Power conversion device

Abstract

The present invention improves power conversion efficiency without directly controlling a plurality of switches for zero-voltage soft switching in a control device. A signal generation circuit (52) of a control system (50) generates a second control signal for each of a plurality of switches (8). When the potential of a sixth end (154) of a regenerative capacitor (15) is smaller than a lower limit threshold value that is less than one-half of a voltage value applied between a first DC terminal (31) and a second DC terminal (32), the control system (50) performs a first control operation for increasing the potential of the sixth end (154) of the regenerative capacitor (15). When the potential of the sixth end (154) of the regenerative capacitor (15) is greater than an upper limit threshold value that is greater than one-half of the voltage value applied between the first DC terminal (31) and the second DC terminal (32), the control system (50) performs a second control operation for lowering the potential of the sixth end (154) of the regenerative capacitor (15).

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 device that converts direct current to multi-phase alternating current. The 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. A main switching circuit is provided for each phase of the multi-phase alternating current, with the interconnection point of the pair of main switching elements serving as an 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) that PWM controls 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) that controls the on / off of each auxiliary switching element and outputs it to the gate of each auxiliary switching element.

[0003] In the power conversion device disclosed in Patent Document 1, the controller needs to generate and output a plurality of first control signals and a plurality of second control signals, which results in an increase in the size of the controller.

[0004] Furthermore, in a power conversion device, the power conversion efficiency may decrease due to changes in the load state.

[0005] JP 2010-233306 A

[0006] An object of the present disclosure is to provide a power conversion device that can improve power conversion efficiency without directly controlling a plurality of switches for zero voltage soft switching in a control device.

[0007] 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. Each of the plurality of switches has a first end 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 includes a control device and a signal generating circuit. The control device provides each of the plurality of first switching elements and the plurality of second switching elements with a first control signal whose potential changes between a high level and a low level.The signal generating circuit provides each of the plurality of switches with a second control signal whose potential changes between a high level and a low level. The control device sets, for each of the plurality of switching circuits, a second dead time period obtained by adding a variable time to a predetermined first dead time period 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 so that on periods of the first switching element and the second switching element do not overlap. The variable time period is determined based on a current value of a load current corresponding to each of the plurality of switching circuits among a plurality of load currents flowing through each of the plurality of AC terminals, an inductance of the resonance inductor, and a potential at the sixth end of the regenerative capacitor. The signal generating circuit generates, for each of the plurality of switches, the second control signal having a high level period corresponding to the second dead time period for a corresponding switching circuit among the plurality of switching circuits. The control system performs a first control action to increase the potential of the sixth terminal of the regenerative capacitor when the potential of the sixth terminal of the regenerative capacitor is smaller than a lower limit threshold that is smaller than half of the voltage value applied between the first DC terminal and the second DC terminal, and a second control action to decrease the potential of the sixth terminal of the regenerative capacitor when the potential of the sixth terminal of the regenerative capacitor is larger than an upper limit threshold that is larger than half of the voltage value applied between the first DC terminal and the second DC terminal.

[0008] A power conversion device according to another 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. Each of the plurality of switches has a first end 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 includes a control device and a signal generating circuit. The control device provides each of the plurality of first switching elements and the plurality of second switching elements with a first control signal whose potential changes between a high level and a low level.The signal generating circuit provides each of the plurality of switches with a second control signal whose potential changes between a high level and a low level. The control device sets, for each of the plurality of switching circuits, a second dead time period obtained by adding a variable time to a predetermined first dead time period 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 so that on periods of the first switching element and the second switching element do not overlap. The variable time period is determined based on a current value of a load current corresponding to each of the plurality of switching circuits among a plurality of load currents flowing through each of the plurality of AC terminals, an inductance of the resonance inductor, and a potential at the sixth end of the regenerative capacitor. The signal generating circuit generates, for each of the plurality of switches, the second control signal having a high level period corresponding to the second dead time period for a corresponding switching circuit among the plurality of switching circuits. The control system performs a first control action to stop the discharge current of the regenerative capacitor when the potential of the sixth terminal of the regenerative capacitor is lower than a lower limit threshold that is lower than half of the voltage value applied between the first DC terminal and the second DC terminal, and a second control action to stop the charge current of the regenerative capacitor when the potential of the sixth terminal of the regenerative capacitor is higher than an upper limit threshold that is higher than half of the voltage value applied between the first DC terminal and the second DC terminal.

[0009] FIG. 1 is a circuit diagram of a system including a power conversion device according to a first embodiment. FIG. 2 is a circuit block diagram of a signal generating circuit in the power conversion device. FIG. 3 is a diagram showing 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. 4 is a timing chart for explaining a third control operation and a fourth control operation of the power conversion device. FIG. 5 is another timing chart for explaining the third control operation and the fourth control operation of the power conversion device. FIG. 6 is a timing chart for explaining a first control operation of the power conversion device. FIG. 7 is a timing chart for explaining a second control operation of the power conversion device. FIG. 8 is a timing chart for explaining the operation of the power conversion device. FIG. 9 is a circuit diagram of a system including a power conversion device according to a second embodiment. FIG. 10 is an explanatory diagram of the operation of the power conversion device during a first period. FIG. 11 is an explanatory diagram of the operation of the power conversion device during a second period. FIG. 12 is an explanatory diagram of the operation of the power conversion device during a second period. FIG. 13 is a timing chart illustrating a second control operation of the power conversion device according to the embodiment 3. FIG. 14 is a timing chart illustrating a second control operation of the power conversion device according to the embodiment 3. FIG. 15 is a circuit diagram of a system including the power conversion device according to the embodiment 4. FIG. 16 is a timing chart illustrating a third control operation and a fourth control operation of the power conversion device according to the embodiment 4. FIG. 17 is a timing chart illustrating a first control operation of the power conversion device according to the embodiment 4. FIG. 18 is a timing chart illustrating a second control operation of the power conversion device according to the embodiment 4. FIG. 19 is a circuit diagram of a system including the power conversion device according to the embodiment 5. FIG. 20 is a timing chart illustrating the operation of the power conversion device according to the embodiment 5. FIG. 21 is a timing chart illustrating the operation of the power conversion device according to the embodiment 5. FIG. 22 is a circuit diagram of a system including the power conversion device according to the embodiment 6. FIG. 23 is a timing chart illustrating the operation of the power conversion device according to the embodiment 6. FIG. 24 is a timing chart illustrating the operation of the power conversion device according to the embodiment 6.Fig. 25 is a circuit diagram of a system including a power conversion apparatus according to embodiment 7. Fig. 26 is a circuit diagram of a system including a power conversion apparatus according to embodiment 8. Fig. 27 is a circuit diagram of a system including a power conversion apparatus according to embodiment 9. Fig. 28 is a circuit diagram of a system including a power conversion apparatus according to embodiment 10. Fig. 29 is a circuit diagram of a system including a power conversion apparatus according to embodiment 11. Fig. 30 is a circuit diagram of a system including a power conversion apparatus according to embodiment 12. Fig. 31 is a timing chart for explaining a third control operation and a fourth control operation of a power conversion apparatus according to a modification of embodiment 1.

[0010] First Embodiment A power conversion device 100 according to a first embodiment will be described below with reference to FIGS. 1 to 8. 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. The power conversion device 100 also includes a capacitor C10.

[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 device 51. 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] The control system 50 includes a control device 51 and a signal generating circuit 52. The control device 51 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.

[0032] In this embodiment, the control system 50 has a plurality of (three) first gate drive circuits (not shown) and a plurality of (three) second 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.

[0033] 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.

[0034] 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.

[0035] In the power conversion device 100, the plurality of first switching elements 1 and the plurality of second switching elements 2 are controlled by a control device 51. Control terminals of the plurality of first switching elements 1 are connected to the control device 51 via corresponding first gate drive circuits. Control terminals of the plurality of second switching elements 2 are connected to the control device 51 via corresponding second gate drive circuits.

[0036] In the power conversion device 100, the multiple switches 8 are controlled by the signal generating 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 generating circuit 52. Control terminals of the multiple third switching elements 6 and the multiple fourth switching elements 7 are connected to the signal generating circuit 52 (see FIG. 2 ).

[0037] 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.

[0038] 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.

[0039] 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.

[0040] The duties 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, vary based on a U-phase voltage command (in FIG. 3, the duty of the first control signal SU1 is shown as a U-phase duty). The control device 51 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 first dead time period Td1 (see FIG. 4) 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.

[0041] The duties 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, vary based on a V-phase voltage command (in FIG. 3, the duty of the first control signal SV1 is shown as a V-phase duty). The control device 51 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 51 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 51 also sets a first dead time period Td1 (see FIG. 4) 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.

[0042] 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 a W-phase voltage command (in FIG. 3, the duty of the first control signal SW1 is shown as a W-phase duty). The control device 51 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 first dead time period Td1 (see FIG. 4) 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.

[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 plurality of resonant inductors 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 (resonant inductor Lu) - 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 (resonant inductor Lu) - regenerative capacitor 15. The discharging current is a current that discharges the charge of 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 (resonant inductor Lv)-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 (resonant inductor Lv)-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 (resonant inductor Lw) - 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 (resonant inductor Lw) - regenerative capacitor 15. The discharging current is a current that discharges the charge of the resonant capacitor 9W.

[0048] 4, 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, for the switch 8 corresponding to any switching circuit 10 including the target switching element, FIG. 4 illustrates the second control signal provided from the control system 50 to the third switching element 6 as a second control signal S6, and the current iL1 flowing through the resonant inductor L1. Also, FIG. 4 illustrates the current flowing through the AC terminal 41 connected to the connection point 3 of any switching circuit 10 including the target switching element as a load current i. Also, FIG. 4 illustrates the voltage across the first switching element 1 of any switching circuit 10 including the target switching element as a voltage V1. Also, FIG. 4 illustrates the voltage value of the DC power supply E1 as Vd. Note that FIG. 4 also illustrates a timing chart for one cycle of the carrier signal.

[0049] In the example of FIG. 4, the polarity of the load current i flowing through the AC terminal 41 connected to the target switching element is positive.

[0050] For example, as shown in FIG. 4 , the control device 51 sets the dead time period between the high-level period of the first control signal S1 to the first switching element 1 and the high-level period of the first control signal S2 to the second switching element 2 for each of the multiple switching circuits 10 to a second dead time period Td2 determined by the first dead time period Td1 and the variable time Tp1. The second dead time period Td2 includes the first dead time period Td1. The second dead time period Td2 has a length obtained by adding the variable time Tp1 to the length of the first dead time period Td1 (the total length of the first dead time period Td1 and the variable time Tp1). From another perspective, the control device 51 sets the second dead time period Td2, which is extended from the first dead time period Td1 by the variable time Tp1, as the dead time period.

[0051] 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, 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 in which both the first switching element 1 and the second switching element 2 are on). The first dead time period Td1 is determined in advance for each of the multiple switching circuits 10 based on the switching characteristics (specification turn-on time and turn-off time) of the first switching element 1 and the second switching element 2, and is stored in the control device 51. In this embodiment, for example, the length of the resonance 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 resonance half period corresponding to each of the multiple switches 8 is half the resonance period, which is the reciprocal of the resonance frequency of the resonance circuit including the switches 8, the resonance inductor L1, and the resonance capacitor 9. Therefore, if the inductance of the resonance inductor L1 is L and the capacitance of the resonance capacitor 9 is C, the resonance half period is π×(L C) １／２ In this embodiment, the length of the resonance half cycle is set to be shorter than the length of the first dead time period Td1, for example.

[0052] The length of the resonant half cycle of the resonant circuit including the resonant inductor L1 and the resonant capacitor 9U is set to be shorter than the length of the first dead time period Td1 (see FIG. 4 ) 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 to be shorter than the length of the first dead time period Td1 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 to be shorter than the length of the first dead time period Td1 set between the high-level period of the first control signal SW1 and the high-level period of the first control signal SW2.

[0053] If the resonant period is Tres, the resonant half period, Tres / 2, is shorter than the length of the first dead time period Td1. The end of the resonant half period preferably coincides 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. 4, the start and end of the first dead time period Td1 are time t1 and time t3, respectively.

[0054] The length of the resonant half cycle of each resonant circuit is not limited to a length shorter than the length of the first dead time period Td1, and may be set to be the same as the length of the first dead time period Td1, for example.

[0055] The second dead time period Td2 is a period obtained by lengthening the first dead time period Td1 by the variable time Tp1. In this embodiment, the control device 51 determines the variable time Tp1 based on the current value of the load current i, the inductance L of the resonant inductor L1, and the potential at the sixth end 154 of the regenerative capacitor 15. The current value of the load current i is, for example, the result of detection of the load current i by a current sensor, a signal-processed value thereof, or an estimated value of the load current i. The detected value of the load current i or the signal-processed value thereof is a value detected in a carrier cycle in which the variable time Tp1 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, a value estimated for the load current i in a carrier cycle in which the variable time Tp1 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 51. The potential V15 at the sixth terminal 154 of the regenerative capacitor 15 is the detected value of the potential V15 at the sixth terminal 154 of the regenerative capacitor 15. In the example of Fig. 4, the variable time Tp1 is the sum of the additional time and the length of the resonance half cycle. If the additional time is Tad, then the value is calculated by Tad = i × (L / V15).

[0056] In the power conversion device 100 , a signal generating circuit 52 separate from the control device 51 controls the multiple switches 8 .

[0057] 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.

[0058] 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. 4 ) 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 (fixed length T2) of the high-level period of the second control signal to each of the multiple switches 8 is longer than the length of the first dead-time period Td1.

[0059] 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 a 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. 2 , 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.

[0060] 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. 2 ) 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 51 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.

[0061] 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 multivibrators M21 and M22 connected in series. 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. 2 ) 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 51 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.

[0062] 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. 2 ) 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 51 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.

[0063] 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. 2 ) 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 logic circuit 524, fixed length T2 is the length of a CR time constant determined by the capacitance of capacitor C42 connected to multivibrator M42 in the subsequent stage and the resistance value of resistor R42. In logic circuit 524, first control signal SV1 output from control device 51 is input to the inverting trigger terminal of multivibrator M41 in the previous stage, and second control signal SV7 is output from output terminal Q of multivibrator M42 in the subsequent stage. Second control signal SV7 is provided to fourth switching element 7V via gate drive circuit 534.

[0064] 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. 2 ) 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 51 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.

[0065] 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. 2 ) 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 51 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. 2) 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.

[0066] 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.

[0067] The capacitor C10 is connected between the first DC terminal 31 and the second DC terminal 32, and is connected in parallel to the power conversion circuit 11. The capacitor C10 is, for example, an electrolytic capacitor.

