Power conversion device

Abstract

For each of a plurality of switching circuits, a control device sets, between a high-level period of a first control signal for a first switching element and a high-level period of the first control signal for a second switching element, a second dead time period which is obtained by adding a prescribed time to a first dead time period which is preset so as to prevent overlapping of ON periods of the first switching element and the second switching element. The prescribed time is determined according to a current value of a load current, the inductance of a resonance inductor, and a voltage value of a regenerative capacitor. For each of a plurality of switches, a signal generation circuit generates a second control signal having a high-level period according to the second dead time period for the corresponding switching circuit among the plurality of switching circuits.

Description

Power conversion device

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

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

[0003] The power conversion system (power conversion device) disclosed in Patent Document 1 includes switching means having a pair of main switch elements (first switching element and second switching element) connected in series with each other, an auxiliary circuit for performing soft switching of each main switch element, and a controller. The auxiliary circuit includes two capacitors, a coil (resonant inductor), and a plurality of auxiliary switch elements. The controller generates a control signal (first control signal) for PWM controlling each main switch element and outputs it to the gate of each main switch element. Further, the controller generates a control signal (second control signal) for controlling the on / off of each auxiliary switch element and outputs it to the gate of each auxiliary switch element.

[0004] Japanese Patent Application Laid-Open No. 2010-233306

[0005] In the power conversion system (power conversion device) disclosed in Patent Document 1, it is necessary for the controller to generate and output a plurality of first control signals and a plurality of second control signals, which causes the controller to become large-sized. Further, the power conversion system disclosed in Patent Document 1 is configured to perform zero-current soft switching and is not configured to support zero-voltage soft switching.

[0006] A power conversion device according to one embodiment of the present disclosure comprises a first DC terminal and a second DC terminal, a power conversion circuit, a plurality of AC terminals, a plurality of switches, a plurality of resonant capacitors, a resonant inductor, a regenerative capacitor, a control device, and a signal generation circuit. The power conversion circuit has a plurality of first switching elements and a plurality of second switching elements. In the power conversion circuit, a plurality of switching circuits, each in which the plurality of first switching elements and the plurality of second switching elements are connected in series at a one-to-one connection point, are connected in parallel to each other. In the power conversion circuit, the plurality of first switching elements are connected to the first DC terminal. In the power conversion circuit, the plurality of second switching elements are connected to the second DC terminal. The plurality of AC terminals correspond one-to-one to the plurality of switching circuits. Each of the plurality of AC terminals is connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit among the plurality of switching circuits, and load current flows through it. The plurality of switches correspond one-to-one to the plurality of switching circuits. Each of the plurality of switches has a first end and a second end, and the first end is connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit among the plurality of switching circuits. The plurality of resonant capacitors correspond one-to-one with the plurality of switches. Each of the plurality of resonant capacitors is connected between the first end and the second DC terminal of the corresponding switch among the plurality of switches. The resonant inductor has a third end and a fourth end. In the resonant inductor, the third end is connected to the second end of the plurality of switches. The regenerative capacitor has a fifth end and a sixth end. In the regenerative capacitor, the fifth end is connected to the second DC terminal, and the sixth end is connected to the fourth end of the resonant inductor. 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 generation 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 a second dead time period for each of the plurality of switching circuits, which is a predetermined period added to a first dead time period, which is set 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 predetermined period is determined according to the current value of the load current, the inductance of the resonant inductor and the voltage value of the regenerative capacitor. The signal generation circuit generates a second control signal for each of the plurality of switches, which has a high-level period corresponding to the second dead time period for the corresponding switching circuit among the plurality of switching circuits. If the control device determines that resonant currents corresponding to two or more switching circuits among the plurality of switching circuits flow simultaneously through the resonant inductor, it performs shift control to shift the high-level periods of the first control signal to the first switching element and the first control signal to the second switching element in at least one of the two or more switching circuits so that the resonant currents corresponding to two or more switching circuits do not flow simultaneously through the resonant inductor.

[0007] The power conversion device of this disclosure has the effect of enabling zero-voltage soft switching without directly controlling multiple switches for zero-voltage soft switching in the control device.

[0008] Figure 1 is a circuit diagram of a system equipped with a power converter according to Embodiment 1. Figure 2 is a circuit block diagram of the signal generation circuit in the same power converter. Figure 3 is a diagram showing the time change of the duty cycle and the time change of the load current corresponding to the voltage command of each of the three phases in an AC load connected to a plurality of AC terminals of the same power converter. Figure 4 is a timing chart for explaining the operation of the same power converter. Figure 5 is a timing chart for explaining the operation of the same power converter. Figure 6 is a timing chart for explaining the operation of the same power converter. Figure 7 is an explanatory diagram of the operation of the same power converter when the load current of the U phase is positive. Figure 8 is an explanatory diagram of the operation of the same power converter when the polarity of the load current of the U phase is negative. Figure 9 is a timing chart for explaining the overlap time when the resonant currents of two phases overlap in the same power converter. Figure 10 is a timing chart for explaining the operation of the same power converter. Figure 11 is a timing chart for explaining the operation of the same power converter. Figure 12 is a circuit diagram of a system equipped with a power converter according to Embodiment 2. Figure 13 is an explanatory diagram of the operation of the power converter described above when the polarity of the U-phase load current is positive. Figure 14 is an explanatory diagram of the operation of the power converter described above when the polarity of the U-phase load current is negative. Figure 15 is a timing chart for explaining the operation of the power converter described above. Figure 16 is a timing chart for explaining the operation of the power converter according to Embodiment 3. Figure 17 is a timing chart for explaining the operation of the power converter according to Embodiment 4. Figure 18 is a timing chart for explaining the operation of the power converter according to Embodiment 5. Figure 19 is a circuit diagram of a system equipped with the power converter according to Embodiment 6. Figure 20 is an explanatory diagram of the operation of the power converter described above when the polarity of the U-phase load current is positive. Figure 21 is an explanatory diagram of the operation of the power converter described above when the polarity of the U-phase load current is negative. Figure 22 is a timing chart for explaining the operation of the power converter described above. Figure 23 is a timing chart for explaining the operation of the power converter according to Embodiment 7.Figure 24 is a timing chart illustrating the operation of a power converter according to Embodiment 8. Figure 25 is a timing chart illustrating the operation of a power converter according to Embodiment 9. Figure 26 is a circuit diagram of a system equipped with a power converter according to Embodiment 10. Figure 27 is an explanatory diagram of the operation of the power converter according to the same when the polarity of the U-phase load current is positive. Figure 28 is an explanatory diagram of the operation of the power converter according to the same when the polarity of the U-phase load current is negative. Figure 29 is a timing chart illustrating the operation of the power converter according to the same. Figure 30 is a timing chart illustrating the operation of a power converter according to Embodiment 11. Figure 31 is a timing chart illustrating the operation of a power converter according to Embodiment 12. Figure 32 is a timing chart illustrating the operation of a power converter according to Embodiment 13. Figure 33 is a timing chart illustrating the operation of a power converter according to Embodiment 14. Figure 34 is a timing chart illustrating the operation of the power converter according to the same. Figure 35 is a timing chart illustrating the operation of a power converter according to Embodiment 15. Figure 36 is a timing chart illustrating the operation of the power converter according to Embodiment 16. Figure 37 is a timing chart illustrating the operation of the power converter according to Embodiment 17. Figure 38 is a circuit diagram of a system equipped with the power converter according to Embodiment 18. Figure 39 is a circuit diagram of a system equipped with the power converter according to Embodiment 19. Figure 40 is a circuit diagram of a system equipped with the power converter according to Embodiment 20.

[0009] (Embodiment 1) Below, the power conversion device 100 according to Embodiment 1 will be described with reference to Figures 1 to 11.

[0010] (1) Overall configuration of the power converter The power converter 100 includes, for example, a first DC terminal 31 and a second DC terminal 32, and a plurality (for example, three) AC terminals 41, as shown in Figure 1. A DC power supply E1 is connected between the first DC terminal 31 and the second DC terminal 32, and an AC load RA1 is connected to the plurality of AC terminals 41. The AC load RA1 is, for example, a three-phase servo motor. The power converter 100 converts the DC output from the DC power supply E1 into AC power and outputs it to the AC load RA1. The DC power supply E1 includes, for example, a solar cell or a fuel cell. The DC power supply E1 may also include a DC-DC converter. In the power converter 100, if the plurality of AC terminals 41 are three AC terminals 41, the AC power is, for example, three-phase AC power having U-phase, V-phase and W-phase.

[0011] The power converter 100 comprises a power conversion circuit 11, a plurality (for example, three) of switches 8, a plurality (for example, three) of resonant capacitors 9, a resonant inductor L1, a regenerative capacitor 15, a control device 51, and a signal generation circuit 52. Each of the plurality of switches 8 is, for example, a bidirectional switch. The power converter 100 further comprises a first clamp diode 13 and a second clamp diode 14.

[0012] The power conversion circuit 11 has a plurality (for example, three) of first switching elements 1 and a plurality (for example, three) of second switching elements 2. In the power conversion circuit 11, a plurality (for example, three) of switching circuits 10, each consisting of a plurality of first switching elements 1 and a plurality of second switching elements 2 connected in series at connection points 3, are connected in parallel to each other. In the power conversion circuit 11, the plurality of first switching elements 1 are connected to a first DC terminal 31, and the plurality of second switching elements 2 are connected to a second DC terminal 32.

[0013] The multiple AC terminals 41 correspond one-to-one with the multiple switching circuits 10. Each of the multiple AC terminals 41 is connected to the connection point 3 of the first switching element 1 and the second switching element 2 in the corresponding switching circuit 10.

[0014] The multiple switches 8 correspond one-to-one with 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 the connection point 3 of the first switching element 1 and the second switching element 2 in the corresponding switching circuit 10 among the multiple switching circuits 10.

[0015] Multiple resonant capacitors 9 correspond one-to-one with multiple switches 8. Each of the multiple resonant capacitors 9 is connected between the first terminal 81 and the second DC terminal 32 of the corresponding switch 8 among the multiple switches 8.

[0016] The resonant inductor L1 has a third terminal and a fourth terminal. In the resonant inductor L1, the third terminal is connected to the second terminal 82 of a plurality (for example, three) switches 8.

[0017] The regenerative capacitor 15 has a fifth terminal 153 and a sixth terminal 154. In the regenerative capacitor 15, the fifth terminal 153 is connected to the second DC terminal 32, and the sixth terminal 154 is connected to the fourth terminal of the resonant inductor L1.

[0018] 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.

[0019] The signal generation circuit 52 provides a second control signal to each of the multiple switches 8.

[0020] (2) Details of the power converter In the following description, for the sake of convenience, the switching circuits 10 corresponding to the U-phase, V-phase, and W-phase may be referred to as switching circuit 10U, switching circuit 10V, and switching circuit 10W, respectively. Also, in the following description, the first switching element 1 and the second switching element 2 of switching circuit 10U may be referred to as the first switching element 1U and the second switching element 2U. Also, in the following description, the first switching element 1 and the second switching element 2 of switching circuit 10V may be referred to as the first switching element 1V and the second switching element 2V. Also, in the following description, the first switching element 1 and the second switching element 2 of switching circuit 10W may be referred to as the first switching element 1W and the second switching element 2W. Furthermore, in the following, the connection point 3 between the first switching element 1U and the second switching element 2U may be referred to as connection point 3U, the connection point 3 between the first switching element 1V and the second switching element 2V may be referred to as connection point 3V, and the connection point 3 between the first switching element 1W and the second switching element 2W may be referred to as connection point 3W. Furthermore, in the following, the AC terminal 41 connected to connection point 3U may be referred to as AC terminal 41U, the AC terminal 41 connected to connection point 3V may be referred to as AC terminal 41V, and the AC terminal 41 connected to connection point 3W may be referred to as AC terminal 41W. Furthermore, in the following, the resonant capacitor 9 connected in parallel to the second switching element 2U may be referred to as resonant capacitor 9U, the resonant capacitor 9 connected in parallel to the second switching element 2V may be referred to as resonant capacitor 9V, and the resonant capacitor 9 connected in parallel to the second switching element 2W may be referred to as resonant capacitor 9W. Furthermore, 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 as switch 8V, and the switch 8 connected to connection point 3W as switch 8W.

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

[0022] In the power conversion circuit 11, each of the multiple (three in the example of Figure 1) first switching elements 1 and each of the multiple (three in the example of Figure 1) second switching elements 2 has a control terminal, a first main terminal, and a second main terminal. The control terminals of the multiple first switching elements 1 and the multiple second switching elements 2 are connected to the control device 51. In each of the multiple switching circuits 10 of the power conversion device 100, the first main terminal of the first switching element 1 is connected to the first DC terminal 31, the second main terminal of the first switching element 1 is connected to the first main terminal of the second switching element 2, and the second main terminal of the second switching element 2 is connected to the second DC terminal 32. In each of the multiple 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 multiple first switching elements 1 and the multiple second switching elements 2 is, for example, an IGBT (Insulated Gate Bipolar Transistor). Therefore, the control terminal, first main terminal, and second main terminal of each of the multiple first switching elements 1 and the multiple second switching elements 2 are the gate terminal, collector terminal, and emitter terminal, respectively.

[0023] The power conversion circuit 11 further includes a plurality of first diodes 4 connected in antiparallel in a one-to-one relationship to a plurality of first switching elements 1 (three), and a plurality of second diodes 5 connected in antiparallel in a one-to-one relationship to a plurality of second switching elements 2 (three). 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] At the connection point 3U between the first switching element 1U and the second switching element 2U, the U-phase terminal of the AC load RA1 is connected via the AC terminal 41U. At the connection point 3V between the first switching element 1V and the second switching element 2V, the V-phase terminal of the AC load RA1 is connected via the AC terminal 41V. At the connection point 3W between the first switching element 1W and the second switching element 2W, the W-phase terminal of the AC load RA1 is connected via the AC terminal 41W.

[0025] Multiple resonant capacitors 9 correspond one-to-one with multiple switches 8. Each of the multiple resonant capacitors 9 is connected between the first terminal 81 and the second DC terminal 32 of the corresponding switch 8. The power converter 100 has multiple (three in the example of Figure 1) resonant circuits. Each of the multiple resonant circuits includes a resonant capacitor 9 and a resonant inductor L1. In this embodiment, the resonant inductor L1 is common to the multiple resonant circuits.

[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 Figure 1) third switching elements 6 and each of the multiple (three in the example of Figure 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 signal generation circuit 52. Each of the multiple third switching elements 6 and the multiple fourth switching elements 7 is, for example, an IGBT. Therefore, the control terminal, first main terminal, and second main terminal of each of the multiple third switching elements 6 and the multiple fourth switching elements 7 are the gate terminal, collector terminal, and emitter terminal, respectively. In each of the multiple switches 8, the third switching element 6 and the fourth switching element 7 are connected in reverse series. In each of the multiple switches 8, the first main terminal (collector terminal) of the third switching element 6 is connected to the first main terminal (collector terminal) of the fourth switching element 7. In each of the multiple switches 8, the second main terminal (emitter terminal) of the third switching element 6 is connected to the connection point 3 of the corresponding switching circuit 10 among the multiple switching circuits 10, and the second main terminal (emitter terminal) of the fourth switching element 7 is connected to the resonant inductor L1. Furthermore, each of the multiple switches 8 has a diode 61 connected in antiparallel to the third switching element 6 and a diode 71 connected in antiparallel to the fourth switching element 7.

[0027] In the power converter 100, switch 8U is connected to the connection point 3U between the first switching element 1U and the second switching element 2U. Switch 8V is connected to the connection point 3V between the first switching element 1V and the second switching element 2V. Switch 8W is connected to the connection point 3W between the first switching element 1W and the second switching element 2W. For convenience of explanation, the third switching element 6 and the fourth switching element 7 of switch 8U may be referred to as the third switching element 6U and the fourth switching element 7U, respectively; the third switching element 6 and the fourth switching element 7 of switch 8V may be referred to as the third switching element 6V and the fourth switching element 7V, respectively; and the third switching element 6 and the fourth switching element 7 of switch 8W may be referred to as the third switching element 6W and the fourth switching element 7W, respectively.

[0028] Multiple switches 8 are controlled by a signal generation circuit 52. In other words, the third switching element 6U, the fourth switching element 7U, the third switching element 6V, the fourth switching element 7V, the third switching element 6W, and the fourth switching element 7W are controlled by the signal generation circuit 52.

[0029] The resonant inductor L1 has a third end and a fourth end. In the resonant inductor L1, the third end is connected to the second end 82 of the plurality of switches 8. In Embodiment 1, the third end of the resonant inductor L1 is connected to a common connection point 25 to which the second ends 82 of the plurality of switches 8 are connected. 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 terminal of the resonant inductor L1 and the second DC terminal 32. The regenerative capacitor 15 is, for example, a film capacitor.

[0031] 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 mainly consists of a processor and memory as hardware. The processor executes a program recorded in the memory of the computer system, thereby realizing the function of the control device 51 in this disclosure. The processor of the computer system is composed of one or more electronic circuits including semiconductor integrated circuits (ICs) or large-scale integrated circuits (LSIs). The integrated circuits such as ICs and LSIs referred to here are named differently depending on the degree of integration, and include integrated circuits called system LSIs, VLSIs (Very Large Scale Integrations), or ULSIs (Ultra Large Scale Integrations). Furthermore, FPGAs (Field-Programmable Gate Arrays) that are programmed after the manufacture of the LSI, or logic devices that allow for the reconstruction of junction relationships or circuit compartments within the LSI, can also be used as processors. The plurality of electronic circuits may be aggregated on a single chip or distributed across multiple chips. Multiple chips may be integrated into a single 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 also consists of one or more electronic circuits, including semiconductor integrated circuits or large-scale integrated circuits.

[0032] The control device 51 outputs first control signals SU1, SV1, and SW1 to control the on / off state of each of the multiple first switching elements 1U, 1V, and 1W. Each of the first control signals SU1, SV1, and SW1 is a PWM (Pulse Width Modulation) signal whose potential level changes between, for example, 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 they are at a low level, respectively. The control device 51 also outputs first control signals SU2, SV2, and SW2 to control the on / off state of each of the multiple second switching elements 2U, 2V, and 2W. Each of the first control signals SU2, SV2, and SW2 is a PWM signal whose potential level changes between, for example, a first potential level (hereinafter also called the low level) and a second potential level (hereinafter also called the high level) which 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 they are at a low level, respectively.

[0033] The control device 51 generates first control signals SU1, SV1, SW1 corresponding to each of the multiple first switching elements 1U, 1V, and 1W, and first control signals SU2, SV2, SW2 corresponding to each of the multiple second switching elements 2U, 2V, and 2W, using a sawtooth wave carrier signal. More specifically, the control device 51 generates first control signals SU1 and SU2 to be given to the first switching element 1U and the second switching element 2U, respectively, based on at least the carrier signal and the U-phase voltage command. The control device 51 also generates first control signals SV1 and SV2 to be given to the first switching element 1V and the second switching element 2V, respectively, based on at least the carrier signal and the V-phase voltage command. Furthermore, the control device 51 generates first control signals SW1 and SW2 to be given to the first switching element 1W and the second switching element 2W, respectively, based on at least the carrier signal and the W-phase voltage command. The U-phase, V-phase, and W-phase voltage commands are, for example, sinusoidal signals with a phase difference of 120° from each other, and their values ​​(voltage command values) change over time. The carrier signal waveform is not limited to a sawtooth wave; for example, it could be a triangular wave. Furthermore, the length of one period for the U-phase, V-phase, and W-phase voltage commands is the same. Also, the length of one period for the U-phase, V-phase, and W-phase voltage commands is longer than the length of one period for the carrier signal.

[0034] The duty cycles of the first control signals SU1 and SU2, which the control device 51 provides to the first switching element 1U and the second switching element 2U respectively, change based on the U-phase voltage command. Figure 3 shows the duty cycle of the first control signal SU1 as the U-phase duty cycle. The control device 51 (see Figure 1) compares the U-phase voltage command with the carrier signal to generate the first control signal SU1 to be 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 to be provided to the second switching element 2U. Furthermore, the control device 51 sets a first dead time period Td1 (see Figure 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.

[0035] The duty cycles of the first control signals SV1 and SV2, which the control device 51 provides to the first switching element 1V and the second switching element 2V respectively, change based on the V-phase voltage command. Figure 3 shows the duty cycle of the first control signal SV1 as the V-phase duty cycle. The control device 51 (see Figure 1) compares the V-phase voltage command with the 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 provided to the first switching element 1V to generate the first control signal SV2 to be provided to the second switching element 2V. Furthermore, the control device 51 sets a first dead time period Td1 (see Figure 5) 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.

[0036] The duty cycles of the first control signals SW1 and SW2, which the control device 51 provides to the first switching element 1W and the second switching element 2W respectively, change based on the W-phase voltage command. Figure 3 shows the duty cycle of the first control signal SW1 as the W-phase duty cycle. The control device 51 (see Figure 1) compares the W-phase voltage command with the 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 provided to the first switching element 1W to generate the first control signal SW2 to be provided to the second switching element 2W. Furthermore, the control device 51 sets a first dead time period Td1 (see Figure 6) 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.

[0037] The U-phase voltage command, V-phase voltage command, and W-phase voltage command are, for example, sinusoidal signals with a phase difference of 120° from each other, and their values ​​change over time. Therefore, the duty cycle of the first control signal SU1 (U-phase duty cycle), the duty cycle of the first control signal SV1 (V-phase duty cycle), and the duty cycle of the first control signal SW1 (W-phase duty cycle) change in a sinusoidal manner with a phase difference of 120° from each other, as shown in Figure 3, for example. Similarly, the duty cycles of the first control signal SU2, the duty cycle of the first control signal SV2, and the duty cycle of the first control signal SW2 change in a sinusoidal manner with a phase difference of 120° from each other.

