Power converter

Abstract

The present invention addresses the problem of reducing size. In a power converter (100), a controller (50) performs a charging control operation for charging a regenerative capacitor (15) as a startup operation, and an inverter control operation. In the charging control operation, a first control operation and a second control operation are performed alternately. In the first control operation, at least one first switching element (1) among a plurality of first switching elements (1) is turned on, and in a path passing through a first DC terminal (31) and the at least one first switching element (1), at least one resonant capacitor (9) corresponding to the at least one first switching element (1), among a plurality of resonant capacitors (9), is charged. In the second control operation, a switch (8) corresponding to at least one first switching element (1), among the plurality of switches (8), is turned on to charge a regenerative capacitor (15) from the at least one resonant capacitor (9).

Description

Power Conversion Device

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

[0002] Patent Document 1 discloses a resonant inverter device (power conversion device).

[0003] In the resonant inverter device disclosed in Patent Document 1, a DC voltage from a DC voltage source is converted to an AC voltage by an inverter unit (power conversion circuit). This inverter unit has six main switching elements bridge-connected in three phases (U phase, V phase, and W phase) between a positive bus and a negative bus.

[0004] In addition, the resonant inverter device has two voltage-dividing capacitors connected in series between the positive bus and the negative bus. These two voltage-dividing capacitors form a voltage-dividing means that divides the DC voltage of the DC voltage source, and a means for generating half the DC voltage of the DC voltage source at the junction between them. Furthermore, a resonant circuit is provided between the two voltage-dividing capacitors and the inverter for resonating when the main switching elements are switched. This resonant circuit is configured such that a series circuit consisting of a resonant reactor and an auxiliary switch is connected between the junction of the two voltage-dividing capacitors and the junction of the upper and lower arms of each phase, and a resonant capacitor is connected in parallel to each series circuit.

[0005] Each switching element and each auxiliary switch is controlled to be turned on and off by a control unit.

[0006] There are cases where power conversion devices are required to be miniaturized.

[0007] Japanese Patent Application Laid-Open No. 2000-32775

[0008] An object of the present disclosure is to provide a power conversion device that can be made smaller.

[0009] A power conversion device according to one aspect of the present disclosure includes a first DC terminal and a second DC terminal, a power conversion circuit, multiple AC terminals, multiple switches, multiple resonant capacitors, at least one resonant inductor, a regenerative capacitor, and a control device. The power conversion circuit includes multiple first switching elements and multiple second switching elements. In the power conversion circuit, multiple switching circuits are connected in parallel, each of which has the multiple first switching elements and the multiple second switching elements connected in series in a one-to-one relationship. In the power conversion circuit, the multiple first switching elements are connected to the first DC terminals, and the multiple second switching elements are connected to the second DC terminals. The multiple AC terminals correspond one-to-one to the multiple switching circuits. Each of the multiple AC terminals is connected to a connection point between the first switching element and the second switching element in 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 on / off of each of the plurality of first switching elements, the plurality of second switching elements, and the plurality of switches.The control device performs, as a startup operation, a charge control operation for charging the regenerative capacitor and an inverter control operation for causing an output current to flow to each of the plurality of AC terminals. The charge control operation alternates between a first control operation and a second control operation. The first control operation turns on at least one first switching element among the plurality of first switching elements to charge at least one resonant capacitor among the plurality of resonant capacitors corresponding to the at least one first switching element via a path passing through the first DC terminal and the at least one first switching element. The second control operation turns on a switch among the plurality of switches corresponding to the at least one first switching element to charge the regenerative capacitor from the at least one resonant capacitor.