[0068] (3) Operation In the following description, the polarity of the current iL1 flowing through the resonant inductor L1 will be defined as positive when it flows in the direction of the arrow in Fig. 1, and as negative when it flows in the opposite direction to the arrow in Fig. 1. Furthermore, in the following description, the polarity of the load currents iU, iV, and iW flowing through the U-phase, V-phase, and W-phase of the AC load RA1 will be defined as positive when it flows in the direction of the arrow in Fig. 1, and as negative when it flows in the opposite direction to the arrow in Fig. 1. Furthermore, the polarity of the currents i9U, i9V, and i9W flowing through the resonant capacitors 9U, 9V, and 9W will be defined as positive when it flows in the direction of the arrow in Fig. 1, and as negative when it flows in the opposite direction to 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.

[0069] 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.

[0070] The operation of the power conversion device 100 will be described below with reference to FIGS. 4 to 8. FIG. 4 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. 2), and the second control signal S6 when the target switching element is the first switching element 1. FIG. 4 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. FIG. 4 also illustrates the voltage value of the DC power supply E1 as Vd.

[0071] The control system 50 is capable of executing a first control operation and a second control operation. The first control operation is a control operation for increasing the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 when the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 is smaller than a lower limit threshold Vth1 (see FIG. 6 ) that is smaller than half the voltage value Vd applied between the first DC terminal 31 and the second DC terminal 32. The second control operation is a control operation for decreasing the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 when the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 is larger than an upper limit threshold Vth2 (see FIG. 7 ) that is larger than half the voltage value Vd applied between the first DC terminal 31 and the second DC terminal 32. The control system 50 stops the discharge current of the regenerative capacitor 15 in the first control operation, and stops the charge current of the regenerative capacitor 15 in the second control operation.

[0072] The control system 50 is also capable of executing a third control operation and a fourth 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 third control operation, at least a part 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 is overlapped with a second dead time period Td2 set for each of the multiple switching circuits 10 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. In the fourth control operation, the high-level period of the second control signal is shifted so that 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, so that the overlap period between the high-level period of the second control signal to be applied to each of the multiple switches 8 and the second dead time period Td2 is shorter than in the third control operation. In the fourth control operation, the variable time Tp1 is changed (the variable time Tp1 is set to 0) to shift the high level period of the second control signal.

[0073] For the sake of convenience, the third and fourth control actions will be described first, followed by a more detailed description of the first and second control actions.

[0074] (3.1) Third Control Operation (3.1.1) When the Target Switching Element is the First Switching Element The third control operation of the control system 50 will be described with reference to FIG.

[0075] 4, 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. 4, 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 second dead time period Td2. Also, in FIG. 4, 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. 4, the current flowing through an AC terminal 41 connected to a node 3 of the any switching circuit 10 including the target switching element is illustrated as a load current i. 4, 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. 4, the voltage value of the DC power supply E1 is shown as Vd. In the example of FIG. 4, the start and end points of the second dead time period Td2 are time t0 and time t3, respectively. Note that FIG. 4 illustrates a timing chart for one cycle of the carrier signal.

[0076] In the example of FIG. 4, the polarity of the load current i flowing through the AC terminal 41 connected to the target switching element is positive.

[0077] In the third control operation, the control system 50 causes a part of the high-level period of the second control signal S6 to the third switching element 6 to overlap with the second dead time period Td2.

[0078] 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 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. 4, 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, and becomes the same value as the load current i at time t2, which is the elapsed additional time Tad from time t1. The current iL1 also becomes the same value as the load current i at time t3, which is the end time of the second dead time period Td2. Finally, the current iL1 becomes zero at time t4, which is the elapsed time equal to the additional time Tad from time t3. The additional time Tad is a value calculated in the control system 50 by, for example, calculating Tad = i × (L / V15) using the load current i detected by a current sensor, its signal processed value, or an estimated value of the load current i, the pre-stored inductance L of the resonant inductor L1, and the detected potential V15 at the sixth terminal 154 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, and the second control signal S6 changes from high to low at time t4 when the total time of the first dead time period Td1 and the additional time Tad has elapsed. 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 to the resonant capacitor 9U via the resonant inductor L1. 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 Fig. 4 flows into the resonant capacitor 9, causing LC resonance. In the example of Fig. 4, the high-level period of the second control signal S6 (length of the high-level period=fixed length T2) continues for the length of a third period T03 described below even after time t3 when the second dead-time period Td2 ends, so the current iL1 continues to flow through the third switching element 6 until the current iL1 becomes zero.

[0079] In the third 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 second dead time period Td2. As a result, the third switching element 6 is turned on during the second dead time period Td2, 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 by 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.

[0080] 4, the first control signal S2 falls from high to low at time t0, the output signal from the inverting output terminal of the preceding multivibrator falls from high to low at time t1, the first control signal S1 changes from low to high at time t3, and the second control signal S6 changes from high to low at time t4.

[0081] In the switching circuit 10, 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. 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. 4 , the current iL1 flowing through the resonant inductor L1 starts to flow at time t1, which is the start point of the high-level period of the second control signal S6. The current iL1 becomes the same as the load current i at time t2, when the additional time Tad (the length of the first period T01 in the example of FIG. 4 ) has elapsed. The current iL1 becomes the same as the load current i at time t3, which is the end point of the second dead time period Td2. The current iL1 then becomes zero at time t4, when the additional time Tad (the length of the third period T03 in the example of FIG. 4 ) has elapsed from time t3. In the signal generating circuit 52, the second control signal S6 changes from low level to high level at time t1, which is a specified time T1 after time t0 when the first control signal S2 changes from high level to low level. The current iL1 flowing between time t2 and time t3 is a resonant current flowing from the regenerative capacitor 15 to the resonant capacitor 9 via the resonant inductor L1.

[0082] For example, if the target first switching element 1 is the first switching element 1U, during the first period T01, 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 the regenerative capacitor 15, the resonant inductor L1 (resonant inductor Lu), the diode 71, the third switching element 6U, and the AC terminal 41U. Also, during the first period T01, the load current iU flows through the second diode 5 connected in anti-parallel to the second switching element 2U, the AC terminal 41U, and the AC load RA1.

[0083] During the second period T02, 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 (resonant inductor Lu), the diode 71, and the third switching element 6U, 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.

[0084] During the third period T03, 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 the path passing through the regenerative capacitor 15, the resonant inductor L1 (resonant inductor Lu), the diode 71, the third switching element 6U, and the AC terminal 41U. This reduces the current iL1 to zero. Also, during the third period T03, the load current iU flows through the path passing through the first DC terminal 31, the first switching element 1U, the AC terminal 41U, and the AC load RA1.

[0085] The fixed length T2 is the total length of the first period T01, the second period T02, and the third period T03.

[0086] The current iL1 flowing in the first period T01, the second period T02, and the third period T03 is the discharge current of the regenerative capacitor 15. In other words, when the target switching element is the first switching element 1, the current iL1 is the discharge current of the regenerative capacitor 15.

[0087] (3.1.2) When the Target Switching Element is the Second Switching Element In the third 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 second dead time period Td2. As a result, the fourth switching element 7 is turned on during the second dead time period Td2, 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. The current iL1 continues to flow through the third switching element 6 even after the end of the second dead time period Td2 until the current iL1 becomes zero.

[0088] In the example of FIG. 5, at time t10, the first control signal S1 falls from high level to low level, at time t11, the output signal from the inverting output terminal of the preceding multivibrator falls from high level to low level, at time t13, the first control signal S2 changes from low level to high level, and at time t14, the second control signal S7 changes from high level to low level.

[0089] In the switching circuit 10, the voltage V1 across the first switching element 1 becomes Vd at time t13 when the second dead time period Td2 immediately before the high-level period of the first control signal S2 ends, and the voltage V2 across the second switching element 2 becomes zero at time t13 when the second dead time period Td2 immediately before the high-level period of the first control signal S2 ends. Therefore, when the first control signal S2 changes from low level to high level at time t13, the second switching element 2 is subjected to zero-voltage soft switching. In the example of FIG. 5 , the current iL1 flowing through the resonant inductor L1 starts at time t11, when the high-level period of the second control signal S7 begins, reaches the same value as the load current i at time t12, when the additional time Tad (the length of the first period T01 in the example of FIG. 5 ) has elapsed, reaches the same value as the load current i at time t13, when the second dead time period Td2 ends, and becomes zero at time t14, when the same time as the additional time Tad (the length of the third period T03 in the example of FIG. 5 ) has elapsed since time t13. In the signal generating circuit 52, the second control signal S7 changes from low to high at time t11, when the specified time T1 has elapsed since time t10, when the first control signal S1 changes from high to low. The current iL1 flowing between time t12 and time t13 is a resonant current (a discharge current of the resonant capacitor 9) flowing from the resonant capacitor 9 to the regenerative capacitor 15 via the resonant inductor L1.

[0090] 5, the first period T01 is the period from time t11 to time t12. 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.

[0091] 5, the second period T02 is the period from time t12 to time t13. 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.

[0092] In FIG. 5 , the third period T03 is the period from time t13 to time t14. During the third period T03, the second switching element 2 is in the ON state, the first switching element 1 and the third switching element 6 are in the OFF state, and the fourth switching element 7 is in the ON state. During the third period T03, the current iL1 flows through the AC terminal 41, the diode 61, the fourth switching element 7, 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 i flows through the AC load RA1, the AC terminal 41, the second switching element 2, and the second DC terminal 32.

[0093] The current iL1 flowing in the first period T01, the second period T02, and the third period T03 described above is a charging current for the regenerative capacitor 15. In other words, when the target switching element is the second switching element 2, the current iL1 is a charging current for the regenerative capacitor 15.

[0094] (3.2) Fourth Control Operation In the fourth 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 second dead time period Td 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.

[0095] (3.2.1) When the Target Switching Element is the First Switching Element In the fourth control operation, as shown in FIG. 4 , for example, 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 second dead time period Td is shorter than in the third 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" 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.

[0096] (3.2.2) When the Target Switching Element is the Second Switching Element In the fourth control operation, for example, as shown in FIG. 5 , the control system 50 shifts the second control signal S7 provided to the fourth switching element 7 so that the overlap period between the high-level period of the second control signal S7 and the second dead time period Td2 is shorter than in the first control operation, causing the entire high-level period of the second control signal S7 to overlap with part of the high-level period of the first control signal S2 provided 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.

[0097] In the fourth control operation, the control system 50 shifts the high-level period of the second control signal S7 so that the overlap period between the high-level period of the second control signal S7 applied to the fourth switching element 7 and the second dead time period Td2 is shorter than in the third control operation, causing the entire high-level period of the second control signal S7 to overlap with part of the high-level period of the first control signal S2 to the target second switching element 2. In this embodiment, since the entire high-level period of the shifted second control signal S7 overlaps with part of the high-level period of the first control signal S2 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.

[0098] (3.3) First Control Operation When the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 is smaller than a lower limit threshold Vth1, the control system 50 performs a first control operation to increase the potential V15 at the sixth terminal 154 of the regenerative capacitor 15. The lower limit threshold Vth1 is a value smaller than half the voltage value Vd applied between the first DC terminal 31 and the second DC terminal 32. The lower limit threshold Vth1 is, for example, a value that is 90% of Vd / 2. When performing the first control operation, the control system 50 overlaps a second control signal sent to one of the multiple switches 8, which is associated with the discharge current of the regenerative capacitor 15, with the high-level period of the first control signal sent to the target first switching element 1.

[0099] The first control operation is an operation for controlling the multiple switches 8 to increase the potential V15 at the sixth end 154 of the regenerative capacitor 15, based on the polarities of the multiple load currents iU, iV, iW flowing through the multiple AC terminals 41. In the first control operation, based on the polarities of the multiple load currents iU, iV, iW flowing through the multiple AC terminals 41, the overlap period between the high-level period of the second control signal to the switch 8 among the multiple switches 8 related to the discharge operation of the regenerative capacitor 15 and the second dead time period Td2 corresponding to the switch related to the discharge operation of the regenerative capacitor 15 is set to zero.

[0100] Figure 6 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, SW1, SW2, the second control signals SU6, SV7, SW7, the load currents iU, iV, iW, the currents iL1, iLu, iLv, iLw, the voltages V2u, V2v, V2w across the second switching elements 2U, 2V, 2W, respectively, and the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 when the control system 50 performs the first control operation.

[0101] FIG. 6 illustrates a timing chart for a portion of one period within one cycle of the carrier signal. In the example of FIG. 6, the polarity of the load current iU is positive, the polarity of the load current iV is negative, and the polarity of the load current iW is negative. Also, in the example of FIG. 6, the absolute value of the load current iU is greater than the absolute value of the load current iV, and the absolute value of the load current iV is greater than the absolute value of the load current iW. In FIG. 6, the timing for detecting the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 (hereinafter also referred to as the detection timing of the potential V15) is indicated by an upward arrow. The potential V15 at the sixth terminal 154 of the regenerative capacitor 15 is detected every cycle of the carrier signal. As a result, the control device 51 obtains the detected potential at the sixth terminal 154 of the regenerative capacitor 15 every cycle of the carrier signal. The timing at which the control device 51 acquires the detected potential at the sixth terminal 154 of the regenerative capacitor 15 is, for example, the same as the timing at which the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 is detected, but is not limited to this. The timing at which the control device 51 acquires the detected potential at the sixth terminal 154 of the regenerative capacitor 15 and the timing at which the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 is detected are each not limited to every cycle of the carrier signal, and may be, for example, every half cycle of the carrier signal or an integer multiple of one cycle of the carrier signal (for example, every two cycles).

[0102] 6, since the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 at the detection timing is smaller than the lower limit threshold Vth1, when the control system 50 performs the first control operation, the control system 50 overlaps the entire high-level period of the second control signal SU6 to the third switching element 6U with the high-level period of the first control signal SU1 to the target first switching element 1 corresponding to the third switching element 6U. In FIG. 6, the current iLu flowing through the resonant inductor Lu and the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 when it is assumed that the control system 50 does not perform the first control operation are respectively indicated by two-dot chain lines.

[0103] As can be seen from Figure 6 , by performing the first control operation, the control system 50 can increase the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 to a value greater than the lower limit threshold Vth1 by one carrier signal cycle after the detection timing indicated by the arrow in Figure 6 (i.e., the next detection timing). In the example of Figure 6 , the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 one carrier signal cycle after the detection timing indicated by the arrow in Figure 6 can be made equal to or greater than the lower limit threshold Vth1. However, the voltage fluctuation value of the potential V15 that can be varied in one carrier signal cycle varies depending on the magnitude of the resonant current. Therefore, it is sufficient that the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 be equal to or greater than the lower limit threshold Vth1 one carrier signal cycle after the detection timing indicated by the arrow in Figure 6 .