[0038] The control device 51 generates first control signals SU1, SU2, SV1, SV2, SW1, and SW2 based on the carrier signal, each voltage command, and information regarding the state of the AC load RA1. For example, if the AC load RA1 is a three-phase motor, the information regarding the state of the AC load RA1 includes, for example, detected values ​​from multiple current sensors that detect the 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.

[0039] Multiple switches 8, resonant inductors L1, multiple resonant capacitors 9, and regenerative capacitors 15 are provided to perform zero-voltage soft switching of multiple first switching elements 1 and multiple second switching elements 2.

[0040] When the third switching element 6U is ON and the fourth switching element 7U is OFF, switch 8U can allow the charging current flowing through the path of regenerative capacitor 15 - resonant inductor L1 - switch 8U - resonant capacitor 9U to pass through. The charging current is the current that charges the resonant capacitor 9U. When the third switching element 6U is OFF and the fourth switching element 7U is ON, switch 8U can allow the discharge current flowing through the path of resonant capacitor 9U - switch 8U - resonant inductor L1 - regenerative capacitor 15 to pass through. The discharge current is the current that discharges the charge from the resonant capacitor 9U.

[0041] Switch 8V allows the charging current flowing through the path of regenerative capacitor 15 - resonant inductor L1 - switch 8V - resonant capacitor 9V to pass through when the third switching element 6V is ON and the fourth switching element 7V is OFF. The charging current is the current that charges the resonant capacitor 9V. Switch 8V allows the discharge current flowing through the path of resonant capacitor 9V - switch 8V - resonant inductor L1 - regenerative capacitor 15 to pass through when the third switching element 6V is OFF and the fourth switching element 7V is ON. The discharge current is the current that discharges the charge from the resonant capacitor 9V.

[0042] Switch 8W can pass the charging current flowing through the path of regenerative capacitor 15 - resonant inductor L1 - switch 8W - resonant capacitor 9W when the third switching element 6W is ON and the fourth switching element 7W is OFF. The charging current is the current that charges the resonant capacitor 9W. Switch 8W can pass the discharge current flowing through the path of resonant capacitor 9W - switch 8W - resonant inductor L1 - regenerative capacitor 15 when the third switching element 6W is OFF and the fourth switching element 7W is ON. The discharge current is the current that discharges the charge from the resonant capacitor 9W.

[0043] In this embodiment, the control device 51 sets the dead time period 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 to a second dead time period Td2, which is determined by the first dead time period Td1 and a predetermined time (additional time Tad). The second dead time period Td2 includes the first dead time period Td1. The second dead time period Td2 has a length equal to the length of the first dead time period Td1 plus a predetermined time (the sum of the length of the first dead time period Td1 and the length of the predetermined time). In other words, the control device 51 uses the second dead time period Td2, which is the first dead time period Td1 extended by a predetermined time, as the dead time period.

[0044] The first dead time period Td1 is a period set between the high-level period of the first control signal to the first switching element 1 and the high-level period of the first control signal to the second switching element 2 for each of the plurality of switching circuits 10, and the on-periods of the first switching element 1 and the second switching element 2 do not overlap (a period in which both the first switching element 1 and the second switching element 2 are on does not occur). It is a period in which both the first control signal to the first switching element 1 and the first control signal to the second switching element 2 are set to the low level. In the present embodiment, for example, the length of the resonance half period corresponding to each of the plurality of switches 8 is designed according to the length of the first dead time period Td1 of each of the plurality of switching circuits 10. The resonance half period is half of the resonance period, which is the reciprocal of the resonance frequency of the resonance circuit including the switch 8, the resonance inductor L1, and one 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 is. The length of the resonance half period is set to be the same as the length of the first dead time period Td1, for example.

[0045] The length of the resonance half period of the resonance circuit including the resonance inductor L1 and the resonance capacitor 9U is set to 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, for example. The length of the resonance half period of the resonance circuit including the resonance inductor L1 and the resonance capacitor 9V is set to the length of the first dead time period Td1 (see FIG. 5) 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 resonance half period of the resonance circuit including the resonance inductor L1 and the resonance capacitor 9W is set to the length of the first dead time period Td1 (see FIG. 6) set between the high-level period of the first control signal SW1 and the high-level period of the first control signal SW2.

[0046] If the resonance period is Tres, then Tres / 2, which is the resonance half-period, is the length of the first dead time period Td1. It is desirable that the time point when the resonance half-period ends coincides with the end time point of the first dead time period Td1 for the switching circuit 10 corresponding to the switch 8. FIG. 4 illustrates the first control signals SU1, SU2, the second control signals SU6, SU7, the first dead time period Td1, the additional time Tad, and the second dead time period Td2. In the example of FIG. 4, the start time point and the end time point of the first dead time period Td1 are time point t12 and time point t13, respectively. Also, FIG. 5 illustrates the first control signals SV1, SV2, the second control signals SV6, SV7, the first dead time period Td1, the additional time Tad, and the second dead time period Td2. In the example of FIG. 5, the start time point and the end time point of the first dead time period Td1 are time point t22 and time point t23, respectively. Also, FIG. 6 illustrates the first control signals SW1, SW2, the second control signals SW6, SW7, the first dead time period Td1, the additional time Tad, and the second dead time period Td2. In the example of FIG. 6, the start time point and the end time point of the first dead time period Td1 are time point t32 and time point t33, respectively.

[0047] The length of the above-mentioned resonance half-period is an ideal design example, and it may also be a length of 90% or more and 110% or less of the length of the first dead time period Td1. The resonance half-period and the first dead time period Td1 may have different lengths.

[0048] The second dead time period Td2 is the first dead time period Td1 plus a predetermined time determined by the load current value and the voltage value of the regenerative capacitor 15. The predetermined time is, for example, an additional time Tad determined by the load current value, the voltage value of the regenerative capacitor 15, and the inductance L of the resonant inductor L1. The load current value is, for example, the detection result of the load current by a current sensor or its signal processing value, or an estimated value of the load current iU. The detection result of the load current or its signal processing value at this time is the detection value at the carrier cycle in which the additional time Tad is added to the first dead time period Td1, or at the timing closest to that carrier cycle. The estimated value of the load current at this time is the value estimated from the load current at the carrier cycle in which the additional time Tad is added to the first dead time period Td1. The inductance L of the resonant inductor L1 is a value stored in advance in the control device 51. The voltage value of the regenerative capacitor 15 is the detected value of the voltage V15 of the regenerative capacitor 15 (the potential V15 at the sixth terminal 154 of the regenerative capacitor 15). In the example in Figure 4, the additional time Tad is the value obtained by the calculation Tad = iU × (L / V15). In the example in Figure 5, the additional time Tad is the value obtained by the calculation Tad = iV × (L / V15). In the example in Figure 6, the additional time Tad is the value obtained by the calculation Tad = iW × (L / V15).

[0049] The length of the specified time is an ideal design example, and may be between 90% and 110% of the additional time Tad.

[0050] In the power converter 100, a signal generation circuit 52, separate from the control device 51, controls multiple switches 8.

[0051] The signal generation circuit 52 generates second control signals SU6, SU7, SV6, SV7, SW6, SW7 to control the on / off state 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.

[0052] The signal generation circuit 52 generates second control signals SU6, SU7, SV6, SV7, SW6, SW7 to control the on / off state 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.

[0053] The signal generation circuit 52 generates a second control signal for each of the multiple switches 8, which has a high-level period corresponding to the second dead time period Td2 for the corresponding switching circuit 10 among the multiple switching circuits 10.

[0054] In the signal generation circuit 52, the start time of the high-level period of the second control signal generated for each of the multiple switches 8 is synchronized with the start timing of the second dead time period Td2. In this disclosure, "synchronizing the start time of the high-level period of the second control signal with the start timing of the second dead time period Td2" means that the start time of the high-level period of the second control signal (start time) is between the start time (start time) and the end time (end time) of the second dead time period Td2, and the time length between the start time (start time) of the high-level period of the second control signal (start time) and the end time (end time) of the second dead time period Td2 is greater than or equal to the length of the first dead time period Td1. In Embodiment 1, the signal generation circuit 52 synchronizes the start time of the high-level period of the second control signal for each of the multiple switches 8 with the start time of the second dead time period Td2. In Embodiment 1, the length of the high-level period of the second control signal for each of the multiple switches 8 is longer than the length of the second dead time period Td2.

[0055] The signal generation 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 the corresponding switching circuit 10 among the multiple switching circuits 10. In this embodiment, as shown in Figure 2, the signal generation circuit 52 has multiple logic circuits 521 to 526 and multiple gate drive circuits 531 to 536. In the signal generation circuit 52, the multiple logic circuits 521 to 526 correspond one-to-one with the multiple gate drive circuits 531 to 536.

[0056] The logic circuit 521 is configured to generate a second control signal SU6 using the first control signal SU1 and the first control signal SU2. The logic circuit 521 is, for example, a two-input, one-output logic circuit, which receives the first control signal SU1 and the first control signal SU2 output from the control device 51 and outputs the second control signal SU6. The second control signal SU6 is supplied to the third switching element 6U via the gate drive circuit 531.

[0057] The logic circuit 522 is configured to generate a second control signal SU7 using the first control signal SU1 and the first control signal SU2. The logic circuit 522 is, for example, a two-input, one-output logic circuit, which receives the first control signal SU1 and the first control signal SU2 output from the control device 51 and outputs the second control signal SU7. The second control signal SU7 is supplied to the fourth switching element 7U via the gate drive circuit 532.

[0058] The logic circuit 523 is configured to generate a second control signal SV6 using the first control signal SV1 and the first control signal SV2. The logic circuit 523 is, for example, a two-input, one-output logic circuit that receives the first control signal SV1 and the first control signal SV2 output from the control device 51 and outputs the second control signal SV6. The second control signal SV6 is supplied to the third switching element 6V via the gate drive circuit 533.

[0059] The logic circuit 524 is configured to generate a second control signal SV7 using the first control signal SV1 and the first control signal SV2. The logic circuit 524 is, for example, a two-input, one-output logic circuit, which receives the first control signal SV1 and the first control signal SV2 output from the control device 51 and outputs the second control signal SV7. The second control signal SV7 is supplied to the fourth switching element 7V via the gate drive circuit 534.

[0060] The logic circuit 525 is configured to generate a second control signal SW6 using the first control signal SW1 and the first control signal SW2. The logic circuit 525 is, for example, a two-input, one-output logic circuit, which receives the first control signal SW1 and the first control signal SW2 output from the control device 51 and outputs the second control signal SW6. The second control signal SW6 is supplied to the third switching element 6W via the gate drive circuit 535.

[0061] The logic circuit 526 is configured to generate a second control signal SW7 using the first control signal SW1 and the first control signal SW2. The logic circuit 526 is, for example, a two-input, one-output logic circuit, which receives the first control signal SW1 and the first control signal SW2 output from the control device 51 and outputs the second control signal SW7. The second control signal SW7 is supplied to the fourth switching element 7W via the gate drive circuit 536.

[0062] The first clamp diode 13 has its anode connected to the third terminal of the resonant inductor L1 and its cathode connected to the first DC terminal 31. The second clamp diode 14 has its cathode connected to the third terminal of the resonant inductor L1 and its anode connected to the second DC terminal 32.

[0063] (3) Operation of the power converter In the following, the current iL1 flowing through the resonant inductor L1 will be described as having a positive polarity when it flows in the direction of the arrow in Figure 1, and a negative polarity when it flows in the opposite direction to the direction of the arrow in Figure 1. Furthermore, in the following, the load currents iU, iV, and iW flowing through the U, V, and W phases of the AC load RA1 will be described as having a positive polarity when it flows in the direction of the arrow from connection point 3 (3U, 3V, 3W) to the AC load RA1, and a negative polarity when it flows in the opposite direction to the direction of the arrow in Figure 1, from the AC load RA1 to connection point 3 (3U, 3V, 3W). Furthermore, for the currents i9U, i9V, and i9W flowing through the resonant capacitors 9U, 9V, and 9W respectively, the polarity will be defined as positive when the current flows in the direction of the arrows in Figure 1 from the resonant capacitors 9U, 9V, and 9W toward connection point 3 (3U, 3V, 3W), and negative when the current flows in the opposite direction from connection point 3 (3U, 3V, 3W) toward the resonant capacitors 9U, 9V, and 9W. 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 will be 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 will be negative.

[0064] Furthermore, in the following, the switching element targeted for zero-voltage soft switching (first switching element 1 or second switching element 2) will also be referred to as the target switching element.

[0065] The following describes the basic operation of zero-voltage soft switching for each of the multiple first switching elements 1 and the multiple second switching elements 2, with reference to Figures 1 to 8. The basic operation is the operation when no resonant currents corresponding to two or more of the multiple switching circuits 10 flow simultaneously through the resonant inductor L1. After describing the basic operation, the operation when the control device 51 determines that no resonant currents corresponding to two of the multiple switching circuits 10 flow simultaneously through the resonant inductor L1 will be described.

[0066] (3.1) Basic Operation In the power converter 100, when the target switching element is the first switching element 1 (hereinafter also referred to as the target first switching element 1), and the polarity of the load current flowing to the AC terminal 41 connected to the target first switching element 1 is positive, the signal generation circuit 52 turns on the third switching element 6 corresponding to the target first switching element 1. As a result, the power converter 100 causes the resonant inductor L1 and the resonant capacitor 9 connected to the target first switching element 1 to resonate, charging the resonant capacitor 9 from the regenerative capacitor 15, and setting the voltage across the target first switching element 1 to zero. As a result, the power converter 100 can achieve zero-voltage soft switching of the target first switching element 1.

[0067] Furthermore, in the power converter 100, if the target switching element is the second switching element 2 (hereinafter also referred to as the target second switching element 2), and the polarity of the load current flowing to the AC terminal 41 connected to the target second switching element 2 is negative, the signal generation circuit 52 turns on the fourth switching element 7 corresponding to the target second switching element 2. As a result, the power converter 100 causes the resonant capacitor 9 and the resonant inductor L1 connected to the target second switching element 2 to resonate, causing the resonant capacitor 9 to discharge and reducing the voltage across the target second switching element 2 to zero. As a result, the power converter 100 can achieve zero-voltage soft switching of the target second switching element 2.

[0068] When the control device 51 sets a 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 predetermined time (additional time Tad) to the first dead time period Td1 by shortening the high-level period of the first control signal to the second switching element 2.

[0069] For example, when the control device 51 sets a second dead time period Td2 for the switching circuit 10U, as shown in Figure 7, if the polarity of the load current iU is positive, it shortens the predetermined time (additional time Tad) of the high-level period of the first control signal SU2 to the second switching element 2U, thereby adding a predetermined time (additional time Tad) to the first dead time period Td1.

[0070] Figure 7 shows the first control signals SU1 and SU2, the second control signal SU6, the current iL1 flowing through the resonant inductor L1, 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. In Figure 7, the voltage value of the DC power supply E1 is shown as Vd.

[0071] 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 preceding 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 preceding the high-level period of the first control signal SU1 ends. Therefore, when the first control signal SU1 changes from a low level to a high level at time t13, the first switching element 1U is soft-switched at zero voltage. In the example shown in Figure 7, the current iL1 flowing through the resonant inductor L1 begins to flow from 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, after a predetermined time (additional time Tad) has elapsed from 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, after a second predetermined time Tad2, which is the same length as the predetermined time (first predetermined time), has elapsed from time t13. In the signal generation circuit 52, at time t11, when the first control signal SU2 changes from a high level to a low level, the second control signal SU6 changes from a low level to a high level, and at time t14, when the sum of the second dead time period Td2 and the second predetermined time Tad has elapsed, the second control signal SU6 changes from a high level to a low level. The current iL1 flowing between time point t12 and time point t13 is the resonant current (charging current of the resonant capacitor 9U) flowing from the regenerative capacitor 15 through the resonant inductor L1 to the resonant capacitor 9U.

[0072] In the following, the period T01 in which the absolute value of the current iL1 increases from zero to the absolute value of the load current (load current iU in the example of Figure 7) will be referred to as the first period T01, the period T02 in which the absolute value of the current iL1 is greater than the load current (load current iU in the example of Figure 7) will be referred to as the second period T02, and the period T03 in which the absolute value of the current iL1 decreases from the absolute value of the load current (load current iU in the example of Figure 7) to zero will be referred to as the third period T03. In the power converter 100, when the current iL1 increases from zero to iL1 = iU in the first period T01, the device transitions from the first period T01 to the second period T02. In the second period T02, a resonant current flows, and when the first control signal to the target switching element changes from a low level to a high level, the device transitions from the second period T02 to the third period T03.

[0073] In Figure 7, the first period T01 is the period from time t11 to t12. The length of the first period T01 is the same as the first predetermined time (additional time Tad). 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 from the regenerative capacitor 15 - resonant inductor L1 - diode 71 - third switching element 6U - AC terminal 41U. Also during the first period T01, the load current iU flows through the path from the second diode 5, which is antiparallel connected to the second switching element 2U - AC terminal 41U - AC load RA1.

[0074] In Figure 7, the second period T02 is the period from time t12 to t13. The length of the second period T02 is the same as the length of the resonant half-period. During the second period T02, 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 second period T02, the current iL1 flows through the path of regenerative capacitor 15 - resonant inductor L1 - diode 71 - 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 9.

[0075] In Figure 7, the third period T03 is the period from time t13 to t14. The length of the third period T03 is the same as the second predetermined time Tad2. During the third period T03, the first switching element 1U and the third switching element 6U are both in the ON state, and the second switching element 2U and the fourth switching element 7U are both in the OFF state. During the third period T03, the current iL1 flows through the path from the regenerative capacitor 15 - resonant inductor L1 - diode 71 - third switching element 6U - connection point 3U - AC terminal 41U. As a result, the current iL1 is reduced to zero. Also during the third period T03, the load current iU flows through the path from the first DC terminal 31 - first switching element 1U - AC terminal 41U - AC load RA1.

[0076] When the control device 51 sets a 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 predetermined time (additional time Tad) to the first dead time period Td1 by shortening the high-level period of the first control signal to the first switching element 1.

[0077] For example, when the control device 51 sets a second dead time period Td2 for the switching circuit 10U, as shown in Figure 8, if the polarity of the load current iU is negative, it adds a predetermined time (additional time Tad) to the first dead time period Td1 by shortening the predetermined time (additional time Tad) of the high-level period of the first control signal SU1 to the first switching element 1U.

[0078] Figure 8 shows the case where the target switching element is the second switching element 2U of the switching circuit 10U, illustrating the first control signals SU1 and SU2, the second control signal SU7, the current iL1 flowing through the resonant inductor L1, and the voltage V2u across the second switching element 2U. In Figure 8, the voltage value of the DC power supply E1 is shown as Vd.

[0079] 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 preceding 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 a low level to a high level at time t43, the second switching element 2U is soft-switched at zero voltage. In the example shown in Figure 8, the current iL1 flowing through the resonant inductor L1 begins to flow from time t41, when the high-level period of the second control signal SU7 starts, reaches the same value as the load current iU at time t42, when the additional time Tad has elapsed, reaches the same value as the load current iU at time t43, when the second dead time period Td2 ends, and becomes zero at time t44, when the second predetermined time Tad2, which is the same length as the first predetermined time, has elapsed from time t43. In the signal generation circuit 52, the second control signal SU7 changes from a low level to a high level at the same time that the first control signal SU1 changes from a high level to a low level. The current iL1 flowing between time t42 and time t43 is the resonant current (discharge current of the resonant capacitor 9U) flowing from the resonant capacitor 9U to the resonant inductor L1.

[0080] In Figure 8, the first period T01 is the period from time t41 to 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 the off state, and the fourth switching element 7U is in the on state. During the first period T01, the current iL1 flows through the path from the AC terminal 41U - diode 61 - fourth switching element 7U - resonant inductor L1 - regenerative capacitor 15. Also during the first period T01, the load current iU flows through the path from the AC load RA1 - AC terminal 41U - first diode 4 which is connected in antiparallel to the first switching element 1U.

[0081] In Figure 8, the second period T02 is the period from time t42 to 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 the off state, and the fourth switching element 7U is in the on state. During the second period T02, the current iL1 flowing through the resonant inductor L1 is the combined current of the current flowing from the AC terminal 41U through the diode 61 - fourth switching element 7U - resonant inductor L1 - regenerative capacitor 15 and the current flowing from the resonant capacitor 9U through the diode 61 - fourth switching element 7U - resonant inductor L1 - regenerative capacitor 15 (resonant current). During the second period T02, the resonant capacitor 9 is discharged.

[0082] In Figure 8, the third period T03 is the period from time t43 to t44. During the third period T03, the second switching element 2U and the fourth switching element 7U are both in the ON state, and the first switching element 1U and the third switching element 6U are both in the OFF state. During the third period T03, the current iL1 flows through the path from the AC terminal 41U - connection point 3U - diode 61 - fourth switching element 7U - resonant inductor L1 - regenerative capacitor 15. As a result, the absolute value of the current iL1 is reduced to zero. Also during the third period T03, the load current iU flows through the path from the AC load RA1 - AC terminal 41U - second switching element 2U - second DC terminal 32.

[0083] The above describes an example of setting the second dead time period Td2 for switching circuit 10U, but the same applies when setting the second dead time period Td2 for switching circuit 10V and switching circuit 10W.

[0084] (3.2) When the shift control operation control device 51 determines that resonant currents corresponding to two of the multiple switching circuits 10 flow simultaneously through the resonant inductor L1, it performs control to shift the ON period of the first switching element 1 and the second switching element 2 in one of the two switching circuits 10. "When it determines that resonant currents corresponding to two of the two switching circuits 10 flow simultaneously" means when it is estimated in advance that resonant currents corresponding to two of the two switching circuits 10 flow simultaneously through the resonant inductor L1. For the sake of explanation, below, "resonant currents corresponding to two of the two switching circuits 10 flow simultaneously through the resonant inductor L1" may be referred to as "two-phase resonant currents flowing simultaneously through the resonant inductor L1".

