Power conversion device

Abstract

The present invention addresses the problem of improving power conversion efficiency. A control device (50) of a power conversion device (100) performs a first control operation in which the high-level periods of control signals for switches (8) of a plurality of switches (8) corresponding to a plurality of respective switching circuits (10) are overlapped with a dead time and the start times of the high-level periods are advanced from the start time of the dead time by an additional time. The control device (50) switches between a second control operation in which the high-level periods of the control signals for two switches (8) of the plurality of switches (8) are overlapped with each other on the basis of the detected voltage potential at the fourth end (154) of a regenerative capacitor (15) and the polarities of a plurality of output currents (iU, iV, iW) output from a plurality of AC terminals (41) and a third control operation in which the high-level periods of the control signals for the plurality of switches (8) are not overlapped with each other.

Description

Power Conversion Device

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

[0002] Patent Document 1 discloses a power conversion device that converts direct current into multi-phase alternating current.

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

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

[0005] JP 2010-233306 A

[0006] An object of the present disclosure is to provide a power conversion device that can improve power conversion efficiency.

[0007] A power conversion device according to one aspect of the present disclosure includes a first DC terminal and a second DC terminal, a power conversion circuit, multiple AC terminals, multiple switches, multiple resonant capacitors, a resonant inductor, a regenerative capacitor, and a control device. The power conversion circuit includes multiple first switching elements and multiple second switching elements. In the power conversion circuit, multiple switching circuits are connected in parallel, with the multiple first switching elements and the multiple second switching elements connected in series in a one-to-one relationship. In the power conversion circuit, the multiple first switching elements are connected to the first DC terminals, and the multiple second switching elements are connected to the second DC terminals. The multiple AC terminals correspond one-to-one to the multiple switching circuits. Each of the multiple AC terminals is connected to a connection point between the first switching element and the second switching element in the corresponding switching circuit. The multiple switches correspond one-to-one to the multiple switching circuits. Each of the plurality of switches has a first end connected to the connection point between the first switching element and the second switching element in the corresponding switching circuit, and a second end commonly connected to a common connection point. The plurality of resonant capacitors correspond one-to-one to the plurality of switches. Each of the plurality of resonant capacitors is connected between the first end and the second DC terminal of the corresponding switch. The resonant inductor has a first end and a second end. The first end of the resonant inductor is connected to the common connection point. The regenerative capacitor has a third end and a fourth end. The third end of the regenerative capacitor is connected to the first DC terminal or the second DC terminal. The control device provides a PWM signal whose potential changes between a high level and a low level to each of the plurality of first switching elements and the plurality of second switching elements. The control device performs a first control operation. In the first control operation, the control device sets a dead time between a high level period of the PWM signal to the first switching element and a high level period of the PWM signal to the second switching element for each of the plurality of switching circuits.In the first control operation, the control device overlaps a high-level period of a control signal for a switch among the plurality of switches corresponding to each of the plurality of switching circuits with the dead time and advances a start point of the high-level period by an additional time from a start point of the dead time. The control device switches between a second control operation in which high-level periods of control signals for two of the plurality of switches overlap, and a third control operation in which high-level periods of control signals for the plurality of switches do not overlap, based on a detected potential at the fourth end of the regenerative capacitor and polarities of a plurality of output currents output from the plurality of AC terminals.

[0008] A power conversion device according to another aspect of the present disclosure includes a first DC terminal and a second DC terminal, a power conversion circuit, a plurality of AC terminals, a plurality of switches, a plurality of resonant circuits, a regenerative capacitor, and a control device. The power conversion circuit includes a plurality of first switching elements and a plurality of second switching elements. In the power conversion circuit, a plurality of switching circuits are connected in parallel, each of which has the plurality of first switching elements and the plurality of second switching elements connected in series in a one-to-one relationship. In the power conversion circuit, 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. 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 a connection point between the first switching element and the second switching element in the corresponding switching circuit. The plurality of switches correspond one-to-one to the plurality of switching circuits. A first end of each of the plurality of switches is connected to the connection point between the first switching element and the second switching element in the corresponding switching circuit. The plurality of resonant circuits correspond one-to-one to the plurality of switches and have variable resonant frequencies. The regenerative capacitor has a third terminal and a fourth terminal. The third terminal of the regenerative capacitor is connected to the first DC terminal or the second DC terminal, and the fourth terminal is connected to the plurality of resonant circuits. The control device applies a PWM signal whose potential changes between a high level and a low level to each of the plurality of first switching elements and the plurality of second switching elements. Each of the plurality of resonant circuits includes a resonant capacitor connected between the first terminal and the second DC terminal of a corresponding switch among the plurality of switches, and a resonant inductor connected between the second terminal of the corresponding switch among the plurality of switches and the fourth terminal of the regenerative capacitor. The control device sets a dead time for each of the plurality of switching circuits between a high-level period of a PWM signal to the first switching element and a high-level period of a PWM signal to the second switching element. The control device performs a first control operation.In the first control operation, the control device overlaps a high-level period of a control signal to a switch among the plurality of switches corresponding to each of the plurality of switching circuits with the dead time, and advances a start point of the high-level period by an additional time from a start point of the dead time. The control device changes a resonant frequency of at least one of the plurality of resonant circuits according to a potential of the fourth end of the regenerative capacitor.

[0009] FIG. 1 is a circuit diagram of a system including a power conversion apparatus according to a first embodiment. FIG. 2 is an explanatory diagram of an operation of the power conversion apparatus when a control device performs a first control operation. FIG. 3 is another explanatory diagram of an operation of the power conversion apparatus when a control device performs a first control operation. FIG. 4 is an explanatory diagram of an operation of the control device in the power conversion apparatus. FIG. 5 is a diagram showing a time change in duty corresponding to a voltage command for each of three phases in an AC load connected to multiple AC terminals of the power conversion apparatus. FIG. 6 is a timing chart showing a case where the control device independently controls two-phase switches in the power conversion apparatus. FIG. 7 is a timing chart showing a case where the control device simultaneously controls two-phase switches in the power conversion apparatus. FIG. 8 is a timing chart showing a case where the control device simultaneously controls two-phase switches in the power conversion apparatus. FIG. 9 is a timing chart showing a case where the control device independently controls two-phase switches in the power conversion apparatus. FIG. 10 is a timing chart showing a case where the control device simultaneously controls two-phase switches in the power conversion apparatus. Fig. 11 is a timing chart showing a case where a control device independently controls two-phase switches in the power conversion device of the same. Fig. 12 is a timing chart showing another example where a control device simultaneously controls two-phase switches in the power conversion device of the same. Fig. 13 is a circuit diagram of a system including a power conversion device according to Modification 1 of Embodiment 1. Fig. 14 is a circuit diagram of a system including a power conversion device according to Modification 2 of Embodiment 1. Fig. 15 is a circuit diagram of a system including a power conversion device according to Modification 3 of Embodiment 1. Fig. 16 is a circuit diagram of a system including a power conversion device according to Modification 4 of Embodiment 1. Fig. 17 is a circuit diagram of a system including a power conversion device according to Modification 5 of Embodiment 1. Fig. 18 is a circuit diagram of a system including a power conversion device according to Embodiment 2. Fig. 19 is a circuit diagram of a system including a power conversion device according to Embodiment 3. Fig. 20 is a circuit diagram of a power conversion device according to Embodiment 4. Fig. 21 is a timing chart for explaining an operation example of the power conversion device of the same.Fig. 22 is a timing chart for explaining another example of operation of the power conversion device of the fifth embodiment Fig. 23 is a circuit diagram of a system including a power conversion device according to the fifth embodiment.

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

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

[0012] The power conversion device 100 includes a power conversion circuit 11, a plurality of (e.g., three) switches 8, a plurality of (e.g., three) resonant capacitors 9, a regenerative capacitor 15, a resonant inductor L0, and a control device 50. The power conversion device 100 also includes a protection circuit 17 and a capacitor C10. Each of the plurality of switches 8 is, for example, a bidirectional switch.

[0013] The power conversion circuit 11 has a plurality of (e.g., three) first switching elements 1 and a plurality of (e.g., three) second switching elements 2. In the power conversion circuit 11, a plurality of (e.g., three) switching circuits 10, each having a plurality of first switching elements 1 and a plurality of second switching elements 2 connected in series in a one-to-one relationship, are connected in parallel to one another. In the power conversion circuit 11, the plurality of first switching elements 1 are connected to first DC terminals 31, and the plurality of second switching elements 2 are connected to second DC terminals 32. The plurality of AC terminals 41 correspond one-to-one to the plurality of switching circuits 10. Each of the plurality of AC terminals 41 is connected to a connection point 3 between the first switching elements 1 and the second switching elements 2 in the corresponding switching circuit 10. The plurality of switches 8 correspond one-to-one to the plurality of switching circuits 10. A first end 81 of each of the plurality of switches 8 is connected to the connection point 3 between the first switching elements 1 and the second switching elements 2 in the corresponding switching circuit 10. The plurality of resonant capacitors 9 correspond one-to-one to the plurality of switches 8. Each of the plurality of resonant capacitors 9 is connected between the first end 81 and the second DC terminal 32 of the corresponding switch 8. The resonant inductor L0 has a first end and a second end, and the first end is connected to the common connection point 25. The regenerative capacitor 15 has a third end 153 and a fourth end 154. The regenerative capacitor 15 has the third end 153 connected to the second DC terminal 32 and the fourth end 154 connected to the common connection point 25. The control device 50 controls the plurality of first switching elements 1, the plurality of second switching elements 2, and the plurality of switches 8.

[0014] (2) Details of the Power Conversion Device Hereinafter, for convenience of explanation, the switching circuits 10 corresponding to the U phase, V phase, and W phase of the multiple switching circuits 10 may be referred to as switching circuit 10U, switching circuit 10V, and switching circuit 10W, respectively. Hereinafter, the first switching element 1 and the second switching element 2 of switching circuit 10U may be referred to as first switching element 1U and second switching element 2U. Hereinafter, the first switching element 1 and the second switching element 2 of switching circuit 10V may be referred to as first switching element 1V and second switching element 2V. Hereinafter, the first switching element 1 and the second switching element 2 of switching circuit 10W may be referred to as first switching element 1W and second switching element 2W. In the following, the connection point 3 between the first switching element 1U and the second switching element 2U will be referred to as connection point 3U, the connection point 3 between the first switching element 1V and the second switching element 2V will be referred to as connection point 3V, and the connection point 3 between the first switching element 1W and the second switching element 2W will be referred to as connection point 3W. In the following, the AC terminal 41 connected to connection point 3U will be referred to as AC terminal 41U, the AC terminal 41 connected to connection point 3V will be referred to as AC terminal 41V, and the AC terminal 41 connected to connection point 3W will be referred to as AC terminal 41W. In the following, the resonant capacitor 9 connected in parallel to the second switching element 2U will be referred to as resonant capacitor 9U, the resonant capacitor 9 connected in parallel to the second switching element 2V will be referred to as resonant capacitor 9V, and the resonant capacitor 9 connected in parallel to the second switching element 2W will be referred to as resonant capacitor 9W. In the following, the switch 8 connected to connection point 3U may be referred to as switch 8U, the switch 8 connected to connection point 3V may be referred to as switch 8V, and the switch 8 connected to connection point 3W may be referred to as switch 8W.

[0015] In the power conversion device 100, a high-potential output terminal (positive electrode) of the DC power supply E1 is connected to the first DC terminal 31, and a low-potential output terminal (negative electrode) of the DC power supply E1 is connected to the second DC terminal 32. In addition, in the power conversion device 100, for example, the U-phase, V-phase, and W-phase of the AC load RA1 are connected to three AC terminals 41U, 41V, and 41W, respectively.

[0016] In the power conversion circuit 11, each of a plurality of (e.g., three) first switching elements 1 and a plurality of (e.g., three) second switching elements 2 has a control terminal, a first main terminal, and a second main terminal. The control terminals of the plurality of first switching elements 1 and the plurality of second switching elements 2 are connected to a control device 50. In each of the plurality of switching circuits 10 of the power conversion device 100, a first main terminal of the first switching element 1 is connected to a first DC terminal 31, a second main terminal of the first switching element 1 is connected to a first main terminal of the second switching element 2, and a second main terminal of the second switching element 2 is connected to a second DC terminal 32. In each of the plurality of switching circuits 10, the first switching element 1 is a high-side switching element (P-side switching element), and the second switching element 2 is a low-side switching element (N-side switching element). Each of the plurality of first switching elements 1 and the plurality of second switching elements 2 is, for example, an IGBT (Insulated Gate Bipolar Transistor). Therefore, the control terminal, the first main terminal and the second main terminal of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 are the gate terminal, the collector terminal and the emitter terminal, respectively.