[0104] (3.4) Second Control Operation When the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 is greater than an upper limit threshold Vth2, the control system 50 performs a second control operation to decrease the potential V15 at the sixth terminal 154 of the regenerative capacitor 15. The upper limit threshold Vth2 is a value greater than half the voltage value Vd applied between the first DC terminal 31 and the second DC terminal 32. The upper limit threshold Vth2 is, for example, a value that is 110% of Vd / 2. When performing the second control operation, the control system 50 overlaps a second control signal sent to one of the multiple switches 8, which is associated with the charging current of the regenerative capacitor 15, with the high-level period of the first control signal sent to the target second switching element 2.

[0105] The second control operation is an operation of controlling the multiple switches 8 to decrease the potential V15 at the sixth end 154 of the regenerative capacitor 15, based on the polarities of the multiple load currents iU, iV, iW flowing through the multiple AC terminals 41. In the second control operation, the overlap period between the high-level period of the second control signal to the switch 8 of the multiple switches 8 related to the charging operation of the regenerative capacitor 15 and the second dead time period Td2 corresponding to the switch 8 related to the charging operation of the regenerative capacitor 15 is set to zero, based on the polarities of the multiple load currents iU, iV, iW flowing through the multiple AC terminals 41.

[0106] Figure 7 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, SW1, SW2, the second control signals SU7, SV6, SW6, the load currents iU, iV, iW, the currents iL1, iLu, iLv, iLw, the voltages V2u, V2v, V2w across the second switching elements 2U, 2V, 2W, respectively, and the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 when the control system 50 performs the second control operation.

[0107] FIG. 7 illustrates a timing chart for a portion of one period within one cycle of the carrier signal. In the example of FIG. 7 , the polarity of the load current iU is negative, the polarity of the load current iV is positive, and the polarity of the load current iW is positive. Also, in the example of FIG. 7 , the absolute value of the load current iU is greater than the absolute value of the load current iV, and the absolute value of the load current iV is greater than the absolute value of the load current iW. In FIG. 7 , the detection timing of the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 is indicated by an upward arrow. The potential V15 at the sixth terminal 154 of the regenerative capacitor 15 is detected every cycle of the carrier signal. The timing at which the control device 51 acquires the detected potential at the sixth terminal 154 of the regenerative capacitor 15 is, for example, the same as the timing at which the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 is detected, but is not limited to this.

[0108] 7, the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 at the detection timing is greater than the upper limit threshold Vth2, and therefore when performing the second control operation, the control system 50 overlaps the entire high-level period of the second control signal SU7 to the fourth switching element 7U with the high-level period of the first control signal SU2 to the target second switching element 2 corresponding to the fourth switching element 7U. In FIG. 7, the current iLu flowing through the resonance inductor Lu and the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 are respectively shown by two-dot chain lines when it is assumed that the control system 50 does not perform the second control operation.

[0109] As can be seen from FIG. 7 , by performing the second control operation, the control system 50 can reduce the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 below the value at the detection timing. In the example of FIG. 7 , the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 one carrier signal cycle later than the detection timing indicated by the arrow in FIG. 7 (i.e., the next detection timing) can be reduced to a value smaller than the upper threshold value Vth2. In the example of FIG. 7 , the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 one carrier signal cycle later than the detection timing indicated by the arrow can be reduced. Because the voltage fluctuation value of the potential V15 that can be varied in one carrier signal cycle varies depending on the magnitude of the resonant current, it is sufficient that the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 becomes equal to or lower than the upper threshold value Vth2 one carrier signal cycle later than the detection timing indicated by the arrow in FIG. 7 .

[0110] (3.5) Cases in which the first control action and the second control action are not executed When the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 is equal to or higher than the lower threshold Vth1 and equal to or lower than the upper threshold Vth2, the control system 50 does not execute either the first control action or the second control action. In this case, the control system 50 of the present embodiment executes the third control action.

[0111] Figure 8 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, SW1, SW2, the second control signals SU7, SV6, SW6, the load currents iU, iV, iW, the currents iL1, iLu, iLv, iLw, the voltages V2u, V2v, V2w across the second switching elements 2U, 2V, 2W, respectively, and the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 when the control system 50 performs the third control operation.

[0112] 8 shows a timing chart for a portion of one period within one cycle of the carrier signal. In the example of FIG. 8, the polarity of the load current iU is negative, the polarity of the load current iV is positive, and the polarity of the load current iW is positive. Also, in the example of FIG. 8, the absolute value of the load current iU is greater than the absolute value of the load current iV, and the absolute value of the load current iV is greater than the absolute value of the load current iW. In FIG. 8, the detection timing of the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 is indicated by an upward arrow.

[0113] As can be seen from Figure 8, by the control system 50 performing the third control operation without performing the first and second control operations, it is possible to maintain the potential V15 of the sixth terminal 154 of the regenerative capacitor 15 at the next detection timing within a range greater than or equal to the lower threshold value Vth1 and less than or equal to the upper threshold value Vth2.

[0114] Furthermore, in the power conversion device 100, the control system 50 performs the third control operation without performing the first control operation and the second control operation, thereby realizing zero voltage soft switching of each target switching element.

[0115] (4) Advantages In the power conversion device 100 according to the first embodiment, the control system 50 includes a control device 51 and a signal generating circuit 52. The control device 51 provides a first control signal, the potential of which changes between high and low levels, 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, the potential of which changes between high and low levels, to each of the plurality of switches 8. The control device 51 sets a second dead time period Td2, which is obtained by adding a variable time Tp1 to a predetermined first dead time period Td1, 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 plurality of switching circuits 10, so that the on-periods of the first switching element 1 and the second switching element 2 do not overlap. The variable time Tp1 is determined based on the current value of a load current corresponding to each of the plurality of switching circuits 10 among the plurality of load currents iU, iV, and iW flowing through the plurality of AC terminals 41, the inductance of the resonance inductor L1, and the potential V15 at the sixth end 154 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. The control system 50 performs a first control operation to increase the potential at the sixth end 154 of the regenerative capacitor 15 when the potential V15 at the sixth end 154 of the regenerative capacitor 15 is smaller than a lower limit threshold Vth1 that is smaller than half the voltage value Vd applied between the first DC terminal 31 and the second DC terminal 32. When the potential V15 of the sixth terminal 154 of the regenerative capacitor 15 is greater than an upper threshold Vth2 that is greater than half the voltage value Vd applied between the first DC terminal 31 and the second DC terminal 32, the control system 50 performs a second control operation to lower the potential V15 of the sixth terminal 154 of the regenerative capacitor 15.

[0116] According to the above configuration, it is possible to improve power conversion efficiency without directly controlling the plurality of zero voltage soft switching switches 8 in the control device 51. More specifically, it is not necessary for the control device 51 to generate second control signals for directly controlling the plurality of zero voltage soft switching switches 8, and it is possible to 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 in the control device 51. Furthermore, according to the above configuration, it is not necessary for the control device 51 to generate and output the plurality of second control signals SU6, SU7, SV6, SV7, SW6, and SW7, so it is possible to simplify the control device 51, and for example, it is possible to suppress an increase in the number of control ports of a microcomputer included in the control device 51 and suppress an increase in the size of the control device 51.

[0117] Furthermore, in the power conversion device 100 according to the first embodiment, the control system 50 performs a first control operation to stop the discharge current of the regenerative capacitor 15 when the potential V15 of the sixth terminal 154 of the regenerative capacitor 15 is smaller than a lower limit threshold Vth1 that is smaller than half the voltage value Vd applied between the first DC terminal 31 and the second DC terminal 32. Furthermore, the control system 50 performs a second control operation to stop the charge current of the regenerative capacitor 15 when the potential V15 of the sixth terminal 154 of the regenerative capacitor 15 is larger than an upper limit threshold Vth2 that is larger than half the voltage value Vd applied between the first DC terminal 31 and the second DC terminal 32.

[0118] According to the above configuration, it is possible to improve the power conversion efficiency without directly controlling the plurality of switches 8 for zero voltage soft switching in the control device 51.

[0119] Furthermore, in the power conversion device 100 according to the first embodiment, the control system 50 does not perform either the first control operation or the second control operation when the potential V15 of the sixth terminal 154 of the regenerative capacitor 15 is equal to or greater than the lower threshold Vth1 and equal to or less than the upper threshold Vth2.

[0120] According to the above configuration, it is possible to realize zero voltage soft switching of the target switching element to be turned on, either the first switching element 1 or the second switching element 2, in each of the plurality of switching circuits 10.

[0121] Furthermore, in the power conversion device 100 according to the first embodiment, the control system 50 can execute a third control operation and a fourth control operation when changing the 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, from low level to high level in each of the multiple switching circuits 10. In the third control operation, the control system 50 causes at least a part of the high level period of the second control signal to be sent to the switch 8 among the multiple switches 8 corresponding to each of the multiple switching circuits 10 to overlap with a second dead time period Td2 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 fourth 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 second dead time period Td2 is shorter than in the third control operation, and causes at least a portion (in the first embodiment, the entirety) of the high-level period of the second control signal to overlap with a portion of the high-level period of the first control signal S1 to the target switching element.

[0122] 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.

[0123] In addition, in the power conversion device 100, the signal generating circuit 52 generates a second control signal for each of the multiple switches 8 using one of the first control signal S1 to the first switching element 1 of the corresponding switching circuit 10 among the multiple switching circuits 10 and the first control signal S2 to the second switching element 2.

[0124] According to the above configuration, the signal generating circuit 52 can be simplified.

[0125] Furthermore, in the power conversion device 100, the signal generation circuit 52 includes a plurality of logic circuits 521 to 526, but does not include a microcontroller.

[0126] According to the above configuration, the signal generating circuit 52 can be simplified.

[0127] Furthermore, in the power conversion device 100, the control system 50 acquires the detected potential of the sixth terminal 154 of the regenerative capacitor 15 for each cycle of the carrier signal. The first control operation is an operation of controlling the multiple switches 8 to increase the potential V15 of the sixth terminal 154 of the regenerative capacitor 15, based on the polarities of the multiple load currents iU, iV, and iW output from the multiple AC terminals 41. The second control operation is an operation of controlling the multiple switches 8 to decrease the potential V15 of the sixth terminal 154 of the regenerative capacitor 15, based on the polarities of the multiple load currents iU, iV, and iW output from the multiple AC terminals 41.

[0128] According to the above configuration, fluctuations in the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 (fluctuations in which the potential V15 becomes smaller than the lower threshold value Vth1, and fluctuations in which the potential V15 becomes larger than the upper threshold value Vth2) can be more quickly suppressed.

[0129] Furthermore, in the power conversion device 100, the control system 50, in the first control operation, sets to zero the overlap period between a high-level period of the second control signal to one of the multiple switches 8 related to the discharging operation of the regenerative capacitor 15 and a second dead time period Td2 corresponding to the switch 8 related to the discharging operation of the regenerative capacitor 15, based on the polarities of each of the multiple load currents iU, iV, iW flowing through the multiple AC terminals 41. In the second control operation, the control system 50, in the power conversion device 100, sets to zero the overlap period between a high-level period of the second control signal to one of the multiple switches 8 related to the charging operation of the regenerative capacitor 15 and a second dead time period Td2 corresponding to the switch 8 related to the charging operation of the regenerative capacitor 15, based on the polarities of each of the multiple load currents iU, iV, iW flowing through the multiple AC terminals 41.

[0130] According to the above configuration, it is possible to perform the first control operation by changing the variable time Tp1 of the second dead time period Td2 corresponding to the switch 8 related to the discharge operation of the regenerative capacitor 15, and it is possible to perform the second control operation by changing the variable time Tp1 of the second dead time period Td2 corresponding to the switch 8 related to the charging operation of the regenerative capacitor 15.

[0131] (Embodiment 2) A power conversion device 100A according to embodiment 2 will be described with reference to Figures 9 to 13. Regarding the power conversion device 100A according to embodiment 2, components that are the same as those of the power conversion device 100 according to embodiment 1 (see Figures 1 and 2) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0132] (1) Configuration As shown in Fig. 9 , 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 this embodiment, the resonant inductor L1 is shared among the three resonant circuits. In this 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.

[0133] 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).

[0134] The control system 50A includes a control device 51A instead of the control device 51 of the control system 50.

[0135] The configuration of the control device 51A is substantially the same as the configuration of the control device 51.

[0136] (2) Operation (2.1) Third Control Operation (2.1.1) When the Target Switching Element is the First Switching Element For example, if the target first switching element 1 is the first switching element 1U, during the first period T01, 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 the path shown by the thick solid line in FIG. 10. That is, the current iL1 flows through the path passing through the regenerative capacitor 15, the resonant inductor L1, the diode 71, the third switching element 6U, and the AC terminal 41U. Furthermore, during the first period T01, the load current iU flows through the path shown by the thick dashed line in FIG. 10. That is, the load current iU flows through the path passing through the second diode 5 connected in anti-parallel to the second switching element 2U, the AC terminal 41U, and the AC load RA1.

[0137] During the second period T02, the first switching element 1U, the second switching element 2U, and the fourth switching element 7U are all 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 the path shown by the thick solid line in FIG. 11. That is, the current iL1 flows through the regenerative capacitor 15, the resonant inductor L1, the diode 71, and the third switching element 6U, 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.

[0138] During the third period T03, 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 along the path shown by the bold solid line in FIG. 12. That is, the current iL1 flows along the path through the regenerative capacitor 15, the resonant inductor L1, the diode 71, the third switching element 6U, and the AC terminal 41U. This reduces the current iL1 to zero. Also, during the third period T03, the load current iU flows along the path shown by the bold dashed line in FIG. 12. That is, the load current iU flows along the path through the first DC terminal 31, the first switching element 1U, the AC terminal 41U, and the AC load RA1.

[0139] As can be seen from the above description, the third control operation when the target switching element is the first switching element is the same as that in the first embodiment.

[0140] Although the case where the target switching element is the first switching element 1U has been described above, the same applies to the cases of the first switching element 1V and the first switching element 1W.

[0141] (2.1.2) When the Target Switching Element is the Second Switching Element The third control operation when the target switching element is the second switching element is the same as in the first embodiment, and therefore description thereof will be omitted.

[0142] (2.2) Fourth Control Operation (2.2.1) When the Target Switching Element is the First Switching Element The fourth control operation when the target switching element is the first switching element is the same as in the first embodiment, and therefore description thereof will be omitted.

[0143] (2.2.2) When the Target Switching Element is the Second Switching Element The fourth control operation when the target switching element is the second switching element is the same as in the first embodiment, and therefore description thereof will be omitted.

