control signal so that the overlap period between the high-level period of the second control signal applied to each of the multiple switches 8 and the dead time period (second dead time period Td2) is shorter than in the first control operation, and the entire high-level period of the second control signal overlaps with part of the high-level period of the first control signal to the target switching element.

[0127] 7 , in the second control operation, the control system 50A shifts the high-level period of the second control signal S6 so that the overlap period of the high-level period of the second control signal S6 supplied to the third switching element 6 and the dead time period (second dead time period Td2) is shorter than in the first control operation, thereby causing part of the high-level period of the second control signal S6 to overlap with part of the high-level period of the first control signal S1 supplied to the target first switching element 1. As a result, the control system 50A stops the zero voltage soft switching of the target first switching element 1.

[0128] (2.2.2) When the Target Switching Element is the Second Switching Element In the second control operation, the control system 50A shifts the high-level period of the second control signal provided to the fourth switching element 7 so that the overlap period between the high-level period of the second control signal and the dead time period (second dead time period Td2) is shorter than in the first control operation, causing the entire high-level period of the second control signal to overlap with part of the high-level period of the first control signal provided to the target second switching element 2. In this embodiment, since the entire high-level period of the shifted second control signal overlaps with part of the high-level period of the first control signal provided to the target second switching element 2, the current iL1 does not flow through the resonant inductor L1 (the current value of the current iL1 is 0), the resonant capacitor 9 is not discharged, and the target second switching element 2 is hard-switched.

[0129] (3) Advantages In the power conversion device 100A according to the third embodiment, the control system 50A can execute a first control operation and a second control operation when changing the first control signal to a target switching element to be turned on, either the first switching element 1 or the second switching element 2, from low to high in each of the multiple switching circuits 10. In the first control operation, the control system 50A overlaps at least a portion of a high-level period of the second control signal to a switch 8 among the multiple switches 8 corresponding to each of the multiple switching circuits 10 with a dead time period Td set for each of the multiple switching circuits 10 between a high-level period of the first control signal S1 to the first switching element 1 and a high-level period of the first control signal S2 to the second switching element 2. In the second control operation, the control system 50A shifts the high-level period of the second control signal so that the overlap period between the high-level period of the second control signal applied to each of the multiple switches 8 and the dead time period (second dead time period Td2) is shorter than in the first control operation, and causes part of the high-level period of the second control signal to overlap with part of the high-level period of the first control signal S1 to the target switching element.

[0130] According to the above configuration, it is possible to stop the zero voltage soft switching without pulse width modulating the second control signal to each of the plurality of switches 8 for zero voltage soft switching.

[0131] In the power conversion device 100A, for example, the control device 51A may have a function of detecting a failure in the power conversion circuit 11 and may be configured to stop the zero voltage soft switching when a failure is detected. Furthermore, the power conversion device 100A may be configured to perform a second control operation to improve efficiency.

[0132] In the power conversion device 100A according to the third embodiment, the control system 50A includes a control device 51A and a signal generating circuit 52. The control device 51A provides a first control signal to each of the plurality of first switching elements 1 and the plurality of second switching elements 2. The signal generating circuit 52 provides a second control signal to each of the plurality of switches 8. The control device 51A sets a second dead time period Td2 as the dead time period by adding a predetermined time (additional time Tad) to a predetermined first dead time period Td1 so that the on periods of the first switching elements 1 and the second switching elements 2 do not overlap. The predetermined time (additional time Tad) is determined based on the current value of the load current, the inductance of the resonance inductor L1, and the voltage value of the regenerative capacitor 15. The signal generating circuit 52 generates, for each of the plurality of switches 8, a second control signal having a high-level period corresponding to the second dead time period Td2 for the corresponding switching circuit 10 among the plurality of switching circuits 10.

[0133] According to the above configuration, the control device 51A can more reliably achieve zero-voltage soft switching without directly controlling the plurality of switches 8 for zero-voltage soft switching. More specifically, the control device 51A does not need to generate second control signals for directly controlling the plurality of switches 8 for zero-voltage soft switching, and the control device 51A can achieve zero-voltage soft switching of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 without directly controlling the plurality of switches 8. Furthermore, according to the above configuration, the control device 51A does not need to generate and output the plurality of second control signals SU6, SU7, SV6, SV7, SW6, and SW7, which simplifies the control device 51A. For example, an increase in the number of control ports of a microcomputer included in the control device 51A can be suppressed, and an increase in the size of the control device 51A can be suppressed.

[0134] In addition, in the power conversion device 100A, the signal generating circuit 52 generates a second control signal for each of the multiple switches 8 using at least one of a first control signal S1 to the first switching element 1 of a corresponding one of the multiple switching circuits 10 and a first control signal S2 to the second switching element 2.

[0135] According to the above configuration, the signal generating circuit 52 can be simplified.

[0136] Furthermore, in the power conversion device 100A, the signal generation circuit 52 includes a plurality of logic circuits 521 to 526, but does not include a microcontroller.

[0137] According to the above configuration, the signal generating circuit 52 can be simplified.

[0138] (Fourth Embodiment) (1) Configuration The configuration of a power conversion device 100A according to the fourth embodiment is the same as the configuration of the power conversion device 100A according to the third embodiment, and therefore will not be illustrated or described again.

[0139] (2) Operation The operation of the power conversion device 100A according to the fourth embodiment is substantially the same as the operation of the power conversion device 100A according to the third embodiment, but differs in the second control operation of the control system 50A.

[0140] (2.1) First Control Operation The first control operation of the control system 50A is the same as the first control operation of the control system 50A of the third embodiment.

[0141] (2.2) Second Control Operation In the second control operation, the control system 50A shifts the high-level period of the second control signal so that the overlap period between the high-level period of the second control signal applied to each of the multiple switches 8 and the dead time period is shorter than in the first control operation, and the entire high-level period of the second control signal overlaps with part of the high-level period of the first control signal to the target switching element.

[0142] (2.2.1) When the Target Switching Element is the First Switching Element In the second control operation, the control system 50A shifts the high-level period of the second control signal S6 applied to the third switching element 6 so that the overlap period between the high-level period of the second control signal S6 and the dead time period Td is shorter than in the first control operation, thereby causing the entire high-level period of the second control signal S6 to overlap with part of the high-level period of the first control signal S1 applied to the target first switching element 1. In this way, the control system 50A stops the zero-voltage soft switching of the target first switching element 1. "Stopping the zero-voltage soft switching" means that the target first switching element 1 is switched (turned on) in a shorter time than the zero-voltage soft switching in the first control operation, without performing zero-voltage soft switching. In this embodiment, the entire high-level period of the shifted second control signal S6 overlaps with part of the high-level period of the first control signal S1 to the target first switching element 1, so no current iL1 flows through the resonant inductor L1 (the current value of the current iL1 is 0), the resonant capacitor 9 is not charged, and the target first switching element 1 is hard-switched.

[0143] In this embodiment, during the overlap period between the high level period of the first control signal S1 and the second control signal S6, the voltage across the resonant capacitor 9 is greater than the voltage V15 of the regenerative capacitor 15. Therefore, in the power conversion device 100A, even if the first switching element 1 is turned on, no resonant current flows through the resonant inductor L1, and instead, as shown by the thick dashed line in FIG. 16, a current flows through the path from the first switching element 1 to the connection point 3 to the AC terminal 41.

[0144] (2.2.2) When the Target Switching Element is the Second Switching Element In the second control operation, the control system 50A shifts the high-level period of the second control signal so that the overlap period between the high-level period of the second control signal applied to the fourth switching element 7 and the dead time period Td is shorter than in the first control operation, causing the entire high-level period of the second control signal to overlap with part of the high-level period of the first control signal applied to the target second switching element 2. In this way, the control system 50A stops the zero-voltage soft switching of the target second switching element 2. "Stopping the zero-voltage soft switching" means that the target second switching element 2 is switched (turned on) without being switched by zero-voltage soft switching, but in a time shorter than the zero-voltage soft switching in the first control operation. In this embodiment, the entire high-level period of the shifted second control signal overlaps with part of the high-level period of the first control signal to the target second switching element 2, so that no current iL1 flows through the resonant inductor L1 (the current value of the current iL1 is 0), the resonant capacitor 9 is not discharged, and the target second switching element 2 is hard-switched.

[0145] (3) Advantages As with the power conversion device 100A according to the third embodiment, the power conversion device 100A according to the fourth embodiment can stop the zero voltage soft switching without pulse width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0146] Furthermore, in the power conversion device 100A according to the fourth embodiment, similarly to the power conversion device 100A according to the third embodiment, the control system 50A includes the control device 51A and the signal generating circuit 52, and therefore, the zero voltage soft switching can be more reliably realized without the control device 51A directly controlling the plurality of switches 8 for zero voltage soft switching. More specifically, the control device 51A does not need to generate a second control signal for directly controlling the plurality of switches 8 for zero voltage soft switching, and the zero voltage soft switching of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 can be realized without the control device 51A directly controlling the plurality of switches 8.

[0147] Fifth Embodiment A power conversion device 100B according to a fifth embodiment will be described below with reference to Fig. 17 to Fig. 20. Note that, with respect to the power conversion device 100B according to the fifth embodiment, components that are the same as those of the power conversion device 100 according to the first embodiment (see Fig. 1) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0148] (1) Configuration The power conversion device 100B according to the fifth embodiment differs from the power conversion device 100 according to the first embodiment (see FIG. 1) in that multiple switches 8 are commonly connected to one resonant inductor L1.

[0149] (2) Operation In this embodiment, when the control system 50 provides a second control signal with a preset high-level duration to each of the multiple switches 8, it determines whether or not a resonant current flows through the resonant inductor L1 simultaneously through each of two or more of the multiple switches 8.

[0150] (2.1) First Control Operation The first control operation of the control system 50 is the same as the first control operation of the control system 50 of the first embodiment.

[0151] (2.2) Second Control Operation When the control system 50 provides a second control signal with a preset high-level duration to each of the multiple switches 8, the control system 50 determines whether or not a resonant current passing through each of two or more of the multiple switches 8 flows simultaneously through the resonant inductor L1, and if it determines that a resonant current passing through each of the two or more switches 8 flows simultaneously, it executes a second control operation on a first switch that is one of the two or more switches 8. "If it determines that a resonant current passing through each of the two or more switches 8 flows simultaneously" means that it has been estimated in advance that a resonant current passing through each of the two or more switches 8 will flow simultaneously through the resonant inductor L1.

[0152] (2.2.1) Determination of Whether Resonant Currents Flow Simultaneously Through Two Switches In the power conversion device 100B, the phases of the voltage commands for three phases (U-phase, V-phase, and W-phase) are different from each other by 120°, but the command values ​​of the voltage commands for two phases approach each other by an electrical angle of 60°, and the duties of the first control signals for the two phases approach each other. The polarity of the resonant current is the same as the polarity of the current iL1. For example, in a first region A1 (see FIG. 2 ) where the duties of the first control signal for the U-phase and the first control signal for the V-phase are near 0.75, the polarity of the resonant current is positive. In a second region A2 (see FIG. 2 ) where the duties of the first control signal for the U-phase and the first control signal for the V-phase are near 0.25, the polarity of the resonant current is negative. In the first region A1, for example, during one cycle of the carrier signal, the time difference between the start of the high-level period of the second control signal SU6 supplied to the third switching element 6U and the start of the high-level period of the second control signal SV6 supplied to the third switching element 6V becomes short, and there is a possibility that the U-phase resonant current and the V-phase resonant current will flow simultaneously through the resonant inductor L1. In the power conversion device 100B, in the second region A2, the direction of the resonant current is opposite to that in the first region A1, but there is a possibility that the U-phase resonant current and the V-phase resonant current will flow simultaneously through the resonant inductor L1.

[0153] Assuming that the capacitance of each of the multiple resonant capacitors 9U, 9V, and 9W is C, if a U-phase current and a V-phase current flow simultaneously through the resonant inductor L1, then in terms of an equivalent circuit, a capacitor having a combined capacitance (=2×C) of the resonant capacitors 9U and 9V is connected in series to the resonant inductor L1. Therefore, in the power conversion device 100B, if two-phase currents flow simultaneously through the resonant inductor L1, the resonant frequency of the resonant circuit including the resonant inductor L1 will change compared to when a single-phase current flows through the resonant inductor L1, and zero-voltage soft switching may not be achieved.

[0154] (2.2.1.1) In the Case of Charging Operation of Resonant Capacitor FIG. 18 is a diagram showing an example of boundary conditions between a case where the U-phase current (current passing through switch 8U) and a V-phase current (current passing through switch 8V) do not overlap (flow simultaneously) and a case where they overlap (flow simultaneously) in resonant inductor L1. These boundary conditions will be described with reference to FIG. 18. FIG. 19 is a diagram showing an example of boundary conditions between a case where the U-phase resonant current and the V-phase resonant current do not overlap (flow simultaneously) and a case where they overlap (flow simultaneously) in resonant inductor L1. These boundary conditions will be described with reference to FIG. 19.

[0155] 18, in the power conversion device 100, if the time difference ΔTuv is equal to or greater than Tau + Tav + (Tres / 2), the U-phase current and the V-phase current do not overlap in the resonant inductor L1, and if the time difference ΔTuv is less than Tau + Tav + (Tres / 2), the U-phase current and the V-phase current overlap. The time difference ΔTuv is the time difference between time t3 when the high-level period of the first control signal SU1 starts and time t13 when the high-level period of the first control signal SV1 starts.

[0156] In the power conversion device 100, as shown in FIG. 19, if the time difference ΔTuv is Tres / 2 or more, the U-phase resonant current and the V-phase resonant current do not overlap in the resonant inductor L1, and if the time difference ΔTuv is less than Tres / 2, the U-phase resonant current and the V-phase resonant current overlap in the resonant inductor L1.

[0157] The control device 51 sets a threshold for the time difference ΔTuv to Tres / 2. If the time difference ΔTuv is less than Tres / 2, the control device 51 estimates that the U-phase resonant current and the V-phase resonant current flow simultaneously in the resonant inductor L1. The above threshold setting is an example, and the threshold may be set to another value. For example, taking into account an error in the value of Tres / 2, the threshold may be set to a value greater than Tres / 2. For example, the threshold may be set to Tau + Tav + (Tres / 2). In this case, the control device 51 estimates that the U-phase current (current passing through the switch 8U) and the V-phase current (current passing through the switch 8V) overlap in the resonant inductor L1 if the time difference ΔTuv is less than Tau + Tav + (Tres / 2). Furthermore, taking into consideration an error in the value of Tau + Tav + (Tres / 2), the threshold value may be set to a value even greater than Tau + Tav + (Tres / 2). Furthermore, the method for calculating the time difference ΔTuv used to determine whether two-phase resonant currents flow simultaneously is not limited to the above example, and any other calculation method may be used as long as it can calculate a time difference equivalent to the time difference ΔTuv. For example, the time difference ΔTuv used to determine whether two-phase resonant currents flow simultaneously may be the time difference between the end point of the high-level period of the first control signal SU2 and the end point of the high-level period of the first control signal SV2.

[0158] In the following description, the time difference between the start point of the high-level period of the first control signal SU1 and the start point of the high-level period of the first control signal SW1 is referred to as ΔTuw. In the power conversion device 100, if the time difference ΔTuw is Tres / 2 or more, the U-phase resonant current and the W-phase resonant current do not overlap in the resonant inductor L1, and if the time difference ΔTuw is less than Tres / 2, the U-phase resonant current and the W-phase resonant current overlap in the resonant inductor L1.

[0159] The control device 51 sets a threshold for the time difference ΔTuw to Tres / 2. If the time difference ΔTuw is less than the threshold, the control device 51 estimates that a U-phase resonant current and a W-phase resonant current flow simultaneously through the resonant inductor L1. The above threshold setting is an example, and the threshold may be set to another value. For example, taking into account an error in the value of Tres / 2, the threshold may be set to a value greater than Tres / 2. For example, the threshold may be set to Tau + Taw + (Tres / 2). In this case, the control device 51 estimates that a U-phase current (current passing through the switch 8U) and a W-phase current (current passing through the switch 8W) overlap in the resonant inductor L1 if the time difference ΔTuw is less than Tau + Taw + (Tres / 2). Furthermore, taking into consideration an error in the value of Tau + Taw + (Tres / 2), the threshold value may be set to a value even greater than Tau + Taw + (Tres / 2). Furthermore, the method for calculating the time difference ΔTuw used to determine whether two-phase resonant currents flow simultaneously is not limited to the above example, and any other calculation method may be used as long as it can calculate a time difference equivalent to the time difference ΔTuw. For example, the time difference ΔTuw used to determine whether two-phase resonant currents flow simultaneously may be the time difference between the end point of the high-level period of the first control signal SU2 and the end point of the high-level period of the first control signal SW2.

[0160] In the following description, the time difference between the start point of the high-level period of the first control signal SV1 provided to the first switching element 1V of the switching circuit 10V and the start point of the high-level period of the first control signal SW1 provided to the first switching element 1W of the switching circuit 10W is referred to as ΔTvw. In the power conversion device 100, if the time difference ΔTvw is Tres / 2 or more, the V-phase resonant current and the W-phase resonant current do not overlap in the resonant inductor L1, and if the time difference ΔTvw is less than Tres / 2, the V-phase resonant current and the W-phase resonant current overlap in the resonant inductor L1.

[0161] The control device 51 sets a threshold for the time difference ΔTvw to Tres / 2. If the time difference ΔTvw is less than the threshold, the control device 51 estimates that a V-phase resonant current and a W-phase resonant current flow simultaneously through the resonant inductor L1. The above threshold setting is an example, and the threshold may be set to another value. For example, taking into account an error in the value of Tres / 2, the threshold may be set to a value greater than Tres / 2. For example, the threshold may be set to Tav + Taw + (Tres / 2). In this case, the control device 51 estimates that a V-phase current (current passing through the switch 8V) and a W-phase current (current passing through the switch 8W) overlap in the resonant inductor L1 if the time difference ΔTvw is less than Tav + Taw + (Tres / 2). Furthermore, taking into consideration an error in the value of Tav + Taw + (Tres / 2), the threshold value may be set to a value even greater than Tav + Taw + (Tres / 2). Furthermore, the method for calculating the time difference ΔTvw used to determine whether two-phase resonant currents flow simultaneously is not limited to the above example, and any other calculation method may be used as long as it can calculate a time difference equivalent to the time difference ΔTvw. For example, the time difference ΔTvw used to determine whether two-phase resonant currents flow simultaneously may be the time difference between the end point of the high-level period of the first control signal SV2 and the end point of the high-level period of the first control signal SW2.