[0085] (3.2.1) Determination of whether two-phase resonant currents flow simultaneously in the resonant inductor The power converter 100 has a three-phase (U-phase, V-phase, and W-phase) voltage command with a phase difference of 120° from each other, but the command values ​​of the two-phase voltage commands approach each other at electrical angles of 60°, and the duty cycles of the two-phase control signals approach each other (see regions A1 and A2 in Figure 3). In region A1 of Figure 3, the duty cycles of the U-phase control signal and the V-phase control signal are around 0.75. In region A2 of Figure 3, the duty cycles of the U-phase control signal and the V-phase control signal are around 0.25. The polarity of the resonant current is the same as the polarity of the current iL1, so in region A1, the polarity of the resonant current is positive, and in region A2, the polarity of the resonant current is negative. In 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 applied to the third switching element 6U (time t11 in Figure 4) and the start of the high-level period of the second control signal SV6 applied to the third switching element 6V (time t21 in Figure 5) becomes shorter, and there is a possibility that the resonant current of the U phase and the resonant current of the V phase will flow simultaneously through the resonant inductor L1. In the power converter 100, in region A2, the direction of the resonant current is reversed compared to region A1, but there is a possibility that the resonant current of the U phase and the resonant current of the V phase will flow simultaneously through the resonant inductor L1.

[0086] If we assume that the capacitance of each of the multiple resonant capacitors 9U, 9V, and 9W is C, then if the U-phase current and the V-phase current flow simultaneously through the resonant inductor L1, the equivalent circuit will have a capacitor with a combined capacitance of resonant capacitor 9U and resonant capacitor 9V (= 2 × C) connected in series with the resonant inductor L1. Therefore, in the power converter 100, if two-phase current flows simultaneously through the resonant inductor L1, the resonant frequency of the resonant circuit including the resonant inductor L1 will change compared to the case where one-phase current flows through the resonant inductor L1, and there is a possibility that zero-voltage soft switching will not be achieved.

[0087] In the following explanation, as shown in Figure 9, the length of the period corresponding to the first period T01 during the high-level period of the second control signal SU6 will be denoted as Tau, the length of the period corresponding to the second period T02 as Tres / 2, and the length of the period corresponding to the third period T03 as Tau. Tau is a value obtained in the control device 51 by the calculation Tau = iU × (L / V15), using, for example, the detection result of the load current iU by the current sensor or its signal processing value, or an estimated value of the load current iU, the inductance L of the resonant inductor L1 which is stored in advance, and the detection result of the voltage V15 of the regenerative capacitor 15 (potential V15 at the sixth terminal 154 of the regenerative capacitor 15).

[0088] Furthermore, as shown in Figure 9, in the high-level period of the second control signal SV6, the length of the period corresponding to the first period T01 will be described as Tab, the length of the period corresponding to the second period T02 will be described as Tres / 2, and the length of the period corresponding to the third period T03 will be described as Tab. Tab is a value obtained in the control device 51 by the calculation Tab = iV × (L / V15), using, for example, the detection result of the load current iV by the current sensor or its signal processing value, or an estimated value of the load current iV, the inductance L of the resonant inductor L1 which is stored in advance, and the detection result of the voltage V15 of the regenerative capacitor 15 (potential V15 at the sixth terminal 154 of the regenerative capacitor 15).

[0089] Furthermore, in the following explanation, the length of the period corresponding to the first period T01 during the high-level period of the second control signal SW6 will be denoted as Taw, the length of the period corresponding to the second period T02 as Tres / 2, and the length of the period corresponding to the third period T03 as Taw. Taw is a value obtained in the control device 51 by the calculation Taw = iW × (L / V15), using, for example, the detection result of the load current iW by the current sensor or its signal processing value, or an estimated value of the load current iW, the inductance L of the resonant inductor L1 which is stored in advance, and the detection result of the voltage V15 of the regenerative capacitor 15 (potential V15 at the sixth terminal 154 of the regenerative capacitor 15).

[0090] Furthermore, the ON period of the first switching element 1U corresponds one-to-one with the high-level period of the first control signal SU1. The ON period of the first switching element 1V corresponds one-to-one with the high-level period of the first control signal SV1. The ON period of the first switching element 1W corresponds one-to-one with the high-level period of the first control signal SW1. Also, the ON period of the second switching element 2U corresponds one-to-one with the high-level period of the first control signal SU2. The ON period of the second switching element 2V corresponds one-to-one with the high-level period of the first control signal SV2. The ON period of the second switching element 2W corresponds one-to-one with the high-level period of the first control signal SW2.

[0091] For example, the control device 51 generates first control signals SU1, SU2, SV1, SV2, SW1, and SW2 for each cycle of the carrier signal, and then determines whether or not there is an overlap in resonant currents before controlling the first switching element 1U, second switching element 2U, first switching element 1V, second switching element 2V, first switching element 1W, and second switching element 2W.

[0092] (3.2.1.1) In the case of charging operation of a resonant capacitor, Figure 9 is an explanatory diagram of how to calculate the overlap time when the resonant current of the U phase and the resonant current of the V phase overlap.

[0093] In the power converter 100, if the time difference ΔTuv is greater than or equal to Tau + Tav + (Tres / 2), the resonant current of the U phase and the resonant current of the V phase do not overlap. If the time difference ΔTuv is less than Tau + Tav + Tres / 2, the resonant current of the U phase and the resonant current of the V phase overlap. The time difference ΔTuv is the time difference between the start of the high-level period of the first control signal SU1 given to the first switching element 1U of the switching circuit 10U and the start of the high-level period of the first control signal SV1 given to the first switching element 1V of the switching circuit 10V. The control device 51 calculates the overlap time Tov_uv by calculating Tov_uv = Tau + Tav + (Tres / 2) - ΔTuv, where Tov_uv is the overlap time during which the resonant current of the U phase and the resonant current of the V phase overlap. The control device 51 estimates that the resonant current of the U phase and the resonant current of the V phase overlap if Tov_uv > 0. The method for calculating the time difference ΔTuv is not limited to the example described above. For example, the time difference between the end of the high-level period of the first control signal SU2 given to the second switching element 2U of the switching circuit 10U and the end of the high-level period of the first control signal SV2 given to the second switching element 2V of the switching circuit 10V may be used.

[0094] Furthermore, in the power converter 100, if the time difference ΔTuw is greater than or equal to Tau + Taw + (Tres / 2), the resonant current of the U phase and the resonant current of the W phase do not overlap, and if the time difference ΔTuw is less than Tau + Taw + (Tres / 2), the resonant current of the U phase and the resonant current of the W phase overlap. The time difference ΔTuw is the time difference between the start of the high-level period of the first control signal SU1 and the start of the high-level period of the first control signal SW1. The control device 51 determines the overlap time Tov_uw, where the resonant current of the U phase and the resonant current of the W phase overlap, by calculating Tov_uw = Tau + Taw + (Tres / 2) - ΔTuw. If Tov_uw > 0, the control device 51 estimates that the resonant current of the U phase and the resonant current of the W phase overlap. The method for calculating the time difference ΔTuw is not limited to the example described above. For example, the time difference between the end of the high-level period of the first control signal SU2 and the end of the high-level period of the first control signal SW2 may be used.

[0095] Furthermore, in the power converter 100, if the time difference ΔTvw is greater than or equal to Tav + Taw + (Tres / 2), the resonant current of the V phase and the resonant current of the W phase do not overlap, and if the time difference ΔTvw is less than Tav + Taw + (Tres / 2), the resonant current of the V phase and the resonant current of the W phase overlap. The time difference ΔTvw is the time difference between the start of the high-level period of the first control signal SV1 given to the first switching element 1V of the switching circuit 10V and the start of the high-level period of the first control signal SW1 given to the first switching element 1W of the switching circuit 10W. The control device 51 calculates the overlap time Tov_vw by calculating Tov_vw = Tav + Taw + (Tres / 2) - ΔTvw, with Tov_vw being the overlap time during which the resonant current of the V phase and the resonant current of the W phase overlap. The control device 51 estimates that the resonant current of the V phase and the resonant current of the W phase overlap if Tov_vw > 0. The method for calculating the time difference ΔTvw is not limited to the example described above; for example, the time difference between the end of the high-level period of the first control signal SV2 and the end of the high-level period of the first control signal SW2 may be used.

[0096] When the control device 51 performs shift control, it shifts the high-level periods of the first control signals to the first switching element 1 and the second switching element 2 of the two switching circuits 10 so that the length of the high-level periods of the first control signals to the first switching element 1 and the second switching element 2 of the two switching circuits 10 does not change. For example, when the control device 51 shifts the high-level periods of the first control signals SU1 and SU2, it shifts the high-level periods of the first control signals SU1 and SU2, but does not change the duty cycles of the first control signals SU1 and SU2 in one cycle of the carrier signal. Similarly, when the control device 51 shifts the high-level periods of the first control signals SV1 and SV2, it shifts the high-level periods of the first control signals SV1 and SV2, but does not change the duty cycles of the first control signals SV1 and SV2 in one cycle of the carrier signal. Furthermore, when the control device 51 shifts the high-level periods of the first control signal SW1 and the first control signal SW2, it shifts the high-level periods of each of the first control signal SW1 and the first control signal SW2, but does not change the duty cycles of each of the first control signal SW1 and the first control signal SW2 in one cycle of the carrier signal. For the sake of explanation, in the following, the shift time when the high-level periods of the first control signal SU1 and the first control signal SU2 are shifted will be denoted as Tus. Also, the shift time when the high-level periods of the first control signal SV1 and the first control signal SV2 are shifted will be denoted as Tvs. Also, the shift time when the high-level periods of the first control signal SW1 and the first control signal SW2 are shifted will be denoted as Tws.

[0097] In this embodiment, when the control device 51 determines that the resonant currents of the U-phase and V-phase flow simultaneously, it sets the shift time Tsu and shift time Tsv such that the sum of the shift time Tsu and shift time Tsv equals the overlap time Tov_uv.

[0098] When performing shift control, the control device 51 shifts 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 each of the two switching circuits 10 in different directions. The control device 51 compares the duty cycles of the two first control signals SU1 and SV1, and shifts the high-level period of the first control signal with the relatively larger duty cycle to be advanced, and shifts the high-level period of the first control signal with the relatively smaller duty cycle to be delayed.

[0099] The upper part of Figure 10 shows an example of a timing chart before the control device 51 performs shift control, and the lower part of Figure 10 shows an example of a timing chart when the control device 51 performs shift control. More specifically, the upper part of Figure 10 shows the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SU7, SV6, SV7, and the current iL1 (in the upper part of Figure 10, the current passing through switch 8U and resonant inductor L1 and the current passing through switch 8V and resonant inductor L1 are shown separately) before the control device 51 determines that the two-phase resonant currents of the U-phase and V-phase are flowing simultaneously. Furthermore, the lower part of Figure 10 shows the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SU7, SV6, SV7, and current iL1 when the control device 51 shifts the high-level period of the first control signal SV1, which has a relatively larger duty cycle, in an advance direction, and shifts the high-level period of the first control signal SU1, which has a relatively smaller duty cycle, in a delay direction. Figure 10 also shows a timing chart for one cycle of the carrier signal.

[0100] As can be seen from the waveform of current iL1 in the lower part of Figure 10, the power converter 100 can suppress the overlap between the resonant current of the U phase and the resonant current of the V phase. As a result, the power converter 100 can perform zero-voltage soft switching of both the first switching element 1U and the first switching element 1V.

[0101] The above example illustrates shift control when the control device 51 determines that the resonant currents of the U-phase and V-phase flow simultaneously. However, in both cases, whether the resonant currents of the U-phase and W-phase flow simultaneously or the resonant currents of the V-phase and W-phase flow simultaneously, the shift control is performed using the same approach (algorithm) as when the resonant currents of the U-phase and V-phase flow simultaneously.

[0102] (3.2.1.2) Discharge operation of the resonant capacitor In the case of the discharge operation of the resonant capacitor 9, the control device 51 uses the same time difference and overlap time as in the case of the charging operation of the resonant capacitor 9 to determine whether or not two-phase resonant currents flow simultaneously.

[0103] For example, the control device 51 estimates that the resonant current of the U phase and the resonant current of the V phase overlap if the time difference ΔTuv between the start of the high-level period of the first control signal SU2 and the start of the high-level period of the first control signal SV2 is less than Tau + Tav + (Tres / 2).

[0104] Furthermore, the control device 51 estimates that the resonant current of the U phase and the resonant current of the W phase overlap if, for example, the time difference ΔTuw between the start of the high-level period of the first control signal SU2 and the start of the high-level period of the first control signal SW2 is less than Tau + Taw + (Tres / 2).

[0105] Furthermore, the control device 51 estimates that the resonant current of the V phase and the resonant current of the W phase overlap if, for example, the time difference ΔTvw between the start of the high-level period of the first control signal SV2 and the start of the high-level period of the first control signal SW2 is less than Tav + Taw + (Tres / 2).

[0106] The upper part of Figure 11 shows an example of a timing chart before the control device 51 performs shift control, and the lower part of Figure 11 shows an example of a timing chart when the control device 51 performs shift control. More specifically, the upper part of Figure 11 shows the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SU7, SV6, SV7, and the current iL1 (in the upper part of Figure 11, the current passing through switch 8U and resonant inductor L1 and the current passing through switch 8V and resonant inductor L1 are shown separately) before the control device 51 determines that the two-phase resonant currents of the U-phase and V-phase are flowing simultaneously. Furthermore, the lower part of Figure 11 shows the first control signals SU1, SU2, SV1, SV2, the second control signals SU6, SU7, SV6, SV7, and current iL1 when the control device 51 shifts the shorter of the two high-level periods of the first control signals SU1 and SV1 in a predetermined direction (in this embodiment, in the direction of advancing on the time axis) by a shift time Ts. Figure 11 also shows a timing chart for one cycle of the carrier signal.

[0107] In this embodiment, when the control device 51 determines that the resonant currents of the U-phase and V-phase flow simultaneously, it sets the shift time Tsu and shift time Tsv such that the sum of the shift time Tsu and shift time Tsv equals the overlap time Tov_uv.

[0108] When the control device 51 performs shift control, it shifts 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 each of the two switching circuits 10 in different directions. The control device 51 compares the duty cycles of the two first control signals SU1 and SV1, and shifts the high-level period of the first control signal with the relatively larger duty cycle in a direction that delays it, and shifts the high-level period of the first control signal with the relatively smaller duty cycle in a direction that advances it.

[0109] As can be seen from the waveform of current iL1 in the lower part of Figure 11, the power converter 100 can suppress the overlap between the resonant current of the U phase and the resonant current of the V phase. As a result, the power converter 100 can perform zero-voltage soft switching of both the second switching element 2U and the second switching element 2V.

[0110] The above example illustrates shift control when the control device 51 determines that the resonant currents of the U-phase and V-phase flow simultaneously. However, in both cases, whether the resonant currents of the U-phase and W-phase flow simultaneously or the resonant currents of the V-phase and W-phase flow simultaneously, the shift control is performed using the same approach (algorithm) as when the resonant currents of the U-phase and V-phase flow simultaneously.

[0111] (4) Advantages The power conversion device 100 according to Embodiment 1 includes a first DC terminal 31 and 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, a resonant inductor L1, a regenerative capacitor 15, a control device 51, and a signal generation circuit 52. 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 a plurality of first switching elements 1 and a plurality of second switching elements 2 are connected in series in a one-to-one relationship, are connected in parallel with each other. The control device 51 sets a second dead time period Td2 for each of the plurality of switching circuits 10, which is a predetermined dead time period Td1 that is set so that the ON periods of the first switching element 1 and the second switching element 2 do not overlap 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. The predetermined time is determined according to the current value of the load current, the inductance of the resonant inductor L1, and the voltage value of the regenerative capacitor 15. The signal generation circuit 52 generates a second control signal for each of the multiple switches 8, which has a high-level period corresponding to the second dead time period Td2 for the corresponding switching circuit 10 among the multiple switching circuits 10. If the control device 51 determines that resonant currents corresponding to two of the multiple switching circuits 10 are flowing simultaneously through the resonant inductor L1, it performs shift control to shift the high-level periods of the first control signal to the first switching element 1 and the first control signal to the second switching element 2 in each of the two switching circuits 10 so that the resonant currents corresponding to the two switching circuits 10 do not flow simultaneously through the resonant inductor L1.

[0112] With the above configuration, zero-voltage soft switching can be achieved without the control device 51 directly controlling the multiple switches 8 for zero-voltage soft switching. More specifically, the control device 51 does not need to generate a second control signal to directly control the multiple switches 8 for zero-voltage soft switching, and zero-voltage soft switching of each of the multiple first switching elements 1 and the multiple second switching elements 2 can be achieved without the control device 51 directly controlling the multiple switches 8. Furthermore, with the above configuration, the control device 51 does not need to generate and output multiple second control signals SU6, SU7, SV6, SV7, SW6, SW7, so the control device 51 can be simplified, for example, it is possible to suppress an increase in the number of control ports of the microcomputer included in the control device 51 and suppress the size increase of the control device 51.

[0113] Furthermore, the power conversion device 100 according to Embodiment 1 further comprises a first clamp diode 13 and a second clamp diode 14. The first clamp diode 13 has its anode connected to the third end of the resonant inductor L1 and its cathode connected to the first DC terminal 31. The second clamp diode 14 has its cathode connected to the third end of the resonant inductor L1 and its anode connected to the second DC terminal 32. When the control device 51 sets a second dead time period Td2 for each of the plurality of switching circuits 10, if the polarity of the load current is positive, it adds a predetermined time (additional time Tad) to the first dead time period Td1 by shortening the high-level period of the first control signal to the second switching element 2. Furthermore, when the control device 51 sets a 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 predetermined time (additional time Tad) to the first dead time period Td1 by shortening the high-level period of the first control signal to the first switching element 1.

[0114] With the above configuration, it becomes possible to achieve zero-voltage soft switching while further reducing dead time loss and dead time error.

[0115] Furthermore, in the power conversion device 100 according to Embodiment 1, the signal generation circuit 52 generates a second control signal for each of the multiple switches 8 using both the first control signal to the first switching element 1 and the first control signal to the second switching element 2 of the corresponding switching circuit 10 among the multiple switching circuits 10.

[0116] According to the above configuration, it becomes possible to easily generate a second control signal having a high-level period corresponding to the second dead time period Td2, and to simplify the signal generation circuit 52.

[0117] Furthermore, in the power conversion device 100 according to Embodiment 1, when the control device 51 performs shift control, it shifts the high-level periods of the first control signals to the first switching element 1 and the second switching element 2 of the two switching circuits 10 so that the length of the high-level periods of the first control signals to the first switching element 1 and the second switching element 2 of the two switching circuits 10 does not change.

[0118] The above configuration makes it possible to suppress changes in line voltage.

[0119] Furthermore, in the power conversion device 100 according to Embodiment 1, when the control device 51 performs shift control, it shifts 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 each of the two switching circuits 10 in different directions.

[0120] With the above configuration, it becomes possible to increase the frequency compared to the case where overlapping resonant currents are avoided by shifting the high-level period of the first control signal to the first switching element 1 of one of the two switching circuits 10 and the high-level period of the first control signal to the second switching element 2.

[0121] Furthermore, in the power conversion device 100 according to Embodiment 1, when the control device 51 determines that resonant currents corresponding to two of the multiple switching circuits 10 flow simultaneously through the resonant inductor L1, and the polarity of the load current flowing through each of the two AC terminals 41 connected to the two switching circuits 10 is positive, the control device 51 compares the duty cycles of the two first control signals for the two first switching elements 1 of the two switching circuits 10. The control device 51 then shifts the high-level period of the first control signal with a relatively large duty cycle forward and the high-level period of the first control signal with a relatively small duty cycle backward. Also, when the polarity of the load current flowing through each of the two AC terminals 41 connected to the two switching circuits 10 is negative, the control device 51 compares the duty cycles of the two first control signals for the two first switching elements 1 of the two switching circuits 10. The control device 51 then shifts the high-level period of the first control signal with a relatively large duty cycle to be delayed, and shifts the high-level period of the first control signal with a relatively small duty cycle to be advanced.

[0122] With the above configuration, it becomes possible to increase the frequency compared to the case where overlapping resonant currents are avoided by shifting the high-level period of the first control signal to the first switching element 1 of one of the two switching circuits 10 and the high-level period of the first control signal to the second switching element 2.

[0123] (Embodiment 2) The power converter 100A according to Embodiment 2 will be described with reference to Figures 12 to 15. With respect to the power converter 100A according to Embodiment 2, components that are the same as those in the power converter 100 according to Embodiment 1 (see Figures 1 and 2) are denoted by the same reference numerals and their description is omitted.

[0124] (1) The configured power converter 100A differs from the power converter 100 in that, as shown in Figure 12, it is equipped with a signal generation circuit 52A instead of the signal generation circuit 52 of the power converter 100.

[0125] In the power converter 100A, the signal generation circuit 52A controls multiple switches 8.

[0126] The signal generation circuit 52A generates second control signals SU6, SU7, SV6, SV7, SW6, SW7 to control the on / off state 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.

[0127] The signal generation circuit 52A generates a second control signal for each of the plurality of switches 8, which has 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. In Embodiment 2, the signal generation circuit 52A synchronizes the start time of the high-level period of the second control signal for each of the plurality of switches 8 with the start time of the second dead time period Td2, and synchronizes the end time of the high-level period of the second control signal for each of the plurality of switches 8 with the end time of the second dead time period Td2. Therefore, in Embodiment 2, the length of the high-level period of the second control signal for each of the plurality of switches 8 is the same as the length of the second dead time period Td2. The signal generation circuit 52A has a plurality of logic circuits 521 to 526 and a plurality of gate drive circuits 531 to 536, similar to the signal generation circuit 52 of Embodiment 1 (see Figure 2). The signal generation circuit 52A synchronizes the end of the high-level period of the second control signal to each of the multiple switches 8 with the end of the second dead time period Td2. Therefore, the configuration of the multiple logic circuits 521 to 526 differs from the configuration of the multiple logic circuits 521 to 526 in the signal generation circuit 52.