[0144] (2.3) Fifth Control Action and Sixth Control Action The control system 50A is configured to be able to perform either a fifth control action (hereinafter also referred to as an independent control action) or a sixth control action (hereinafter also referred to as a simultaneous control action) when the control device 51A determines in advance that two-phase resonant currents corresponding to two of the multiple switching circuits 10 will flow simultaneously through the resonant inductor L1. "When it is determined that two-phase resonant currents will flow simultaneously" means that the control device 51A has estimated in advance that two-phase resonant currents will flow simultaneously through the resonant inductor L1.

[0145] The power conversion device 100A resonates a resonant capacitor 9 associated with a target switching element among the plurality of first switching elements 1 and the plurality of second switching elements 2, and a resonant inductor L1. At this time, the voltage across the resonant capacitor 9 associated with the target switching element varies depending on the amplitude of a resonant voltage centered on a potential V15 at a sixth terminal 154 of the regenerative capacitor 15. The voltage across the target switching element varies from the voltage value Vd of the DC power supply E1 to zero, thereby achieving zero-voltage soft switching. The potential V15 at the sixth terminal 154 of the regenerative capacitor 15 varies depending on the amount of charge charged or discharged in the regenerative capacitor 15 for each period during which a resonant current flows in a resonant circuit including the resonant capacitor 9 and the resonant inductor L1. Furthermore, the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 varies depending on the amount of charge charged or discharged in the regenerative capacitor 15 for each cycle of the carrier signal. In the regenerative capacitor 15, the charge or discharge amount associated with the load currents iU, iV, and iW of the U, V, and W phases is determined for each cycle of the carrier signal. The largest absolute value of the load currents iU, iV, and iW results in the largest charge. Therefore, in the power conversion device 100A, the charge or discharge amount of the regenerative capacitor 15 changes with each cycle of the carrier signal. However, in the power conversion device 100A, when the three-phase servo motor serving as the AC load RA1 is rotating normally, the load currents iU, iV, and iW of each phase are sinusoidal and out of phase with each other by 120°. This ensures a balanced charge and discharge in the regenerative capacitor 15, thereby suppressing fluctuations in the potential V15 at the sixth terminal 154 of the regenerative capacitor 15.

[0146] In the power conversion device 100A, if the control device 51A only performs the third control operation described above, for example, if the three-phase servo motor serving as the AC load RA1 locks due to a load state change, the load currents iU, iV, and iW for the U, V, and W phases will each have a different constant value. This results in a large difference between the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 and half the voltage Vd (Vd / 2) of the DC power supply E1. This reduces the amplitude of the resonant voltage when resonating the resonant capacitors 9U, 9V, and 9W with the resonant inductor L1 to achieve zero-voltage soft switching in the power conversion device 100A, potentially making it impossible to achieve zero-voltage soft switching.

[0147] (2.3.1) Determination of whether two-phase resonant currents flow simultaneously In the power conversion device 100A, 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 (see areas A1 and A2 in FIG. 3 ). In area A1 in FIG. 3 , the duties of the first control signal for the U phase and the first control signal for the V phase are approximately 0.75. In area A2 in FIG. 3 , the duties of the first control signal for the U phase and the first control signal for the V phase are approximately 0.25. The polarity of the resonant current is the same as the polarity of the current iL1. In area A1, the polarity of the resonant current is positive, and in area A2, the polarity of the resonant current is negative. In the case of 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 100A, in the case of region A2, the direction of the resonant current is opposite to that in 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.

[0148] 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 100A, if two-phase currents flow simultaneously through the resonant inductor L1, the resonant frequency of the resonant circuit including the resonant inductor L1 changes compared to when a single-phase current flows through the resonant inductor L1.

[0149] 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.

[0150] (2.3.2) Fifth Control Operation The fifth control operation (independent control operation) includes a control operation for shifting the high-level period of at least one of the two second control signals to two switches 8 through which the resonant current flows among the multiple switches 8 when it is determined that a two-phase resonant current flows through the resonant inductor L1, so as to eliminate overlapping periods between the high-level periods of the two second control signals. In other words, in the fifth control operation, the control system 50A generates second control signals to the two switches 8 so that the resonant currents passing through the two switches 8 do not flow simultaneously through the resonant inductor L1 but flow independently in different periods.

[0151] (2.3.3) Sixth Control Action The sixth control action (simultaneous control action) includes a control action of overlapping the high level periods of two second control signals to two switches 8 through which a resonant current flows among the multiple switches 8 when it is determined that a two-phase resonant current flows through the resonant inductor L1. "Overlapping the high level periods of two second control signals" is not limited to overlapping the entire high level period of one of the two second control signals with the entire high level period of the remaining second control signal.

[0152] In the sixth control operation, for example, within one cycle of the carrier signal, the high-level periods of the two second control signals SV7 and SW7 of two of the three switches 8U, 8V, and 8W are shifted so that the high-level periods of the two second control signals SV7 and SW7 of two of the three switches 8U, 8V, and 8W overlap. More specifically, the high-level periods of the two second control signals SV7 and SW7 of two of the three switches 8U, 8V, and 8W are shifted so that the high-level periods of the two second control signals SV7 and SW7 of two of the three switches 8V and 8W overlap entirely. It is not essential that the high-level periods of the two second control signals SV7 and SW7 of the two switches 8V and 8W overlap entirely. For example, it is sufficient that the second control signal to one of the two switches 8V and 8W remains high until the current iL1 of the three switches 8U, 8V, and 8W reaches the load currents iV and iW of the V-phase and W-phase, respectively. The absolute value of current iL1 is greatest during the period when the high-level periods of the two second control signals SV7 and SW7 overlap, and therefore the fluctuation range of potential V15 at the sixth terminal 154 of regenerative capacitor 15 is greatest during the period when the high-level periods of two of the three second control signals SU6, SV7, and SW7 overlap.

[0153] (2.3.4) Details of the Fifth Control Operation and the Sixth Control Operation In the control system 50A, the control device 51A acquires a detected potential of the potential V15 at the sixth terminal 154 of the regenerative capacitor 15. The control device 51A acquires the detected potential for each cycle of the carrier signal, for example. For example, the control device 51A may store the voltage value Vd of the DC power supply E1 in advance, or may acquire the detected result of the voltage value Vd. The control system 50A determines the content of the control operation in the control device 51A based on the detected potential at the sixth terminal 154 of the regenerative capacitor 15, the value of Vd / 2, and the detected results of the load currents iU, iV, and iW.

[0154] In the control system 50A, the control device 51A switches between the fifth control operation and the sixth control operation based on the detected potential of the sixth terminal 154 of the regenerative capacitor 15 and the polarity of the multiple load currents iU, iV, iW flowing through each of the multiple AC terminals 41.

[0155] In the fifth control operation (independent control operation), the control system 50A shifts the high-level periods of two second control signals for two of the multiple switches 8 to prevent overlap between the high-level periods. In the fifth control operation, for example, the end point of the high-level period of one of the two second control signals is the same as the start point of the high-level period of the remaining second control signal. However, this is not limited to this, and the high-level period of the remaining second control signal may start after the end of the high-level period of one second control signal. In the independent control operation, the control system 50A prevents overlap between the high-level periods of the second control signals for the multiple switches 8.

[0156] In the sixth control operation (simultaneous control operation), the control system 50A shifts the high-level periods of two second control signals to two of the multiple switches 8, causing the high-level periods of the two second control signals to overlap.

[0157] When the control system 50A determines that resonant currents passing through two or more switches 8 of the multiple switches 8 simultaneously flow through the resonant inductor L1, and performs the sixth control operation, the control system 50A determines the variable time Tp1 to be the sum of two or more additional times Tad corresponding one-to-one to the two or more switches 8, and the difference (ΔTres / 2) between a first resonant half cycle when the resonant currents do not flow simultaneously and a second resonant half cycle when the resonant currents flow simultaneously. Each of the two or more additional times Tad is determined using the current value of the load current flowing through the corresponding switch 8 of the two or more switches 8, the inductance of the resonant inductor L1, and the potential V15 at the sixth end 154 of the regenerative capacitor 15. The first resonant half cycle is half the length (Tres / 2) of the resonant cycle (Tres) of a first resonant circuit including the resonant inductor L1 and only one of the multiple resonant capacitors 9. The second resonant half period is half the length of the resonant period (Tres2) of the second resonant circuit including the resonant inductor L1 and two or more resonant capacitors 9 corresponding to two or more switches 8 among the plurality of resonant capacitors 9. When the second resonant circuit includes two resonant capacitors 9, the second resonant half period is Tres2 / 2=2 １／２ When the second resonant circuit includes three resonant capacitors 9, the second resonant half period is Tres2 / 2=3 １／２ ×(Tres / 2).

[0158] The control system 50A performs a fifth control action when the first condition or the second condition is satisfied, and performs a sixth control action when the third condition or the fourth condition is satisfied.

[0159] The first condition is that the detected potential at the sixth terminal 154 of the regenerative capacitor 15 is greater than the upper threshold Vth2, and the product of the multiple load currents iU, iV, and iW is positive. When calculating iU x iV x iW, iU, iV, and iW are instantaneous values, and are positive, zero, or negative.

[0160] The second condition is that the detected potential at the sixth terminal 154 of the regenerative capacitor 15 is smaller than the lower threshold Vth1, and the product of the multiple load currents iU, iV, and iW (iU×iV×iW) is positive.

[0161] The third condition is that the detected potential at the sixth terminal 154 of the regenerative capacitor 15 is smaller than the lower limit threshold Vth1, and the product of the multiple load currents iU, iV, iW is negative.

[0162] The fourth condition is that the detected potential at the sixth terminal 154 of the regenerative capacitor 15 is greater than the upper limit threshold Vth2, and the product of the multiple load currents iU, iV, iW is negative.

[0163] The control system 50A performs the third control operation described above when the detected potential at the sixth terminal 154 of the regenerative capacitor 15 is equal to or greater than the lower threshold Vth1 and equal to or less than the upper threshold Vth2.

[0164] The relationship between the first, second, third and fourth conditions and the fifth control action (independent control action) and sixth control action (simultaneous control action) is as shown in Table 1.

[0165]

[0166] Note that "iU x iV x iW" is the product of the load currents iU, iV, and iW, with the polarity being positive when they flow in the direction of the arrow in Fig. 9 and negative when they flow in the opposite direction. Instead of "iU x iV x iW", the control device 51A may determine that the product of the multiple load currents iU, iV, and iW is positive when the value of sgn(iU) x sgn(iV) x sgn(iW) is positive "1", and may determine that the product of the multiple load currents iU, iV, and iW is negative when the value of sgn(iU) x sgn(iV) x sgn(iW) is "-1".

[0167] (2.3.5) First Control Action The first control action is similar to any one of the third control action, the fifth control action, and the sixth control action, and therefore a description thereof will be omitted.

[0168] (2.3.6) Second Control Operation Figure 13 shows a timing chart of the first control signals SU1, SU2, SV1, SV2, SW1, SW2, the second control signals SU6, SV7, SW7, the load currents iU, iV, iW, the currents iL1, iLu, iLv, iLw, the voltages V2u, V2v, V2w across the second switching elements 2U, 2V, 2W, respectively, and the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 when the control system 50A performs the simultaneous control operation and the second control operation. In this embodiment, three switches 8U, 8V, and 8W are connected to one resonant inductor L1, so in Figure 13, current iLu is the current of current iL1 that flows through switch 8U, current iLv is the current of current iL1 that flows through switch 8V, and current iLw is the current of current iL1 that flows through switch 8W.

[0169] FIG. 13 illustrates a timing chart for a portion of one period within one cycle of the carrier signal. In the example of FIG. 13, the polarity of the load current iU is positive, the polarity of the load current iV is negative, and the polarity of the load current iW is negative. Also, in the example of FIG. 13, the absolute value of the load current iU is greater than the absolute value of the load current iV, and the absolute value of the load current iV is greater than the absolute value of the load current iW. In FIG. 13, the potential V15 of the sixth terminal 154 of the regenerative capacitor 15 is detected every cycle of the carrier signal. As a result, the control device 51A obtains the detected potential of the sixth terminal 154 of the regenerative capacitor 15 every cycle of the carrier signal.

[0170] 13, the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 at the detection timing is greater than the upper limit threshold Vth2, and therefore, when performing the second control operation, the control system 50A overlaps the entire high-level period of the second control signal SW7 to the fourth switching element 7W with the high-level period of the first control signal SW2 to the target second switching element 2W corresponding to the fourth switching element 7W. In Fig. 13, the current iLw and the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 are respectively shown by two-dot chain lines when it is assumed that the control system 50A performs the simultaneous control operation without performing the second control operation.

[0171] As can be seen from Figure 13, by performing the second control operation, the control system 50A can reduce the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 below the value at the detection timing. In the example of Figure 13, the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 one carrier signal cycle after the detection timing indicated by the arrow in Figure 13 (i.e., the next detection timing) can be reduced to a value smaller than the upper limit threshold Vth2. In the example of Figure 13, the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 one carrier signal cycle after the detection timing indicated by the arrow can be set to be equal to or lower than the upper limit threshold Vth2. However, since the voltage fluctuation value of the potential V15 that can be varied in one carrier signal cycle varies depending on the magnitude of the resonant current, it is sufficient that the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 be equal to or lower than the upper limit threshold Vth2 one carrier signal cycle after the detection timing indicated by the arrow in Figure 13.

[0172] (3) Advantages In the power conversion device 100A according to the second embodiment, the control system 50A has a control device 51A and a signal generating circuit 52, and the control system 50A performs the first control operation and the second control operation. Therefore, similar to the power conversion device 100 according to the first embodiment, it is possible to improve the power conversion efficiency without directly controlling the multiple switches 8 for zero voltage soft switching in the control device 51A.

[0173] Furthermore, in the power conversion device 100A according to the second embodiment, the second terminals 82 of the multiple switches 8 are commonly connected to one resonant inductor L1. When the control system 50A determines that two-phase resonant currents corresponding to two of the multiple switching circuits 10 simultaneously flow through the resonant inductor L1 while performing the first control operation, the control system 50A can execute a simultaneous control operation in which high-level periods of two second control signals for two switches 8 corresponding to the two switching circuits 10 among the multiple switches 8 overlap. When performing the first control operation while performing the simultaneous control operation, the control system 50A overlaps the entire high-level period of the second control signal for one of the two switches 8 with the high-level period of the first control signal for the target switching element (first switching element 1 or second switching element 2) corresponding to that switch 8.

[0174] According to the above configuration, it is possible to control the potential V15 of the sixth terminal 154 of the regenerative capacitor 15 to a constant value.