[0162] (2.2.1.2) In the case of discharging operation of the resonant capacitor In the case of discharging operation of the resonant capacitor 9, the control device 51 can determine whether two-phase resonant currents flow simultaneously using the same time difference and threshold value as in the case of charging operation of the resonant capacitor 9.

[0163] For example, if the time difference between the start of the high-level period of the first control signal SU2 and the start of the high-level period of the first control signal SV2 is less than a threshold value (e.g., Tres / 2), the control device 51 estimates that the U-phase resonant current and the V-phase resonant current overlap. The above threshold value is an example, and the threshold value may be set to another value. For example, the threshold value may be set to a value greater than Tres / 2, taking into account errors in the value of Tres / 2, etc. For example, the threshold value may be set to Tau + Tav + (Tres / 2). In this case, the control device 51 estimates that the U-phase current (current passing through the switch 8U) and the V-phase current (current passing through the switch 8V) overlap in the resonant inductor L1 if the time difference ΔTuv is less than Tau + Tav + (Tres / 2). Furthermore, taking into consideration an error in the value of Tau+Tav+(Tres / 2), the threshold value may be set to a value even greater than Tau+Tav+(Tres / 2).

[0164] Furthermore, if the time difference between the start of the high-level period of the first control signal SU2 and the start of the high-level period of the first control signal SW2 is less than a threshold value (e.g., Tres / 2), the control device 51 estimates that the U-phase resonant current and the W-phase resonant current overlap. The above threshold value is an example, and the threshold value may be set to another value. For example, the threshold value may be set to a value greater than Tres / 2, taking into account an error in the value of Tres / 2, etc. For example, the threshold value may be set to Tau + Taw + (Tres / 2). In this case, the control device 51 estimates that the U-phase current (current passing through the switch 8U) and the W-phase current (current passing through the switch 8W) overlap in the resonant inductor L1 if the time difference ΔTuw is less than Tau + Taw + (Tres / 2). Furthermore, taking into consideration an error in the value of Tau+Taw+(Tres / 2), the threshold value may be set to a value even greater than Tau+Taw+(Tres / 2).

[0165] Furthermore, if the time difference between the start of the high-level period of the first control signal SV2 and the start of the high-level period of the first control signal SW2 is less than a threshold value (e.g., Tres / 2), the control device 51 estimates that the V-phase resonant current and the W-phase resonant current overlap. The above threshold value is an example, and the threshold value may be set to another value. For example, the threshold value may be set to a value greater than Tres / 2, taking into account an error in the value of Tres / 2, etc. For example, the threshold value may be set to Tav + Taw + (Tres / 2). In this case, the control device 51 estimates that the V-phase current (current passing through the switch 8V) and the W-phase current (current passing through the switch 8W) overlap in the resonant inductor L1 if the time difference ΔTvw is less than Tav + Taw + (Tres / 2). Furthermore, taking into consideration an error in the value of Tav+Taw+(Tres / 2), the threshold value may be set to a value even greater than Tav+Taw+(Tres / 2).

[0166] (2.2.2) When it is determined that two-phase resonant currents flow simultaneously, the control device 51 executes a second control operation on a first switch that is one of the two or more switches 8. The control device 51 executes a first control operation on a second switch that is different from the first switch among the two or more switches 8. When the control device 51 executes the second control operation, the first switch is the switch 8 corresponding to the switching circuit 10 that has the largest absolute value of the load current flowing through each of the two or more switching circuits 10 that correspond to the two or more switches 8 in the multiple switching circuits 10.

[0167] The upper part of Figure 20 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and iL1 before the control system 50 determines that the U-phase resonant current and the V-phase resonant current flow simultaneously and before the second control operation is performed. The upper part of Figure 20 shows the current passing through the switch 8U and the resonant inductor L1 and the current passing through the switch 8V and the resonant inductor L1 separately. In the example of Figure 20, the absolute value of the load current iU is greater than the absolute value of the load current iV. Therefore, the first switch is the switch 8U.

[0168] The lower part of Fig. 20 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and the current iL1 when the control system 50 performs a shift based on the second control operation. Note that Fig. 20 shows a timing chart for a portion of one period within one cycle of the carrier signal.

[0169] In the power conversion device 100B, when the control device 51 does not perform the second control operation, the charging of the resonant capacitors 9U and 9V does not finish at the time when each of the first control signals SU1 and SV1 changes from a low level period to a high level period (the time when the dead time period Td corresponding to the U phase and the V phase ends), and the voltages across each of the first switching elements 1U and 1V do not decrease to zero. As a result, in the power conversion device 100B, the switching of the first switching elements 1U and 1V becomes hard switching.

[0170] (2.2.2.1) Resonant Capacitor Charging Operation When the control device 51 determines that the U-phase resonant current and the V-phase resonant current flow simultaneously, it shifts the high-level period of the second control signal SU6 to the U-phase third switching element 6U by a shift time Ts in a direction that delays the time axis, thereby shortening the overlap period between the high-level period of the second control signal SU6 and the dead time period Td immediately preceding the high-level period of the first control signal SU1. The shift time Ts set by the control device 51 can be set to any time as long as it is shorter than Tau + (Tres / 2). By performing the second control operation by the control device 51, in the power conversion device 100B, hard switching of the first switching element 1U is alleviated and zero-voltage soft switching of the first switching element 1V is performed. Since the voltage across the first switching circuit 10U is Vd, the sum of the voltage across the first switching element 1U and the voltage across the second switching element 2U is Vd. 20 , when the control device 51 determines in advance that two-phase resonant currents of the U phase and the V phase will flow simultaneously, the control device 51 performs the second control operation on the switch 8U (the third switching element 6U of the switch 8U), thereby shortening the overlap period of the U-phase resonant current and the V-phase resonant current.

[0171] Note that the control device 51 may shift the high-level period of the second control signal SV6, rather than the high-level period of the second control signal SU6, by a shift time Ts in a direction that delays the high-level period on the time axis to shorten the overlap period between the high-level period of the second control signal SV6 and the dead time period Td immediately before the high-level period of the first control signal SV1. In this case, the shift time Ts set by the control device 51 may be set to any time as long as it is shorter than Tav + (Tres / 2). When the control device 51 performs the second control operation, in the power conversion device 100B, the first switching element 1U is soft-switched and the hard switching of the first switching element 1V is alleviated.

[0172] Furthermore, in the power conversion device 100B, when the control device 51 determines in advance that two-phase resonant currents, U-phase and W-phase, will flow simultaneously, the control device 51 shifts the high-level period of the second control signal SU6 to the U-phase third switching element 6U by the shift time Ts in a direction that delays the time axis, thereby shortening the overlap period between the high-level period of the second control signal SU6 and the dead time period Td immediately preceding the high-level period of the first control signal SU1. As a result, in the power conversion device 100B, the overlap period between the U-phase resonant current and the W-phase resonant current can be shortened, hard switching of the first switching element 1U is alleviated, and zero-voltage soft switching of the first switching element 1W is performed.

[0173] Note that the control device 51 may shift the high-level period of the second control signal SW6 by the shift time Ts in a direction that delays the high-level period of the second control signal SW6 on the time axis, rather than the high-level period of the second control signal SU6, to shorten the overlap period between the high-level period of the second control signal SW6 and the dead time period Td immediately before the high-level period of the first control signal SW1. In this case, in the power conversion device 100B, the first switching element 1U is soft-switched and the hard switching of the first switching element 1W is alleviated.

[0174] Furthermore, in power conversion device 100B, when control device 51 determines in advance that two-phase resonant currents, V-phase and W-phase, will flow simultaneously, it shifts the high-level period of second control signal SV6 to V-phase third switching element 6V by shift time Ts in the direction that delays the time axis, thereby shortening the overlap period between the high-level period of second control signal SV6 and dead time period Td immediately before the high-level period of first control signal SV1. As a result, in power conversion device 100B, it is possible to shorten the overlap period between V-phase resonant current and W-phase resonant current, alleviate hard switching of first switching element 1V, and perform zero-voltage soft switching of first switching element 1W.

[0175] Note that the control device 51 may shift the high-level period of the second control signal SW6 by the shift time Ts in a direction that delays the high-level period of the second control signal SW6 on the time axis, rather than the high-level period of the second control signal SU6, to shorten the overlap period between the high-level period of the second control signal SW6 and the dead time period Td immediately before the high-level period of the first control signal SW1. In this case, in the power conversion device 100B, the first switching element 1U is soft-switched and the hard switching of the first switching element 1W is alleviated.

[0176] (2.2.2.2) Discharging Operation of Resonant Capacitor This differs from the charging operation of the resonant capacitor 9 in that the polarity of the load current and the polarity of the current iL1 are negative. Also, this differs from the charging operation of the resonant capacitor in that the fourth switching element 7, instead of the third switching element 6, is shifted in the direction slowing down on the time axis, thereby shortening the overlap period between the high-level period of the second control signal to the fourth switching element and the dead time period Td immediately before the high-level period of the first control signal to the second switching element 2.

[0177] In the power conversion device 100B, the control device 51 performs the second control operation on the first switch when it has determined in advance that two-phase resonant currents will flow simultaneously, thereby shortening the overlap period of the two-phase resonant currents. In the power conversion device 100B, the control device 51 performs the second control operation on the first switch, thereby alleviating hard switching of the second switching element 2 corresponding to the first switch of the two switches 8, and performing zero-voltage soft switching on the second switching element 2 corresponding to the switch 8 other than the first switch.

[0178] (3) Advantages As with the power conversion device 100 according to the first embodiment, the power conversion device 100B according to the fifth embodiment can stop the zero voltage soft switching without pulse width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0179] In addition, in the power conversion device 100B according to the fifth embodiment, when the control system 50 determines that a resonant current flows simultaneously through each of two or more switches 8 among the plurality of switches 8 in the resonant inductor L1 when a second control signal with a predetermined high level period is given to each of the plurality of switches 8, the control system 50 executes a second control operation on a first switch, which is one of the two or more switches 8.

[0180] According to the above configuration, when it is determined that resonant currents passing through two or more of the multiple switches 8 simultaneously flow through the resonant inductor L1, the control system 50 can realize zero-voltage soft switching of the target switching element corresponding to the switch 8 for which the first control operation is being performed, and the control system 50 can stop zero-voltage soft switching of the target switching element corresponding to the first switch for which the second control operation is being performed.

[0181] Sixth Embodiment (1) Configuration The configuration of a power conversion device 100A according to the sixth embodiment is the same as the configuration of the power conversion device 100A according to the third embodiment (see FIG. 5), and therefore will not be illustrated or described again.

[0182] (2) Operation In this embodiment, when the control system 50A provides a second control signal with a preset high-level duration to each of the multiple switches 8, it determines whether or not a resonant current flows through the resonant inductor L1 simultaneously through each of two or more of the multiple switches 8.

[0183] (2.1) Second Control Operation When the control system 50A provides a second control signal with a preset high-level duration to each of the multiple switches 8, the control system 50A determines whether or not a resonant current passing through each of two or more of the multiple switches 8 flows simultaneously through the resonant inductor L1, and if it determines that a resonant current passing through each of the two or more switches 8 flows simultaneously, it executes a second control operation on a first switch that is one of the two or more switches 8. "If it determines that a resonant current passing through each of the two or more switches 8 flows simultaneously" means that it has been estimated in advance that a resonant current passing through each of the two or more switches 8 will flow simultaneously through the resonant inductor L1.

[0184] (2.1.1) Determination of Whether Resonant Currents Flow Simultaneously Through the Two Switches In the following description, the length of the period (hereinafter also referred to as the run-up time) corresponding to the first period T01 (see FIG. 11) during the high-level period of the second control signal SU6 is defined as Tau, the length of the period corresponding to the second period T02 (see FIG. 11) as Tres / 2, and the length of the period corresponding to the third period T03 (see FIG. 11) as Tau. Tau is a value determined in the control device 51A by, for example, calculating Tau = iU × (L / V15) using the detection result of the load current iU by the current sensor or its signal-processed value, or the estimated value of the load current iU, the inductance L of the resonant inductor L1 that is stored in advance, and the detection result of the voltage V15 of the regenerative capacitor 15 (the potential V15 at the fourth end of the regenerative capacitor 15).

[0185] In the following description, the length of the period corresponding to the first period T01 during the high-level period of the second control signal SV6 (hereinafter also referred to as the run-up time) is denoted as Tav, the length of the period corresponding to the second period T02 is denoted as Tres / 2, and the length of the period corresponding to the third period T03 is denoted as Tav. Tav is a value determined in the control device 51A by calculating Tav = iV × (L / V15) using, for example, the detection result of the load current iV by the current sensor or its signal processed value, or the estimated value of the load current iV, the inductance L of the resonance inductor L1 that is stored in advance, and the detection result of the voltage V15 of the regenerative capacitor 15 (the potential V15 at the fourth end of the regenerative capacitor 15).

[0186] In the following description, the length of the period (hereinafter also referred to as the run-up time) corresponding to the first period T01 during the high-level period of the second control signal SW6 is denoted as Taw, the length of the period corresponding to the second period T02 is denoted as Tres / 2, and the length of the period corresponding to the third period T03 is denoted as Taw. Taw is a value determined in the control device 51A by calculating Taw=iW×(L / V15) using, for example, the detection result of the load current iW by the current sensor or its signal processed value, or the estimated value of the load current iW, the inductance L of the resonance inductor L1 that is stored in advance, and the detection result of the voltage V15 of the regenerative capacitor 15 (the potential V15 at the fourth end of the regenerative capacitor 15).

[0187] The on-period of the first switching element 1U corresponds one-to-one to the high-level period of the first control signal SU1. The on-period of the first switching element 1V corresponds one-to-one to the high-level period of the first control signal SV1. The on-period of the first switching element 1W corresponds one-to-one to the high-level period of the first control signal SW1. Furthermore, the on-period of the second switching element 2U corresponds one-to-one to the high-level period of the first control signal SU2. The on-period of the second switching element 2V corresponds one-to-one to the high-level period of the first control signal SV2. The on-period of the second switching element 2W corresponds one-to-one to the high-level period of the first control signal SW2.

[0188] The control device 51A generates the first control signals SU1, SU2, SV1, SV2, SW1, and SW2, for example, for each cycle of the carrier signal, and then determines whether or not there is overlap in the resonant currents before controlling the first switching element 1U, the second switching element 2U, the first switching element 1V, the second switching element 2V, the first switching element 1W, and the second switching element 2W.

[0189] (2.1.1.1) In the case of charging operation of the resonant capacitor In the power conversion device 100A, if the time difference ΔTuv is equal to or greater than Tau + Tav + (Tres / 2), the U-phase current and the V-phase current do not overlap, and if the time difference ΔTuv is less than Tau + Tav + Tres / 2, the U-phase current and the V-phase current overlap. The time difference ΔTuv is the time difference between the start of the high-level period of the first control signal SU1 given to the first switching element 1U of the switching circuit 10U and the start of the high-level period of the first control signal SV1 given to the first switching element 1V of the switching circuit 10V. The control device 51A determines the overlap time Tov_uv during which the U-phase current and the V-phase current overlap by calculating Tov_uv = Tau + Tav + (Tres / 2) - ΔTuv. If Tov_uv > 0, the control device 51A estimates that the U-phase current and the V-phase current overlap. Furthermore, if Tov_uv ≥ Tres / 2, the control device 51A estimates that the U-phase resonant current and the V-phase resonant current overlap. The method for calculating the time difference ΔTuv is not limited to the above example, and for example, the time difference between the end point of the high-level period of the first control signal SU2 provided to the second switching element 2U of the switching circuit 10U and the end point of the high-level period of the first control signal SV2 provided to the second switching element 2V of the switching circuit 10V may be used.

[0190] Furthermore, in the power conversion device 100A, if the time difference ΔTuw is equal to or greater than Tau + Taw + (Tres / 2), the U-phase current and the W-phase current do not overlap, and if the time difference ΔTuw is less than Tau + Taw + (Tres / 2), the U-phase current and the W-phase current overlap. The time difference ΔTuw is the time difference between the start point of the high-level period of the first control signal SU1 and the start point of the high-level period of the first control signal SW1. The control device 51A determines the overlap time Tov_uw by calculating Tov_uw = Tau + Taw + (Tres / 2) - ΔTuw, where Tov_uw is the overlap time during which the U-phase current and the W-phase current overlap. If Tov_uw > 0, the control device 51A estimates that the U-phase current and the W-phase current overlap. Furthermore, if Tov_uw≧Tres / 2, the control device 51A estimates that the U-phase resonant current and the W-phase resonant current overlap. The method for calculating the time difference ΔTuw is not limited to the above example, and for example, the time difference between the end point of the high level period of the first control signal SU2 and the end point of the high level period of the first control signal SW2 may be used.

[0191] Furthermore, in the power conversion device 100A, if the time difference ΔTvw is equal to or greater than Tav + Taw + (Tres / 2), the V-phase current and the W-phase current do not overlap, and if the time difference ΔTvw is less than Tav + Taw + (Tres / 2), the V-phase current and the W-phase current overlap. The time difference ΔTvw is the time difference between the start of a high-level period of the first control signal SV1 provided to the first switching element 1V of the switching circuit 10V and the start of a high-level period of the first control signal SW1 provided to the first switching element 1W of the switching circuit 10W. The control device 51A determines the overlap time Tov_vw during which the V-phase current and the W-phase current overlap by calculating Tov_vw = Tav + Taw + (Tres / 2) - ΔTvw. The control device 51A estimates that the V-phase current and the W-phase current overlap if Tov_vw>0. Furthermore, the control device 51A estimates that the V-phase resonant current and the W-phase resonant current overlap if Tov_vw≧Tres / 2. The method for calculating the time difference ΔTvw is not limited to the above example, and may use, for example, the time difference between the end point of the high-level period of the first control signal SV2 and the end point of the high-level period of the first control signal SW2.