[0128] (2) Operation (2.1) Basic Operation Figure 13 shows the first control signals SU1 and SU2, the second control signal SU6, the current iL1 flowing through the resonant inductor L1, 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 Figure 13, the voltage value of the DC power supply E1 is shown as Vd.

[0129] 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 preceding 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 preceding the high-level period of the first control signal SU1 ends. Therefore, when the first control signal SU1 changes from a low level to a high level at time t13, the first switching element 1U is soft-switched at zero voltage. In the example shown in Figure 13, the current iL1 flowing through the resonant inductor L1 begins to flow from 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 predetermined time (additional time Tad) has elapsed, 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 a second predetermined time Tad2, which is the same length as the first predetermined time, has elapsed from time t13. In the signal generation circuit 52A, at time t11, when the first control signal SU2 changes from a high level to a low level, the second control signal SU6 changes from a low level to a high level. The current iL1 flowing between time t12 and time t13 is the resonant current (charging current of the resonant capacitor 9U) flowing from the regenerative capacitor 15 through the resonant inductor L1 to the resonant capacitor 9U.

[0130] 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 from the regenerative capacitor 15 - resonant inductor L1 - diode 71 - third switching element 6U - AC terminal 41U. Also during the first period T01, the load current iU flows through the path from the second diode 5, which is antiparallel connected to the second switching element 2U - AC terminal 41U - AC load RA1.

[0131] During the second period T02, the first switching element 1U, the second switching element 2U, and the fourth switching element 7U are all in the off state, while the third switching element 6U is in the on state. During the second period T02, the current iL1 flows through the path from the regenerative capacitor 15 - resonant inductor L1 - diode 71 - 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 9.

[0132] During the third period T03, the first switching element 1U is ON, and the second switching element 2U, the third switching element 6U, and the fourth switching element 7U are each OFF. During the third period T03, the first switching element 1U is ON, and the second switching element 2U, the third switching element 6U, and the fourth switching element 7U are each OFF. During the third period T03, the current iL1 flows through the path from the regenerative capacitor 15 - resonant inductor L1 - first clamp diode 13. As a result, the current iL1 is reduced to zero. Also during the third period T03, the load current iU flows through the path from the first DC terminal 31 - first switching element 1U - AC terminal 41U - AC load RA1.

[0133] When the control device 51 sets a 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 predetermined time to the first dead time period Td1 by shortening the high-level period of the first control signal to the first switching element 1.

[0134] For example, when the control device 51 sets a second dead time period Td2 for the switching circuit 10U, as shown in Figure 14, if the polarity of the load current iU is negative, it adds a predetermined time (additional time Tad) to the first dead time period Td1 by shortening the predetermined time (additional time Tad) of the high-level period of the first control signal SU1 to the first switching element 1U.

[0135] Figure 14 shows the case where the target switching element is the second switching element 2U of the switching circuit 10U, illustrating the first control signals SU1 and SU2, the second control signal SU7, the current iL1 flowing through the resonant inductor L1, and the voltage V2u across the second switching element 2U. In Figure 14, the voltage value of the DC power supply E1 is shown as Vd.

[0136] 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 preceding 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 a low level to a high level at time t43, the second switching element 2U is soft-switched at zero voltage. In the example shown in Figure 14, the current iL1 flowing through the resonant inductor L1 begins to flow from time t41, when the high-level period of the second control signal SU7 begins, becomes equal to the load current iU at time t42, when the additional time Tad has elapsed, becomes equal to the load current iU at time t43, when the second dead time period Td2 ends, and becomes zero at time t44, when the second predetermined time Tad2, which is the same length as the first predetermined time, has elapsed from time t43. In the signal generation circuit 52A, the second control signal SU7 changes from a low level to a high level at the same time that the first control signal SU1 changes from a high level to a low level. The current iL1 flowing between time t42 and time t43 is the resonant current (discharge current of the resonant capacitor 9U) flowing from the resonant capacitor 9U to the resonant inductor L1.

[0137] In Figure 14, the first period T01 is the period from time t41 to 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 the off state, and the fourth switching element 7U is in the on state. During the first period T01, the current iL1 flows through the path from the AC terminal 41U - diode 61 - fourth switching element 7U - resonant inductor L1 - regenerative capacitor 15. Also during the first period T01, the load current iU flows through the path from the AC load RA1 - AC terminal 41U - first diode 4 which is connected in antiparallel to the first switching element 1U.

[0138] In Figure 14, the second period T02 is the period from time t42 to 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 the off state, and the fourth switching element 7U is in the on state. During the second period T02, the current iL1 flowing through the resonant inductor L1 is the combined current of the current flowing from the AC terminal 41U through the diode 61 - fourth switching element 7U - resonant inductor L1 - regenerative capacitor 15 and the current flowing from the resonant capacitor 9U through the diode 61 - fourth switching element 7U - resonant inductor L1 - regenerative capacitor 15 (resonant current). During the second period T02, the resonant capacitor 9 is discharged.

[0139] In Figure 14, the third period T03 is the period from time t43 to t44. During the third period T03, the second switching element 2U is in the ON state, and the first switching element 1U, the third switching element 6U, and the fourth switching element 7U are all in the OFF state. During the third period T03, the current iL1 flows through the path from the second clamp diode 14 - resonant inductor L1 - regenerative capacitor 15. As a result, the absolute value of the current iL1 is reduced to zero. Also during the third period T03, the load current iU flows through the path from the AC load RA1 - AC terminal 41U - second switching element 2U - second DC terminal 32.

[0140] The above describes an example of setting the second dead time period Td2 for switching circuit 10U, but the same applies when setting the second dead time period Td2 for switching circuit 10V and switching circuit 10W.

[0141] (2.2) Shift Control The upper part of Figure 15 shows an example of a timing chart before the control device 51 performs shift control in the case of charging the resonant capacitor, and the lower part of Figure 15 shows an example of a timing chart when the control device 51 performs shift control. The way to read Figure 15 is the same as in Figure 10.

[0142] Similar to Embodiment 1, when the control device 51 determines that the resonant currents of the U-phase and V-phase flow simultaneously, it sets the shift time Tsu and shift time Tsv such that the sum of the shift time Tsu and shift time Tsv equals the overlap time Tov_uv.

[0143] When the control device 51 performs shift control, it shifts 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 each of the two switching circuits 10 in different directions.

[0144] (2.2.1) In the case of charging operation of the resonant capacitor, the control device 51 compares the duty cycles of the two first control signals SU1 and SV1, and shifts the high-level period of the first control signal with the relatively larger duty cycle to be advanced, and shifts the high-level period of the first control signal with the relatively smaller duty cycle to be delayed.

[0145] As can be seen from the waveform of current iL1 in the lower part of Figure 15, the power converter 100A is able to suppress the overlap between the resonant current of the U phase and the resonant current of the V phase.

[0146] The above examples illustrate shift control when the control device 51 determines that the resonant currents of the U-phase and V-phase flow simultaneously (overlap). However, in both cases, whether the resonant currents of the U-phase and W-phase flow simultaneously or the resonant currents of the V-phase and W-phase flow simultaneously, the shift control is performed using the same approach (algorithm) as when the control device determines that the resonant currents of the U-phase and V-phase flow simultaneously.

[0147] (2.2.2) In the case of discharge operation of the resonant capacitor, the control device 51 compares the duty cycles of the two first control signals SU1 and SV1, and shifts the high-level period of the first control signal with the relatively larger duty cycle toward a slower time, and shifts the high-level period of the first control signal with the relatively smaller duty cycle toward a faster time.

[0148] In this case as well, the power converter 100A can suppress the overlap between the resonant current of the U phase and the resonant current of the V phase.

[0149] The above examples illustrate shift control when the control device 51 determines that the resonant currents of the U-phase and V-phase flow simultaneously (overlap). However, in both cases, whether the resonant currents of the U-phase and W-phase flow simultaneously or the resonant currents of the V-phase and W-phase flow simultaneously, the shift control is performed using the same approach (algorithm) as when the control device determines that the resonant currents of the U-phase and V-phase flow simultaneously.

[0150] (3) Advantages The power converter 100A according to Embodiment 2, like the power converter 100 according to Embodiment 1, can more reliably achieve zero voltage soft switching without the control device 51 directly controlling the multiple switches 8 for zero voltage soft switching.

[0151] (Embodiment 3) The circuit configuration of the power converter 100 according to Embodiment 3 is the same as that of the power converter 100 according to Embodiment 1 (see Figure 1), so the circuit diagram is omitted. The operation of the power converter 100 according to Embodiment 3 will be described below based on Figures 1 and 16. Note that the way to read Figure 16 is the same as the way to read Figure 10.

[0152] (1) Operation (1.1) Basic Operation The basic operation is the same as in Embodiment 1, so the explanation will be omitted.

[0153] (1.2) In the power converter 100 according to the shift control embodiment 3, the shift time in the shift control executed when the control device 51 determines that the two-phase resonant currents overlap is different from the shift time when the control device 51 of embodiment 1 performs shift control.

[0154] In the power conversion device 100 according to Embodiment 3, the control device 51 sets the shift time of the first control signal to the first switching element 1 and the first control signal to the second switching element 2 of each of the two switching circuits 10 to an arbitrary time that is longer than the overlap time of the two-phase resonant current and less than or equal to the maximum value that can be set within one cycle of the carrier signal. The "maximum value that can be set within one cycle of the carrier signal" means the shift time when the time between the end of one cycle of the carrier signal and the end of the high-level period of the first control signal that has been shifted in the direction of delaying is a specified time or zero, and when the first control signal is shifted in the direction of advancing is a specified time or zero.

[0155] The example in Figure 16 shows that, in the case of charging a resonant capacitor, when the control device 51 determines that the resonant currents of the U-phase and V-phase flow simultaneously, it sets the shift time Tsu and shift time Tsv to the maximum value that can be set within one period of the carrier signal, which is longer than the overlap time Tov_uv.

[0156] As can be seen from the waveform of current iL1 in the lower part of Figure 16, the power converter 100 according to Embodiment 3 is able to suppress the overlap between the resonant current of the U phase and the resonant current of the V phase. As a result, the power converter 100 according to Embodiment 3 is able to perform zero-voltage soft switching of the first switching element 1U and the first switching element 1V, respectively.

[0157] The above example illustrates shift control when the control device 51 determines that the resonant currents of the U-phase and V-phase flow simultaneously. However, in both cases, whether the resonant currents of the U-phase and W-phase flow simultaneously or the resonant currents of the V-phase and W-phase flow simultaneously, the shift control is performed using the same approach (algorithm) as when the resonant currents of the U-phase and V-phase flow simultaneously.

[0158] (2) Advantages The power converter 100 according to Embodiment 3, like the power converter 100 according to Embodiment 1, can more reliably achieve zero voltage soft switching without the control device 51 directly controlling the multiple switches 8 for zero voltage soft switching.

[0159] Furthermore, in the power conversion device 100 according to Embodiment 3, the control device 51 sets the shift time of the high-level period for the first control signal to the first switching element 1 and the first control signal to the second switching element 2 in each of the two switching circuits 10 to an arbitrary time that is longer than the overlap time of the two-phase resonant current and less than or equal to the maximum value that can be set within one cycle of the carrier signal.

[0160] With the above configuration, compared to the power conversion device 100 according to Embodiment 1, it becomes possible to distribute the period during which the resonant current flows through the resonant inductor L1, thereby reducing the thermal load on the resonant inductor L1.

[0161] (Embodiment 4) The circuit configuration of the power converter 100 according to Embodiment 4 is the same as that of the power converter 100 according to Embodiment 1 (see Figure 1), so the circuit diagram is omitted. The operation of the power converter 100 according to Embodiment 4 will be described below based on Figures 1 and 17. Note that the way to read Figure 17 is the same as the way to read Figure 10.

[0162] (1) Operation (1.1) Basic Operation The basic operation is the same as in Embodiment 1, so the explanation will be omitted.

[0163] (1.2) In the power converter 100 according to the shift control embodiment 4, the direction in which the high-level period of the first control signal is shifted in the shift control performed by the control device 51 when it determines that the two-phase resonant currents overlap is the opposite direction to the direction in which the high-level period of the first control signal is shifted in the shift control of the control device 51 in embodiment 1.

[0164] When the control device 51 performs shift control, it shifts 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 each of the two switching circuits 10 in different directions.

[0165] (1.2.1) In the case of charging operation of the resonant capacitor, the control device 51 compares the duty cycles of the two first control signals SU1 and SV1, and shifts the high-level period of the first control signal with the relatively larger duty cycle toward a slower time, and shifts the high-level period of the first control signal with the relatively smaller duty cycle toward a faster time.

[0166] The upper part of Figure 17 shows an example of a timing chart before the control device 51 performs shift control, and the lower part of Figure 17 shows an example of a timing chart when the control device 51 performs shift control.

[0167] As can be seen from the waveform of current iL1 in the lower part of Figure 17, the power converter 100 can suppress the overlap between the resonant current of the U phase and the resonant current of the V phase. As a result, the power converter 100 can perform zero-voltage soft switching of both the first switching element 1U and the first switching element 1V.

[0168] The above example illustrates shift control when the control device 51 determines that the resonant currents of the U-phase and V-phase flow simultaneously. However, in both cases, whether the resonant currents of the U-phase and W-phase flow simultaneously or the resonant currents of the V-phase and W-phase flow simultaneously, the shift control is performed using the same approach (algorithm) as when the resonant currents of the U-phase and V-phase flow simultaneously.

[0169] (1.2.2) In the case of discharge operation of the resonant capacitor, when the polarity of the load current flowing through each of the two AC terminals 41 connected to the two switching circuits 10 is negative, the control device 51 compares the duty cycles of the two first control signals SU1 and SV1, and shifts the high-level period of the first control signal with the relatively larger duty cycle to be advanced, and shifts the high-level period of the first control signal with the relatively smaller duty cycle to be delayed.

[0170] The above example illustrates shift control when the control device 51 determines that the resonant currents of the U-phase and V-phase flow simultaneously. However, in both cases, whether the resonant currents of the U-phase and W-phase flow simultaneously or the resonant currents of the V-phase and W-phase flow simultaneously, the shift control is performed using the same approach (algorithm) as when the resonant currents of the U-phase and V-phase flow simultaneously.

[0171] (2) Advantages The power converter 100 according to Embodiment 4, like the power converter 100 according to Embodiment 1, can more reliably achieve zero voltage soft switching without the control device 51 directly controlling the multiple switches 8 for zero voltage soft switching.

[0172] Furthermore, in the power conversion device 100 according to Embodiment 4, when the control device 51 determines that resonant currents corresponding to two of the multiple switching circuits 10 are simultaneously flowing through the resonant inductor L1, if the polarity of the load current flowing through each of the two AC terminals 41 connected to the two switching circuits 10 is positive, the control device 51 compares the duty cycles of the two first control signals for the two first switching elements 1 of the two switching circuits 10, and shifts the high-level period of the first control signal with the relatively larger duty cycle toward a slower direction, and shifts the high-level period of the first control signal with the relatively smaller duty cycle toward a slower direction. When the polarity of the load current flowing through each of the two AC terminals 41 connected to the two switching circuits 10 is negative, the control device 51 compares the duty cycles of the two first control signals for the two first switching elements 1 of the two switching circuits 10, and shifts the high-level period of the first control signal with the relatively larger duty cycle toward a faster direction, and shifts the high-level period of the first control signal with the relatively smaller duty cycle toward a slower direction.

[0173] With the above configuration, it becomes possible to increase the frequency compared to the case where overlapping resonant currents are avoided by shifting the high-level period of the first control signal to the first switching element 1 of one of the two switching circuits 10 and the high-level period of the first control signal to the second switching element 2.

[0174] (Embodiment 5) The circuit configuration of the power converter 100 according to Embodiment 5 is the same as that of the power converter 100 according to Embodiment 1 (see Figure 1), so the circuit diagram is omitted. The operation of the power converter 100 according to Embodiment 5 will be described below based on Figures 1 and 18. Note that the way to read Figure 18 is the same as the way to read Figure 10.

[0175] (1) Operation (1.1) Basic Operation The basic operation is the same as in Embodiment 1, so the explanation will be omitted.

[0176] (1.2) In the power converter 100 according to the shift control embodiment 5, the shift time in the shift control performed by the control device 51 when it determines that the two-phase resonant currents overlap is different from the shift time when the control device 51 of embodiment 4 performs shift control.

[0177] In the power conversion device 100 according to Embodiment 5, the control device 51 sets the shift time of the first control signal to the first switching element 1 and the first control signal to the second switching element 2 of each of the two switching circuits 10 to an arbitrary time that is longer than the overlap time of the two-phase resonant current and less than or equal to the maximum value that can be set within one cycle of the carrier signal. The "maximum value that can be set within one cycle of the carrier signal" means the shift time when the time between the end of one cycle of the carrier signal and the end of the high-level period of the first control signal that has been shifted in the direction of delaying is a specified time or zero, and when the first control signal is shifted in the direction of advancing is a specified time or zero.

[0178] The example in Figure 18 shows that, in the case of charging a resonant capacitor, when the control device 51 determines that the resonant currents of the U-phase and V-phase flow simultaneously, it sets the shift time Tsu and shift time Tsv to the maximum value that can be set within one period of the carrier signal, which is longer than the overlap time Tov_uv.

[0179] As can be seen from the waveform of current iL1 in the lower part of Figure 18, the power converter 100 according to Embodiment 5 is able to suppress the overlap between the resonant current of the U phase and the resonant current of the V phase. As a result, the power converter 100 according to Embodiment 5 is able to perform zero-voltage soft switching of the first switching element 1U and the first switching element 1V, respectively.

[0180] The above example illustrates shift control when the control device 51 determines that the resonant currents of the U-phase and V-phase flow simultaneously. However, in both cases, whether the resonant currents of the U-phase and W-phase flow simultaneously or the resonant currents of the V-phase and W-phase flow simultaneously, the shift control is performed using the same approach (algorithm) as when the resonant currents of the U-phase and V-phase flow simultaneously.

[0181] (2) Advantages The power converter 100 according to Embodiment 5, like the power converter 100 according to Embodiment 1, can more reliably achieve zero voltage soft switching without the control device 51 directly controlling the multiple switches 8 for zero voltage soft switching.

[0182] Furthermore, in the power conversion device 100 according to Embodiment 5, the control device 51 sets the shift time of the high-level period for the first control signal to the first switching element 1 and the first control signal to the second switching element 2 in each of the two switching circuits 10 to an arbitrary time that is longer than the overlap time of the two-phase resonant current and less than or equal to the maximum value that can be set within one cycle of the carrier signal.

[0183] With the above configuration, compared to the power conversion device 100 according to Embodiment 4, it becomes possible to distribute the period during which the resonant current flows through the resonant inductor L1, thereby reducing the thermal load on the resonant inductor L1.

[0184] (Embodiment 6) The power converter 100B according to Embodiment 6 will be described with reference to Figures 19 to 22. With respect to the power converter 100B according to Embodiment 6, components that are the same as those in the power converter 100 according to Embodiment 1 (see Figure 1) are denoted by the same reference numerals and their description is omitted.

[0185] (1) The configured power converter 100B differs from the power converter 100 in that, as shown in Figure 19, it is equipped with a control device 51B instead of the control device 51 of the power converter 100.

[0186] In the power converter 100B, the control device 51B generates first control signals SU1, SU2, SV1, SV2, SV2, SW1, SW2, similar to the control device 51, to control the multiple first switching elements 1 and the multiple second switching elements 2.

[0187] When the control device 51B sets a second dead time period Td2 for each of the multiple switching circuits 10, if the polarity of the load current is positive, it lengthens the first dead time period Td1 by a predetermined time (additional time Tad) by advancing the end time of the high-level period of the first control signal to the second switching element 2 and delaying the start time of the high-level period of the first control signal to the first switching element 1. If the time by which the end time of the high-level period of the first control signal to the second switching element 2 is advanced is Ta21 (see Figure 20), and the time by which the start time of the high-level period of the first control signal to the first switching element 1 is delayed is Ta11 (see Figure 20), then the predetermined time (additional time Tad) is Ta11 + Ta21. Ta11 = Ta21 = 0.5 * Tad.

[0188] When the control device 51B sets a second dead time period Td2 for each of the multiple switching circuits 10, if the polarity of the load current is negative, it lengthens the first dead time period Td1 by a predetermined time (additional time Tad) by advancing the end time of the high-level period of the first control signal to the first switching element 1 and delaying the start time of the high-level period of the first control signal to the second switching element 2. If the time for advancing the end time of the high-level period of the first control signal to the first switching element 1 is Ta12 (see Figure 21), and the time for delaying the start time of the high-level period of the first control signal to the second switching element 2 is Ta22 (see Figure 21), then the predetermined time (additional time Tad) is Ta12 + Ta22. Ta12 = Ta22 = 0.5 * Tad.

[0189] Similar to Embodiment 1, the signal generation circuit 52 generates a second control signal for each of the multiple switches 8 using the first control signal to the first switching element 1 and the first control signal to the second switching element 2 of the corresponding switching circuit 10 among the multiple switching circuits 10.

[0190] (2) Operation (2.1) Basic Operation Diagram 20 shows the first control signals SU1 and SU2, the second control signal SU6, the current iL1 flowing through the resonant inductor L1, 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 Figure 20, the voltage value of the DC power supply E1 is shown as Vd.

[0191] 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 preceding 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 preceding the high-level period of the first control signal SU1 ends. Therefore, when the first control signal SU1 changes from a low level to a high level at time t13, the first switching element 1U is soft-switched at zero voltage. In the example shown in Figure 20, the current iL1 flowing through the resonant inductor L1 begins to flow from 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 equal to the length of the additional time Tad has elapsed, 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 T03 has elapsed from time t13. In the signal generation circuit 52, at time t11, when the first control signal SU2 changes from a high level to a low level, the second control signal SU6 changes from a low level to a high level. The current iL1 flowing between time t12 and time t13 is the resonant current (charging current of the resonant capacitor 9U) flowing from the regenerative capacitor 15 through the resonant inductor L1 to the resonant capacitor 9U.