[0175] Third Embodiment A power conversion device 100A according to a third embodiment will be described with reference to Fig. 14. Regarding the power conversion device 100A according to the third embodiment, components similar to those of the power conversion device 100A according to the second embodiment (see Fig. 9) are denoted by the same reference numerals, and description thereof will be omitted.

[0176] (1) Configuration The configuration of the power conversion device 100A according to the third embodiment is the same as the configuration of the power conversion device 100A according to the second embodiment, and therefore will not be illustrated or described.

[0177] (2) Operation The operation of the power conversion device 100A according to the third embodiment is substantially the same as the operation of the power conversion device 100A according to the second embodiment. In this embodiment, when the control system 50A performs the first control operation while executing the simultaneous control operation, the entire high-level period of the second control signal for each of the two switches 8 is made to overlap with the high-level period of the first control signal for the target switching element (the first switching element 1 or the second switching element 2) corresponding to each of the two switches 8. In the example of Fig. 14, the entire high-level period of the second control signal SV7 for the switch 8V (the fourth switching element 7V) is made to overlap with part of the high-level period of the first control signal SV2, and the entire high-level period of the second control signal SW7 for the switch 8W (the fourth switching element 7W) is made to overlap with part of the high-level period of the first control signal SW2.

[0178] (3) Advantages As with the power conversion device 100A according to the second embodiment, the power conversion device 100A according to the third embodiment can improve power conversion efficiency without directly controlling the multiple switches 8 for zero voltage soft switching in the control device 51A.

[0179] Furthermore, the power conversion device 100A according to the third embodiment can reduce the fluctuation of the potential V15 compared to the power conversion device 100A according to the second embodiment when the fluctuation of the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 is large when the first control operation is not performed.

[0180] A power conversion device 100B according to a fourth embodiment will be described with reference to Fig. 15 to Fig. 18. Regarding the power conversion device 100B according to the fourth embodiment, components similar to those of the power conversion device 100A according to the second embodiment (see Fig. 9) are denoted by the same reference numerals, and description thereof will be omitted.

[0181] (1) Configuration The power conversion device 100B according to the fourth embodiment differs from the power conversion device 100A in that it includes a control system 50B instead of the control system 50A of the power conversion device 100A (see FIG. 9).

[0182] The control system 50B includes a control device 51B instead of the control device 51A of the control system 50A.

[0183] The configuration of the control device 51B is substantially the same as the configuration of the control device 51A.

[0184] (2) Operation The operation of the power conversion device 100B according to the fourth embodiment is substantially the same as the operation of the power conversion device 100A according to the second embodiment, but differs in the first control operation, the second control operation, and the fourth control operation.

[0185] (2.1) Third Control Operation The third control operation of the control system 50B (see, for example, FIG. 16) is the same as the third control operation of the control system 50A of the second embodiment.

[0186] (2.2) Fourth Control Operation In the fourth control operation, the control system 50B shifts the high-level period of the second control signal so that part of the 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, so that the overlap period between the high-level period of the second control signal and the second dead time period Td2 provided to each of the multiple switches 8 is shorter than in the third control operation. Note that in the fourth control operation, the high-level period of the second control signal is shifted by changing the variable time Tp1 (shortening the variable time Tp1).

[0187] 16 , a portion of the high-level period of the shifted second control signal S6 overlaps with a portion 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 a portion of the second dead time period Td. In the present embodiment, when the control system 50B performs the fourth control operation, 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, compared to when the control system 50A of embodiment 2 performs the fourth control operation.

[0188] (2.3) First Control Operation In the first control operation, the control system 50B shortens the overlap period between the high-level period of the second control signal to the switch 8 related to the discharge operation of the regenerative capacitor 15 and the second dead time period Td2 so that the integral value of the discharge current flowing through the regenerative capacitor 15 in one cycle of the carrier signal is smaller than the charge current.

[0189] 17 illustrates a timing chart of the first control signals SU1, SU2, SV1, SV2, SW1, SW2, the second control signals SU6, SV7, SW7, the load currents iU, iV, iW, the currents iL1, iLu, iLv, iLw, the voltages V2u, V2v, V2w across the second switching elements 2U, 2V, 2W, respectively, and the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 when the control system 50B is performing the simultaneous control operation and the first control operation is performed. Note that in this embodiment, the three switches 8U, 8V, 8W are connected to one resonant inductor L1, and therefore in FIG. 17, the current iLu is the current of the current iL1 that flows through the switch 8U, the current iLv is the current of the current iL1 that flows through the switch 8V, and the current iLw is the current of the current iL1 that flows through the switch 8W.

[0190] FIG. 17 illustrates a timing chart for a portion of one period within one cycle of the carrier signal. In the example of FIG. 17, the polarity of the load current iU is positive, the polarity of the load current iV is negative, and the polarity of the load current iW is negative. Also, in the example of FIG. 17, the absolute value of the load current iU is greater than the absolute value of the load current iV, and the absolute value of the load current iV is greater than the absolute value of the load current iW. In FIG. 17, the potential V15 of the sixth terminal 154 of the regenerative capacitor 15 is detected every cycle of the carrier signal. As a result, the control device 51B obtains the detected potential of the sixth terminal 154 of the regenerative capacitor 15 every cycle of the carrier signal.

[0191] In the example of Figure 17, the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 at the detection timing is smaller than the lower threshold Vth1. Therefore, when performing the first control operation, the control system 50B overlaps part of the high-level period of the second control signal SU6 to the third switching element 6U with the high-level period of the first control signal SU1 to the target first switching element 1U corresponding to the third switching element 6U. In Figure 17, the current iLu and the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 are shown by two-dot chain lines when it is assumed that the control system 50B performs the simultaneous control operation without performing the first control operation. In the example of Figure 17, when the control system 50B performs the first control operation, the integrated value of iLu becomes smaller than the sum of the integrated values ​​of iLv and iLw.

[0192] As can be seen from FIG. 17, by the control system 50B performing the first control operation, the potential V15 of the sixth terminal 154 of the regenerative capacitor 15 can be increased to a value higher than the value at the detection timing.

[0193] (2.4) Second Control Operation In the second control operation, the control system 50B shortens the overlap period between the high-level period of the second control signal to the switch 8 related to the charging operation of the regenerative capacitor 15 and the second dead time period Td2 so that the integral value of the discharge current flowing through the regenerative capacitor 15 in one cycle of the carrier signal becomes larger than the integral value of the charge current.

[0194] 18 illustrates a timing chart of the first control signals SU1, SU2, SV1, SV2, SW1, SW2, the second control signals SU7, SV6, SW6, the load currents iU, iV, iW, the currents iL1, iLu, iLv, iLw, the voltages V2u, V2v, V2w across the second switching elements 2U, 2V, 2W, respectively, and the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 when the control system 50B is performing the simultaneous control operation and the second control operation is performed. Note that in this embodiment, the three switches 8U, 8V, 8W are connected to one resonant inductor L1, and therefore in FIG. 18, the current iLu is the part of the current iL1 that flows through the switch 8U, the current iLv is the part of the current iL1 that flows through the switch 8V, and the current iLw is the part of the current iL1 that flows through the switch 8W.

[0195] FIG. 18 illustrates a timing chart for a portion of one period within one cycle of the carrier signal. In the example of FIG. 18, the polarity of the load current iU is negative, the polarity of the load current iV is positive, and the polarity of the load current iW is positive. Also, in the example of FIG. 18, the absolute value of the load current iU is greater than the absolute value of the load current iV, and the absolute value of the load current iV is greater than the absolute value of the load current iW. In FIG. 18, the potential V15 of the sixth terminal 154 of the regenerative capacitor 15 is detected every cycle of the carrier signal. As a result, the control device 51B obtains the detected potential of the sixth terminal 154 of the regenerative capacitor 15 every cycle of the carrier signal.

[0196] In the example of Figure 18, the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 at the detection timing is greater than the upper limit threshold Vth2. Therefore, when performing the second control operation, the control system 50B overlaps part of the high-level period of the second control signal SU7 to the switch 8U (the fourth switching element 7U of the switch 8U) with the high-level period of the first control signal SU2 to the target second switching element 2U corresponding to the switch 8U. In Figure 18, the two-dot chain lines indicate the current iLu and the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 when it is assumed that the control system 50B performs the simultaneous control operation without performing the second control operation. In the example of Figure 18, when the control system 50B performs the second control operation, the integrated value of iLu becomes smaller than the sum of the integrated values ​​of iLv and iLw.

[0197] As can be seen from Figure 18, by performing the second control operation, the control system 50B can reduce the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 below the value at the detection timing. In the example of Figure 18, the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 can be reduced one carrier signal cycle after the detection timing indicated by the arrow (i.e., the next detection timing). In the example of Figure 18, the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 one carrier signal cycle after the detection timing indicated by the arrow is not equal to or lower than the upper limit threshold Vth2. However, since the voltage fluctuation value of the potential V15 that can be varied in one carrier signal cycle varies depending on the magnitude of the resonant current, it is sufficient that the potential V15 at the sixth terminal 154 of the regenerative capacitor 15 is equal to or lower than the upper limit threshold Vth2 one carrier signal cycle after the detection timing indicated by the arrow in Figure 18.

[0198] (3) Advantages In the power conversion device 100B according to the fourth embodiment, similar to the power conversion device 100A according to the second embodiment, it is possible to improve the power conversion efficiency without directly controlling the multiple switches 8 for zero voltage soft switching in the control device 51B.

[0199] Fifth Embodiment A power conversion device 100C according to a fifth embodiment will be described with reference to Figures 19 to 21. Regarding the power conversion device 100B according to the third embodiment, components similar to those of the power conversion device 100A according to the second embodiment (see Figure 9) are denoted by the same reference numerals, and description thereof will be omitted.

[0200] (1) Configuration As shown in Fig. 19, the power conversion device 100C differs from the power conversion device 100A in that it includes a control system 50C instead of the control system 50A of the power conversion device 100A. The control system 50C includes a control device 51C instead of the control device 51A of the control system 50A.

[0201] In the power conversion device 100C, the control device 51C generates first control signals SU1, SU2, SV1, SV2, SV2, SW1, and SW2, similar to the control device 51A, to control a plurality of first switching elements 1 and a plurality of second switching elements 2.

[0202] When setting the second dead time period Td2 for each of the multiple switching circuits 10, if the polarity of the load current is positive, the control device 51C advances the end point of the high-level period of the first control signal to the second switching element 2 and delays the start point of the high-level period of the first control signal to the first switching element 1, thereby lengthening the first dead time period Td1 by a variable time Tp1. If the time by which the end point of the high-level period of the first control signal to the second switching element 2 is advanced is Ta21 (see FIG. 20 ) and the time by which the start point of the high-level period of the first control signal to the first switching element 1 is delayed is Ta11 (see FIG. 20 ), then the variable time Tp1 is Ta11 + Ta21, i.e., Ta11 = Ta21 = 0.5 × Tp1.

[0203] When setting the second dead time period Td2 for each of the multiple switching circuits 10, if the polarity of the load current is negative, the control device 51C advances the end point of the high-level period of the first control signal to the first switching element 1 and delays the start point of the high-level period of the first control signal to the second switching element 2, thereby lengthening the first dead time period Td1 by a variable time Tp1. If the time by which the end point of the high-level period of the first control signal to the first switching element 1 is advanced is Ta12 (see FIG. 21 ) and the time by which the start point of the high-level period of the first control signal to the second switching element 2 is delayed is Ta22 (see FIG. 21 ), then the variable time Tp1 is Ta12 + Ta22, where Ta12 = Ta22 = 0.5 × Tp1.

[0204] As in embodiment 2, the signal generating circuit 52 generates a second control signal for each of the multiple 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 multiple switching circuits 10.

[0205] (2) Operation (2.1) Basic Operation Fig. 20 illustrates the first control signals SU1 and SU2, the second control signal SU6, the current iL1 flowing through the resonant inductor L1, the load current iU, and the voltage V1u across the first switching element 1U when the target switching element is the first switching element 1U of the switching circuit 10U. Also, in Fig. 20, the voltage value of the DC power supply E1 is illustrated as Vd.

[0206] When the target switching element is the first switching element 1U, in the switching circuit 10U, the voltage V2u across the second switching element 2U becomes Vd at time t13 when the second dead time period Td2 immediately before the high-level period of the first control signal SU1 ends, and the voltage V1u across the first switching element 1U becomes zero at time t13 when the second dead time period Td2 immediately before the high-level period of the first control signal SU1 ends. Therefore, when the first control signal SU1 changes from low level to high level at time t13, the first switching element 1U is subjected to zero-voltage soft switching. 20 , the current iL1 flowing through the resonant inductor L1 starts at time t11, when the high-level period of the second control signal SU6 begins, reaches the same value as the load current iU at time t12, when a time period equal to the variable time Tp1 has elapsed, reaches the same value as the load current iU at time t13, when the second dead time period Td2 ends, and reaches zero at time t14, when the third period T03 has elapsed since time t13. In the signal generating circuit 52, the second control signal SU6 changes from low to high at time t11, when the first control signal SU2 changes from high to low. The current iL1 flowing between time t12 and time t13 is a resonant current (a charging current for the resonant capacitor 9U) that flows from the regenerative capacitor 15 through the resonant inductor L1 to the resonant capacitor 9U.

[0207] During the first period T01, the first switching element 1U, the second switching element 2U, and the fourth switching element 7U are all in an OFF state, and the third switching element 6U is in an ON state. During the first period T01, the current iL1 flows through the path passing through the regenerative capacitor 15, the resonant inductor L1, the diode 71, the third switching element 6U, and the AC terminal 41U, as in Fig. 10. Also, during the first period T01, the load current iU flows through the path passing 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 in Fig. 11.

[0208] During the second period T02, the first switching element 1U, the second switching element 2U, and the fourth switching element 7U are all 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 the path passing through the regenerative capacitor 15, the resonant inductor L1, the diode 71, and the third switching element 6U, as in Fig. 12, 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.

[0209] During the third period T03, 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 the path passing through the regenerative capacitor 15, the resonant inductor L1, the diode 71, the third switching element 6U, and the AC terminal 41U, as in FIG. 13. This reduces the current iL1 to zero. Also, during the third period T03, the load current iU flows through the path passing through the first DC terminal 31, the first switching element 1U, the AC terminal 41U, and the AC load RA1, as in FIG. 13.

[0210] 21 illustrates the first control signals SU1 and SU2, the second control signal SU7, the current iL1 flowing through the resonant inductor L1, the load current iU, and the voltage V2u across the second switching element 2U when the target switching element is the second switching element 2U of the switching circuit 10U. Also, in FIG. 21, the voltage value of the DC power supply E1 is illustrated as Vd.