[0192] The control system 50A executes a second control operation on a first switch that is one of the two or more switches 8. The control system 50A executes a first control operation on a second switch that is different from the first switch among the two or more switches 8. When the control system 50A executes the second control operation, the first switch is the switch 8 among the two or more switches 8 that corresponds to the switching circuit 10 that has the largest absolute value of the load current flowing through each of the two or more switching circuits 10 that correspond to the two or more switches 8 in the plurality of switching circuits 10.

[0193] The upper part of Figure 21 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and iL1 before the second control operation shifts when the control system 50A determines that the U-phase resonant current and the V-phase resonant current flow simultaneously. In the example of Figure 21, the absolute value of the load current iU is greater than the absolute value of the load current iV. Therefore, the first switch is switch 8U.

[0194] 21 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and the current iL1 when the control system 50 performs a shift based on the second control operation. Note that FIG. 21 shows a timing chart for a portion of one period within one cycle of the carrier signal.

[0195] In the power conversion device 100A, when the control system 50A does not perform the second control operation, the charging of the resonant capacitors 9U and 9V does not finish at the time when each of the first control signals SU1 and SV1 changes from a low level period to a high level period (the time when the dead time period Td corresponding to the U phase and the V phase ends), and the voltages across each of the first switching elements 1U and 1V do not decrease to zero. As a result, in the power conversion device 100A, the switching of the first switching elements 1U and 1V becomes hard switching.

[0196] When the control device 51A determines that the U-phase resonant current and the V-phase resonant current flow simultaneously during the charging operation of the resonant capacitor 9, it sets the additional time Tad in the second dead time period Td2 (= Td1 + Tad) of the U-phase to an arbitrary time shorter than Tau + (Tres / 2). As a result, the high-level period of the second control signal SU6 to the U-phase third switching element 6U is shifted later on the time axis without the control device 51A directly controlling the U-phase switch 8U, thereby shortening the overlap period between the high-level period of the second control signal SU6 and the dead time period (second dead time period Td2) immediately before the high-level period of the first control signal SU1. By the control system 50A performing the second control operation, in the power conversion device 100A, hard switching of the first switching element 1U is alleviated and zero-voltage soft switching of the first switching element 1V is performed. Since the value of the voltage across first switching circuit 10U is Vd, the sum of the voltage across first switching element 1U and the voltage across second switching element 2U is Vd. Mitigating hard switching of first switching element 1U means that the value of the voltage across first switching element 1U when first switching element 1U is turned on is reduced below Vd. As can be seen from the waveform of current iL1 in the upper part and the waveform of current iL1 in the lower part of Figure 21 , in power conversion device 100A, when control system 50A determines in advance that two-phase resonant currents, U-phase and V-phase, will flow simultaneously, it performs a second control operation on switch 8U (third switching element 6U of switch 8U), thereby shortening the overlap period of the U-phase resonant current and the V-phase resonant current.

[0197] Note that the control system 50A may set the second dead time period Td2 (= Td1 + Tad) of the V phase to any time shorter than Tav + (Tres / 2), rather than the additional time Tad in the second dead time period Td2 (= Td1 + Tad) of the U phase. This shortens the overlap period between the high-level period of the second control signal SV6 and the dead time period (second dead time period Td2) immediately before the high-level period of the first control signal SV1. As a result, in the power conversion device 100A, the first switching element 1U is subjected to zero-voltage soft switching, and hard switching of the first switching element 1V is alleviated.

[0198] Furthermore, in the power conversion device 100A, if the control system 50A determines in advance that two-phase resonant currents, the U-phase and the W-phase, flow simultaneously, the control system 50A sets the additional time Tad in the second dead time period Td2 (= Td1 + Tad) of the U-phase to an arbitrary time shorter than Tau + (Tres / 2). As a result, the control device 51A does not directly control the U-phase switch 8U, and the high-level period of the second control signal SU6 to the third switching element 6U of the U-phase is shifted later on the time axis, thereby shortening the overlap period between the high-level period of the second control signal SU6 and the dead time period (second dead time period Td2) immediately before the high-level period of the first control signal SU1. By the control system 50A performing the second control operation, in the power conversion device 100A, hard switching of the first switching element 1U is alleviated and zero-voltage soft switching of the first switching element 1W is performed.

[0199] Note that the control system 50A may set the second dead time period Td2 (= Td1 + Tad) of the W phase to an arbitrary time shorter than Taw + (Tres / 2), rather than the additional time Tad in the second dead time period Td2 (= Td1 + Tad) of the U phase. This shortens the overlap period between the high-level period of the second control signal SW6 and the dead time period (second dead time period Td2) immediately before the high-level period of the first control signal SW1. As a result, in the power conversion device 100A, the first switching element 1U is zero-voltage soft-switched, and hard switching of the first switching element 1W is alleviated.

[0200] Furthermore, in the power conversion device 100A, if the control system 50A determines in advance that two-phase resonant currents, the V-phase and the W-phase, flow simultaneously, the control system 50A sets the additional time Tad in the second dead time period Td2 (= Td1 + Tad) of the V-phase to an arbitrary time shorter than Tav + (Tres / 2). As a result, the control device 51A does not directly control the V-phase switch 8V, and the high-level period of the second control signal SV6 to the V-phase third switching element 6V is shifted later on the time axis, thereby shortening the overlap period between the high-level period of the second control signal SV6 and the dead time period (second dead time period Td2) immediately before the high-level period of the first control signal SV1. By the control system 50A performing the second control operation, in the power conversion device 100A, hard switching of the first switching element 1V is alleviated and zero-voltage soft switching of the first switching element 1W is performed.

[0201] Note that the control system 50A may set the second dead time period Td2 (= Td1 + Tad) of the W phase to an arbitrary time shorter than Taw + (Tres / 2), rather than the additional time Tad in the second dead time period Td2 (= Td1 + Tad) of the V phase. This shortens the overlap period between the high-level period of the second control signal SW6 and the dead time period (second dead time period Td2) immediately before the high-level period of the first control signal SW1. As a result, in the power conversion device 100A, the first switching element 1V is zero-voltage soft-switched, and hard switching of the first switching element 1W is alleviated.

[0202] (2.1.1.2) Discharging Operation of Resonant Capacitor The discharging operation of the resonant capacitor 9 differs from the charging operation of the resonant capacitor 9 in that the polarity of the load current and the polarity of the current iL1 are negative. Also, it differs from the charging operation of the resonant capacitor in that the fourth switching element 7, instead of the third switching element 6, is shifted in the direction slowing down on the time axis, thereby shortening the overlap period between the high-level period of the second control signal to the fourth switching element and the dead time period (second dead time period Td2) immediately before the high-level period of the first control signal to the second switching element 2.

[0203] In the power conversion device 100A, the control system 50A performs a second control operation on the first switch when it has determined in advance that two-phase resonant currents will flow simultaneously, thereby shortening the overlap period of the two-phase resonant currents. In the power conversion device 100A, the control system 50A performs the second control operation on the first switch, thereby alleviating hard switching of the second switching element 2 corresponding to the first switch of the two switches 8, and performing zero-voltage soft switching on the second switching element 2 corresponding to the switch 8 other than the first switch.

[0204] (3) Advantages As with the power conversion device 100A according to the third embodiment, the power conversion device 100A according to the sixth embodiment can stop the zero voltage soft switching without pulse width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0205] Furthermore, in the power conversion device 100A according to the sixth embodiment, similarly to the power conversion device 100A according to the third embodiment, the control system 50A includes the control device 51A and the signal generating circuit 52, and therefore, the zero voltage soft switching can be more reliably realized without the control device 51A directly controlling the plurality of switches 8 for zero voltage soft switching. More specifically, the control device 51A does not need to generate a second control signal for directly controlling the plurality of switches 8 for zero voltage soft switching, and the zero voltage soft switching of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 can be realized without the control device 51A directly controlling the plurality of switches 8.

[0206] In addition, in the power conversion device 100A according to the sixth embodiment, when the control system 50A determines that a resonant current flows simultaneously through each of two or more switches 8 among the multiple switches 8 in the resonant inductor L1 when a second control signal with a predetermined high level period is given to each of the multiple switches 8, the control system 50A executes a second control operation on a first switch, which is one of the two or more switches 8.

[0207] According to the above configuration, when it is determined that resonant currents passing through two or more of the multiple switches 8 simultaneously flow through the resonant inductor L1, the control system 50A can realize zero-voltage soft switching of the target switching element corresponding to the switch 8 for which it performs the first control operation, and it becomes possible to stop the zero-voltage soft switching of the target switching element corresponding to the first switch for which it performs the second control operation without pulse-width modulating the second control signal sent to each of the multiple switches 8 for zero-voltage soft switching.

[0208] Seventh Embodiment (1) Configuration The configuration of a power conversion device 100B according to the seventh embodiment is the same as the configuration of the power conversion device 100B according to the fifth embodiment (see FIG. 17), and therefore will not be illustrated or described again.

[0209] (2) Operation The operation of the power conversion device 100B according to the seventh embodiment is substantially the same as the operation of the power conversion device 100B according to the fifth embodiment. The control system 50 according to the seventh embodiment differs from the second control operation of the control system 50 according to the fifth embodiment in that, in the second control operation, the entire high-level period of the second control signal to the first switch is overlapped with a part of the high-level period of the first control signal to the target switching element corresponding to the first switch.

[0210] The upper part of Figure 22 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and iL1 before the control device 51 performs a shift based on the second control operation when it determines that the U-phase resonant current and the V-phase resonant current flow simultaneously. In the example of Figure 22, the absolute value of the load current iU is greater than the absolute value of the load current iV. Note that, although the control device 51 designates the switch 8U, which has a larger absolute value of the load current, as the first switch in this embodiment, the control device 51 may designate the switch 8V, which has a smaller absolute value of the load current, as the first switch.

[0211] 22 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and the current iL1 when the control device 51 performs a shift based on the second control operation. Note that FIG. 22 shows a timing chart for a portion of one period within one cycle of the carrier signal.

[0212] In the power conversion device 100B according to the seventh embodiment, when the control device 51 does not perform the second control operation, the charging of the resonant capacitors 9U and 9V does not finish at the time when each of the first control signals SU1 and SV1 changes from a low level period to a high level period (the time when the dead time period Td corresponding to the U phase and the V phase ends), and the voltages across each of the first switching elements 1U and 1V do not decrease to zero. As a result, in the power conversion device 100B, the switching of the first switching elements 1U and 1V becomes hard switching.

[0213] When the control device 51 determines that the U-phase resonant current and the V-phase resonant current flow simultaneously during the charging operation of the resonant capacitor 9, it shifts the high-level period of the second control signal SU6 to the U-phase third switching element 6U by a shift time Ts in a direction that delays the time axis, so that the entire high-level period of the second control signal SU6 overlaps with the high-level period of the first control signal SU1. The shift time Ts set by the control device 51 is Ts = Tau + (Tres / 2). By performing the second control operation, the control device 51 stops the zero-voltage soft switching of the first switching element 1U in the power conversion device 100B without pulse-width modulating the second control signal to each of the multiple zero-voltage soft switching switches 8, and the first switching element 1V is zero-voltage soft switched.

[0214] Note that the control device 51 may shift the high-level period of the second control signal SV6, rather than the high-level period of the second control signal SU6, by a shift time Ts in a direction that delays the high-level period of the second control signal SV6 on the time axis, so that the entire high-level period of the second control signal SV6 overlaps with the high-level period of the first control signal SV1. In this case, the shift time Ts set by the control device 51 is Ts = Tav + (Tres / 2). When the control device 51 performs the second control operation, the first switching element 1U in the power conversion device 100B is subjected to zero-voltage soft switching.

[0215] The above describes an example of a shift by the second control operation when the control device 51 determines that two-phase resonant currents, U phase and V phase, flow simultaneously (overlap). However, in both cases where two-phase resonant currents, U phase and W phase, flow simultaneously, and where two-phase resonant currents, V phase and W phase, flow simultaneously, a shift by the second control operation is performed using the same concept (algorithm) as the shift by the second control operation when it is determined that two-phase resonant currents, U phase and V phase, flow simultaneously.

[0216] (3) Advantages As with the power conversion device 100B according to the fifth embodiment, the power conversion device 100B according to the seventh embodiment can stop the zero voltage soft switching without pulse width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0217] Furthermore, similar to the power conversion device 100B according to the fifth embodiment, when it is determined that a resonant current passing through each of two or more of the multiple switches 8 simultaneously flows through the resonant inductor L1, the power conversion device 100B according to the seventh embodiment can realize zero-voltage soft switching of the target switching element corresponding to the switch 8 for which the control system 50 executes the first control operation, and can stop the zero-voltage soft switching of the target switching element corresponding to the first switch for which the control system 50 executes the second control operation without pulse-width modulating the second control signal sent to each of the multiple switches 8 for zero-voltage soft switching.

[0218] Eighth Embodiment (1) Configuration The configuration of a power conversion device 100A according to the eighth embodiment is the same as the configuration of the power conversion device 100A according to the third embodiment (see FIG. 5), and therefore will not be illustrated or described again.

[0219] (2) Operation The operation of the power conversion device 100A according to the eighth embodiment is substantially the same as the operation of the power conversion device 100A according to the sixth embodiment. The control system 50A according to the eighth embodiment differs from the second control operation of the control system 50A according to the sixth embodiment in that, in the second control operation, the entire high-level period of the second control signal to the first switch is overlapped with the high-level period of the first control signal to the target switching element corresponding to the first switch.

[0220] The upper part of Figure 23 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and iL1 before the control system 50A determines that the U-phase resonant current and the V-phase resonant current flow simultaneously and performs a shift based on the second control operation. In the example of Figure 23, the absolute value of the load current iU is greater than the absolute value of the load current iV. Note that, although the control system 50A designates the switch 8U, which has a larger absolute value of the load current, as the first switch in this embodiment, the control system 50A may designate the switch 8V, which has a smaller absolute value of the load current, as the first switch.

[0221] The lower part of Fig. 23 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and the current iL1 when the control system 50A performs a shift based on the second control operation. Note that Fig. 23 shows a timing chart for a portion of one period within one cycle of the carrier signal.

[0222] In the power conversion device 100A according to the eighth embodiment, when the control system 50A does not perform the second control operation, charging of the resonant capacitors 9U and 9V does not finish at the time when each of the first control signals SU1 and SV1 changes from a low level period to a high level period (the time when the dead time period Td corresponding to the U phase and the V phase ends), and the voltages across each of the first switching elements 1U and 1V do not decrease to zero. As a result, in the power conversion device 100A, the switching of the first switching elements 1U and 1V becomes hard switching.

[0223] When the control system 50A determines that the U-phase resonant current and the V-phase resonant current flow simultaneously during the charging operation of the resonant capacitor 9, it shifts the high-level period of the second control signal SU6 to the U-phase third switching element 6U by a shift time Ts in a direction that delays the time axis, so that the entire high-level period of the second control signal SU6 overlaps with the high-level period of the first control signal SU1. The shift time Ts set by the control device 51A of the control system 50A is Ts = Tau + (Tres / 2). By performing the second control operation by the control system 50A, in the power conversion device 100A, the zero-voltage soft switching of the first switching element 1U is stopped without pulse-width modulating the second control signal to each of the multiple zero-voltage soft switching switches 8, and the first switching element 1V is zero-voltage soft switched.

[0224] Note that the control system 50A may shift the high-level period of the second control signal SV6, rather than the high-level period of the second control signal SU6, by a shift time Ts in a direction that delays the high-level period of the second control signal SV6 on the time axis, so that the entire high-level period of the second control signal SV6 overlaps with the high-level period of the first control signal SV1. In this case, the shift time Ts set by the control device 51A is Ts = Tav + (Tres / 2). When the control system 50A performs the second control operation, in the power conversion device 100A, the first switching element 1U is subjected to zero-voltage soft switching and the hard switching of the first switching element 1V is alleviated.

[0225] The above describes an example of a shift by the second control operation when the control system 50A determines that two-phase resonant currents, U phase and V phase, flow simultaneously (overlap). However, in both cases where two-phase resonant currents, U phase and W phase, flow simultaneously, and where two-phase resonant currents, V phase and W phase, flow simultaneously, the shift by the second control operation is performed using the same concept (algorithm) as the shift by the second control operation when it is determined that two-phase resonant currents, U phase and V phase, flow simultaneously.

[0226] (3) Advantages As with the power conversion device 100A according to the third embodiment, the power conversion device 100A according to the eighth embodiment can stop the zero voltage soft switching without pulse width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0227] Furthermore, in the power conversion device 100A according to the eighth embodiment, similarly to the power conversion device 100A according to the third embodiment, the control system 50A includes the control device 51A and the signal generating circuit 52, and therefore, the zero voltage soft switching can be more reliably realized without the control device 51A directly controlling the plurality of switches 8 for zero voltage soft switching. More specifically, the control device 51A does not need to generate a second control signal for directly controlling the plurality of switches 8 for zero voltage soft switching, and the zero voltage soft switching of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 can be realized without the control device 51A directly controlling the plurality of switches 8.

[0228] As with the power conversion device 100A according to the sixth embodiment, when it is determined that a resonant current flows through each of two or more of the multiple switches 8 simultaneously in the resonant inductor L1, the power conversion device 100A according to the eighth embodiment can realize zero-voltage soft switching of the target switching element corresponding to the switch 8 for which the control system 50A executes the first control operation, and can stop the zero-voltage soft switching of the target switching element corresponding to the first switch for which the control system 50A executes the second control operation without pulse-width modulating the second control signal sent to each of the multiple switches 8 for zero-voltage soft switching.

[0229] Ninth Embodiment (1) Configuration The configuration of a power conversion device 100B according to the ninth embodiment is the same as the configuration of the power conversion device 100B according to the fifth embodiment (see FIG. 17), and therefore will not be illustrated or described.