[0192] 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 from the regenerative capacitor 15 - resonant inductor L1 - diode 71 - third switching element 6U - AC terminal 41U. Also during the first period T01, the load current iU flows through the path from the second diode 5, which is antiparallel connected to the second switching element 2U - AC terminal 41U - AC load RA1.

[0193] During the second period T02, the first switching element 1U, the second switching element 2U, and the fourth switching element 7U are all in the off state, while the third switching element 6U is in the on state. During the second period T02, the current iL1 flows through the path from the regenerative capacitor 15 - resonant inductor L1 - diode 71 - 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 9.

[0194] During the third period T03, the first switching element 1U and the third switching element 6U are both in the ON state, while the second switching element 2U and the fourth switching element 7U are both in the OFF state. During the third period T03, the current iL1 flows through the path from the regenerative capacitor 15 - resonant inductor L1 - diode 71 - third switching element 6U - AC terminal 41U. This reduces the current iL1 to zero. Also during the third period T03, the load current iU flows through the path from the first DC terminal 31 - first switching element 1U - AC terminal 41U - AC load RA1.

[0195] Figure 21 shows the case where the target switching element is the second switching element 2U of the switching circuit 10U, illustrating the first control signals SU1 and SU2, the second control signal SU7, the current iL1 flowing through the resonant inductor L1, and the voltage V2u across the second switching element 2U. In Figure 21, the voltage value of the DC power supply E1 is shown as Vd.

[0196] 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 preceding 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 a low level to a high level at time t43, the second switching element 2U is soft-switched at zero voltage.

[0197] In the example shown in Figure 21, the current iL1 flowing through the resonant inductor L1 begins to flow from 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, after a predetermined time (additional time Tad) has elapsed, reaches the same value as the load current iU at time t43, when the second dead time period Td2 ends, and becomes zero at time t44, after a predetermined time (additional time Tad) has elapsed from time t43. In the signal generation circuit 52, the second control signal SU7 changes from a low level to a high level at the same time that the first control signal SU1 changes from a high level to a low level. The current iL1 flowing between time t42 and time t43 is the resonant current (discharge current of the resonant capacitor 9U) flowing from the resonant capacitor 9U to the resonant inductor L1.

[0198] In Figure 21, the first period T01 is the period from time t41 to 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 the off state, and the fourth switching element 7U is in the on state. During the first period T01, the current iL1 flows through the path from the AC terminal 41U - diode 61 - fourth switching element 7U - resonant inductor L1 - regenerative capacitor 15. Also during the first period T01, the load current iU flows through the path from the AC load RA1 - AC terminal 41U - first diode 4 which is connected in antiparallel to the first switching element 1U.

[0199] In Figure 21, the second period T02 is the period from time t42 to 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 the off state, and the fourth switching element 7U is in the on state. During the second period T02, the current iL1 flowing through the resonant inductor L1 is the combined current of the current flowing from the AC terminal 41U through the diode 61 - fourth switching element 7U - resonant inductor L1 - regenerative capacitor 15 and the current flowing from the resonant capacitor 9U through the diode 61 - fourth switching element 7U - resonant inductor L1 - regenerative capacitor 15 (resonant current). During the second period T02, the resonant capacitor 9 is discharged.

[0200] In Figure 21, the third period T03 is the period from time t43 to t44. During the third period T03, the second switching element 2U and the fourth switching element 7U are both in the ON state, and the first switching element 1U and the third switching element 6U are both in the OFF state. During the third period T03, the current iL1 flows through the path from the AC terminal 41U - connection point 3U - diode 61 - fourth switching element 7U - resonant inductor L1 - regenerative capacitor 15. As a result, the absolute value of the current iL1 is reduced to zero. Also during the third period T03, the load current iU flows through the path from the AC load RA1 - AC terminal 41U - second switching element 2U - second DC terminal 32.

[0201] The above describes an example of setting the second dead time period Td2 for switching circuit 10U, but the same applies when setting the second dead time period Td2 for switching circuit 10V and switching circuit 10W.

[0202] (2.2) Shift control The control device 51B of this embodiment performs shift control when it determines that two-phase resonant currents corresponding to two of the multiple switching circuits 10 are flowing simultaneously through the resonant inductor L1, similar to the control device 51 of Embodiment 1.

[0203] When the control device 51B performs shift control, it shifts 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 each of the two switching circuits 10 in different directions, similar to the control device 51 in Embodiment 1.

[0204] (2.2.1) In the case of charging operation of the resonant capacitor, the control device 51B compares the duty cycles of the two first control signals SU1 and SV1, and shifts the high-level period of the first control signal with the relatively larger duty cycle to be advanced, and shifts the high-level period of the first control signal with the relatively smaller duty cycle to be delayed.

[0205] The upper part of Figure 22 shows an example of a timing chart before the control device 51B performs shift control, and the lower part of Figure 22 shows an example of a timing chart when the control device 51B performs shift control.

[0206] As can be seen from the waveform of current iL1 in the lower part of Figure 22, the power converter 100B can suppress the overlap between the resonant current of the U phase and the resonant current of the V phase. As a result, the power converter 100B can perform zero-voltage soft switching of both the first switching element 1U and the first switching element 1V.

[0207] The above example illustrates shift control when the control device 51B determines that the resonant currents of the U-phase and V-phase flow simultaneously. However, in both cases, where the resonant currents of the U-phase and W-phase flow simultaneously, and where the resonant currents of the V-phase and W-phase flow simultaneously, the shift control is performed using the same approach (algorithm) as when the resonant currents of the U-phase and V-phase flow simultaneously.

[0208] (2.2.2) In the case of discharge operation of the resonant capacitor, when the polarity of the load current flowing through each of the two AC terminals 41 connected to the two switching circuits 10 is negative, the control device 51B compares the duty cycles of the two first control signals SU1 and SV1, and shifts the high-level period of the first control signal with the relatively larger duty cycle toward the slower direction, and shifts the high-level period of the first control signal with the relatively smaller duty cycle toward the faster direction.

[0209] The above example illustrates shift control when the control device 51B determines that the resonant currents of the U-phase and V-phase flow simultaneously. However, in both cases, where the resonant currents of the U-phase and W-phase flow simultaneously, and where the resonant currents of the V-phase and W-phase flow simultaneously, the shift control is performed using the same approach (algorithm) as when the resonant currents of the U-phase and V-phase flow simultaneously.

[0210] (3) Advantages The power converter 100B according to Embodiment 6, like the power converter 100 according to Embodiment 1, can more reliably achieve zero voltage soft switching without the control device 51B directly controlling the multiple switches 8 for zero voltage soft switching.

[0211] Furthermore, in the power converter 100B, when the control device 51B sets a 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 predetermined time (additional time Tad) to the first dead time period Td1 by advancing the end time of the high-level period of the first control signal to the second switching element 2 and delaying the start time of the high-level period of the first control signal to the first switching element 1. If the polarity of the load current is negative, it adds a predetermined time (additional time Tad) to the first dead time period Td1 by advancing the end time of the high-level period of the first control signal to the first switching element 1 and delaying the start time of the high-level period of the first control signal to the second switching element 2.

[0212] With the above configuration, it is possible to achieve zero-voltage soft switching while reducing dead-time loss and dead-time error.

[0213] Furthermore, the power converter 100B according to Embodiment 6 can achieve higher frequencies, similar to the power converter 100 according to Embodiment 1.

[0214] (Embodiment 7) The circuit configuration of the power converter 100B according to Embodiment 7 is the same as that of the power converter 100B according to Embodiment 6 (see Figure 19), so the circuit diagram is omitted. The operation of the power converter 100B according to Embodiment 7 will be described below based on Figures 19 and 23. Note that the way to read Figure 23 is the same as the way to read Figure 22.

[0215] (1) Operation (1.1) Basic Operation The basic operation is the same as in Embodiment 6, so the explanation will be omitted.

[0216] (1.2) In the power converter 100B according to the shift control embodiment 7, the shift time in the shift control executed when the control device 51B determines that the two-phase resonant currents overlap is different from the shift time when the control device 51B of embodiment 6 performs shift control.

[0217] In the power converter 100B according to Embodiment 7, the control device 51B sets the shift time of the first control signal to the first switching element 1 and the first control signal to the second switching element 2 of each of the two switching circuits 10 to an arbitrary time that is longer than the overlap time of the two-phase resonant current and less than or equal to the maximum value that can be set within one cycle of the carrier signal. The "maximum value that can be set within one cycle of the carrier signal" means the shift time when the time between the end of one cycle of the carrier signal and the end of the high-level period of the first control signal that has been shifted in the direction of delaying is a specified time or zero, and when the first control signal is shifted in the direction of advancing is a specified time or zero.

[0218] The example in Figure 23 shows that, in the case of charging a resonant capacitor, when the control device 51B determines that the resonant currents of the U-phase and V-phase flow simultaneously, it sets the shift time Tsu and shift time Tsv to the maximum value that can be set within one period of the carrier signal, which is longer than the overlap time Tov_uv.

[0219] As can be seen from the waveform of current iL1 in the lower part of Figure 23, the power converter 100B according to Embodiment 7 is able to suppress the overlap between the resonant current of the U phase and the resonant current of the V phase. As a result, the power converter 100B according to Embodiment 7 is able to perform zero-voltage soft switching of the first switching element 1U and the first switching element 1V, respectively.

[0220] The above example illustrates shift control when the control device 51B determines that the resonant currents of the U-phase and V-phase flow simultaneously. However, in both cases, where the resonant currents of the U-phase and W-phase flow simultaneously, and where the resonant currents of the V-phase and W-phase flow simultaneously, the shift control is performed using the same approach (algorithm) as when the resonant currents of the U-phase and V-phase flow simultaneously.

[0221] (2) Advantages The power converter 100B according to Embodiment 7, like the power converter 100B according to Embodiment 6, can more reliably achieve zero voltage soft switching without the control device 51B directly controlling the multiple switches 8 for zero voltage soft switching.

[0222] Furthermore, in the power conversion device 100B according to Embodiment 7, the control device 51B sets the shift time of the high-level period for the first control signal to the first switching element 1 and the first control signal to the second switching element 2 in each of the two switching circuits 10 to an arbitrary time that is longer than the overlap time of the two-phase resonant current and less than or equal to the maximum value that can be set within one cycle of the carrier signal.

[0223] With the above configuration, compared to the power converter 100B according to Embodiment 6, it becomes possible to distribute the period during which the resonant current flows through the resonant inductor L1, thereby reducing the thermal load on the resonant inductor L1.

[0224] (Embodiment 8) The circuit configuration of the power converter 100B according to Embodiment 8 is the same as that of the power converter 100B according to Embodiment 6 (see Figure 19), so the circuit diagram is omitted. The operation of the power converter 100B according to Embodiment 8 will be described below based on Figures 19 and 24. Note that the way to read Figure 24 is the same as the way to read Figure 22.

[0225] (1) Operation (1.1) Basic Operation The basic operation is the same as in Embodiment 6, so the explanation will be omitted.

[0226] (1.2) In the power converter 100B according to the shift control embodiment 8, the direction in which the high-level period of the first control signal is shifted in the shift control performed by the control device 51B when it determines that the two-phase resonant currents overlap is the opposite direction to the direction in which the high-level period of the first control signal is shifted in the shift control of the control device 51B in embodiment 6.

[0227] In the power conversion device 100B according to Embodiment 8, when the control device 51B performs shift control, it shifts 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 each of the two switching circuits 10 in different directions.

[0228] (1.2.1) In the case of charging operation of the resonant capacitor, the control device 51B compares the duty cycles of the two first control signals SU1 and SV1, and shifts the high-level period of the first control signal with the relatively larger duty cycle toward a slower direction, and shifts the high-level period of the first control signal with the relatively smaller duty cycle toward an earlier direction.

[0229] The upper part of Figure 24 shows an example of a timing chart before the control device 51B performs shift control, and the lower part of Figure 24 shows an example of a timing chart when the control device 51B performs shift control.

[0230] As can be seen from the waveform of current iL1 in the lower part of Figure 24, the power converter 100B according to Embodiment 8 is able to suppress the overlap between the resonant current of the U phase and the resonant current of the V phase. As a result, the power converter 100B according to Embodiment 8 is able to perform zero-voltage soft switching of the first switching element 1U and the first switching element 1V, respectively.

[0231] The above example illustrates shift control when the control device 51B determines that the resonant currents of the U-phase and V-phase flow simultaneously. However, in both cases, where the resonant currents of the U-phase and W-phase flow simultaneously, and where the resonant currents of the V-phase and W-phase flow simultaneously, the shift control is performed using the same approach (algorithm) as when the resonant currents of the U-phase and V-phase flow simultaneously.

[0232] (1.2.2) In the case of discharge operation of the resonant capacitor, when the polarity of the load current flowing through each of the two AC terminals 41 connected to the two switching circuits 10 is negative, the control device 51B compares the duty cycles of the two first control signals SU1 and SV1, and shifts the high-level period of the first control signal with the relatively larger duty cycle to be advanced, and shifts the high-level period of the first control signal with the relatively smaller duty cycle to be delayed.

[0233] The above example illustrates shift control when the control device 51B determines that the resonant currents of the U-phase and V-phase flow simultaneously. However, in both cases, where the resonant currents of the U-phase and W-phase flow simultaneously, and where the resonant currents of the V-phase and W-phase flow simultaneously, the shift control is performed using the same approach (algorithm) as when the resonant currents of the U-phase and V-phase flow simultaneously.

[0234] (2) Advantages The power converter 100B according to Embodiment 8, like the power converter 100B according to Embodiment 6, can more reliably achieve zero voltage soft switching without the control device 51B directly controlling the multiple switches 8 for zero voltage soft switching.

[0235] Furthermore, in the power conversion device 100B according to Embodiment 8, when the control device 51B determines that resonant currents corresponding to two of the multiple switching circuits 10 are simultaneously flowing through the resonant inductor L1, and the polarity of the load current flowing through the two AC terminals 41 connected to the two switching circuits 10 is positive, the control device 51B compares the duty cycles of the two first control signals for the two first switching elements 1 of the two switching circuits 10, and shifts the high-level period of the first control signal with the relatively larger duty cycle toward a slower period, and the high-level period of the first control signal with the relatively smaller duty cycle toward an earlier period. When the polarity of the load current flowing through each of the two AC terminals 41 connected to the two switching circuits 10 is negative, the control device 51B compares the duty cycles of the two first control signals for the two first switching elements 1 of the two switching circuits 10, and shifts the high-level period of the first control signal with the relatively larger duty cycle forward, and shifts the high-level period of the first control signal with the relatively smaller duty cycle backward.

[0236] With the above configuration, it becomes possible to increase the frequency compared to the case where overlapping resonant currents are avoided by shifting the high-level period of the first control signal to the first switching element 1 of one of the two switching circuits 10 and the high-level period of the first control signal to the second switching element 2.

[0237] (Embodiment 9) The circuit configuration of the power converter 100B according to Embodiment 9 is the same as that of the power converter 100B according to Embodiment 6 (see Figure 19), so the circuit diagram is omitted. The operation of the power converter 100B according to Embodiment 9 will be described below based on Figures 19 and 25. Note that the way to read Figure 25 is the same as the way to read Figure 22.

[0238] (1) Operation (1.1) Basic Operation The basic operation is the same as in Embodiment 6, so the explanation will be omitted.

[0239] (1.2) In the power converter 100B according to the shift control embodiment 9, the shift time in the shift control executed when the control device 51B determines that the two-phase resonant currents overlap is different from the shift time when the control device 51B of embodiment 8 performs shift control.

[0240] In the power converter 100B according to Embodiment 9, the control device 51B sets the shift time of the first control signal to the first switching element 1 and the first control signal to the second switching element 2 of each of the two switching circuits 10 to an arbitrary time that is longer than the overlap time of the two-phase resonant current and less than or equal to the maximum value that can be set within one cycle of the carrier signal. The "maximum value that can be set within one cycle of the carrier signal" means the shift time when the time between the end of one cycle of the carrier signal and the end of the high-level period of the first control signal that has been shifted in the direction of delaying is a specified time or zero, and when the first control signal is shifted in the direction of advancing is a specified time or zero.

[0241] The example in Figure 25 shows that, in the case of charging a resonant capacitor, when the control device 51 determines that the resonant currents of the U-phase and V-phase flow simultaneously, it sets the shift time Tsu and shift time Tsv to the maximum value that can be set within one period of the carrier signal, which is longer than the overlap time Tov_uv.

[0242] As can be seen from the waveform of current iL1 in the lower part of Figure 25, the power converter 100B according to Embodiment 9 is able to suppress the overlap between the resonant current of the U phase and the resonant current of the V phase. As a result, the power converter 100B according to Embodiment 9 is able to perform zero-voltage soft switching of the first switching element 1U and the first switching element 1V, respectively.

[0243] The above example illustrates shift control when the control device 51B determines that the resonant currents of the U-phase and V-phase flow simultaneously. However, in both cases, where the resonant currents of the U-phase and W-phase flow simultaneously, and where the resonant currents of the V-phase and W-phase flow simultaneously, the shift control is performed using the same approach (algorithm) as when the resonant currents of the U-phase and V-phase flow simultaneously.

[0244] (2) Advantages The power converter 100B according to Embodiment 9, like the power converter 100B according to Embodiment 6, can more reliably achieve zero voltage soft switching without the control device 51B directly controlling the multiple switches 8 for zero voltage soft switching.

[0245] Furthermore, in the power conversion device 100B according to Embodiment 9, the control device 51B sets the shift time of the high-level period for the first control signal to the first switching element 1 and the first control signal to the second switching element 2 in each of the two switching circuits 10 to an arbitrary time that is longer than the overlap time of the two-phase resonant current and less than or equal to the maximum value that can be set within one cycle of the carrier signal.

[0246] With the above configuration, compared to the power converter 100B according to Embodiment 8, it becomes possible to distribute the period during which the resonant current flows through the resonant inductor L1, thereby reducing the thermal load on the resonant inductor L1.

[0247] (Embodiment 10) The power converter 100C according to Embodiment 10 will be described with reference to Figures 26 to 29. With respect to the power converter 100C according to Embodiment 10, components that are the same as those in the power converter 100 according to Embodiment 1 (see Figure 1) are denoted by the same reference numerals and their description is omitted.

[0248] (1) The configured power converter 100C differs from the power converter 100 in that, as shown in Figure 26, it is equipped with a control device 51C instead of the control device 51 of the power converter 100.

[0249] In the power converter 100C, the control device 51C generates first control signals SU1, SU2, SV1, SV2, SV2, SW1, SW2, similar to the control device 51, to control the multiple first switching elements 1 and the multiple second switching elements 2.

[0250] When the control device 51C sets a 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 predetermined time (additional time Tad) to the first dead time period Td1 by shortening the high-level period of the first control signal to the first switching element 1.

[0251] When the control device 51C sets a second dead time period Td2 for each of the multiple switching circuits 10, if the polarity of the load current is negative, it shortens the high-level period of the first control signal to the second switching element 2 to add a predetermined time (additional time Tad) to the first dead time period Td1.

[0252] Similar to Embodiment 1, the signal generation circuit 52 generates a second control signal for each of the multiple switches 8 using the first control signal to the first switching element 1 and the first control signal to the second switching element 2 of the corresponding switching circuit 10 among the multiple switching circuits 10.

[0253] (2) Operation (2.1) Basic Operation Figure 27 shows the case where the target switching element is the first switching element 1U of the switching circuit 10U, illustrating the first control signals SU1 and SU2, the second control signal SU6, the current iL1 flowing through the resonant inductor L1, and the voltage V1u across the first switching element 1U. Also in Figure 27, the voltage value of the DC power supply E1 is shown as Vd.

[0254] 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 preceding 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 preceding the high-level period of the first control signal SU1 ends. Therefore, when the first control signal SU1 changes from a low level to a high level at time t13, the first switching element 1U is soft-switched at zero voltage. In the example shown in Figure 27, the current iL1 flowing through the resonant inductor L1 begins to flow from time t11, when the high-level period of the second control signal SU6 starts, reaches the same value as the load current iU at time t12, when the first period T01 has elapsed from 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 from time t13. In the signal generation circuit 52, at time t11, when the first control signal SU2 changes from a high level to a low level, the second control signal SU6 changes from a low level to a high level. The current iL1 flowing between time t12 and time t13 is the resonant current (charging current of the resonant capacitor 9U) flowing from the regenerative capacitor 15 through the resonant inductor L1 to the resonant capacitor 9U.

[0255] 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 from the regenerative capacitor 15 - resonant inductor L1 - diode 71 - third switching element 6U - AC terminal 41U. Also during the first period T01, the load current iU flows through the path from the second diode 5, which is antiparallel connected to the second switching element 2U - AC terminal 41U - AC load RA1.

[0256] During the second period T02, the first switching element 1U, the second switching element 2U, and the fourth switching element 7U are all in the off state, while the third switching element 6U is in the on state. During the second period T02, the current iL1 flows through the path from the regenerative capacitor 15 - resonant inductor L1 - diode 71 - 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 9.

[0257] During the third period T03, the first switching element 1U and the third switching element 6U are both in the ON state, while the second switching element 2U and the fourth switching element 7U are both in the OFF state. During the third period T03, the current iL1 flows through the path from the regenerative capacitor 15 - resonant inductor L1 - diode 71 - third switching element 6U - AC terminal 41U. This reduces the current iL1 to zero. Also during the third period T03, the load current iU flows through the path from the first DC terminal 31 - first switching element 1U - AC terminal 41U - AC load RA1.

[0258] Figure 28 shows the case where the target switching element is the second switching element 2U of the switching circuit 10U, illustrating the first control signals SU1 and SU2, the second control signal SU7, the current iL1 flowing through the resonant inductor L1, and the voltage V2u across the second switching element 2U. In Figure 28, the voltage value of the DC power supply E1 is shown as Vd.

