Electric power conversion apparatus

Abstract

The present invention addresses the problem of reducing radiation noise. An electric power conversion apparatus (100) is provided with a power conversion circuit (11), a switch (8), a resonance capacitor (9), a resonance inductor (L1), a regeneration capacitor (15), and a control device (50). The switch (8) includes a third switching element (6) and a fourth switching element (7). The control device (50) controls a first switching element (1), a second switching element (2), the third switching element (6), and the fourth switching element (7). The control device (50) makes at least a portion of a high-level period of a control signal to the switch (8) overlap a dead time period thereof. During a ringing period in which ringing occurs at both end voltages of the third switching element (6), the control device (50) makes the third switching element (6) maintain the state immediately before the ringing period.

Description

Power Conversion Device

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

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

[0003] The power conversion system (power conversion device) disclosed in Patent Document 1 includes a switching means having a pair of main switching elements (first switching element and second switching element) connected in series with each other, diodes (first diode and second diode) connected in anti-parallel to each main switching element, an auxiliary circuit for performing soft switching of each main switching element, and a controller. The auxiliary circuit includes two capacitors, a coil (resonant inductor), and an auxiliary switch. The controller generates control signals for PWM control of each main switching element and outputs them to the gates of each main switching element. The controller also generates control signals for controlling the on / off of the auxiliary switches and outputs them to the gates of the auxiliary switches.

[0004] In a power conversion device, radiation noise may increase.

[0005] JP 2010-233306 A

[0006] An object of the present disclosure is to provide a power conversion device capable of reducing radiation noise.

[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, a switch, a resonant capacitor, a resonant inductor, a regenerative capacitor, and a control device. The power conversion circuit includes a switching circuit. The switching circuit includes a first switching element and a second switching element connected in series to each other, a first diode connected in anti-parallel to the first switching element, and a second diode connected in anti-parallel to the second switching element. In the switching circuit, the first switching element is connected to the first DC terminal, and the second switching element is connected to the second DC terminal. The switch has a first end and a second end. The first end of the switch is connected to a connection point between the first switching element and the second switching element. The resonant capacitor is connected between the first end and the second DC terminal of the switch. The resonant inductor is connected to the second end of the switch. The regenerative capacitor is connected between the resonant inductor and the second DC terminal. The control device controls the first switching element, the second switching element, and the switch. The switch includes a third switching element and a fourth switching element. When the third switching element is in an on state, a current flows from the resonant inductor side. When the fourth switching element is in an on state, a current flows in the opposite direction to that of the third switching element. The control device provides a control signal whose potential changes between a high level and a low level to each of the first switching element, the second switching element, the third switching element, and the fourth switching element. The control device sets a dead time period between a high level period of the control signal to the first switching element and a high level period of the control signal to the second switching element. The control device overlaps at least a portion of the high level period of the control signal to the third switching element with the dead time period. During a ringing period in which ringing occurs in the voltage across the third switching element, the control device causes the third switching element to maintain a state immediately before the ringing period.

[0008] FIG. 1 is a circuit diagram of a system including a power conversion apparatus according to a first embodiment. FIG. 2 is a diagram illustrating time variations in duty and load current corresponding to voltage commands for each of three phases in an AC load connected to multiple AC terminals of the power conversion apparatus. FIG. 3 is an explanatory diagram of the basic operation of the power conversion apparatus. FIG. 4 is an explanatory diagram of the basic operation of the power conversion apparatus. FIG. 5 is an explanatory diagram of the basic operation of the power conversion apparatus. FIG. 6 is an explanatory diagram of the operation of the power conversion apparatus. FIG. 7 is an explanatory diagram of the operation of the power conversion apparatus. FIG. 8 is a timing chart illustrating the operation of the power conversion apparatus. FIG. 9 is a timing chart illustrating the operation of a comparative example of the power conversion apparatus. FIG. 10 is a characteristic diagram illustrating measurement results of radiation noise of an example and a comparative example of the power conversion apparatus. FIG. 11 is a circuit diagram of a system including a power conversion apparatus according to a second embodiment. FIG. 12 is a circuit diagram of a system including a power conversion apparatus according to a third embodiment. FIG. 13 is a circuit diagram of a system including a power conversion apparatus according to a fourth embodiment. FIG. 14 is a circuit diagram of a system including a power conversion apparatus according to a fifth embodiment. Fig. 15 is a timing chart for explaining the operation of the above power conversion device. Fig. 16 is a circuit diagram of a system including a power conversion device according to embodiment 6. Fig. 17 is a circuit diagram of a system including a power conversion device according to embodiment 7. Fig. 18 is a circuit diagram of a system including a power conversion device according to embodiment 8.

[0009] First Embodiment A power conversion device 100 according to a first embodiment will be described below with reference to FIGS.

[0010] (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 (three in the example of FIG. 1 ) AC terminals 41. In the power conversion device 100, 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.

[0011] The power conversion device 100 includes a power conversion circuit 11, a plurality of switches 8 (three in the example of FIG. 1 ), a plurality of resonant capacitors 9 (three in the example of FIG. 1 ), a regenerative capacitor 15, a plurality of resonant inductors L1 (three in the example of FIG. 1 ), and a control device 50. Each of the plurality of switches 8 is, for example, a bidirectional switch.

[0012] The power conversion circuit 11 has a plurality (three in the example of FIG. 1 ) of first switching elements 1 and a plurality (three in the example of FIG. 1 ) of second switching elements 2. In the power conversion circuit 11, a plurality (three in the example of FIG. 1 ) of switching circuits 10, each having a plurality of first switching elements 1 and a plurality of second switching elements 2 connected in series in a one-to-one relationship, are connected in parallel to each other. In the power conversion circuit 11, the plurality of first switching elements 1 are connected to first DC terminals 31, and the plurality of second switching elements 2 are connected to second DC terminals 32.

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

[0014] The multiple switches 8 correspond one-to-one to the multiple switching circuits 10. Each of the multiple switches 8 has a first end 81 and a second end 82. The first end 81 of each of the multiple switches 8 is connected to a connection point 3 between a first switching element 1 and a second switching element 2 in a corresponding one of the multiple switching circuits 10.

[0015] The plurality of resonance capacitors 9 correspond one-to-one to the plurality of switches 8. Each of the plurality of resonance capacitors 9 is connected between the first end 81 of the corresponding switch 8 among the plurality of switches 8 and the second DC terminal 32.

[0016] Each of the plurality of resonant inductors L1 has a third end and a fourth end. The fourth end of each of the plurality of resonant inductors L1 is connected to the regenerative capacitor 15. The third end of each of the plurality of resonant inductors L1 is connected to the second end 82 of a corresponding one of the plurality of switches 8.

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

[0018] 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 .

[0019] (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.

[0020] In the power conversion device 100, for example, a high-potential output terminal (positive electrode) of the DC power supply E1 is connected to the first DC terminal 31, and a low-potential output terminal (negative electrode) of the DC power supply E1 is connected to the second DC terminal 32. In addition, in the power conversion device 100, for example, a U-phase terminal, a V-phase terminal, and a W-phase terminal of the AC load RA1 are connected to three AC terminals 41U, 41V, and 41W, respectively.

[0021] In the power conversion circuit 11, each of a plurality of (three in the example of FIG. 1 ) first switching elements 1 and a plurality of (three in the example of FIG. 1 ) second switching elements 2 has a control terminal, a first main terminal, and a second main terminal. The control terminals of the plurality of first switching elements 1 and the plurality of second switching elements 2 are connected to a control device 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.

[0022] 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.

[0023] A connection point 3U between the first switching element 1U and the second switching element 2U is connected to, for example, the U-phase terminal of the AC load RA1 via an AC terminal 41U. A connection point 3V between the first switching element 1V and the second switching element 2V is connected to, for example, the V-phase of the AC load RA1 via an AC terminal 41V. A connection point 3W between the first switching element 1W and the second switching element 2W is connected to, for example, the W-phase of the AC load RA1 via an AC terminal 41W.

[0024] The plurality of resonant capacitors 9 correspond one-to-one to the plurality of switches 8. Each of the plurality of resonant capacitors 9 is connected between the first end 81 and the second DC terminal 32 of the corresponding switch 8. The power conversion device 100 has a plurality of resonant circuits. Each of the plurality of resonant circuits includes a resonant capacitor 9 and a resonant inductor L1.