[0010] FIG. 1 is a circuit diagram of a system including a power conversion device according to a first embodiment. FIG. 2 is an explanatory diagram illustrating an operation of the control device of the power conversion device when the control device performs a basic operation in the case where the load current is greater than 0 and the resonant capacitor is charging. FIG. 3 is another explanatory diagram illustrating an operation of the control device of the power conversion device when the control device performs a basic operation in the case where the load current is greater than 0 and the resonant capacitor is charging. FIG. 4 is a diagram illustrating a time change in duty corresponding to a voltage command for each of three phases in an AC load connected to multiple AC terminals of the power conversion device, and a time change in load current. FIG. 5 is an explanatory diagram illustrating a first current threshold and a second current threshold used by the control device of the power conversion device. FIG. 6 is an explanatory diagram illustrating an operation of the control device of the power conversion device when the control device performs a basic operation in the case where the load current is greater than 0 and the resonant capacitor is discharging. FIG. 7 is an explanatory diagram illustrating an operation of the control device of the power conversion device when the load current is less than 0 and the resonant capacitor is discharging. FIG. 8 is an explanatory diagram illustrating an operation of the control device of the power conversion device when the control device performs a basic operation in the case where the load current is less than 0 and the resonant capacitor is charging. FIG. 9 is an explanatory diagram of a voltage across a regenerative capacitor in the power conversion device of the same. FIG. 10 is a timing chart for explaining a charge control operation of a control device in the same power conversion device. FIG. 11 is an explanatory diagram of an operation when a control device in the same power conversion device performs a first control operation of a charge control operation. FIG. 12 is an explanatory diagram of an operation when a control device in the same power conversion device performs a second control operation of a charge control operation. FIG. 13 is a circuit diagram of a system including a power conversion device according to a first modification of the first embodiment. FIG. 14 is a circuit diagram of a system including a power conversion device according to a second modification of the first embodiment. FIG. 15 is a circuit diagram of a system including a power conversion device according to a third modification of the first embodiment. FIG. 16 is a circuit diagram of a system including a power conversion device according to a fourth modification of the first embodiment. FIG. 17 is a circuit diagram of a system including a power conversion device according to a fifth modification of the first embodiment. FIG. 18 is a circuit diagram of a system including a power conversion device according to a sixth modification of the first embodiment. FIG. 19 is a circuit diagram of a system including a power conversion device according to the second embodiment.

[0011] First Embodiment A power conversion device 100 according to a first embodiment will be described below with reference to FIGS.

[0012] (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.

[0013] The power conversion device 100 includes a power conversion circuit 11, a plurality of (e.g., three) switches 8, a plurality of (e.g., three) resonant capacitors 9, a regenerative capacitor 15, a resonant inductor L1, and a control device 50. The power conversion device 100 also includes a protection circuit 17 and a capacitor C10. Each of the plurality of switches 8 is, for example, a bidirectional switch.

[0014] 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 switches 8 has a first end 81 connected to a connection point 3 between the first switching element 1 and the second switching element 2 in a corresponding one of the switching circuits 10. The resonant capacitors 9 correspond one-to-one to the switches 8. Each of the resonant capacitors 9 is connected between the first end 81 and the second DC terminal 32 of a corresponding one of the switches 8. The resonant inductor L1 has a third end and a fourth end. The third end of the resonant inductor L1 is connected to the second end 82 of a corresponding one of the switches 8 (three switches 8 in the example of FIG. 1 ). 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 resonant inductor L1. The control device 50 controls the first switching elements 1, the second switching elements 2, and the switches 8.

[0015] (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.

[0016] In the power conversion device 100, a high-potential output terminal (positive electrode) of the DC power supply E1 is connected to the first DC terminal 31, and a low-potential output terminal (negative electrode) of the DC power supply E1 is connected to the second DC terminal 32. In addition, in the power conversion device 100, for example, a U-phase terminal, a V-phase terminal, and a W-phase terminal of an AC load RA1 are connected to three AC terminals 41U, 41V, and 41W, respectively.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] The multiple resonant capacitors 9 correspond one-to-one to the multiple switches 8. Each of the multiple resonant capacitors 9 is connected between the first end 81 and the second DC terminal 32 of the corresponding switch 8. The power conversion device 100 has multiple resonant circuits. The multiple resonant circuits include a resonant circuit having a resonant capacitor 9U and a resonant inductor L1, a resonant circuit having a resonant capacitor 9V and a resonant inductor L1, and a resonant circuit having a resonant capacitor 9W and a resonant inductor L1. The multiple resonant circuits share the resonant inductor L1 in common.

