Electric power converting device

Abstract

The present invention addresses the problem of reducing noise while suppressing switching losses. An electric power converting device (100) comprises a plurality of switches (8), a plurality of resonance capacitors (9), at least one resonance inductor (L1), a control device (50), a voltage-dividing circuit (20), and a plurality of common mode filters (21). The voltage-dividing circuit (20) includes a first capacitor (C1) and a second capacitor (C2) connected in series with one another. The plurality of common mode filters (21) correspond on a one-to-one basis with a plurality of switching circuits (10). The voltage-dividing circuit (20) has an intermediate potential point (N1) between the first capacitor (C1) and the second capacitor (C2). Each of the plurality of common mode filters (21) includes a third capacitor (C3) connected between a connecting point (3) of each of the plurality of switching circuits (10) and the intermediate potential point (N1).

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 an inverter type drive device (power conversion device).

[0003] 18 of Patent Document 1 includes a smoothing capacitor, two capacitors (a first capacitor and a second capacitor) connected in series, six switching elements (a plurality of first switching elements and a plurality of second switching elements), and a plurality of filter circuits (common mode filters) each including a capacitor (a third capacitor). In this inverter drive device, the intermediate connection point (an intermediate potential point) of the two capacitors is connected to the common connection point of the plurality of filter circuits.

[0004] In the power conversion device disclosed in Patent Document 1, for example, a series circuit of a third capacitor and one of two capacitors (a first capacitor and a second capacitor) is connected across the switching element, which raises concerns about increased switching loss. In power conversion devices, it is sometimes required to suppress switching loss while reducing noise.

[0005] Japanese Patent Application Laid-Open No. 2001-69762

[0006] An object of the present disclosure is to provide a power conversion device that can reduce noise while suppressing switching loss.

[0007] A power conversion device according to one aspect of the present disclosure includes a first DC terminal and a second DC terminal, a power conversion circuit, multiple AC terminals, multiple switches, multiple resonant capacitors, at least one resonant inductor, a regenerative capacitor, a control device, a voltage divider circuit, and multiple common mode filters. The power conversion circuit includes multiple first switching elements and multiple second switching elements. In the power conversion circuit, multiple switching circuits, each of which is connected in series with the multiple first switching elements and the multiple second switching elements in a one-to-one relationship, are connected in parallel to each other. In the power conversion circuit, the multiple first switching elements are connected to the first DC terminals, and the multiple second switching elements are connected to the second DC terminals. The multiple AC terminals correspond one-to-one to the multiple switching circuits. Each of the multiple AC terminals is connected to a connection point between the first switching element and the second switching element in a corresponding one of the multiple switching circuits. The multiple switches correspond one-to-one to the multiple switching circuits. Each of the plurality of switches has a first end and a second end, and the first end is connected to the connection point between the first switching element and the second switching element in a corresponding switching circuit among the plurality of switching circuits. The plurality of resonant capacitors correspond one-to-one to the plurality of switches. Each of the plurality of resonant capacitors is connected between the first end and the second DC terminal of a corresponding switch among the plurality of switches. The at least one resonant inductor has a third end and a fourth end. The third end of the at least one resonant inductor is connected to the second end of the corresponding switch among the plurality of switches. The regenerative capacitor has a fifth end and a sixth end. The fifth end of the regenerative capacitor is connected to the second DC terminal, and the sixth end is connected to the fourth end of the at least one resonant inductor. The control device controls the plurality of first switching elements, the plurality of second switching elements, and the plurality of switches. The voltage divider circuit has a first capacitor and a second capacitor connected in series to each other.In the voltage divider circuit, the first capacitor is connected to the first DC terminal and the second capacitor is connected to the second DC terminal. The voltage divider circuit has an intermediate potential point between the first capacitor and the second capacitor. The plurality of common mode filters correspond one-to-one to the plurality of switching circuits. Each of the plurality of common mode filters includes a third capacitor connected between the intermediate potential point and the connection point of a corresponding one of the plurality of switching circuits.

[0008] FIG. 1 is a circuit diagram of a system including a power conversion device according to a first embodiment, with multiple protection circuits omitted. FIG. 2 is a circuit diagram of a system including the power conversion device, with multiple common mode filters omitted. FIG. 3 is an explanatory diagram of the operation of a control device in the power conversion device when performing a basic operation in a case where the load current is greater than 0 and the resonant capacitor is charging. FIG. 4 is another explanatory diagram of the operation of a control device in the power conversion device when performing a basic operation in a case where the load current is greater than 0 and the resonant capacitor is charging. FIG. 5 is a diagram showing the time variation of duty and load current corresponding to voltage commands for each of three phases in an AC load connected to multiple AC terminals of the power conversion device. FIG. 6 is an explanatory diagram of a first current threshold and a second current threshold used by the control device in the power conversion device. FIG. 7 is an explanatory diagram of the operation of a control device in the power conversion device when performing a basic operation in a case where the load current is greater than 0 and the resonant capacitor is discharging. FIG. 8 is an explanatory diagram of the operation of a control device in the power conversion device when performing a basic operation in a case where the load current is less than 0 and the resonant capacitor is discharging. FIG. 9 is an explanatory diagram of an operation of the power conversion device of the same when the control device performs a basic operation in a case where the load current is less than 0 and the resonant capacitor is being charged. FIG. 10 is a timing chart for explaining the operation of the power conversion device of the same. FIG. 11 is an explanatory diagram of a charging operation in the power conversion device of the same. FIG. 12 is an explanatory diagram of a discharging operation in the power conversion device of the same. FIG. 13 is an explanatory diagram of the operation of the power conversion device of the same. FIG. 14 is a circuit diagram of a system including a power conversion device according to a first modification of the first embodiment, in which illustration of multiple protection circuits is omitted. FIG. 15 is a circuit diagram of a system including a power conversion device according to a second modification of the first embodiment, in which illustration of multiple protection circuits is omitted. FIG. 16 is a circuit diagram of a system including a power conversion device according to the second embodiment, in which illustration of multiple protection circuits is omitted. FIG. 17 is a circuit diagram of a system including a power conversion device according to the third embodiment, in which illustration of multiple protection circuits is omitted. FIG. 18 is a circuit diagram of a system including a power conversion device according to the fourth embodiment, in which illustration of protection circuits is omitted.Fig. 19 is a circuit diagram of a system including the above power conversion device, omitting illustration of a plurality of common mode filters. Fig. 20 is an explanatory diagram of a charging operation in the above power conversion device. Fig. 21 is an explanatory diagram of a discharging operation in the above power conversion device. Fig. 22 is a circuit diagram of a system including a power conversion device according to Modification 1 of Embodiment 4, omitting illustration of a protection circuit. Fig. 23 is a circuit diagram of a system including a power conversion device according to Modification 2 of Embodiment 4, omitting illustration of a protection circuit. Fig. 24 is a circuit diagram of a system including a power conversion device according to Modification 3 of Embodiment 4, omitting illustration of a protection circuit. Fig. 25 is a circuit diagram of a system including a power conversion device according to Modification 4 of Embodiment 4, omitting illustration of a protection circuit. Fig. 26 is a circuit diagram of a system including a power conversion device according to Modification 5 of Embodiment 4, omitting illustration of a protection circuit. Fig. 27 is a circuit diagram of a system including a power conversion device according to Modification 6 of Embodiment 4, omitting illustration of a protection circuit. Fig. 28 is a circuit diagram of a system including a power conversion device according to Embodiment 5.

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

[0011] The power conversion device 100 includes a power conversion circuit 11, a plurality of (e.g., three) switches 8, a plurality of (e.g., three) resonant capacitors 9, a regenerative capacitor 15, a plurality of (e.g., three) resonant inductors L1, a control device 50, a voltage divider circuit 20, and a plurality of (e.g., three) common mode filters 21. Each of the plurality of switches 8 is, for example, a bidirectional switch. The power conversion device 100 also includes a protection circuit 17 (see FIG. 2). Note that the protection circuit 17 shown in FIG. 2 is not shown in FIG. 1, and the plurality of common mode filters 21 shown in FIG. 1 are also not shown in FIG. 2.

[0012] The power conversion circuit 11 has a plurality of (e.g., three) first switching elements 1 and a plurality of (e.g., three) second switching elements 2. In the power conversion circuit 11, a plurality of (e.g., three) switching circuits 10, each having a plurality of first switching elements 1 and a plurality of second switching elements 2 connected in series in a one-to-one relationship, are connected in parallel to one another. In the power conversion circuit 11, the plurality of first switching elements 1 are connected to first DC terminals 31, and the plurality of second switching elements 2 are connected to second DC terminals 32. The plurality of AC terminals 41 correspond one-to-one to the plurality of switching circuits 10. Each of the plurality of AC terminals 41 is connected to a connection point 3 between the first switching element 1 and the second switching element 2 in a corresponding one of the plurality of switching circuits 10. The plurality of switches 8 correspond one-to-one to the plurality of switching circuits 10. Each of the plurality of switches 8 has a first end 81 and a second end 82. Each of the multiple switches 8 has a first end 81 connected to a connection point 3 between the first switching element 1 and the second switching element 2 in a corresponding switching circuit 10 among 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 the first end 81 and the second DC terminal 32 of a corresponding switch 8 among the multiple switches 8. Each of the multiple resonant inductors L1 has a third end and a fourth end. The fourth end of each of the multiple resonant inductors L1 is connected to the regenerative capacitor 15. The third end of each of the multiple resonant inductors L1 is connected to the second end 82 of a corresponding switch 8 among the multiple switches 8. The regenerative capacitor 15 has a fifth end 153 and a sixth end 154. The fifth end 153 of the regenerative capacitor 15 is connected to the second DC terminal 32, and the sixth end 154 is connected to the fourth end of the multiple resonant inductors L1. 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. The voltage dividing circuit 20 has a first capacitor C1 and a second capacitor C2 connected in series to each other. In the voltage dividing circuit 20, the first capacitor C1 is connected to a first DC terminal 31, and the second capacitor C2 is connected to a second DC terminal 32.The voltage divider circuit 20 has an intermediate potential point N1 between the first capacitor C1 and the second capacitor C2. The common mode filters 21 correspond one-to-one to the switching circuits 10. Each of the common mode filters 21 includes a third capacitor C3 connected between the intermediate potential point N1 and a connection point 3 in a corresponding one of the switching circuits 10.

[0013] (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.

[0014] 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.

[0015] In the power conversion circuit 11, each of a plurality of (e.g., three) first switching elements 1 and a plurality of (e.g., three) second switching elements 2 has a control terminal, a first main terminal, and a second main terminal. The control terminals of the plurality of first switching elements 1 and the plurality of second switching elements 2 are connected to a control device 50. In each of the plurality of switching circuits 10 of the power conversion device 100, a first main terminal of the first switching element 1 is connected to a first DC terminal 31, a second main terminal of the first switching element 1 is connected to a first main terminal of the second switching element 2, and a second main terminal of the second switching element 2 is connected to a second DC terminal 32. In each of the plurality of switching circuits 10, the first switching element 1 is a high-side switching element (P-side switching element), and the second switching element 2 is a low-side switching element (N-side switching element). Each of the plurality of first switching elements 1 and the plurality of second switching elements 2 is, for example, an IGBT (Insulated Gate Bipolar Transistor). Therefore, the control terminal, the first main terminal and the second main terminal of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 are the gate terminal, the collector terminal and the emitter terminal, respectively.

[0016] 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.

[0017] 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.

[0018] 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 switch 8 among the plurality of switches 8 and the second DC terminal 32. 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. Each of the plurality of resonant circuits further includes a second capacitor C2 and a third capacitor C3.

[0019] Each of the multiple switches 8 has, for example, two IGBTs, a first IGBT 6 and a second IGBT 7, connected in anti-parallel. In each of the switches 8, the collector terminal of the first IGBT 6 is connected to the emitter terminal of the second IGBT 7, and the emitter terminal of the first IGBT 6 is connected to the collector terminal of the second IGBT 7. In each of the multiple switches 8, the emitter terminal of the first IGBT 6 is connected to the connection point 3 of the switching circuit 10 corresponding to the switch 8 having the first IGBT 6. In each of the multiple switches 8, the collector terminal of the second IGBT 7 is connected to the connection point 3 of the switching circuit 10 corresponding to the switch 8 having the second IGBT 7. The switch 8U is connected to the connection point 3U between the first switching element 1U and the second switching element 2U. The switch 8V is connected to the connection point 3V between the first switching element 1V and the second switching element 2V. The switch 8W is connected to a connection point 3W between the first switching element 1W and the second switching element 2W. Hereinafter, for convenience of explanation, the first IGBT 6 and the second IGBT 7 of the switch 8U may be referred to as the first IGBT 6U and the second IGBT 7U, the first IGBT 6 and the second IGBT 7 of the switch 8V may be referred to as the first IGBT 6V and the second IGBT 7V, and the first IGBT 6 and the second IGBT 7 of the switch 8W may be referred to as the first IGBT 6W and the second IGBT 7W, respectively.