[0025] Each of the multiple switches 8 has a third switching element 6 and a fourth switching element 7. Each of the multiple (three in the example of FIG. 1 ) third switching elements 6 and the multiple (three in the example of FIG. 1 ) fourth switching elements 7 has a control terminal, a first main terminal, and a second main terminal. The control terminals of the multiple third switching elements 6 and the multiple fourth switching elements 7 are connected to the control device 50. Each of the multiple third switching elements 6 and the multiple fourth switching elements 7 is, for example, an IGBT. Therefore, the control terminal, the first main terminal, and the second main terminal of each of the multiple third switching elements 6 and the multiple fourth switching elements 7 are a gate terminal, a collector terminal, and an emitter terminal, respectively. In each of the multiple switches 8, the third switching element 6 and the fourth switching element 7 are connected in anti-series. In each of the multiple switches 8, the first main terminal (collector terminal) of the third switching element 6 and the first main terminal (collector terminal) of the fourth switching element 7 are connected. In each of the switches 8, the second main terminal (emitter terminal) of the third switching element 6 is connected to the connection point 3 of a corresponding one of the switching circuits 10, and the second main terminal (emitter terminal) of the fourth switching element 7 is connected to the corresponding one of the resonance inductors L1. Each of the switches 8 further includes a diode 61 connected in anti-parallel to the third switching element 6 and a diode 71 connected in anti-parallel to the fourth switching element 7.

[0026] In the power conversion device 100, the switch 8U is connected to a connection point 3U between the first switching element 1U and the second switching element 2U. The switch 8V is connected to a connection point 3V between the first switching element 1V and the second switching element 2V. The switch 8W is connected to a connection point 3W between the first switching element 1W and the second switching element 2W. Hereinafter, for convenience of explanation, the third switching element 6 and the fourth switching element 7 of the switch 8U will be referred to as the third switching element 6U and the fourth switching element 7U, the third switching element 6 and the fourth switching element 7 of the switch 8V will be referred to as the third switching element 6V and the fourth switching element 7V, and the third switching element 6 and the fourth switching element 7 of the switch 8W will be referred to as the third switching element 6W and the fourth switching element 7W, respectively.

[0027] The multiple switches 8 are controlled by the control device 50. In other words, the third switching element 6U, the fourth switching element 7U, the third switching element 6V, the fourth switching element 7V, the third switching element 6W, and the fourth switching element 7W are controlled by the control device 50.

[0028] Each of the multiple resonant inductors L1 has a third end and a fourth end. The third end of each of the multiple resonant inductors L1 is connected to the second end 82 of a corresponding one of the multiple switches 8. The fourth end of each of the multiple resonant inductors L1 is connected to the sixth end 154 of the regenerative capacitor 15. The multiple resonant inductors L1 have the same inductance. That is, the inductances of the three resonant inductors L1 are the same. "The inductances of the three resonant inductors L1 are the same" does not necessarily mean that the inductances of two of the three resonant inductors L1 are completely equal to the inductance of the remaining resonant inductor L1, but may mean that the inductance of each of the two resonant inductors L1 is within a range of 95% to 105% of the inductance of the remaining resonant inductor L1.

[0029] The regenerative capacitor 15 is connected between the fourth ends of the plurality of resonance inductors L1 and the second DC terminal 32. The regenerative capacitor 15 is, for example, a film capacitor.

[0030] 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.

[0031] The control device 50 outputs control signals SU1, SV1, and SW1 that control the on / off of the multiple first switching elements 1U, 1V, and 1W, respectively. Each of the control signals SU1, SV1, and SW1 is, for example, a PWM (Pulse Width Modulation) signal whose potential level changes between a first potential level (hereinafter also referred to as a low level) and a second potential level (hereinafter also referred to as a high level) that is higher than the first potential level. The first switching elements 1U, 1V, and 1W are turned on when the control signals SU1, SV1, and SW1 are at a high level, and turned off when the control signals SU1, SV1, and SW1 are at a low level. The control device 50 also outputs control signals SU2, SV2, and SW2 that control the on / off of the multiple second switching elements 2U, 2V, and 2W, respectively. Each of the control signals SU2, SV2, and SW2 is, for example, a PWM signal whose potential level changes between a first potential level (hereinafter also referred to as a low level) and a second potential level (hereinafter also referred to as a high level) that is higher than the first potential level. The second switching elements 2U, 2V, and 2W are turned on when the control signals SU2, SV2, and SW2 are at a high level, and turned off when they are at a low level.

[0032] The control device 50 uses a sawtooth-wave carrier signal to generate control signals SU1, SV1, SW1 corresponding to the multiple first switching elements 1U, 1V, and 1W, respectively, and control signals SU2, SV2, and SW2 corresponding to the multiple second switching elements 2U, 2V, and 2W, respectively. More specifically, the control device 50 generates the control signals SU1 and SU2 to be provided 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 control signals SV1 and SV2 to be provided 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 control signals SW1 and SW2 to be provided to the first switching element 1W and the second switching element 2W, respectively, based on at least the carrier signal and a W-phase voltage command. The U-phase voltage command, V-phase voltage command, and W-phase voltage command are, for example, sinusoidal signals whose phases differ by 120°, and whose values ​​(voltage command values) change over time. Note that the waveform of the carrier signal is not limited to a sawtooth waveform and may be, for example, a triangular wave. The U-phase voltage command, V-phase voltage command, and W-phase voltage command each have the same length per cycle. The U-phase voltage command, V-phase voltage command, and W-phase voltage command each have a longer length per cycle than the carrier signal.

[0033] The duty of the control signals SU1 and SU2 provided by the control device 50 to the first switching element 1U and the second switching element 2U, respectively, varies based on the U-phase voltage command. In FIG. 2, the duty of the control signal SU1 is shown as the U-phase duty. The control device 50 (see FIG. 1) compares the U-phase voltage command with a carrier signal to generate the control signal SU1 provided to the first switching element 1U. The control device 50 also inverts the control signal SU1 provided to the first switching element 1U to generate the control signal SU2 provided to the second switching element 2U. The control device 50 also sets a dead time Td (see FIG. 3) between the high-level period of the control signal SU1 and the high-level period of the control signal SU2 so that the on periods of the first switching element 1U and the second switching element 2U do not overlap.

[0034] The duties of the control signals SV1 and SV2 provided by the control device 50 to the first switching element 1V and the second switching element 2V, respectively, vary based on the V-phase voltage command. In FIG. 2, the duty of the control signal SV1 is shown as the V-phase duty. The control device 50 (see FIG. 1) compares the V-phase voltage command with a carrier signal to generate the control signal SV1 provided to the first switching element 1V. The control device 50 also inverts the control signal SV1 provided to the first switching element 1V to generate the control signal SV2 provided to the second switching element 2V. The control device 50 also sets a dead time period between the high-level period of the control signal SV1 and the high-level period of the control signal SV2 so that the on periods of the first switching element 1V and the second switching element 2V do not overlap.

[0035] The duties of the control signals SW1 and SW2 provided by the control device 50 to the first switching element 1W and the second switching element 2W, respectively, vary based on the W-phase voltage command. In FIG. 2, the duty of the control signal SW1 is shown as the W-phase duty. The control device 50 (see FIG. 1) compares the W-phase voltage command with a carrier signal to generate the control signal SW1 provided to the first switching element 1W. The control device 50 also inverts the control signal SW1 provided to the first switching element 1W to generate the control signal SW2 provided to the second switching element 2W. The control device 50 also sets a dead time period between the high-level period of the control signal SW1 and the high-level period of the control signal SW2 so that the on periods of the first switching element 1W and the second switching element 2W do not overlap.

[0036] The U-phase voltage command, V-phase voltage command, and W-phase voltage command are, for example, sinusoidal signals whose phases are different from each other by 120°, and whose values ​​change over time. Therefore, the duty of the control signal SU1 (U-phase duty), the duty of the control signal SV1 (V-phase duty), and the duty of the control signal SW1 (W-phase duty) change like sinusoidal waves whose phases are different from each other by 120°, as shown in Figure 2. Similarly, the duty of the control signal SU2, the duty of the control signal SV2, and the duty of the control signal SW2 change like sinusoidal waves whose phases are different from each other by 120°.

[0037] The control device 50 generates the control signals SU1, SU2, SV1, SV2, SW1, and SW2 based on the carrier signal, the voltage commands, and information about the state of the AC load RA1. For example, if the AC load RA1 is a three-phase motor, the information about the state of the AC load RA1 includes, for example, detection values ​​from a plurality of current sensors that detect output currents (hereinafter also referred to as load currents) iU, iV, and iW flowing through the U-phase, V-phase, and W-phase of the AC load RA1, respectively.

[0038] The multiple switches 8, multiple resonance inductors L1, multiple resonance capacitors 9, and regenerative capacitor 15 are provided to perform zero-voltage soft switching of the multiple first switching elements 1 and multiple second switching elements 2. In Fig. 1, the voltage across regenerative capacitor 15 is indicated as V15.

[0039] 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 .

[0040] The control device 50 generates control signals SU6, SU7, SV6, SV7, SW6, and SW7 that control the on / off of the third switching element 6U, the fourth switching element 7U, the third switching element 6V, the fourth switching element 7V, the third switching element 6W, and the fourth switching element 7W, respectively, and outputs these signals to the gate terminals of the third switching element 6U, the fourth switching element 7U, the third switching element 6V, the fourth switching element 7V, the third switching element 6W, and the fourth switching element 7W, respectively.