[0021] 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.

[0022] 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.

[0023] The resonant inductor L1 has a third end and a fourth end. 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. The fourth end of the resonant inductor L1 is connected to a sixth end 154 of the regenerative capacitor 15.

[0024] The regenerative capacitor 15 is connected between the fourth end of the resonance inductor L1 and the second DC terminal 32. The regenerative capacitor 15 is, for example, a film capacitor.

[0025] The protection circuit 17 includes a third diode 13 and a fourth diode 14. The third diode 13 is connected between the common connection point 25 and the first DC terminal 31. In the third diode 13, the anode of the third diode 13 is connected to the common connection point 25. In addition, in the third diode 13, the cathode of the third diode 13 is connected to the first DC terminal 31. The fourth diode 14 is connected between the common connection point 25 and the second DC terminal 32. In the fourth diode 14, the anode of the fourth diode 14 is connected to the second DC terminal 32. In the fourth diode 14, the cathode of the fourth diode 14 is connected to the common connection point 25. Therefore, the fourth diode 14 is connected in series with the third diode 13.

[0026] The capacitor C10 is connected between the first DC terminal 31 and the second DC terminal 32, and is connected in parallel to the power conversion circuit 11. The capacitor C10 is, for example, an electrolytic capacitor.

[0027] 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.

[0028] 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.

[0029] The control device 50 uses a sawtooth carrier signal (see FIG. 2 ) 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 are different from each other by 120°, 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. 2 . 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.

[0030] 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. 4, 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. 2) 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.

[0031] 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. 4, the duty of the control signal SV1 is shown as the V-phase duty. The control device 50 (see FIG. 1) compares the V-phase voltage command with a carrier signal to generate the control signal SV1 provided to the first switching element 1V. The control device 50 also inverts the control signal SV1 provided to the first switching element 1V to generate the control signal SV2 provided to the second switching element 2V. The control device 50 also sets a dead time period Td (see FIG. 2) 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.

[0032] 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. 4, 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. 3) 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.

[0033] 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. 4, for example. 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°.

[0034] 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.

[0035] The plurality of switches 8, the resonant inductor 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.

[0036] 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 .

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] (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.

[0042] The control device 50 performs a charging control operation to charge the regenerative capacitor 15 as a startup operation of the power conversion device 100, and an inverter control operation to flow output currents iU, iV, and iW to each of the multiple AC terminals 41 as a steady-state operation of the power conversion device 100.

[0043] In the following, the operation of the power conversion device 100 when the control device 50 performs an inverter control operation will be described first, and then the operation of the power conversion device 100 when the control device 50 performs a charge control operation will be described.

[0044] (3.1) Operation of the Power Conversion Device When the Control Device Performs Inverter Control Operation In the power conversion device 100, for example, the first IGBT 6U of the switch 8U may change from an ON state in which the first IGBT 6U of the switch 8U is ON and current iL1 is flowing through the resonant inductor L1 with positive polarity to an OFF state in which the first IGBT 6U of the switch 8U is OFF. In this case, the current iL1 flowing through the resonant inductor L1 is regenerated to the power conversion circuit 11 via the third diode 13 until the energy of the resonant inductor L1 is consumed and the current iL1 becomes zero. Also, in the power conversion device 100, for example, the second IGBT 7U of the switch 8U may change from an ON state in which the second IGBT 7U of the switch 8U is ON and current iL1 is flowing through the resonant inductor L1 with negative polarity to an OFF state in which the second IGBT 7U of the switch 8U is OFF. In this case, the current iL1 flowing through the resonant inductor L1 flows through the path of the fourth diode 14, the resonant inductor L1, and the regenerative capacitor 15 until the energy of the resonant inductor L1 is consumed and the current iL1 becomes zero.