[0020] The plurality of switches 8 are controlled by the control device 50. In other words, the first IGBT 6U, the second IGBT 7U, the first IGBT 6V, the second IGBT 7V, the first IGBT 6W, and the second IGBT 7W are controlled by the control device 50.

[0021] 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 completely match the inductance of the remaining resonant inductor L1, but may mean that the inductances of the two resonant inductors L1 are within a range of 95% to 105% of the inductance of the remaining resonant inductor L1.

[0022] 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.

[0023] Each of the multiple protection circuits 17 (see FIG. 2 ) includes a third diode 13 and a fourth diode 14. In each of the multiple protection circuits 17, the third diode 13 is connected between the connection point between the resonant inductor L1 and the switch 8 and the first DC terminal 31. The anode of the third diode 13 is connected to the connection point between the resonant inductor L1 and the switch 8. The cathode of the third diode 13 is connected to the first DC terminal 31. The fourth diode 14 is connected between the connection point between the resonant inductor L1 and the switch 8 and the second DC terminal 32. The anode of the fourth diode 14 is connected to the second DC terminal 32. The cathode of the fourth diode 14 is connected to the connection point between the resonant inductor L1 and the switch 8. Therefore, in each of the multiple protection circuits 17, the fourth diode 14 is connected in series with the third diode 13.

[0024] 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.

[0025] 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.

[0026] The control device 50 uses a sawtooth carrier signal (see FIG. 3 ) to generate control signals SU1, SV1, and 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° from each other, and whose values ​​(voltage command values) change over time. The waveform of the carrier signal is not limited to a sawtooth waveform and may be, for example, a triangular wave or a sawtooth wave obtained by inverting the sawtooth wave shown in FIG. 3 . The U-phase voltage command, V-phase voltage command, and W-phase voltage command each have the same cycle length. The U-phase voltage command, V-phase voltage command, and W-phase voltage command each have a longer cycle length than the carrier signal.

[0027] 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. 5, 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.

[0028] 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. 5, 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 Td (see FIG. 3) 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.

[0029] 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. 5, 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 Td (see FIG. 4) 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.

[0030] 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 Fig. 5 . 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°.

[0031] 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.

[0032] The plurality of switches 8, the plurality of resonant inductors L1, the plurality of resonant capacitors 9 and the regenerative capacitor 15 are provided to perform zero voltage soft switching of the plurality of first switching elements 1 and the plurality of second switching elements 2.

[0033] 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 .

[0034] The control device 50 generates control signals SU6, SU7, SV6, SV7, SW6, and SW7 that control the on / off of the first IGBT6U, the second IGBT7U, the first IGBT6V, the second IGBT7V, the first IGBT6W, and the second IGBT7W, respectively, and outputs them to the gate terminals of the first IGBT6U, the second IGBT7U, the first IGBT6V, the second IGBT7V, the first IGBT6W, and the second IGBT7W, respectively.

[0035] When the first IGBT 6U is in the ON state and the second IGBT 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, and resonant capacitor 9U. The charging current is a current that charges the resonant capacitor 9U. When the first IGBT 6U is in the OFF state and the second IGBT 7U is in the ON state, the switch 8U allows a discharging current to pass through the path of the resonant capacitor 9U, switch 8U, resonant inductor L1, and regenerative capacitor 15. The discharging current is a current that discharges the charge of the resonant capacitor 9U.

[0036] When the first IGBT 6V is in the ON state and the second IGBT 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 first IGBT 6V is in the OFF state and the second IGBT 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.

[0037] When the first IGBT 6W is in the ON state and the second IGBT 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, and resonant capacitor 9W. The charging current is a current that charges the resonant capacitor 9W. When the first IGBT 6W is in the OFF state and the second IGBT 7W is in the ON state, the switch 8W allows a discharging current to pass through the path of the resonant capacitor 9W, switch 8W, resonant inductor L1, and regenerative capacitor 15. The discharging current is a current that discharges the charge of the resonant capacitor 9W.

[0038] The voltage-dividing circuit 20 includes a first capacitor C1 and a second capacitor C2. In the voltage-dividing circuit 20, the first capacitor C1 and the second capacitor C2 are connected in series. In the voltage-dividing circuit 20, the first capacitor C1 is connected to a first DC terminal 31, and the second capacitor C2 is connected to a second DC terminal 32. The voltage-dividing circuit 20 includes an intermediate potential point N1 between the first capacitor C1 and the second capacitor C2. The intermediate potential point N1 is, for example, the connection point between the first capacitor C1 and the second capacitor C2. The potential of the intermediate potential point N1 is half the voltage of the output voltage of the DC power supply E1. The capacitance of the second capacitor C2 is the same as the capacitance of the first capacitor C1. "The capacitance of the second capacitor C2 is the same as the capacitance of the first capacitor C1" does not necessarily mean that the capacitance of the second capacitor C2 exactly matches the capacitance of the first capacitor C1, but may be within the range of 95% to 105% of the capacitance of the first capacitor C1.

[0039] In each of the plurality of common mode filters 21, the third capacitor C3 is connected between the connection point 3 in a corresponding one of the plurality of switching circuits 10 and the midpoint potential point N1 in the voltage divider circuit 20. The capacitances of the third capacitors C3 included in each of the plurality of common mode filters 21 are the same. That is, the capacitances of the three third capacitors C3 are the same. The phrase "the capacitances of the three third capacitors C3 are the same" does not necessarily mean that the capacitances of two of the three third capacitors C3 are exactly the same as the capacitance of the remaining third capacitor C3, but may mean that the capacitances of the two third capacitors C3 are within a range of 95% to 105% of the capacitance of the remaining third capacitor C3.

[0040] (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.

[0041] 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.

[0042] 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 9, and then the operation of the common mode filter 21 will be explained with reference to Figures 10 to 12.

[0043] (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.

[0044] 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.

[0045] (3.1.1) Operation for Soft-Switching the First Switching Element When Load Current > 0 When the target of soft switching is the first switching element 1 (hereinafter also referred to as the target first switching element 1), and the polarity of the load current flowing through the AC terminal 41 connected to the target first switching element 1 is positive, the control device 50 turns on the first IGBT 6 corresponding to the target first switching element 1. As a result, the control device 50 causes resonance between the resonant inductor L1 and the resonant capacitor 9 connected to the target first switching element 1, 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.

[0046] 3 illustrates control signals SU1 and SU2 provided from the control device 50 to the first switching element 1U and the second switching element 2U of the switching circuit 10U when the target first switching element is the first switching element 1U of the switching circuit 10U. Also illustrated in FIG. 3 are a control signal SU6 provided from the control device 50 to the first IGBT 6U of the switch 8U, a load current iU flowing through the U-phase of the AC load RA1, a current iL1 flowing through the resonant inductor L1, a voltage V1u across the first switching element 1U, and a voltage V2u across the second switching element 2U. Also illustrated in FIG. 3 are control signals SV1 and SV2 provided from the control device 50 to the first switching element 1V and the second switching element 2V of the switching circuit 10V when the target first switching element is the first switching element 1V of the switching circuit 10V. FIG. 3 also illustrates the control signal SV6 given from the control device 50 to the first IGBT 6V of the switch 8V, the load current iV flowing through the V phase of the AC load RA1, the current iL1 flowing through the resonant inductor L1, the voltage V1v across the first switching element 1V, and the voltage V2v across the second switching element 2V.

[0047] 3 also shows a dead time period Td set in the control device 50 to prevent the first switching element 1 and the second switching element 2, which are in phase, from being turned on simultaneously. Also shown in FIG. 3 is an additional time Tau set in the control device 50 for the control signal SU6 of the first IGBT 6U of the switch 8U, and an additional time Tav set in the control device 50 for the control signal SV6 of the first IGBT 6V of the switch 8V. The additional time Tau and the additional time Tav will be described later.

[0048] FIG. 4 illustrates control signals SW1 and SW2 provided from the control device 50 to the first switching element 1W and the second switching element 2W of the switching circuit 10W, respectively, when the target first switching element is the first switching element 1W of the switching circuit 10W. FIG. 4 also illustrates the control signal SW6 provided from the control device 50 to the first IGBT 6W of the switch 8W and the load current iW flowing through the W-phase of the AC load RA1. FIG. 4 also illustrates the current iL1 flowing through the resonant inductor L1. FIG. 4 also illustrates the voltage V1w across the first switching element 1W and the voltage V2w across the second switching element 2W. In FIG. 4, the voltage value of the DC power supply E1 is indicated as Vd.

[0049] 4 also shows a dead time period Td set in the control device 50 to prevent the first switching element 1W and the second switching element 2W from being turned on simultaneously. Also, Fig. 4 shows an additional time Taw set in the control device 50 for the control signal SW6 of the first IGBT 6W of the switch 8W. The additional time Taw will be described later.

[0050] As shown in FIG. 3 , the additional time Tau is set to advance the start time t1 of the high-level period of the control signal SU6 to earlier than the start time t2 of the dead time period Td (hereinafter also referred to as the start time t2), thereby making the high-level period of the control signal SU6 longer than the dead time period Td. The length of the additional time Tau is set based on the value of the load current iU. To start LC resonance at the start time t2 of the dead time period Td, it is desirable that the value of the current iL1 match the value of the load current iU at the start time t2 of the dead time period Td. This is because, while iL1 < iU, all of the current iL1 flows through the AC load RA1, preventing the resonant capacitor 9U from being charged. The end time of the high-level period of the control signal SU6 may be the same as or later than the end time t3 of the dead time period Td (hereinafter also referred to as the end time t3). FIG. 3 shows an example in which the end time of the high-level period of the control signal SU6 is set to the same as the end time t3 of the dead time period Td. The control device 50 sets the high-level period of the control signal SU6 to Tau + Td. In the switching circuit 10U, the voltage V2u across the second switching element 2U becomes Vd at the end t3 of the dead time period Td, and the voltage V1u across the first switching element 1U becomes zero at the end t3 of the dead time period Td. In the example of FIG. 3 , the current iL1 flowing through the resonant inductor L1 begins at the start t1 of the high-level period of the control signal SU6 and becomes zero at the end t4 of the dead time period Tau, which is the time when the additional time Tau has elapsed since the end t3 of the dead time period Td. Since iL1≧iU from the start t2 of the dead time period Td, the current iL1 in the shaded region of the current waveform in the fifth row from the top in FIG. 3 flows into the resonant capacitor 9U, generating LC resonance. After the end time t3 of the dead time period Td, the current iL1 is regenerated in the power conversion circuit 11 via the third diode 13 directly connected to the resonance inductor L1.

[0051] As described above, the control device 50 determines the additional time Tau based on the load current iU so that iL1 = iU at the start time t2 of the dead time period Td, in order to start LC resonance at the start time t2 of the dead time period Td and end the resonant half cycle at the end time of the dead time period Td. More specifically, the control device 50 determines the additional time Tau by calculating Tau = iU × (L / V15) using, for example, the detection result of the load current iU by a current sensor, its signal-processed value, or an estimated value of the load current iU, the pre-stored inductance L of the resonance inductor L1, and the detection result of the voltage V15 across the regenerative capacitor 15. The detection result of the load current iU or its signal-processed value is a detection value at the carrier cycle to which the additional time Tau is added, or at a timing closest to that carrier cycle. The estimated value of the load current iU is, for example, an estimated value of the load current iU at the carrier cycle to which the additional time Tau is added. The resonant half period is half the resonant period, which is the reciprocal of the resonant frequency of a resonant circuit including one resonant inductor L1 and one resonant capacitor 9. The formula for calculating the resonant half period will be explained in the section "(3.2) Operation of the Common Mode Filter." In the control device 50, the resonant half period is set to be equal to or shorter than the length of the dead time period Td, for example, to be the same as the length of the dead time period Td.

[0052] As shown in FIG. 3 , the additional time Tav is set to advance the start time t5 of the high-level period of the control signal SV6 to earlier than the start time t6 of the dead time period Td (hereinafter also referred to as the start time t6), thereby making the high-level period of the control signal SV6 longer than the dead time period Td. The length of the additional time Tav is set based on the value of the load current iV. To start LC resonance at the start time t6 of the dead time period Td, it is desirable that the value of the current iL1 match the value of the load current iV at the start time t6 of the dead time period Td. This is because, while iL1 < iV, all of the current iL1 flows through the AC load RA1, preventing the resonant capacitor 9V from being charged. The end time of the high-level period of the control signal SV6 may be the same as or later than the end time t7 of the dead time period Td (hereinafter also referred to as the end time t7). FIG. 3 shows an example in which the end time of the high-level period of the control signal SV6 is set to the same as the end time t7 of the dead time period Td. The control device 50 sets the high-level period of the control signal SV6 to Tav+Td. The voltage V1v across the first switching element 1V becomes zero at the end t7 of the dead time period Td. In the example of FIG. 3 , the current iL1 flowing through the resonant inductor L1 begins at the start t5 of the high-level period of the control signal SV6 and becomes zero at the end t8 of the dead time period Td, which is the additional time Tav. Since iL1≧iV from the start t6 of the dead time period Td, the current iL1 in the shaded region of the current waveform in the tenth row from the top in FIG. 3 flows into the resonant capacitor 9V, generating LC resonance. After the end t7 of the dead time period Td, the current iL1 is regenerated in the power conversion circuit 11 via the third diode 13 directly connected to the resonant inductor L1.