[0211] When the target switching element is the second switching element 2U, in the switching circuit 10U, the voltage V1u across the first switching element 1U becomes Vd at time t43 when the second dead time period Td2 immediately before the high-level period of the first control signal SU2 ends, and the voltage V2u across the second switching element 2U becomes zero at time t43 when the second dead time period Td2 ends. Therefore, when the first control signal SU2 changes from low level to high level at time t43, the second switching element 2U is subjected to zero-voltage soft switching.

[0212] 21 , the current iL1 flowing through the resonant inductor L1 starts at time t41, when the high-level period of the second control signal SU7 begins, reaches the same value as the load current iU at time t42, when a time equal to the variable time Tp1 has elapsed, reaches the same value as the load current iU at time t43, when the second dead time period Td2 ends, and reaches zero at time t44, when a time equal to the variable time Tp1 has elapsed from time t43. In the signal generating circuit 52, the second control signal SU7 changes from low to high when the first control signal SU1 changes from high to low. The current iL1 flowing between time t42 and time t43 is the resonant current (the discharge current of the resonant capacitor 9U) flowing from the resonant capacitor 9U to the resonant inductor L1.

[0213] 21, the first period T01 is the period from time t41 to time t42. During the first period T01, the first switching element 1U, the second switching element 2U, and the third switching element 6U are all in an OFF state, and the fourth switching element 7U is in an ON state. During the first period T01, the current iL1 flows through a path that passes through the AC terminal 41U, the diode 61, the fourth switching element 7U, the resonant inductor L1, and the regenerative capacitor 15. Also, during the first period T01, the load current iU flows through a path that passes through the AC load RA1, the AC terminal 41U, and the first diode 4 connected in anti-parallel to the first switching element 1U.

[0214] In FIG. 21 , the second period T02 is the period from time t42 to time t43. During the second period T02, the first switching element 1U, the second switching element 2U, and the third switching element 6U are all in an OFF state, and the fourth switching element 7U 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 41U through the diode 61, the fourth switching element 7U, the resonant inductor L1, and the regenerative capacitor 15, and a current (resonant current) flowing from the resonant capacitor 9U through the diode 61, the fourth switching element 7U, the resonant inductor L1, and the regenerative capacitor 15. During the second period T02, the resonant capacitor 9 is discharged.

[0215] In FIG. 21 , the third period T03 is the period from time t43 to time t44. During the third period T03, the second switching element 2U and the fourth switching element 7U are each in an ON state, and the first switching element 1U and the third switching element 6U are each in an OFF state. During the third period T03, the current iL1 flows through the AC terminal 41U, the connection point 3U, 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.

[0216] Although an example of setting the second dead time period Td2 for the switching circuit 10U has been described above, the same applies to the switching circuit 10V and the switching circuit 10W.

[0217] (2.2) First Control Operation and Second Control Operation The first control operation and second control operation are similar to the first control operation and second control operation of the second embodiment, and therefore a description thereof will be omitted.

[0218] (3) Advantages As with the power conversion device 100A according to the second embodiment, the power conversion device 100C according to the fifth embodiment can improve power conversion efficiency without directly controlling the multiple switches 8 for zero voltage soft switching in the control device 51C.

[0219] Furthermore, in the power conversion device 100C, when the control device 51C sets the second dead time period Td2 for each of the multiple switching circuits 10, if the polarity of the load current is positive, the control device 51C advances the end point of the high-level period of the first control signal to the second switching element 2 and delays the start point of the high-level period of the first control signal to the first switching element 1, thereby adding a variable time Tp1 to the first dead time period Td1, and if the polarity of the load current is negative, the control device 51C advances the end point of the high-level period of the first control signal to the first switching element 1 and delays the start point of the high-level period of the first control signal to the second switching element 2, thereby adding a variable time Tp1 to the first dead time period Td1.

[0220] According to the above configuration, it is possible to achieve zero voltage soft switching while reducing dead time loss and dead time error.

[0221] Sixth Embodiment A power conversion device 100D according to a sixth embodiment will be described with reference to Figures 22 to 24. With respect to the power conversion device 100D according to the sixth embodiment, components that are the same as those of the power conversion device 100A according to the second embodiment (see Figure 9) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0222] (1) Configuration As shown in Fig. 22 , the power conversion device 100D differs from the power conversion device 100A in that it includes a control system 50D instead of the control system 50A of the power conversion device 100A. The control system 50D includes a control device 51D instead of the control device 51A of the control system 50A.

[0223] In the power conversion device 100D, the control device 51D generates first control signals SU1, SU2, SV1, SV2, SV2, SW1, and SW2, similar to the control device 51A, to control a plurality of first switching elements 1 and a plurality of second switching elements 2.

[0224] When the control device 51D sets the second dead time period Td2 for each of the multiple switching circuits 10, if the polarity of the load current is positive, it adds a variable time Tp1 to the first dead time period Td1 by shortening the high-level period of the first control signal to the first switching element 1.

[0225] When the control device 51D sets the second dead time period Td2 for each of the multiple switching circuits 10, if the polarity of the load current is negative, it adds a variable time Tp1 to the first dead time period Td1 by shortening the high-level period of the first control signal to the second switching element 2.

[0226] As in embodiment 2, the signal generating circuit 52 generates a second control signal for each of the multiple 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 multiple switching circuits 10.

[0227] (2) Operation (2.1) Basic Operation Fig. 23 shows the first control signals SU1 and SU2, the second control signal SU6, the current iL1 flowing through the resonant inductor L1, the load current iU, and the voltage V1u across the first switching element 1U when the target switching element is the first switching element 1U of the switching circuit 10U. Also, in Fig. 23, the voltage value of the DC power supply E1 is shown as Vd.

[0228] When the target switching element is the first switching element 1U, in the switching circuit 10U, the voltage V2u across the second switching element 2U becomes Vd at time t13 when the second dead time period Td2 immediately before the high-level period of the first control signal SU1 ends, and the voltage V1u across the first switching element 1U becomes zero at time t13 when the second dead time period Td2 immediately before the high-level period of the first control signal SU1 ends. Therefore, when the first control signal SU1 changes from low level to high level at time t13, the first switching element 1U is subjected to zero-voltage soft switching. 23 , the current iL1 flowing through the resonant inductor L1 starts at time t11, when the high-level period of the second control signal SU6 begins, reaches the same value as the load current iU at time t12, when the first period T01 has elapsed since time t11, reaches the same value as the load current iU at time t13, when the second dead time period Td2 ends, and becomes zero at time t14, when the third period has elapsed since time t13. In the signal generating circuit 52, the second control signal SU6 changes from low to high at time t11, when the first control signal SU2 changes from high to low. The current iL1 flowing between time t12 and time t13 is a resonant current (a charging current for the resonant capacitor 9U) that flows from the regenerative capacitor 15 through the resonant inductor L1 to the resonant capacitor 9U.

[0229] During the first period T01, the first switching element 1U, the second switching element 2U, and the fourth switching element 7U are all in an OFF state, and the third switching element 6U is in an ON state. During the first period T01, the current iL1 flows through the path passing through the regenerative capacitor 15, the resonant inductor L1, the diode 71, the third switching element 6U, and the AC terminal 41U, as in Fig. 10. Also, during the first period T01, the load current iU flows through the path passing 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 in Fig. 10.

[0230] During the second period T02, the first switching element 1U, the second switching element 2U, and the fourth switching element 7U are all 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 the path passing through the regenerative capacitor 15, the resonant inductor L1, the diode 71, and the third switching element 6U, as in Fig. 11, 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.

[0231] During the third period T03, 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 the path passing through the regenerative capacitor 15, the resonant inductor L1, the diode 71, the third switching element 6U, and the AC terminal 41U, as in FIG. 12. This reduces the current iL1 to zero. Also, during the third period T03, the load current iU flows through the path passing through the first DC terminal 31, the first switching element 1U, the AC terminal 41U, and the AC load RA1, as in FIG. 12.

[0232] 24 illustrates the first control signals SU1 and SU2, the second control signal SU7, the current iL1 flowing through the resonant inductor L1, the load current iU, and the voltage V2u across the second switching element 2U when the target switching element is the second switching element 2U of the switching circuit 10U. Also, in FIG. 24, the voltage value of the DC power supply E1 is illustrated as Vd.

[0233] When the target switching element is the second switching element 2U, in the switching circuit 10U, the voltage V1u across the first switching element 1U becomes Vd at time t43 when the second dead time period Td2 immediately before the high-level period of the first control signal SU2 ends, and the voltage V2u across the second switching element 2U becomes zero at time t43 when the second dead time period Td2 ends. Therefore, when the first control signal SU2 changes from low level to high level at time t43, the second switching element 2U is subjected to zero-voltage soft switching. 24 , the current iL1 flowing through the resonant inductor L1 starts at time t41, when the high-level period of the second control signal SU7 begins, reaches the same value as the load current iU at time t42, when a time equal to the variable time Tp1 has elapsed, reaches the same value as the load current iU at time t43, when the second dead time period Td2 ends, and reaches zero at time t44, when a time Tad2 equal to the variable time Tp1 has elapsed from time t43. In the signal generating circuit 52, the second control signal SU7 changes from low to high when the first control signal SU1 changes from high to low. The current iL1 flowing between time t42 and time t43 is the resonant current (the discharge current of the resonant capacitor 9U) flowing from the resonant capacitor 9U to the resonant inductor L1.

[0234] 24, the first period T01 is the period from time t41 to time t42. During the first period T01, the first switching element 1U, the second switching element 2U, and the third switching element 6U are all in an OFF state, and the fourth switching element 7U is in an ON state. During the first period T01, the current iL1 flows through a path that passes through the AC terminal 41U, the diode 61, the fourth switching element 7U, the resonant inductor L1, and the regenerative capacitor 15. Also, during the first period T01, the load current iU flows through a path that passes through the AC load RA1, the AC terminal 41U, and the first diode 4 connected in anti-parallel to the first switching element 1U.

[0235] In FIG. 24 , the second period T02 is the period from time t42 to time t43. During the second period T02, the first switching element 1U, the second switching element 2U, and the third switching element 6U are all in an OFF state, and the fourth switching element 7U 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 41U through the diode 61, the fourth switching element 7U, the resonant inductor L1, and the regenerative capacitor 15, and a current (resonant current) flowing from the resonant capacitor 9U through the diode 61, the fourth switching element 7U, the resonant inductor L1, and the regenerative capacitor 15. During the second period T02, the resonant capacitor 9 is discharged.

[0236] In FIG. 24, the third period T03 is the period from time t43 to time t44. During the third period T03, the second switching element 2U and the fourth switching element 7U are each in an ON state, and the first switching element 1U and the third switching element 6U are each in an OFF 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.

[0237] The above describes an example in which the first dead time period Td1 is extended to the second dead time period Td2 for the switching circuit 10U, but the same applies to the switching circuits 10V and 10W.

[0238] (2.2) First Control Operation and Second Control Operation The first control operation and second control operation are similar to the first control operation and second control operation of the second embodiment, and therefore a description thereof will be omitted.

[0239] (3) Advantages As with the power conversion device 100A according to the second embodiment, the power conversion device 100D according to the sixth embodiment can improve power conversion efficiency without directly controlling the multiple switches 8 for zero voltage soft switching in the control device 51D.

[0240] Seventh Embodiment A power conversion device 100A according to a seventh embodiment will be described with reference to Fig. 25. Regarding the power conversion device 100A according to the seventh embodiment, components similar to those of the power conversion device 100A according to the second embodiment (see Fig. 9) are denoted by the same reference numerals, and description thereof will be omitted.

[0241] In a power conversion device 100A according to the seventh embodiment, a third switching element 6 and a fourth switching element 7 are connected in anti-series in each of a plurality of switches 8. In the power conversion device 100A according to the seventh embodiment, 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 in each of the plurality of switches 8, 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.

[0242] The power conversion device 100A according to the seventh embodiment has the same advantages as the power conversion device 100A according to the second embodiment.

[0243] In the power conversion device 100A according to the seventh 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. 25 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 seventh embodiment, the diode 61 and the diode 71 are not limited to being externally connected to the third switching element 6 and the fourth switching element 7, but may be built into the chip.

[0244] Eighth Embodiment A power conversion device 100A according to an eighth embodiment will be described with reference to Fig. 26. Regarding the power conversion device 100A according to the eighth embodiment, components similar to those of the power conversion device 100A according to the second embodiment (see Fig. 9) are denoted by the same reference numerals, and description thereof will be omitted.

[0245] In a power conversion device 100A according to the eighth 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 eighth 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.

[0246] The power conversion device 100A according to the eighth embodiment has the same advantages as the power conversion device 100A according to the second embodiment.

[0247] Ninth Embodiment A power conversion device 100A according to a ninth embodiment will be described with reference to Fig. 27. Regarding the power conversion device 100A according to the ninth embodiment, components similar to those of the power conversion device 100A according to the second embodiment (see Fig. 9) are denoted by the same reference numerals, and description thereof will be omitted.

[0248] In the power conversion device 100A according to the ninth 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 ninth 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.

[0249] The power conversion device 100A according to the ninth embodiment has the same advantages as the power conversion device 100A according to the second embodiment.

[0250] Tenth Embodiment A power conversion device 100E according to a tenth embodiment will be described with reference to Fig. 28. Regarding the power conversion device 100E according to the tenth embodiment, components similar to those of the power conversion device 100A according to the second embodiment (see Fig. 9) are denoted by the same reference numerals, and description thereof will be omitted.

[0251] In a power conversion device 100E according to the tenth 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.

[0252] The power conversion apparatus 100E according to the tenth embodiment differs from the power conversion apparatus 100A in that a control system 50E is provided instead of the control system 50A of the power conversion apparatus 100A according to the second embodiment. The control system 50E includes a signal generation circuit 52E instead of the signal generation circuit 52 (see FIG. 9 ) of the power conversion apparatus 100A according to the second embodiment.

[0253] The MOSFETs 80 of the multiple switches 8 are controlled by a signal generation circuit 52E. The signal generation circuit 52E 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 52E generates the second control signal SU8 using the first control signals SU1 and SU2. The signal generation circuit 52E also generates the second control signal SV8 using the first control signals SV1 and SV2. The signal generation circuit 52E generates the second control signal SW8 using the first control signals SW1 and SW2.

[0254] 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 100E according to the tenth 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 100E according to the tenth 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.

[0255] The power conversion device 100E according to the tenth embodiment has the same advantages as the power conversion device 100A according to the second embodiment.

[0256] In the power conversion device 100E according to the tenth embodiment, each of the plurality of MOSFETs 80 may be replaced with an IGBT. Furthermore, in the power conversion device 100E according to the tenth 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.