[0045] Furthermore, in the power conversion device 100, for example, a state in which the first IGBT 6V of the switch 8V is in the on state and current iL1 is flowing through the resonant inductor L1 with positive polarity may change to an off state, where the first IGBT 6V of the switch 8V is in the on state. In this case, the current iL1 flowing through the resonant inductor L1 is regenerated to the power conversion circuit 11 via the third diode 13 until the energy of the resonant inductor L1 is consumed and the current iL1 becomes zero. Also, in the power conversion device 100, for example, a state in which the second IGBT 7V of the switch 8V is in the on state and current iL1 is flowing through the resonant inductor L1 with negative polarity may change to an off state, where the current iL1 flowing through the resonant inductor L1 flows through the path of the fourth diode 14, resonant inductor L1, and regenerative capacitor 15 until the energy of the resonant inductor L1 is consumed and the current iL1 becomes zero.

[0046] Furthermore, in the power conversion device 100, for example, the first IGBT 6W of the switch 8W may be switched from an ON state in which the current iL1 is flowing through the resonant inductor L1 with positive polarity to an OFF state in which the first IGBT 6W of the switch 8W is switched. In this case, the current iL1 flowing through the resonant inductor L1 is regenerated to the power conversion circuit 11 via the third diode 13 until the energy of the resonant inductor L1 is consumed and the current iL1 becomes zero. Furthermore, in the power conversion device 100, for example, the second IGBT 7W of the switch 8W may be switched from an ON state in which the current iL1 is flowing through the resonant inductor L1 with negative polarity to an OFF state in which the second IGBT 7W of the switch 8W is switched. In this case, the current iL1 flowing through the resonant inductor L1 flows through the path of the fourth diode 14, the resonant inductor L1, and the regenerative capacitor 15 until the energy of the resonant inductor L1 is consumed and the current iL1 becomes zero.

[0047] 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.

[0048] 1 to 8, the basic operation of the zero voltage soft switching of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 is described below. The basic operation is an operation performed when a resonant current passing through two or more of the plurality of switches 8 does not flow simultaneously through the resonant inductor L1. After describing the basic operation, the operation performed when the control device 50 determines that a resonant current passing through two or more of the plurality of switches 8 will flow simultaneously will be described.

[0049] (3.1.1) 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, which is the target of zero voltage soft switching, must be set to zero immediately before the second switching element 2 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.

[0050] 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 current is 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.

[0051] (3.1.1.1) 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.

[0052] 2 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. 2 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. 2 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. 2 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.

[0053] 2 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. 2 is an additional time Tau set in the control device 50 for the control signal SU6 of the first IGBT 6U of the switch 8U, and an additional time Tav set in the control device 50 for the control signal SV6 of the first IGBT 6V of the switch 8V. The additional time Tau and the additional time Tav will be described later.

[0054] FIG. 3 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. 3 also illustrates a control signal SW6 provided from the control device 50 to the first IGBT 6W of the switch 8W and a load current iW flowing through the W-phase of the AC load RA1. FIG. 3 also illustrates a current iL1 flowing through the resonant inductor L1. FIG. 3 also illustrates a voltage V1w across the first switching element 1W and a voltage V2w across the second switching element 2W. In FIG. 3, the voltage value of the DC power supply E1 is indicated as Vd.

[0055] 3 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. 3 shows an additional time Taw set in the control device 50 for the control signal SW6 of the first IGBT 6W of the switch 8W. The additional time Taw will be described later.

[0056] As shown in FIG. 2 , the additional time Tau is set to advance the start point (time t1) of the high-level period of the control signal SU6 relative to the start point (time t2) of the dead time period Td, 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 point (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 point (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 point of the high-level period of the control signal SU6 may be the same as or later than the end point (time t3) of the dead time period Td. FIG. 2 shows an example in which the end point of the high-level period of the control signal SU6 is set to the same as the end point (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 of the dead time period Td (time t3), and the voltage V1u across the first switching element 1U becomes zero at the end of the dead time period Td (time t3). In the example of FIG. 2 , the current iL1 flowing through the resonant inductor L1 begins at the start of the high-level period of the control signal SU6 (time t1) and becomes zero at time t4, when the additional time Tau has elapsed since the end of the dead time period Td (time t3). Since iL1≧iU holds true from the start of the dead time period Td (time t2), the current iL1 in the shaded region of the current waveform in the fifth row from the top in FIG. 2 flows into the resonant capacitor 9U, generating LC resonance. After the end of the dead time period Td (time t3), the current iL1 is regenerated in the power conversion circuit 11 via the third diode 13 directly connected to the resonance inductor L1.