[0259] 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 preceding 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 a low level to a high level at time t43, the second switching element 2U is soft-switched at zero voltage. In the example shown in Figure 28, the current iL1 flowing through the resonant inductor L1 begins to flow from 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, after a predetermined time (additional time Tad) has elapsed, reaches the same value as the load current iU at time t43, when the second dead time period Td2 ends, and becomes zero at time t44, after a second predetermined time Tad2, which is the same length as the predetermined time (additional time Tad), has elapsed from time t43. In the signal generation circuit 52, the second control signal SU7 changes from a low level to a high level at the same time that the first control signal SU1 changes from a high level to a low level. The current iL1 flowing between time t42 and time t43 is the resonant current (discharge current of the resonant capacitor 9U) flowing from the resonant capacitor 9U to the resonant inductor L1.

[0260] In Figure 28, the first period T01 is the period from time t41 to 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 the off state, and the fourth switching element 7U is in the on state. During the first period T01, the current iL1 flows through the path from the AC terminal 41U - diode 61 - fourth switching element 7U - resonant inductor L1 - regenerative capacitor 15. Also during the first period T01, the load current iU flows through the path from the AC load RA1 - AC terminal 41U - first diode 4 which is connected in antiparallel to the first switching element 1U.

[0261] In Figure 28, the second period T02 is the period from time t42 to 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 the off state, and the fourth switching element 7U is in the on state. During the second period T02, the current iL1 flowing through the resonant inductor L1 is the combined current of the current flowing from the AC terminal 41U through the diode 61 - fourth switching element 7U - resonant inductor L1 - regenerative capacitor 15 and the current flowing from the resonant capacitor 9U through the diode 61 - fourth switching element 7U - resonant inductor L1 - regenerative capacitor 15 (resonant current). During the second period T02, the resonant capacitor 9 is discharged.

[0262] In Figure 28, the third period T03 is the period from time t43 to t44. During the third period T03, the second switching element 2U and the fourth switching element 7U are both in the ON state, and the first switching element 1U and the third switching element 6U are both in the OFF state. During the third period T03, the current iL1 flows through the path from the AC terminal 41U - diode 61 - fourth switching element 7U - resonant inductor L1 - regenerative capacitor 15. As a result, the absolute value of the current iL1 is reduced to zero. Also during the third period T03, the load current iU flows through the path from the AC load RA1 - AC terminal 41U - second switching element 2U - second DC terminal 32.

[0263] The above describes an example of setting the first dead time period Td1 to the second dead time period Td2 for the switching circuit 10U, but the same applies when setting the first dead time period Td1 to the second dead time period Td2 for the switching circuit 10V and the switching circuit 10W.

[0264] (2.2) Shift control The control device 51C of this embodiment performs shift control when it determines that two-phase resonant currents corresponding to two of the multiple switching circuits 10 are flowing simultaneously through the resonant inductor L1, similar to the control device 51 of Embodiment 1.

[0265] When the control device 51C performs shift control, it shifts 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 each of the two switching circuits 10 in different directions, similar to the control device 51 in Embodiment 1.

[0266] (2.2.1) In the case of charging operation of the resonant capacitor, the control device 51C compares the duty cycles of the two first control signals SU1 and SV1, and shifts the high-level period of the first control signal with the relatively larger duty cycle to be advanced, and shifts the high-level period of the first control signal with the relatively smaller duty cycle to be delayed.

[0267] The upper part of Figure 29 shows an example of a timing chart before the control device 51C performs shift control, and the lower part of Figure 29 shows an example of a timing chart when the control device 51C performs shift control.

[0268] As can be seen from the waveform of current iL1 in the lower part of Figure 29, the power converter 100C can suppress the overlap between the resonant current of the U phase and the resonant current of the V phase. As a result, the power converter 100C can perform zero-voltage soft switching of both the first switching element 1U and the first switching element 1V.

[0269] The above example illustrates shift control when the control device 51C determines that the resonant currents of the U-phase and V-phase flow simultaneously. However, in both cases—when the resonant currents of the U-phase and W-phase flow simultaneously, and when the resonant currents of the V-phase and W-phase flow simultaneously—shift control is performed using the same approach (algorithm) as when the resonant currents of the U-phase and V-phase flow simultaneously.

[0270] (2.2.2) In the case of discharge operation of the resonant capacitor, when the polarity of the load current flowing through each of the two AC terminals 41 connected to the two switching circuits 10 is negative, the control device 51C compares the duty cycles of the two first control signals SU1 and SV1, and shifts the high-level period of the first control signal with the relatively larger duty cycle toward the slower direction, and shifts the high-level period of the first control signal with the relatively smaller duty cycle toward the faster direction.

[0271] The above example illustrates shift control when the control device 51C determines that the resonant currents of the U-phase and V-phase flow simultaneously. However, in both cases—when the resonant currents of the U-phase and W-phase flow simultaneously, and when the resonant currents of the V-phase and W-phase flow simultaneously—shift control is performed using the same approach (algorithm) as when the resonant currents of the U-phase and V-phase flow simultaneously.

[0272] (3) Advantages The power converter 100C according to Embodiment 10, like the power converter 100 according to Embodiment 1, can more reliably achieve zero voltage soft switching without the control device 51C directly controlling the multiple switches 8 for zero voltage soft switching.

[0273] (Embodiment 11) The circuit configuration of the power converter 100C according to Embodiment 11 is the same as that of the power converter 100C according to Embodiment 10 (see Figure 26), so the circuit diagram is omitted. The operation of the power converter 100C according to Embodiment 11 will be described below based on Figures 26 and 30. Note that the way to read Figure 30 is the same as the way to read Figure 29.

[0274] (1) Operation (1.1) Basic Operation The basic operation is the same as in Embodiment 10, so the explanation will be omitted.

[0275] (1.2) In the power converter 100C according to the shift control embodiment 11, the shift time in the shift control executed when the control device 51C determines that the two-phase resonant currents overlap is different from the shift time when the control device 51C of embodiment 10 performs shift control.

[0276] In the power converter 100C according to Embodiment 11, the control device 51C sets the shift time of the first control signal to the first switching element 1 and the first control signal to the second switching element 2 of each of the two switching circuits 10 to an arbitrary time that is longer than the overlap time of the two-phase resonant current and less than or equal to the maximum value that can be set within one cycle of the carrier signal. The "maximum value that can be set within one cycle of the carrier signal" means the shift time when the time between the end of one cycle of the carrier signal and the end of the high-level period of the first control signal that has been shifted in the direction of delaying is a specified time or zero, and when the first control signal is shifted in the direction of advancing is a specified time or zero.

[0277] The example in Figure 30 shows that, in the case of charging a resonant capacitor, when the control device 51C determines that the resonant currents of the U-phase and V-phase flow simultaneously, it sets the shift time Tsu and shift time Tsv to the maximum value that can be set within one period of the carrier signal, which is longer than the overlap time Tov_uv.

[0278] As can be seen from the waveform of current iL1 in the lower part of Figure 30, the power converter 100C according to Embodiment 11 is able to suppress the overlap between the resonant current of the U phase and the resonant current of the V phase. As a result, the power converter 100C according to Embodiment 11 is able to perform zero-voltage soft switching of the first switching element 1U and the first switching element 1V, respectively.

[0279] The above example illustrates shift control when the control device 51C determines that the resonant currents of the U-phase and V-phase flow simultaneously. However, in both cases—when the resonant currents of the U-phase and W-phase flow simultaneously, and when the resonant currents of the V-phase and W-phase flow simultaneously—shift control is performed using the same approach (algorithm) as when the resonant currents of the U-phase and V-phase flow simultaneously.

[0280] (2) Advantages The power converter 100C according to Embodiment 11, like the power converter 100C according to Embodiment 10, can more reliably achieve zero voltage soft switching without the control device 51C directly controlling the multiple switches 8 for zero voltage soft switching.

[0281] Furthermore, in the power conversion device 100C according to embodiment 11, the control device 51C sets the shift time of the high-level period for the first control signal to the first switching element 1 and the first control signal to the second switching element 2 in each of the two switching circuits 10 to an arbitrary time that is longer than the overlap time of the two-phase resonant current and less than or equal to the maximum value that can be set within one cycle of the carrier signal.

[0282] With the above configuration, compared to the power conversion device 100C according to Embodiment 10, it becomes possible to distribute the period during which the resonant current flows through the resonant inductor L1, thereby reducing the thermal load on the resonant inductor L1.

[0283] (Embodiment 12) The circuit configuration of the power converter 100C according to Embodiment 12 is the same as that of the power converter 100C according to Embodiment 10 (see Figure 26), so the circuit diagram is omitted. The operation of the power converter 100C according to Embodiment 12 will be described below based on Figures 26 and 31. Note that the way to read Figure 31 is the same as the way to read Figure 29.

[0284] (1) Operation (1.1) Basic Operation The basic operation is the same as in Embodiment 10, so the explanation will be omitted.

[0285] (1.2) In the power converter 100C according to the shift control embodiment 12, the direction in which the high-level period of the first control signal is shifted in the shift control that the control device 51C executes when it determines that the two-phase resonant currents overlap is the opposite direction to the direction in which the high-level period of the first control signal is shifted in the shift control of the control device 51C in embodiment 10.

[0286] In the power converter 100C according to Embodiment 12, when the control device 51C performs shift control, it shifts 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 each of the two switching circuits 10 in different directions.

[0287] (1.2.1) In the case of charging operation of the resonant capacitor, the control device 51C compares the duty cycles of the two first control signals SU1 and SV1, and shifts the high-level period of the first control signal with the relatively larger duty cycle toward a slower time, and shifts the high-level period of the first control signal with the relatively smaller duty cycle toward an earlier time.

[0288] The upper part of Figure 31 shows an example of a timing chart before the control device 51C performs shift control, and the lower part of Figure 31 shows an example of a timing chart when the control device 51C performs shift control.

[0289] As can be seen from the waveform of current iL1 in the lower part of Figure 31, the power converter 100C according to Embodiment 12 is able to suppress the overlap between the resonant current of the U phase and the resonant current of the V phase. As a result, the power converter 100C according to Embodiment 12 is able to perform zero-voltage soft switching of the first switching element 1U and the first switching element 1V, respectively.

[0290] The above example illustrates shift control when the control device 51C determines that the resonant currents of the U-phase and V-phase flow simultaneously. However, in both cases—when the resonant currents of the U-phase and W-phase flow simultaneously, and when the resonant currents of the V-phase and W-phase flow simultaneously—shift control is performed using the same approach (algorithm) as when the resonant currents of the U-phase and V-phase flow simultaneously.

[0291] (1.2.2) In the case of discharge operation of the resonant capacitor, when the polarity of the load current flowing through each of the two AC terminals 41 connected to the two switching circuits 10 is negative, the control device 51C compares the duty cycles of the two first control signals SU1 and SV1, and shifts the high-level period of the first control signal with the relatively larger duty cycle to be advanced, and shifts the high-level period of the first control signal with the relatively smaller duty cycle to be delayed.

[0292] The above example illustrates shift control when the control device 51C determines that the resonant currents of the U-phase and V-phase flow simultaneously. However, in both cases—when the resonant currents of the U-phase and W-phase flow simultaneously, and when the resonant currents of the V-phase and W-phase flow simultaneously—shift control is performed using the same approach (algorithm) as when the resonant currents of the U-phase and V-phase flow simultaneously.

[0293] (2) Advantages The power converter 100C according to Embodiment 12, like the power converter 100C according to Embodiment 10, can more reliably achieve zero voltage soft switching without the control device 51C directly controlling the multiple switches 8 for zero voltage soft switching.

[0294] Furthermore, in the power conversion device 100C according to Embodiment 12, when the control device 51C determines that resonant currents corresponding to two of the multiple switching circuits 10 flow simultaneously through the resonant inductor L1, and the polarity of the load current flowing through the two AC terminals 41 connected to the two switching circuits 10 is positive, the control device 51C compares the duty cycles of the two first control signals for the two first switching elements 1 of the two switching circuits 10, and shifts the high-level period of the first control signal with the relatively larger duty cycle toward a slower period, and the high-level period of the first control signal with the relatively smaller duty cycle toward an earlier period. When the polarity of the load current flowing through each of the two AC terminals 41 connected to the two switching circuits 10 is negative, the control device 51C compares the duty cycles of the two first control signals for the two first switching elements 1 of the two switching circuits 10, and shifts the high-level period of the first control signal with the relatively larger duty cycle forward, and shifts the high-level period of the first control signal with the relatively smaller duty cycle backward.

[0295] With the above configuration, it becomes possible to increase the frequency compared to the case where overlapping resonant currents are avoided by shifting the high-level period of the first control signal to the first switching element 1 of one of the two switching circuits 10 and the high-level period of the first control signal to the second switching element 2.

[0296] (Embodiment 13) The circuit configuration of the power converter 100C according to Embodiment 13 is the same as that of the power converter 100C according to Embodiment 10 (see Figure 26), so the circuit diagram is omitted. The operation of the power converter 100C according to Embodiment 13 will be described below based on Figures 26 and 32. Note that the way to read Figure 32 is the same as the way to read Figure 29.

[0297] (1) Operation (1.1) Basic Operation The basic operation is the same as in Embodiment 10, so the explanation will be omitted.

[0298] (1.2) In the power converter 100C according to the shift control embodiment 13, the shift time in the shift control executed when the control device 51C determines that the two-phase resonant currents overlap is different from the shift time when the control device 51C of embodiment 12 performs shift control.

[0299] In the power converter 100C according to Embodiment 13, the control device 51C sets the shift time of the first control signal to the first switching element 1 and the first control signal to the second switching element 2 of each of the two switching circuits 10 to an arbitrary time that is longer than the overlap time of the two-phase resonant current and less than or equal to the maximum value that can be set within one cycle of the carrier signal. The "maximum value that can be set within one cycle of the carrier signal" means the shift time when the time between the end of one cycle of the carrier signal and the end of the high-level period of the first control signal that has been shifted in the direction of delaying is a specified time or zero, and when the first control signal is shifted in the direction of advancing is a specified time or zero.

[0300] The example in Figure 32 shows that, in the case of charging a resonant capacitor, when the control device 51 determines that the resonant currents of the U-phase and V-phase flow simultaneously, it sets the shift time Tsu and shift time Tsv to the maximum value that can be set within one period of the carrier signal, which is longer than the overlap time Tov_uv.

[0301] As can be seen from the waveform of current iL1 in the lower part of Figure 32, the power converter 100C according to Embodiment 13 is able to suppress the overlap between the resonant current of the U phase and the resonant current of the V phase. As a result, the power converter 100C according to Embodiment 13 is able to perform zero-voltage soft switching of the first switching element 1U and the first switching element 1V, respectively.

[0302] The above example illustrates shift control when the control device 51C determines that the resonant currents of the U-phase and V-phase flow simultaneously. However, in both cases—when the resonant currents of the U-phase and W-phase flow simultaneously, and when the resonant currents of the V-phase and W-phase flow simultaneously—shift control is performed using the same approach (algorithm) as when the resonant currents of the U-phase and V-phase flow simultaneously.

[0303] (2) Advantages The power converter 100C according to Embodiment 13, like the power converter 100C according to Embodiment 10, can more reliably achieve zero voltage soft switching without the control device 51C directly controlling the multiple switches 8 for zero voltage soft switching.

[0304] Furthermore, in the power conversion device 100C according to embodiment 13, the control device 51C sets the shift time of the high-level period for the first control signal to the first switching element 1 and the first control signal to the second switching element 2 in each of the two switching circuits 10 to an arbitrary time that is longer than the overlap time of the two-phase resonant current and less than or equal to the maximum value that can be set within one cycle of the carrier signal.

[0305] With the above configuration, compared to the power converter 100C according to Embodiment 12, it becomes possible to distribute the period during which the resonant current flows through the resonant inductor L1, thereby reducing the thermal load on the resonant inductor L1.

[0306] (Embodiment 14) The circuit configuration of the power converter 100 according to Embodiment 14 is the same as that of the power converter 100 according to Embodiment 1 (see Figure 1), so the circuit diagram is omitted. The operation of the power converter 100 according to Embodiment 14 will be described below based on Figures 1, 33, and 34. Note that the way to read Figure 33 is the same as the way to read Figure 10. Also, the way to read Figure 34 is the same as the way to read Figure 11.

[0307] (1) Operation (1.1) Basic Operation The basic operation is the same as in Embodiment 1, so the explanation will be omitted.

[0308] (1.2) Shift control (1.2.1) When the control device 51 determines that two-phase resonant currents are flowing simultaneously, the shift control is the same as in Embodiment 1, so the explanation is omitted.

[0309] (1.2.2) When it is determined that three-phase resonant currents are flowing simultaneously (1.2.2.1) When the resonant capacitor is being charged, the control device 51 determines that three of the multiple switching circuits 10 are flowing simultaneously through the resonant inductor L1, and performs shift control on the first control signal to the first switching element 1 and the first control signal to the second switching element 2 in each of the two phases of the switching circuit 10 that are to be shifted (arbitrary) out of the three phases.

[0310] When the control device 51 performs shift control, it shifts the high-level periods of the first control signal to the first switching element 1 and the first control signal to the second switching element 2 of the two switching circuits 10 to be shifted, so that the length of the high-level period of each of the first control signals to the first switching element 1 and the first control signal to the second switching element 2 of the two switching circuits 10 to be shifted does not change.

[0311] When the control device 51 determines that resonant currents of the U-phase, V-phase, and W-phase are flowing simultaneously, it shifts two switching circuits 10 corresponding to any two of the three phases.

[0312] When the control device 51 performs shift control, it shifts 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 each of the two switching circuits 10 to be shifted, in opposite directions.

[0313] The following describes the shift control when the control device 51, for example, has two switching circuits 10 to be shifted, which are a switching circuit 10U corresponding to the U phase and a switching circuit 10W corresponding to the W phase, with reference to Figure 33.

[0314] The upper part of Figure 33 shows an example of a timing chart before the control device 51 performs shift control, and the lower part of Figure 33 shows an example of a timing chart when the control device 51 performs shift control. More specifically, the upper part of Figure 33 shows the first control signals SU1, SU2, SV1, SV2, SW1, SW2, the second control signals SU6, SU7, SV6, SV7, SW6, SW7, and current iL1 before the control device 51 determines that the resonant currents of the U-phase, V-phase, and W-phase flow simultaneously. However, in the upper part of Figure 33, the currents passing through switch 8U and resonant inductor L1, the currents passing through switch 8V and resonant inductor L1, and the currents passing through switch 8W and resonant inductor L1 are shown separately. Furthermore, the lower part of Figure 33 shows the first control signals SU1, SU2, SV1, SV2, SW1, SW2, the second control signals SU6, SU7, SV6, SV7, SW6, SW7, and the current iL1 when shift control is performed. Figure 33 also shows the timing chart for one cycle of the carrier signal.

[0315] The control device 51 shifts the high-level period of the first control signal SU1 to the first switching element 1U and the high-level period of the first control signal SU2 to the second switching element 2U of one phase switching circuit 10U of the two switching circuits 10 to be shifted in an advance direction, and shifts the high-level period of the first control signal SW1 to the first switching element 1W and the high-level period of the first control signal SW2 to the second switching element 2W of the remaining phase switching circuit 10W of the two switching circuits 10 to be shifted in an advance direction.

[0316] In this case, the control device 51 sets the shift time Tsu so that there is no overlap between the resonant current corresponding to the U-phase switching circuit 10U and the resonant current corresponding to the V-phase switching circuit 10V which is not subject to shifting (so that the resonant currents do not flow simultaneously). The control device 51 also sets the shift time Tsw so that the resonant current corresponding to the W-phase switching circuit 10W does not overlap with the resonant currents of the other two phases. Figure 33 shows an example where the shift time Tsu is set to Tsu = (Tresu / 2) + (Tresv / 2) - Tov_uv + Δ and the shift time Tsw is set to Tsw = (Tresw / 2) + (Tresv / 2) - Tov_wv + Δ. Tresu / 2 is the time width of the period during which the current iL1 flows through the U-phase switch 8U to the resonant inductor L1. Tresv / 2 is the time width of the current iL1 flowing through the V-phase switch 8V to the resonant inductor L1. Tresw / 2 is the time width of the current iL1 flowing through the W-phase switch 8W to the resonant inductor L1. Tov_uv is the length of the overlap period between the current iL1 through switch 8U and the current iL1 through switch 8V. Tov_wv is the length of the overlap period between the current iL1 through switch 8W and the current iL1 through switch 8V. Δ is the time margin to more reliably avoid the overlap of the two-phase resonant currents.

[0317] As can be seen from the waveform of current iL1 in the lower part of Figure 33, the power converter 100 is able to suppress the overlap of the resonant currents of the U phase, V phase, and W phase. As a result, the power converter 100 is able to perform zero-voltage soft switching of the first switching element 1U, the first switching element 1V, and the first switching element 1W, respectively.

[0318] Furthermore, the example in Figure 33 is not limited to this case. The high-level period of the first control signal SU1 to the first switching element 1U and the high-level period of the first control signal SU2 to the second switching element 2U may be shifted to a slower direction, while the high-level period of the first control signal SW1 to the first switching element 1W and the high-level period of the first control signal SW2 to the second switching element 2W may be shifted to a faster direction.

[0319] The above example illustrates the shift control when the control device 51 determines that three-phase resonant currents are flowing simultaneously, specifically when the shift targets are the U-phase switching circuit 10U and the W-phase switching circuit 10W. However, in cases where the shift targets are the U-phase switching circuit 10U and the V-phase switching circuit 10V, or the V-phase switching circuit 10V and the W-phase switching circuit 10W, the shift control is performed using the same approach (algorithm) as in the case where the shift targets are the U-phase switching circuit 10U and the W-phase switching circuit 10W.

[0320] (1.2.2.2) In the case of discharge operation of the resonant capacitor, if the control device 51 determines that a resonant current corresponding to each of three of the multiple switching circuits 10 flows simultaneously through the resonant inductor L1, it performs shift control on the first control signal to the first switching element 1 and the first control signal to the second switching element 2 in each of the two phases of switching circuits 10 that are to be shifted (arbitrary) out of the three phases.