[0041] When the third switching element 6U is in the ON state and the fourth switching element 7U is in the OFF state, the switch 8U allows a charging current to pass through the path of the regenerative capacitor 15-resonant inductor L1-switch 8U-resonant capacitor 9U. The charging current is a current that charges the resonant capacitor 9U. When the third switching element 6U is in the OFF state and the fourth switching element 7U is in the ON state, the switch 8U allows a discharging current to pass through the path of the resonant capacitor 9U-switch 8U-resonant inductor L1-regenerative capacitor 15. The discharging current is a current that discharges the charge in the resonant capacitor 9U.

[0042] When the third switching element 6V is in the ON state and the fourth switching element 7V is in the OFF state, the switch 8V allows a charging current to pass through the path of the regenerative capacitor 15-resonant inductor L1-switch 8V-resonant capacitor 9V. The charging current is a current that charges the resonant capacitor 9V. When the third switching element 6V is in the OFF state and the fourth switching element 7V is in the ON state, the switch 8V allows a discharging current to pass through the path of the resonant capacitor 9V-switch 8V-resonant inductor L1-regenerative capacitor 15. The discharging current is a current that discharges the charge of the resonant capacitor 9V.

[0043] When the third switching element 6W is in the ON state and the fourth switching element 7W is in the OFF state, the switch 8W allows a charging current to pass through the path of the regenerative capacitor 15 - resonant inductor L1 - switch 8W - resonant capacitor 9W. The charging current is a current that charges the resonant capacitor 9W. When the third switching element 6W is in the OFF state and the fourth switching element 7W is in the ON state, the switch 8W allows a discharging current to pass through the path of the resonant capacitor 9W - switch 8W - resonant inductor L1 - regenerative capacitor 15. The discharging current is a current that discharges the charge in the resonant capacitor 9W.

[0044] (3) Operation of the Power Conversion Device In the following description, the polarity of current iL1 flowing through resonant inductor L1 will be defined as positive when flowing in the direction of the arrow in Fig. 1, and as negative when flowing in the direction opposite to the direction of the arrow in Fig. 1. Also, in the following description, the polarity of load currents iU, iV, and iW flowing through the U, V, and W phases of AC load RA1 will be defined as positive when flowing in the direction of the arrow in Fig. 1, and as negative when flowing in the direction opposite to the direction of the arrow in Fig. 1. Also, in the following description, the polarity of currents i9U, i9V, and i9W flowing through resonant capacitors 9U, 9V, and 9W will be defined as positive when flowing in the direction of the arrow in Fig. 1, and as negative when flowing in the direction opposite to the direction of the arrow in Fig. 1. Therefore, in the case of a discharge operation in which the resonant capacitors 9U, 9V, and 9W are discharged, the polarity of the currents i9U, i9V, and i9W is positive, and in the case of a charge operation in which the resonant capacitors 9U, 9V, and 9W are charged, the polarity of the currents i9U, i9V, and i9W is negative.

[0045] The control device 50 sets a dead time period Td between the high level period of the control signals SU1, SV1, SW1 to the first switching elements 1U, 1V, 1W and the high level period of the control signals SU2, SV2, SW2 to the second switching elements 2U, 2V, 2W for each of the multiple switching circuits 10.

[0046] Below, the basic operation of the zero voltage soft switching of each of the multiple first switching elements 1 and the multiple second switching elements 2 will be explained with reference to Figures 1 to 5, and then the ringing period in which ringing occurs and the operation before and after that will be explained with reference to Figures 6 to 8.

[0047] (3.1) Basic Operation In zero voltage soft switching of the first switching element 1, the voltage across the first switching element 1 must be set to zero immediately before the first switching element 1, which is the target of zero voltage soft switching, is turned on. In addition, in zero voltage soft switching 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, which is the target of zero voltage soft switching, is turned on. Hereinafter, the switching element (first switching element 1 or second switching element 2) that is the target of zero voltage soft switching is also referred to as the target switching element.

[0048] The basic operation of the control device 50 differs depending on the polarity (positive / negative) of the load current flowing through the AC terminal 41 connected to the target switching element and the operation (charging operation / discharging operation) of the resonant capacitor 9 connected in series or parallel to the target switching element. The load currents iU, iV, and iW are positive when flowing from the AC terminal 41 to the AC load RA1, and negative when flowing from the AC load RA1 to the AC terminal 41. When the resonant capacitor 9 is charging, the voltage across the resonant capacitor 9 increases. When the resonant capacitor 9 is discharging, the voltage across the resonant capacitor 9 decreases. The voltage across each of the multiple second switching elements 2 is the same as the voltage across the resonant capacitor 9 connected in parallel to the second switching element 2.

[0049] When the target of soft switching is a first switching element 1 (hereinafter also referred to as the target first switching element 1), and the polarity of the load current flowing through the AC terminal 41 connected to the target first switching element 1 is positive, the control device 50 turns on the third switching element 6 corresponding to the target first switching element 1. As a result, the control device 50 causes resonance between the resonant inductor L1 connected to the target 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 target first switching element 1 to zero. In this way, the power conversion device 100 can achieve zero-voltage soft switching of the target first switching element 1.

[0050] Furthermore, when the polarity of the load current flowing through the AC terminal 41 connected to the target second switching element 2 is negative, the control device 50 turns on the fourth switching element 7 corresponding to the target second switching element 2. As a result, the control device 50 causes the resonant capacitor 9 and the resonant inductor L1 connected to the target second switching element 2 to resonate, discharging the resonant capacitor 9 and setting the voltage across the target second switching element 2 to zero. This allows the power conversion device 100 to achieve zero-voltage soft switching of the target second switching element 2.

[0051] 3 illustrates the control signals SU1, SU2, SU6, and SU7, the current iL1 flowing through the resonant inductor L1, the voltage V1u across the first switching element 1U, and the voltage V2u across the second switching element 2U for the cases where the target switching elements are the first switching element 1U and the second switching element 2U of the switching circuit 10U. Also illustrated in FIG. 3 is the dead time Td set in the control device 50 to prevent the first switching element 1U and the second switching element 2U, which are in phase, from being turned on simultaneously. Also illustrated in FIG. 3 is the voltage value of the DC power supply E1, denoted as Vd.

[0052] In the switching circuit 10U, when the target switching element is the first switching element 1U, the voltage V2u across the second switching element 2U becomes Vd at time t2, the end of the dead time period Td immediately before the high-level period of the control signal SU1, and the voltage V1u across the first switching element 1U becomes zero at time t2, the end of the dead time period Td immediately before the high-level period of the control signal SU1. Therefore, when the control signal SU1 changes from low to high at time t2, the first switching element 1U undergoes zero-voltage soft switching. In the example of FIG. 3 , the current iL1 flowing through the resonant inductor L1 begins at time t1, the start of the high-level period of the control signal SU6, and becomes zero at time t2, the end of the dead time period Td. The control signal SU6 changes from high to low at time t3, which is after time t2. Time t3 will be described in the section "(3.2) Ringing Period During Which Ringing Occurs and Operations Before and After It." The current iL1 that flows between time t1 and time t2 is a resonant current (a charging current for the resonant capacitor 9U) that flows from the regenerative capacitor 15 through the resonant inductor L1 to the resonant capacitor 9U.

[0053] In the switching circuit 10U, when the target switching element is the second switching element 2U, the voltage V1u across the first switching element 1U becomes Vd at time t5, which is the end of the dead time period Td immediately before the high-level period of the control signal SU2, and the voltage V2u across the second switching element 2U becomes zero at time t5, which is the end of the dead time period Td. Therefore, when the control signal SU2 changes from low to high at time t5, the second switching element 2U undergoes zero-voltage soft switching. In the example of FIG. 3 , the current iL1 flowing through the resonant inductor L1 begins at time t4, which is the start of the high-level period of the control signal SU7, and becomes zero at time t5, which is the end of the dead time period Td. The control signal SU7 changes from high to low at time t6, which is after time t5. Time t6 occurs before time t7 (see FIG. 8 ) when the control signal SU2 changes from high to low, but it may also be the same as time t7. That is, time t6 may be any time before time t7. The current iL1 flowing between time t4 and time t5 is the resonant current (discharge current of the resonant capacitor 9U) flowing from the resonant capacitor 9U to the resonant inductor L1.

[0054] FIG. 4 illustrates the control signals SV1, SV2, control signals SV6, SV7, current iL1, voltage V1v across the first switching element 1V, and voltage V2v across the second switching element 2V when the target switching element is the first switching element 1V and the second switching element 2V of the switching circuit 10V.