[0057] 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 of the dead time period Td (time t2) and the end of the resonant half cycle at the end 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 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 an estimated value of the load current iU at the carrier cycle to which the additional time Tau is added. The resonance half period in the case of basic operation is half the resonance period, which is the reciprocal of the resonance frequency of the resonance circuit including the resonance inductor L1 and one resonance capacitor 9. Therefore, if the inductance of the resonance inductor L1 is L and the capacitance of the resonance capacitor 9 is C, the resonance half period is π × (L C) １／２ In the control device 50, the resonance half cycle during basic operation is set to be equal to the length of the dead time period Td, for example.

[0058] As shown in FIG. 2 , the additional time Tav is set to advance the start point (time t5) of the high-level period of the control signal SV6 relative to the start point (time t6) of the dead time period Td, 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 point (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 point (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 point of the high-level period of the control signal SV6 may be the same as or later than the end point (time t7) of the dead time period Td. FIG. 2 shows an example in which the end point of the high-level period of the control signal SV6 is set to the same as the end point (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 of the dead time period Td (time t7). In the example of FIG. 2 , the current iL1 flowing through the resonant inductor L1 begins flowing at the start of the high-level period of the control signal SV6 (time t5) and becomes zero at time t8, when the additional time Tav has elapsed since the end of the dead time period Td (time t7). Since iL1≧iV holds true from the start of the dead time period Td (time t6), the current iL1 in the shaded region of the current waveform in the tenth row from the top in FIG. 2 flows into the resonant capacitor 9V, generating LC resonance. After the end of the dead time period Td (time t7), the current iL1 is regenerated in the power conversion circuit 11 via the third diode 13 directly connected to the resonant inductor L1.

[0059] As described above, in order to start LC resonance at the start of the dead time period Td (time t6), the control device 50 determines the additional time Tav based on the load current iV so that iL1 = iV at the start of the dead time period Td (time t6). 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 or 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 a value, for example, an estimate of the load current iV at the carrier cycle to which the additional time Tav is added.

[0060] As shown in FIG. 3 , the additional time Taw is set to advance the start point (time t9) of the high-level period of the control signal SW6 to earlier than the start point (time t10) of the dead time period Td, 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 point (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 point (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 point of the high-level period of the control signal SW6 may be the same as or later than the end point (time t11) of the dead time period Td. FIG. 3 illustrates an example in which the end point of the high-level period of the control signal SW6 is set to the same as the end point (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 of the dead time period Td (time t11). In the example of FIG. 3 , the current iL1 flowing through the resonant inductor L1 begins at the start of the high-level period of the control signal SW6 (time t9) and becomes zero at time t12, when the additional time Taw has elapsed since the end of the dead time period Td (time t11). Since iL1≧iW holds true from the start of the dead time period Td (time t10), the current iL1 in the shaded region of the current waveform in the fourth row from the top in FIG. 3 flows into the resonant capacitor 9W, generating LC resonance. After the end of the dead time period Td (time t11), the current iL1 is regenerated in the power conversion circuit 11 via the third diode 13 directly connected to the resonant inductor L1.

[0061] 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.

[0062] (3.1.1.2) 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. 5 ). 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 9U connected in parallel to the target second switching element 2 using the load current iU 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.

[0063] 6 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 is greater than the first current threshold I1. Also illustrated in FIG. 6 is the dead time period Td and the additional time Tau that the control device 50 sets for the control signal SU7 of the second IGBT 7U of the switch 8U.

[0064] 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 of the dead time period Td (time t22), and the current i9U decreases to zero before the end of the dead time period Td (time t23). As a result, in the power conversion device 100, the second switching element 2U is subjected to zero-voltage soft switching when the control signal SU2 changes from low to high at the end of the dead time period Td (time t23).