[0230] (2) Operation The operation of the power conversion device 100B according to the ninth embodiment is substantially the same as the operation of the power conversion device 100B according to the fifth embodiment.

[0231] The power conversion device 100B according to the ninth embodiment differs from the power conversion device 100B according to the fifth embodiment in that the control system 50 also performs the second control operation when the control system 50 determines that resonant currents passing through three of the multiple switches 8 will flow simultaneously (i.e., when it is determined in advance that three-phase resonant currents will flow simultaneously). "When it is determined that resonant currents passing through three of the multiple switches 8 will flow simultaneously" means when it is estimated in advance that resonant currents passing through the three switches 8 will flow simultaneously through the resonant inductor L1. The control device 51 determines that three-phase resonant currents are flowing simultaneously when, for example, the time difference between the start of the high-level period of the second control signal SU6 corresponding to the U phase and the start of the high-level period of the first control signal SV1 corresponding to the V phase, the time difference between the start of the high-level period of the second control signal SV6 corresponding to the V phase and the start of the high-level period of the first control signal SW1 corresponding to the W phase, and the time difference between the start of the high-level period of the second control signal SW6 corresponding to the W phase and the start of the high-level period of the first control signal SU1 corresponding to the U phase are all less than a threshold value.

[0232] Assuming that the capacitance of each of the multiple resonant capacitors 9U, 9V, and 9W is C, if U-phase, V-phase, and W-phase currents simultaneously flow through the resonant inductor L1, then in terms of an equivalent circuit, a capacitor having a combined capacitance (=3×C) of the resonant capacitors 9U, 9V, and 9W is connected in series with the resonant inductor L1. Therefore, in the power conversion device 100B, if three-phase currents simultaneously flow through the resonant inductor L1, the resonant frequency of the resonant circuit including the resonant inductor L1 changes compared to when one-phase current flows through the resonant inductor L1, potentially making it impossible to achieve zero-voltage soft switching. Furthermore, if the control system 50 does not perform the second control operation, three-phase resonant currents are likely to flow simultaneously, for example, when the servo motor, which is the AC load RA1, is rotating at low speed.

[0233] In the second control operation, the control system 50 shifts a predetermined second control signal by a shift time Ts for a first switch that is one of the three switches 8, thereby shortening the overlap period between the second control signal and the dead time period Td, and supplies a predetermined second control signal to a second switch that is different from the first switch 8. The control system 50 also shifts a predetermined second control signal by a shift time Ts for a third switch that is different from the first and second switches 8, thereby shortening the overlap period between the second control signal and the dead time period Td. When the control system 50 performs the second control operation, the first switch 8 is the switch 8 of the three switches 8 corresponding to the switching circuit 10 that has the largest absolute value of the load current flowing through each of the three switching circuits 10 corresponding to the three switches 8. The third switch 8 is the switch 8 of the three switches 8 corresponding to the switching circuit 10 that has the second largest absolute value of the load current flowing through each of the three switching circuits 10 corresponding to the three switches 8.

[0234] (2.1) In the case of charging operation of the resonant capacitor Below, we will explain the second control operation when the control system 50 has determined in advance that three-phase resonant currents, namely U phase, V phase, and W phase, will flow simultaneously, with reference to Figures 24 and 25.

[0235] Figure 24 shows timing charts of the first control signals SU1, SU2, SV1, SV2, SW1, SW2, the second control signals SU6, SV6, SW6, the load currents iU, iV, iW, and current iL1 before the control system 50 performs the second control operation when it determines that three-phase resonant currents are flowing simultaneously. Figure 25 shows timing charts of the first control signals SU1, SU2, SV1, SV2, SW1, SW2, the second control signals SU6, SV6, SW6, the load currents iU, iV, iW, and current iL1 when the control system 50 performs the second control operation. Note that Figures 24 and 25 show timing charts for a portion of one period of the carrier signal.

[0236] In the power conversion device 100B, unless the control system 50 performs the second control operation, charging of the resonant capacitors 9U, 9V, and 9W does not finish at the end of the dead time period Td corresponding to each of the U, V, and W phases. Therefore, unless the control system 50 performs the second control operation, the voltages across the first switching elements 1U, 1V, and 1W do not decrease to zero at the end of the dead time period Td corresponding to each of the U, V, and W phases. As a result, in the power conversion device 100B, the switching of the first switching elements 1U, 1V, and 1W becomes hard switching.

[0237] The control system 50 compares the absolute values ​​of the load current iU, iV, and iW, and shifts the high-level period of the second control signal SW6 to the switch 8W having the largest absolute value of the load current by a shift time Ts (Tsw), and shifts the high-level period of the second control signal SU6 to the switch 8U having the second largest absolute value of the load current by a shift time Ts (Tsu). It can be seen from the waveform of the current iL1 in Figure 25 that zero-voltage soft switching of the first switching element 1V is achieved and hard switching of the first switching elements 1U and 1W is mitigated.

[0238] (2.2) In the Case of Discharge Operation of Resonant Capacitors In the power conversion device 100B, if the control system 50 does not perform the second control operation when the three-phase resonant currents overlap, the voltages V2u, V2v, and V2w across the second switching elements 2U, 2V, and 2W do not decrease to zero when the first control signals SU2, SV2, and SW2 change from low to high (the end of the dead time periods corresponding to the U, V, and W phases, respectively). In other words, if the control system 50 does not perform the second control operation, the discharge of the resonant capacitors 9U, 9V, and 9W does not finish when the dead time periods corresponding to the U, V, and W phases, respectively, end. As a result, in the power conversion device 100B, the switching of the second switching elements 2U, 2V, and 2W becomes hard switching.

[0239] In response to this, when the control system 50 determines that the three-phase resonant currents overlap, it performs a second control operation on each of the first switch and the third switch, and performs a first control operation on the second switch, thereby performing zero-voltage soft switching on the second switching element 2 corresponding to the second switch, and stopping the zero-voltage soft switching of each of the second switching element 2 corresponding to the first switch and the second switching element 2 corresponding to the third switch.

[0240] (3) Advantages As with the power conversion device 100B according to the fifth embodiment, the power conversion device 100B according to the ninth embodiment can stop the zero voltage soft switching without pulse-width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0241] In addition, in the power conversion device 100B of embodiment 9, when the control system 50 determines that a resonant current flows simultaneously through each of three of the multiple switches 8 in the resonant inductor L1 when a second control signal with a predetermined high-level period is given to each of the multiple switches 8, the control system 50 executes a second control operation on the first switch and the third switch of the three switches 8.

[0242] According to the above configuration, when it is determined that resonant currents passing through three of the multiple switches 8 simultaneously flow through the resonant inductor L1, zero-voltage soft switching of the target switching elements corresponding to the switches 8 for which the control system 50 executes the first control operation can be realized, and hard switching of the target switching elements corresponding to the first and third switches for which the control system 50 executes the second control operation can be mitigated without pulse-width modulating the second control signal to each of the multiple switches 8 for zero-voltage soft switching.

[0243] The control system 50 may be configured to stop the zero voltage soft switching of any of the first switches and third switches, regardless of the magnitude of the absolute value of the load current.

[0244] Tenth Embodiment (1) Configuration The configuration of a power conversion device 100A according to the tenth embodiment is the same as the configuration of the power conversion device 100A according to the third embodiment (see FIG. 5), and therefore will not be illustrated or described again.

[0245] (2) Operation The operation of the power conversion device 100A according to the tenth embodiment is substantially the same as the operation of the power conversion device 100A according to the sixth embodiment.

[0246] The power conversion device 100A according to the tenth embodiment differs from the power conversion device 100A according to the sixth embodiment in that the control system 50A also performs the second control operation when the control system 50A determines that resonant currents passing through three of the multiple switches 8 will flow simultaneously (i.e., when it is determined in advance that three-phase resonant currents will flow simultaneously). The phrase "when it is determined that resonant currents passing through three of the multiple switches 8 will flow simultaneously" refers to a case where it is estimated in advance that resonant currents passing through the three switches 8 will flow simultaneously through the resonant inductor L1. The control device 51 determines that three-phase resonant currents are flowing simultaneously when, for example, the time difference between the start of the high-level period of the second control signal SU6 corresponding to the U phase and the start of the high-level period of the first control signal SV1 corresponding to the V phase, the time difference between the start of the high-level period of the second control signal SV6 corresponding to the V phase and the start of the high-level period of the first control signal SW1 corresponding to the W phase, and the time difference between the start of the high-level period of the second control signal SW6 corresponding to the W phase and the start of the high-level period of the first control signal SU1 corresponding to the U phase are all less than a threshold value.

[0247] In the second control operation, for a first switch that is one of the three switches 8, the control system 50A shortens the additional time Tad of the dead time period of the switching circuit 10 corresponding to the first switch so that the start point of the high level period of the second control signal to the first switch coincides with the start point of the high level period of the target switching element of the switching circuit 10 corresponding to the second switch. Furthermore, the control system 50A shortens the additional time Tad of the dead time period of the switching circuit 10 corresponding to the third switch so that the start point of the high level period of the second control signal to a third switch among the three switches 8 that is different from the first and second switches coincides with the start point of the high level period of the target switching element of the switching circuit 10 corresponding to the first switch. When the control system 50A performs the second control operation, the first switch is the switch 8 of the three switches 8 that corresponds to the switching circuit 10 that has the largest absolute value of the load current flowing through each of the three switching circuits 10 corresponding to the three switches 8 in the multiple switching circuits 10. The third switch is the switch 8 corresponding to the switching circuit 10 among the three switches 8 that has the second largest absolute value of the load current flowing through each of the three switching circuits 10 corresponding to the three switches 8 in the multiple switching circuits 10.

[0248] (2.1) In the case of charging operation of the resonant capacitor Below, we will explain the second control operation when the control system 50A has determined in advance that three-phase resonant currents, namely U phase, V phase, and W phase, will flow simultaneously, with reference to Figures 26 and 27.

[0249] Figure 26 shows timing charts of the first control signals SU1, SU2, SV1, SV2, SW1, SW2, the second control signals SU6, SV6, SW6, the load currents iU, iV, iW, and current iL1 before the control system 50A performs the second control operation when it determines that three-phase resonant currents are flowing simultaneously. Figure 27 shows timing charts of the first control signals SU1, SU2, SV1, SV2, SW1, SW2, the second control signals SU6, SV6, SW6, the load currents iU, iV, iW, and current iL1 after the control system 50A performs the second control operation. Note that Figures 26 and 27 show timing charts for a portion of one period of the carrier signal.

[0250] In the power conversion device 100A, unless the control system 50A performs the second control operation, charging of the resonant capacitors 9U, 9V, and 9W does not finish at the end of the dead time period Td corresponding to each of the U, V, and W phases. Therefore, unless the control system 50A performs the second control operation, the voltages across the first switching elements 1U, 1V, and 1W do not decrease to zero at the end of the dead time period Td corresponding to each of the U, V, and W phases. As a result, in the power conversion device 100A, the switching of the first switching elements 1U, 1V, and 1W becomes hard switching.

[0251] The control system 50A compares the absolute values ​​of the load current iU, iV, and iW, and shortens the high-level period of the second control signal SW6 sent to the first switch (switch 8W) whose absolute value of the load current is the largest, and shortens the high-level period of the second control signal SU6 sent to the third switch (switch 8U) whose absolute value of the load current is the second largest. It can be seen from the waveform of the current iL1 in Figure 27 that zero-voltage soft switching of the first switching element 1V is achieved, and hard switching of the first switching elements 1U and 1W is mitigated.

[0252] (2.2) In the Case of Discharge Operation of Resonant Capacitors In the power conversion device 100A, if the control system 50A does not perform the second control operation when the three-phase resonant currents overlap, the voltages V2u, V2v, and V2w across the second switching elements 2U, 2V, and 2W do not decrease to zero when the first control signals SU2, SV2, and SW2 change from low to high (the end of the dead time periods corresponding to the U, V, and W phases, respectively). In other words, if the control system 50A does not perform the second control operation, the discharge of the resonant capacitors 9U, 9V, and 9W does not finish when the dead time periods corresponding to the U, V, and W phases, respectively, end. As a result, in the power conversion device 100A, the switching of the second switching elements 2U, 2V, and 2W becomes hard switching.

[0253] In contrast, when the control system 50A determines that the three-phase resonant currents overlap, it performs a second control operation on each of the first switch and the third switch, and performs a first control operation on the second switch, thereby causing the second switching element 2 corresponding to the second switch to be zero-voltage soft-switched, and mitigating the hard switching of each of the second switching element 2 corresponding to the first switch and the second switching element 2 corresponding to the third switch.

[0254] (3) Advantages As with the power conversion device 100A according to the third embodiment, the power conversion device 100A according to the tenth embodiment can stop the zero voltage soft switching without pulse width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0255] Furthermore, in the power conversion device 100A according to the tenth embodiment, similarly to the power conversion device 100A according to the third embodiment, the control system 50A includes the control device 51A and the signal generating circuit 52, and therefore, the zero voltage soft switching can be more reliably realized without the control device 51A directly controlling the plurality of switches 8 for zero voltage soft switching. More specifically, the control device 51A does not need to generate a second control signal for directly controlling the plurality of switches 8 for zero voltage soft switching, and the zero voltage soft switching of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 can be realized without the control device 51A directly controlling the plurality of switches 8.

[0256] Furthermore, in the power conversion device 100A according to the tenth embodiment, when the control system 50A determines that a resonant current flows through each of three of the switches 8 simultaneously in the resonant inductor L1 when a second control signal with a predetermined high-level period is given to each of the switches 8, the control system 50A executes a second control operation on the first switch and the third switch of the three switches 8.

[0257] According to the above configuration, when it is determined that resonant currents passing through three of the multiple switches 8 simultaneously flow through the resonant inductor L1, the control system 50A can realize zero-voltage soft switching of the target switching elements corresponding to the switches 8 for which it performs the first control operation, and it becomes possible to stop the zero-voltage soft switching of the target switching elements corresponding to the first and third switches for which it performs the second control operation without pulse-width modulating the second control signal sent to each of the multiple switches 8 for zero-voltage soft switching.

[0258] The control system 50A may be configured to stop the zero voltage soft switching of any of the first switches and third switches, regardless of the magnitude of the absolute value of the load current.

[0259] Eleventh Embodiment (1) Configuration The configuration of a power conversion device 100B according to the eleventh embodiment is the same as the configuration of the power conversion device 100B according to the fifth embodiment (see FIG. 17), and therefore will not be illustrated or described again.

[0260] (2) Operation The operation of the power conversion device 100B according to the eleventh embodiment is substantially the same as the operation of the power conversion device 100B according to the 9th embodiment. The control system 50 according to the eleventh embodiment differs from the second control operation of the control system 50 according to the 9th embodiment in that, in the second control operation, the entire high-level period of the first switch is made to overlap with part of the high-level period of the first control signal to the target switching element corresponding to the first switch, and the entire high-level period of the third switch is made to overlap with part of the high-level period of the first control signal to the target switching element corresponding to the third switch.

[0261] The timing chart before the shift by the second control operation is performed when the control device 51 determines that three-phase resonant currents are flowing simultaneously is the same as that shown in Figure 24 described in embodiment 9, so it will not be shown or described here.

[0262] 28 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and the current iL1 when the control device 51 performs a shift based on the second control operation. Note that FIG. 28 shows a timing chart for a portion of one period of the carrier signal.

[0263] In the power conversion device 100B of embodiment 11, if the control device 51 determines that three-phase resonant currents are flowing simultaneously and does not perform the second control operation, the switching of each of the first switching elements 1U, 1V, and 1W becomes hard switching.

[0264] When the control device 51 determines that three-phase resonant currents flow simultaneously during the charging operation of the resonant capacitor 9, it shifts the high-level period of the second control signal SW6 to the W-phase third switching element 6W by the shift time Ts in the direction of delaying the high-level period on the time axis so that the entire high-level period of the second control signal SW6 overlaps with part of the high-level period of the first control signal SW1. At this time, the control device 51 sets the shift time Ts (Tsw) to the time difference between the start of the high-level period of the second control signal SW6 before the shift (shown by a two-dot chain line in FIG. 28) and the start of the first control signal SW1.

[0265] Furthermore, the control device 51 shifts the high-level period of the second control signal SU6 to the third switching element 6U of the U phase by the shift time Ts (Tsu) in the direction of delaying the high-level period on the time axis so that the entire high-level period of the second control signal SU6 overlaps with part of the high-level period of the first control signal SU1. At this time, the control device 51 sets the shift time Ts to the time difference between the start of the high-level period of the second control signal SU6 before the shift (shown by a two-dot chain line in FIG. 28) and the start of the first control signal SU1.

[0266] When the control device 51 performs the second control operation, in the power conversion device 100B, the first switching element 1U and the first switching element 1W are hard-switched, and the first switching element 1V is zero-voltage soft-switched.

[0267] (3) Advantages As with the power conversion device 100B according to the fifth embodiment, the power conversion device 100B according to the eleventh embodiment can stop the zero voltage soft switching without pulse width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0268] In the power conversion device 100B of embodiment 11, when the control system 50 determines that a resonant current flows simultaneously through each of three of the multiple switches 8 in the resonant inductor L1 when a second control signal with a predetermined high level period is given to each of the multiple switches 8, the control system 50 executes a second control operation on the first switch and the third switch of the three switches 8.

[0269] According to the above configuration, when it is determined that resonant currents passing through three of the multiple switches 8 simultaneously flow through the resonant inductor L1, the control system 50 can realize zero-voltage soft switching of the target switching elements corresponding to the switches 8 for which it performs the first control operation, and it becomes possible to stop the zero-voltage soft switching of the target switching elements corresponding to the first and third switches for which it performs the second control operation without pulse-width modulating the second control signal sent to each of the multiple switches 8 for zero-voltage soft switching.

[0270] The control system 50 may be configured to stop the zero voltage soft switching of any of the first switches and third switches, regardless of the magnitude of the absolute value of the load current.

[0271] Twelfth Embodiment (1) Configuration The configuration of a power conversion device 100A according to the twelfth embodiment is the same as the configuration of the power conversion device 100A according to the third embodiment (see FIG. 5), and therefore will not be illustrated or described again.