[0053] As described above, in order to start LC resonance at the start time t6 of the dead time period Td, the control device 50 determines the additional time Tav based on the load current iV so that iL1 = iV at the start time t6 of the dead time period Td. More specifically, the control device 50 determines the additional time Tav by calculating Tav = iV × (L / V15) using, for example, the detection result of the load current iV by a current sensor, its signal-processed value, or an estimated value of the load current iV, the inductance L of the resonance inductor L1 that is stored in advance, and the detection result of the voltage V15 across the regenerative capacitor 15. The detection result of the load current iV or its signal-processed value is a detection value at the carrier cycle to which the additional time Tav is added, or at a timing closest to that carrier cycle. The estimated value of the load current iV is, for example, an estimated value of the load current iV at the carrier cycle to which the additional time Tav is added.

[0054] As shown in FIG. 4 , the additional time Taw is set to advance the start time t9 of the high-level period of the control signal SW6 to earlier than the start time t10 of the dead time period Td (hereinafter also referred to as the start time t10), thereby making the high-level period of the control signal SW6 longer than the dead time period Td. The length of the additional time Taw is set based on the value of the load current iW. To start LC resonance at the start time t10 of the dead time period Td, it is desirable that the value of the current iL1 match the value of the load current iW at the start time t10 of the dead time period Td. This is because, while iL1 < iW, all of the current iL1 flows through the AC load RA1, preventing the resonant capacitor 9W from being charged. The end time of the high-level period of the control signal SW6 may be the same as or later than the end time t11 of the dead time period Td. FIG. 4 illustrates an example in which the end time of the high-level period of the control signal SW6 is set to the same as the end time t11 of the dead time period Td. The control device 50 sets the high-level period of the control signal SW6 to Taw+Td. The voltage V1w across the first switching element 1W becomes zero at the end t11 of the dead time period Td. In the example of FIG. 4 , the current iL1 flowing through the resonant inductor L1 begins at the start t9 of the high-level period of the control signal SW6 and becomes zero at the time t12, when the additional time Taw has elapsed since the end t11 of the dead time period Td. Since iL1≧iW holds true from the start t10 of the dead time period Td, the current iL1 in the shaded region of the current waveform in the fourth row from the top in FIG. 4 flows into the resonant capacitor 9W, generating LC resonance. After the end t11 of the dead time period Td, the current iL1 is regenerated in the power conversion circuit 11 via the third diode 13 directly connected to the resonant inductor L1.

[0055] The control device 50 determines the additional time Taw based on the load current iW. More specifically, the control device 50 determines the additional time Taw by calculating Taw = iW × (L / V15) using the detection result of the load current iW by the current sensor, the inductance L of the resonance inductor L1 that is stored in advance, and the detection result of the voltage V15 across the regenerative capacitor 15. The detection result of the load current iW or its signal processed value at this time uses a detection value at the carrier cycle to which the additional time Taw is added or at a timing closest to that carrier cycle. Furthermore, the estimated value of the load current iW at this time uses, for example, a value estimated from the load current iW at the carrier cycle to which the additional time Taw is added.

[0056] (3.1.2) Operation for Soft-Switching the Second Switching Element When Load Current > 0 When the soft-switching target is the second switching element 2 (hereinafter also referred to as the target second switching element 2), and when the polarity of the load current (load current iU, load current iV, or load current iW) flowing through the AC terminal 41 connected to the target second switching element 2 is positive, the control device 50 compares the current value of the load current with the first current threshold I1 (=Ith, see FIG. 6 ). When the current value of the load current is greater than the first current threshold I1, the control device 50 does not turn on the switch 8, and when the current value of the load current is less than the first current threshold I1, the control device 50 turns on the switch 8 during the dead time period Td. In the power conversion device 100, when the current value of the load current is greater than the first current threshold I1, the control device 50 can discharge the resonant capacitor 9 connected in parallel to the target second switching element 2 using the load current without turning on the switch 8 corresponding to the target second switching element 2. This allows the power conversion device 100 to achieve zero voltage soft switching of the target second switching element 2.

[0057] 7 illustrates the control signals SU1, SU2, and SU7, the load current iU, the current i9U flowing from the resonant capacitor 9U, and the voltage V2u across the second switching element 2U when the target second switching element 2 is the second switching element 2U of the switching circuit 10U and the current value of the load current iU is greater than the first current threshold I1. Also illustrated in FIG. 7 is the dead time period Td and the additional time Tau that the control device 50 sets for the control signal SU7 to the second IGBT 7U of the switch 8U.

[0058] When the current value of the load current iU is greater than the first current threshold I1, the control device 50 does not provide a high-level period for the control signal SU7. In this case, in the power conversion device 100, the current i9U begins to flow from the resonant capacitor 9U at the start time t22 of the dead time period Td, and the current i9U decreases to zero before the end time t23 of the dead time period Td, causing the voltage V2u across the second switching element 2U to become zero before the end time t23 of the dead time period Td. As a result, in the power conversion device 100, when the control signal SU2 changes from low level to high level at the end time t23 of the dead time period Td, the second switching element 2U is subjected to zero-voltage soft switching.

[0059] When the current value of the load current iU is smaller than the first current threshold I1, the control device 50 provides a high-level period for the control signal SU7, as shown by the two-dot chain line in FIG. 7 . The start point of the high-level period of the control signal SU7 in this case is, for example, the same as the start point t22 of the dead time period Td. The end point of the high-level period of the control signal SU7 is the same as the end point t23 of the dead time period Td. As a result, in the power conversion device 100, the voltage V2u across the second switching element 2U becomes zero before the end point t23 of the dead time period Td. Therefore, in the power conversion device 100, when the control signal SU2 changes from low to high at the end point t23 of the dead time period Td, the second switching element 2U is subjected to zero-voltage soft switching. The start point of the high-level period of the control signal SU7 may be time t21, which is earlier than the start point of the dead time period Td by an additional time Tau. The end point of the high level period of the control signal SU7 may be time t24, which is later than the end point t23 of the dead time period Td by the additional time Tau. Note that the time before and after the period in the high level period that overlaps with the dead time period Td is not limited to the additional time Tau and may be another set time.

[0060] (3.1.3) Operation for Soft-Switching the Second Switching Element When Load Current<0 When the polarity of the load current (load current iU, load current iV, or load current iW) flowing through the AC terminal 41 connected to the target second switching element 2 is negative, the control device 50 turns on the second IGBT 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.

[0061] Figure 8 illustrates the control signals SU1, SU2, and SU7, the load current iU, the current iL1 flowing through the resonant inductor L1, and the voltage V2u across the second switching element 2U when the target second switching element 2 is the second switching element 2U of the switching circuit 10U.

[0062] FIG. 8 also illustrates the dead time period Td set in the control device 50 to prevent the first switching element 1 and the second switching element 2, which are in phase, from being simultaneously turned on. FIG. 8 also illustrates the additional time Tau set in the control device 50 for the control signal SU7 of the second IGBT 7U of the switch 8U. The end point of the high-level period of the control signal SU7 may be the same as or later than the end point t33 of the dead time period Td. FIG. 8 illustrates an example in which the end point of the high-level period of the control signal SU7 is set to the same as the end point t33 of the dead time period Td. The control device 50 sets the high-level period of the control signal SU7 to Tau + Td. In the switching circuit 10U, the voltage V2u across the second switching element 2U becomes zero at the end point t33 of the dead time period Td. 8 , the current iL1 flowing through the resonant inductor L1 starts at time t31 (start time t31), when the high-level period of the control signal SU7 starts, and becomes zero at time t34, when the additional time Tau has elapsed since time t33, when the dead time period Td ends. With regard to the current iL1, when iL1≦iU is satisfied from time t32, when the dead time period Td starts, LC resonance occurs, and a resonant current (discharge current of the resonant capacitor 9U) flows from the resonant capacitor 9U toward the resonant inductor L1. After time t33, when the dead time period Td ends, the current iL1 is regenerated in the power conversion circuit 11 via the fourth diode 14, which is directly connected to the resonant inductor L1.

[0063] The control device 50 determines the additional time Tau based on the load current iU so that iL1 = iU at the start time t32 of the dead time period Td, in order to start LC resonance at the start time t32 of the dead time period Td and end the resonant half cycle at the end time t33 of the dead time period Td. More specifically, the control device 50 determines the additional time Tau by calculating Tau = |iU| × (L / V15) using, for example, the detection result of the output current iU by a current sensor or its signal-processed value, or an estimated value of the load current iU, the inductance L of the resonance inductor L1 that is stored in advance, and the detection result of the voltage V15 across the regenerative capacitor 15. The detection result of the load current iU or its signal-processed value is a detection value at the carrier cycle to which the additional time Tau is added, or at a timing closest to that carrier cycle. The estimated value of the load current iU is a value, for example, an estimated value of the load current iU at the carrier cycle to which the additional time Tau is added.

[0064] (3.1.4) Operation for Soft-Switching the First Switching Element When Load Current < 0 When the polarity of the load current (load current iU, load current iV, or load current iW) flowing through the AC terminal 41 connected to the target first switching element 1 is negative, the control device 50 compares the current value of the load current with the second current threshold I2 (= −Ith, see FIG. 6 ). When the current value of the load current is smaller than the second current threshold I2, the control device 50 does not turn on the switch 8. When the current value of the load current is larger than the second current threshold I2, the control device 50 turns on the switch 8 during the dead time period Td. When the current value of the load current is smaller than the second current threshold I2, the power conversion device 100 can charge the resonant capacitor 9 connected in series to the target first switching element 1 with the load current without turning on the switch 8 corresponding to the target first switching element 1. This allows the power conversion device 100 to achieve zero-voltage soft switching of the target first switching element 1.

[0065] 9 illustrates the control signals SU1, SU2, and SU6, the load current iU, the current i9U flowing from the resonant capacitor 9U, and the voltage V2u across the second switching element 2U when the target first switching element 1 is the first switching element 1U of the switching circuit 10U and the current value of the load current iU is greater than the second current threshold I2 (in other words, when the absolute value of the current value of the load current is smaller than the absolute value of the second current threshold I2). Also illustrated in FIG. 9 is the dead time period Td.

[0066] When the current value of the load current iU is smaller than the second current threshold I2 (in other words, when the absolute value of the load current is greater than the absolute value of the second current threshold I2), the control device 50 does not provide a high-level period for the control signal SU6. In this case, in the power conversion device 100, the current i9U begins to flow through the resonant capacitor 9U at the start time t41 of the dead time period Td. As a result, in the power conversion device 100, the resonant capacitor 9U is charged, and the voltage V2u across the second switching element 2U increases. The current i9U becomes zero before the end time t23 of the dead time period Td, and the voltage V1u across the first switching element 1U becomes zero before the end time t42 of the dead time period Td. As a result, in the power conversion device 100, the first switching element 1U is subjected to zero-voltage soft switching when the control signal SU1 changes from low to high at the end time t42 of the dead time period Td.

[0067] When the current value of the load current iU is greater than the second current threshold I2 (in other words, when the absolute value of the load current is smaller than the absolute value of the second current threshold), the control device 50 sets a high-level period for the control signal SU6, as shown by the two-dot chain line in FIG. 9 . The start point of the high-level period of the control signal SU6 at this time is the same as the start point t41 of the dead time period Td. The end point of the high-level period of the control signal SU6 is the same as the end point t42 of the dead time period Td. As a result, in the power conversion device 100, the voltage V1u across the first switching element 1U becomes zero before the end point t42 of the dead time period Td. Therefore, in the power conversion device 100, when the control signal SU1 changes from low to high at the end point t42 of the dead time period Td, the first switching element 1U is subjected to zero-voltage soft switching.

[0068] (3.2) Operation of the Common Mode Filter The operation of the common mode filter 21 will be described in more detail below with reference to Figures 10 to 12. Note that in Figures 11 and 12, as in Figure 1, the protection circuit 17 in Figure 2 is omitted.