[0065] 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. 6 . 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 of the dead time period Td (time t22). The end point of the high-level period of the control signal SU7 is the same as the end point of the dead time period Td (time t23). As a result, in the power conversion device 100, the voltage V2u across the second switching element 2U becomes zero before the end point of the dead time period Td (time t23). Therefore, in the power conversion device 100, when the control signal SU2 changes from low to high at the end point of the dead time period Td (time t23), 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 (time 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.

[0066] (3.1.1.3) 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. In this way, the power conversion device 100 can achieve zero-voltage soft switching of the target second switching element 2.

[0067] Figure 7 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.

[0068] FIG. 7 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. 7 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 of the dead time period Td (time t33). In FIG. 7, an example is shown in which the end point of the high-level period of the control signal SU7 is set to the same as the end point of the dead time period Td (time t33). 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 of the dead time period Td (time t33). 7 , the current iL1 flowing through the resonant inductor L1 starts flowing at the start of the high-level period of the control signal SU7 (time t31) and becomes zero at time t34, when the additional time Tau has elapsed since the end of the dead time period Td (time t33). With regard to the current iL1, since the start of the dead time period Td (time t32), iL1≦iU is satisfied, causing LC resonance and causing a resonant current (discharge current of the resonant capacitor 9U) to flow from the resonant capacitor 9U toward the resonant inductor L1. After the end of the dead time period Td (time t33), 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.

[0069] The control device 50 determines the additional time Tau based on the load current iU so that iL1 = iU at the start of the dead time period Td (time t32) to start LC resonance and end the resonance half cycle at the end of the dead time period Td (time t33). 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. In this case, the detection result of the load current iU or its signal-processed value is the detection value at the carrier period to which the additional time Tau is added, or at the timing closest to that carrier period. The estimated value of the load current iU at this time is, for example, a value obtained by estimating the load current iU in the carrier period to which the additional time Tau is added. The resonance half period in the case of basic operation is half the resonance period, which is the reciprocal of the resonance frequency of the resonance circuit including the resonance inductor L1 and one resonance capacitor 9. Therefore, if the inductance of the resonance inductor L1 is L and the capacitance of the resonance capacitor 9 is C, then the resonance half period is π × (L C) １／２ In the control device 50, the resonance half cycle during basic operation is set to be equal to the length of the dead time period Td, for example.

[0070] (3.1.1.4) 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. 5 ). 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 9U 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.

[0071] 8 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 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. 8 is the dead time period Td.

[0072] When the load current value 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 of the dead time period Td (time t41). 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 of the dead time period Td (time t42), and the voltage V1u across the first switching element 1U becomes zero before the end of the dead time period Td (time t42). 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 of the dead time period Td (time t42).

[0073] When the current value of the load current 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. 8 . The start point of the high-level period of the control signal SU6 at this time is the same as the start point (time 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 (time 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 (time 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 (time t42) of the dead time period Td, the first switching element 1U is subjected to zero-voltage soft switching.

[0074] (3.1.2) Operation of Shift Control When the control device 50 determines that resonant currents passing through two switches 8 out of the multiple switches 8 flow simultaneously 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 flow simultaneously through the resonant inductor L1. "When it is determined that resonant currents passing through two switches 8 out of the multiple switches 8 will flow simultaneously" means that it has been estimated in advance that the resonant currents passing through the two switches 8 will flow simultaneously through the resonant inductor L1.

[0075] (3.1.2.1) Determination of whether two-phase resonant currents flow simultaneously In the power conversion device 100, the phases of the voltage commands for three phases (U phase, V phase, and W phase) differ from each other by 120°, but the command values ​​of the voltage commands for two phases approach each other by an electrical angle of 60°, and the duties of the control signals for the two phases approach each other (see areas A1 and A2 in FIG. 4 ). In area A1 in FIG. 4 , the duties of the control signals for the U phase and the V phase are near 0.75. In area A2 in FIG. 4 , the duties of the control signals for the U phase and the V phase are near 0.25. The polarity of the resonant current is the same as the polarity of the current iL1, and in area A1, the polarity of the resonant current is positive, and in area A2, the polarity of the resonant current is negative. In the case of region A1, for example, during one cycle of the carrier signal, the time difference between the start point (time t1, see FIG. 2) of the high-level period of the control signal SU6 supplied to the first IGBT 6U and the start point (time t5, see FIG. 2) 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 100, 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.