[0017] The power conversion circuit 11 further includes a plurality of (three) first diodes 4 connected in anti-parallel to the plurality of (three) first switching elements 1 in a one-to-one relationship, and a plurality of (three) second diodes 5 connected in anti-parallel to the plurality of (three) second switching elements 2 in a one-to-one relationship. In each of the plurality of first diodes 4, the anode of the first diode 4 is connected to the second main terminal (emitter terminal) of the first switching element 1 corresponding to the first diode 4, and the cathode of the first diode 4 is connected to the first main terminal (collector terminal) of the first switching element 1 corresponding to the first diode 4. In each of the plurality of second diodes 5, the anode of the second diode 5 is connected to the second main terminal (emitter terminal) of the second switching element 2 corresponding to the second diode 5, and the cathode of the second diode 5 is connected to the first main terminal (collector terminal) of the second switching element 2 corresponding to the second diode 5.

[0018] For example, the U-phase of the AC load RA1 is connected to a connection point 3U between the first switching element 1U and the second switching element 2U via an AC terminal 41U. For example, the V-phase of the AC load RA1 is connected to a connection point 3V between the first switching element 1V and the second switching element 2V via an AC terminal 41V. For example, the W-phase of the AC load RA1 is connected to a connection point 3W between the first switching element 1W and the second switching element 2W via an AC terminal 41W.

[0019] The multiple resonant capacitors 9 correspond one-to-one to the multiple switches 8. Each of the multiple resonant capacitors 9 is connected between the first end 81 and the second DC terminal 32 of the corresponding switch 8. The power conversion device 100 has multiple resonant circuits. The multiple resonant circuits include a resonant circuit having a resonant capacitor 9U and a resonant inductor L0, a resonant circuit having a resonant capacitor 9V and a resonant inductor L0, and a resonant circuit having a resonant capacitor 9W and a resonant inductor L0. The multiple resonant circuits share the resonant inductor L0.

[0020] Each of the multiple switches 8 has, for example, two IGBTs, a first IGBT 6 and a second IGBT 7, connected in anti-parallel. In each of the switches 8, the collector terminal of the first IGBT 6 is connected to the emitter terminal of the second IGBT 7, and the emitter terminal of the first IGBT 6 is connected to the collector terminal of the second IGBT 7. In each of the multiple switches 8, the emitter terminal of the first IGBT 6 is connected to the connection point 3 of the switching circuit 10 corresponding to the switch 8 having the first IGBT 6. In each of the multiple switches 8, the collector terminal of the second IGBT 7 is connected to the connection point 3 of the switching circuit 10 corresponding to the switch 8 having the second IGBT 7. The switch 8U is connected to the connection point 3U between the first switching element 1U and the second switching element 2U. The switch 8V is connected to the connection point 3V between the first switching element 1V and the second switching element 2V. The switch 8W is connected to a connection point 3W between the first switching element 1W and the second switching element 2W. Hereinafter, for convenience of explanation, the first IGBT 6 and the second IGBT 7 of the switch 8U may be referred to as the first IGBT 6U and the second IGBT 7U, the first IGBT 6 and the second IGBT 7 of the switch 8V may be referred to as the first IGBT 6V and the second IGBT 7V, and the first IGBT 6 and the second IGBT 7 of the switch 8W may be referred to as the first IGBT 6W and the second IGBT 7W, respectively.

[0021] The plurality of switches 8 are controlled by the control device 50. In other words, the first IGBT 6U, the second IGBT 7U, the first IGBT 6V, the second IGBT 7V, the first IGBT 6W, and the second IGBT 7W are controlled by the control device 50.

[0022] The resonant inductor L0 has a first end and a second end. The first end of the resonant inductor L0 is connected to the common connection point 25. The second end of the resonant inductor L0 is connected to the fourth end 154 of the regenerative capacitor 15.

[0023] The regenerative capacitor 15 is connected between the second end of the resonance inductor L0 and the second DC terminal 32. The regenerative capacitor 15 is, for example, a film capacitor.

[0024] The protection circuit 17 includes a third diode 13 and a fourth diode 14. The third diode 13 is connected between the common connection point 25 and the first DC terminal 31. In the third diode 13, the anode of the third diode 13 is connected to the common connection point 25. In addition, in the third diode 13, the cathode of the third diode 13 is connected to the first DC terminal 31. The fourth diode 14 is connected between the common connection point 25 and the second DC terminal 32. In the fourth diode 14, the anode of the fourth diode 14 is connected to the second DC terminal 32. In the fourth diode 14, the cathode of the fourth diode 14 is connected to the common connection point 25. Therefore, the fourth diode 14 is connected in series with the third diode 13.

[0025] The capacitor C10 is connected between the first DC terminal 31 and the second DC terminal 32, and is connected in parallel to the power conversion circuit 11. The capacitor C10 is, for example, an electrolytic capacitor.

[0026] The control device 50 controls a plurality of first switching elements 1, a plurality of second switching elements 2, and a plurality of switches 8. The execution entity of the control device 50 includes a computer system. The computer system has one or more computers. The computer system is mainly composed 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 50 as the execution entity in the present disclosure. The program may be pre-recorded in the memory of the computer system, provided via a telecommunications line, or recorded and provided on a non-transitory recording medium such as a memory card, optical disk, or hard disk drive (magnetic disk) readable by the computer system. The processor of the computer system is composed of one or more electronic circuits including a semiconductor integrated circuit (IC) or a large-scale integrated circuit (LSI). The multiple electronic circuits may be integrated into a single chip or distributed across multiple chips. The multiple chips may be integrated into a single device or distributed across multiple devices.

[0027] The control device 50 outputs PWM (Pulse Width Modulation) signals SU1, SV1, and SW1 that control the on / off states of the multiple first switching elements 1U, 1V, and 1W, respectively. Each of the PWM signals SU1, SV1, and SW1 is a 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 PWM signals SU1, SV1, and SW1 are at a high level, and turned off when the PWM signals SU1, SV1, and SW1 are at a low level. The control device 50 also outputs PWM signals SU2, SV2, and SW2 that control the on / off states of the multiple second switching elements 2U, 2V, and 2W, respectively. Each of the PWM signals SU2, SV2, and SW2 is a 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 second switching elements 2U, 2V, and 2W are turned on when the PWM signals SU2, SV2, and SW2 are at a high level, and turned off when they are at a low level.

[0028] The control device 50 uses a sawtooth-wave carrier signal (see FIG. 2 ) to generate PWM signals SU1, SV1, and SW1 corresponding to the plurality of first switching elements 1U, 1V, and 1W, respectively, and PWM signals SU2, SV2, and SW2 corresponding to the plurality of second switching elements 2U, 2V, and 2W, respectively. More specifically, the control device 50 generates the PWM signals SU1 and SU2 to be applied to the first switching element 1U and the second switching element 2U, respectively, based on at least the carrier signal and a U-phase voltage command. The control device 50 also generates the PWM signals SV1 and SV2 to be applied to the first switching element 1V and the second switching element 2V, respectively, based on at least the carrier signal and a V-phase voltage command. The control device 50 also generates the PWM signals SW1 and SW2 to be applied to the first switching element 1W and the second switching element 2W, respectively, based on at least the carrier signal and a W-phase voltage command. The U-phase voltage command, V-phase voltage command, and W-phase voltage command are, for example, sinusoidal signals whose phases differ from each other by 120°, and whose amplitudes (voltage command values) change over time. The U-phase voltage command, V-phase voltage command, and W-phase voltage command have the same cycle length. Furthermore, the U-phase voltage command, V-phase voltage command, and W-phase voltage command have a cycle length longer than that of the carrier signal.

[0029] The duties of the PWM signals SU1 and SU2 provided by the control device 50 to the first switching element 1U and the second switching element 2U, respectively, vary based on the U-phase voltage command. The control device 50 compares the U-phase voltage command with a carrier signal to generate the PWM signal SU1 to be provided to the first switching element 1U. The control device 50 also inverts the PWM signal SU1 provided to the first switching element 1U to generate the PWM signal SU2 to be provided to the second switching element 2U. The control device 50 also sets a dead time Td (see FIG. 2) between the period when the PWM signal SU1 is at a high level and the period when the PWM signal SU2 is at a high level so that the on periods of the first switching element 1U and the second switching element 2U do not overlap.

[0030] The duties of the PWM signals SV1 and SV2 provided by the control device 50 to the first switching element 1V and the second switching element 2V, respectively, change based on a V-phase voltage command. The control device 50 compares the V-phase voltage command with a carrier signal to generate the PWM signal SV1 to be provided to the first switching element 1V. The control device 50 also inverts the PWM signal SV1 to be provided to the first switching element 1V to generate the PWM signal SV2 to be provided to the second switching element 2V. The control device 50 also sets a dead time Td (see FIG. 2 ) between the period when the PWM signal SV1 is at a high level and the period when the PWM signal SV2 is at a high level so that the on periods of the first switching element 1V and the second switching element 2V do not overlap.

[0031] The duties of the PWM signals SW1 and SW2 provided by the control device 50 to the first switching element 1W and the second switching element 2W, respectively, change based on a W-phase voltage command. The control device 50 compares the W-phase voltage command with a carrier signal to generate the PWM signal SW1 to be provided to the first switching element 1W. The control device 50 also inverts the PWM signal SW1 to be provided to the first switching element 1W to generate the PWM signal SW2 to be provided to the second switching element 2W. The control device 50 also sets a dead time Td (see FIG. 3 ) between the period when the PWM signal SW1 is at a high level and the period when the PWM signal SW2 is at a high level so that the on periods of the first switching element 1W and the second switching element 2W do not overlap.

[0032] The U-phase voltage command, V-phase voltage command, and W-phase voltage command are, for example, sinusoidal signals that are out of phase with each other by 120°, and their amplitudes change over time. Therefore, the duties of PWM signals SU1, SV1, and SW1 change into sinusoidal signals that are out of phase with each other by 120°, as shown in Figure 5, for example. Similarly, the duties of PWM signals SU2, SV2, and SW2 change into sinusoidal signals that are out of phase with each other by 120°.

[0033] The control device 50 generates the PWM signals SU1, SU2, SV1, SV2, SW1, and SW2 based on the carrier signal, the voltage commands, and information about the state of the AC load RA1. For example, if the AC load RA1 is a three-phase motor, the information about the state of the AC load RA1 includes, for example, detection values ​​from a plurality of current sensors that detect output currents iU, iV, and iW flowing through the U-phase, V-phase, and W-phase of the AC load RA1, respectively.

[0034] The plurality of switches 8, the resonant inductor L0, the plurality of resonant capacitors 9, and the regenerative capacitor 15 are provided to perform zero-voltage soft switching of the plurality of first switching elements 1 and the plurality of second switching elements 2.

[0035] In the power conversion device 100 , the control device 50 controls the plurality of switches 8 in addition to the plurality of first switching elements 1 and second switching elements 2 of the power conversion circuit 11 .

[0036] The control device 50 generates control signals SU6, SU7, SV6, SV7, SW6, and SW7 that control the on / off of the first IGBT6U, the second IGBT7U, the first IGBT6V, the second IGBT7V, the first IGBT6W, and the second IGBT7W, respectively, and outputs them to the gate terminals of the first IGBT6U, the second IGBT7U, the first IGBT6V, the second IGBT7V, the first IGBT6W, and the second IGBT7W, respectively.

[0037] When the first IGBT 6U is in the ON state and the second IGBT 7U is in the OFF state, the switch 8U passes a charging current that flows through the path of the regenerative capacitor 15-resonant inductor L0-switch 8U-resonant capacitor 9U to charge the resonant capacitor 9U. When the first IGBT 6U is in the OFF state and the second IGBT 7U is in the ON state, the switch 8U passes a discharging current that flows through the path of the resonant capacitor 9U-switch 8U-resonant inductor L0-regenerative capacitor 15 to discharge the charge of the resonant capacitor 9U.