[0069] FIG. 10 shows, as an example, control signals SU1, SU2, SU6, and SU7 to explain the charging and discharging operations of the third capacitor C3 of the common mode filter 21 connected to the U-phase switch 8U. Also shown in FIG. 10 are the current Ic1 flowing through the first switching element 1U and the voltage V1u across the first switching element 1U. Also shown in FIG. 10 are the current Ic2 flowing through the second switching element 2U and the voltage V2u across the second switching element 2U. Also shown in FIG. 10 are the current i9U flowing through the resonant capacitor 9U, the voltage VC3 across the third capacitor C3 of the common mode filter 21 connected to the switch 8U, and the current i3 flowing through the third capacitor C3. Also shown in FIG. 10 are the voltage VC2 across the second capacitor C2 of the voltage divider circuit 20 and the current i2 flowing through the second capacitor C2. In Fig. 10, the polarity of the current i9U flowing through the resonant capacitor 9U is defined as positive when flowing in the direction of the arrow in Fig. 11, and as negative when flowing in the direction opposite to the direction of the arrow in Fig. 11. Therefore, in the charging operation in which the resonant capacitor 9U is charged, the polarity of the current i9U is negative, and in the discharging operation in which the resonant capacitor 9U is discharged, the polarity of the current i9U is positive. Similarly, in Fig. 10, the polarity of the current i3 flowing through the third capacitor C3 is defined as positive when flowing in the direction of the arrow in Figs. 11 and 12, and as negative when flowing in the direction opposite to the direction of the arrow in Figs. 11 and 12. Therefore, in the charging operation in which the third capacitor C3 is charged, the polarity of the current i3 is negative, and in the discharging operation in which the third capacitor C3 is discharged, the polarity of the current i3 is positive. Similarly, in Fig. 10, the polarity of the current i2 flowing through the second capacitor C2 will be described as positive when it flows in the direction of the arrow in Fig. 11 and Fig. 12, and as negative when it flows in the opposite direction to the arrow in Fig. 11 and Fig. 12. Therefore, in the charging operation in which the second capacitor C2 is charged, the polarity of the current i2 is negative, and in the discharging operation in which the second capacitor C2 is discharged, the polarity of the current i2 is positive. Note that the load currents iU, iV, and iW are not shown in Fig. 11 and Fig. 12.

[0070] FIG. 10 illustrates the charging and discharging operations of the third capacitor C3 of the common mode filter 21 connected to the U-phase switch 8U, but the charging and discharging operations of the third capacitor C3 of the common mode filter 21 connected to the V-phase switch 8V are similar, and the charging and discharging operations of the third capacitor C3 of the common mode filter 21 connected to the W-phase switch 8W are also similar.

[0071] (3.2.1) Charging Operation The control device 50 performs a first control operation to charge the third capacitor C3 of the common mode filter 21. In the first control operation, the control device 50 controls the multiple first switching elements 1, the multiple second switching elements 2, and the multiple switches 8 so that the third capacitor C3 connected to one of the multiple switches 8 is charged from the regenerative capacitor 15 via the switch 8.

[0072] More specifically, as shown in FIG. 10, for example, the control device 50 charges the resonant capacitor 9U and also charges the third capacitor C3 of the common mode filter 21 during the dead time period Td between the end time t31 (end time t31) of the high level period of the control signal SU2 and the start time t32 of the high level period of the control signal SU1.

[0073] When the control device 50 performs the first control operation, as shown in FIG. 10 , the dead time period Td overlaps with the high-level period of the control signal SU6. As a result, as shown in FIG. 11 , the resonant capacitor 9U is charged by a first current I11 flowing from the regenerative capacitor 15 through the first IGBT 6U of the switch 8U. The first current I11 is a part of the resonant current flowing due to LC resonance. The path through which the first current I11 flows is the path through the regenerative capacitor 15, the resonant inductor L1, the switch 8, and the resonant capacitor 9U. Furthermore, the third capacitor C3 and the second capacitor C2 are charged by a second current I12 flowing from the regenerative capacitor 15 through the first IGBT 6U of the switch 8U to the third capacitor C3 of the common mode filter 21. As a result, the voltage VC3 across the third capacitor C3 and the voltage VC2 across the second capacitor C2 increase. The second current I12 is a part of the resonant current flowing due to LC resonance. The path through which the second current I12 flows is a path passing through the regenerative capacitor 15, the resonant inductor L1, the switch 8, the third capacitor C3, and the second capacitor C2.

[0074] The above-mentioned resonance period is expressed by equation (1), where Lr is the inductance of the resonance inductor L1, Cr is the capacitance of the resonance capacitor 9, Cy is the capacitance of the third capacitor C3, Cn is the capacitance of the second capacitor C2, and Tre is the resonance period.

[0075]

[0076] Therefore, the above-mentioned resonance half period can be obtained by the formula (2) where the resonance half period is Tr1.

[0077]

[0078] From equation (2), the combined capacitance of the resonance capacitor 9, the third capacitor C3, and the second capacitor C2 is expressed by equation (3).

[0079]

[0080] In the power conversion device 100, when the length of the dead time period Td is Td1 and the inductance of the resonant inductor L1 is Lr, the combined capacitance of the resonant capacitor 9, the third capacitor C3, and the second capacitor C2 is, for example, 4·(Td1 / π) ２ Here, the combined capacitance of the resonance capacitor 9, the third capacitor C3, and the second capacitor C2 is (Td1 / π) ２ In the power conversion device 100, the combined capacitance of the resonant capacitor 9, the third capacitor C3, and the second capacitor C2 is (Td1 / π). ２ Since it is smaller than (1 / Lr), it becomes easier to perform zero-voltage soft switching of the first switching element 1U (in other words, it becomes possible to suppress hard switching of the first switching element 1U).

[0081] In the power conversion device 100, the combined capacitance of the resonant capacitor 9, the third capacitor C3, and the second capacitor C2 is (1 / 2)·(Td1 / π) ２ - By being smaller than (1 / Lr), it is possible to prevent current from starting to flow through the first switching element 1U before the voltage V1u across the first switching element 1U drops to zero volts, and it is possible to more reliably perform zero-voltage soft switching of the first switching element 1U while suppressing an increase in switching loss of the first switching element 1U.

[0082] In the power conversion device 100, the combined capacitance of the third capacitor C3 and the second capacitor C2 is preferably smaller than the capacitance of the resonant capacitor 9.

[0083] (3.2.2) Discharge Operation The control device 50 performs a second control operation to discharge the third capacitor C3 of the common mode filter 21. In the second control operation, the control device 50 controls the multiple first switching elements 1, the multiple second switching elements 2, and the multiple switches 8 so as to discharge from the third capacitor C3 of the common mode filter 21 via one switch 8 of the multiple switches 8 that is connected to the third capacitor C3.

[0084] More specifically, as shown in FIG. 10, for example, the control device 50 discharges the resonant capacitor 9U and also discharges the third capacitor C3 of the common mode filter 21 during the dead time period Td between the end point t33 of the high level period of the control signal SU1 and the start point t34 of the high level period of the control signal SU2.

[0085] When the control device 50 performs the second control operation, as shown in FIG. 10 , the dead time period Td overlaps with the high-level period of the control signal SU7. As a result, as shown in FIG. 12 , a third current I13 flows from the resonant capacitor 9U to the regenerative capacitor 15 via the second IGBT 7U of the switch 8U, thereby discharging the resonant capacitor 9U. The third current I13 is part of the resonant current flowing due to LC resonance. The path through which the third current I13 flows is the path through the resonant capacitor 9, the switch 8, the resonant inductor L1, and the regenerative capacitor 15. Furthermore, a fourth current I14 flows from the third capacitor C3 of the common mode filter 21 to the regenerative capacitor 15 via the second IGBT 7U of the switch 8U, thereby discharging the third capacitor C3 and the second capacitor C2. As a result, the voltage VC3 across the third capacitor C3 and the voltage VC2 across the second capacitor C2 decrease. The fourth current I14 is part of the resonant current flowing due to LC resonance. The path through which the fourth current I14 flows is a path that passes through the third capacitor C3, the switch 8, the resonance inductor L1, the regenerative capacitor 15, and the second capacitor C2.

[0086] In the power conversion device 100, the combined capacitance of the resonant capacitor 9, the third capacitor C3, and the second capacitor C2 is (Td1 / 2π)２ Since the capacitance is smaller than (1 / Lr), the second switching element 2U can be easily subjected to zero-voltage soft switching (in other words, hard switching of the second switching element 2U can be suppressed). In addition, in the power conversion device 100, the combined capacitance of the resonant capacitor 9, the third capacitor C3, and the second capacitor C2 is (1 / 2)·(Td1 / 2π). ２ Since it is smaller than (1 / Lr), it is possible to prevent the current Ic2 from starting to flow through the second switching element 2U before the voltage V2u across the second switching element 2U drops to zero volts, and it is possible to more reliably perform zero-voltage soft switching of the second switching element 2U while suppressing an increase in the switching loss of the second switching element 2U.

[0087] In the power conversion device 100, it is preferable that the combined capacitance of the third capacitor C3 and the second capacitor C2 is smaller than the capacitance of the resonant capacitor 9. This enables the power conversion device 100 to further reduce leakage current (common mode current).

[0088] (4) Summary The power conversion device 100 according to the first embodiment includes a plurality of switches 8, a plurality of resonant capacitors 9, a resonant inductor L1, a control device 50, a voltage-dividing circuit 20, and a plurality of common mode filters 21. In the power conversion device 100, 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 voltage-dividing circuit 20 includes a first capacitor C1 and a second capacitor C2 connected in series. In the voltage-dividing circuit 20, the first capacitor C1 is connected to the first DC terminal 31, and the second capacitor C2 is connected to the second DC terminal 32. The voltage-dividing circuit 20 includes an intermediate potential point N1 between the first capacitor C1 and the second capacitor C2. The plurality of common mode filters 21 correspond one-to-one to the plurality of switching circuits 10. Each of the plurality of common mode filters 21 includes a third capacitor C3 connected between the intermediate potential point N1 and the node 3 in a corresponding one of the plurality of switching circuits 10.

[0089] The power conversion device 100 according to the first embodiment can reduce noise while suppressing switching loss. More specifically, the power conversion device 100 according to the first embodiment includes multiple common mode filters 21, each including a third capacitor C3. This prevents noise from leaking from the AC terminals 41U, 41V, and 41W of the U, V, and W phases to the AC load RA1, thereby reducing noise. The power conversion device 100 according to the first embodiment can charge the third capacitor C3 connected to the resonant capacitor 9 when charging the resonant capacitor 9 via the switch 8 to perform zero-voltage soft switching of the first switching element 1, thereby reducing switching loss of the first switching element 1. Furthermore, the power conversion device 100 according to the first embodiment can discharge the third capacitor C3 connected to the resonant capacitor 9 when discharging the resonant capacitor 9 via the switch 8 to perform zero-voltage soft switching of the second switching element 2, thereby reducing switching loss of the second switching element 2.

[0090] 13 , for example, in the power conversion device 100, a ground wire 110 connected to an AC load RA1 is connected to an intermediate potential point N1 via a housing (chassis) 101 of the power conversion device 100A. The power conversion device 100 can suppress a common mode current Ico flowing from the AC load RA1 via the ground wire 110 and the housing 101.

[0091] (5) Modifications of Embodiment 1 (5.1) Modification 1 A power conversion device 100A according to Modification 1 differs from the power conversion device 100 according to Embodiment 1 in that, as shown in Fig. 14 , a plurality of common mode filters 21 are connected to an intermediate potential point N1 via a housing 101. With regard to the power conversion device 100A according to Modification 1, components that are the same as those of the power conversion device 100 according to Embodiment 1 are denoted by the same reference numerals, and description thereof will be omitted.

[0092] The power conversion device 100A according to the first modification can suppress the common mode current Ico that flows from the AC load RA1 via the earth wire 110 and the housing 101.

[0093] 15 , in a power conversion device 100F according to Modification 2, each of a plurality of common mode filters 21 includes an inductor L3 connected in series to the third capacitor C3. The inductor L3 included in the common mode filter 21 is provided, for example, between the connection point between the switch 8 and the resonant capacitor 9 and the third capacitor C3, but is not limited to this and may be provided between the third capacitor C3 and the second capacitor C2.

[0094] In the second modification, when the length of the dead time period Td is Td1, the inductance of each resonance inductor L1 is Lr, and the inductance of each inductor L3 of the plurality of common mode filters 21 is L0, the combined capacitance of the resonance capacitor 9, the third capacitor C3, and the second capacitor C2 is (Td1 / π) ２ This combined capacitance is smaller than {1 / (Lr+L0)}. This combined capacitance is (1 / 2)(Td1 / π) ２ It is preferable that it is smaller than {1 / (Lr+L0)}.

[0095] Second Embodiment A power conversion device 100B according to a second embodiment will be described with reference to Fig. 16. Regarding the power conversion device 100B 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.

[0096] The power conversion device 100B of embodiment 2 differs from the power conversion device 100 of embodiment 1 in that it further includes a regenerative capacitor 16 (hereinafter also referred to as the second regenerative capacitor 16) connected between the sixth terminal 154 of the regenerative capacitor 15 (hereinafter also referred to as the first regenerative capacitor 15) and the first DC terminal 31.

[0097] The second regenerative capacitor 16 is connected in series to the first regenerative capacitor 15. Therefore, in the power conversion device 100B, 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.

[0098] In the power conversion device 100B 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 voltage value Vd of the DC power supply E1 divided by the voltages of the second regenerative capacitor 16 and the first regenerative capacitor 15. Therefore, the voltage V15 across the first regenerative capacitor 15 is Vd / 2. In the power conversion device 100B according to the second embodiment, the control device 50 may store the value of the voltage V15 across the first regenerative capacitor 15 in advance.