[0055] In the switching circuit 10V, when the target switching element is the first switching element 1V, the voltage V2v across the second switching element 2V becomes Vd at time t12, when the dead time period Td immediately before the high-level period of the control signal SV1 ends, and the voltage V1v across the first switching element 1V becomes zero at time t12, when the dead time period Td immediately before the high-level period of the control signal SV1 ends. Therefore, when the control signal SV1 changes from low to high at time t12, the first switching element 1V undergoes zero-voltage soft switching. In the example of FIG. 4 , the current iL1 flowing through the resonant inductor L1 begins at time t11, when the high-level period of the control signal SV6 begins, and becomes zero at time t12, when the dead time period Td ends. The control signal SV6 changes from high to low at time t13, which is later than time t12. The current iL1 that flows between time t11 and time t12 is a resonant current (a charging current for the resonant capacitor 9V) that flows from the regenerative capacitor 15 through the resonant inductor L1 to the resonant capacitor 9V.

[0056] In the switching circuit 10V, when the target switching element is the second switching element 2V, the voltage V1v across the first switching element 1V becomes Vd at time t15, which is the end of the dead time period Td immediately before the high-level period of the control signal SV2, and the voltage V2v across the second switching element 2V becomes zero at time t15, which is the end of the dead time period Td. Therefore, when the control signal SV2 changes from low to high at time t15, the second switching element 2V undergoes zero-voltage soft switching. In the example of FIG. 4 , the current iL1 flowing through the resonant inductor L1 begins at time t14, which is the start of the high-level period of the control signal SV7, and becomes zero at time t15, which is the end of the dead time period Td. The control signal SV7 changes from high to low at time t16, which is after time t15. Time t16 is a time before the control signal SV2 changes from high to low. The current iL1 that flows between time t14 and time t15 is a resonant current (discharge current of the resonant capacitor 9V) that flows from the resonant capacitor 9V to the resonant inductor L1.

[0057] FIG. 5 also illustrates the control signals SW1, SW2, SW6, SW7, current iL1, voltage V1w across the first switching element 1W, and voltage V2w across the second switching element 2W when the target switching element is the first switching element 1W or the second switching element 2W of the switching circuit 10W.

[0058] In the switching circuit 10W, when the target switching element is the first switching element 1W, the voltage V2w across the second switching element 2W becomes Vd at time t22, when the dead time period Td immediately before the high-level period of the control signal SW1 ends, and the voltage V1w across the first switching element 1W becomes zero at time t22, when the dead time period Td immediately before the high-level period of the control signal SW1 ends. Therefore, when the control signal SW1 changes from low to high at time t22, the first switching element 1W undergoes zero-voltage soft switching. In the example of FIG. 5 , the current iL1 flowing through the resonant inductor L1 begins at time t21, when the high-level period of the control signal SW6 begins, and becomes zero at time t22, when the dead time period Td ends. The control signal SW6 changes from high to low at time t23, which is later than time t22. The current iL1 that flows between time t21 and time t22 is a resonant current (a charging current for the resonant capacitor 9W) that flows from the regenerative capacitor 15 through the resonant inductor L1 to the resonant capacitor 9W.

[0059] In the switching circuit 10W, when the target switching element is the second switching element 2W, the voltage V1w across the first switching element 1W becomes Vd at time t25, which is the end of the dead time period Td immediately before the high-level period of the control signal SW2, and the voltage V2w across the second switching element 2W becomes zero at time t25, which is the end of the dead time period Td. Therefore, when the control signal SW2 changes from low to high at time t25, the second switching element 2W undergoes zero-voltage soft switching. In the example of FIG. 5 , the current iL1 flowing through the resonant inductor L1 begins at time t24, which is the start of the high-level period of the control signal SW7, and becomes zero at time t25, which is the end of the dead time period Td. The control signal SW7 changes from high to low at time t26, which is after time t25. Time t26 is a time before the control signal SW2 changes from high to low. The current iL1 that flows between time t24 and time t25 is a resonant current (discharge current of the resonant capacitor 9W) that flows from the resonant capacitor 9W to the resonant inductor L1.

[0060] (3.2) Ringing Period When Ringing Occurs and Operations Before and After That Period The ringing period when ringing occurs and operations before and after that period will be described below with reference to FIGS.

[0061] As an example, in Fig. 6, the thick line shows the current path of the current iL1 flowing through the resonant inductor L1 immediately after the current iL1 flowing through the resonant inductor L1 becomes zero when the third switching element 6U of the U-phase switch 8U is on and the fourth switching element 7U is off (first operating mode). Also, in Fig. 7, the thick line shows the current path of the current iL1 flowing through the resonant inductor L1 immediately after the third switching element 6U of the switch 8U is turned off when the state transitions from Fig. 6 to a state where the third switching element 6U and the fourth switching element 7U are off (second operating mode). Also, Fig. 7 illustrates the parasitic capacitance 62 of the third switching element 6U.

[0062] In the power conversion device 100, immediately after the current flowing through the resonant inductor L1 becomes zero, a recovery current flows through the switch 8U, and the current iL flows through the current path shown in Fig. 6. That is, the current iL1 flows through the current path of the regenerative capacitor 15 - resonant inductor L1 - diode 71 - third switching element 6U - resonant capacitor 9U - regenerative capacitor 15.

[0063] In the power conversion device 100, when the operation mode is shifted from the first operation mode to the second operation mode, the current iL1 flows through the current path shown in Fig. 7. That is, the current iL1 flows through the current path of the regenerative capacitor 15 - the resonant inductor L1 - the diode 71 - the parasitic capacitance 62 - the resonant capacitor 9U - the regenerative capacitor 15. Note that in Fig. 7, parasitic capacitances other than the parasitic capacitance 62 are omitted from illustration. Also, in Fig. 1, all parasitic capacitances including the parasitic capacitance 62 are omitted from illustration.

[0064] In the power conversion device 100, ringing occurs after the current iL1 flowing through the resonant inductor L1 becomes zero. Also, in the power conversion device 100, ringing occurs when the voltage V6u across the third switching element 6U of the switch 8U rises from zero volts. Ringing occurs in the voltage V6u across the third switching element 6U at the timing when the current iL1 flowing through the resonant inductor L1 becomes zero.

[0065] In the comparative example of the power conversion device 100 according to the first embodiment, the control signal SU6 changes from high level to low level when ringing occurs in the voltage V6u across the third switching element 6U, as shown in Fig. 9. In this case, as shown in Fig. 9, distortion occurs in the ringing waveform of the voltage V6u across the third switching element 6U (ringing waveform noise is superimposed) at the timing when the third switching element 6U is turned off (time t2 in the example of Fig. 9).

[0066] In contrast, in the power conversion device 100 according to the first embodiment, as shown in FIG. 8 , the control device 50 causes the third switching element 6U to maintain the state immediately before the ringing period (the ON state in the example of FIG. 8 ) during a ringing period in which ringing occurs in the voltage V6u across the third switching element 6U. Here, the "ringing period in which ringing occurs" refers to a period during which ringing is estimated to occur in the voltage V6u across the third switching element 6U and is determined during the design stage of the power conversion device 100. In this embodiment, "causing the third switching element 6U to maintain the state immediately before the ringing period" means maintaining the control signal SU6 at a high level to maintain the ON state of the third switching element 6U. Therefore, the control device 50 can estimate the ringing period in which ringing occurs before the timing (time t2 in the example of FIG. 8 ) at which the control signal SU6 sent to the third switching element 6U is switched from a high level to a low level, without monitoring the voltage V6u across the third switching element 6U. The control device 50 maintains the third switching element 6U in the state it was in immediately before the estimated ringing period during the estimated ringing period, thereby suppressing distortion of the ringing waveform. In the power conversion device 100 according to the first embodiment, the control device 50 changes the control signal SU6 from high to low at the timing at which the ringing period of the voltage V6u across the third switching element 6U ends (time t3 in FIG. 8 ). The “timing at which the ringing period of the voltage V6u across the third switching element 6U ends” refers to the timing at which the amplitude of the ringing becomes zero, but it is not limited to the timing at which the amplitude of the ringing becomes zero, and may also be the timing at which the amplitude of the ringing becomes equal to or less than a threshold. The threshold is a value determined during the design stage of the power conversion device 100, such as 10% of the steady-state voltage of the voltage V6u across the third switching element 6U, which is determined during the design stage. 8 and 9 show the control signals SU1, SU2, SU6, and SU7, the current iL1 flowing through the resonance inductor L1, and the voltage V6u across the third switching element 6U.

[0067] 6 to 8 illustrate the ringing period of the ringing that occurs when the voltage V6u across the U-phase third switching element 6U rises from zero volts and the operation of the control device 50, but the same applies to the ringing period that occurs when the voltage across the V-phase third switching element 6V rises from zero volts and the operation of the control device 50, and the ringing period that occurs when the voltage across the W-phase third switching element 6W rises from zero volts and the operation of the control device 50. Furthermore, the ringing period that occurs when the voltage across the U-phase fourth switching element 7U rises from zero volts and the operation of the control device 50, the ringing period that occurs when the voltage across the V-phase fourth switching element 7V rises from zero volts and the operation of the control device 50, and the ringing period that occurs when the voltage across the W-phase fourth switching element 7W rises from zero volts and the operation of the control device 50 are also similar to the ringing period of the ringing that occurs when the voltage V6u across the U-phase third switching element 6U rises from zero volts and the operation of the control device 50.