[0272] (2) Operation The operation of the power conversion device 100A according to the twelfth embodiment is substantially the same as the operation of the power conversion device 100A according to the tenth embodiment. The control system 50A according to the present embodiment differs from the second control operation of the control system 50A according to the tenth embodiment in that, in the second control operation, the entire high-level period of the second control signal to the first switch is overlapped with part of the high-level period of the first control signal to the target switching element corresponding to the first switch, and the entire high-level period of the second control signal to the third switch is overlapped with part of the high-level period of the first control signal to the target switching element corresponding to the third switch.

[0273] The timing chart before the shift due to the second control operation is performed when the control system 50A determines that three-phase resonant currents are flowing simultaneously is the same as that shown in Figure 26 described in embodiment 9, so it will not be shown or described here.

[0274] 29 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and the current iL1 when the control system 50A performs a shift based on the second control operation. Note that FIG. 29 shows a timing chart for a portion of one period of the carrier signal.

[0275] In the power conversion device 100A of embodiment 12, if the control system 50A determines that three-phase resonant currents are flowing simultaneously and does not perform the second control operation, the switching of each of the first switching elements 1U, 1V, and 1W becomes hard switching.

[0276] When the control system 50A determines that three-phase resonant currents flow simultaneously during the charging operation of the resonant capacitor 9, it sets the additional time Tad in the second dead time period Td2 of the switching circuit 10W corresponding to the third switching element 6W of the W phase to zero, and overlaps the entire high-level period of the second control signal SW6 with part of the high-level period of the first control signal SW1.

[0277] In addition, the control system 50A sets the additional time Tad in the second dead time period Td2 of the switching circuit 10U corresponding to the third switching element 6U of the U phase to zero, thereby overlapping the entire high-level period of the second control signal SU6 with part of the high-level period of the first control signal SU1.

[0278] When the control system 50A performs the second control operation, in the power conversion device 100A, the first switching element 1U and the first switching element 1W are hard-switched, and the first switching element 1V is zero-voltage soft-switched.

[0279] (3) Advantages As with the power conversion device 100A according to the third embodiment, the power conversion device 100A according to the twelfth embodiment can stop the zero voltage soft switching without pulse width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0280] Furthermore, in the power conversion device 100A according to the twelfth embodiment, similarly to the power conversion device 100A according to the third embodiment, the control system 50A includes the control device 51A and the signal generating circuit 52, and therefore, the zero voltage soft switching can be more reliably realized without the control device 51A directly controlling the plurality of switches 8 for zero voltage soft switching. More specifically, the control device 51A does not need to generate a second control signal for directly controlling the plurality of switches 8 for zero voltage soft switching, and the zero voltage soft switching of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 can be realized without the control device 51A directly controlling the plurality of switches 8.

[0281] In addition, in the power conversion device 100A according to the twelfth embodiment, when the control system 50A determines that a resonant current flows through each of three of the multiple switches 8 simultaneously in the resonant inductor L1 when a second control signal with a predetermined high level period is given to each of the multiple switches 8, the control system 50A executes a second control operation on the first switch and the third switch of the three switches 8.

[0282] According to the above configuration, when it is determined that resonant currents passing through three of the multiple switches 8 simultaneously flow through the resonant inductor L1, the control system 50A can realize zero-voltage soft switching of the target switching elements corresponding to the switches 8 for which it performs the first control operation, and it becomes possible to stop the zero-voltage soft switching of the target switching elements corresponding to the first and third switches for which it performs the second control operation without pulse-width modulating the second control signal sent to each of the multiple switches 8 for zero-voltage soft switching.

[0283] The control system 50A may be configured to stop the zero voltage soft switching of any of the first switches and third switches, regardless of the magnitude of the absolute value of the load current.

[0284] (Thirteenth Embodiment) (1) Configuration The configuration of a power conversion device 100B according to the thirteenth embodiment is the same as the configuration of the power conversion device 100B according to the fifth embodiment (see FIG. 17), and therefore will not be illustrated or described again.

[0285] (2) Operation The operation of the power conversion device 100B according to the thirteenth embodiment is substantially the same as the operation of the power conversion device 100B according to the seventh embodiment. The control system 50 according to the thirteenth embodiment is different from the second control operation of the control system 50 according to the seventh embodiment in that the switch 8 corresponding to the phase having the smallest absolute value of the load current among the multiple switches 8 is set as the first switch, and the switch 8 corresponding to the phase having the largest absolute value of the load current is set as the second switch.

[0286] The control system 50 of this embodiment differs from the second control operation of the control system 50 of embodiment 7 in that, in the second control operation, the high-level period of the second control signal to the first switch is shifted later on the time axis to shorten the overlapping period between the high-level period of the first switch and the dead time period immediately preceding the high-level period of the target switching element corresponding to the first switch, thereby increasing the overlapping period between the high-level period of the second control signal and the high-level period of the first control signal to the target switching element.

[0287] The upper part of Figure 30 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and iL1 before the control device 51 performs a shift based on the second control operation when it determines that the U-phase resonant current and the V-phase resonant current are flowing simultaneously. In the example of Figure 30, the absolute value of the load current iV is greater than the absolute value of the load current iU. In this embodiment, the control device 51 designates the switch 8U with the smaller absolute value of the load current as the first switch.

[0288] The lower part of Fig. 30 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and the current iL1 when the control device 51 performs a shift based on the second control operation. Note that Fig. 30 shows a timing chart for a portion of one period within one cycle of the carrier signal.

[0289] In the power conversion device 100B according to the thirteenth embodiment, when the control device 51 does not perform the second control operation, the charging of the resonant capacitors 9U and 9V does not finish at the time when each of the first control signals SU1 and SV1 changes from a low level period to a high level period (the time when the dead time period Td corresponding to the U phase and the V phase ends), and the voltages across each of the first switching elements 1U and 1V do not decrease to zero. As a result, in the power conversion device 100B, the switching of the first switching elements 1U and 1V becomes hard switching.

[0290] When the control device 51 determines that the U-phase resonant current and the V-phase resonant current flow simultaneously during the charging operation of the resonant capacitor 9, it shifts the high-level period of the second control signal SU6 to the U-phase third switching element 6U by a shift time Ts in a direction that delays the time axis, so that the entire high-level period of the second control signal SU6 overlaps with part of the high-level period of the first control signal SU1. The shift time Ts set by the control device 51 is Ts<Tau+(Tres / 2). By the control device 51 performing the second control operation, in the power conversion device 100B, hard switching of the first switching element 1U is alleviated and zero-voltage soft switching of the first switching element 1V is performed.

[0291] The control device 51 may overlap the entire high-level period of the second control signal SU6 with the high-level period of the first control signal SU1. In this case, the shift time Ts set by the control device 51 is Ts = Tau + (Tres / 2). When the control device 51 performs the second control operation, in the power conversion device 100B, the first switching element 1U is zero-voltage soft-switched and the first switching element 1V is hard-switched.

[0292] The above describes an example of a shift by the second control operation when the control device 51 determines that two-phase resonant currents, U phase and V phase, flow simultaneously (overlap). However, in both cases where two-phase resonant currents, U phase and W phase, flow simultaneously, and where two-phase resonant currents, V phase and W phase, flow simultaneously, a shift by the second control operation is performed using the same concept (algorithm) as the shift by the second control operation when it is determined that two-phase resonant currents, U phase and V phase, flow simultaneously.

[0293] (3) Advantages As with the power conversion device 100B according to the fifth embodiment, the power conversion device 100B according to the thirteenth embodiment can stop the zero voltage soft switching without pulse width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0294] In addition, in the power conversion device 100B according to the thirteenth embodiment, when the control system 50 determines that a resonant current flows simultaneously through each of two or more switches 8 among the plurality of switches 8 in the resonant inductor L1 when a second control signal with a predetermined high level period is given to each of the plurality of switches 8, the control system 50 executes a second control operation on a first switch, which is one of the two or more switches 8.

[0295] According to the above configuration, when it is determined that resonant currents passing through two or more switches 8 out of the plurality of switches 8 simultaneously flow through the resonant inductor L1, the control system 50 can realize zero voltage soft switching of the target switching element corresponding to the switch 8 for which the first control operation is performed, and the control system 50 can stop the zero voltage soft switching of the target switching element corresponding to the first switch for which the second control operation is performed, without pulse width modulating the second control signal to each of the plurality of switches 8 for zero voltage soft switching. Furthermore, according to the above configuration, the effect of zero voltage soft switching can be further enhanced by performing zero voltage soft switching on the target switching element of the phase in which the absolute value of the load current is large.

[0296] Fourteenth Embodiment (1) Configuration The configuration of a power conversion device 100A according to the fourteenth embodiment is the same as the configuration of the power conversion device 100A according to the sixth embodiment (see FIG. 5), and therefore will not be illustrated or described again.

[0297] (2) Operation The operation of the power conversion device 100A according to the fourteenth embodiment is substantially the same as the operation of the power conversion device 100A according to the eighth embodiment. The control system 50A according to the fourteenth embodiment is different from the second control operation of the control system 50A according to the eighth embodiment in that the switch 8 corresponding to the phase having the smallest absolute value of the load current among the multiple switches 8 is set as the first switch, and the switch 8 corresponding to the phase having the largest absolute value of the load current is set as the second switch.

[0298] In the second control operation, the control system 50A of this embodiment sets the additional time Tad in the second dead time period Td2 immediately before the high level period of the first control signal to the target switching element corresponding to the first switch to an arbitrary time shorter than the total time of the run-up time and the length of the resonance half cycle so as to shorten the overlapping period between the high level period of the first switch and the dead time period immediately before the high level period of the target switching element corresponding to the first switch. As a result, the control system 50A shifts the high level period of the second control signal to the first switch in a direction that delays it on the time axis.

[0299] The upper part of Figure 31 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and iL1 before the control system 50A determines that the U-phase resonant current and the V-phase resonant current flow simultaneously and performs a shift based on the second control operation. In the example of Figure 31, the absolute value of the load current iV is greater than the absolute value of the load current iU. In this embodiment, the control system 50A designates the switch 8U with the smaller absolute value of the load current as the first switch.

[0300] The lower part of Fig. 31 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and the current iL1 when the control system 50A performs a shift based on the second control operation. Note that Fig. 31 shows a timing chart for a portion of one period within one cycle of the carrier signal.

[0301] In the power conversion device 100A according to the fourteenth embodiment, when the control system 50A does not perform the second control operation, the switching of the first switching elements 1U and 1V is hard switching.

[0302] When the control system 50A determines that the U-phase resonant current and the V-phase resonant current flow simultaneously, it shifts the high-level period of the second control signal SU6 to the U-phase third switching element 6U in a direction that delays the high-level period on the time axis to shorten the overlap period between the high-level period of the second control signal SU6 and the second dead time period Td2. Therefore, when the control system 50A performs the second control operation, in the power conversion device 100A, the hard switching of the first switching element 1U is alleviated and the first switching element 1V is zero-voltage soft-switched.

[0303] The control system 50A may set the additional time Tad in the second dead time period Td2 to zero so that the entire high-level period of the second control signal SU6 overlaps with part of the high-level period of the first control signal SU1. In this case, in the power conversion device 100A, the first switching element 1U is hard-switched and the first switching element 1V is zero-voltage soft-switched.

[0304] The above describes an example of a shift by the second control operation when the control device 51A determines that two-phase resonant currents, U phase and V phase, flow simultaneously (overlap). However, in both cases where two-phase resonant currents, U phase and W phase, flow simultaneously, and where two-phase resonant currents, V phase and W phase, flow simultaneously, the shift by the second control operation is performed using the same concept (algorithm) as the shift by the second control operation when it is determined that two-phase resonant currents, U phase and V phase, flow simultaneously.

[0305] (3) Advantages As with the power conversion device 100A according to the eighth embodiment, the power conversion device 100A according to the fourteenth embodiment can stop the zero voltage soft switching without pulse width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0306] Furthermore, in the power conversion device 100A according to the fourteenth embodiment, similarly to the power conversion device 100A according to the eighth embodiment, the control system 50A includes the control device 51A and the signal generating circuit 52, and therefore, the zero voltage soft switching can be more reliably realized without the control device 51A directly controlling the plurality of switches 8 for zero voltage soft switching. More specifically, the control device 51A does not need to generate a second control signal for directly controlling the plurality of switches 8 for zero voltage soft switching, and the zero voltage soft switching of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 can be realized without the control device 51A directly controlling the plurality of switches 8.

[0307] In the power conversion device 100A according to the fourteenth embodiment, when the control system 50A determines that a resonant current flows simultaneously through each of two or more switches 8 among the plurality of switches 8 in the resonant inductor L1 when a second control signal having a predetermined high level period is given to each of the plurality of switches 8, the control system 50A executes a second control operation on a first switch, which is one of the two or more switches 8.

[0308] According to the above configuration, when it is determined that a resonant current passing through each of two or more switches 8 out of the plurality of switches 8 simultaneously flows through the resonant inductor L1, the control system 50A can realize zero voltage soft switching of the target switching element corresponding to the switch 8 for which the first control operation is performed, and the control system 50A can stop the zero voltage soft switching of the target switching element corresponding to the first switch for which the second control operation is performed, without pulse width modulating the second control signal for the plurality of zero voltage soft switching switches 8. Furthermore, according to the above configuration, the effect of the zero voltage soft switching can be further enhanced by performing zero voltage soft switching on the target switching element of the phase in which the absolute value of the load current is large.

[0309] Fifteenth Embodiment (1) Configuration The configuration of a power conversion device 100A according to the fifteenth embodiment is the same as the configuration of the power conversion device 100A according to the sixth embodiment (see FIG. 5), and therefore will not be illustrated or described again.

[0310] (2) Operation The operation of the power conversion device 100A according to the fifteenth embodiment is substantially the same as the operation of the power conversion device 100A according to the eighth embodiment. The control system 50A according to the present embodiment differs from the second control operation of the control system 50A according to the eighth embodiment in that, among the multiple switches 8, the switch 8 corresponding to the phase whose absolute value of the load current is smallest is set as the first switch, the switch 8 corresponding to the phase whose absolute value of the load current is largest is set as the second switch, and the switch 8 corresponding to the phase whose absolute value of the load current is second smallest is set as the third switch.

[0311] For example, when two-phase resonant currents overlap when |load current iW| > |load current iU| > |load current iV| as shown in FIG. 32, the control system 50A performs a second control operation on the first switch, switch 8V, as shown in FIG. 33, a first control operation on the second switch, switch 8W (its third switching element 6W), and a second control operation on the third switch, switch 8U (its third switching element 6U).

[0312] In FIG. 32, the additional time Tad in the second dead time period Td2 corresponding to each of the U-phase, V-phase, and W-phase is the sum of the run-up time and the length of the resonance half cycle.

[0313] In response to this, the control system 50A sets the additional time Tad in the second dead time period Td2 corresponding to the U phase so that the start of the high-level period of the second control signal SU6 coincides with the start of the high-level period of the first control signal SV1, as shown in Fig. 33. Furthermore, the control system 50A sets the additional time Tad in the second dead time period Td2 corresponding to the V phase so that the start of the high-level period of the second control signal SV6 coincides with the start of the high-level period of the first control signal SW1, as shown in Fig. 33.

[0314] As the second control operation, the control system 50A may set the additional time Tad in the second dead time period Td2 corresponding to the V phase to zero so that the entire high-level period of the second control signal SV6 overlaps with part of the high-level period of the first control signal SV1. Alternatively, as the second control operation, the control system 50A may set the additional time Tad in the second dead time period Td2 corresponding to the U phase to zero so that the entire high-level period of the second control signal SU6 overlaps with part of the high-level period of the first control signal SU1.

[0315] (3) Advantages As with the power conversion device 100A according to the eighth embodiment, the power conversion device 100A according to the fifteenth embodiment can stop the zero voltage soft switching without pulse width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0316] Furthermore, in the power conversion device 100A according to the fifteenth embodiment, similarly to the power conversion device 100A according to the eighth embodiment, the control system 50A includes the control device 51A and the signal generating circuit 52, and therefore, the zero voltage soft switching can be more reliably realized without the control device 51A directly controlling the plurality of switches 8 for zero voltage soft switching. More specifically, the control device 51A does not need to generate a second control signal for directly controlling the plurality of switches 8 for zero voltage soft switching, and the zero voltage soft switching of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 can be realized without the control device 51A directly controlling the plurality of switches 8.

[0317] In the power conversion device 100A according to the fifteenth embodiment, similarly to the power conversion device 100 according to the eighth embodiment, when the control system 50A determines that a resonant current passing through each of two or more switches 8 among the plurality of switches 8 simultaneously flows through the resonant inductor L1, the control system 50A can realize zero-voltage soft switching of the target switching element corresponding to the switch 8 for which the control system 50A executes the first control operation, and can stop the zero-voltage soft switching of the target switching element corresponding to the first switch for which the control system 50A executes the second control operation without pulse-width modulating the second control signal for the plurality of switches 8 for zero-voltage soft switching. Furthermore, according to the above configuration, the effect of zero-voltage soft switching can be further enhanced by performing zero-voltage soft switching on the target switching element of the phase in which the absolute value of the load current is large.

[0318] Sixteenth Embodiment (1) Configuration The configuration of a power conversion device 100B according to the sixteenth embodiment is the same as the configuration of the power conversion device 100B according to the fifth embodiment (see FIG. 17), and therefore will not be illustrated or described again.

[0319] (2) Operation The operation of the power conversion device 100B according to the sixteenth embodiment is substantially the same as the operation of the power conversion device 100B according to the 9th embodiment. The control system 50 according to the sixteenth embodiment differs from the second control operation of the control system 50 according to the 9th embodiment in that, in the second control operation, the high-level period of the second control signal to the first switch is shifted so that part of the second control signal overlaps part of the high-level period of the first control signal to the target switching element corresponding to the first switch, and the high-level period of the second control signal to the third switch is shifted so that the whole of the second control signal overlaps part of the high-level period of the first control signal to the target switching element corresponding to the third switch.