[0099] The operation of the control device 50 of the power conversion device 100B 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, like the power conversion device 100 according to the first embodiment, the power conversion device 100B according to the second embodiment can reduce noise while suppressing switching loss.

[0100] Third Embodiment A power conversion device 100C according to a third embodiment will be described with reference to Fig. 17. Regarding the power conversion device 100C according to the third embodiment, components similar to those of the power conversion device 100 according to the first embodiment are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0101] The power conversion device 100C further includes a second voltage-dividing circuit 22 separate from the voltage-dividing circuit 20 (hereinafter also referred to as the first voltage-dividing circuit 20). Similar to the first voltage-dividing circuit 20, the second voltage-dividing circuit 22 is connected between the first DC terminal 31 and the second DC terminal 32. Therefore, the second voltage-dividing circuit 22 is connected in parallel to the first voltage-dividing circuit 20.

[0102] The second voltage-dividing circuit 22 has a fourth capacitor C4 and a fifth capacitor C5 connected in series. In the second voltage-dividing circuit 22, the fourth capacitor C4 is connected to the first DC terminal 31, and the fifth capacitor C5 is connected to the second DC terminal 32. The second voltage-dividing circuit 22 has a neutral point N2 between the fourth capacitor C4 and the fifth capacitor C5. The intermediate potential point N1 is electrically isolated from the neutral point N2.

[0103] Furthermore, the power conversion device 100C differs from the power conversion device 100 of embodiment 1 in that the earth wire 110 connected to the AC load RA1 is connected to the neutral point N2 via the housing (chassis) 101 in the power conversion device 100C.

[0104] In the power conversion device 100C according to the second embodiment, the common mode current Ico flowing from the AC load RA1 via the earth wire 110 and the housing 101 flows to the neutral point N2, and therefore leakage current can be prevented from flowing to the third capacitor C3 of each of the plurality of common mode filters 21.

[0105] (Fourth Embodiment) A power conversion device 100D according to a fourth embodiment will be described with reference to Figures 18 to 21. With respect to the power conversion device 100D according to the fourth embodiment, components similar to those of the power conversion device 100 according to the first embodiment are denoted by the same reference numerals, and descriptions thereof will be omitted. Note that in Figure 18, the protection circuit 17 shown in Figure 19 is omitted, and in Figure 19, the multiple common mode filters 21 shown in Figure 18 are omitted.

[0106] (1) Configuration As shown in Fig. 18 , the power conversion device 100D 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 100D, the resonant inductor L1 is common to the multiple resonant circuits. In the power conversion device 100D, the third end of the resonant inductor L1 is connected to a common connection point 25. The second ends 82 of the multiple switches 8 are commonly connected to the common connection point 25.

[0107] The power conversion device 100D also differs from the power conversion device 100 according to the first embodiment in that it includes only one protection circuit 17 (see FIG. 19).

[0108] In the power conversion device 100D, the third diode 13 in the protection circuit 17 is connected between the common connection point 25 and the first DC terminal 31. In the third diode 13, the anode of the third diode 13 is connected to the common connection point 25. In addition, in the third diode 13, the cathode of the third diode 13 is connected to the first DC terminal 31. The fourth diode 14 in the protection circuit 17 is connected between the common connection point 25 and the second DC terminal 32. In the fourth diode 14, the anode of the fourth diode 14 is connected to the second DC terminal 32. In the fourth diode 14, the cathode of the fourth diode 14 is connected to the common connection point 25. Therefore, the fourth diode 14 is connected in series with the third diode 13.

[0109] (2) Operation of the Power Conversion Device In the power conversion device 100D, similarly to the power conversion device 100, the control device 50 controls a plurality of (e.g., three) first switching elements 1, a plurality of (e.g., three) second switching elements 2, and a plurality of (e.g., three) switches 8. The control device 50 performs basic operations and shift control operations.

[0110] (2.1) Basic Operation The basic operation of the control device 50 is the same as the operation of the control device 50 in the power conversion device 100 according to embodiment 1. The basic operation is an operation performed when no resonant current flows through two or more of the multiple switches 8 simultaneously through the resonant inductor L1.

[0111] (2.2) Shift Control Operation The shift control operation is an operation of the control device 50 when the control device 50 determines that resonant currents flow simultaneously through two or more of the switches 8 .

[0112] When the control device 50 determines that resonant currents passing through two switches 8 out of the plurality of switches 8 simultaneously flow through the resonant inductor L1, the control device 50 performs shift control to shift the high-level period of the control signal to one of the two switches 8 so that the resonant currents passing through the two switches 8 do not simultaneously flow through the resonant inductor L1. "When it is determined that resonant currents passing through two switches 8 out of the plurality of switches 8 simultaneously flow" means that it has been estimated in advance that the resonant currents passing through the two switches 8 simultaneously flow through the resonant inductor L1.

[0113] (2.2.1) Determination of whether two-phase resonant currents flow simultaneously In the power conversion device 100D, the phases of the voltage commands for three phases (U phase, V phase, and W phase) differ by 120° from one another, but the command values ​​of the voltage commands for two phases approach each other by an electrical angle of 60°, and the duties of the control signals for the two phases approach each other (see areas A1 and A2 in FIG. 5 ). In area A1 in FIG. 5 , the duties of the U-phase control signal and the V-phase control signal are approximately 0.75. In area A2 in FIG. 5 , the duties of the U-phase control signal and the V-phase control signal are approximately 0.25. The polarity of the resonant current is the same as the polarity of the current iL1; in area A1, the polarity of the resonant current is positive, and in area A2, the polarity of the resonant current is negative. In the case of region A1, for example, during one cycle of the carrier signal, the time difference between start time t1 (see FIG. 3) of the high-level period of the control signal SU6 supplied to the first IGBT 6U and start time t5 (see FIG. 3) of the high-level period of the control signal SV6 supplied to the first IGBT 6V becomes short, and there is a possibility that the U-phase resonant current and the V-phase resonant current will flow simultaneously through the resonant inductor L1. In the power conversion device 100D, in the case of region A2, the direction of the resonant current is opposite to that in region A1, but there is a possibility that the U-phase resonant current and the V-phase resonant current will flow simultaneously through the resonant inductor L1.

[0114] Assuming that the capacitance of each of the multiple resonant capacitors 9U, 9V, and 9W is Cr, if a U-phase current and a V-phase current flow simultaneously through the resonant inductor L1, then in terms of an equivalent circuit, a capacitor having a combined capacitance (=2×Cr) of the resonant capacitors 9U and 9V is connected in series to the resonant inductor L1. Therefore, in the power conversion device 100D, if two-phase currents flow simultaneously through the resonant inductor L1, the resonant frequency of the resonant circuit including the resonant inductor L1 will change compared to when a single-phase current flows through the resonant inductor L1, and zero-voltage soft switching may not be achieved.

[0115] (2.2.2) In the case of charging operation of the resonant capacitor The boundary conditions for when the U-phase resonant current and the V-phase resonant current do not overlap (do not flow simultaneously) and when they overlap (flow simultaneously) will be described with reference to Figure 3.

[0116] In the power conversion device 100D (see FIGS. 18 and 19 ), if the time difference ΔTuv between the start time t3 of the high-level period of the control signal SU1 and the start time t7 of the high-level period of the control signal SV1 is equal to or greater than (Tau + Tav + Td), the U-phase resonant current and the V-phase resonant current do not overlap, and if the time difference ΔTuv is less than (Tau + Tav + Td), the U-phase resonant current and the V-phase resonant current overlap. The control device 50 sets a threshold for the time difference ΔTuv to, for example, (Tau + Tav + Td), and if the time difference ΔTuv is less than the threshold, it estimates that resonant currents corresponding to two phases, switching circuit 10U and switching circuit 10V, of the multiple switching circuits 10, will simultaneously flow through the resonant inductor L1. The above threshold setting is merely an example, and other values ​​may also be considered. For example, it is possible to set the threshold value to a value greater than (Tau + Tav + Td) taking into account errors in the additional times Tau and Tav. Furthermore, the method for calculating the time difference ΔTuv used to determine whether two-phase resonant currents flow simultaneously is not limited to the above example, and any other calculation method may be used as long as it can calculate a time difference equivalent to the time difference. For example, the time difference ΔTuv used to determine whether two-phase resonant currents flow simultaneously may be the time difference between time t2 at which the high-level period of the control signal SU2 ends (hereinafter also referred to as end time t2) and time t6 at which the high-level period of the control signal SV2 ends (hereinafter also referred to as end time t6).

[0117] Furthermore, in the power conversion device 100D, if the time difference between time t3 (hereinafter also referred to as start time t3) at which the high-level period of the control signal SU1 starts and time t11 at which the high-level period of the control signal SW1 starts is (Tau + Taw + Td) or more, the U-phase resonant current and the W-phase resonant current do not overlap, and if the time difference is less than (Tau + Taw + Td), the U-phase resonant current and the W-phase resonant current overlap. The control device 50 sets a threshold for this time difference to, for example, (Tau + Taw + Td), and if the time difference is less than this threshold, it estimates that resonant currents corresponding to two phases, switching circuit 10U and switching circuit 10W, of the multiple switching circuits 10, will flow simultaneously through the resonant inductor L1. The above threshold setting is just an example, and it is also possible to set the threshold to another value. For example, it is possible to set the threshold value to a value greater than (Tau + Taw + Td) taking into account errors in the additional time Tau and the additional time Taw. Furthermore, the method for calculating the time difference used to determine whether two-phase resonant currents flow simultaneously is not limited to the above example, and any other calculation method may be used as long as it can calculate a time difference equivalent to the time difference. For example, the time difference used to determine whether two-phase resonant currents flow simultaneously may be the time difference between the end time t2 of the high-level period of the control signal SU2 and the end time t10 (hereinafter also referred to as the end time t10) of the high-level period of the control signal SW2 (see FIG. 4).

[0118] Furthermore, in the power conversion device 100D, if the time difference between time t7 (hereinafter also referred to as start time t7) at which the high-level period of the control signal SV1 provided to the first switching element 1V of the switching circuit 10V starts and time t11 at which the high-level period of the control signal SW1 (see FIG. 4) provided to the first switching element 1W of the switching circuit 10W starts is (Tav + Taw + Td) or more, the V-phase resonant current and the W-phase resonant current do not overlap. If the time difference is less than (Tav + Taw + Td), the V-phase resonant current and the W-phase resonant current overlap. The control device 50 sets a threshold for this time difference to, for example, (Tav + Taw + Td), and if the time difference is less than the threshold, it estimates that resonant currents corresponding to two phases, the switching circuit 10V and the switching circuit 10W, of the multiple switching circuits 10 simultaneously flow through the resonant inductor L1. The above threshold setting is merely an example, and other values ​​may also be considered. For example, it is possible to set the threshold value to a value greater than (Tav + Taw + Td) in consideration of errors in the additional times Tav and Taw. Furthermore, the method for calculating the time difference used to determine whether two-phase resonant currents flow simultaneously is not limited to the above example, and any other calculation method may be used as long as it can calculate a time difference equivalent to the time difference. For example, the time difference used to determine whether two-phase resonant currents flow simultaneously may be the time difference between the end point t6 of the high-level period of the control signal SV2 and the end point t10 of the high-level period of the control signal SW2.

[0119] (2.2.3) In the case of discharging operation of the resonant capacitor In the case of discharging operation of the resonant capacitor 9, the control device 50 can determine whether two-phase resonant currents flow simultaneously using the same time difference and threshold value as in the case of charging operation of the resonant capacitor 9.

[0120] For example, the control device 50 estimates that the U-phase resonant current and the V-phase resonant current overlap if the time difference between the start point of the high-level period of the control signal SU2 and the start point of the high-level period of the control signal SV2 is less than a threshold value (e.g., Tau + Tav + Td).

[0121] In addition, the control device 50 estimates that the U-phase resonant current and the W-phase resonant current overlap if the time difference between the start point of the high-level period of the control signal SU2 and the start point of the high-level period of the control signal SW2 is less than a threshold value (e.g., Tau + Taw + Td).

[0122] In addition, the control device 50 estimates that the V-phase resonant current and the W-phase resonant current overlap if the time difference between the start of the high-level period of the control signal SV2 and the start of the high-level period of the control signal SW2 is less than a threshold value (e.g., Tav + Taw + Td).

[0123] (2.2.4) Shift Control When It is Determined that Two-Phase Resonant Currents Flow Simultaneously The control device 50 performs shift control to shift the high-level period of the control signal to one of the two switches 8, for example, so that the resonant currents passing through the two switches 8 respectively do not flow simultaneously through the resonant inductor L1.