[0038] When the first IGBT 6V is in the ON state and the second IGBT 7V is in the OFF state, the switch 8V passes a charging current that flows through the path of the regenerative capacitor 15-resonant inductor L0-switch 8V-resonant capacitor 9V to charge the resonant capacitor 9V. When the first IGBT 6V is in the OFF state and the second IGBT 7V is in the ON state, the switch 8V passes a discharging current that flows through the path of the resonant capacitor 9V-switch 8V-resonant inductor L0-regenerative capacitor 15 to discharge the charge of the resonant capacitor 9V.

[0039] When the first IGBT 6W is in the ON state and the second IGBT 7W is in the OFF state, the switch 8W passes a charging current that flows through the path of the regenerative capacitor 15, resonant inductor L0, switch 8W, and resonant capacitor 9W to charge the resonant capacitor 9W. When the first IGBT 6W is in the OFF state and the second IGBT 7W is in the ON state, the switch 8W passes a discharging current that flows through the path of the resonant capacitor 9W, switch 8W, resonant inductor L0, and regenerative capacitor 15 to discharge the charge of the resonant capacitor 9W.

[0040] (3) Operation of the Power Conversion Device In the following description, the polarity of current iL0 flowing through resonant inductor L0 is defined as positive when flowing in the direction of the arrow in Fig. 1, and as negative when flowing in the opposite direction to the arrow in Fig. 1. Also, in the following description, the polarity of output currents iU, iV, and iW flowing through the U, V, and W phases of AC load RA1 is defined as positive when flowing in the direction of the arrow in Fig. 1, and as negative when flowing in the opposite direction to the arrow in Fig. 1. Also, in the following description, the polarity of currents i9U, i9V, and i9W flowing through resonant capacitors 9U, 9V, and 9W, respectively, is defined as positive when flowing in the direction of the arrow in Fig. 1, and as negative when flowing in the opposite direction to the arrow in Fig. 1.

[0041] In the power conversion device 100, for example, the first IGBT 6U of the switch 8U may change from an ON state in which the first IGBT 6U of the switch 8U is in an ON state and current iL0 is flowing through the resonant inductor L0 with positive polarity to an OFF state. In this case, the current iL0 flowing through the resonant inductor L0 is regenerated to the power conversion circuit 11 via the third diode 13 until the energy of the resonant inductor L0 is consumed and the current iL0 becomes zero. In addition, in the power conversion device 100, for example, the second IGBT 7U of the switch 8U may change from an ON state in which the second IGBT 7U of the switch 8U is in an ON state and current iL0 is flowing through the resonant inductor L0 with negative polarity to an OFF state. In this case, the current iL0 flowing through the resonant inductor L0 flows through the path of the fourth diode 14, the resonant inductor L0, and the regenerative capacitor 15 until the energy of the resonant inductor L0 is consumed and the current iL0 becomes zero.

[0042] Furthermore, in the power conversion device 100, for example, a state in which the first IGBT 6V of the switch 8V is in the on state and current iL0 is flowing through the resonant inductor L0 with positive polarity may change to an off state, where the first IGBT 6V of the switch 8V is in the on state. In this case, the current iL0 flowing through the resonant inductor L0 is regenerated in the power conversion circuit 11 via the third diode 13 until the energy of the resonant inductor L0 is consumed and the current iL0 becomes zero. Furthermore, in the power conversion device 100, for example, a state in which the second IGBT 7V of the switch 8V is in the on state and current iL0 is flowing through the resonant inductor L0 with negative polarity may change to an off state, where the current iL0 flowing through the resonant inductor L0 passes through the path of the fourth diode 14, the resonant inductor L0, and the regenerative capacitor 15 until the energy of the resonant inductor L0 is consumed and the current iL0 becomes zero.

[0043] Furthermore, in the power conversion device 100, for example, the first IGBT 6W of the switch 8W may be switched from an ON state in which the current iL0 is flowing through the resonant inductor L0 with positive polarity to an OFF state in which the first IGBT 6W of the switch 8W is switched. In this case, the current iL0 flowing through the resonant inductor L0 is regenerated in the power conversion circuit 11 via the third diode 13 until the energy of the resonant inductor L0 is consumed and the current iL0 becomes zero. Furthermore, in the power conversion device 100, for example, the second IGBT 7W of the switch 8W may be switched from an ON state in which the current iL0 is flowing through the resonant inductor L0 with negative polarity to an OFF state in which the second IGBT 7W of the switch 8W is switched. In this case, the current iL0 flowing through the resonant inductor L0 flows through the path of the fourth diode 14, the resonant inductor L0, and the regenerative capacitor 15 until the energy of the resonant inductor L0 is consumed and the current iL0 becomes zero.

[0044] Hereinafter, the operation of the control device 50 when performing zero voltage soft switching control on each of the plurality of first switching elements 1 and the plurality of second switching elements 2 will be described with reference to FIGS.

[0045] In the first control operation, the control device 50 sets a dead time Td between the high-level period of the PWM signals SU1, SV1, SW1 to the first switching elements 1U, 1V, 1W and the high-level period of the PWM signals SU2, SV2, SW2 to the second switching elements 2U, 2V, 2W for each of the multiple switching circuits 10. In the first control operation, the control device 50 overlaps the high-level period of the control signal to the switch 8 among the multiple switches 8 corresponding to each of the multiple switching circuits 10 with the dead time Td, and advances the start of the high-level period by an additional time from the start of the dead time Td.

[0046] The first control operation will be described in more detail below.

[0047] In the zero voltage soft switching control of the first switching element 1, it is necessary to set the voltage across the first switching element 1 to zero immediately before turning on the first switching element 1 that is the target of zero voltage soft switching. For this reason, the control device 50 turns on the first IGBT 6 that corresponds to the first switching element 1 that is the target of zero voltage soft switching control. As a result, the control device 50 causes resonance between the resonant inductor L0 connected to the first switching element 1 and the resonant capacitor 9, charging the resonant capacitor 9 from the regenerative capacitor 15, and setting the voltage across the first switching element 1 to zero.

[0048] Furthermore, in the zero-voltage soft switching control of the second switching element 2, the voltage across the second switching element 2 must be set to zero immediately before the second switching element 2 targeted for the zero-voltage soft switching control is turned on. Therefore, the control device 50 turns on the second IGBT 7 corresponding to the second switching element 2 targeted for the zero-voltage soft switching control. This causes the resonant inductor L0 and the resonant capacitor 9 connected to the second switching element 2 to resonate, discharging from the resonant capacitor 9 to the regenerative capacitor 15 and setting the voltage across the second switching element 2 to zero. The control device 50 charges and discharges the resonant capacitor 9 via the switch 8 so that the dead time Td coincides with the half cycle (π × √LC) of the LC resonance. This allows the power conversion device 100 to achieve zero-voltage soft switching. In the equation π × √LC representing the half cycle of the LC resonance, "L" is the inductance of the resonant inductor L0, and "C" is the capacitance of the resonant capacitor 9.

[0049] 2 shows PWM signals SU1 and SU2 respectively given from the control device 50 to the first switching element 1U and the second switching element 2U of the switching circuit 10U. Also shown in FIG. 2 are a control signal SU6 given from the control device 50 to the first IGBT 6U of the switch 8U, an output current iU flowing in the U-phase of the AC load RA1, a current iL0 flowing in the resonant inductor L0, and a voltage V across the first switching element 1U. １Ｕ2 also shows the PWM signals SV1 and SV2 given from the control device 50 to the first switching element 1V and the second switching element 2V of the switching circuit 10V, respectively. Also shown in FIG. 2 are the control signal SV6 given from the control device 50 to the first IGBT 6V of the switch 8V, the output current iV flowing in the V-phase of the AC load RA1, the current iL0 flowing in the resonant inductor L0, and the voltage V across the first switching element 1V. １Ｖ and are illustrated.

[0050] 2 also shows a dead time Td set in the control device 50 to prevent the first switching element 1 and the second switching element 2, which are in phase, from being turned on simultaneously. Also shown in Fig. 2 is an additional time Tau set in the control device 50 for the control signal SU6 of the first IGBT 6U of the switch 8U, and an additional time Tav set in the control device 50 for the control signal SV6 of the first IGBT 6V of the switch 8V. The additional time Tau and the additional time Tav will be described later.

[0051] 3 shows the PWM signals SW1 and SW2 respectively given from the control device 50 to the first switching element 1W and the second switching element 2W of the switching circuit 10W. Also shown in FIG. 3 is the control signal SW6 given from the control device 50 to the first IGBT 6W of the switch 8W, and the output current iW flowing through the W-phase of the AC load RA1. Also shown in FIG. 3 is the current iL0 flowing through the resonant inductor L0. Also shown in FIG. 3 is the voltage V across the first switching element 1W. １Ｗ is illustrated.

[0052] 3 also shows a dead time Td set in the control device 50 to prevent the first switching element 1W and the second switching element 2W from being turned on simultaneously. Also, Fig. 3 shows an additional time Taw set in the control device 50 for the control signal SW6 of the first IGBT 6W of the switch 8W. The additional time Taw will be described later.

[0053] As shown in FIG. 2, the additional time Tau is set to advance the start point t1 of the high-level period of the control signal SU6 relative to the start point t2 of the dead time Td, thereby extending the high-level period of the control signal SU6 beyond the dead time Td. The length of the additional time Tau is set based on the value of the output current iU. To start LC resonance at the start point t2 of the dead time Td, it is desirable that the value of the current iL0 at the start point t2 of the dead time Td be equal to the value of the output current iU. This is because, while iL0 < iU, all current flows through the AC load RA1, preventing the resonant capacitor 9U from being charged. The end point of the high-level period of the control signal SU6 may be the same as or later than the end point t3 of the dead time Td. FIG. 2 shows an example in which the end point of the high-level period of the control signal SU6 is set to the same as the end point t3 of the dead time Td. The control device 50 sets the high-level period of the control signal SU6 to Tau + Td. The voltage V across the first switching element 1U is １Ｕ becomes zero at the end t3 of the dead time Td. In the example of FIG. 2 , the current iL0 flowing through the resonant inductor L0 starts flowing at the start t1 of the high-level period of the control signal SU6 and becomes zero at the time t4, when the additional time Tau has elapsed from the end t3 of the dead time Td. With regard to the current iL0 at this time, since iL0≧iU from the start t2 of the dead time Td, the current iL0 in the shaded region of the current waveform in the fifth row from the top in FIG. 2 flows into the resonant capacitor 9U, causing LC resonance. After the end t3 of the dead time Td, the current iL0 is regenerated in the power conversion circuit 11 via the third diode 13 directly connected to the resonant inductor L0.

[0054] As described above, in order to start LC resonance at the start time t2 of the dead time Td, the control device 50 determines the additional time Tau based on the output current iU so that iL0 = iU at the start time t2 of the dead time Td. More specifically, the control device 50 determines the additional time Tau by calculating Tau = iU × (L / V15) using, for example, the detection result of the output current iU by a current sensor, its signal processed value, or an estimated value of the output current iU, the inductance L of the resonance inductor L0 that is stored in advance, and the detection result of the potential V15 of the regenerative capacitor 15. As the detection result of the output current iU or its signal processed value, a detection value at the carrier cycle to which the additional time Tau is added or at a timing closest to that carrier cycle is used. Furthermore, as the estimated value of the output current iU, a value estimated from the output current iU at the carrier cycle to which the additional time Tau is added is used.

[0055] In the power conversion device 100, as shown in Fig. 4, when the polarity of the output current iU is negative, the resonance capacitor 9U can be charged without turning on the first IGBT 6U of the switch 8U, and zero-voltage soft switching of the first switching element 1U can be realized. １Ｕ and the voltage V across the second switching element 2U. ２Ｕ In addition, in the case of a discharging operation in which the resonant capacitors 9U, 9V, and 9W are discharged, the polarities of the currents i9U, i9V, and i9W are positive, and in the case of a charging operation in which the resonant capacitors 9U, 9V, and 9W are charged, the polarities of the currents i9U, i9V, and i9W are negative. In Figure 4, the current i9U is also shown.