[0068] (3.3) Characteristics A1 in Fig. 10 indicates the measured value of radiated noise generated by the power conversion device 100 according to the first embodiment. A2 in Fig. 10 indicates the measured value of radiated noise generated by the power conversion device of the comparative example. The horizontal axis in Fig. 10 indicates the frequency of the radiated noise, and the vertical axis indicates the level of the radiated noise. The measurement conditions for the radiated noise were in accordance with CISPR32, and measurements were performed using the 3m method. It can be seen that the power conversion device 100 according to the first embodiment can reduce radiated noise compared to the power conversion device of the comparative example.

[0069] (4) Advantages The power conversion device 100 according to the first embodiment includes a first DC terminal 31 and a second DC terminal 32, a power conversion circuit 11, a plurality of switches 8, a plurality of resonant capacitors 9, a plurality of resonant inductors L1, a regenerative capacitor 15, a plurality of AC terminals 41, and a control device 50. The power conversion circuit 11 has a plurality of switching circuits 10. Each of the plurality of switching circuits 10 includes a first switching element 1 and a second switching element 2 connected in series to each other, a first diode 4 connected in anti-parallel to the first switching element 1, and a second diode 5 connected in anti-parallel to the second switching element 2. In the plurality of switching circuits 10, the first switching element 1 is connected to the first DC terminal 31, and the second switching element 2 is connected to the second DC terminal 32. Each of the plurality of switches 8 has a first end 81 and a second end 82. The plurality of switches 8 correspond one-to-one to the plurality of switching circuits 10. Each of the multiple switches 8 is connected to a connection point 3 between the first switching element 1 and the second switching element 2 in a corresponding one of the multiple switching circuits 10. The multiple resonant capacitors 9 correspond one-to-one to the multiple switches 8. Each of the multiple resonant capacitors 9 is connected between a first end 81 and a second DC terminal 32 of a corresponding one of the multiple switches 8. The multiple resonant inductors L1 correspond one-to-one to the multiple switches 8. Each of the multiple resonant inductors L1 is connected to a second end 82 of a corresponding one of the multiple switches 8. The multiple AC terminals 41 correspond one-to-one to the multiple switching circuits 10. Each of the multiple AC terminals 41 is connected to a connection point 3 between the first switching element 1 and the second switching element 2 in a corresponding one of the multiple switching circuits 10. The control device 50 controls the multiple first switching elements 1, the multiple second switching elements 2, and the multiple switches 8. Each of the multiple switches 8 includes a third switching element 6 and a fourth switching element 7. When the third switching element 6 is in the ON state, a current iL1 from the resonance inductor L1 flows through it. When the fourth switching element 7 is in the ON state, a current flows through it in the opposite direction to that of the third switching element 6.The control device 50 provides a control signal whose potential changes between high and low to each of the plurality of first switching elements 1, the plurality of second switching elements 2, the plurality of third switching elements 6, and the plurality of fourth switching elements 7. For each of the plurality of switching circuits 10, the control device 50 sets a dead time period Td between a high-level period of the control signal to the first switching element 1 and a high-level period of the control signal to the second switching element 2. The control device 50 overlaps at least a portion of the high-level period of the control signal to each of the plurality of switches 8 with the dead time period Td. For each of the plurality of switches 8, during a ringing period in which ringing occurs in the voltage across the third switching element 6, the control device 50 causes the third switching element 6 to maintain the state (on state) that was in place immediately before the ringing period.

[0070] According to the above configuration, it is possible to reduce radiation noise.

[0071] In the power conversion device 100 according to the first embodiment, the control device 50 turns off the third switching elements 6 that correspond one-to-one to the multiple switching circuits 10 before the timing at which the first switching elements 1 are turned off in each of the multiple switching circuits 10. "Before the timing at which the first switching elements 1 are turned off" is not limited to the timing before the timing at which the first switching elements 1 are turned off, but also includes the timing at which the first switching elements 1 are turned off.

[0072] According to the above configuration, zero voltage soft switching of the first switching element 1 can be realized.

[0073] Furthermore, during a ringing period in which ringing occurs in the voltage across the fourth switching element 7, the control device 50 causes the fourth switching element 7 to maintain the state it was in immediately before the ringing period. This enables the power conversion device 100 according to the first embodiment to further reduce radiation noise.

[0074] Second Embodiment A power conversion device 100A according to a second embodiment will be described with reference to Fig. 11. Regarding the power conversion device 100A according to the second 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.

[0075] (1) Configuration The power conversion device 100A differs from the power conversion device 100 in that it further includes a regenerative capacitor 16 (hereinafter also referred to as the second regenerative capacitor 16) connected between the sixth end 154 of the regenerative capacitor 15 (hereinafter also referred to as the first regenerative capacitor 15) and the first DC terminal 31.

[0076] The second regenerative capacitor 16 is connected in series to the first regenerative capacitor 15. Therefore, in the power conversion device 100A, a series circuit of the second regenerative capacitor 16 and the first regenerative capacitor 15 is connected between the first DC terminal 31 and the second DC terminal 32. In the power conversion device 100A, a plurality of resonant inductors L1 are connected to a path between the first regenerative capacitor 15 and the second regenerative capacitor 16. The capacitance of the second regenerative capacitor 16 is the same as the capacitance of the first regenerative capacitor 15. The phrase "the capacitance of the second regenerative capacitor 16 is the same as the capacitance of the first regenerative capacitor 15" does not necessarily mean that the capacitance of the second regenerative capacitor 16 exactly matches the capacitance of the first regenerative capacitor 15, but may mean that the capacitance of the second regenerative capacitor 16 is within a range of 95% to 105% of the capacitance of the first regenerative capacitor 15.

[0077] In the power conversion device 100A according to the second embodiment, the voltage V15 across the first regenerative capacitor 15 (the potential at the sixth terminal 154 of the first regenerative capacitor 15) is equal to the value obtained by dividing the voltage Vd of the DC power supply E1 between the second regenerative capacitor 16 and the first regenerative capacitor 15. Therefore, the voltage V15 across the first regenerative capacitor 15 is approximately Vd / 2. In the power conversion device 100A according to the second embodiment, the control device 50 may store the value of the voltage V15 across the first regenerative capacitor 15 in advance.

[0078] (2) Advantages The operation of the control device 50 of the power conversion device 100A according to the second embodiment is similar to the operation of the control device 50 of the power conversion device 100 according to the first embodiment. Therefore, the power conversion device 100A according to the second embodiment can reduce radiation noise, similar to the power conversion device 100 according to the first embodiment.

[0079] Third Embodiment A power conversion device 100B according to a third embodiment will be described with reference to Fig. 12. Regarding the power conversion device 100B 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.

[0080] (1) Configuration The power conversion device 100B differs from the power conversion device 100 according to the first embodiment in that it includes only one resonant inductor L1. In the power conversion device 100B, the resonant inductor L1 is common to a plurality of resonant circuits. In the power conversion device 100B, a third end of the resonant inductor L1 is connected to a common connection point 25. The second ends 82 of a plurality of switches 8 are commonly connected to the common connection point 25.

[0081] (2) Operation of the Power Conversion Device In the power conversion device 100B, similarly to the power conversion device 100, the control device 50 controls a plurality of (three in the example of FIG. 12 ) first switching elements 1, a plurality of (three in the example of FIG. 12 ) second switching elements 2, and a plurality of (three in the example of FIG. 12 ) switches 8. The operation of the control device 50 is similar to that of the control device 50 of the power conversion device 100.

[0082] (3) Advantages In the power conversion device 100B according to the third embodiment, similarly to the power conversion device 100 according to the first embodiment, the control device 50 causes each of the plurality of third switching elements 6 to maintain the state (on state) immediately before the ringing period during which ringing occurs in the voltage across the third switching element 6. Therefore, similarly to the power conversion device 100 according to the first embodiment, the power conversion device 100B according to the third embodiment can reduce radiation noise.

[0083] Furthermore, the power conversion device 100B according to the third embodiment has one resonant inductor L1, and the second ends 82 of the multiple switches 8 are commonly connected to the single resonant inductor L1, which allows the power conversion device 100B according to the third embodiment to be miniaturized.

[0084] (Fourth embodiment) A power conversion device 100C according to a fourth embodiment will be described with reference to Fig. 13. Regarding the power conversion device 100C according to the fourth embodiment, components similar to those of the power conversion device 100B according to the third embodiment will be denoted by the same reference numerals, and description thereof will be omitted.

[0085] (1) Configuration The power conversion device 100C differs from the power conversion device 100B in that it further includes a regenerative capacitor 16 (hereinafter also referred to as the second regenerative capacitor 16) connected between the sixth end 154 of the regenerative capacitor 15 (hereinafter also referred to as the first regenerative capacitor 15) and the first DC terminal 31.