[0320] The timing chart before the shift by the second control operation is performed when the control device 51 determines that three-phase resonant currents are flowing simultaneously is the same as that shown in Figure 24 described in embodiment 9, so it will not be shown or described here.

[0321] FIG. 34 is a timing chart when the control device 51 performs a shift based on the second control action.

[0322] In the power conversion device 100B of embodiment 16, if the control device 51 determines that three-phase resonant currents are flowing simultaneously and does not perform the second control operation, the switching of each of the first switching elements 1U, 1V, and 1W becomes hard switching.

[0323] When the control device 51 determines that three-phase resonant currents flow simultaneously during the charging operation of the resonant capacitor 9, it shifts the high-level period of the second control signal SW6 to the W-phase third switching element 6W by the shift time Ts in the direction of delaying the high-level period on the time axis so that the entire high-level period of the second control signal SW6 overlaps with part of the high-level period of the first control signal SW1. At this time, the control device 51 sets the shift time Ts (Tsw) to the time difference between the start of the high-level period of the second control signal SW6 before the shift (shown by a two-dot chain line in FIG. 34) and the start of the high-level period of the first control signal SW1 before the shift.

[0324] Furthermore, the control device 51 shifts the high-level period of the second control signal SU6 to the U-phase third switching element 6U by the shift time Ts (Tsu) in the direction of delaying the high-level period on the time axis, so that part of the high-level period of the second control signal SU6 overlaps with the high-level period of the first control signal SU1. At this time, the control device 51 sets the shift time Ts to the time difference between the start of the high-level period of the second control signal SU6 before the shift (shown by a two-dot chain line in FIG. 34) and the start of the high-level period of the first control signal SW1 before the shift.

[0325] When the control device 51 performs the second control operation, in the power conversion device 100B, the zero voltage soft switching of the first switching element 1U and the first switching element 1W is stopped, and the zero voltage soft switching of the first switching element 1V is performed. The first switching element 1W is hard switched, and the first switching element 1U is switched in a manner that alleviates the hard switching.

[0326] (3) Advantages As with the power conversion device 100B according to the fifth embodiment, the power conversion device 100B according to the sixteenth embodiment can stop the zero voltage soft switching without pulse width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0327] In the power conversion device 100B of embodiment 16, when the control system 50 determines that a resonant current flows simultaneously through each of three of the multiple switches 8 in the resonant inductor L1 when a second control signal with a predetermined high-level period is given to each of the multiple switches 8, the control system 50 executes a second control operation on the first switch and the third switch of the three switches 8.

[0328] According to the above configuration, when it is determined that resonant currents passing through three of the multiple switches 8 simultaneously flow through the resonant inductor L1, the control system 50 can realize zero-voltage soft switching of the target switching elements corresponding to the switches 8 for which it performs the first control operation, and it becomes possible to stop the zero-voltage soft switching of the target switching elements corresponding to the first and third switches for which it performs the second control operation without pulse-width modulating the second control signal sent to each of the multiple switches 8 for zero-voltage soft switching.

[0329] The control system 50 may be configured to shorten the overlap period between the high-level period of the second control signal to any first switch and any third switch and the corresponding second dead time period Td2 to any time or to zero, regardless of the magnitude relationship of the absolute value of the load current.

[0330] Seventeenth Embodiment (1) Configuration The configuration of a power conversion device 100A according to the seventeenth embodiment is the same as the configuration of the power conversion device 100A according to the third embodiment (see FIG. 5), and therefore will not be illustrated or described again.

[0331] (2) Operation The operation of the power conversion device 100A according to embodiment 17 is substantially the same as the operation of the power conversion device 100A according to embodiment 10. The control system 50A according to this embodiment differs from the second control operation of the control system 50A according to embodiment 10 in that, in the second control operation, the high-level period of the second control signal to the first switch is shifted so that part of the high-level period of the second control signal overlaps with the high-level period of the first control signal to the target switching element corresponding to the first switch, and the high-level period of the second control signal to the third switch overlaps with the high-level period of the first control signal to the target switching element corresponding to the third switch.

[0332] The timing chart before the shift due to the second control operation is performed when the control system 50A determines that three-phase resonant currents are flowing simultaneously is the same as that shown in Figure 26 described in embodiment 9, so it will not be shown or described here.

[0333] FIG. 35 is a timing chart when the control device 51A performs a shift based on the second control action.

[0334] In the power conversion device 100A of embodiment 17, if the control device 51A determines that three-phase resonant currents are flowing simultaneously and does not perform the second control operation, the switching of each of the first switching elements 1U, 1V, and 1W becomes hard switching.

[0335] When the control device 51A determines that three-phase resonant currents flow simultaneously during the charging operation of the resonant capacitor 9, it sets the additional time Tad to 0 so as to shorten the overlap period between the high-level period of the second control signal SW6 to the third switching element 6W of the W phase and the second dead time period Td2 to 0.

[0336] Furthermore, when the control device 51A determines that three-phase resonant currents flow simultaneously during the charging operation of the resonant capacitor 9, it sets the additional time Tad so as to shorten the overlap period between the high-level period of the second control signal SU6 to the third switching element 6U of the U phase and the second dead time period Td2. At this time, the control device 51A sets the additional time Tad so that the start point of the high-level period of the second control signal SU6 coincides with the start point of the high-level period of the first control signal SW1.

[0337] When the control device 51A performs the second control operation, in the power conversion device 100A, the hard switching of the first switching element 1U is relaxed, the zero voltage soft switching of the first switching element 1W is stopped, and the first switching element 1V is zero voltage soft switched.

[0338] (3) Advantages As with the power conversion device 100A according to the tenth embodiment, the power conversion device 100A according to the seventeenth embodiment can stop the zero voltage soft switching without pulse width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0339] Furthermore, in the power conversion device 100A according to the seventeenth embodiment, similarly to the power conversion device 100A according to the tenth embodiment, the control system 50A includes the control device 51A and the signal generating circuit 52, and therefore, the zero voltage soft switching can be more reliably realized without the control device 51A directly controlling the plurality of switches 8 for zero voltage soft switching. More specifically, the control device 51A does not need to generate a second control signal for directly controlling the plurality of switches 8 for zero voltage soft switching, and the zero voltage soft switching of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 can be realized without the control device 51A directly controlling the plurality of switches 8.

[0340] In the power conversion device 100A according to the seventeenth embodiment, when the control system 50A determines that a resonant current flows simultaneously through each of three of the switches 8 in the resonant inductor L1 when a second control signal with a predetermined high level period is given to each of the switches 8, the control system 50A executes a second control operation on the first switch and the third switch of the three switches 8.

[0341] According to the above configuration, when it is determined that resonant currents passing through three of the multiple switches 8 simultaneously flow through the resonant inductor L1, the control system 50A can realize zero-voltage soft switching of the target switching elements corresponding to the switches 8 for which it performs the first control operation, and it becomes possible to stop the zero-voltage soft switching of the target switching elements corresponding to the first and third switches for which it performs the second control operation without pulse-width modulating the second control signal sent to each of the multiple switches 8 for zero-voltage soft switching.

[0342] In the control system 50A, the U-phase switch 8U may be the first switch and the W-phase switch 8W may be the third switch. Furthermore, the control system 50A may employ a combination of the U-phase switch 8U and the V-phase switch 8V as the first switch and the third switch, or may employ a combination of the V-phase switch 8V and the W-phase switch 8W.

[0343] Eighteenth Embodiment (1) Configuration The configuration of a power conversion device 100A according to the eighteenth embodiment is the same as the configuration of the power conversion device 100A according to the third embodiment (see FIG. 5), and therefore will not be illustrated or described again.

[0344] (2) Operation The operation of the power conversion device 100A according to the eighteenth embodiment is substantially the same as the operation of the power conversion device 100A according to the fifteenth embodiment. In the control system 50A according to the present embodiment, the switch 8 corresponding to the phase having the smallest absolute value of the load current among the plurality of switches 8 is designated as a first switch, the switch 8 corresponding to the phase having the largest absolute value of the load current is designated as a second switch, and the switch 8 corresponding to the phase having the second smallest absolute value of the load current is designated as a third switch.

[0345] In the fifteenth embodiment, when two-phase resonant currents overlap when |load current iW| > |load current iU| > |load current iV|, for example, as shown in FIG. 32, the control system 50A performs a second control operation on the switch 8V, which is the first switch, a first control operation on the switch 8W, which is the second switch (its third switching element 6W), and a second control operation on the switch 8U, which is the third switch (its third switching element 6U).

[0346] In FIG. 32, the additional time Tad in the second dead time period Td2 corresponding to each of the U-phase, V-phase, and W-phase is the sum of the run-up time and the length of the resonance half cycle.

[0347] In contrast, in the present embodiment, the control system 50A sets the additional time Tad in the second dead time period Td2 corresponding to the V phase to 0, as shown in FIG. 36 . This sets the start point of the high-level period of the second control signal SV6 to coincide with the start point of the high-level period of the first control signal SV1. Furthermore, the control system 50A sets the additional time Tad in the second dead time period Td2 corresponding to the U phase to coincide with the start point of the high-level period of the second control signal SU6.

[0348] (3) Advantages As with the power conversion device 100A according to the 15th embodiment, the power conversion device 100A according to the 18th embodiment can stop the zero voltage soft switching without pulse width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0349] Furthermore, in the power conversion device 100A according to the eighteenth embodiment, similarly to the power conversion device 100A according to the fifteenth embodiment, the control system 50A includes the control device 51A and the signal generating circuit 52, and therefore, the zero voltage soft switching can be more reliably realized without the control device 51A directly controlling the plurality of switches 8 for zero voltage soft switching. More specifically, the control device 51A does not need to generate a second control signal for directly controlling the plurality of switches 8 for zero voltage soft switching, and the zero voltage soft switching of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 can be realized without the control device 51A directly controlling the plurality of switches 8.

[0350] Furthermore, in the power conversion device 100A according to the eighteenth embodiment, similarly to the power conversion device 100A according to the fifteenth embodiment, when the control system 50A determines that a resonant current passing through each of two or more switches 8 among the plurality of switches 8 simultaneously flows through the resonant inductor L1, the control system 50A can realize zero-voltage soft switching of the target switching element corresponding to the switch 8 for which the control system 50A executes the first control operation, and can stop the zero-voltage soft switching of the target switching element corresponding to the first switch for which the control system 50A executes the second control operation, without pulse-width modulating the second control signal to each of the plurality of switches 8 for zero-voltage soft switching. Furthermore, according to the above configuration, the effect of zero-voltage soft switching can be further enhanced by performing zero-voltage soft switching on the target switching element of the phase in which the absolute value of the load current is large.

[0351] The same concept as that of this embodiment can also be applied to a conventional zero voltage switching configuration in which a plurality of switches for zero voltage soft switching are directly controlled by a microcomputer.

[0352] Nineteenth Embodiment (1) Configuration The configuration of a power conversion device 100A according to the nineteenth embodiment is the same as the configuration of the power conversion device 100A according to the third embodiment (see FIG. 5), and therefore will not be illustrated or described again.

[0353] (2) Operation The operation of the power conversion device 100A according to the 19th embodiment is substantially the same as the operation of the power conversion device 100A according to the 15th embodiment. In the control system 50A according to the present embodiment, the switch 8 corresponding to the phase having the smallest absolute value of the load current among the multiple switches 8 is designated as a first switch, the switch 8 corresponding to the phase having the largest absolute value of the load current is designated as a second switch, and the switch 8 corresponding to the phase having the second smallest absolute value of the load current is designated as a third switch.

[0354] In the fifteenth embodiment, when two-phase resonant currents overlap when |load current iW| > |load current iU| > |load current iV|, for example, as shown in FIG. 32, the control system 50A performs a second control operation on the switch 8V, which is the first switch, a first control operation on the switch 8W, which is the second switch (its third switching element 6W), and a second control operation on the switch 8U, which is the third switch (its third switching element 6U).

[0355] In FIG. 32, the additional time Tad in the second dead time period Td2 corresponding to each of the U-phase, V-phase, and W-phase is the sum of the run-up time and the length of the resonance half cycle.

[0356] In contrast, in the present embodiment, the control system 50A sets the additional time Tad in the second dead time period Td2 corresponding to the U-phase to 0, as shown in, for example, FIG. 37. This sets the start point of the high-level period of the second control signal SU6 to coincide with the start point of the high-level period of the first control signal SU1. Furthermore, the control system 50A sets the additional time Tad in the second dead time period Td2 corresponding to the V-phase to coincide with the start point of the high-level period of the second control signal SV6.

[0357] (3) Advantages As with the power conversion device 100A according to the 15th embodiment, the power conversion device 100A according to the 19th embodiment can stop the zero voltage soft switching without pulse width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0358] Furthermore, in the power conversion device 100A according to the nineteenth embodiment, similarly to the power conversion device 100A according to the fifteenth embodiment, the control system 50A includes the control device 51A and the signal generating circuit 52, and therefore, the zero voltage soft switching can be more reliably realized without the control device 51A directly controlling the plurality of switches 8 for zero voltage soft switching. More specifically, the control device 51A does not need to generate a second control signal for directly controlling the plurality of switches 8 for zero voltage soft switching, and the zero voltage soft switching of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 can be realized without the control device 51A directly controlling the plurality of switches 8.

[0359] In the power conversion device 100A according to the 19th embodiment, similarly to the power conversion device 100A according to the 15th embodiment, when the control system 50A determines that a resonant current passing through each of two or more switches 8 out of the plurality of switches 8 simultaneously flows through the resonant inductor L1, the control system 50A can realize zero voltage soft switching of the target switching element corresponding to the switch 8 for which the control system 50A executes the first control operation, and can stop the zero voltage soft switching of the target switching element corresponding to the first switch for which the control system 50A executes the second control operation without pulse width modulation of the second control signal for the plurality of switches 8 for zero voltage soft switching. Furthermore, according to the above configuration, the effect of zero voltage soft switching can be further enhanced by performing zero voltage soft switching on the target switching element of the phase in which the absolute value of the load current is large.

[0360] The same concept as that of this embodiment can also be applied to a conventional zero voltage switching configuration in which a plurality of switches for zero voltage soft switching are directly controlled by a microcomputer.

[0361] Twentieth Embodiment (1) Configuration The configuration of a power conversion device 100B according to the twentieth embodiment is the same as the configuration of the power conversion device 100B according to the fifth embodiment (see FIG. 17), and therefore will not be illustrated or described again.

[0362] (2) Operation The operation of the power conversion device 100B according to the twentieth embodiment is substantially the same as the operation of the power conversion device 100B according to the fifth embodiment.

[0363] The control system 50 of this embodiment differs from the second control operation of the control system 50 of embodiment 5 in that, in the second control operation, the high-level period of the second control signal to the first switch is shifted, and the high-level period of the target switching element corresponding to the first switch is shifted in the direction that becomes later on the time axis.

[0364] The upper part of Figure 38 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and iL1 before the control device 51 performs a shift based on the second control operation when it determines that the U-phase resonant current and the V-phase resonant current are flowing simultaneously. In the example of Figure 38, the absolute value of the load current iU is greater than the absolute value of the load current iV. In the example of Figure 38, the control device 51 designates the switch 8U with the larger absolute value of the load current as the first switch.

[0365] The lower part of Fig. 38 shows timing charts of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and the current iL1 when the control device 51 shifts the second control signal and the first control signal through the second control operation. Note that Fig. 38 shows timing charts for a portion of one period within one cycle of the carrier signal.

[0366] When the control device 51 determines that the U-phase resonant current and the V-phase resonant current flow simultaneously during the charging operation of the resonant capacitor 9, it shifts the high-level period of the second control signal SU6 to the U-phase third switching element 6U by a shift time Ts in a direction to delay the time axis, and also shifts the high-level period of the first control signal SU1 to the U-phase first switching element 1U by a shift time Ts1 in a direction to delay the time axis. The shift time Ts set by the control device 51 is Ts<Tau+(Tres / 2). The length of the shift time Ts1 is arbitrary.

[0367] The above describes an example of a shift by the second control operation when the control device 51 determines that two-phase resonant currents, U phase and V phase, flow simultaneously (overlap). However, in both cases where two-phase resonant currents, U phase and W phase, flow simultaneously, and where two-phase resonant currents, V phase and W phase, flow simultaneously, a shift by the second control operation is performed using the same concept (algorithm) as the shift by the second control operation when it is determined that two-phase resonant currents, U phase and V phase, flow simultaneously.

[0368] (3) Advantages As with the power conversion device 100B according to the fifth embodiment, the power conversion device 100B according to the twentieth embodiment can stop the zero voltage soft switching without pulse width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0369] In the power conversion device 100B of embodiment 20, similarly to the power conversion device 100B of embodiment 5, when the control system 50 determines that a resonant current passing through each of two or more switches 8 out of the plurality of switches 8 flows simultaneously through the resonant inductor L1, the control system 50 can realize zero voltage soft switching of the target switching element corresponding to the switch 8 for which the control system 50 executes the first control operation, and it becomes possible to stop the zero voltage soft switching of the target switching element corresponding to the first switch for which the control system 50 executes the second control operation without pulse width modulating the second control signal to each of the plurality of switches 8 for zero voltage soft switching.

[0370] Not limited to the control system 50 of the power conversion device 100B of this embodiment, the control systems 50, 50A of the power conversion devices 100, 100A of other embodiments may be configured to shift the first control signal to the target switching element by the shift time Ts1.

[0371] Twenty-First Embodiment (1) Configuration The configuration of a power conversion device 100A according to the twenty-first embodiment is the same as the configuration of the power conversion device 100A according to the third embodiment (see FIG. 5), and therefore will not be illustrated or described again.

[0372] (2) Operation The operation of the power conversion device 100A according to the twenty-first embodiment is substantially the same as the operation of the power conversion device 100A according to the sixth embodiment.

[0373] The control system 50A of this embodiment differs from the second control operation of the control system 50A of embodiment 6 in that, in the second control operation, the high-level period of the second control signal to the first switch is shifted, and the high-level period of the target switching element corresponding to the first switch is shifted in the direction that becomes later on the time axis.