[0124] When performing shift control, the control device 50 shifts the high-level period of the control signal to one of the two switches 8 so as not to change the length of the high-level period of the control signal supplied to each of the first switching element 1 and the second switching element 2 of one switching circuit 10 corresponding to one of the two switches 8. For example, when shifting the high-level period of the control signal SU6 or SU7 supplied to switch 8U, the control device 50 shifts the high-level periods of the control signal SU1 and the control signal SU2, but does not change the duties of the control signal SU1 and the control signal SU2 in one period of the carrier signal. Furthermore, when shifting the high-level period of the control signal SV6 or SV7 supplied to switch 8V, the control device 50 shifts the high-level periods of the control signal SV1 and the control signal SV2, but does not change the duties of the control signal SV1 and the control signal SV2 in one period of the carrier signal. Furthermore, when the control device 50 shifts the high-level period of the control signal SW6 or SW7 provided to the switch 8W, it shifts the high-level period of each of the control signal SW1 and the control signal SW2, but does not change the duty of each of the control signal SW1 and the control signal SW2 in one cycle of the carrier signal.

[0125] In the power conversion device 100D, when the control device 50 executes shift control to soft-switch the first switching element 1, for example, the voltages V2u and V2v across the second switching elements 2U and 2V rise to Vd at the point in time when the control signals SU1 and SV1 change from a low-level period to a high-level period (the end point of the dead time period Td corresponding to the U phase and the V phase, respectively). In other words, when the control device 50 executes shift control, charging of the resonant capacitors 9U and 9V ends at the end of the dead time period Td corresponding to the U phase and the V phase, respectively. Therefore, in the power conversion device 100D, when the control device 50 executes shift control, the switching of the first switching elements 1U and 1V becomes zero-voltage soft switching.

[0126] Although the above example shows an example of shift control when the control device 50 determines in advance that a U-phase resonant current and a V-phase resonant current will simultaneously flow through the resonant inductor L1, the present invention is not limited to this. For example, when the control device 50 determines in advance that a V-phase resonant current and a W-phase resonant current will simultaneously flow through the resonant inductor L1, the control device 50 also performs shift control in a case where it has determined in advance that a W-phase resonant current and a U-phase resonant current will simultaneously flow through the resonant inductor L1, thereby enabling zero-voltage soft switching.

[0127] Furthermore, in the power conversion device 100D, when the control device 50 executes shift control to soft-switch the second switching element 2, for example, the voltages V1u and V1v across the first switching elements 1U and 1V rise to Vd at the point in time when the control signals SU2 and SV2 change from a low-level period to a high-level period (the end point of the dead time period Td corresponding to the U phase and the V phase, respectively). In other words, when the control device 50 executes shift control, the discharge of the resonant capacitors 9U and 9V ends at the end of the dead time period Td corresponding to the U phase and the V phase, respectively. Therefore, in the power conversion device 100D, when the control device 50 executes shift control, the switching of the second switching elements 2U and 2V becomes zero-voltage soft switching.

[0128] Although the above example shows an example of shift control when the control device 50 determines in advance that a U-phase resonant current and a V-phase resonant current will simultaneously flow through the resonant inductor L1, the present invention is not limited to this. For example, when the control device 50 determines in advance that a V-phase resonant current and a W-phase resonant current will simultaneously flow through the resonant inductor L1, the control device 50 also performs shift control in a case where it has determined in advance that a W-phase resonant current and a U-phase resonant current will simultaneously flow through the resonant inductor L1, thereby enabling zero-voltage soft switching.

[0129] (2.3) Operation of Common Mode Filter The operation of the common mode filter 21 is the same as the operation of the common mode filter 21 in the power conversion device 100 according to the first embodiment. Therefore, in each of the multiple common mode filters 21, when the control device 50 performs the first control operation, the third capacitor C3 is charged by LC resonance. Also, in each of the multiple common mode filters 21, when the control device 50 performs the second control operation, the third capacitor C3 is discharged by LC resonance.

[0130] (2.3.1) Charging Operation The control device 50 performs a first control operation to charge the third capacitor C3 of the common mode filter 21. In the first control operation, the control device 50 controls the multiple first switching elements 1, the multiple second switching elements 2, and the multiple switches 8 so as to charge the third capacitor C3 connected to one of the multiple switches 8 via the switch 8 from the regenerative capacitor 15.

[0131] When the control device 50 performs the first control operation, for example, as shown in FIG. 10 , the dead time period Td and the high-level period of the control signal SU6 overlap. As a result, as shown in FIG. 20 , a first current I11 flows from the regenerative capacitor 15 to the resonant capacitor 9U via the first IGBT 6U of the switch 8U, charging the resonant capacitor 9U. The first current I11 is a part of the resonant current flowing due to LC resonance. The path through which the first current I11 flows is the path through the regenerative capacitor 15, the resonant inductor L1, the switch 8, and the resonant capacitor 9. Furthermore, a second current I12 flows from the regenerative capacitor 15 to the third capacitor C3 of the common mode filter 21 via the first IGBT 6U of the switch 8U, charging the third capacitor C3 and the second capacitor C2. The second current I12 is a part of the resonant current flowing due to LC resonance. The path through which the second current I12 flows is a path passing through the regenerative capacitor 15, the resonant inductor L1, the switch 8, the third capacitor C3, and the second capacitor C2.

[0132] In the power conversion device 100D, when the length of the dead time period Td is Td1 and the inductance of the resonance inductor L1 is Lr, the combined capacitance of the resonance capacitor 9, the third capacitor C3, and the second capacitor C2 is, for example, 4·(Td1 / π) ２ Here, the combined capacitance of the resonance capacitor 9, the third capacitor C3, and the second capacitor C2 is (Td1 / π) ２ In the power conversion device 100D, the combined capacitance of the resonant capacitor 9, the third capacitor C3, and the second capacitor C2 is (Td1 / π). ２ Since it is smaller than (1 / Lr), it becomes easier to perform zero-voltage soft switching of the first switching element 1U (in other words, it becomes possible to suppress hard switching of the first switching element 1U).

[0133] In the power conversion device 100D, the combined capacitance of the resonant capacitor 9, the third capacitor C3, and the second capacitor C2 is (1 / 2)·(Td1 / π) ２ - By being smaller than (1 / Lr), it is possible to prevent current from starting to flow through the first switching element 1U before the voltage V1u across the first switching element 1U drops to zero volts, and it is possible to more reliably perform zero-voltage soft switching of the first switching element 1U while suppressing an increase in switching loss of the first switching element 1U.

[0134] Furthermore, in the power conversion device 100D, it is preferable that the combined capacitance of the third capacitor C3 and the second capacitor C2 is smaller than the capacitance of the resonant capacitor 9. This enables the power conversion device 100D to further reduce leakage current (common mode current).

[0135] (2.3.2) Discharge Operation The control device 50 performs a second control operation to discharge the third capacitor C3 of the common mode filter 21. In the second control operation, the control device 50 controls the multiple first switching elements 1, the multiple second switching elements 2, and the multiple switches 8 so as to discharge from the third capacitor C3 of the common mode filter 21 via one switch 8 of the multiple switches 8 that is connected to the third capacitor C3.

[0136] More specifically, as shown in FIG. 10, for example, the control device 50 discharges the resonant capacitor 9U and also discharges the third capacitor C3 of the common mode filter 21 during the dead time period Td between the end of the high level period of the control signal SU1 and the start of the high level period of the control signal SU2.

[0137] When the control device 50 performs the second control operation, as shown in FIG. 10 , the dead time period Td and the high-level period of the control signal SU7 overlap. As a result, as shown in FIG. 21 , a third current I13 flows from the resonant capacitor 9U to the regenerative capacitor 15 via the second IGBT 7U of the switch 8U, thereby discharging the resonant capacitor 9U. The third current I13 is a part of the resonant current flowing due to LC resonance. The path through which the third current I13 flows is the path through the resonant capacitor 9, the switch 8, the resonant inductor L1, and the regenerative capacitor 15. Furthermore, a fourth current I14 flows from the third capacitor C3 of the common mode filter 21 to the regenerative capacitor 15 via the second IGBT 7U of the switch 8U, thereby discharging the third capacitor C3 and the second capacitor C2. The fourth current I14 is a part of the resonant current flowing due to LC resonance. The path through which the fourth current I14 flows is a path that passes through the third capacitor C3, the switch 8, the resonance inductor L1, the regenerative capacitor 15, and the second capacitor C2.

[0138] In the power conversion device 100D, the combined capacitance of the resonant capacitor 9, the third capacitor C3, and the second capacitor C2 is (Td1 / π) ２Since the capacitance is smaller than (1 / Lr), the second switching element 2U can be easily subjected to zero-voltage soft switching (in other words, hard switching of the second switching element 2U can be suppressed). In addition, in the power conversion device 100D, the combined capacitance of the resonant capacitor 9, the third capacitor C3, and the second capacitor C2 is (1 / 2)·(Td1 / π). ２ Since it is smaller than (1 / Lr), it is possible to prevent the current Ic2 from starting to flow through the second switching element 2U before the voltage V2u across the second switching element 2U drops to zero volts, and it is possible to more reliably perform zero-voltage soft switching of the second switching element 2U while suppressing an increase in the switching loss of the second switching element 2U.

[0139] In the power conversion device 100D, it is preferable that the combined capacitance of the third capacitor C3 and the second capacitor C2 is smaller than the capacitance of the resonant capacitor 9.

[0140] (3) Summary The power conversion device 100D according to the fourth embodiment includes a plurality of switches 8, a plurality of resonant capacitors 9, a resonant inductor L1, a control device 50, a voltage-dividing circuit 20, and a plurality of common mode filters 21. In the power conversion device 100D, 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 voltage-dividing circuit 20 includes a first capacitor C1 and a second capacitor C2 connected in series. In the voltage-dividing circuit 20, the first capacitor C1 is connected to the first DC terminal 31, and the second capacitor C2 is connected to the second DC terminal 32. The voltage-dividing circuit 20 includes an intermediate potential point N1 between the first capacitor C1 and the second capacitor C2. The plurality of common mode filters 21 correspond one-to-one to the plurality of switching circuits 10. Each of the plurality of common mode filters 21 includes a third capacitor C3 connected between the node 3 in the corresponding switching circuit 10 and the intermediate potential point N1.

[0141] The power conversion device 100D according to the fourth embodiment can reduce noise while suppressing switching loss. More specifically, the power conversion device 100D according to the fourth embodiment includes multiple common mode filters 21, each including a third capacitor C3. This prevents noise from leaking from the AC terminals 41U, 41V, and 41W of the U, V, and W phases to the AC load RA1, thereby reducing noise. The power conversion device 100D according to the fourth embodiment can charge the third capacitor C3 when connected to the resonant capacitor 9 when charging the resonant capacitor 9 via the switch 8 to perform zero-voltage soft switching of the first switching element 1, thereby reducing switching loss of the first switching element 1. Furthermore, the power conversion device 100D according to the fourth embodiment can discharge the third capacitor C3 connected to the resonant capacitor 9 when discharging the resonant capacitor 9 via the switch 8 to perform zero-voltage soft switching of the second switching element 2, thereby reducing switching loss of the second switching element 2.

[0142] Furthermore, the power conversion device 100D according to the fourth 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 100D according to the fourth embodiment to be miniaturized.

[0143] Furthermore, in the power conversion device 100D according to the fourth embodiment, when the control device 50 determines that resonant currents passing through two of the multiple switches 8 respectively flow through one resonant inductor L1 simultaneously, the control device 50 performs control to shift the high-level periods of the control signals to the two switches 8 respectively so that the resonant currents passing through the two switches 8 respectively do not flow through the one resonant inductor L1 simultaneously. This makes it possible for the power conversion device 100D according to the fourth embodiment to more reliably achieve soft switching.

[0144] (4) Modifications of the Fourth Embodiment (4.1) Modification 1 A power conversion device 100D according to Modification 1 will be described with reference to Fig. 22. Constituent elements of the power conversion device 100D according to Modification 1 that are the same as those of the power conversion device 100D according to the fourth embodiment will be denoted by the same reference numerals, and description thereof will be omitted.

[0145] In a power conversion device 100D according to the first modification, a first IGBT 6 and a second IGBT 7 are connected in anti-series in each of the plurality of switches 8. In the power conversion device 100D according to the first modification, a collector terminal of the first IGBT 6 and a collector terminal of the second IGBT 7 are connected in each of the plurality of switches 8, an emitter terminal of the first IGBT 6 is connected to a connection point 3 of a corresponding one of the plurality of switching circuits 10, and an emitter terminal of the second IGBT 7 is connected to a common connection point 25. Each of the plurality of switches 8 further includes a diode 61 connected in anti-parallel to the first IGBT 6 and a diode 71 connected in anti-parallel to the second IGBT 7.

[0146] In the power conversion device 100D according to the first modification, each of the first IGBT 6 and the second IGBT 7 may be replaced with a MOSFET or a bipolar transistor. In this case, the diode 61 and the diode 71 in FIG. 22 may be substituted with a parasitic diode of the replaced element, or an element built into the chip of the replaced element. Furthermore, in the power conversion device 100D according to the first modification, the diode 61 and the diode 71 are not limited to being externally connected to the first IGBT 6 and the second IGBT 7, but may be built into the chip.

[0147] The operation of the control device 50 is the same as that of the control device 50 of the fourth embodiment, for example.