[0056] As shown in FIG. 2, the additional time Tav is set to advance the start point t5 of the high-level period of the control signal SV6 relative to the start point t6 of the dead time Td, thereby extending the high-level period of the control signal SV6 beyond the dead time Td. The length of the additional time Tav is set based on the value of the output current iV. To start LC resonance at the start point t6 of the dead time Td, it is desirable that the value of the current iL0 at the start point t6 of the dead time Td be equal to the value of the output current iV. This is because, while iL0 < iV, all current flows through the AC load RA1, preventing the resonant capacitor 9V from being charged. The end point of the high-level period of the control signal SV6 may be the same as or later than the end point t7 of the dead time Td. FIG. 2 shows an example in which the end point of the high-level period of the control signal SV6 is set to the same as the end point t7 of the dead time Td. The control device 50 sets the high-level period of the control signal SV6 to Tav + Td. The voltage V across the first switching element 1V １Ｖ becomes zero at the end t7 of the dead time Td. In the example of FIG. 2 , the current iL0 flowing through the resonant inductor L0 starts to flow at the start t5 of the high-level period of the control signal SV6, and becomes zero at the time t8 when the additional time Tav has elapsed from the end t7 of the dead time Td. With regard to the current iL0 at this time, since iL0≧iV from the start t6 of the dead time Td, the current iL0 in the shaded region of the current waveform in the tenth row from the top in FIG. 2 flows into the resonant capacitor 9V, causing LC resonance. After the end t7 of the dead time Td, the current iL0 is regenerated in the power conversion circuit 11 via the third diode 13 directly connected to the resonant inductor L0.

[0057] As described above, in order to start LC resonance at the start time t6 of the dead time Td, the control device 50 determines the additional time Tav based on the output current iV so that iL0 = iV at the start time t6 of the dead time Td. More specifically, the control device 50 determines the additional time Tav by calculating Tav = iV × (L / V15) using, for example, the detection result of the output current iV by a current sensor, its signal processed value, or an estimated value of the output current iV, the inductance L of the resonance inductor L0 that is stored in advance, and the detection result of the potential V15 of the regenerative capacitor 15. As the detection result of the output current iV or its signal processed value, a detection value at the carrier cycle to which the additional time Tav is added or at a timing closest to that carrier cycle is used. Furthermore, as the estimated value of the output current iV, a value estimated from the output current iV at the carrier cycle to which the additional time Tav is added is used.

[0058] In the power conversion device 100, when the polarity of the output current iV is negative, the resonant capacitor 9V can be charged without turning on the first IGBT 6V of the switch 8V, thereby realizing zero-voltage soft switching of the first switching element 1V.

[0059] As shown in FIG. 3 , the additional time Taw is set to advance the start point t9 of the high-level period of the control signal SW6 relative to the start point t10 of the dead time Td, thereby extending the high-level period of the control signal SW6 beyond the dead time Td. The length of the additional time Taw is set based on the value of the output current iW. To start LC resonance at the start point t10 of the dead time Td, it is desirable for the value of the current iL0 to match the value of the output current iW at the start point t10 of the dead time Td. This is because, while iL0 < iW, all current flows through the AC load RA1, preventing the resonant capacitor 9W from being charged. The end point of the high-level period of the control signal SW6 may be the same as or later than the end point t11 ​​of the dead time Td. FIG. 3 illustrates an example in which the end point of the high-level period of the control signal SW6 is set to the same as the end point t11 ​​of the dead time Td. The control device 50 sets the high-level period of the control signal SW6 to Taw + Td. The voltage V across the first switching element 1W １Ｗ becomes zero at the end t11 of the dead time Td. In the example of FIG. 3 , the current iL0 flowing through the resonant inductor L0 starts flowing at the start t9 of the high-level period of the control signal SW6 and becomes zero at the time t12, when the additional time Taw has elapsed from the end t11 of the dead time Td. With regard to the current iL0 at this time, since iL0≧iW from the start t10 of the dead time Td, the current iL0 in the shaded region of the current waveform in the fourth row from the top in FIG. 3 flows into the resonant capacitor 9W, causing LC resonance. After the end t11 of the dead time Td, the current iL0 is regenerated in the power conversion circuit 11 via the third diode 13 directly connected to the resonant inductor L0.

[0060] The control device 50 determines the additional time Taw based on the output current iW. More specifically, the control device 50 determines the additional time Taw by calculating Taw = iW × (L / V15) using the detection result of the output current iW by the current sensor, the inductance L of the resonance inductor L0 that is stored in advance, and the detection result of the potential V15 of the regenerative capacitor 15. As the detection result of the output current iW or its signal processed value at this time, a detection value at the carrier cycle to which the additional time Taw is added or at a timing closest to that carrier cycle is used. Furthermore, as the estimated value of the output current iW at this time, a value estimated from the output current iW at the carrier cycle to which the additional time Taw is added is used.

[0061] In addition, in the power conversion device 100, when the polarity of the output current iW is negative, the resonant capacitor 9W can be charged without turning on the first IGBT 6W of the switch 8W, thereby achieving zero-voltage soft switching of the first switching element 1W.

[0062] The power conversion device 100 resonates a resonant capacitor 9 associated with a switching element, one of the plurality of first switching elements 1 and the plurality of second switching elements 2, that is subject to zero-voltage soft switching, with a resonant inductor L0. At this time, the voltage across the resonant capacitor 9 associated with the switching element subject to zero-voltage soft switching varies depending on the amplitude of the resonant voltage, centered on the potential V15 at the fourth terminal 154 of the regenerative capacitor 15. The voltage across the switching element varies from the voltage value Vd (see FIGS. 2 and 3 ) of the DC power source E1 applied between the first DC terminal 31 and the second DC terminal 32 to zero, thereby achieving zero-voltage soft switching. The potential V15 at the fourth terminal 154 of the regenerative capacitor 15 varies depending on the amount of charge charged or discharged to the regenerative capacitor 15 for each resonance between the resonant capacitor 9 and the resonant inductor L0. Furthermore, the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 varies depending on the amount of charge charged or discharged to the regenerative capacitor 15 per carrier cycle. In the regenerative capacitor 15, the charge amount or discharge amount associated with the output currents iU, iV, and iW of the U, V, and W phases is determined for each carrier cycle, but the charge amount associated with the current with the largest absolute value among the output currents iU, iV, and iW of the U, V, and W phases is the largest. Therefore, in the power conversion device 100, the charge amount of the regenerative capacitor 15 varies with each carrier cycle. However, in the power conversion device 100, when the motor serving as the AC load RA1 is rotating normally, the output currents iU, iV, and iW of each phase are sinusoidal and out of phase with each other by 120°. This ensures a balance between charge and discharge in the regenerative capacitor 15, thereby suppressing fluctuations in the potential V15 at the fourth terminal 154 of the regenerative capacitor 15.

[0063] In the first control operation, the control device 50 sets a dead time Td between the high-level period of the PWM signals SU1, SV1, SW1 to the first switching elements 1U, 1V, 1W and the high-level period of the PWM signals SU2, SV2, SW2 to the second switching elements 2U, 2V, 2W for each of the multiple switching circuits 10. In the first control operation, the control device 50 overlaps the high-level period of the control signal to the switch 8 among the multiple switches 8 corresponding to each of the multiple switching circuits 10 with the dead time Td, and advances the start of the high-level period by an additional time from the start of the dead time Td.

[0064] In the power conversion apparatus 100, if the control device 50 performs only the first control operation, for example, when a load state change occurs, such as when the AC load RA1 (motor) locks up, the output currents iU, iV, and iW of each phase will each have a different constant value. This results in a large difference between the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 relative to the ground potential and half the voltage Vd (Vd / 2) of the DC power supply E1. This reduces the amplitude of the resonant voltage when the resonant capacitors 9U, 9V, and 9W are resonated with the resonant inductor L0 to achieve zero-voltage soft switching in the power conversion apparatus 100, potentially making it impossible to achieve zero-voltage soft switching.

[0065] Incidentally, when the control device 50 is performing the first control operation, if it determines that two-phase resonant currents corresponding to two of the multiple switching circuits 10 are flowing simultaneously through the resonant inductor L0, the control device 50 is configured to be able to perform either independent control or simultaneous control.

[0066] The independent control includes a control for shifting the high level period of at least one of the two control signals to two of the multiple switches 8 through which the resonant current flows when it is determined that a two-phase resonant current flows through the resonant inductor L0, so as to eliminate an overlapping period between the high level periods of the two control signals.

[0067] 6 illustrates the control signals SV7 and SW7 when the high-level periods of the two control signals SV7 and SW7 for two of the three switches 8U, 8V, and 8W are shifted so as to eliminate overlapping periods between the high-level periods of the two control signals SV7 and SW7 for two of the three switches 8V and 8W within one cycle of the carrier signal. Here, FIG. 6 illustrates the control signals SU6, SV7, and SW7, the multiple output currents iU, iV, and iW, the current iL0 flowing through the resonant inductor L0, and the potential V15 at the fourth end 154 of the regenerative capacitor 15 for an example case in which the motor, which is the AC load RA1, is locked and the output currents iU, iV, and iW each assume a different constant value. In FIG. 6, the absolute value of the output current iU > the absolute value of the output current iW > the absolute value of the output current iV, and the high-level period of the control signal SU7 > the high-level period of the control signal SW6 > the high-level period of the control signal SV6. The amplitude of current iL0 is greatest during the high level period of the control signal SU6 of switch 8U, which corresponds to output current iU having the largest absolute value among output currents iU, iV, and iW. As a result, the fluctuation range of potential V15 of regenerative capacitor 15 is greatest during the high level period of control signal SU6, among the high level periods of control signals SU6, SV7, and SW7.

[0068] The simultaneous control includes control for overlapping the high-level periods of two control signals sent to two of the multiple switches 8 through which a resonant current flows when it is determined that a two-phase resonant current flows through the resonant inductor L0. "Overlapping the high-level periods of two control signals" is not limited to overlapping the entire high-level period of a first control signal, which is one of the two control signals, with the entire high-level period of a second control signal, which is the remaining one of the two control signals. "Overlapping the high-level periods of two control signals" includes at least overlapping the entire period corresponding to the dead time Td between the two PWM signals for determining the high-level period of the first control signal, with the entire period corresponding to the dead time Td between the two PWM signals for determining the high-level period of the second control signal.

[0069] 7 and 8 show the control signals SV7 and SW7 when the high-level periods of the two control signals SV7 and SW7 for two of the three switches 8U, 8V, and 8W are shifted so that the high-level periods of the two control signals SV7 and SW7 overlap within one cycle of the carrier signal. Here, Figures 7 and 8 show the control signals SU6, SV7, and SW7, the multiple output currents iU, iV, and iW, and the current iL0 flowing through the resonant inductor L0 for an example case in which the AC load RA1, i.e., the motor, is locked and the output currents iU, iV, and iW each assume a different constant value. Also shown in Figure 7 is the potential V15 at the fourth terminal 154 of the regenerative capacitor 15. 7 and 8, the absolute value of output current iU > the absolute value of output current iW > the absolute value of output current iV, and in FIG. 7, the high-level period of control signal SV7 = the high-level period of control signal SW7. The amplitude of current iL0 is greatest during the period when the high-level periods of the two control signals SV7 and SW7 overlap. As a result, the fluctuation range of potential V15 of regenerative capacitor 15 is greatest during the period when the high-level periods of two of the three control signals SU6, SV7, and SW7, SV7 and SW7, overlap.

[0070] Therefore, the control device 50 of the power conversion device 100 acquires a detected potential of the potential V15 at the fourth terminal 154 of the regenerative capacitor 15. The control device 50 acquires the detected potential, for example, for each cycle of the carrier signal. For example, the control device 50 may store in advance the voltage value Vd of the DC voltage applied between the first DC terminal 31 and the second DC terminal 32, or may acquire the detection result of the voltage value Vd. The control device 50 determines the content of the control operation based on the detected potential at the fourth terminal 154 of the regenerative capacitor 15, the value of Vd / 2, and the detection results of the output currents iU, iV, and iW.

[0071] The control device 50 switches between a second control operation and a third control operation based on the detected potential of the fourth terminal 154 of the regenerative capacitor 15 and the polarities of the multiple output currents iU, iV, and iW output from the multiple AC terminals 41. The "detected potential of the fourth terminal 154 of the regenerative capacitor 15" refers to the detected potential of the potential V15 of the fourth terminal 154 of the regenerative capacitor 15 relative to the ground potential. The second control operation is an operation for simultaneously controlling two of the multiple switches 8. The third control operation is an operation for independently controlling two of the multiple switches 8.

[0072] In the second control operation, the control device 50 shifts the high-level periods of two control signals to two of the multiple switches 8 so that the high-level periods of the two control signals overlap each other.