[0086] The second regenerative capacitor 16 is connected in series to the first regenerative capacitor 15. Therefore, in the power conversion device 100C, a series circuit of the second regenerative capacitor 16 and the first regenerative capacitor 15 is connected between the first DC terminal 31 and the second DC terminal 32. The capacitance of the second regenerative capacitor 16 is the same as the capacitance of the first regenerative capacitor 15. The phrase "the capacitance of the second regenerative capacitor 16 is the same as the capacitance of the first regenerative capacitor 15" does not necessarily mean that the capacitance of the second regenerative capacitor 16 exactly matches the capacitance of the first regenerative capacitor 15, but may mean that the capacitance of the second regenerative capacitor 16 is within a range of 95% to 105% of the capacitance of the first regenerative capacitor 15.

[0087] In the power conversion device 100C according to the fourth embodiment, the voltage V15 across the first regenerative capacitor 15 (the potential at the sixth terminal 154 of the first regenerative capacitor 15) is equal to the value obtained by dividing the voltage Vd of the DC power supply E1 between the second regenerative capacitor 16 and the first regenerative capacitor 15. Therefore, the voltage V15 across the first regenerative capacitor 15 is approximately Vd / 2. In the power conversion device 100C according to the fourth embodiment, the control device 50 may store the value of the voltage V15 across the first regenerative capacitor 15 in advance.

[0088] (2) Operation The operation of the control device 50 of the power conversion device 100C according to the fourth embodiment is similar to the operation of the control device 50 of the power conversion device 100B according to the third embodiment.

[0089] (3) Advantages The power conversion device 100C according to the fourth embodiment can reduce radiation noise, similarly to the power conversion device 100B according to the third embodiment.

[0090] Fifth Embodiment A power conversion device 100D according to a fifth embodiment will be described with reference to Figures 14 and 15. Regarding the power conversion device 100D according to the fifth embodiment, components similar to those of the power conversion device 100B according to the third embodiment will be denoted by the same reference numerals, and description thereof will be omitted.

[0091] (1) Configuration The power conversion device 100D differs from the power conversion device 100B in that the power conversion device 100D further includes a third diode 13 and a fourth diode 14.

[0092] In the third diode 13, an anode of the third diode 13 is connected to a connection point between the resonance inductor L1 and the plurality of switches 8. In addition, in the third diode 13, a cathode of the third diode 13 is connected to a first DC terminal 31. The fourth diode 14 is connected between the connection point between the resonance inductor L1 and the plurality of switches 8 and a second DC terminal 32. In the fourth diode 14, an anode of the fourth diode 14 is connected to the second DC terminal 32. In the fourth diode 14, a cathode of the fourth diode 14 is connected to a connection point between the resonance inductor L1 and the plurality of switches 8. Therefore, the fourth diode 14 is connected in series with the third diode 13.

[0093] (2) Operation The control device 50 in the power conversion device 100D according to the fifth embodiment changes the state of the third switching element 6 to the off state before the current iL1 flowing through the resonant inductor L1 becomes zero, and maintains the previous state (off state) of the third switching element 6 during a ringing period in which ringing occurs in the voltage across the third switching element 6. More specifically, when performing zero-voltage soft switching on the U-phase first switching element 1U, the control device 50 changes the control signal SU6 sent to the third switching element 6U of the switch 8U from high to low before the current iL1 flowing through the resonant inductor L1 becomes zero, and maintains the potential level of the control signal SU6 at a low level during a ringing period in which ringing occurs in the voltage V6u across the third switching element 6U, as shown in FIG.

[0094] Since the power conversion device 100D is equipped with the third diode 13, even if the third switching element 6U is turned off before the current iL1 flowing through the resonant inductor L1 becomes zero, the current iL1 can flow through a path passing through the third diode 13.

[0095] Figure 15 explains the ringing period of the ringing that occurs when the voltage V6u across the third switching element 6U of the U phase rises from zero volts and the operation of the control device 50, but the same applies to the ringing period that occurs when the voltage across the third switching element 6V of the V phase rises from zero volts and the operation of the control device 50, and the ringing period that occurs when the voltage across the third switching element 6W of the W phase rises from zero volts and the operation of the control device 50.

[0096] (3) Advantages The power conversion device 100D according to the fifth embodiment maintains the third switching element 6 in the immediately preceding state (off state) for each of the multiple switches 8 during the ringing period when ringing occurs in the voltage across the third switching element 6, thereby making it possible to reduce radiation noise.

[0097] (4) Modification of Embodiment 5 As in the first embodiment, the control device 50 causes the third switching element 6 to maintain its immediately preceding on state during the ringing period, and turns off the third switching element 6 at the end of the ringing period.

[0098] In the modification of the fifth embodiment, radiation noise can be reduced in the same manner as in the first embodiment.

[0099] Sixth Embodiment A power conversion device 100E according to a sixth embodiment will be described with reference to Fig. 16. Regarding the power conversion device 100E according to the sixth embodiment, components similar to those of the power conversion device 100 according to the first embodiment will be denoted by the same reference numerals and descriptions thereof will be omitted.

[0100] (1) Configuration The power conversion device 100E differs from the power conversion device 100 in that each of the multiple switches 8 includes a third switching element 6A and a fourth switching element 7A instead of the third switching element 6 and the fourth switching element 7. Each of the multiple third switching elements 6A and the multiple fourth switching elements 7A is a MOSFET. In the power conversion device 100E, the control terminal, the first main terminal, and the second main terminal of each of the multiple third switching elements 6A and the multiple fourth switching elements 7A are a gate terminal, a drain terminal, and a source terminal, respectively. In each of the multiple switches 8, the third switching element 6A and the fourth switching element 7A are connected in anti-series. In the power conversion device 100E, in each of the multiple switches 8, the first main terminal (drain terminal) of the third switching element 6A and the first main terminal (drain terminal) of the fourth switching element 7A are connected. Each of the switches 8 further includes a diode 61 connected in anti-parallel to the third switching element 6A and a diode 71 connected in anti-parallel to the fourth switching element 7A. In each of the switches 8, the second main terminal (source terminal) of the fourth switching element 7A is connected to the resonance inductor L1. In each of the switches 8, the second main terminal (source terminal) of the third switching element 6A is connected to the connection point 3 of the switching circuit 10 corresponding to the switch 8 having that third switching element 6A. Control signals SU6 and SU7 are provided from the control device 50 to the third switching element 6A and the fourth switching element 7A of the switch 8U. Control signals SV6 and SV7 are provided from the control device 50 to the third switching element 6A and the fourth switching element 7A of the switch 8V. Control signals SW6 and SW7 are provided from the control device 50 to the third switching element 6A and the fourth switching element 7A of the switch 8W.

[0101] (2) Operation of the Power Converter The operation of the power converter 100E is similar to the operation of the power converter 100, for example.

[0102] (3) Advantages The power conversion device 100E according to the sixth embodiment can reduce radiation noise, similarly to the power conversion device 100 according to the first embodiment.

[0103] Seventh Embodiment A power conversion device 100F according to a seventh embodiment will be described with reference to Fig. 17. Regarding the power conversion device 100F according to the seventh embodiment, components similar to those of the power conversion device 100 according to the first embodiment will be denoted by the same reference numerals and descriptions thereof will be omitted.

[0104] (1) Configuration Each of the multiple switches 8 in the power conversion device 100F has, for example, two third switching elements 6 and four switching elements 7 connected in anti-parallel. In each of the switches 8, the first main terminal (collector terminal) of the third switching element 6 is connected to the second main terminal (emitter terminal) of the fourth switching element 7, and the second main terminal (emitter terminal) of the third switching element is connected to the first main terminal (collector terminal) of the fourth switching element 7. In each of the multiple switches 8, the second main terminal (emitter terminal) of the third switching element 6 is connected to the connection point 3 of the switching circuit 10 corresponding to the switch 8 having the third switching element 6. In each of the multiple switches 8, the first main terminal (collector terminal) of the fourth switching element is connected to the connection point 3 of the switching circuit 10 corresponding to the switch 8 having the fourth switching element 7. More specifically, the switch 8U is connected to the connection point 3U of the first switching element 1U and the second switching element 2U. The switch 8V is connected to a connection point 3V between the first switching element 1V and the second switching element 2V. The switch 8W is connected to a connection point 3W between the first switching element 1W and the second switching element 2W.

[0105] (2) Operation of the Power Converter The operation of the power converter 100F is similar to the operation of the power converter 100, for example.

[0106] (3) Advantages The power conversion device 100F according to the seventh embodiment can reduce radiation noise, similar to the power conversion device 100 according to the first embodiment.

[0107] Eighth Embodiment A power conversion device 100G according to an eighth embodiment will be described with reference to Fig. 18. Regarding the power conversion device 100G according to the eighth embodiment, components similar to those of the power conversion device 100 according to the first embodiment will be denoted by the same reference numerals and descriptions thereof will be omitted.