[0321] When the control device 51 performs shift control, it shifts the high-level periods of the first control signal to the first switching element 1 and the first control signal to the second switching element 2 of the two switching circuits 10 to be shifted, so that the length of the high-level period of each of the first control signals to the first switching element 1 and the first control signal to the second switching element 2 of the two switching circuits 10 to be shifted does not change.

[0322] When the control device 51 determines that resonant currents of the U-phase, V-phase, and W-phase are flowing simultaneously, it shifts two switching circuits 10 corresponding to any two of the three phases.

[0323] When the control device 51 performs shift control, it shifts 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 each of the two switching circuits 10 to be shifted, in opposite directions.

[0324] The following describes the shift control when the control device 51, for example, has two switching circuits 10 to be shifted, one switching circuit 10U corresponding to the U phase and the other switching circuit 10W corresponding to the W phase, with reference to Figure 34.

[0325] The upper part of Figure 34 shows an example of a timing chart before the control device 51 performs shift control, and the lower part of Figure 34 shows an example of a timing chart when the control device 51 performs shift control. The way to read Figure 34 is the same as the way to read Figure 33.

[0326] The shift control in the control device 51 is the same as the shift control in the case of the charging operation of the resonant capacitor 9.

[0327] As can be seen from the waveform of current iL1 in the lower part of Figure 34, the power converter 100 is able to suppress the overlap of the resonant currents of the U phase, V phase, and W phase. As a result, the power converter 100 is able to perform zero-voltage soft switching of each of the second switching elements 2U, 2V, and 2W.

[0328] It should be noted that the example in Figure 34 is not limited to this case. The high-level period of the first control signal SU1 to the first switching element 1U and the high-level period of the first control signal SU2 to the second switching element 2U may be shifted to a later position, while the high-level period of the first control signal SW1 to the first switching element 1W and the high-level period of the first control signal SW2 to the second switching element 2W may be shifted to a later position.

[0329] The above example illustrates the shift control when the control device 51 determines that three-phase resonant currents are flowing simultaneously, specifically when the shift targets are the U-phase switching circuit 10U and the W-phase switching circuit 10W. However, in cases where the shift targets are the U-phase switching circuit 10U and the V-phase switching circuit 10V, or the V-phase switching circuit 10V and the W-phase switching circuit 10W, the shift control is performed using the same approach (algorithm) as in the case where the shift targets are the U-phase switching circuit 10U and the W-phase switching circuit 10W.

[0330] (2) Advantages The power converter 100 according to Embodiment 14, like the power converter 100 according to Embodiment 1, can more reliably achieve zero voltage soft switching without the control device 51 directly controlling the multiple switches 8 for zero voltage soft switching.

[0331] Furthermore, in the power conversion device 100 according to Embodiment 14, when the control device 51 determines that resonant currents corresponding to three of the multiple switching circuits 10 are simultaneously flowing through the resonant inductor L1, in the shift control, it shifts 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 each of the two switching circuits 10 in different directions.

[0332] The above configuration makes it possible to increase the frequency.

[0333] Furthermore, in the power converter 100 according to Embodiment 14, the control device 51 performs shift control whether it determines that two-phase resonant currents are flowing simultaneously through the resonant inductor L1 or whether three-phase resonant currents are flowing simultaneously. This makes it possible to achieve zero-voltage soft switching in the entire load range.

[0334] (Embodiment 15) The circuit configuration of the power converter 100A according to Embodiment 15 is the same as that of the power converter 100A according to Embodiment 2 (see Figure 12), so the circuit diagram is omitted. The operation of the power converter 100A according to Embodiment 15 will be described below based on Figures 12 and 35. Note that the way to read Figure 35 is the same as the way to read Figure 15.

[0335] (1) Operation (1.1) Basic Operation The basic operation is the same as in Embodiment 2, so the explanation will be omitted.

[0336] (1.2) Shift control (1.2.1) When the control device 51 determines that two-phase resonant currents are flowing simultaneously, the shift control is the same as in Embodiment 2, so the explanation is omitted.

[0337] (1.2.2) When it is determined that the three-phase resonant current flows simultaneously (1.2.2.1) In the case of charging operation of the resonant capacitor, the shift control of the control device 51 is the same as in Embodiment 14.

[0338] The upper part of Figure 35 shows an example of a timing chart before the control device 51 performs shift control, and the lower part of Figure 35 shows an example of a timing chart when the control device 51 performs shift control. The way to read Figure 35 is the same as the way to read Figure 33.

[0339] As can be seen from the waveform of current iL1 in the lower part of Figure 35, the power converter 100A can suppress the overlap of the resonant currents of the U phase, V phase, and W phase. As a result, the power converter 100A can perform zero-voltage soft switching of the first switching element 1U, the first switching element 1V, and the first switching element 1W.

[0340] Furthermore, the example in Figure 35 is not limited to this case. The high-level period of the first control signal SU1 to the first switching element 1U and the high-level period of the first control signal SU2 to the second switching element 2U may be shifted to a slower direction, while the high-level period of the first control signal SW1 to the first switching element 1W and the high-level period of the first control signal SW2 to the second switching element 2W may be shifted to a faster direction.

[0341] The above example illustrates the shift control when the control device 51 determines that three-phase resonant currents are flowing simultaneously, specifically when the shift targets are the U-phase switching circuit 10U and the W-phase switching circuit 10W. However, in cases where the shift targets are the U-phase switching circuit 10U and the V-phase switching circuit 10V, or the V-phase switching circuit 10V and the W-phase switching circuit 10W, the shift control is performed using the same approach (algorithm) as in the case where the shift targets are the U-phase switching circuit 10U and the W-phase switching circuit 10W.

[0342] (1.2.2.2) In the case of the discharge operation of the resonant capacitor, the shift control of the control device 51 is the same as in Embodiment 14, so the explanation is omitted.

[0343] (2) Advantages The power converter 100A according to Embodiment 15, like the power converter 100A according to Embodiment 2, can more reliably achieve zero voltage soft switching without the control device 51 directly controlling the multiple switches 8 for zero voltage soft switching.

[0344] Furthermore, in the power converter 100A according to Embodiment 15, when the control device 51 determines that resonant currents corresponding to three of the multiple switching circuits 10 flow simultaneously through the resonant inductor L1, in the shift control, it shifts 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 each of the two switching circuits 10 in different directions.

[0345] The above configuration makes it possible to increase the frequency.

[0346] Furthermore, in the power converter 100A according to embodiment 15, the control device 51 performs shift control in both cases: when it determines that two-phase resonant currents are flowing simultaneously through the resonant inductor L1, and when it determines that three-phase resonant currents are flowing simultaneously. This makes it possible to achieve zero-voltage soft switching in the entire load range.

[0347] (Embodiment 16) The circuit configuration of the power converter 100 according to Embodiment 16 is the same as that of the power converter 100 according to Embodiment 1 (see Figure 1), so the circuit diagram is omitted. The operation of the power converter 100 according to Embodiment 16 will be described below based on Figures 1 and 36.

[0348] (1) Operation (1.1) Basic Operation The basic operation is the same as in Embodiment 1, so the explanation will be omitted.

[0349] (1.2) Shift control (1.2.1) When the control device 51 determines that two-phase resonant currents are flowing simultaneously, the shift control is the same as in Embodiment 1, so the explanation is omitted.

[0350] (1.2.2) When it is determined that three-phase resonant currents are flowing simultaneously (1.2.2.1) When the resonant capacitor is being charged, the control device 51 determines that three of the multiple switching circuits 10 are flowing simultaneously through the resonant inductor L1, and performs shift control on the first control signal to the first switching element 1 and the first control signal to the second switching element 2 in each of the two phases of the switching circuit 10 that are to be shifted (arbitrary) out of the three phases.

[0351] When the control device 51 performs shift control, it shifts the high-level periods of the first control signal to the first switching element 1 and the first control signal to the second switching element 2 of the two switching circuits 10 to be shifted, so that the length of the high-level period of each of the first control signals to the first switching element 1 and the first control signal to the second switching element 2 of the two switching circuits 10 to be shifted does not change.

[0352] When the control device 51 determines that resonant currents of the U-phase, V-phase, and W-phase are flowing simultaneously, it shifts two switching circuits 10 corresponding to any two of the three phases.

[0353] When the control device 51 performs shift control, it shifts 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 same direction for each of the two switching circuits 10 to be shifted.

[0354] The following describes the shift control when the control device 51, for example, has two switching circuits 10 to be shifted, one switching circuit 10V corresponding to the V phase and the other switching circuit 10W corresponding to the W phase, with reference to Figure 36.

[0355] The upper part of Figure 36 shows an example of a timing chart before the control device 51 performs shift control, and the lower part of Figure 36 shows an example of a timing chart when the control device 51 performs shift control. The way to read Figure 36 is the same as the way to read Figure 33.

[0356] The control device 51 shifts the high-level period of the first control signal SV1 to the first switching element 1V and the high-level period of the first control signal SV2 to the second switching element 2V of the switching circuit 10V to be shifted in a way that delays them, and shifts the high-level period of the first control signal SW1 to the first switching element 1W and the high-level period of the first control signal SW2 to the second switching element 2W of the switching circuit 10W to be shifted in a way that delays them.

[0357] In this case, the control device 51 sets the shift time Tsv so that there is no overlap between the resonant current corresponding to the V-phase switching circuit 10V and the resonant current corresponding to the U-phase switching circuit 10U, which is not subject to shifting (so that the resonant currents do not flow simultaneously). The control device 51 also sets the shift time Tsw so that the resonant current corresponding to the W-phase switching circuit 10W does not overlap with the resonant currents of the other two phases. Figure 36 shows an example where the shift time Tsv is set to Tsv = (Tresv / 2) + (Tresu / 2) - Tov_uv + Δ and the shift time Tsw is set to Tsw = (Tresw / 2) + (Tresv / 2) + (Tresu / 2) - Tov_wu + Δ. Tresu / 2 is the time width of the period during which current iL1 flows through the U-phase switch 8U to the resonant inductor L1. Tresv / 2 is the time width of the current iL1 flowing through the V-phase switch 8V to the resonant inductor L1. Tresw / 2 is the time width of the current iL1 flowing through the W-phase switch 8W to the resonant inductor L1. Tov_uv is the length of the overlap period between the current iL1 flowing through switch 8U and the current iL1 flowing through switch 8V. Tov_wu is the length of the overlap period between the current iL1 flowing through switch 8W and the current iL1 flowing through switch 8U. Δ is the time margin to more reliably avoid the overlap of the two-phase resonant currents.

[0358] As can be seen from the waveform of current iL1 in the lower part of Figure 36, the power converter 100 is able to suppress the overlap of the resonant currents of the U phase, the V phase, and the W phase. As a result, the power converter 100 is able to perform zero-voltage soft switching of each of the first switching elements 1U, 1V, and 1W.

[0359] In the example shown in Figure 36, the shift time Tsw is longer than the shift time Tsv, but the shift times Tsw and Tsv may be set so that the shift time Tsw is shorter than the shift time Tsv. Furthermore, the control device 51 is not limited to the example shown in Figure 36, and may shift the high-level period of the first control signal SU1 to the first switching element 1U and the high-level period of the first control signal SU2 to the second switching element 2U in a direction that advances them, and may also shift the high-level period of the first control signal SW1 to the first switching element 1W and the high-level period of the first control signal SW2 to the second switching element 2W in a direction that advances them.

[0360] The above example illustrates the shift control when the control device 51 determines that three-phase resonant currents are flowing simultaneously, specifically when the shift targets are the V-phase switching circuit 10V and the W-phase switching circuit 10W. However, in cases where the shift targets are the U-phase switching circuit 10U and the V-phase switching circuit 10V, or the U-phase switching circuit 10U and the W-phase switching circuit 10W, the shift control is performed using the same approach (algorithm) as in the case where the shift targets are the V-phase switching circuit 10V and the W-phase switching circuit 10W.

[0361] (1.2.2.2) In the case of discharge operation of the resonant capacitor, if the control device 51 determines that a resonant current corresponding to each of three of the multiple switching circuits 10 flows simultaneously through the resonant inductor L1, it performs shift control on the first control signal to the first switching element 1 and the first control signal to the second switching element 2 in each of the two phases of switching circuits 10 that are to be shifted (arbitrary) out of the three phases.

[0362] When the control device 51 performs shift control, it shifts the high-level periods of the first control signal to the first switching element 1 and the first control signal to the second switching element 2 of the two switching circuits 10 to be shifted, so that the length of the high-level period of each of the first control signals to the first switching element 1 and the first control signal to the second switching element 2 of the two switching circuits 10 to be shifted does not change.

[0363] When the control device 51 determines that resonant currents of the U-phase, V-phase, and W-phase are flowing simultaneously, it shifts two switching circuits 10 corresponding to any two of the three phases.

[0364] When the control device 51 performs shift control, it shifts 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 same direction (advancing them on the time axis) for each of the two switching circuits 10 to be shifted. For example, the setting examples of the shift times Tsv and Tsw are the same as the setting examples of the shift times Tsv and Tsw in the case of the charging operation of the resonant capacitor 9.

[0365] (2) Advantages The power converter 100 according to Embodiment 16, like the power converter 100 according to Embodiment 1, can more reliably achieve zero voltage soft switching without the control device 51 directly controlling the multiple switches 8 for zero voltage soft switching.

[0366] Furthermore, in the power conversion device 100 according to Embodiment 16, when the control device 51 determines that resonant currents corresponding to three of the multiple switching circuits 10 flow simultaneously through the resonant inductor L1, in the shift control, it shifts 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 each of the two switching circuits 10 in the same direction.

[0367] The above configuration makes it possible to increase the frequency.

[0368] Furthermore, in the power converter 100 according to embodiment 16, the control device 51 performs shift control in both cases: when it determines that two-phase resonant currents are flowing simultaneously through the resonant inductor L1, and when it determines that three-phase resonant currents are flowing simultaneously. This makes it possible to achieve zero-voltage soft switching in the entire load range.

[0369] (Embodiment 17) The circuit configuration of the power converter 100 according to Embodiment 17 is the same as that of the power converter 100 according to Embodiment 1 (see Figure 1), so the circuit diagram is omitted. The operation of the power converter 100 according to Embodiment 17 will be described below based on Figures 1 and 37.

[0370] (1) Operation (1.1) Basic Operation The basic operation is the same as in Embodiment 1, so the explanation will be omitted.

[0371] (1.2) Shift control (1.2.1) When the control device 51 determines that two-phase resonant currents are flowing simultaneously, the shift control is the same as in Embodiment 1, so the explanation is omitted.

[0372] (1.2.2) When it is determined that the three-phase resonant currents flow simultaneously, in the power converter 100 according to Embodiment 17, the operation of the shift control performed by the control device 50 when it is determined that the three-phase resonant currents overlap differs from the operation of the shift control device 51 in Embodiment 15. In Embodiment 17, the control device 51 performs shift control so that the resonant currents do not overlap in each combination of one of the three switching circuits 10 and the remaining two switching circuits 10.

[0373] In this embodiment, when the control device 51 determines that a resonant current corresponding to each of the three switching circuits 10 flows simultaneously through the resonant inductor L1, it performs a first shift control as a shift control when the first condition is met in the case of a charging operation to charge the multiple resonant capacitors 9, and performs a second shift control as a shift control when the second condition is met in the case of a discharge operation to discharge the multiple resonant capacitors 9.

[0374] The first condition is that the time difference between the start times of the high-level periods of the first control signal having the longest high-level period and the first control signal having the shortest high-level period among the first control signals SU1, SV1, and SW1 applied to each of the three first switching elements 1 is longer than the resonant half-period Tres. The resonant half-period Tres is half the value of the resonant period, which is determined by the reciprocal of the resonant frequency of the resonant circuit including the resonant inductor L1 and one of the multiple resonant capacitors 9. The first shift control includes a control that shifts the high-level period of the first control signal applied to the first switching element 1 that receives the first control signal having the second longest high-level period among the first control signals SU1, SV1, and SW1 applied to each of the three first switching elements 1. The second condition is that the time difference between the start times of the high-level periods of the first control signal having the longest high-level period among the first control signals SU2, SV2, and SW2 applied to each of the three second switching elements 2 is longer than the resonant half-period Tres. The second shift control includes a control that shifts the high-level period of the first control signal applied to the second switching element 2 that receives the first control signal having the second longest high-level period among the first control signals SU2, SV2, and SW2 applied to each of the three second switching elements 2. When the control device 51 performs shift control (first shift control or second shift control), it shifts the high-level period of the first control signal so that the length of the high-level period of the first control signal does not change.

[0375] An example of operation when the control device 51 performs first shift control will be explained with reference to Figure 37. The upper part of Figure 37 shows an example of a timing chart before the control device 51 performs shift control, and the lower part of Figure 37 shows an example of a timing chart when the control device 51 performs shift control. The way to read Figure 37 is the same as the way to read Figure 33.

[0376] In the example shown in Figure 37, since [length of high-level period of first control signal SU1] > [length of high-level period of first control signal SV1] > [length of high-level period of first control signal SW1], the control device 51 shifts the high-level periods of the first control signal SV1 and the first control signal SV2 by a shift time Tsv in the direction of advancing them.

[0377] Figure 37 shows an example where the shift time Tsv is set to Tsv = (Tresu / 2) + (Tresuv / 2) - Tov_vu + Δ. Tresu / 2 is the time width of the period during which current iL1 flows through the U-phase switch 8U to the resonant inductor L1. Tresuv / 2 is the time width of the current iL1 flowing through the V-phase switch 8V to the resonant inductor L1. Tov_vu is the length of the overlap period between the current iL1 flowing through switch 8V and the current iL1 flowing through switch 8U. Δ is a time margin to more reliably avoid the overlap of the two-phase resonant currents.

[0378] As can be seen from the waveform of current iL1 in the lower part of Figure 37, the power converter 100 is able to suppress the overlap of the resonant currents of the U phase, V phase, and W phase. As a result, the power converter 100 is able to perform zero-voltage soft switching of each of the first switching elements 1U, 1V, and 1W.

[0379] Furthermore, the direction in which the high-level period of the first control signal SV1 and the high-level period of the first control signal SV2 are shifted is not limited to the direction of advancing the high-level period; it may also be the direction of delaying the high-level period.

[0380] Furthermore, in the power conversion device 100 according to Embodiment 17, the control device 51 performs a second shift control when the second condition is met, thereby enabling zero-voltage shift switching of the second switching elements 2U, 2V, and 2W.

[0381] (2) Advantages The power converter 100 according to Embodiment 17, like the power converter 100 according to Embodiment 1, can more reliably achieve zero voltage soft switching without the control device 51 directly controlling the multiple switches 8 for zero voltage soft switching.

[0382] Furthermore, in the power conversion device 100 according to Embodiment 17, when the control device 51 determines that a resonant current corresponding to each of the three switching circuits 10 flows simultaneously through the resonant inductor L1, it performs a first shift control when the first condition is met in the case of a charging operation to charge the multiple resonant capacitors 9, and performs a second shift control when the second condition is met in the case of a discharge operation to discharge the multiple resonant capacitors 9. The first condition is that the time difference between the start times of the high-level periods of the first control signal having the longest high-level period and the first control signal having the shortest high-level period among the three first control signals given to the three first switching elements 1 is longer than the resonant half-period. The resonant half-period is half the value of the resonant period determined by the reciprocal of the resonant frequency of the resonant circuit including the resonant inductor L1 and one of the multiple resonant capacitors 9. The first shift control includes a control to shift the high-level period of the first control signal having the second longest high-level period among the three first control signals given to the three first switching elements 1. The second condition is that the time difference between the start times of the high-level periods of the first control signal having the longest high-level period and the first control signal having the shortest high-level period among the three first control signals given to the three second switching elements 2 is longer than the resonant half-period. The second shift control includes a control that shifts the high-level period of the first control signal having the second longest high-level period among the three first control signals given to the three second switching elements 2.

[0383] The above configuration makes it possible to suppress changes in line voltage.

[0384] Furthermore, in the power converter 100 according to Embodiment 17, the control device 51 performs shift control whether it determines that two-phase resonant currents are flowing simultaneously through the resonant inductor L1 or whether three-phase resonant currents are flowing simultaneously. This makes it possible to achieve zero-voltage soft switching in the entire load range.

[0385] (Embodiment 18) The power converter 100 according to Embodiment 18 will be described with reference to Figure 38. With respect to the power converter 100 according to Embodiment 18, components that are the same as those in the power converter 100 according to Embodiment 1 (see Figure 1) are denoted by the same reference numerals and their description is omitted.

[0386] In the power conversion device 100 according to Embodiment 18, the third switching element 6 and the fourth switching element 7 are connected in reverse series in each of the multiple switches 8. In the power conversion device 100 according to Embodiment 18, the second main terminal (emitter terminal) of the third switching element 6 and the second main terminal (emitter terminal) of the fourth switching element 7 are connected in each of the multiple switches 8, the first main terminal (collector terminal) of the third switching element 6 is connected to the connection point 3 of the corresponding switching circuit 10 among the multiple switching circuits 10, and the first terminal (collector terminal) of the fourth switching element 7 is connected to the resonant inductor L1. Furthermore, each of the multiple switches 8 further includes a diode 61 connected in reverse parallel to the third switching element 6 and a diode 71 connected in reverse parallel to the fourth switching element 7.

[0387] In the power conversion device 100 according to Embodiment 18, the third switching element 6 and the fourth switching element 7 may each be replaced with a MOSFET or a bipolar transistor. In this case, the diodes 61 and 71 in Figure 38 may each be replaced with parasitic diodes of the replaced elements, or elements built into a single chip of the replaced elements. Furthermore, in the power conversion device 100 according to Embodiment 18, the diodes 61 and 71 are not limited to being externally attached to the third switching element 6 and the fourth switching element 7, but may also be elements built into a single chip.

[0388] The power converter 100 according to Embodiment 18 offers the same advantages as the power converter 100 according to Embodiment 1.