[0073] In the third control operation, the control device 50 shifts the high-level periods of two control signals to two of the multiple switches 8 to prevent overlap between the high-level periods. In the third control operation, for example, as shown in FIG. 6 , the end point of the high-level period of a first control signal, which is one of the two control signals, is the same as the start point of the high-level period of a second control signal, which is the remaining one of the two control signals. However, this is not limited to this, and the high-level period of the second control signal, which is the remaining one of the two control signals, may start after the end of the high-level period of the first control signal. In the third control operation, the control device 50 prevents overlap between the high-level periods of the control signals of the multiple switches 8.

[0074] The control device 50 performs the second control action when the first condition or the second condition is satisfied, and performs the third control action when the third condition or the fourth condition is satisfied.

[0075] The first condition is that the detected potential at the fourth terminal 154 of the regenerative capacitor 15 is smaller than the first threshold value Vth1, and the product (iU x iV x iW) of the multiple output currents iU, iV, and iW is positive. When calculating iU x iV x iW, iU, iV, and iW are instantaneous values ​​and are positive, zero, or negative. The second condition is that the detected potential at the fourth terminal 154 of the regenerative capacitor 15 is larger than the second threshold value Vth2, and the product of the multiple output currents iU, iV, and iW is negative. The third condition is that the detected potential at the fourth terminal 154 of the regenerative capacitor 15 is smaller than the first threshold value Vth1, and the product of the multiple output currents iU, iV, and iW is negative. The fourth condition is that the detected potential at the fourth terminal 154 of the regenerative capacitor 15 is greater than the second threshold Vth2, and the product of the multiple output currents iU, iV, and iW is positive. The first threshold Vth1 is smaller than half the voltage Vd applied between the first DC terminal 31 and the second DC terminal 32 (i.e., Vd / 2). The second threshold Vth2 is greater than Vd / 2. The first threshold Vth1 is, for example, 90% of Vd / 2. The second threshold Vth2 is, for example, 110% of Vd / 2. The control device 50 performs the first control operation described above when the detected potential at the fourth terminal 154 of the regenerative capacitor 15 is greater than the first threshold Vth1 and less than the second threshold Vth2.

[0076] The relationship between the first, second, third and fourth conditions and the second control operation (two-phase simultaneous control) and the third control operation (two-phase independent control) is as shown in Table 1.

[0077]

[0078] Note that "iU x iV x iW" is the product of the output currents iU, iV, and iW, where the polarity of the output currents iU, iV, and iW flowing in the direction of the arrow in Fig. 1 is positive and the polarity of the output currents iU, iV, and iW flowing in the opposite direction is negative. Instead of "iU x iV x iW", it is also possible to determine that the product of the multiple output currents iU, iV, and iW is positive when the value of sgn(iU) x sgn(iV) x sgn(iW) is positive "1", and to determine that the product of the multiple output currents iU, iV, and iW is negative when the value of sgn(iU) x sgn(iV) x sgn(iW) is "-1".

[0079] As described above, the first control operation is an operation in which the high-level period of the control signal to each of the switches 8 corresponding to each of the switching circuits 10 among the multiple switches 8 overlaps with the dead time Td and the start of the high-level period is advanced by an additional time from the start of the dead time Td. The high-level period of the control signal to the switch 8U is the period in which the potential level of the control signal SU6 to the first IGBT 6U is high or the period in which the potential level of the control signal SU7 to the second IGBT 7U is high. The high-level period of the control signal to the switch 8V is the period in which the potential level of the control signal SV6 to the first IGBT 6V is high or the period in which the potential level of the control signal SV7 to the second IGBT 7V is high. The high-level period of the control signal to the switch 8W is the period in which the potential level of the control signal SW6 to the first IGBT 6W is high or the period in which the potential level of the control signal SW7 to the second IGBT 7W is high. The additional time by which the high-level period of the control signal to the switch 8U is advanced from the start of the dead time Td is the additional time Tau described above. The additional time by which the high-level period of the control signal to the switch 8V is advanced from the start of the dead time Td is the additional time Tav described above. The additional time by which the high-level period of the control signal to the switch 8W is advanced from the start of the dead time Td is the additional time Taw described above.

[0080] The control device 50 performs the second control action when it determines that the first condition or the second condition is satisfied, as described above, and performs the third control action when it determines that the third condition or the fourth condition is satisfied. Examples of the second control action and the third control action will be described below with reference to FIGS.

[0081] Fig. 9 shows a time chart of an example when the control device 50 determines that the first condition is satisfied and performs the second control operation (two-phase simultaneous control). Fig. 10 shows a time chart of an example when the control device 50 determines that the second condition is satisfied and performs the second control operation (two-phase simultaneous control). Fig. 11 shows a time chart of an example when the control device 50 determines that the third condition is satisfied and performs the third control operation (two-phase independent control). Fig. 12 shows a time chart of an example when the control device 50 determines that the fourth condition is satisfied and performs the third control operation (two-phase independent control).

[0082] 9 to 12 show a carrier signal, six PWM signals SU1, SU2, SV1, SV2, SW1, and SW2, and three control signals out of six control signals SU6, SU7, SV6, SV7, SW6, and SW7. Also shown in FIGS. 9 to 12 are a current iL0, three output currents iU, iV, and iW, and voltages V across each of the three second switching elements 2U, 2V, and 2W. ２Ｕ , V ２Ｖ , V ２Ｗ9 to 12, when the high-level periods of the PWM signals SU1, SU2, SV1, SV2, SW1, and SW2 and the three control signals SU6, SV7, and SV8 are changed, the states before the change are indicated by two-dot chain lines. When the control device 50 shifts the high-level periods of the control signals (SU6, SU7, SV6, SV7, SW6, and SW7), it also changes the high-level periods of the PWM signals (SU1, SU2, SV1, SV2, SW1, and SW2) associated with those control signals. The PWM signals associated with the control signal SU6 are the PWM signals SU1 and SU2. The PWM signals associated with the control signal SU7 are the PWM signals SU1 and SU2. The PWM signals associated with the control signal SV6 are the PWM signals SV1 and SV2. The PWM signals associated with the control signal SV7 are the PWM signals SV1 and SV2. The PWM signals associated with the control signal SW6 are the PWM signals SW1 and SW2. The PWM signals associated with the control signal SW7 are the PWM signals SW1 and SW2. Furthermore, in FIGS. 9 to 12, when the high-level periods of the three control signals SU6, SV7, and SV7 are changed, the current iL0 of the resonant inductor L0 before the high-level periods are changed is indicated by a two-dot chain line. In FIGS. 9 to 12, the timing for detecting the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 is indicated by an arrow. The potential V15 at the fourth terminal 154 of the regenerative capacitor 15 is detected every carrier cycle. As a result, the control device 50 obtains the detected potential at the fourth terminal 154 of the regenerative capacitor 15 every carrier cycle. The timing at which the control device 50 acquires the detected potential of the fourth terminal 154 of the regenerative capacitor 15 is, for example, the same as the timing at which the potential V15 of the fourth terminal 154 of the regenerative capacitor 15 is detected, but is not limited to this.

[0083] 9 , when the detected potential at the fourth terminal 154 of the regenerative capacitor 15 is smaller than the first threshold Vth1, the control device 50 performs the second control operation so that the high-level period of the control signal SV7 overlaps with the high-level period of the control signal SW7 because the product of the three output currents iU, iV, and iW is positive. As a result, in the power conversion device 100, the amplitude of the current iL0 flowing through the resonance inductor L0 increases and the amount of charge stored in the regenerative capacitor 15 increases, so that the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 can be made equal to or higher than the first threshold Vth1. As a result, in the power conversion device 100, soft switching of the three first switching elements 1 and the three second switching elements 2 is realized.

[0084] 10 , when the detected potential at the fourth terminal 154 of the regenerative capacitor 15 is greater than the second threshold Vth2, the product of the three output currents iU, iV, and iW is negative, so the control device 50 performs the second control operation so that the high-level period of the control signal SV6 overlaps with the high-level period of the control signal SW6. As a result, in the power conversion device 100, the amplitude of the current iL0 flowing through the resonance inductor L0 increases and the amount of charge discharged to the regenerative capacitor 15 increases, so that the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 can be set to or less than the second threshold Vth2. As a result, in the power conversion device 100, soft switching of the three first switching elements 1 and the three second switching elements 2 is realized.

[0085] 11 , when the detected potential at the fourth terminal 154 of the regenerative capacitor 15 is smaller than the first threshold Vth1, the product of the three output currents iU, iV, and iW is negative, so the control device 50 performs the third control operation so that the high-level period of the control signal SV7 does not overlap with the high-level period of the control signal SW7. As a result, in the power conversion device 100, the amount of charge stored in the regenerative capacitor 15 increases, so that the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 can be made equal to or higher than the first threshold Vth1. As a result, in the power conversion device 100, soft switching of the three first switching elements 1 and the three second switching elements 2 is realized.

[0086] 12 , when the detected potential at the fourth terminal 154 of the regenerative capacitor 15 is greater than the second threshold Vth2, the control device 50 performs the third control operation so that the high-level period of the control signal SV7 does not overlap with the high-level period of the control signal SW7 because the product of the three output currents iU, iV, and iW is positive. As a result, in the power conversion device 100, the amplitude of the current iL0 flowing through the resonant inductor L0 when its polarity is negative is reduced, so that the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 can be set to or below the second threshold Vth2. As a result, in the power conversion device 100, soft switching of the three first switching elements 1 and the three second switching elements 2 is realized.

[0087] The control device 50 may include control that does not shift the high-level periods of the two control signals to two of the multiple switches 8 in the second control operation and the third control operation.

[0088] (4) Summary In the power conversion device 100 according to the first embodiment, the control device 50 performs a first control operation in which the high-level period of a control signal sent to each of the switches 8 corresponding to the switching circuits 10 among the multiple switches 8 overlaps with the dead time Td and the start point of the high-level period is advanced by an additional time from the start point of the dead time Td. This enables the power conversion device 100 to achieve zero-voltage soft switching of each of the multiple first switching elements 1 and the multiple second switching elements 2. The control device 50 of the power conversion device 100 also switches between a second control operation in which two of the multiple switches 8 are simultaneously controlled and a third control operation in which two of the multiple switches 8 are independently controlled, based on the detected potential at the fourth end 154 of the regenerative capacitor 15 and the polarities of the multiple output currents iU, iV, and iW output from the multiple AC terminals 41. This enables the power conversion device 100 to suppress fluctuations in the potential V15 of the regenerative capacitor 15, and increases the proportion of soft switching compared to when nothing is done to address fluctuations in the potential V15 of the regenerative capacitor 15, thereby improving power conversion efficiency and reducing noise.

[0089] Furthermore, in the power conversion device 100 according to embodiment 1, the control device 50 performs the second control operation when the first condition or the second condition is satisfied, and performs the third control operation when the third condition or the fourth condition is satisfied, thereby making it possible to suppress fluctuations in the potential V15 of the regenerative capacitor 15 regardless of the polarities of the multiple output currents iU, iV, iW output from the multiple AC terminals 41.

[0090] Furthermore, in the second control operation, the control device 50 in the power conversion device 100 according to the first embodiment shifts the high-level periods of two control signals to two of the multiple switches 8 to overlap each other. This enables the power conversion device 100 to increase the absolute value of the current iL0 flowing through the resonance inductor L0, and to increase the adjustment amount (range of change) of the potential V15 of the regenerative capacitor 15.

[0091] Furthermore, in the third control operation, the control device 50 in the power conversion device 100 according to the first embodiment shifts the high-level periods of two control signals to two of the multiple switches 8 to eliminate overlap between the high-level periods. This enables the power conversion device 100 to reduce the absolute value of the current iL0 flowing through the resonant inductor L0.

[0092] (Modification 1) A power conversion device 100A according to Modification 1 of Embodiment 1 will be described with reference to Fig. 13. Regarding the power conversion device 100A according to Modification 1 of Embodiment 1, components that are the same as those of the power conversion device 100 according to Embodiment 1 (see Fig. 1) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0093] In a power conversion device 100A according to the first modification, a first IGBT 6 and a second IGBT 7 are connected in anti-series in each of the plurality of switches 8. In the power conversion device 100A according to the first modification, a collector terminal of the first IGBT 6 and a collector terminal of the second IGBT 7 are connected in each of the plurality of switches 8, an emitter terminal of the first IGBT 6 is connected to a connection point 3 of a corresponding one of the plurality of switching circuits 10, and an emitter terminal of the second IGBT 7 is connected to a common connection point 25. Each of the plurality of switches 8 further includes a diode 61 connected in anti-parallel to the first IGBT 6 and a diode 71 connected in anti-parallel to the second IGBT 7.