[0108] (1) Configuration As shown in FIG. 18 , for example, the power conversion device 100G includes a first DC terminal 31, a second DC terminal 32, and two AC terminals 41. In the power conversion device 100G, 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 two AC terminals 41. The AC load RA1 is, for example, an AC motor. The power conversion device 100G 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 include a DC-DC converter.

[0109] The power conversion device 100G according to the eighth embodiment differs from the power conversion device 100 according to the first embodiment in that the power conversion circuit 11 includes only one switching circuit 10. The power conversion device 100G according to the eighth embodiment also differs from the power conversion device 100 in that one of the two AC terminals 41 is connected to the connection point 3 between the first switching element 1 and the second switching element 2, and the other AC terminal is connected to the second DC terminal 32. The power conversion device 100G according to the eighth embodiment also differs from the power conversion device 100 in that the power conversion device 100G according to the eighth embodiment includes only one switch 8, one resonant inductor L1, and one resonant capacitor 9.

[0110] The control device 50 controls each of the first switching element 1, the second switching element 2, and the switch 8. The control device 50 outputs a control signal S1 to control the first switching element 1, a control signal S2 to control the second switching element 2, a control signal S6 to control the third switching element 6, and a control signal S7 to control the fourth switching element 7.

[0111] (2) Operation of the Power Conversion Device In the power conversion device 100G, the control device 50 controls the first switching element 1, the second switching element 2, and the switch 8. The operation of the control device 50 is similar to that of the control device 50 of the power conversion device 100. More specifically, the control signals S1, S2, S6, and S7 output from the control device 50 of the power conversion device 100G are similar to the control signals SU1, SU2, SU6, and SU7 output from the control device 50 of the power conversion device 100 (see FIGS. 1, 3, and 8).

[0112] (3) Advantages The power conversion device 100G according to the eighth embodiment includes a first DC terminal 31, a second DC terminal 32, a power conversion circuit 11, a switch 8, a resonant capacitor 9, a resonant inductor L1, a regenerative capacitor 15, and a control device 50. The power conversion circuit 11 includes a switching circuit 10. The switching circuit 10 includes a first switching element 1 and a second switching element 2 connected in series to each other, a first diode 4 connected in anti-parallel to the first switching element 1, and a second diode 5 connected in anti-parallel to the second switching element 2. In the switching circuit 10, the first switching element 1 is connected to the first DC terminal 31, and the second switching element 2 is connected to the second DC terminal 32. The switch 8 has a first end 81 and a second end 82. The first end 81 of the switch 8 is connected to the connection point 3 between the first switching element 1 and the second switching element 2. The resonant capacitor 9 is connected between the first end 81 of the switch 8 and the second DC terminal 32. The resonant inductor L1 is connected to the second end 82 of the switch 8. The regenerative capacitor 15 is connected between the resonant inductor L1 and the second DC terminal 32. The control device 50 controls the first switching element 1, the second switching element 2, and the switch 8. The switch 8 includes a third switching element 6 and a fourth switching element 7. When the third switching element 6 is in the on state, a current iL1 flows from the resonant inductor L1 side. When the fourth switching element 7 is in the on state, a current flows in the opposite direction to that of the third switching element 6. The control device 50 provides control signals S1, S2, S6, and S7, the potentials of which change between high and low levels, to the first switching element 1, the second switching element 2, the third switching element 6, and the fourth switching element 7, respectively. The control device 50 sets a dead time period Td (see FIG. 8 ) between the high level period of the control signal S1 to the first switching element 1 and the high level period of the control signal S2 to the second switching element 2. The control device 50 overlaps at least a part of the high level period of the control signal S6 to the third switching element 6 with the dead time period Td.During a ringing period in which ringing occurs in the voltage across the third switching element 6, the control device 50 causes the third switching element 6 to maintain the state it was in immediately before the ringing period.

[0113] According to the above configuration, it is possible to reduce radiation noise.

[0114] (Other Modifications) The above-described first to eighth embodiments are merely examples of various embodiments of the present disclosure. The above-described first to eighth embodiments can be modified in various ways depending on the design, etc., as long as the object of the present disclosure can be achieved.

[0115] In the power conversion device 100, the diode 61 and the diode 71 are not limited to being externally attached to the third switching element 6 and the fourth switching element 7, respectively, but may be elements built into one chip.

[0116] Furthermore, in power conversion device 100G, the configuration of switch 8 is the same as the configuration of switch 8 in power conversion device 100, but it may also be the same as the configuration of switch 8 in power conversion device 100E, or the same as the configuration of switch 8 in power conversion device 100F.

[0117] Furthermore, in the power conversion devices 100, 100A, 100B, 100C, 100D, 100E, 100F, and 100G, 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.

[0118] The length of the dead time period Td is set to be the same as the resonance half period, but may be set to a length different from the resonance half period. The resonance half period is half the resonance period, which is the reciprocal of the resonance frequency of the resonance circuit including the resonance inductor L1 and one resonance capacitor 9.

[0119] The dead time period Td may be set by a dead time generation circuit included in a gate driver IC (Integrated Circuit) or the like that is provided separately from the control device 50. Alternatively, the control device 50 may include a gate driver IC, and the dead time period Td may be set by a dead time generation circuit included in the gate driver IC.

[0120] Furthermore, the power conversion devices 100, 100A, 100B, 100C, 100D, 100E, and 100F are not limited to being configured to output three-phase AC, but may be configured to output polyphase AC with three or more phases.

[0121] The control device 50 may also advance the start of the high-level period of each of the control signals SU6, SV6, and SW6 by the additional time from the start of the dead time period Td. To start LC resonance at the start of the dead time period Td, the control device 50 determines the additional time based on the load current so that the in-phase current iL1 and the load current are equal at the start of the dead time period Td. More specifically, the control device 50 determines the additional time by calculating the additional time = load current × (L / V15) using, for example, the load current detection result from a current sensor, its signal-processed value, or an estimated load current value, the pre-stored inductance L of the resonance inductor L1, and the detection result of the voltage V15 across the regenerative capacitor 15. The load current detection result or its signal-processed value is a detected value at the carrier cycle to which the additional time is to be added, or at a timing closest to that carrier cycle. The estimated load current value is, for example, an estimated load current value at the carrier cycle to which the additional time is to be added.

[0122] (Aspects) The following aspects are disclosed in this specification.

[0123] A power conversion device (100; 100A; 100B; 100C; 100D; 100E; 100F; 100G) according to a first aspect includes a first DC terminal (31), a second DC terminal (32), a power conversion circuit (11), a switch (8), a resonant capacitor (9), a resonant inductor (L1), a regenerative capacitor (15), and a control device (50). The power conversion circuit (11) has a switching circuit (10). The switching circuit (10) includes a first switching element (1) and a second switching element (2) connected in series with each other, a first diode (4) connected in anti-parallel to the first switching element (1), and a second diode (5) connected in anti-parallel to the second switching element (2). In the switching circuit (10), the first switching element (1) is connected to the first DC terminal (31), and the second switching element (2) is connected to the second DC terminal (32). The switch (8) has a first end (81) and a second end (82). The first end (81) of the switch (8) is connected to a connection point (3) between the first switching element (1) and the second switching element (2). The resonant capacitor (9) is connected between the first end (81) of the switch (8) and the second DC terminal (32). The resonant inductor (L1) is connected to the second end (82) of the switch (8). The regenerative capacitor (15) is connected between the resonant inductor (L1) and the second DC terminal (32). The control device (50) controls the first switching element (1), the second switching element (2), and the switch (8). The switch (8) includes a third switching element (6; 6A) and a fourth switching element (7; 7A). When the third switching element (6; 6A) is in an on state, a current (iL1) flows from the resonant inductor (L1). When the fourth switching element (7; 7A) is in an on state, a current flows in the opposite direction to that of the third switching element (6; 6A). The control device (50) provides each of the first switching element (1), the second switching element (2), the third switching element (6; 6A), and the fourth switching element (7; 7A) with a control signal whose potential changes between a high level and a low level.The control device (50) sets a dead time period (Td) between a high level period of a control signal to the first switching element (1) and a high level period of a control signal to the second switching element (2). The control device (50) overlaps at least a part of the high level period of the control signal to the third switching element (6; 6A) with the dead time period (Td). During a ringing period in which ringing occurs in the voltage across the third switching element (6; 6A), the control device (50) causes the third switching element (6; 6A) to maintain the state it had immediately before the ringing period.

[0124] According to this aspect, it is possible to reduce radiation noise.

[0125] In the power conversion device (100; 100A; 100B; 100C; 100E; 100F; 100G) according to the second aspect, in the first aspect, the control device (50) maintains the third switching element (6; 6A) in an on state during the ringing period.

[0126] In the power conversion device (100; 100A; 100B; 100C; 100D; 100E; 100F; 100G) according to the third aspect, in the first aspect, the control device (50) turns off the third switching element (6; 6A) before the timing to turn off the switching element that is the target of zero voltage soft switching, out of the first switching element (1) and the second switching element (2).