[0257] (Embodiment 11) A power conversion device 100A according to embodiment 11 will be described with reference to Fig. 29. Regarding the power conversion device 100A according to embodiment 11, components similar to those of the power conversion device 100A according to embodiment 2 (see Fig. 9) are denoted by the same reference numerals, and description thereof will be omitted.

[0258] In the power conversion device 100A according to the eleventh 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 eleventh 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.

[0259] The power conversion device 100A according to the eleventh embodiment has the same advantages as the power conversion device 100A according to the second embodiment.

[0260] Twelfth Embodiment A power conversion device 100F according to a twelfth embodiment will be described with reference to Fig. 30. Regarding the power conversion device 100F according to the twelfth embodiment, components similar to those of the power conversion device 100A according to the second embodiment (see Fig. 9) are denoted by the same reference numerals, and description thereof will be omitted.

[0261] (1) Configuration The power conversion device 100F 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.

[0262] The second regenerative capacitor 16 is connected in series to the first regenerative capacitor 15. Therefore, in the power conversion device 100F, 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 100F, a fourth end of one resonant inductor L1 is connected to the 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.

[0263] In the power conversion device 100F according to the twelfth embodiment, the potential V15 at the sixth terminal 154 of the first regenerative capacitor 15 is equal to the value obtained by dividing Vd, which is the voltage value of the DC power supply E1, between the second regenerative capacitor 16 and the first regenerative capacitor 15. Therefore, the potential V15 at the sixth terminal 154 of the first regenerative capacitor 15 is approximately Vd / 2.

[0264] (2) Advantages The operation of the control device 51A and the signal generating circuit 52 of the power conversion device 100F according to the twelfth 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 second embodiment. Therefore, like the power conversion device 100A according to the second embodiment, the power conversion device 100F according to the twelfth embodiment can improve the power conversion efficiency without directly controlling the multiple switches 8 for zero voltage soft switching in the control device 51A.

[0265] (Embodiment 13) The power conversion device 100 according to embodiment 13 includes a programmable logic device (PLD) instead of the plurality of logic circuits 521 to 526 (see FIG. 2) in the signal generation circuit 52 of the power conversion device 100 according to embodiment 1. The circuit configuration of the power conversion device 100 according to embodiment 13 is similar to that of the power conversion device 100 according to embodiment 1 (see FIG. 1), and will be described with reference to FIG. 1.

[0266] (1) Configuration 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 high and low levels for each of the multiple switches 8. The signal generation circuit 52 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.

[0267] 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.

[0268] In the signal generating circuit 52 of the present embodiment, the PLD generates a second control signal for each of the multiple switches 8 using a first control signal to the first switching element 1 and a second control signal to the second switching element 2 of a corresponding switching circuit 10 among the multiple switching circuits 10. The PLD 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.

[0269] In the signal generation circuit 52 of this embodiment, the PLD synchronizes the start of the high-level period of the first 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 of the high-level period of the second control signal to each of the multiple switches 8 with the start 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.

[0270] (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.

[0271] 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.

[0272] (3) Advantages The power conversion device 100 according to the thirteenth embodiment has the same advantages as the power conversion device 100 according to the first embodiment.

[0273] (Other Modifications) The above-described first to thirteenth embodiments are merely examples of various embodiments of the present disclosure. The above-described first to thirteenth embodiments can be modified in various ways depending on the design, etc., as long as the object of the present disclosure can be achieved.

[0274] 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.

[0275] In the power conversion device 100 according to the first 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, respectively, but may also be elements built into one chip.

[0276] In addition, in the power conversion devices 100A, 100B, 100C, and 100D according to embodiments 2 to 5, the configuration of the switch 8 is the same as the configuration of the switch 8 in the power conversion device 100 according to embodiment 1, but may be the same as the configuration of the switch 8 in any of embodiments 6 to 12.

[0277] Furthermore, the power conversion devices 100, 100A to 100F may not be provided with the first clamp diode 13 and the second clamp diode 14.

[0278] 4 described in the first embodiment, the high-level period of the second control signal S6 (the period of fixed length T2) includes the third period T03, and the high-level period of the second control signal S6 continues after time point t3, and the second control signal S6 changes to low level at time point t4. However, as shown in Fig. 31, the fixed length T2 may be set so that the second control signal S6 goes to low level at time point t3 when the second dead time period Td2 ends. In this case, the current iL1 is regenerated to the power conversion circuit 11 via the first clamp diode 13 directly connected to the resonance inductor L1 after time point t3 when the second dead time period Td2 ends.

[0279] Furthermore, in the power conversion devices 100, 100A to 100F, if the capacitance of each of the multiple resonant capacitors 9 is relatively small, instead of attaching the multiple resonant capacitors 9 externally, the parasitic capacitance between both ends of the multiple second switching elements 2 may also serve as the multiple resonant capacitors 9.

[0280] Furthermore, the power conversion devices 100, 100A to 100F are not limited to a configuration that outputs three-phase AC, but may be configured to output polyphase AC with three or more phases.

[0281] (Aspects) The following aspects are disclosed in this specification.

[0282] A power conversion device (100; 100A; 100B; 100C; 100D; 100E; 100F) according to a first aspect includes a first DC terminal (31), a second DC terminal (32), a power conversion circuit (11), a plurality of AC terminals (41), a plurality of switches (8), a plurality of resonant capacitors (9), at least one resonant inductor (L1), a regenerative capacitor (15), and a control system (50; 50A; 50B; 50C; 50D; 50E). The power conversion circuit (11) has a plurality of first switching elements (1) and a plurality of second switching elements (2). In the power conversion circuit (11), a plurality of switching circuits (10), each of which has 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), a plurality of first switching elements (1) are connected to a first DC terminal (31). In the power conversion circuit (11), a plurality of second switching elements (2) are connected to a second DC terminal (32). A 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) between the first switching element (1) and the second switching element (2) in a corresponding one of the plurality of switching circuits (10), through which a load current flows. A plurality of switches (8) correspond one-to-one to the plurality of switching circuits (10). Each of the plurality of switches (8) has a first end (81) connected to a connection point (3) between the first switching element (1) and the second switching element (2) in a corresponding one of the plurality of switching circuits (10). A 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 a first end (81) of a corresponding switch (8) among the plurality of switches (8) and the second DC terminal (32). The at least one resonant inductor (L1) has a third end and a fourth end. The third end of the at least one resonant inductor (L1) is connected to a second end (82) of the corresponding switch (8) among the plurality of switches (8). The regenerative capacitor (15) has a fifth end (153) and a sixth end (154).The regenerative capacitor (15) has a fifth terminal (153) connected to the second DC terminal (32) and a sixth terminal (154) connected to the fourth terminal of the at least one resonant inductor (L1). The control system (50; 50A; 50B; 50C; 50D; 50E) includes a control device (51; 51A; 51B; 51C; 51D) and a signal generating circuit (52; 52E). The control device (51; 51A; 51B; 51C; 51D; 51E) 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 (1) and the plurality of second switching elements (2). The signal generating circuit (52; 52E) provides a second control signal, the potential of which changes between a high level and a low level, to each of the plurality of switches (8). The control device (51; 51A; 51B; 51C; 51D) sets a second dead time period (Td2) for each of the plurality of switching circuits (10) between a high-level period of a first control signal to the first switching element (1) and a high-level period of the first control signal to the second switching element (2) so that the on periods of the first switching element (1) and the second switching element (2) do not overlap. The variable time (Tp1) is determined according to the current value of a load current corresponding to each of the plurality of switching circuits (10) among a plurality of load currents (iU, iV, iW) flowing through the plurality of AC terminals (41), the inductance of the resonance inductor (L1), and the potential (V15) of a sixth end (154) of the regenerative capacitor (15). The signal generating circuit (52; 52E) generates, for each of the plurality of switches (8), a second control signal having a high-level period corresponding to a second dead time period (Td2) for a corresponding one of the plurality of switching circuits (10). The control system (50; 50A; 50B; 50C; 50D; 50E) performs a first control action to increase the potential (V15) of the sixth terminal (154) of the regenerative capacitor (15) when the potential (V15) of the sixth terminal (154) of the regenerative capacitor (15) is smaller than a lower limit threshold (Vth1) that is smaller than half the voltage value (Vd) applied between the first DC terminal (31) and the second DC terminal (32).The control system (50; 50A; 50B; 50C; 50D; 50E) performs a second control operation to lower the potential of the sixth terminal (154) of the regenerative capacitor (15) when the potential (V15) of the sixth terminal (154) of the regenerative capacitor (15) is greater than an upper limit threshold (Vth2) that is greater than half the voltage value (Vd) applied between the first DC terminal (31) and the second DC terminal (32).

[0283] According to this aspect, it is possible to improve the power conversion efficiency without directly controlling the plurality of switches (8) for zero voltage soft switching in the control device (51; 51A; 51B; 51C; 51D).

[0284] A power conversion device (100; 100A; 100B; 100C; 100D; 100E; 100F) according to a second aspect includes a first DC terminal (31), a second DC terminal (32), a power conversion circuit (11), a plurality of AC terminals (41), a plurality of switches (8), a plurality of resonant capacitors (9), at least one resonant inductor (L1), a regenerative capacitor (15), and a control system (50; 50A; 50B; 50C; 50D; 50E). The power conversion circuit (11) has a plurality of first switching elements (1) and a plurality of second switching elements (2). In the power conversion circuit (11), a plurality of switching circuits (10), each including 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), a plurality of first switching elements (1) are connected to a first DC terminal (31). In the power conversion circuit (11), a plurality of second switching elements (2) are connected to a second DC terminal (32). A 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) between the first switching element (1) and the second switching element (2) in a corresponding one of the plurality of switching circuits (10), through which a load current flows. A plurality of switches (8) correspond one-to-one to the plurality of switching circuits (10). Each of the plurality of switches (8) has a first end (81) connected to a connection point (3) between the first switching element (1) and the second switching element (2) in a corresponding one of the plurality of switching circuits (10). A 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 a first end (81) of a corresponding switch (8) among the plurality of switches (8) and the second DC terminal (32). The at least one resonant inductor (L1) has a third end and a fourth end. The third end of the at least one resonant inductor (L1) is connected to a second end (82) of the corresponding switch (8) among the plurality of switches (8). The regenerative capacitor (15) has a fifth end (153) and a sixth end (154).The regenerative capacitor (15) has a fifth terminal (153) connected to the second DC terminal (32) and a sixth terminal (154) connected to the fourth terminal of the at least one resonant inductor (L1). The control system (50; 50A; 50B; 50C; 50D; 50E) includes a control device (51; 51A; 51B; 51C; 51D) and a signal generating circuit (52; 52E). The control device (51; 51A; 51B; 51C; 51D) 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 (1) and the plurality of second switching elements (2). The signal generating circuit (52; 52E) provides a second control signal, the potential of which changes between a high level and a low level, to each of the plurality of switches (8). The control device (51; 51A; 51B; 51C; 51D; 51E) sets a second dead time period (Td2) for each of the plurality of switching circuits (10) between a high-level period of a first control signal to the first switching element (1) and a high-level period of the first control signal to the second switching element (2), the second dead time period (Td2) being obtained by adding a variable time (Tp1) 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 variable time (Tp1) is determined according to the current value of a load current corresponding to each of the plurality of switching circuits (10) among a plurality of load currents (iU, iV, iW) flowing through the plurality of AC terminals (41), the inductance of the resonance inductor (L1), and the potential of a sixth end (154) of the regenerative capacitor (15). The signal generating circuit (52; 52E) generates, for each of the plurality of switches (8), a second control signal having a high-level period corresponding to a second dead time period (Td2) for a corresponding one of the plurality of switching circuits (10). The control system (50; 50A; 50B; 50C; 50D; 50E) performs a first control action to stop the discharge current of the regenerative capacitor (15) when the potential (V15) of the sixth terminal (154) of the regenerative capacitor (15) is smaller than a lower limit threshold (Vth1) that is smaller than half the voltage value (Vd) applied between the first DC terminal (31) and the second DC terminal (32).The control system (50; 50A; 50B; 50C; 50D; 50E) performs a second control operation to stop the charging current of the regenerative capacitor (15) when the potential (V15) of the sixth terminal (154) of the regenerative capacitor (15) is greater than an upper limit threshold (Vth2) that is greater than half the voltage value (Vd) applied between the first DC terminal (31) and the second DC terminal (32).

[0285] According to this aspect, it is possible to improve the power conversion efficiency without directly controlling the plurality of switches (8) for zero voltage soft switching in the control device (51; 51A; 51B; 51c; 51D).

[0286] In the power conversion device (100; 100A; 100B; 100C; 100D; 100E; 100F) according to the third aspect, in the first or second aspect, the control system (50; 50A; 50B; 50C; 50D; 50E) does not perform either the first control operation or the second control operation when the potential (V15) of the sixth terminal (154) of the regenerative capacitor (15) is equal to or greater than the lower threshold (Vth1) and equal to or less than the upper threshold (Vth2).

[0287] According to this aspect, it is possible to realize zero voltage soft switching of the target switching element to be turned on, either the first switching element (1) or the second switching element (2), in each of the plurality of switching circuits (10).

[0288] In a power conversion device (100; 100A; 100B; 100C; 100D; 100E; 100F) according to a fourth aspect, in any one of the first to third aspects, the control system (50; 50A; 50B; 50C; 50D; 50E) is capable of executing a third control operation and a fourth control operation when changing a first control signal to a target switching element to be turned on, of a first switching element (1) and a second switching element (2) in each of the plurality of switching circuits (10), from a low level to a high level. In the third control operation, at least a part of a high-level period of the second control signal to a switch (8) among the plurality of switches (8) corresponding to each of the plurality of switching circuits (10) is overlapped with a second dead time period (Td2) set for each of the plurality of switching circuits (10) between a high-level period of the first control signal to the first switching element (1) and a high-level period of the first control signal to the second switching element (2). In the fourth control operation, the high-level period of the second control signal is shifted so that the overlap period between the high-level period of the second control signal applied to each of the plurality of switches (8) and the second dead time period (Td2) is shorter than in the third 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.

[0289] According to this aspect, 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.

[0290] A power conversion device (100; 100A; 100E; 100F) according to a fifth aspect is any one of the first to fourth aspects, wherein when the control device (51) sets the second dead time period (Td2) for each of the plurality of switching circuits (10), if the polarity of the load current is positive, a variable time (Tp1) is added to the first dead time period (Td1) by shortening the high-level period of the first control signal to the second switching element (2), and if the polarity of the load current is negative, the variable time (Tp1) is added to the first dead time period (Td1) by shortening the high-level period of the first control signal to the first switching element (1).

[0291] According to this aspect, it is possible to achieve zero-voltage soft switching while further reducing the dead-time loss and the dead-time error.