[0148] (4.2) Modification 2 A power conversion device 100D according to Modification 2 will be described with reference to Fig. 23. Constituent elements of the power conversion device 100D according to Modification 2 that are the same as those of the power conversion device 100D according to the fourth embodiment will be denoted by the same reference numerals, and description thereof will be omitted.

[0149] In a power conversion device 100D according to the second modification, the first IGBT 6 and the second IGBT 7 are connected in anti-series in each of the multiple switches 8. In the power conversion device 100D according to the second modification, the emitter terminal of the first IGBT 6 and the emitter terminal of the second IGBT 7 are connected in each of the multiple switches 8, the collector terminal of the first IGBT 6 is connected to a common connection point 25, and the collector terminal of the second IGBT 7 is connected to a connection point 3 of a corresponding one of the multiple switching circuits 10. Each of the multiple switches 8 further includes a diode 61 connected in anti-parallel to the first IGBT 6 and a diode 71 connected in anti-parallel to the second IGBT 7.

[0150] In the power conversion device 100D according to the second modification, each of the first IGBT 6 and the second IGBT 7 may be replaced with a MOSFET or a bipolar transistor. In this case, the diode 61 and the diode 71 in FIG. 23 may be substituted with a parasitic diode of the replaced element, or an element built into the chip of the replaced element. Furthermore, in the power conversion device 100D according to the second modification, the diode 61 and the diode 71 are not limited to being externally connected to the first IGBT 6 and the second IGBT 7, but may also be an element built into the chip.

[0151] The operation of the control device 50 is the same as that of the control device 50 of the fourth embodiment, for example.

[0152] (4.3) Modification 3 A power conversion device 100D according to Modification 3 will be described with reference to Fig. 24. Constituent elements of the power conversion device 100D according to Modification 3 that are the same as those of the power conversion device 100D according to the fourth embodiment will be denoted by the same reference numerals, and description thereof will be omitted.

[0153] In a power conversion device 100D according to the third modification, a first MOSFET 6A and a second MOSFET 7A are connected in anti-series in each of the multiple switches 8. In the power conversion device 100D according to the third modification, the drain terminal of the first MOSFET 6A and the drain terminal of the second MOSFET 7A are connected in anti-parallel in each of the multiple switches 8. Each of the multiple switches 8 further includes a diode 61 connected in anti-parallel to the first MOSFET 6A and a diode 71 connected in anti-parallel to the second MOSFET 7A. In each of the multiple switches 8, the source terminal of the second MOSFET 7A is connected to a common connection point 25. In each of the multiple switches 8, the source terminal of the first MOSFET 6A is connected to a connection point 3 of the switching circuit 10 corresponding to the switch 8 having the first MOSFET 6A. Control signals SU6 and SU7 are provided from a control device 50 to the first MOSFET 6A and the second MOSFET 7A of the switch 8U. The first MOSFET 6A and the second MOSFET 7A of the switch 8V are supplied with control signals SV6 and SV7 from the control device 50. The first MOSFET 6A and the second MOSFET 7A of the switch 8W are supplied with control signals SW6 and SW7 from the control device 50.

[0154] The operation of the control device 50 is similar to that of the control device 50 of the fourth embodiment, for example.

[0155] (4.4) Modification 4 A power conversion device 100D according to Modification 4 will be described with reference to Fig. 25. Constituent elements of the power conversion device 100D according to Modification 4 that are the same as those of the power conversion device 100D according to the fourth embodiment will be denoted by the same reference numerals, and description thereof will be omitted.

[0156] In a power conversion device 100D according to the fourth modification, a diode 63 is connected in series to the first MOSFET 6A, and a diode 73 is connected in series to the second MOSFET 7A in each of the multiple switches 8. In the power conversion device 100D according to the fourth modification, a series circuit of the first MOSFET 6A and the diode 63 and a series circuit of the second MOSFET 7A and the diode 73 are connected in anti-parallel.

[0157] The operation of the control device 50 is similar to that of the control device 50 of the fourth embodiment, for example.

[0158] (4.5) Modification 5 A power conversion device 100D according to Modification 5 will be described with reference to Fig. 26. Constituent elements of the power conversion device 100D according to Modification 5 that are the same as those of the power conversion device 100D according to the fourth embodiment will be denoted by the same reference numerals, and description thereof will be omitted.

[0159] In a power conversion device 100D according to the fifth modification, each of the multiple switches 8 includes one MOSFET 80, a diode 83 connected in anti-parallel to the MOSFET 80, a series circuit of two diodes 84 and 85 connected in anti-parallel to the MOSFET 80, and a series circuit of two diodes 86 and 87 connected in anti-parallel to the MOSFET 80. In each of the multiple switches 8, a connection point between the diode 84 and the diode 85 in the switch 8 (a first end 81 of the switch 8) is connected to a connection point 3 of a corresponding switching circuit 10 among the multiple switching circuits 10, and a connection point between the diode 86 and the diode 87 (a second end 82 of the switch 8) is connected to the common connection point 25. In each of the switches 8, when the MOSFET 80 is in an on state, the switch 8 is in an on state, and when the MOSFET 80 is in an off state, the switch 8 is in an off state.

[0160] The MOSFETs 80 of the multiple switches 8 are controlled by a control device 50. The control device 50 outputs a control signal SU8 that controls the on / off state of the MOSFET 80 of the switch 8U, a control signal SV8 that controls the on / off state of the MOSFET 80 of the switch 8V, and a control signal SW8 that controls the on / off state of the MOSFET 80 of the switch 8W.

[0161] In the switch 8, when the MOSFET 80 is in the on state, a resonant current flows due to a resonant circuit including the resonant inductor L1 and the resonant capacitor 9. In the power conversion device 100D, with regard to the charging operation of the resonant capacitor 9, when one of the multiple switches 8 is in the on state, a charging current including the resonant current flows through the path of the regenerative capacitor 15 - the resonant inductor L1 - the diode 86 - the MOSFET 80 - the diode 85 - and the resonant capacitor 9. In addition, in the power conversion device 100D, with regard to the discharging operation of the resonant capacitor 9, when one of the multiple switches 8 is in the on state, a discharging current including the resonant current flows through the path of the resonant capacitor 9 - the diode 84 - the MOSFET 80 - the diode 87 - the resonant inductor L1 - and the regenerative capacitor 15.

[0162] In the power conversion device 100D according to the fifth modification, each of the plurality of MOSFETs 80 may be replaced with an IGBT. Furthermore, in the power conversion device 100D according to the fifth modification, each of the plurality of switches 8 may have, instead of the MOSFET 80, a bipolar transistor or a GaN-based GIT (Gate Injection Transistor), for example.

[0163] The operation of the control device 50 is similar to that of the control device 50 of the fourth embodiment, for example.

[0164] (4.6) Modification 6 A power conversion device 100D according to Modification 6 will be described with reference to Fig. 27. Constituent elements of the power conversion device 100D according to Modification 6 that are the same as those of the power conversion device 100D according to the fourth embodiment will be denoted by the same reference numerals, and description thereof will be omitted.

[0165] In a power conversion device 100D according to the sixth modification, each of the multiple switches 8 is a dual-gate GaN-based GIT having a first source terminal, a first gate terminal, a second gate terminal, and a second source terminal. In the power conversion device 100D according to the sixth modification, a control signal SU6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT constituting the switch 8U, and a control signal SU7 is applied between the second gate terminal and the second source terminal. Furthermore, a control signal SV6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT constituting the switch 8V, and a control signal SV7 is applied between the second gate terminal and the second source terminal. Furthermore, a control signal SW6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT constituting the switch 8W, and a control signal SW7 is applied between the second gate terminal and the second source terminal.

[0166] The operation of the control device 50 is similar to that of the control device 50 of the fourth embodiment, for example.

[0167] Fifth Embodiment A power conversion device 100E according to a fifth embodiment will be described with reference to Fig. 28. Regarding the power conversion device 100E according to the fifth embodiment, components similar to those of the power conversion device 100D according to the fourth embodiment will be denoted by the same reference numerals, and description thereof will be omitted.

[0168] The power conversion device 100E of embodiment 5 differs from the power conversion device 100D of embodiment 4 in that it further includes a regenerative capacitor 16 (hereinafter also referred to as the second regenerative capacitor 16) connected between the sixth terminal 154 of the regenerative capacitor 15 (hereinafter also referred to as the first regenerative capacitor 15) and the first DC terminal 31.

[0169] The second regenerative capacitor 16 is connected in series to the first regenerative capacitor 15. Therefore, in the power conversion device 100E, 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.

[0170] In the power conversion device 100E according to the fifth 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 voltage value Vd of the DC power supply E1 divided by the voltages of the second regenerative capacitor 16 and the first regenerative capacitor 15. Therefore, the voltage V15 across the first regenerative capacitor 15 is Vd / 2. In the power conversion device 100E 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.

[0171] The operation of the control device 50 of the power conversion device 100E according to the fifth embodiment is similar to the operation of the control device 50 of the power conversion device 100D according to the fourth embodiment. Therefore, like the power conversion device 100D according to the fourth embodiment, the power conversion device 100E according to the fifth embodiment can reduce noise while suppressing switching loss.

[0172] (Other Modifications) The above-described first to fifth embodiments are merely examples of various embodiments of the present disclosure. The above-described first to fifth embodiments can be modified in various ways depending on the design, etc., as long as the object of the present disclosure can be achieved.

[0173] For example, in the control device 50 of the power conversion device 100D according to the fourth embodiment, the operation of "determining that two-phase resonant currents are flowing simultaneously" is not limited to the operation of "determining that two-phase resonant currents are flowing simultaneously" when the time difference described in the fourth embodiment is less than the threshold value.

[0174] For example, the control device 50 may determine that two-phase resonant currents are flowing simultaneously when any one of the current difference between the U-phase load current iU and the V-phase load current iV, the current difference between the V-phase load current iV and the W-phase load current iW, and the current difference between the W-phase load current iW and the U-phase load current iU is less than a current difference threshold.

[0175] In addition, the control device 50 may determine that "two-phase resonant currents flow simultaneously" when the electrical angle calculated from sensor information output from a sensor device (e.g., an encoder or resolver) for detecting the rotation speed of the motor, or the estimated electrical angle, is within a first rotation angle range (e.g., 55 degrees or more and 65 degrees or less), a second rotation angle range (e.g., 115 degrees or more and 125 degrees or less), a third rotation angle range (e.g., 175 degrees or more and 185 degrees or less), a fourth rotation angle range (e.g., 235 degrees or more and 245 degrees or less), a fifth rotation angle range (295 degrees or more and 305 degrees or less), or a sixth rotation angle range (e.g., 355 degrees or more and 365 degrees or less).

[0176] Furthermore, each of the plurality of first switching elements 1 and the plurality of second switching elements 2 is not limited to an IGBT, but may be a MOSFET. In this case, each of the plurality of first diodes 4 may be substituted with a parasitic diode of the MOSFET constituting the corresponding first switching element 1. Also, each of the plurality of second diodes 5 may be substituted with a parasitic diode of the MOSFET constituting the corresponding second switching element 2. The MOSFET is, for example, a Si-based MOSFET or a SiC-based MOSFET. Each of the plurality of first switching elements 1 and the plurality of second switching elements 2 may be, for example, a bipolar transistor or a GaN-based GIT.

[0177] In addition, in the power conversion devices 100, 100A, 100B, 100C, 100D, 100E, and 100F, if the capacitance of each of the multiple resonant capacitors 9 is relatively small, instead of attaching the multiple resonant capacitors 9 externally, the parasitic capacitance between both ends of the multiple second switching elements 2 may also serve as the multiple resonant capacitors 9.

[0178] Furthermore, the length of the dead time period Td is not limited to being set to be the same as the resonance half cycle, and may be set to a length different from the resonance half cycle.

[0179] 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.

[0180] 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.

[0181] (Aspects) The following aspects are disclosed in this specification.