[0094] In the power conversion device 100A according to the first modification, each of the first IGBT 6 and the second IGBT 7 may be replaced with a MOSFET or a bipolar transistor. In this case, the diode 61 and the diode 71 in FIG. 26 may be substituted with a parasitic diode of the replaced element, or an element built into the chip of the replaced element. Furthermore, in the power conversion device 100A according to the first modification, the diode 61 and the diode 71 are not limited to being externally connected to the first IGBT 6 and the second IGBT 7, but may also be an element built into the chip.

[0095] (Modification 2) A power conversion device 100A according to Modification 2 of Embodiment 1 will be described with reference to Fig. 14. Regarding the power conversion device 100A according to Modification 2 of Embodiment 1, components that are the same as those of the power conversion device 100 according to Embodiment 1 (see Fig. 1) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0096] In a power conversion device 100A according to the second modification, a first MOSFET 6A and a second MOSFET 7A are connected in anti-series in each of the multiple switches 8. In the power conversion device 100A according to the second modification, the drain terminal of the first MOSFET 6A and the drain terminal of the second MOSFET 7A are connected in anti-parallel in each of the multiple switches 8. Each of the multiple switches 8 further includes a diode 61 connected in anti-parallel to the first MOSFET 6A and a diode 71 connected in anti-parallel to the second MOSFET 7A. In each of the multiple switches 8, the source terminal of the second MOSFET 7A is connected to a common connection point 25. In each of the multiple switches 8, the source terminal of the first MOSFET 6A is connected to a connection point 3 of a switching circuit 10 corresponding to the switch 8 having the first MOSFET 6A. Control signals SU6 and SU7 are provided from a control device 50 to the first MOSFET 6A and the second MOSFET 7A of the switch 8U. The first MOSFET 6A and the second MOSFET 7A of the switch 8V are supplied with control signals SV6 and SV7 from the control device 50. The first MOSFET 6A and the second MOSFET 7A of the switch 8W are supplied with control signals SW6 and SW7 from the control device 50.

[0097] (Modification 3) A power conversion device 100A according to Modification 3 of Embodiment 1 will be described with reference to Fig. 15. With regard to the power conversion device 100A according to Modification 3 of Embodiment 1, components that are the same as those of the power conversion device 100 according to Embodiment 1 (see Fig. 1) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0098] In the power conversion device 100A according to the third modification, a diode 63 is connected in series to the first MOSFET 6A, and a diode 73 is connected in series to the second MOSFET 7A in each of the multiple switches 8. In the power conversion device 100A according to the third modification, the series circuit of the first MOSFET 6A and the diode 63 and the series circuit of the second MOSFET 7A and the diode 73 are connected in anti-parallel.

[0099] (Modification 4) A power conversion device 100A according to Modification 4 of Embodiment 1 will be described with reference to Fig. 16. With regard to the power conversion device 100A according to Modification 4 of Embodiment 1, components that are the same as those of the power conversion device 100 according to Embodiment 1 (see Fig. 1) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0100] In the power conversion device 100A according to the fourth modification, each of the multiple switches 8 includes one MOSFET 80, a diode 83 connected in anti-parallel to the MOSFET 80, a series circuit of two diodes 84 and 85 connected in anti-parallel to the MOSFET 80, and a series circuit of two diodes 86 and 87 connected in anti-parallel to the MOSFET 80. In each of the multiple switches 8, a connection point between the diode 84 and the diode 85 in the switch 8 (a first end 81 of the switch 8) is connected to a connection point 3 of a corresponding switching circuit 10 among the multiple switching circuits 10, and a connection point between the diode 86 and the diode 87 (a second end 82 of the switch 8) is connected to the common connection point 25. In each of the switches 8, when the MOSFET 80 is in an on state, the switch 8 is in an on state, and when the MOSFET 80 is in an off state, the switch 8 is in an off state.

[0101] The MOSFETs 80 of the multiple switches 8 are controlled by a control device 50. The control device 50 outputs a control signal SU8 that controls the on / off state of the MOSFET 80 of the switch 8U, a control signal SV8 that controls the on / off state of the MOSFET 80 of the switch 8V, and a control signal SW8 that controls the on / off state of the MOSFET 80 of the switch 8W.

[0102] In the switch 8, when the MOSFET 80 is in the on state, a resonant current flows due to a resonant circuit including the resonant inductor L0 and the resonant capacitor 9. In the power conversion device 100A, when one of the multiple switches 8 is in the on state, a charging current including the resonant current flows through the path of the regenerative capacitor 15, the resonant inductor L0, the diode 86, the MOSFET 80, the diode 85, and the resonant capacitor 9. In addition, in the power conversion device 100A, when one of the multiple switches 8 is in the on state, a discharging current including the resonant current flows through the path of the resonant capacitor 9, the diode 84, the MOSFET 80, the diode 87, the resonant inductor L0, and the regenerative capacitor 15.

[0103] In the power conversion device 100A according to the fourth modification, each of the plurality of MOSFETs 80 may be replaced with an IGBT. Furthermore, in the power conversion device 100A according to the fourth modification, each of the plurality of switches 8 may have, instead of the MOSFET 80, a bipolar transistor or a GaN-based GIT (Gate Injection Transistor), for example.

[0104] (Modification 5) A power conversion device 100A according to Modification 5 of Embodiment 1 will be described with reference to Fig. 17. With regard to the power conversion device 100A according to Modification 5 of Embodiment 1, components that are the same as those of the power conversion device 100 according to Embodiment 1 (see Fig. 1) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0105] In the power conversion device 100 according to the fifth modification, each of the multiple switches 8 is a dual-gate GaN-based GIT having a first source terminal, a first gate terminal, a second gate terminal, and a second source terminal. In the power conversion device 100A according to the fifth modification, a control signal SU6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT constituting the switch 8U, and a control signal SU7 is applied between the second gate terminal and the second source terminal. Furthermore, a control signal SV6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT constituting the switch 8V, and a control signal SV7 is applied between the second gate terminal and the second source terminal. Furthermore, a control signal SW6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT constituting the switch 8W, and a control signal SW7 is applied between the second gate terminal and the second source terminal.

[0106] (Embodiment 2) A power conversion device 100B according to embodiment 2 will be described below with reference to Fig. 18. The power conversion device 100B according to embodiment 2 differs from the power conversion device 100 according to embodiment 1 (see Fig. 1) in that it further includes a capacitor 16 connected between the second end of the resonance inductor L0 and the first DC terminal 31. In the power conversion device 100B according to embodiment 2, components similar to those of the power conversion device 100 according to embodiment 1 are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0107] The power conversion device 100B does not include the capacitor C10 in the power conversion device 100 according to the first embodiment. The capacitor 16 is connected in series with the regenerative capacitor 15. Therefore, in the power conversion device 100B, the series circuit of the capacitor 16 and the regenerative capacitor 15 is connected between the first DC terminal 31 and the second DC terminal 32. The capacitance of the capacitor 16 is the same as the capacitance of the regenerative capacitor 15. The phrase "the capacitance of the capacitor 16 is the same as the capacitance of the regenerative capacitor 15" does not necessarily mean that the capacitance of the capacitor 16 exactly matches the capacitance of the regenerative capacitor 15, but may mean that the capacitance of the capacitor 16 is within a range of 95% to 105% of the capacitance of the regenerative capacitor 15.

[0108] In the power conversion device 100B according to the second embodiment, the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 is equal to the voltage value Vd of the DC power supply E1 divided by the capacitor 16 and the regenerative capacitor 15. Therefore, the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 is Vd / 2. In the power conversion device 100B according to the second embodiment, the control device 50 may store the value of the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 in advance.

[0109] The control device 50 of the power conversion device 100B according to the second embodiment performs the first control operation, the second control operation, and the third control operation, similar to the control device 50 of the power conversion device 100 according to the first embodiment. Therefore, the power conversion device 100B according to the second embodiment can improve the power conversion efficiency, similar to the power conversion device 100 according to the first embodiment.

[0110] (Third embodiment) A power conversion device 100C according to a third embodiment will be described below with reference to Fig. 19. The power conversion device 100C according to the third embodiment differs from the power conversion device 100 according to the first embodiment (see Fig. 1) in that a regenerative capacitor 15 is connected between the second end of the resonance inductor L0 and the first DC terminal 31. In the power conversion device 100C according to the third embodiment, components similar to those of the power conversion device 100 according to the first embodiment are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0111] The control device 50 of the power conversion device 100C according to the third embodiment performs the first control operation, the second control operation, and the third control operation, similar to the control device 50 of the power conversion device 100 according to the first embodiment. Therefore, the power conversion device 100C according to the third embodiment can improve the power conversion efficiency, similar to the power conversion device 100 according to the first embodiment.

[0112] Fourth Embodiment A power conversion device 100D according to a fourth embodiment will be described below with reference to Fig. 20. In the power conversion device 100D according to the fourth embodiment, components similar to those of the power conversion device 100 according to the first embodiment (see Fig. 1) are designated by the same reference numerals, and description thereof will be omitted.

[0113] In the power conversion device 100D, the fourth end 154 of the regenerative capacitor 15 is connected to a plurality of resonant circuits 20. Each of the plurality of resonant circuits 20 includes a resonant capacitor 9 and a resonant inductor L4. The resonant capacitor 9 is connected between the first end 81 of a corresponding one of the plurality of switches 8 and the second DC terminal 32. The resonant inductor L4 is connected between the second end 82 of a corresponding one of the plurality of switches 8 and the fourth end 154 of the regenerative capacitor 15. Hereinafter, the resonant inductor L4 connected to the switch 8U will be referred to as the resonant inductor L11, the resonant inductor L4 connected to the switch 8V will be referred to as the resonant inductor L21, and the resonant inductor L4 connected to the switch 8W will be referred to as the resonant inductor L31. The inductances of the resonant inductors L11, L21, and L31 are the same.

[0114] Each of the multiple resonant circuits 20 includes a second resonant inductor L5, which is separate from the first resonant inductor L4, and a selector switch 18 connected to the second resonant inductor L5. In each of the multiple resonant circuits 20, a series circuit including the second resonant inductor L5 and the selector switch 18 is connected in parallel to the first resonant inductor L4. The resonant frequency of each of the multiple resonant circuits 20 changes depending on whether the selector switch 18 is turned on or off. Hereinafter, the second resonant inductor L5 and the selector switch 18 of the series circuit connected in parallel to the first resonant inductor L11 may also be referred to as the second resonant inductor L12 and the selector switch 18U. Furthermore, the second resonant inductor L5 and the selector switch 18 of the series circuit connected in parallel to the first resonant inductor L21 may also be referred to as the second resonant inductor L22 and the selector switch 18V. Furthermore, the second resonant inductor L5 and the changeover switch 18 of the series circuit connected in parallel to the first resonant inductor L31 may also be referred to as the second resonant inductor L32 and the changeover switch 18W.

[0115] The inductance of the second resonant inductor L12, the inductance of the second resonant inductor L22, and the inductance of the second resonant inductor L32 are the same.

[0116] Each of the changeover switches 18U, 18V, and 18W is, for example, an IGBT. The changeover switches 18U, 18V, and 18W are controlled by control signals SU3, SV3, and SW3 from the control device 50. Each of the changeover switches 18U, 18V, and 18W is not limited to an IGBT, and may be, for example, a MOSFET, a GIT, or a bipolar transistor.

[0117] The control device 50 sets a dead time Td between the high level period of the PWM signals SU1, SV1, SW1 to the first switching element 1 and the high level period of the PWM signals SU2, SV2, SW2 to the second switching element for each of the multiple switching circuits 10.

[0118] The control device 50 performs a first control operation. In the first control operation, the high-level period of a control signal to each of the switches 8 corresponding to the plurality of switching circuits 10 among the plurality of switches 8 is overlapped with the dead time Td, and the start point of the high-level period is advanced by an additional time from the start point of the dead time Td. The control device 50 changes the resonant frequency of at least one of the plurality of resonant circuits 20 in accordance with the potential V15 of the fourth end 154 of the regenerative capacitor 15.