[0374] The upper part of Figure 39 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and the current iL1 before the second control operation is performed when the control device 51A determines that the U-phase resonant current and the V-phase resonant current flow simultaneously. In Figure 39, the additional time Tad during the second dead time period Td2 between the high-level period of the first control signal SU2 and the high-level period of the first control signal SU1 is Tad = Tau + (Tres / 2). Also, the additional time Tad during the second dead time period Td2 between the high-level period of the first control signal SV2 and the high-level period of the first control signal SV1 is Tad = Tav + (Tres / 2). Figure 39 shows a timing chart for a portion of one cycle of the carrier signal. In the example of Fig. 39, the absolute value of the load current iU is greater than the absolute value of the load current iV. In the example of Fig. 39, the control device 51A designates the switch 8U having the greater absolute value of the load current as the first switch.

[0375] In addition, the lower part of Figure 39 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and the current iL1 when the control device 51A shifts the second control signal and the first control signal through the second control operation.

[0376] When the control device 51A determines that the U-phase resonant current and the V-phase resonant current flow simultaneously during the charging operation of the resonant capacitor 9, it shifts the high-level period of the second control signal SU6 to the U-phase third switching element 6U in a later direction on the time axis, and also shifts the high-level period of the first control signal SU1 to the U-phase first switching element 1U in a later direction on the time axis by a shift time Ts1. The control device 51A shifts the high-level period of the second control signal SU6 by setting the additional time Tad in the second dead time period Td2 to Tad < Tau + (Tres / 2). The additional time Tad is an arbitrary length shorter than Tau + (Tres / 2). The length of the shift time Ts1 is an arbitrary length.

[0377] The above describes an example of a shift by the second control operation when the control device 51A determines that two-phase resonant currents, U phase and V phase, flow simultaneously (overlap). However, in both cases where two-phase resonant currents, U phase and W phase, flow simultaneously, and where two-phase resonant currents, V phase and W phase, flow simultaneously, the shift by the second control operation is performed using the same concept (algorithm) as the shift by the second control operation when it is determined that two-phase resonant currents, U phase and V phase, flow simultaneously.

[0378] (3) Advantages As with the power conversion device 100A according to the sixth embodiment, the power conversion device 100A according to the twenty-first embodiment can stop the zero voltage soft switching without pulse-width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0379] Furthermore, in the power conversion device 100A according to the twenty-first embodiment, similarly to the power conversion device 100A according to the sixth embodiment, the control system 50A includes the control device 51A and the signal generating circuit 52, and therefore, the zero voltage soft switching can be more reliably realized without the control device 51A directly controlling the plurality of switches 8 for zero voltage soft switching. More specifically, the control device 51A does not need to generate a second control signal for directly controlling the plurality of switches 8 for zero voltage soft switching, and the zero voltage soft switching of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 can be realized without the control device 51A directly controlling the plurality of switches 8.

[0380] In the power conversion device 100A of embodiment 21, similar to the power conversion device 100A of embodiment 6, when the control system 50A determines that a resonant current passing through each of two or more switches 8 out of the plurality of switches 8 flows simultaneously through the resonant inductor L1, the control system 50A can realize zero voltage soft switching of the target switching element corresponding to the switch 8 for which the control system 50A executes the first control operation, and it becomes possible to stop the zero voltage soft switching of the target switching element corresponding to the first switch for which the control system 50A executes the second control operation without pulse width modulating the second control signal to each of the plurality of switches 8 for zero voltage soft switching.

[0381] The control system 50A of the power conversion device 100A of other embodiments, not limited to the control system 50A of the power conversion device 100A of this embodiment, may be configured to shift the second control signal to the first switch and shift the first control signal to the target switching element by the shift time Ts1.

[0382] Twenty-Second Embodiment (1) Configuration The configuration of a power conversion device 100B according to the twenty-second embodiment is the same as the configuration of the power conversion device 100B according to the fifth embodiment (see FIG. 17), and therefore will not be illustrated or described again.

[0383] (2) Operation The operation of the power conversion device 100B according to the twenty-second embodiment is substantially the same as the operation of the power conversion device 100B according to the fifth embodiment.

[0384] The control system 50 of this embodiment differs from the second control operation of the control system 50 of embodiment 5 in that, in the second control operation, the high-level period of the second control signal to the first switch is shifted, and the high-level period of the target switching element corresponding to the first switch is shifted in the direction that becomes later on the time axis.

[0385] The upper part of Figure 40 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and iL1 before the second control operation is performed when the control device 51 determines that the U-phase resonant current and the V-phase resonant current flow simultaneously. In the example of Figure 40, the absolute value of the load current iU is greater than the absolute value of the load current iV. In this embodiment, the control device 51 designates the switch 8V, which has the smallest absolute value of the load current, as the first switch.

[0386] The lower part of Fig. 40 shows timing charts of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and the current iL1 when the control device 51 shifts the second control signal and the first control signal through the second control operation. Fig. 40 shows timing charts for a part of one period within one cycle of the carrier signal.

[0387] When the control device 51 determines that the U-phase resonant current and the V-phase resonant current flow simultaneously during the charging operation of the resonant capacitor 9, it shifts the high-level period of the second control signal SV6 to the V-phase third switching element 6V by a shift time Ts in a direction to delay the high-level period on the time axis, and also shifts the high-level period of the first control signal SV1 to the V-phase first switching element 1V by a shift time Ts1 in a direction to delay the high-level period on the time axis. The shift time Ts set by the control device 51 is Ts<Tau+(Tres / 2). The shift time Ts1 can be any length.

[0388] The above describes an example of a shift by the second control operation when the control device 51 determines that two-phase resonant currents, U phase and V phase, flow simultaneously (overlap). However, in both cases where two-phase resonant currents, U phase and W phase, flow simultaneously, and where two-phase resonant currents, V phase and W phase, flow simultaneously, a shift by the second control operation is performed using the same concept (algorithm) as the shift by the second control operation when it is determined that two-phase resonant currents, U phase and V phase, flow simultaneously.

[0389] (3) Advantages As with the power conversion device 100B according to the fifth embodiment, the power conversion device 100B according to the twenty-second embodiment can stop the zero voltage soft switching without pulse-width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0390] In the power conversion device 100B of embodiment 22, similar to the power conversion device 100B of embodiment 5, when the control system 50 determines that a resonant current passing through each of two or more switches 8 out of the plurality of switches 8 flows simultaneously through the resonant inductor L1, the control system 50 can realize zero voltage soft switching of the target switching element corresponding to the switch 8 for which the control system 50 executes the first control operation, and it becomes possible to stop the zero voltage soft switching of the target switching element corresponding to the first switch for which the control system 50 executes the second control operation without pulse width modulating the second control signal to each of the plurality of switches 8 for zero voltage soft switching.

[0391] Twenty-third embodiment (1) Configuration The configuration of a power conversion device 100A according to the twenty-third embodiment is the same as the configuration of the power conversion device 100A according to the third embodiment (see FIG. 5), and therefore will not be illustrated or described again.

[0392] (2) Operation The operation of the power conversion device 100A according to the twenty-third embodiment is substantially the same as the operation of the power conversion device 100A according to the sixth embodiment.

[0393] The control system 50A of this embodiment differs from the second control operation of the control system 50A of embodiment 6 in that, in the second control operation, the high-level period of the second control signal to the first switch is shifted, and the high-level period of the target switching element corresponding to the first switch is shifted in the direction that becomes later on the time axis.

[0394] The upper part of Figure 41 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and the current iL1 before the second control operation is performed when the control device 51A determines that the U-phase resonant current and the V-phase resonant current flow simultaneously. In the upper part of Figure 41, the additional time Tad during the second dead time period Td2 between the high-level period of the first control signal SU2 and the high-level period of the first control signal SU1 is Tad = Tau + (Tres / 2). Also, the additional time Tad during the second dead time period Td2 between the high-level period of the first control signal SV2 and the high-level period of the first control signal SV1 is Tad = Tav + (Tres / 2). Figure 41 shows a timing chart for a portion of one cycle of the carrier signal. In the example of Fig. 41, the absolute value of the load current iU is greater than the absolute value of the load current iV. In the example of Fig. 41, the control device 51A designates the switch 8V, which has the smaller absolute value of the load current, as the first switch.

[0395] In addition, the lower part of Figure 41 shows timing charts of the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SV6, the load currents iU, iV, and the current iL1 when the control device 51A shifts the second control signal and the first control signal through the second control operation.

[0396] When the control device 51A determines that the U-phase resonant current and the V-phase resonant current flow simultaneously during the charging operation of the resonant capacitor 9, it shifts the high-level period of the second control signal SV6 to the V-phase third switching element 6V in a direction to delay the time axis, and also shifts the high-level period of the first control signal SV1 to the V-phase first switching element 1V in a direction to delay the time axis by a shift time Ts1. The control device 51A shifts the high-level period of the second control signal SV6 by setting the additional time Tad in the second dead time period Td2 to Tad < Tav + (Tres / 2). The additional time Tad is an arbitrary length shorter than Tav + (Tres / 2). The length of the shift time Ts1 is an arbitrary length.

[0397] The above describes an example of a shift by the second control operation when the control device 51A determines that two-phase resonant currents, U phase and V phase, flow simultaneously (overlap). However, in both cases where two-phase resonant currents, U phase and W phase, flow simultaneously, and where two-phase resonant currents, V phase and W phase, flow simultaneously, the shift by the second control operation is performed using the same concept (algorithm) as the shift by the second control operation when it is determined that two-phase resonant currents, U phase and V phase, flow simultaneously.

[0398] (3) Advantages As with the power conversion device 100A according to the sixth embodiment, the power conversion device 100A according to the twenty-third embodiment can stop the zero voltage soft switching without pulse-width modulating the second control signal sent to each of the multiple switches 8 for zero voltage soft switching.

[0399] Furthermore, in the power conversion device 100A according to the twenty-third embodiment, similarly to the power conversion device 100A according to the sixth embodiment, the control system 50A includes the control device 51A and the signal generating circuit 52, and therefore, the zero voltage soft switching can be more reliably realized without the control device 51A directly controlling the plurality of switches 8 for zero voltage soft switching. More specifically, the control device 51A does not need to generate a second control signal for directly controlling the plurality of switches 8 for zero voltage soft switching, and the zero voltage soft switching of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 can be realized without the control device 51A directly controlling the plurality of switches 8.

[0400] In the power conversion device 100A of embodiment 23, similarly to the power conversion device 100A of embodiment 6, when the control system 50A determines that a resonant current passing through each of two or more switches 8 out of the plurality of switches 8 flows simultaneously through the resonant inductor L1, the control system 50A can realize zero voltage soft switching of the target switching element corresponding to the switch 8 for which the control system 50A executes the first control operation, and it becomes possible to stop the zero voltage soft switching of the target switching element corresponding to the first switch for which the control system 50A executes the second control operation without pulse width modulating the second control signal to each of the plurality of switches 8 for zero voltage soft switching.

[0401] The control system 50A of the power conversion device 100A of other embodiments, not limited to the control system 50A of the power conversion device 100A of this embodiment, may be configured to shift the second control signal to the first switch and shift the first control signal to the target switching element by the shift time Ts1.

[0402] Twenty-fourth embodiment A power conversion device 100A according to a twenty-fourth embodiment will be described with reference to Fig. 42. Regarding the power conversion device 100A according to the twenty-fourth embodiment, components similar to those of the power conversion device 100A according to the third embodiment (see Fig. 5) are denoted by the same reference numerals, and description thereof will be omitted.

[0403] In a power conversion device 100A according to the twenty-fourth embodiment, a third switching element 6 and a fourth switching element 7 are connected in anti-series in each of the plurality of switches 8. In the power conversion device 100A according to the twenty-fourth embodiment, in each of the plurality of switches 8, a second main terminal (emitter terminal) of the third switching element 6 and a second main terminal (emitter terminal) of the fourth switching element 7 are connected, a first main terminal (collector terminal) of the third switching element 6 is connected to a connection point 3 of a corresponding one of the plurality of switching circuits 10, and a first terminal (collector terminal) of the fourth switching element 7 is connected to a resonance inductor L1. Each of the plurality of switches 8 further includes a diode 61 connected in anti-parallel to the third switching element 6 and a diode 71 connected in anti-parallel to the fourth switching element 7.

[0404] The power conversion device 100A according to the twenty-fourth embodiment has the same advantages as the power conversion device 100A according to the third embodiment.

[0405] In the power conversion device 100A according to the twenty-fourth embodiment, each of the third switching element 6 and the fourth switching element 7 may be replaced with a MOSFET or a bipolar transistor. In this case, the diode 61 and the diode 71 in FIG. 42 may be substituted with a parasitic diode of the replaced element, or an element built into the chip of the replaced element. Furthermore, in the power conversion device 100A according to the twenty-fourth embodiment, the diode 61 and the diode 71 are not limited to being externally attached to the third switching element 6 and the fourth switching element 7, but may be built into the chip.

[0406] Twenty-fifth Embodiment A power conversion device 100A according to a twenty-fifth embodiment will be described with reference to Fig. 43. Regarding the power conversion device 100A according to the twenty-fifth embodiment, components similar to those of the power conversion device 100A according to the third embodiment (see Fig. 5) are denoted by the same reference numerals, and description thereof will be omitted.

[0407] In a power conversion device 100A according to the twenty-fifth embodiment, in each of the multiple switches 8, the third switching element 6 and the fourth switching element 7 are each a MOSFET, and the third switching element 6 and the fourth switching element 7 are connected in anti-series. In the power conversion device 100A according to the twenty-fifth embodiment, in each of the multiple switches 8, a first main terminal (drain terminal) of the third switching element 6 is connected to a first main terminal (drain terminal) of the fourth switching element 7. Each of the multiple switches 8 further includes a diode 61 connected in anti-parallel to the third switching element 6 and a diode 71 connected in anti-parallel to the fourth switching element 7. In each of the multiple switches 8, a second main terminal (source terminal) of the fourth switching element 7 is connected to a resonance inductor L1. In each of the multiple switches 8, a second main terminal (source terminal) of the third switching element 6 is connected to a connection point 3 of a switching circuit 10 corresponding to the switch 8 having the third switching element 6.

[0408] The power conversion device 100A according to the twenty-fifth embodiment has the same advantages as the power conversion device 100A according to the third embodiment.

[0409] Twenty-sixth embodiment A power conversion device 100A according to a twenty-sixth embodiment will be described with reference to Fig. 44. Regarding the power conversion device 100A according to the twenty-sixth embodiment, components similar to those of the power conversion device 100A according to the third embodiment (see Fig. 5) are denoted by the same reference numerals, and description thereof will be omitted.

[0410] In the power conversion device 100A according to the twenty-sixth embodiment, in each of the plurality of switches 8, the third switching element 6 and the fourth switching element 7 are each a MOSFET, a diode 63 is connected in series to the third switching element 6, and a diode 73 is connected in series to the fourth switching element 7. In the power conversion device 100A according to the twenty-sixth embodiment, in each of the plurality of switches 8, a series circuit of the third switching element 6 and the diode 63 and a series circuit of the fourth switching element 7 and the diode 73 are connected in anti-parallel.

[0411] The power conversion device 100A according to the twenty-sixth embodiment has the same advantages as the power conversion device 100A according to the third embodiment.

[0412] Twenty-seventh embodiment A power conversion device 100C according to a twenty-seventh embodiment will be described with reference to Fig. 45. With respect to the power conversion device 100C according to the twenty-seventh embodiment, components similar to those of the power conversion device 100A according to the third embodiment (see Fig. 5) are denoted by the same reference numerals, and description thereof will be omitted.

[0413] In a power conversion device 100C according to the twenty-seventh embodiment, each of the multiple switches 8 includes one MOSFET 80, a diode 83 connected in anti-parallel to the MOSFET 80, a series circuit of two diodes 84 and 85 connected in anti-parallel to the MOSFET 80, and a series circuit of two diodes 86 and 87 connected in anti-parallel to the MOSFET 80. In each of the multiple switches 8, a connection point between the diode 84 and the diode 85 in the switch 8 (a first end 81 of the switch 8) is connected to a connection point 3 of a corresponding switching circuit 10 among the multiple switching circuits 10, and a connection point between the diode 86 and the diode 87 (a second end 82 of the switch 8) is connected to the common connection point 25. In each of the switches 8, when the MOSFET 80 is in an on state, the switch 8 is in an on state, and when the MOSFET 80 is in an off state, the switch 8 is in an off state.

[0414] The power conversion device 100C according to the twenty-seventh embodiment includes a signal generation circuit 52D instead of the signal generation circuit 52 (see FIG. 5) of the power conversion device 100A according to the third embodiment.

[0415] The MOSFETs 80 of the multiple switches 8 are controlled by a signal generation circuit 52D. The signal generation circuit 52D outputs a second control signal SU8 that controls the on / off state of the MOSFET 80 of the switch 8U, a second control signal SV8 that controls the on / off state of the MOSFET 80 of the switch 8V, and a second control signal SW8 that controls the on / off state of the MOSFET 80 of the switch 8W. The signal generation circuit 52D generates the second control signal SU8 using the first control signals SU1 and SU2. The signal generation circuit 52D also generates the second control signal SV8 using the first control signals SV1 and SV2. The signal generation circuit 52D generates the second control signal SW8 using the first control signals SW1 and SW2.

[0416] In the switch 8, when the MOSFET 80 is in the on state, a resonant current flows due to a resonant circuit including the resonant inductor L1 and the resonant capacitor 9. In the power conversion device 100C according to the twenty-seventh embodiment, when one of the multiple switches 8 is in the on state, a charging current including the resonant current flows through the path of the regenerative capacitor 15, the resonant inductor L1, the diode 86, the MOSFET 80, the diode 85, and the resonant capacitor 9. In addition, in the power conversion device 100C according to the twenty-seventh embodiment, when one of the multiple switches 8 is in the on state, a discharging current including the resonant current flows through the path of the resonant capacitor 9, the diode 84, the MOSFET 80, the diode 87, the resonant inductor L1, and the regenerative capacitor 15.