[0182] A power conversion device (100; 100A; 100B; 100C; 100D; 100E; 100F) according to a first aspect includes a first DC terminal (31), a second DC terminal (32), a power conversion circuit (11), a plurality of AC terminals (41), a plurality of switches (8), a plurality of resonant capacitors (9), at least one resonant inductor (L1), a regenerative capacitor (15), a control device (50), a voltage divider circuit (20), and a plurality of common mode filters (21). The power conversion circuit (11) has a plurality of first switching elements (1) and a plurality of second switching elements (2). In the power conversion circuit (11), a plurality of switching circuits (10), each including a plurality of first switching elements (1) and a plurality of second switching elements (2) connected in series in a one-to-one relationship, are connected in parallel to each other. In the power conversion circuit (11), a plurality of first switching elements (1) are connected to a first DC terminal (31), and a plurality of second switching elements (2) are connected to 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 the first switching element (1) and the second switching element (2) in a corresponding one of the plurality of switching circuits (10). The plurality of switches (8) correspond one-to-one to the plurality of switching circuits (10). Each of the plurality of switches (8) has a first terminal (81) and a second terminal (82) connected to a connection point (3) between the first switching element (1) and the second switching element (2) in a corresponding one of the plurality of switching circuits (10). The plurality of resonance capacitors (9) correspond one-to-one to the plurality of switches (8). Each of the plurality of resonant capacitors (9) is connected between a first end (81) of a corresponding switch (8) among the plurality of switches (8) and the second DC terminal (32). At least one resonant inductor (L1) has a third end and a fourth end. In at least one resonant inductor (L1), the third end is connected to a second end (82) of the corresponding switch (8) among the plurality of switches (8). The regenerative capacitor (15) has a fifth end (153) and a sixth end (154).The regenerative capacitor (15) has a fifth terminal (153) connected to the second DC terminal (32) and a sixth terminal (154) connected to the fourth terminal of at least one resonant inductor (L1). A control device (50) controls the plurality of first switching elements (1), the plurality of second switching elements (2), and the plurality of switches (8). The voltage divider circuit (20) has a first capacitor (C1) and a second capacitor (C2) connected in series with each other. In the voltage divider circuit (20), the first capacitor (C1) is connected to the first DC terminal (31), and the second capacitor (C2) is connected to the second DC terminal (32). The voltage divider circuit (20) has an intermediate potential point (N1) between the first capacitor (C1) and the second capacitor (C2). The plurality of common mode filters (21) correspond one-to-one to the plurality of switching circuits (10). Each of the plurality of common mode filters (21) includes a third capacitor (C3) connected between the connection point (3) in the corresponding switching circuit (10) and the intermediate potential point (N1).

[0183] According to this aspect, it is possible to reduce noise while suppressing switching loss.

[0184] In a power conversion device (100; 100A; 100B; 100C; 100D; 100E) according to the second aspect, in the first aspect, a control device (50) provides a control signal whose potential changes between a high level and a low level to each of a plurality of first switching elements (1), a plurality of second switching elements (2), and a plurality of switches (8). The control device (50) also 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) for each of the plurality of switching circuits (10). The control device (50) also overlaps the control signal to each of the plurality of switches (8) with the dead time period (Td) for the switching circuit (10) corresponding to each of the plurality of switches (8) among the plurality of switching circuits (10). In the power conversion device (100; 100A; 100B; 100C; 100D; 100E), when the length of the dead time period (Td) is Td1 and the inductance of at least one resonance inductor (L1) is Lr, the combined capacitance of the resonance capacitor (9), the third capacitor (C3), and the second capacitor (C2) is 4·(Td1 / π) ２ - Smaller than (1 / Lr).

[0185] In the power conversion device (100; 100A; 100B; 100C; 100D; 100E) according to the third aspect, in the second aspect, the combined capacitance is (Td1 / π) ２ - Smaller than (1 / Lr).

[0186] According to this aspect, it becomes easier to perform zero voltage soft switching for each of the plurality of first switching elements (1) and the plurality of second switching elements (2) while suppressing an increase in switching loss.

[0187] In a power conversion device (100F) according to a fourth aspect, in the first aspect, a control device (50) provides a plurality of first switching elements (1), a plurality of second switching elements (2), and a plurality of switches (8) with a control signal whose potential changes between a high level and a low level. The control device (50) also 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) for each of the plurality of switching circuits (10). The control device (50) also overlaps the control signal to each of the plurality of switches (8) with the dead time period (Td) for the switching circuit (10) corresponding to each of the plurality of switches (8) among the plurality of switching circuits (10). In the power conversion device (100F), when the length of the dead time period (Td) is Td1, the inductance of at least one resonance inductor (L1) is Lr, and the inductance component of each of the plurality of common mode filters is L0, the combined capacitance of the resonance capacitor (9), the third capacitor (C3), and the second capacitor (C2) is (Td1 / π) ２ - Smaller than {1 / (Lr+L0)}.

[0188] According to this aspect, it becomes easier to perform zero voltage soft switching for each of the plurality of first switching elements (1) and the plurality of second switching elements (2) while suppressing an increase in switching loss.

[0189] In the power conversion device (100F) according to the fifth aspect, in the fourth aspect, the combined capacitance is (1 / 2)(Td1 / π) ２ - Smaller than {1 / (Lr+L0)}.

[0190] According to this aspect, it is possible to more reliably perform zero-voltage soft switching for each of the plurality of first switching elements (1) and the plurality of second switching elements (2) while suppressing an increase in switching loss.

[0191] The power conversion device (100; 100A; 100B; 100C; 100D; 100E; 100F) according to the sixth aspect is any one of the second to fifth aspects, in which the combined capacitance of the third capacitor (C3) and the second capacitor (C2) is smaller than the capacitance of the resonant capacitor (9).

[0192] According to this aspect, it is possible to further reduce leakage current.

[0193] In a power conversion device (100; 100A; 100B; 100C; 100D; 100E; 100F) according to a seventh aspect, in any one of the first to sixth aspects, the control device (50) performs a first control operation and a second control operation. In the first control operation, 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) so that a resonant capacitor (9) connected to one switch (8) of a plurality of switches (8) among a plurality of resonant capacitors (9) and a third capacitor (C3) of a common mode filter (21) connected to the one switch (8) among a plurality of common mode filters (21) are charged from a regenerative capacitor (15) via the one switch (8). In the second control operation, the plurality of first switching elements (1), the plurality of second switching elements (2) and the plurality of switches (8) are controlled so as to discharge a resonant capacitor (9) connected to one of the plurality of switches (8) among the plurality of resonant capacitors (9) and a third capacitor (C3) of a common mode filter (21) connected to the one of the plurality of common mode filters (21) via the one switch (8).

[0194] According to this aspect, it becomes easier to perform zero voltage soft switching for each of the plurality of first switching elements (1) and the plurality of second switching elements (2) while suppressing an increase in switching loss.

[0195] A power conversion device (100C) according to an eighth aspect is the power conversion device (100C) of any one of the first to seventh aspects, further including a second voltage-dividing circuit (22) in addition to the first voltage-dividing circuit, which is a voltage-dividing circuit. The second voltage-dividing circuit (22) is connected between a first DC terminal (31) and a second DC terminal (32). The second voltage-dividing circuit (22) has a fourth capacitor (C4) and a fifth capacitor (C5) connected in series with each other. In the second voltage-dividing circuit (22), the fourth capacitor (C4) is connected to the first DC terminal (31), and the fifth capacitor (C5) is connected to the second DC terminal (32). The second voltage-dividing circuit (22) has a neutral point (N2) between the fourth capacitor (C4) and the fifth capacitor (C5). The intermediate potential point (N1) is electrically isolated from the neutral point (N2).

[0196] According to this aspect, it is possible to prevent leakage current from flowing through the third capacitor (C3) of each of the plurality of common mode filters (21).

[0197] In the power conversion device (100D; 100E) according to the ninth aspect, in any one of the first to eighth aspects, at least one resonant inductor (L1) is a single resonant inductor (L1), and the second ends (82) of the multiple switches (8) are commonly connected to the single resonant inductor (L1).

[0198] According to this aspect, the number of resonance inductors (L1) can be reduced to one, making it possible to achieve miniaturization.

[0199] 1 First switching element 2 Second switching element 3 Connection point 8 Switch 81 First terminal 82 Second terminal 9 Resonant capacitor 10 Switching circuit 11 Power conversion circuit 15 Regenerative capacitor 153 Fifth terminal 154 Sixth terminal 20 Voltage divider circuit (first voltage divider circuit) 21 Common mode filter 22 Second voltage divider circuit 31 First DC terminal 32 Second DC terminal 41 AC terminal 50 Control device 100, 100A, 100B, 100C, 100D, 100E, 100F Power conversion device C1 First capacitor C2 Second capacitor C3 Third capacitor C4 Fourth capacitor C5 Fifth capacitor iU, iV, iW Output current (load current) L1 Resonant inductor L3 Inductor N1 Midpoint potential point N2 Neutral point 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 across both ends Vth Threshold

Claims

1. a first DC terminal and a second DC terminal; a plurality of first switching elements and a plurality of second switching elements, wherein a plurality of switching circuits in which the plurality of first switching elements and the plurality of second switching elements are connected in series one-to-one are connected in parallel to each other, the plurality of first switching elements are connected to the first DC terminal, and the plurality of second switching elements are connected to the second DC terminal; a power conversion circuit; a plurality of AC terminals corresponding one-to-one to the plurality of switching circuits, each connected to a connection point of the first switching element and the second switching element in the corresponding switching circuit; a plurality of switches corresponding one-to-one to the plurality of switching circuits, each having the first end of the first end and the second end connected to the connection point of the first switching element and the second switching element in the corresponding switching circuit; a plurality of resonance capacitors corresponding one-to-one to the plurality of switches, each connected between the first end of the corresponding switch and the second DC terminal; at least one resonance inductor having a third end and a fourth end, the third end being connected to the second end of the corresponding switch among the plurality of switches; a regeneration capacitor having a fifth end and a sixth end, the fifth end being connected to the second DC terminal, and the sixth end being connected to the fourth end of the at least one resonance inductor; a control device for controlling the plurality of first switching elements, the plurality of second switching elements, and the plurality of switches; a voltage dividing circuit having a first capacitor and a second capacitor connected in series to each other, the first capacitor being connected to the first DC terminal, the second capacitor being connected to the second DC terminal, and having an intermediate potential point between the first capacitor and the second capacitor; a plurality of common mode filters including a third capacitor corresponding one-to-one to the plurality of switching circuits, each connected between the connection point and the intermediate potential point in the corresponding switching circuit; and a power conversion device.

2. The control device: applies a control signal whose potential changes between a high level and a low level to each of the plurality of first switching elements, the plurality of second switching elements, and the plurality of switches. For each of the plurality of switching circuits, a dead time period is set between the high level period of the control signal to the first switching element and the high level period of the control signal to the second switching element. The control signals to each of the plurality of switches are overlapped with the dead time period for the switching circuit corresponding to each of the plurality of switches among the plurality of switching circuits. In the power conversion device, When the length of the dead time period is Td1 and the inductance of the at least one resonance inductor is Lr, the combined capacitance of the resonance capacitor, the third capacitor, and the second capacitor is less than 4·(Td1 / π)·(1 / Lr). ２ ·(1 / Lr), The power conversion device according to claim 1.

3. The synthetic capacitance is less than (Td1 / π) ２ ・ (1 / Lr), The power conversion device according to claim 2.

4. The control device gives a control signal whose potential changes between high level and low level to each of the plurality of first switching elements, the plurality of second switching elements, and the plurality of switches. For each of the plurality of switching circuits, a dead time period is set between the high level period of the control signal to the first switching element and the high level period of the control signal to the second switching element. The control signals to each of the plurality of switches are overlapped with the dead time period for the switching circuit corresponding to each of the plurality of switches among the plurality of switching circuits. In the power conversion device, When the length of the dead time period is Td1, the inductance of the at least one inductor for resonance is Lr, and the inductance of the inductor of each of the plurality of common mode filters is L0, the combined capacitance of the resonance capacitor, the third capacitor, and the second capacitor is less than (Td1 / π) ２ · {1 / (Lr + L0)}, The power conversion device according to claim 1.

5. The synthesized capacitance is smaller than (1 / 2)(Td1 / π) ２ ·{1 / (Lr + L0)}, The power conversion device according to claim 4.

6. The combined capacitance of the third capacitor and the second capacitor is smaller than the capacitance of the resonance capacitor. The power conversion device according to any one of claims 2 to 5.

7. The control device a first control operation for controlling the plurality of first switching elements, the plurality of second switching elements, and the plurality of switches so that the resonance capacitor connected to one of the plurality of switches among the plurality of resonance capacitors and the third capacitor of the common mode filter connected to the one switch among the plurality of common mode filters are charged from the regeneration capacitor through the one switch. A second control operation for controlling the plurality of first switching elements, the plurality of second switching elements, and the plurality of switches so as to discharge, via the one switch, a resonance capacitor connected to one of the plurality of switches among the plurality of resonance capacitors and the third capacitor of the common mode filter connected to the one switch among the plurality of common mode filters. The power conversion device according to any one of claims 1 to 5.

8. Further comprising a second voltage dividing circuit connected between the first DC terminal and the second DC terminal separately from the first voltage dividing circuit which is the voltage dividing circuit. The second voltage dividing circuit Has a fourth capacitor and a fifth capacitor connected in series with each other, the fourth capacitor is connected to the first DC terminal, and the fifth capacitor is connected to the second DC terminal. The second voltage dividing circuit has a neutral point between the fourth capacitor and the fifth capacitor. The intermediate potential point is electrically separated from the neutral point. The power conversion device according to any one of claims 1 to 5.

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

10. The at least one resonance inductor is one resonance inductor. The second ends of the plurality of switches are commonly connected to the one resonance inductor. The power conversion device according to claim 6.

11. The at least one resonance inductor is one resonance inductor. The second ends of the plurality of switches are commonly connected to the one resonance inductor. The power conversion device according to claim 7.

12. The at least one resonance inductor is one resonance inductor. The second ends of the plurality of switches are commonly connected to the one resonance inductor. The power conversion device according to claim 8.