[0389] (Embodiment 19) The power converter 100 according to Embodiment 19 will be described with reference to Figure 39. With respect to the power converter 100 according to Embodiment 19, components that are the same as those in the power converter 100 according to Embodiment 1 (see Figure 1) are denoted by the same reference numerals and their description is omitted.

[0390] In the power converter 100 according to Embodiment 19, in each of the plurality of switches 8, the third switching element 6 and the fourth switching element 7 are each MOSFETs, and the third switching element 6 and the fourth switching element 7 are connected in reverse series. In the power converter 100 according to Embodiment 19, in each of the plurality of switches 8, the first main terminal (drain terminal) of the third switching element 6 is connected to the first main terminal (drain terminal) of the fourth switching element 7. Furthermore, each of the plurality of switches 8 has a diode 61 connected in reverse parallel to the third switching element 6 and a diode 71 connected in reverse parallel to the fourth switching element 7. In each of the plurality of switches 8, the second main terminal (source terminal) of the fourth switching element 7 is connected to a resonant inductor L1. In each of the plurality of switches 8, the second main terminal (source terminal) of the third switching element 6 is connected to the connection point 3 of the switching circuit 10 corresponding to the switch 8 having the third switching element 6.

[0391] The power converter 100 according to Embodiment 19 offers the same advantages as the power converter 100 according to Embodiment 1.

[0392] (Embodiment 20) The power converter 100 according to Embodiment 20 will be described with reference to Figure 40. With respect to the power converter 100 according to Embodiment 20, components that are the same as those in the power converter 100 according to Embodiment 1 (see Figure 1) are denoted by the same reference numerals and their description is omitted.

[0393] In the power conversion device 100 according to Embodiment 20, in each of the multiple switches 8, the third switching element 6 and the fourth switching element 7 are MOSFETs, a diode 63 is connected in series with the third switching element 6, and a diode 73 is connected in series with the fourth switching element 7. In the power conversion device 100 according to Embodiment 20, in each of the multiple switches 8, the series circuit of the third switching element 6 and the diode 63 and the series circuit of the fourth switching element 7 and the diode 73 are connected in antiparallel.

[0394] The power converter 100 according to Embodiment 20 offers the same advantages as the power converter 100 according to Embodiment 1.

[0395] (Modifications) Embodiments 1 to 20 described above are merely one of many embodiments of the present disclosure. Embodiments 1 to 20 described above can be modified in various ways depending on the design, etc., as long as the objectives of the present disclosure are achieved.

[0396] For example, the power converters 100, 100B, and 100C according to Embodiment 1 may be configured without the first clamp diode 13 and the second clamp diode 14.

[0397] Furthermore, the signal generation circuits 52 and 52A may be configured to generate a second control signal for each of the plurality of switches 8 using at least one of the first control signal to the first switching element 1 and the first control signal to the second switching element 2 of the corresponding switching circuit 10 among the plurality of switching circuits 10.

[0398] Furthermore, in the power conversion device 100 according to Embodiment 1, the diodes 61 and 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 a single chip.

[0399] Furthermore, in power converters 100A to 100C, the configuration of switch 8 is the same as that of switch 8 in power converter 100 according to Embodiment 1, but it may also be the same as that of switch 8 in any of Embodiments 18 to 20.

[0400] Furthermore, in power converters 100, 100A to 100C, if the capacitance of each of the multiple resonant capacitors 9 is relatively small, instead of externally mounting multiple resonant capacitors 9, the parasitic capacitance between the ends of the multiple second switching elements 2 may serve as the multiple resonant capacitors 9.

[0401] Furthermore, in power converters 100, 100A to 100C, the length of the first dead time period Td1 is set to be the same as the resonant half-period, but it may be set to a length different from the resonant half-period.

[0402] Furthermore, the power converters 100, 100A to 100C may also include a second regenerative capacitor connected between the sixth terminal 154 of the regenerative capacitor 15 (hereinafter also referred to as the first regenerative capacitor 15) and the first DC terminal 31. The capacitance of the second regenerative capacitor is the same as the capacitance of the first regenerative capacitor 15. "The capacitance of the second regenerative capacitor is the same as the capacitance of the first regenerative capacitor 15" is not limited to the case where the capacitance of the second regenerative capacitor perfectly matches the capacitance of the first regenerative capacitor 15, but is sufficient if the capacitance of the second regenerative capacitor is within the range of 90% to 110% of the capacitance of the first regenerative capacitor 15.

[0403] Furthermore, the power converters 100, 100A to 100C are not limited to a configuration that outputs three-phase AC, but may be configured to output three or more phases of multi-phase AC.

[0404] (Aspects) The following aspects are disclosed herein.

[0405] The power conversion device (100; 100A; 100B; 100C) according to the first embodiment comprises a first DC terminal (31) and 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), a control device (51; 51B; 51C), and a signal generation circuit (52; 52A). 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 in which a plurality of first switching elements (1) and a plurality of second switching elements (2) are connected in series at a connection point (3) in a one-to-one relationship, are connected in parallel with each other. In the power conversion circuit (11), multiple first switching elements (1) are connected to the first DC terminal (31). In the power conversion circuit (11), multiple second switching elements (2) are connected to the second DC terminal (32). Multiple AC terminals (41) correspond one-to-one with multiple switching circuits (10). Each of the multiple AC terminals (41) is connected to the connection point (3) of the first switching element (1) and the second switching element (2) in the corresponding switching circuit (10) among the multiple switching circuits (10), and load current flows through it. Multiple switches (8) correspond one-to-one with multiple switching circuits (10). Each of the multiple switches (8) has a first terminal (81) and a second terminal (82), and the first terminal (81) is connected to the connection point (3) of the first switching element (1) and the second switching element (2) in the corresponding switching circuit (10) among the multiple switching circuits (10). Multiple resonant capacitors (9) correspond one-to-one with multiple switches (8). Each of the multiple resonant capacitors (9) is connected between the first terminal (81) and the second DC terminal (32) of the corresponding switch (8) among the multiple switches (8). At least one resonant inductor (L1) has a third terminal and a fourth terminal. In at least one resonant inductor (L1), the third terminal is connected to the second terminal (82) of the corresponding switch (8) among the multiple switches (8). The regenerative capacitor (15) has a fifth terminal (153) and a sixth terminal (154).In the regenerative capacitor (15), the fifth terminal (153) is connected to the second DC terminal (32), and the sixth terminal (154) is connected to the fourth terminal of at least one resonant inductor (L1). The control devices (51; 51B; 51C) provide each of the plurality of first switching elements (1) and the plurality of second switching elements (2) with a first control signal whose potential changes between a high level during the high-level period and a low level during the low-level period. The signal generation circuits (52; 52A) provide each of the plurality of switches (8) with a second control signal whose potential changes between a high level during the high-level period and a low level during the low-level period. The control devices (51; 51B; 51C) set a second dead time period (Td2) for each of the plurality of switching circuits (10) by adding a predetermined time (additional time Tad) to a first dead time period (Td1) which is set so that the ON periods of the first switching element (1) and the second switching element (2) do not overlap 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). The predetermined time (additional time Tad) is determined according to the current value of the load current, the inductance of the resonant inductor (L1), and the voltage value of the regenerative capacitor (15). The signal generation circuits (52; 52A) generate a second control signal for each of the plurality of switches (8) which has 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). If the control device (51; 51B; 51C) determines that resonant currents corresponding to two or more switching circuits (10) among the multiple switching circuits (10) flow simultaneously through the resonant inductor (L1), it performs shift control to shift the high-level period of the first control signal to the first switching element (1) and the first control signal to the second switching element (2) in at least one of the two or more switching circuits (10) so that resonant currents corresponding to two or more switching circuits (10) flow simultaneously through the resonant inductor (L1).

[0406] According to this embodiment, zero-voltage soft switching can be achieved in the control device (51; 51B; 51C) without directly controlling the multiple switches (8) for zero-voltage soft switching.

[0407] The power converter (100; 100A) according to the second embodiment further comprises, in the first embodiment, a first clamp diode (13) and a second clamp diode (14). The first clamp diode (13) has its anode connected to the third end of a resonant inductor (L1) and its cathode connected to a first DC terminal (31). The second clamp diode (14) has its cathode connected to the third end of a resonant inductor (L1) and its anode connected to a second DC terminal (32). When the control device (51) sets a 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 predetermined time (additional time Tad) 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, it adds a predetermined time (additional time Tad) to the first dead time period (Td1) by shortening the high-level period of the first control signal to the first switching element (1).

[0408] According to this embodiment, it is possible to achieve zero-voltage soft switching while further reducing dead time loss and dead time error.

[0409] In the power converter (100B) according to the third embodiment, in the first embodiment, when the control device (51B) sets a second dead time period (Td2) for each of the plurality of switching circuits (10), if the polarity of the load current is positive, it adds a predetermined time (Ta11 + Ta21) to the first dead time period (Td1) by advancing the end time of the high-level period of the first control signal to the second switching element (2) and delaying the start time of 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, it adds a predetermined time (Ta12 + Ta22) to the first dead time period (Td1) by advancing the end time of the high-level period of the first control signal to the first switching element (1) and delaying the start time of the high-level period of the first control signal to the second switching element (2).

[0410] According to this embodiment, it is possible to achieve zero-voltage soft switching while reducing dead time loss and dead time error.

[0411] In the power converter (100C) according to the fourth embodiment, in the first embodiment, when the control device (51C) sets a second dead time period (Td2) for each of the plurality of switching circuits (10), if the polarity of the load current is positive, a predetermined time (additional time Tad) 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 predetermined time (additional time Tad) 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).

[0412] According to this embodiment, zero-voltage soft switching can be achieved.

[0413] In the power converter (100; 100A; 100B; 100C) according to the fifth embodiment, in any one of the first to fourth embodiments, the control device (51; 51B; 51C) shifts the high-level periods of the first control signal to the first switching element (1) and the first control signal to the second switching element (2) of the at least one switching circuit (10) when performing shift control, so as not to change the length of the high-level period of the first control signal to the first switching element (1) and the first control signal to the second switching element (2) of the at least one switching circuit (10).

[0414] According to this embodiment, it is possible to suppress changes in line voltage.

[0415] In the power converter according to the sixth embodiment (100; 100A; 100B; 100C), in any one of the first to fifth embodiments, the control device (51; 51B; 51C) performs shift control by shifting 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 each of the two or more switching circuits (10) in opposite directions.

[0416] According to this embodiment, it becomes possible to increase the frequency.

[0417] In the power converter according to the seventh embodiment (100; 100A; 100B; 100C), in any one of the first to sixth embodiments, if the control device (51; 51B; 51C) determines that resonant currents corresponding to two of the multiple switching circuits (10) flow simultaneously through the resonant inductor (L1), and the polarity of the load current flowing through the two AC terminals (41) connected to the two switching circuits (10) is positive, the control device compares the duty cycles of two first control signals for the two first switching elements (1) of the two switching circuits (10), and shifts the high-level period of the first control signal with the relatively larger duty cycle forward, and shifts the high-level period of the first control signal with the relatively smaller duty cycle backward. When the polarity of the load current flowing through each of the two AC terminals (41) connected to the two switching circuits (10) among the plurality of AC terminals (41) is negative, the control device (51) compares the duty cycles of the two first control signals for the two first switching elements (1) of the two switching circuits (10), and shifts the high-level period of the first control signal with the relatively larger duty cycle toward a slower direction, and shifts the high-level period of the first control signal with the relatively smaller duty cycle toward an earlier direction.

[0418] According to this embodiment, it becomes possible to increase the frequency.

[0419] In the power converter according to the eighth embodiment (100; 100A; 100B; 100C), in any one of the first to sixth embodiments, if the control device (51; 51B; 51C) determines that resonant currents corresponding to two of the multiple switching circuits (10) flow simultaneously through the resonant inductor (L1), and the polarity of the load current flowing through the two AC terminals (41) connected to the two switching circuits (10) is positive, the control device compares the duty cycles of the two first control signals for the two first switching elements (1) of the two switching circuits (10), and shifts the high-level period of the first control signal with the relatively larger duty cycle toward the latent direction, and the high-level period of the first control signal with the relatively smaller duty cycle toward the early direction. When the polarity of the load current flowing through each of the two AC terminals (41) connected to two of the multiple AC terminals (41) connected to the two switching circuits (10) is negative, the control device (51) compares the duty cycles of the two first control signals for the two first switching elements (1) of the two switching circuits (10), and shifts the high-level period of the first control signal with the relatively larger duty cycle forward, and shifts the high-level period of the first control signal with the relatively smaller duty cycle backward.

[0420] According to this embodiment, it becomes possible to increase the frequency.

[0421] In the power converter according to the ninth embodiment (100; 100A; 100B; 100C), in any one of the first to eighth embodiments, if the control device (51) determines that a resonant current corresponding to each of three of the multiple switching circuits (10) flows simultaneously through the resonant inductor (L1), in the shift control, 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 each of the three switching circuits (10) are shifted in the same direction in the two switching circuits (10).

[0422] According to this embodiment, it becomes possible to increase the frequency.

[0423] In the power converter according to the tenth embodiment (100; 100A; 100B; 100C), in any one of the first to eight embodiments, a plurality of first switching elements (1) includes three first switching elements (1), a plurality of second switching elements (2) includes three second switching elements (2), and a plurality of switches (8) includes three switches (8). When the control device (51; 51B; 51C) determines that a resonant current corresponding to three of the plurality of switching circuits (10) flows simultaneously through the resonant inductor (L1), it performs a first shift control when the first condition is met in the case of a charging operation to charge a plurality of resonant capacitors (9), and performs a second shift control when the second condition is met in the case of a discharge operation to discharge a plurality of resonant capacitors (9). The first condition is that the time difference between the start times of the high-level periods of the first control signal having the longest high-level period and the first control signal having the shortest high-level period among the three first control signals given to the three first switching elements (1) is longer than the resonant half-period. The resonant half-period is half the value of the resonant period, which is determined by the reciprocal of the resonant frequency of the resonant circuit including the resonant inductor (L1) and one of the multiple resonant capacitors (9). The first shift control includes a control that shifts the high-level period of the first control signal having the second longest high-level period among the three first control signals given to the three first switching elements (1). The second condition is that the time difference between the start times of the high-level periods of the first control signal having the longest high-level period and the first control signal having the shortest high-level period among the three first control signals given to the three second switching elements (2) is longer than the resonant half-period. The second shift control includes a control that shifts the high-level period of the first control signal having the second longest high-level period among the three first control signals given to the three second switching elements (2).

[0424] According to this embodiment, it is possible to suppress changes in line voltage.

[0425] 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 51, 51B, 51C Control device 52, 52A Signal generation circuit 100, 100A, 100B, 100C Power converter iU, iV, iW Output current (load current) L1 Resonant inductor RA1 AC load SU1, SU2, SV1, SV2, SW1, SW2 First control signal SU6, SU7, SU8, SV6, SV7, SV8, SW6, SW7, SW8 Second control signal Ta11 Time Ta12 Time Ta21 Time Ta22 Time Tad Additional time Td1 First dead time period Td2 Second dead time period

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 the plurality of first switching elements and the plurality of second switching elements are connected in series with each other at a connection point, and 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 point of the first switching element and the second switching element in the corresponding switching circuit, through which load current flows, a plurality of switches each having a first end and a second end, corresponding one-to-one to the plurality of switching circuits, with the first end connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit, a plurality of resonant capacitors corresponding one-to-one to the plurality of switches, each connected between the first end and the second DC terminal of the corresponding switch, The system comprises: a resonant inductor having a third and a fourth terminal, the third terminal of which is connected to the second terminal of the plurality of switches; a regenerative capacitor having a fifth and a sixth terminal, the fifth terminal of which is connected to the second DC terminal, and the sixth terminal of which is connected to the fourth terminal of the resonant inductor; a control device that 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 during a high-level period and a low level during a low-level period; and a signal generation circuit that provides each of the plurality of switches with a second control signal whose potential changes between a high level during a high-level period and a low level during a low-level period, wherein the control device sets a second dead time period for each of the plurality of switching circuits, which is a predetermined time added to a first dead time period that is set in advance 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 predetermined time is determined according to the current value of the load current, the inductance of the resonant inductor, and the voltage value of the regenerative capacitor. The signal generation circuit generates a second control signal for each of the plurality of switches, 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 device, when it determines that resonant currents corresponding to two or more of the plurality of switching circuits flow simultaneously through the resonant inductor, performs shift control to shift the high-level periods of the first control signal to the first switching element and the first control signal to the second switching element in at least one of the two or more switching circuits, so that the resonant currents corresponding to two or more of the switching circuits flow simultaneously through the resonant inductor.

2. The power conversion device according to claim 1, further comprising: a first clamp diode having its anode connected to the third end of the resonant inductor and its cathode connected to the first DC terminal; and a second clamp diode having its cathode connected to the third end of the resonant inductor and its anode connected to the second DC terminal, wherein when the control device sets the second dead time period for each of the plurality of switching circuits, if the polarity of the load current is positive, it adds the predetermined time to the first dead time period by shortening the high-level period of the first control signal to the second switching element; and if the polarity of the load current is negative, it adds the predetermined time to the first dead time period by shortening the high-level period of the first control signal to the first switching element.

3. The power conversion device according to claim 1, wherein when the control device sets the second dead time period for each of the plurality of switching circuits, if the polarity of the load current is positive, it adds the predetermined time to the first dead time period by advancing the end time of the high-level period of the first control signal to the second switching element and delaying the start time of the high-level period of the first control signal to the first switching element, and if the polarity of the load current is negative, it adds the predetermined time to the first dead time period by advancing the end time of the high-level period of the first control signal to the first switching element and delaying the start time of the high-level period of the first control signal to the second switching element.

4. The power conversion device according to claim 1, wherein when the control device sets the second dead time period for each of the plurality of switching circuits, if the polarity of the load current is positive, it adds the predetermined time to the first dead time period by shortening the high-level period of the first control signal to the first switching element, and if the polarity of the load current is negative, it adds the predetermined time to the first dead time period by shortening the high-level period of the first control signal to the second switching element.

5. The power conversion device according to any one of claims 1 to 4, wherein when the control device performs the shift control, it shifts the high-level periods of the first control signal to the first switching element and the first control signal to the second switching element of the at least one switching circuit so that the length of the high-level period of each of the first control signal to the first switching element and the first control signal to the second switching element of the at least one switching circuit does not change.

6. The power conversion device according to any one of claims 1 to 5, wherein when the control device performs the shift control, it shifts the high-level period of the first control signal to the first switching element and the high-level period of the first control signal to the second switching element in each of the two or more switching circuits in different directions.

7. The power conversion device according to any one of claims 1 to 6, wherein the control device determines that a resonant current corresponding to each of the two switching circuits among the plurality of switching circuits flows simultaneously through the resonant inductor, and when the polarity of the load current flowing through each of the two AC terminals among the plurality of AC terminals connected to the two switching circuits is positive, it compares the duty cycles of the two first control signals for the two first switching elements of the two switching circuits, and shifts the high-level period of the first control signal with a relatively large duty cycle in the direction of advancing, and the high-level period of the first control signal with a relatively small duty cycle in the direction of delaying, and when the polarity of the load current flowing through each of the two AC terminals among the plurality of AC terminals connected to the two switching circuits is negative, it compares the duty cycles of the two first control signals for the two first switching elements of the two switching circuits, and shifts the high-level period of the first control signal with a relatively large duty cycle in the direction of delaying, and shifts the high-level period of the first control signal with a relatively small duty cycle in the direction of advancing.

8. The power conversion device according to any one of claims 1 to 6, wherein the control device determines that a resonant current corresponding to each of the two switching circuits among the plurality of switching circuits flows simultaneously through the resonant inductor, and when the polarity of the load current flowing through each of the two AC terminals among the plurality of AC terminals connected to the two switching circuits is positive, it compares the duty cycles of the two first control signals for the two first switching elements of the two switching circuits, and shifts the high-level period of the first control signal with a relatively large duty cycle toward a slower direction and the high-level period of the first control signal with a relatively small duty cycle toward a faster direction; and when the polarity of the load current flowing through each of the two AC terminals among the plurality of AC terminals connected to the two switching circuits is negative, it compares the duty cycles of the two first control signals for the two first switching elements of the two switching circuits, and shifts the high-level period of the first control signal with a relatively large duty cycle toward a faster direction and the high-level period of the first control signal with a relatively small duty cycle toward a slower direction.

9. The power conversion device according to any one of claims 1 to 8, wherein the control device determines that a resonant current corresponding to each of the three switching circuits among the plurality of switching circuits flows simultaneously through the resonant inductor, and in the shift control, shifts the high-level period of the first control signal to the first switching element and the high-level period of the first control signal to the second switching element in each of the two switching circuits among the three switching circuits in the same direction.

10. The plurality of first switching elements includes three of the first switching elements, the plurality of second switching elements includes three of the second switching elements, the plurality of switches includes three of the switches, and when the control device determines that a resonant current corresponding to each of the three switching circuits among the plurality of switching circuits flows simultaneously through the resonant inductor, it performs a first shift control when a first condition is met during a charging operation to charge the plurality of resonant capacitors, the first condition is that the time difference between the start times of the high-level periods of the first control signal having the longest high-level period and the first control signal having the shortest high-level period among the three first control signals given to the three first switching elements is longer than the resonant half-period, the resonant half-period is half the value of the resonant period determined by the reciprocal of the resonant frequency of the resonant circuit including the resonant inductor and one of the plurality of resonant capacitors, and the first shift control includes a control to shift the high-level period of the first control signal having the second longest high-level period among the three first control signals given to the three first switching elements. In the case of a discharge operation that discharges the plurality of resonant capacitors, a second shift control is performed when a second condition is met, the second condition being that the time difference between the start times of the high-level periods of the first control signal having the longest high-level period and the first control signal having the shortest high-level period among the three first control signals given to the three second switching elements is longer than the half-period of the resonance, and the second shift control includes a control that shifts the high-level period of the first control signal having the second longest high-level period among the three first control signals given to the three second switching elements, according to any one of claims 1 to 8.

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