[0119] 21 and 22 show a carrier signal, three control signals among the three control signals SU6, SU7, SV6, SV7, SW6, and SW7, currents iL1, iL2, and iL3, and voltages V across each of the three second switching elements 2U, 2V, and 2W. ２Ｕ , V ２Ｖ , V ２Ｗ21 and 22 , the timing for detecting the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 is indicated by an arrow. The potential V15 at the fourth terminal 154 of the regenerative capacitor 15 is detected every carrier cycle. As a result, the control device 50 obtains the detected potential at the fourth terminal 154 of the regenerative capacitor 15 every carrier cycle. The timing for obtaining the detected potential at the fourth terminal 154 of the regenerative capacitor 15 in the control device 50 is, for example, the same as the timing for detecting the potential V15 at the fourth terminal 154 of the regenerative capacitor 15, but is not limited to this.

[0120] When the detected potential at the fourth end 154 of the regenerative capacitor 15 is smaller than the first threshold value Vth1, the control device 50 turns on, for example, one of the three changeover switches 18U, 18V, and 18W, to shorten the high-level period of the control signal SU6 sent to the first IGBT 6U of the switch 8U (in FIG. 21 , the control signal SU6 before shortening is indicated by a two-dot chain line). As a result, the power conversion device 100D shortens the resonance period of the resonant circuit 20 including the first resonant inductor L11 and the resonant capacitor 9U out of the three resonant circuits 20, thereby reducing the amount of charge discharged from the regenerative capacitor 15 and making it possible to make the potential V15 at the fourth end 154 of the regenerative capacitor 15 larger than the first threshold value Vth1.

[0121] Furthermore, when the detected potential at the fourth end 154 of the regenerative capacitor 15 is greater than the second threshold value Vth2, the control device 50 turns on, for example, one of the three changeover switches 18U, 18V, and 18W, to shorten the high-level period of the control signal SU7 sent to the second IGBT 7U of the switch 8U (the control signal SU7 before shortening is shown by a two-dot chain line in FIG. 22 ). As a result, the power conversion device 100 shortens the resonance period of the resonant circuit 20 including the first resonant inductor L11 and the resonant capacitor 9U out of the three resonant circuits 20, thereby reducing the amount of charge stored in the regenerative capacitor 15 and making it possible to make the potential V15 at the fourth end 154 of the regenerative capacitor 15 greater than the first threshold value Vth1.

[0122] In the power conversion device 100D according to the fourth embodiment, the control device 50 changes the resonance period of at least one of the multiple resonance circuits 20 in accordance with the potential V15 at the fourth end 154 of the regenerative capacitor 15. As a result, the power conversion device 100D according to the fourth embodiment can suppress fluctuations in the potential V15 at the fourth end 154 of the regenerative capacitor 15, even when, for example, the motor of the AC load RA1 locks and the load state changes, thereby enabling improvement in power conversion efficiency.

[0123] Fifth Embodiment A power conversion device 100E according to a fifth embodiment will be described below with reference to Fig. 23. With respect to the power conversion device 100E according to the fifth embodiment, components similar to those of the power conversion device 100D according to the fourth embodiment will be denoted by the same reference numerals, and description thereof will be omitted.

[0124] In the power conversion device 100E, each of the multiple (three) resonant circuits 20 has a resonant inductor L4. Hereinafter, the resonant inductor L4 connected to the switch 8U will be referred to as the resonant inductor L1, the resonant inductor L4 connected to the switch 8V will be referred to as the resonant inductor L2, and the resonant inductor L4 connected to the switch 8W will be referred to as the resonant inductor L3. The inductance of the resonant inductor L1, the inductance of the resonant inductor L2, and the inductance of the resonant inductor L3 are all the same.

[0125] Moreover, in the power conversion device 100E, each of the plurality of resonant circuits 20 has a second resonant capacitor 91 that is separate from the first resonant capacitor 9, which is the resonant capacitor 9, and a selector switch 92 that is connected to the second resonant capacitor 91. In each of the plurality of resonant circuits 20, a series circuit of the second resonant capacitor 91 and the selector switch 92 is connected in parallel to the first resonant capacitor 9. The resonant frequency of each of the plurality of resonant circuits 20 changes depending on whether the selector switch 92 is turned on or off.

[0126] Hereinafter, the first resonant capacitor 9 connected to the switch 8U will be referred to as the first resonant capacitor 9U, the first resonant capacitor 9 connected to the switch 8V will be referred to as the first resonant capacitor 9V, and the first resonant capacitor 9 connected to the switch 8W will be referred to as the first resonant capacitor 9W. Also, the second resonant capacitor 91 connected to the switch 8U will be referred to as the second resonant capacitor 91U, the second resonant capacitor 91 connected to the switch 8V will be referred to as the second resonant capacitor 91V, and the second resonant capacitor 91 connected to the switch 8W will be referred to as the second resonant capacitor 91W. Also, the changeover switch 92 connected in series to the second resonant capacitor 91U will be referred to as the changeover switch 92U, the changeover switch 92 connected in series to the second resonant capacitor 91V will be referred to as the changeover switch 92V, and the changeover switch 92 connected in series to the second resonant capacitor 91W will be referred to as the changeover switch 92W.

[0127] The capacitance of the second resonant capacitor 91U, the capacitance of the second resonant capacitor 91V, and the capacitance of the second resonant capacitor 91W are the same.

[0128] The changeover switches 92U, 92V, and 92W are each, for example, an IGBT, and are controlled by control signals SU9, SV9, and SW9 from the control device 50. The changeover switches 92U, 92V, and 92W are not limited to being an IGBT, and may be, for example, a MOSFET, a GIT, or a bipolar transistor.

[0129] The control device 50 sets a dead time Td between the high level period of the PWM signals SU1, SV1, SW1 to the first switching element 1 and the high level period of the PWM signals SU2, SV2, SW2 to the second switching element for each of the multiple switching circuits 10.

[0130] The control device 50 performs a first control operation. In the first control operation, the high-level period of the control signal for each of the switches 8 corresponding to the switching circuits 10 among the multiple switches 8 is overlapped with the dead time Td, and the start point of the high-level period is advanced by an additional time from the start point of the dead time Td. The control device 50 changes the resonant period by switching the selector switch 92 of at least one of the multiple resonant circuits 20 on and off in accordance with the potential V15 of the fourth terminal 154 of the regenerative capacitor 15. As a result, the power conversion device 100E according to the fifth embodiment can suppress fluctuations in the potential V15 of the fourth terminal 154 of the regenerative capacitor 15, even when, for example, the motor of the AC load RA1 locks and the load state changes. This suppresses fluctuations in the potential V15 of the fourth terminal 154 of the regenerative capacitor 15, thereby improving power conversion efficiency.

[0131] (Other Modifications) The above-described first to fifth embodiments are merely examples of various embodiments of the present disclosure. The above-described first to fifth embodiments can be modified in various ways depending on the design, etc., as long as the object of the present disclosure can be achieved.

[0132] For example, each of the plurality of first switching elements 1 and the plurality of second switching elements 2 is not limited to an IGBT but may be a MOSFET. In this case, each of the plurality of first diodes 4 may be substituted with a parasitic diode of the MOSFET constituting the corresponding first switching element 1. Also, each of the plurality of second diodes 5 may be substituted with a parasitic diode of the MOSFET constituting the corresponding second switching element 2. The MOSFET is, for example, a Si-based MOSFET or a SiC-based MOSFET. Each of the plurality of first switching elements 1 and the plurality of second switching elements 2 may be, for example, a bipolar transistor or a GaN-based GIT.

[0133] In addition, in the power conversion devices 100, 100A, 100B, 100C, 100D, and 100E, if the capacitance of each of the multiple resonant capacitors 9 is relatively small, instead of attaching the multiple resonant capacitors 9 externally, the parasitic capacitance between both ends of the multiple second switching elements 2 may also serve as the multiple resonant capacitors 9.

[0134] Furthermore, each of the switches 8 in the second to fifth embodiments other than the first embodiment may have the configuration shown in any one of the examples of FIGS.

[0135] Furthermore, the power conversion devices 100, 100A, 100B, 100C, 100D, and 100E are not limited to being configured to output three-phase AC, but may be configured to output polyphase AC with three or more phases.

[0136] (Aspects) The following aspects are disclosed in this specification.

[0137] A power conversion device (100; 100A; 100B; 100C) according to a first aspect includes a first DC terminal (31), a second DC terminal (32), a power conversion circuit (11), a plurality of AC terminals (41), a plurality of switches (8), a plurality of resonant capacitors (9), a resonant inductor (L0), a regenerative capacitor (15), and a control device (50). 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) are connected in parallel to each other, each of which has a plurality of first switching elements (1) and a plurality of second switching elements (2) connected in series in a one-to-one relationship. In the power conversion circuit (11), the plurality of first switching elements (1) are connected to the first DC terminal (31), and the plurality of second switching elements (2) are connected to the second DC terminal (32). The plurality of AC terminals (41) correspond one-to-one to the plurality of switching circuits (10). Each of the plurality of AC terminals (41) is connected to a connection point (3) between a first switching element (1) and a second switching element (2) in the corresponding switching circuit (10). The plurality of switches (8) correspond one-to-one to the plurality of switching circuits (10). Each of the plurality of switches (8) has a first end (81) connected to a connection point (3) between the first switching element (1) and the second switching element (2) in the corresponding switching circuit (10), and a second end (82) commonly connected to a common connection point (25). The plurality of resonant capacitors (9) correspond one-to-one to the plurality of switches (8). Each of the plurality of resonant capacitors (9) is connected between a first end (81) of the corresponding switch (8) and a second DC terminal (32). The resonant inductor (L0) has a first end and a second end. In the resonant inductor (L0), a first end of the resonant inductor (L0) is connected to the common connection point (25). The regenerative capacitor (15) has a third end (153) and a fourth end (154). In the regenerative capacitor (15), the third end (153) is connected to the first DC terminal (31) or the second DC terminal (32).A control device (50) supplies PWM signals (SU1, SV1, SW1, SU2, SV2, SW2) whose potential changes between high and low levels to each of a plurality of first switching elements (1) and a plurality of second switching elements (2). The control device (50) performs a first control operation. In the first control operation, the control device (50) sets a dead time (Td) between a high-level period of the PWM signals (SU1, SV1, SW1) to the first switching elements (1) and a high-level period of the PWM signals (SU2, SV2, SW2) to the second switching elements (2) for each of the plurality of switching circuits (10). In a first control operation, the control device (50) overlaps a high-level period of a control signal to a switch (8) among the plurality of switches (8) corresponding to each of the plurality of switching circuits (10) with a dead time (Td) and advances the start point of the high-level period by an additional time from the start point of the dead time (Td). The control device (50) switches between a second control operation in which the high-level periods of the control signals of two of the plurality of switches (8) overlap, and a third control operation in which the high-level periods of the control signals of the plurality of switches (8) do not overlap, based on the detected potential at the fourth end (154) of the regenerative capacitor (15) and the polarities of the plurality of output currents (iU, iV, iW) output from the plurality of AC terminals (41).

[0138] According to this aspect, it is possible to improve the power conversion efficiency.

[0139] In the power conversion device (100; 100A; 100B; 100C) according to the second aspect, in the first aspect, the control device (50) performs the second control action when the first condition or the second condition is satisfied, and performs the third control action when the third condition or the fourth condition is satisfied. The first condition is that the detected potential at the fourth end (154) of the regenerative capacitor (15) is smaller than a first threshold (Vth1) that is smaller than half the voltage value (Vd) applied between the first DC terminal (31) and the second DC terminal (32), and the product of the multiple output currents (iU, iV, iW) is positive. The second condition is that the detected potential at the fourth end (154) of the regenerative capacitor (15) is greater than a second threshold (Vth2) that is greater than half the voltage value (Vd) applied between the first DC terminal (31) and the second DC terminal (32), and the product of the plurality of output currents (iU, iV, iW) is negative. The third condition is that the detected potential at the fourth end (154) of the regenerative capacitor (15) is smaller than a first threshold (Vth1) that is less than half the voltage value (Vd) applied between the first DC terminal (31) and the second DC terminal (32), and the product of the plurality of output currents (iU, iV, iW) is negative. The fourth condition is that the detected potential at the fourth terminal (154) of the regenerative capacitor (15) is greater than a second threshold value (Vth2) that is greater than half the voltage value (Vd) applied between the first DC terminal (31) and the second DC terminal (32), and the product of the multiple output currents (iU, iV, iW) is positive.