[0417] The power conversion device 100C according to the twenty-seventh embodiment has the same advantages as the power conversion device 100A according to the third embodiment.

[0418] In the power conversion device 100C according to the twenty-seventh embodiment, each of the plurality of MOSFETs 80 may be replaced with an IGBT. Also, in the power conversion device 100C according to the twenty-seventh embodiment, each of the plurality of switches 8 may have, instead of the MOSFET 80, a bipolar transistor or a GaN-based GIT (Gate Injection Transistor), for example.

[0419] Twenty-eighth Embodiment A power conversion device 100A according to a twenty-eighth embodiment will be described with reference to Fig. 46. With respect to the power conversion device 100 according to the twenty-eighth embodiment, components similar to those of the power conversion device 100A according to the third embodiment (see Fig. 5) are denoted by the same reference numerals, and description thereof will be omitted.

[0420] In the power conversion device 100A according to the twenty-eighth embodiment, each of the multiple switches 8 is a dual-gate GaN-based GIT having a first source terminal, a first gate terminal, a second gate terminal, and a second source terminal. In the power conversion device 100A according to the twenty-eighth embodiment, a second control signal SU6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT constituting the switch 8U, and a second control signal SU7 is applied between the second gate terminal and the second source terminal of the dual-gate GaN-based GIT constituting the switch 8V. A second control signal SV6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT constituting the switch 8V, and a second control signal SV7 is applied between the second gate terminal and the second source terminal of the dual-gate GaN-based GIT constituting the switch 8W. A second control signal SW6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT, and a second control signal SW7 is applied between the second gate terminal and the second source terminal of the dual-gate GaN-based GIT constituting the switch 8W.

[0421] The power conversion device 100A according to the twenty-eighth embodiment has the same advantages as the power conversion device 100A according to the third embodiment.

[0422] Twenty-ninth embodiment A power conversion device 100D according to a twenty-ninth embodiment will be described with reference to Fig. 47. With respect to the power conversion device 100D according to the twenty-ninth embodiment, components similar to those of the power conversion device 100A according to the third embodiment (see Fig. 5) are denoted by the same reference numerals, and description thereof will be omitted.

[0423] (1) Configuration The power conversion device 100D differs from the power conversion device 100A in that it further includes a regenerative capacitor 16 (hereinafter also referred to as the second regenerative capacitor 16) connected between the sixth end 154 of the regenerative capacitor 15 (hereinafter also referred to as the first regenerative capacitor 15) and the first DC terminal 31.

[0424] The second regenerative capacitor 16 is connected in series to the first regenerative capacitor 15. Therefore, in the power conversion device 100D, a series circuit of the second regenerative capacitor 16 and the first regenerative capacitor 15 is connected between the first DC terminal 31 and the second DC terminal 32. In the power conversion device 100D, fourth ends of multiple resonant inductors L1 are connected to a path between the first regenerative capacitor 15 and the second regenerative capacitor 16. The capacitance of the second regenerative capacitor 16 is the same as the capacitance of the first regenerative capacitor 15. The phrase "the capacitance of the second regenerative capacitor 16 is the same as the capacitance of the first regenerative capacitor 15" does not necessarily mean that the capacitance of the second regenerative capacitor 16 exactly matches the capacitance of the first regenerative capacitor 15, but may mean that the capacitance of the second regenerative capacitor 16 is within a range of 95% to 105% of the capacitance of the first regenerative capacitor 15.

[0425] In the power conversion device 100D according to the twenty-ninth embodiment, the voltage V15 of the first regeneration capacitor 15 (the potential at the sixth terminal 154 of the first regeneration capacitor 15) is equal to the value obtained by dividing the voltage Vd of the DC power supply E1 between the second regeneration capacitor 16 and the first regeneration capacitor 15. Therefore, the voltage V15 of the first regeneration capacitor 15 is approximately Vd / 2. In the power conversion device 100D according to the twenty-ninth embodiment, the control device 51A may store the value of the voltage V15 of the first regeneration capacitor 15 in advance.

[0426] (2) Advantages The operation of the control device 51A and the signal generating circuit 52 of the power conversion device 100D according to the twenty-ninth embodiment is similar to the operation of the control device 51A and the signal generating circuit 52 of the power conversion device 100A according to the third embodiment. Therefore, similar to the power conversion device 100A according to the third embodiment, the power conversion device 100D according to the twenty-ninth embodiment can more reliably achieve zero voltage soft switching without directly controlling the multiple switches 8 for zero voltage soft switching in the control device 51A.

[0427] Thirtyth Embodiment A power conversion device 100E according to a 30th embodiment will be described with reference to Fig. 48. With respect to the power conversion device 100E according to the 30th embodiment, components similar to those of the power conversion device 100A according to the third embodiment (see Fig. 5) are denoted by the same reference numerals, and description thereof will be omitted.

[0428] (1) Configuration The power conversion device 100E differs from the power conversion device 100 in that the fifth end 153 of the regenerative capacitor 15 is connected to the first DC terminal 31.

[0429] (2) Operation The operation of the control device 51A and the signal generating circuit 52 of the power conversion device 100E according to the 30th embodiment is similar to the operation of the control device 51A and the signal generating circuit 52 of the power conversion device 100A according to the third embodiment.

[0430] (3) Advantages As with the power conversion device 100A according to the third embodiment, the power conversion device 100E according to the thirtyth embodiment can more reliably achieve zero voltage soft switching without directly controlling the multiple switches 8 for zero voltage soft switching in the control device 51A.

[0431] (Thirty-first embodiment) A power conversion device 100F according to a thirty-first embodiment will be described with reference to Fig. 49. With respect to the power conversion device 100F according to the thirty-first embodiment, components similar to those of the power conversion device 100A according to the third embodiment (see Fig. 5) are denoted by the same reference numerals, and description thereof will be omitted.

[0432] The power conversion device 100F differs from the power conversion device 100A in that it includes three resonance inductors L1. Note that the example of Fig. 49 does not include the three first clamp diodes 13 and the three second clamp diodes 14 shown in Fig. 1.

[0433] (Thirty-Second Embodiment) (1) Configuration The power conversion device 100 according to the thirty-second embodiment includes a programmable logic device (PLD) instead of the plurality of logic circuits 521 to 526 (see FIG. 2) in the signal generating circuit 52 of the power conversion device 100 according to the first embodiment. The circuit configuration of the power conversion device 100 according to the thirty-second embodiment is the same as that of the power conversion device 100 according to the first embodiment (see FIG. 1), and will be described with reference to FIG. 1.

[0434] Similar to the signal generation circuit 52 of the first embodiment, the signal generation circuit 52 of the present embodiment generates a second control signal whose potential changes between a high level and a low level for each of the multiple switches 8. The signal generation circuit of the present embodiment generates, for each of the multiple switches 8, a second control signal having a high level period corresponding to the second dead time period Td2 for the corresponding switching circuit 10 among the multiple switching circuits 10.

[0435] Similar to the signal generation circuit 52 of the first embodiment, the signal generation circuit 52 of the present embodiment synchronizes the start point of the high-level period of the second control signal generated for each of the multiple switches 8 with the start timing of the second dead time period Td2. In the present embodiment, the signal generation circuit 52 synchronizes the start point of the high-level period of the second control signal to each of the multiple switches 8 with the start point of the second dead time period Td2. In the present embodiment, the length of the high-level period of the second control signal to each of the multiple switches 8 is longer than the length of the second dead time period Td2.

[0436] In the signal generating circuit 52 of the present embodiment, the PLD generates a second control signal for each of the plurality of switches 8 using a first control signal to the first switching element 1 and a first control signal to the second switching element 2 of a corresponding switching circuit 10 among the plurality of switching circuits 10. The PLD generates, for each of the plurality of switches 8, a second control signal having a high-level period corresponding to the second dead time period Td2 for the corresponding switching circuit 10 among the plurality of switching circuits 10.

[0437] In the signal generation circuit 52 of this embodiment, the PLD synchronizes the start point of the high-level period of the second control signal generated for each of the multiple switches 8 with the start timing of the second dead time period Td2. In the signal generation circuit 52 of this embodiment, the PLD is configured to synchronize the start point of the high-level period of the second control signal to each of the multiple switches 8 with the start point of the second dead time period Td2. In this embodiment, the length of the high-level period of the second control signal to each of the multiple switches 8 is longer than the length of the second dead time period Td2.

[0438] (2) Operation of the Power Conversion Device The operation of the control device 51 is the same as the operation of the control device 51 described in the first embodiment, and therefore a description thereof will be omitted.

[0439] Furthermore, the operation of the signal generating circuit 52 of this embodiment is the same as the relationship between the input and output of the signal generating circuit 52 of the first embodiment, and therefore a description thereof will be omitted.

[0440] (3) Advantages The power conversion device 100 according to the thirty-second embodiment has the same advantages as the power conversion device 100 according to the first embodiment.

[0441] (Other Modifications) The above-described embodiments 1 to 32 are merely examples of various embodiments of the present disclosure. The above-described embodiments 1 to 32 can be modified in various ways depending on the design, etc., as long as the object of the present disclosure can be achieved.

[0442] For example, the signal generating circuit 52 may be configured to generate a second control signal for each of the plurality of switches 8 using one of the first control signal to the first switching element 1 and the first control signal to the second switching element 2 of a corresponding one of the plurality of switching circuits 10.

[0443] Furthermore, in the fifth to twenty-third embodiments, the control system 50 or the control system 50A determines the first switch and the second switch among the plurality of switches 8 based on the magnitude relationship between the absolute values ​​of the load currents corresponding to the plurality of switches 8, but instead of the magnitude relationship between the absolute values ​​of the load currents, the first switch and the second switch among the plurality of switches 8 may be determined based on the magnitude relationship between the absolute values ​​of the voltage command values, or the first switch and the second switch among the plurality of switches 8 may be determined based on the magnitude relationship between the duties. Furthermore, in the fifth to twenty-third embodiments, the control system 50 or the control system 50A determines the first switch, the second switch, and the third switch among the plurality of switches 8 based on the magnitude relationship between the absolute values ​​of the load currents corresponding to the plurality of switches 8, but instead of the magnitude relationship between the absolute values ​​of the load currents, the first switch, the second switch, and the third switch among the plurality of switches 8 may be determined based on the magnitude relationship between the absolute values ​​of the voltage command values, or the first switch, the second switch, and the third switch among the plurality of switches 8 may be determined based on the magnitude relationship between the duties.

[0444] Furthermore, when the control system 50A determines that a resonant current flows simultaneously through the resonant inductor L1 through each of two or more of the switches 8 when a second control signal with a preset high-level period is given to each of the multiple switches 8, the control system 50A executes a second control operation on a first switch that is one of the two or more switches 8, and executes a first control operation on a second switch that is different from the first switch among the two or more switches 8. However, without being limited to this, the control system 50A may be configured to execute the first control opera...

Claims

1. A first DC terminal and a second DC terminal, a power conversion circuit having a plurality of first switching elements and a plurality of second switching elements, wherein a plurality of switching circuits in which the plurality of first switching elements and the plurality of second switching elements are connected in series one-to-one are connected in parallel with each other, the plurality of first switching elements are connected to the first DC terminal, and the plurality of second switching elements are connected to the second DC terminal; a plurality of AC terminals corresponding one-to-one to the plurality of switching circuits, each of which is connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit and through which a load current flows; a plurality of switches corresponding one-to-one to the plurality of switching circuits, each of which has a first end connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit; a plurality of resonance capacitors corresponding one-to-one to the plurality of switches, each of which is connected between the first end of the corresponding switch and the second DC terminal; at least one resonance inductor having a third end and a fourth end, the third end of which is connected to the second end of the corresponding switch among the plurality of switches; a regeneration capacitor having a fifth end and a sixth end, the fifth end of which is connected to the second DC terminal and the sixth end of which is connected to the fourth end of the at least one resonance inductor; and a control system that gives a first control signal whose potential changes between a high level and a low level to each of the plurality of first switching elements and the plurality of second switching elements, and gives a second control signal whose potential changes between a high level and a low level to each of the plurality of switches. The control system is capable of executing a first control operation and a second control operation when changing the first control signal to the target switching element to be turned on among the first switching element and the second switching element in each of the plurality of switching circuits from a low level to a high level.In the first control operation, for each of the plurality of switching circuits, at least a part of the high-level period of the second control signal to the switch corresponding to each of the plurality of switching circuits among the plurality of switches overlaps with the dead time period set between the high-level period of the first control signal to the first switching element and the high-level period of the first control signal to the second switching element. In the second control operation, the high-level period of the second control signal is shifted so that the overlapping period between the high-level period of the second control signal applied to each of the plurality of switches and the dead time period is shorter than that in the case of the first control operation, and at least a part of the high-level period of the second control signal overlaps with the high-level period of the first control signal to the target switching element. Power conversion device.

2. The control system includes a control device that supplies the first control signal to each of the plurality of first switching elements and the plurality of second switching elements, and a signal generation circuit that supplies the second control signal to each of the plurality of switches. The control device sets a second dead time period obtained by adding a predetermined time to a first dead time period preset so that the on periods of the first switching element and the second switching element do not overlap as the dead time period. The predetermined time is determined according to the current value of the load current, the inductance of the resonance inductor, and the voltage value of the regeneration capacitor. The signal generation circuit generates the second control signal having a high level period corresponding to the second dead time period for the corresponding switching circuit among the plurality of switching circuits for each of the plurality of switches. The power conversion device according to claim 1.

3. The signal generation circuit generates the second control signal using at least one of the first control signal to the first switching element and the first control signal to the second switching element in the corresponding switching circuit among the plurality of switching circuits for each of the plurality of switches. The power conversion device according to claim 2.

4. The signal generation circuit includes a plurality of logic circuits and does not include a microcontroller. The power conversion device according to claim 3.

5. The at least one resonance inductor is one resonance inductor, and the second ends of the plurality of switches are commonly connected to the one resonance inductor. The power conversion device according to any one of claims 1 to 4.

6. When the control system determines that a resonance current flowing through two or more of the plurality of switches simultaneously flows through the resonance inductor when the second control signal having a preset high level period is supplied to each of the plurality of switches, the control system executes the second control operation on a first switch that is one of the two or more switches, and executes the first control operation on a second switch that is different from the first switch among the two or more switches. The power conversion device according to claim 5.

7. The first switch is a switch corresponding to a switching circuit in which, among the two or more switches, the absolute value of the load current flowing through each of the two or more switching circuits corresponding to the two or more switches in the plurality of switching circuits is the smallest, according to the power conversion device of claim 6.

8. The first switch is a switch corresponding to a switching circuit in which, among the two or more switches, the absolute value of the voltage command value for each of the two or more switching circuits corresponding to the two or more switches in the plurality of switching circuits is the smallest, according to the power conversion device of claim 6.

9. The first switch is a switch corresponding to a switching circuit in which, among the two or more switches, the absolute value of the voltage command value for each of the two or more switching circuits corresponding to the two or more switches in the plurality of switching circuits is the largest, according to the power conversion device of claim 6.

10. The two or more switches are three switches. When the control system performs the second control operation, for the first switch, the entire high-level period of the second control signal is overlapped with the high-level period of the first control signal to the target switching element corresponding to the first switch. For the third switch, which is different from the first switch and the second switch among the three switches, a part of the high-level period of the second control signal is overlapped with the high-level period of the first control signal to the target switching element corresponding to the third switch, according to the power conversion device of claim 6.

11. The first switch is a switch corresponding to a switching circuit in which, among the three switches, the absolute value of the load current flowing through each of the three switching circuits corresponding to the three switches in the plurality of switching circuits is the smallest. The third switch is a switch corresponding to a switching circuit in which, among the three switches, the absolute value of the load current flowing through each of the three switching circuits corresponding to the three switches in the plurality of switching circuits is the second smallest, according to the power conversion device of claim 10.

12. The third switch is the switch corresponding to the switching circuit among the three switching circuits corresponding to the three switches in the plurality of switching circuits, in which the absolute value of the load current flowing through each of the three switching circuits is the smallest. The first switch is the switch corresponding to the switching circuit among the three switching circuits corresponding to the three switches in the plurality of switching circuits, in which the absolute value of the load current flowing through each of the three switching circuits is the second smallest. The power conversion device according to claim 10.

13. The first switch is the switch corresponding to the switching circuit among the three switching circuits corresponding to the three switches in the plurality of switching circuits, in which the absolute value of the voltage command value for each of the three switching circuits is the smallest. The third switch is the switch corresponding to the switching circuit among the three switching circuits corresponding to the three switches in the plurality of switching circuits, in which the absolute value of the voltage command value for each of the three switching circuits is the second smallest. The power conversion device according to claim 10.

14. The third switch is the switch corresponding to the switching circuit among the three switching circuits corresponding to the three switches in the plurality of switching circuits, in which the absolute value of the voltage command value for each of the three switching circuits is the smallest. The first switch is the switch corresponding to the switching circuit among the three switching circuits corresponding to the three switches in the plurality of switching circuits, in which the absolute value of the voltage command value for each of the three switching circuits is the second smallest. The power conversion device according to claim 10.

15. The first switch is the switch corresponding to the switching circuit among the three switching circuits corresponding to the three switches in the plurality of switching circuits, in which the absolute value of the voltage command value for each of the three switching circuits is the largest. The third switch is the switch corresponding to the switching circuit among the three switching circuits corresponding to the three switches in the plurality of switching circuits, in which the absolute value of the voltage command value for each of the three switching circuits is the second largest. The power conversion device according to claim 10.

16. The third switch is the switch corresponding to the switching circuit with the largest absolute value of the voltage command value for each of the three switching circuits corresponding to the three switches among the plurality of switching circuits. The first switch is the switch corresponding to the switching circuit with the second largest absolute value of the voltage command value for each of the three switching circuits corresponding to the three switches among the plurality of switching circuits. The power conversion device according to claim 10.

17. When the control system determines that a resonance current flowing through two or more of the plurality of switches simultaneously flows through the resonance inductor when a second control signal with a preset high-level period is applied to each of the plurality of switches, the control system executes the first control operation or the second control operation for at least one of the two or more switches. The power conversion device according to claim 5.

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