[0292] In a power conversion device (100B) according to a sixth aspect, in any one of the first to fourth aspects, when setting the second dead time period (Td2) for each of the plurality of switching circuits (10), if the polarity of the load current is positive, the control device (51B) advances the end point of the high-level period of the first control signal to the second switching element (2) and delays the start point of the high-level period of the first control signal to the first switching element (1), thereby adding a variable time (Tp1) to the first dead time period (Td1), and if the polarity of the load current is negative, the control device (51B) advances the end point of the high-level period of the first control signal to the first switching element (1) and delays the start point of the high-level period of the first control signal to the second switching element (2), thereby adding a variable time (Tp1) to the first dead time period (Td1).

[0293] According to this aspect, it is possible to achieve zero voltage soft switching while reducing dead time loss and dead time error.

[0294] In a power conversion device (100C) according to a seventh aspect, in any one of the first to fourth aspects, when the control device (51C) sets the second dead time period (Td2) for each of the plurality of switching circuits (10), if the polarity of the load current is positive, a variable time (Tp1) is added to the first dead time period (Td1) by shortening the high-level period of the first control signal to the first switching element (1), and if the polarity of the load current is negative, a variable time (Tp1) is added to the first dead time period (Td1) by shortening the high-level period of the first control signal to the second switching element (2).

[0295] According to this embodiment, it is possible to realize zero-voltage soft switching.

[0296] In a power conversion device (100; 100A; 100B; 100C; 100D; 100E; 100F) according to an eighth aspect, in any one of the first to seventh aspects, the signal generation circuit (52; 52E) generates a second control signal for each of the plurality of switches (8) using at least one of a first control signal to a first switching element (1) and a first control signal to a second switching element (2) of a corresponding switching circuit (10) among a plurality of switching circuits (10).

[0297] According to this aspect, it is possible to simplify the signal generating circuit (52; 52E).

[0298] In a power conversion device (100; 100A; 100B; 100C; 100D; 100E; 100F) according to a ninth aspect, in the eighth aspect, the signal generating circuit (52; 52E) includes a plurality of logic circuits (521-526) and does not include a microcontroller.

[0299] According to this aspect, it is possible to simplify the signal generating circuit (52; 52E).

[0300] In a power conversion device (100; 100A; 100B; 100C; 100D; 100E; 100F) according to a tenth aspect, in any one of the first to ninth aspects, the control system (50) acquires a detected potential at the sixth terminal (154) of the regenerative capacitor (15) for each cycle or each half cycle of the carrier signal. The first control operation is an operation of controlling the multiple switches (8) to increase the potential (V15) at the sixth terminal (154) of the regenerative capacitor (15) based on the polarities of the multiple load currents (iU, iV, iW) flowing through the multiple AC terminals (41). The second control operation is an operation of controlling the multiple switches (8) to decrease the potential (V15) at the sixth terminal (154) of the regenerative capacitor (15) based on the polarities of the multiple load currents (iU, iV, iW) flowing through the multiple AC terminals (41).

[0301] According to this aspect, it is possible to more quickly suppress fluctuations in the potential (V15) of the sixth terminal (154) of the regenerative capacitor (15).

[0302] A power conversion device (100; 100A; 100B; 100C; 100D; 100E; 100F) according to an eleventh aspect is based on any one of aspects 1 to 9. In a first control operation, the control system (50) sets to zero an overlap period between a high level period of a second control signal to a switch (8) among the plurality of switches (8) that is involved in the discharge operation of the regenerative capacitor (15) and a second dead time period (Td2) corresponding to the switch involved in the discharge operation of the regenerative capacitor (15), based on the polarities of each of a plurality of load currents (iU, iV, iW) flowing through a plurality of AC terminals (41). In the second control operation, based on the polarities of the respective load currents (iU, iV, iW) flowing through the plurality of AC terminals (41), the overlap period between the high level period of the second control signal to the switch (8) among the plurality of switches (8) related to the charging operation of the regenerative capacitor (15) and the second dead time period (Td2) corresponding to the switch (8) related to the charging operation of the regenerative capacitor (15) is set to zero.

[0303] According to this aspect, it is possible to perform the first control operation by changing the variable time (Tp1) of the second dead time period (Td2) corresponding to the switch (8) related to the discharge operation of the regenerative capacitor (15), and it is possible to perform the second control operation by changing the variable time (Tp1) of the second dead time period (Td2) corresponding to the switch (8) related to the charge operation of the regenerative capacitor (15).

[0304] In a power conversion device (100; 100A; 100B; 100C; 100D; 100E; 100F) according to a twelfth aspect, in any one of the first to ninth aspects, the at least one resonant inductor (L1) is a single resonant inductor (L1). Second ends (82) of the multiple switches (8) are commonly connected to the single resonant inductor (L1). When the control system (50A; 50B; 50C; 50D; 50E) determines that two-phase resonant currents corresponding to two of the multiple switching circuits (10) simultaneously flow through the resonant inductor (L1), the control system (50A; 50B; 50C; 50D; 50E) is capable of performing a simultaneous control operation of overlapping high-level periods of two second control signals to two of the multiple switches (8) corresponding to the two switching circuits (10). When the control system (50A; 50B; 50C; 50D; 50E) is executing a simultaneous control operation, when performing a first control operation, the control system (50A; 50B; 50C; 50D; 50E) causes the entire high-level period of the second control signal for at least one switch (8) of the two switches (8) to overlap with the high-level period of the first control signal for the first switching element (1) or the second switching element (2) corresponding to the at least one switch (8).

[0305] According to this embodiment, it is possible to control the potential (V15) of the sixth terminal (154) of the regenerative capacitor (15) to a constant value.

[0306] A power conversion device (100B) according to a thirteenth aspect is based on any one of the first to ninth aspects. In a first control operation, the control system (50B) shortens an overlap period between a high-level period of a second control signal to a switch (8) related to a discharging operation of the regenerative capacitor (15) and a second dead time period (Td2) so that an integral value of a discharging current flowing through the regenerative capacitor (15) in one cycle of the carrier signal is smaller than an integral value of a charging current. In a second control operation, the control system (50B) shortens an overlap period between a high-level period of a second control signal to a switch (8) related to a charging operation of the regenerative capacitor (15) and a second dead time period (Td2) so that an integral value of a discharging current flowing through the regenerative capacitor (15) in one cycle of the carrier signal is larger than an integral value of a charging current.

[0307] According to this embodiment, it is possible to control the potential (V15) of the sixth terminal (154) of the regenerative capacitor (15) to a constant value.

[0308] 1 First switching element 2 Second switching element 3 Connection point 4 First diode 5 Second diode 6 Third switching element 7 Fourth switching element 8 Switch 81 First terminal 82 Second terminal 9 Resonant capacitor 10 Switching circuit 13 First clamp diode 14 Second clamp diode 11 Power conversion circuit 15 Regenerative capacitor 153 Fifth terminal 154 Sixth terminal 31 First DC terminal 32 Second DC terminal 41 AC terminal 50, 50A, 50B, 50C, 50D, 50E Control system 51, 51A, 51B, 51C, 51D, 51E Control device 52, 52E Signal generating circuit 100, 100A, 100B, 100C, 100D, 100E, 100F Power conversion device iU, iV, iW Load current L1 Resonant inductor RA1 AC load S1, S2 First control signal SU1, SU2, SV1, SV2, SW1, SW2 First control signal S6 Second control signal SU6, SU7, SU8, SV6, SV7, SV8, SW6, SW7, SW8 Second control signal T01 First period T02 Second period T03 Third period Td1 First dead time period Td2 Second dead time period Tp1 Variable time V15 Electric potential

Claims

1. A power conversion circuit having a first DC terminal and a second DC terminal, 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 to 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 connected to the connection points 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 having a first end connected to the connection points 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 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 being 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 being connected to the second DC terminal, and the sixth end being connected to the fourth end of the at least one resonance inductor; A control system; The control system includes: A control device that provides 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; A signal generation circuit that provides a second control signal whose potential changes between a high level and a low level to each of the plurality of switches; The control device sets, for each of the plurality of switching circuits, a second dead time period obtained by adding a variable 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 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.The variable time is determined according to the current value of the load current corresponding to each of the plurality of switching circuits among the plurality of load currents flowing through the plurality of AC terminals, the inductance of the resonance inductor, and the potential of the sixth terminal of the regeneration capacitor. The signal generation circuit generates, for each of the plurality of switches, 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. The control system performs a first control operation to increase the potential of the sixth terminal of the regeneration capacitor when the potential of the sixth terminal of the regeneration capacitor is lower than a lower threshold value smaller than half of the voltage value applied between the first DC terminal and the second DC terminal, and performs a second control operation to decrease the potential of the sixth terminal of the regeneration capacitor when the potential of the sixth terminal of the regeneration capacitor is higher than an upper threshold value larger than half of the voltage value applied between the first DC terminal and the second DC terminal. Power conversion device.

2. 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 connected to the connection points of the first switching element and the second switching element in the corresponding switching circuit through which a load current flows; a plurality of switches corresponding one-to-one to the plurality of switching circuits, each having a first end connected to the connection points 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 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 being 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 being connected to the second DC terminal, and the sixth end being connected to the fourth end of the at least one resonance inductor; and a control system, wherein the control system includes a control device 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 a signal generation circuit that gives a second control signal whose potential changes between a high level and a low level to each of the plurality of switches, and the control device sets a second dead time period obtained by adding a variable 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 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 for each of the plurality of switching circuits.The variable time is determined according to the current value of the load current corresponding to each of the plurality of switching circuits among the plurality of load currents flowing through the plurality of AC terminals, the inductance of the resonance inductor, and the potential of the sixth terminal of the regeneration capacitor. The signal generation circuit generates, for each of the plurality of switches, 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. The control system performs a first control operation to stop the discharge current of the regeneration capacitor when the potential of the sixth terminal of the regeneration capacitor is lower than a lower threshold value smaller than half of the voltage value applied between the first DC terminal and the second DC terminal, and performs a second control operation to stop the charging current of the regeneration capacitor when the potential of the sixth terminal of the regeneration capacitor is higher than an upper threshold value larger than half of the voltage value applied between the first DC terminal and the second DC terminal. Power conversion device.

3. When the potential of the sixth terminal of the regenerative capacitor is equal to or higher than the lower threshold value and equal to or lower than the upper threshold value, the control system does not perform either the first control operation or the second control operation. The power conversion device according to claim 1 or 2.

4. When changing the first control signal to the target switching element to be turned on from the low level to the high level among the first switching element and the second switching element in each of the plurality of switching circuits, the control system can execute a third control operation and a fourth control operation. In the third control operation, 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 is overlapped with the second 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 for each of the plurality of switching circuits. In the fourth 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 second dead time period is shorter than that in the case of the third control operation, and at least 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. The power conversion device according to any one of claims 1 to 3.

5. When setting the second dead time period for each of the plurality of switching circuits, the control device adds the variable time to the first dead time period by shortening the high-level period of the first control signal to the second switching element when the polarity of the load current is positive, and adds the variable time to the first dead time period by shortening the high-level period of the first control signal to the first switching element when the polarity of the load current is negative. The power conversion device according to any one of claims 1 to 4.

6. When setting the second dead time period for each of the plurality of switching circuits, the control device, when the polarity of the load current is positive, advances the end point of the high level period of the first control signal to the second switching element and delays the start point of the high level period of the first control signal to the first switching element, thereby adding the variable time to the first dead time period; when the polarity of the load current is negative, advances the end point of the high level period of the first control signal to the first switching element and delays the start point of the high level period of the first control signal to the second switching element, thereby adding the variable time to the first dead time period. The power conversion device according to any one of claims 1 to 4.

7. When setting the second dead time period for each of the plurality of switching circuits, the control device, when the polarity of the load current is positive, adds the variable time to the first dead time period by shortening the high level period of the first control signal to the first switching element; when the polarity of the load current is negative, adds the variable time to the first dead time period by shortening the high level period of the first control signal to the second switching element. The power conversion device according to any one of claims 1 to 4.

8. 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 of the corresponding switching circuit among the plurality of switching circuits for each of the plurality of switches. The power conversion device according to any one of claims 1 to 7.

9. The signal generation circuit includes a plurality of logic circuits and does not include a microcontroller. The power conversion device according to claim 8.

10. The control system acquires the detected potential of the sixth terminal of the regenerative capacitor every one cycle or every half cycle of the carrier signal, and the first control operation is an operation of controlling the plurality of switches so as to increase the potential of the sixth terminal of the regenerative capacitor based on the polarity of each of the plurality of load currents flowing through the plurality of AC terminals. The second control operation is an operation of controlling the plurality of switches so as to decrease the potential of the sixth terminal of the regenerative capacitor based on the polarity of each of the plurality of load currents flowing through the plurality of AC terminals. The power conversion device according to any one of claims 1 to 9.

11. In the first control operation, the control system sets the overlapping period between the high-level period of the second control signal to the switch related to the discharging operation of the regenerative capacitor among the plurality of switches and the second dead time period corresponding to the switch related to the discharging operation to zero based on the polarity of each of the plurality of load currents flowing through the plurality of AC terminals. In the second control operation, the control system sets the overlapping period between the high-level period of the second control signal to the switch related to the charging operation of the regenerative capacitor among the plurality of switches and the second dead time period corresponding to the switch related to the charging operation to zero based on the polarity of each of the plurality of output currents flowing through the plurality of AC terminals. The power conversion device according to any one of claims 1 to 9.

12. The at least one resonance inductor is one resonance inductor, the second ends of the plurality of switches are commonly connected to the one resonance inductor, and when the control system determines that two-phase resonance currents corresponding to two of the plurality of switching circuits flow through the resonance inductor simultaneously, the control system is capable of performing a simultaneous control operation of overlapping high-level periods of two second control signals to two switches corresponding to the two switching circuits among the plurality of switches; and when performing the simultaneous control operation, if performing the first control operation, overlapping all of the high-level periods of the second control signals for at least one of the two switches with the high-level period of the first control signal to the first switching element or the second switching element 2 corresponding to the at least one switch. The power conversion device according to any one of claims 1 to 9.

13. In the first control operation, the control system shortens an overlapping period between a high-level period of a second control signal to a switch related to a discharging operation of the regeneration capacitor and the second dead time period so that an integrated value of a discharging current of the regeneration capacitor is smaller than an integrated value of a charging current in one period of a carrier signal; and in the second control operation, the control system shortens an overlapping period between a high-level period of a second control signal to a switch related to a charging operation of the regeneration capacitor and the second dead time period so that an integrated value of a discharging current flowing through the regeneration capacitor is larger than an integrated value of a charging current in one period of the carrier signal. The power conversion device according to any one of claims 1 to 9.

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