[0140] According to this aspect, it is possible to suppress fluctuations in the potential (V15) of the regenerative capacitor (15) regardless of the polarity of the multiple output currents (iU, iV, iW) output from the multiple AC terminals (41).

[0141] A power conversion device (100; 100A; 100B; 100C) according to a third aspect is based on the first or second aspect. In a second control operation, the control device (50) shifts high-level periods of two control signals to two switches (8) among the plurality of switches (8) so that the high-level periods overlap each other.

[0142] According to this aspect, the absolute value of the current (iL0) flowing through the resonance inductor (L0) can be increased, and the adjustment amount (variation range) of the potential (V15) of the regenerative capacitor (15) can be increased.

[0143] A power conversion device (100; 100A; 100B; 100C) according to a fourth aspect is based on the first or second aspect. In a second control operation, the control device (50) shifts high-level periods of two control signals to two switches (8) among the plurality of switches (8) so that the high-level periods partially overlap each other.

[0144] According to this aspect, the absolute value of the current (iL0) flowing through the resonance inductor (L0) can be increased, and the adjustment amount (variation range) of the potential (V15) of the regenerative capacitor (15) can be increased.

[0145] A power conversion device (100; 100A; 100B; 100C) according to a fifth aspect is based on any one of the first to fourth aspects. In a third control operation, the control device (50) shifts high-level periods of two control signals to two of the multiple switches (8) to eliminate overlap between the high-level periods.

[0146] According to this aspect, the absolute value of the current (iL0) flowing through the resonant inductor (L0) can be reduced.

[0147] A power conversion device (100; 100A; 100B; 100C) according to a sixth aspect is based on any one of the first to fifth aspects. In the second control operation and the third control operation, the control device (50) includes control that does not shift high-level periods of two control signals to two switches (8) among the plurality of switches (8).

[0148] A power conversion device (100D; 100E) according to a seventh aspect includes a first DC terminal (31), a second DC terminal (32), a power conversion circuit (11), a plurality of AC terminals (41), a plurality of switches (8), a plurality of resonant circuits (20), a regenerative capacitor (15), and a control device (50). 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) are connected in parallel to each other, each of which has a plurality of first switching elements (1) and a plurality of second switching elements (2) connected in series in a one-to-one relationship. In the power conversion circuit (11), the plurality of first switching elements (1) are connected to the first DC terminal (31), and the plurality of second switching elements (2) are connected to the second DC terminal (32). The plurality of AC terminals (41) correspond one-to-one to the plurality of switching circuits (10). Each of the multiple AC terminals (41) is connected to a connection point (3) between a first switching element (1) and a second switching element (2) in a corresponding switching circuit (10). The multiple switches (8) correspond one-to-one to the multiple switching circuits (10). Each of the multiple switches (8) has a first end (81) connected to a connection point (3) between the first switching element (1) and the second switching element (2) in the corresponding switching circuit (10). The multiple resonant circuits (20) correspond one-to-one to the multiple switches (8) and have variable resonant frequencies. The regenerative capacitor (15) has a third end (153) and a fourth end (154). The third end (153) of the regenerative capacitor (15) is connected to the first DC terminal (31) or the second DC terminal (32), and the fourth end (154) is connected to the multiple resonant circuits (20). A control device (50) applies a PWM signal whose potential changes between a high level and a low level to each of a plurality of first switching elements (1) and a plurality of second switching elements (2).Each of the plurality of resonant circuits (20) has a resonant capacitor (9) connected between a first end (81) of a corresponding switch (8) among the plurality of switches (8) and a second DC terminal (32), and a resonant inductor (L4) connected between a second end (82) of the corresponding switch (8) among the plurality of switches (8) and a fourth end (154) of the regenerative capacitor (15). The control device (50) sets a dead time (Td) between a high-level period of a PWM signal to a first switching element (1) and a high-level period of a PWM signal to a second switching element (2) for each of the plurality of switching circuits (10). The control device (50) performs a first control operation. In the first control operation, the control device (50) overlaps the high-level period of a control signal to a switch (8) among the plurality of switches (8) corresponding to each of the plurality of switching circuits (10) with the dead time (Td), and advances the start of the high-level period by an additional time from the start of the dead time (Td). The control device (50) changes the resonance period of at least one of the plurality of resonance circuits (20) according to the potential (V15) of the fourth terminal (154) of the regenerative capacitor (15).

[0149] According to this aspect, it is possible to improve the power conversion efficiency.

[0150] In a power conversion device (100D) according to an eighth aspect, in the seventh aspect, each of the plurality of resonant circuits (20) has a second resonant inductor (L5) separate from the first resonant inductor (L4) that is the resonant inductor (L4), and a changeover switch (18) connected to the second resonant inductor (L5). In each of the plurality of resonant circuits (20), a series circuit of the second resonant inductor (L5) and the changeover switch (18) is connected in parallel to the first resonant inductor (L4). The resonant frequency of each of the plurality of resonant circuits (20) changes depending on whether the changeover switch (18) is turned on or off.

[0151] In a power conversion device (100E) according to a ninth aspect, in the seventh aspect, each of the plurality of resonant circuits (20) has a second resonant capacitor (91) separate from the first resonant capacitor (9) that is the resonant capacitor (9), and a selector switch (92) connected to the second resonant capacitor (91). In each of the plurality of resonant circuits (20), a series circuit of the second resonant capacitor (91) and the selector switch (92) is connected in parallel to the first resonant capacitor (9). The resonant frequency of each of the plurality of resonant circuits (20) changes depending on whether the selector switch (92) is turned on or off.

[0152] 1 First switching element 2 Second switching element 3 Connection point 8 Switch 81 First terminal 82 Second terminal 9 Resonant capacitor (first resonant capacitor) 10 Switching circuit 11 Power conversion circuit 15 Regenerative capacitor 153 Third terminal 154 Fourth terminal 18 Changeover switch 20 Resonant circuit 31 First DC terminal 32 Second DC terminal 41 AC terminal 50 Control device 91 Second resonant capacitor 92 Changeover switch 100, 100A, 100B, 100C, 100D, 100E Power conversion device iU, iV, iW Output current L0 Resonant inductor L1 First resonant inductor L2 Second resonant inductor L3 Third resonant inductor L4 First resonant inductor L5 Second resonant inductor Td Dead time Vd Voltage value Vth1 First threshold Vth2 Second threshold

Claims

1. A first DC terminal and a second DC terminal; a power conversion circuit including a plurality of first switching elements and a plurality of second switching elements, the plurality of first switching elements being connected in series to the plurality of second switching elements in a one-to-one relationship, the plurality of switching circuits being connected in parallel to each other, the plurality of first switching elements being connected to the first DC terminal, and the plurality of second switching elements being connected to the second DC terminal; a plurality of AC terminals in one-to-one correspondence with the plurality of switching circuits, each AC terminal being connected to a connection point of the first switching element and the second switching element in the corresponding switching circuit; a plurality of switches each corresponding to the plurality of switching circuits, each having a first end connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit and a second end commonly connected to a common connection point; a plurality of resonance capacitors corresponding to the plurality of switches one-to-one, each of the resonance capacitors being connected between the first end and the second DC terminal of the corresponding switch; a resonant inductor having a first end and a second end, the first end being connected to the common connection point; a regenerative capacitor having a third end and a fourth end, the third end being connected to the first DC terminal or the second DC terminal; a control device that applies a PWM signal whose potential changes between a high level and a low level to each of the first switching elements and the second switching elements; The control device includes: a first control operation is performed to set a dead time between a high level period of a PWM signal to the first switching element and a high level period of a PWM signal to the second switching element for each of the plurality of switching circuits, overlap a high level period of a control signal to a switch among the plurality of switches corresponding to each of the plurality of switching circuits with the dead time, and advance a start point of the high level period by an additional time from a start point of the dead time; switching between a second control operation in which high-level periods of control signals for two of the plurality of switches are overlapped and a third control operation in which high-level periods of control signals for the plurality of switches are not overlapped, based on a detected potential at the fourth end of the regenerative capacitor and polarities of a plurality of output currents output from the plurality of AC terminals; Power conversion equipment.

2. The control device includes: performing the second control action when the first condition or the second condition is satisfied; performing the third control action when a third condition or a fourth condition is satisfied; The first condition is: a detected potential at the fourth end of the regenerative capacitor is smaller than a first threshold value that is smaller than half of a voltage value applied between the first DC terminal and the second DC terminal, and a product of the plurality of output currents is positive; The second condition is: a detected potential at the fourth end of the regenerative capacitor is greater than a second threshold value that is greater than half of a voltage value applied between the first DC terminal and the second DC terminal, and a product of the plurality of output currents is negative; The third condition is: a detected potential at the fourth end of the regenerative capacitor is smaller than a first threshold value that is smaller than half of a voltage value applied between the first DC terminal and the second DC terminal, and a product of the plurality of output currents is negative; The fourth condition is: a detected potential at the fourth end of the regenerative capacitor is greater than a second threshold value that is greater than half the voltage value applied between the first DC terminal and the second DC terminal, and a product of the plurality of output currents is positive; The power conversion device according to claim 1 .

3. The control device includes: In the second control operation, shifting high-level periods of two control signals to two switches among the plurality of switches to overlap each other; The power conversion device according to claim 1 or 2.

4. The control device includes: In the second control operation, shifting high level periods of two control signals to two switches among the plurality of switches so that the high level periods partially overlap each other; The power conversion device according to claim 1 or 2.

5. The control device includes: In the third control operation, shifting high-level periods of two control signals to two switches among the plurality of switches to eliminate overlap between the high-level periods; The power conversion device according to claim 1 or 2.

6. The control device includes: In the second control operation and the third control operation, a control is included in which high level periods of two control signals to two switches among the plurality of switches are not shifted. The power conversion device according to claim 1 or 2.

7. A first DC terminal and a second DC terminal; a power conversion circuit including a plurality of first switching elements and a plurality of second switching elements, the plurality of first switching elements being connected in series to the plurality of second switching elements in a one-to-one relationship, the plurality of switching circuits being connected in parallel to each other, the plurality of first switching elements being connected to the first DC terminal, and the plurality of second switching elements being connected to the second DC terminal; a plurality of AC terminals in one-to-one correspondence with the plurality of switching circuits, each AC terminal being connected to a connection point of the first switching element and the second switching element in the corresponding switching circuit; a plurality of switches corresponding one-to-one to the plurality of switching circuits, each having a first end connected to the connection point between the first switching element and the second switching element in the corresponding switching circuit; a plurality of resonant circuits each corresponding to the plurality of switches and each having a variable resonant frequency; a regenerative capacitor having a third end and a fourth end, the third end being connected to the first DC terminal or the second DC terminal, and the fourth end being connected to the plurality of resonant circuits; a control device that applies a PWM signal whose potential changes between a high level and a low level to each of the first switching elements and the second switching elements; Each of the plurality of resonant circuits is a resonance capacitor connected between the first end and the second DC terminal of a corresponding switch among the plurality of switches; a resonance inductor connected between a second terminal of a corresponding one of the plurality of switches and the fourth terminal of the regenerative capacitor, The control device includes: a first control operation is performed to set a dead time between a high level period of a PWM signal to the first switching element and a high level period of a PWM signal to the second switching element for each of the plurality of switching circuits, overlap a high level period of a control signal to a switch among the plurality of switches corresponding to each of the plurality of switching circuits with the dead time, and advance a start point of the high level period by an additional time from a start point of the dead time; changing a resonance period of at least one of the plurality of resonance circuits in response to a potential of the fourth end of the regenerative capacitor; Power conversion equipment.

8. Each of the plurality of resonant circuits is a second resonant inductor separate from the first resonant inductor, which is the resonant inductor; and a changeover switch connected to the second resonant inductor, a series circuit of the second resonant inductor and the changeover switch is connected in parallel to the first resonant inductor; The resonant frequency changes depending on whether the changeover switch is turned on or off. The power converter according to claim 7.

9. Each of the plurality of resonant circuits is a second resonant capacitor separate from the first resonant capacitor, which is the resonant capacitor; and a changeover switch connected to the second resonant capacitor, a series circuit of the second resonant capacitor and the changeover switch is connected in parallel to the first resonant capacitor; The resonant frequency changes depending on whether the changeover switch is turned on or off. The power converter according to claim 7.