[0127] According to this aspect, it is possible to realize zero-voltage soft switching of the first switching element (1).

[0128] A power conversion device (100; 100A; 100B; 100C; 100E; 100F; 100G) according to a fourth aspect is based on the first aspect. The control device (50) is configured to control the third switching element (6; 6A) using the timing when the voltage across the third switching element (6; 6A) becomes equal to or lower than a threshold as the end timing of a ringing period. The control device (50) maintains the third switching element (6; 6A) in an ON state during the ringing period and turns off the third switching element (6; 6A) at the end timing of the ringing period.

[0129] According to this aspect, it is possible to realize zero-voltage soft switching of the first switching element (1).

[0130] The power conversion device (100D) according to the fifth aspect is the same as that of the first aspect, but further includes a third diode (13) and a fourth diode (14). The third diode (13) has an anode connected to the connection point of the switch (8) and the resonant inductor (L1) and a cathode connected to the first DC terminal (31). The fourth diode (14) has an anode connected to the connection point of the switch (8) and the resonant inductor (L1) and a cathode connected to the second DC terminal (32).

[0131] According to this aspect, it is possible to control the state of the third switching element (6; 6A) to be maintained in the OFF state during the ringing period.

[0132] A power conversion device (100; 100A; 100E; 100F) according to a sixth aspect is any one of the first to fifth aspects, wherein the power conversion circuit (11) has a plurality of switching circuits (10). The power conversion device (100) includes a plurality of switches (8), a plurality of resonant capacitors (9), a plurality of resonant inductors (L1), and further includes a plurality of AC terminals (41). The plurality of switches (8) correspond one-to-one to the plurality of switching circuits (10). Each of the plurality of switches (8) is connected to a connection point (3) between a first switching element (1) and a second switching element (2) in a corresponding one of the plurality of switching circuits (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 a first end (81) of a corresponding one of the plurality of switches (8) and a second DC terminal (32). The plurality of resonant inductors (L1) correspond one-to-one to the plurality of switches (8). Each of the plurality of resonant inductors (L1) is connected to a second end (82) of a corresponding one of the plurality of switches (8). The plurality of AC terminals (41) correspond one-to-one to the plurality of switching circuits (10). Each of the plurality of AC terminals (41) is connected to a connection point (3) of a first switching element (1) and a second switching element (2) in a corresponding one of the plurality of switching circuits (10). The plurality of switches (8) include a plurality of third switching elements (6; 6A) and a plurality of fourth switching elements (7; 7A). The control device (50) controls the plurality of first switching elements (1), the plurality of second switching elements (2), the plurality of third switching elements (6; 6A), and the plurality of fourth switching elements (7; 7A).

[0133] A power conversion device (100B; 100C; 100D) according to a seventh aspect is the same as any one of the first to fifth aspects, wherein the power conversion circuit (11) has a plurality of switching circuits (10). The power conversion device (100) includes a plurality of switches (8), a plurality of resonant capacitors (9), and a plurality of AC terminals (41). The plurality of switches (8) correspond one-to-one to the plurality of switching circuits (10). Each of the plurality of switches (8) is connected to a connection point (3) between a first switching element (1) and a second switching element (2) in a corresponding one of the plurality of switching circuits (10). Each of the plurality of resonant capacitors (9) corresponds one-to-one to the plurality of switches (8). Each of the plurality of resonant capacitors (9) is connected between a first end (81) of a corresponding one of the plurality of switches (8) and a 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 a corresponding one of the plurality of switching circuits (10). Second ends (82) of the plurality of switches (8) are commonly connected to a resonance inductor (L1). The plurality of switches (8) include a plurality of third switching elements (6; 6A) and a plurality of fourth switching elements (7; 7A). A control device (50) controls the plurality of first switching elements (1), the plurality of second switching elements (2), the plurality of third switching elements (6; 6A), and the plurality of fourth switching elements (7; 7A).

[0134] According to this aspect, the number of resonance inductors (L1) can be reduced to one, making it possible to achieve miniaturization.

[0135] 1 First switching element 2 Second switching element 3 Connection point 4 First diode 5 Second diode 6, 6A Third switching element 7, 7A Fourth switching element 8 Switch 81 First terminal 82 Second terminal 9 Resonant capacitor 10 Switching circuit 13 Third diode 14 Fourth diode 11 Power conversion circuit 15 Regenerative capacitor 153 Fifth terminal 154 Sixth terminal 31 First DC terminal 32 Second DC terminal 41 AC terminal 50 Control device 100, 100A, 100B, 100C, 100D, 100E, 100F, 100G Power conversion device iU, iV, iW Output current (load current) L1 Resonant inductor RA1 AC load SU1, SU2, SU6, SU7 Control signal SV1, SV2, SV6, SV7 Control signal SW1, SW2, SW6, SW7 Control signal Td Dead time period V15 Voltage at both ends

Claims

1. a first DC terminal and a second DC terminal; a power conversion circuit having a switching circuit including a first switching element and a second switching element connected in series to each other, a first diode connected in anti-parallel to the first switching element, and a second diode connected in anti-parallel to the second switching element, wherein the first switching element is connected to the first DC terminal and the second switching element is connected to the second DC terminal; a switch having a first end and a second end, the first end being connected to a connection point between the first switching element and the second switching element; a resonance capacitor connected between the first end and the second DC terminal of the switch; a resonant inductor connected to the second end of the switch; a regenerative capacitor connected between the resonance inductor and the second DC terminal; a control device that controls the first switching element, the second switching element, and the switch, The switch is a third switching element through which a current flows from the resonant inductor when in an on state; a fourth switching element through which a current flows in a direction opposite to that of the third switching element when the fourth switching element is in an on state; The control device applying a control signal whose potential changes between a high level and a low level to each of the first switching element, the second switching element, the third switching element, and the fourth switching element; a dead time period is set between a high level period of the control signal to the first switching element and a high level period of the control signal to the second switching element; at least a part of a high level period of the control signal to the third switching element is overlapped with the dead time period; During a ringing period in which ringing occurs in the voltage across the third switching element, the third switching element is maintained in a state immediately before the ringing period. Power conversion device.

2. the control device maintains the third switching element in an on state during the ringing period. The power conversion device according to claim 1 .

3. the control device turns off the third switching element before a timing at which one of the first switching element and the second switching element that is a switching element subject to zero voltage soft switching is turned off; The power conversion device according to claim 1 .

4. the control device is configured to control the switch by setting a timing at which a voltage across the third switching element becomes equal to or lower than a threshold as an end timing of the ringing period, The control device maintaining the switch in an on state during the ringing period; turning off the third switching element at the end timing; The power conversion device according to claim 1 .

5. a third diode having an anode connected to a connection point between the switch and the resonant inductor and a cathode connected to the first DC terminal; a fourth diode having an anode connected to the connection point between the switch and the resonant inductor and a cathode connected to the second DC terminal, The power conversion device according to claim 1 .

6. the power conversion circuit includes a plurality of the switching circuits; The power conversion device is A plurality of the switches are provided, a plurality of the resonance capacitors; a plurality of the resonance inductors; Further comprising a plurality of AC terminals; the plurality of switches correspond one-to-one to the plurality of switching circuits, and each switch is connected to a connection point of the first switching element and the second switching element in the corresponding switching circuit; the plurality of resonance capacitors correspond one-to-one to the plurality of switches, and each resonance capacitor is connected between the first end and the second DC terminal of the corresponding switch; the plurality of resonant inductors correspond one-to-one to the plurality of switches, and each resonant inductor is connected to the second end of the corresponding switch; the plurality of AC terminals correspond one-to-one to the plurality of switching circuits, and each AC terminal is connected to a connection point of the first switching element and the second switching element in the corresponding switching circuit; the plurality of switches include a plurality of the third switching elements and a plurality of the fourth switching elements; the control device controls the first switching elements, the second switching elements, the third switching elements, and the fourth switching elements. The power conversion device according to any one of claims 1 to 5.

7. the power conversion circuit includes a plurality of the switching circuits; The power conversion device is A plurality of the switches are provided, a plurality of the resonance capacitors; Further comprising a plurality of AC terminals; the plurality of switches correspond one-to-one to the plurality of switching circuits, and each switch is connected to a connection point of the first switching element and the second switching element in the corresponding switching circuit; each of the plurality of resonance capacitors corresponds to one of the plurality of switches, and each resonance capacitor is connected between the first end and the second DC terminal of the corresponding switch; the plurality of AC terminals correspond one-to-one to the plurality of switching circuits, and each AC terminal is connected to a connection point of the first switching element and the second switching element in the corresponding switching circuit; the second terminals of the plurality of switches are commonly connected to the resonant inductor, the plurality of switches include a plurality of the third switching elements and a plurality of the fourth switching elements; the control device controls the first switching elements, the second switching elements, the third switching elements, and the fourth switching elements. The power conversion device according to any one of claims 1 to 5.