[0076] Assuming that the capacitance of each of the multiple resonant capacitors 9U, 9V, and 9W is C, if a U-phase current and a V-phase current flow simultaneously through the resonant inductor L1, then in terms of an equivalent circuit, a capacitor having a combined capacitance (=2×C) of the resonant capacitors 9U and 9V is connected in series to the resonant inductor L1. Therefore, in the power conversion device 100, 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.

[0077] (3.1.2.1.1) In the case of charging the resonant capacitor Figure 2 is a diagram showing an example of the boundary conditions between the case where the U-phase resonant current and the V-phase resonant current do not overlap (flow simultaneously) and the case where they overlap (flow simultaneously). The boundary conditions will be described with reference to Figure 2.

[0078] In the power conversion device 100, if the time difference ΔTuv between the start point (time t3) of the high-level period of the control signal SU1 and the start point (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 flow simultaneously through the resonant inductor L1. The above threshold setting is merely an example, and other values ​​may also be considered. For example, it is conceivable to set the threshold value to a value even greater than (Tau + Tav + Td) taking into account errors in the additional time Tau and errors in the additional time Tav. Furthermore, in the control device 50, the threshold value for the time difference ΔTuv may be set to, for example, the same value as the resonant half cycle (in this embodiment, the resonant half cycle = the dead time period Td). In this case, if the time difference ΔTuv is less than the length of the dead time period Td, the control device 50 estimates that resonant currents corresponding to the two phases of the switching circuit 10U and the switching circuit 10V flow simultaneously in the resonant inductor L1. Furthermore, the method for calculating the time difference ΔTuv used to determine whether the 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 the end point of the high-level period of the control signal SU2 (time t2) and the end point of the high-level period of the control signal SV2 (time t6).

[0079] Furthermore, in the power conversion device 100, if the time difference between the start point (time t3) of the high-level period of the control signal SU1 and the start point (time t11) of the high-level period of the control signal SW1 is equal to or greater than (Tau + Taw + Td), 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 the time difference to, for example, (Tau + Taw + Td), and if the time difference is less than the 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 merely an example, and other values ​​may also be considered. For example, it is possible to set the threshold value greater than (Tau + Taw + Td) by taking into account errors in the additional time Tau and the additional time Taw. Furthermore, in the control device 50, the threshold value for the time difference may be set to, for example, the same value as the resonant half cycle (in this embodiment, the resonant half cycle = the dead time period Td). In this case, if the time difference is less than the length of the dead time period Td, the control device 50 estimates that resonant currents corresponding to the two phases of the switching circuit 10U and the switching circuit 10W flow simultaneously in the resonant inductor L1. Furthermore, the method for calculating the time difference used to determine whether the two-phase resonant currents flow simultaneously is not limited to the above example; 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 the two-phase resonant currents flow simultaneously may be the time difference between the end point of the high-level period of the control signal SU2 (time t2) and the end point of the high-level period of the control signal SW2 (time t10).

[0080] Furthermore, in the power conversion device 100, if the time difference between the start point (time t7) of the high-level period of the control signal SV1 provided to the first switching element 1V of the switching circuit 10V and the start point (time t11) of the high-level period of the control signal SW1 provided to the first switching element 1W of the switching circuit 10W is (Tav + Taw + Td) or more, the V-phase resonant current and the W-phase resonant current do not overlap, and 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 the 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 will flow simultaneously 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 greater than (Tav + Taw + Td) in consideration of errors in the additional times Tav and Taw. Furthermore, in the control device 50, the threshold value for the time difference may be set to, for example, the same value as the resonant half cycle (in this embodiment, the resonant half cycle = the dead time period Td). In this case, if the time difference is less than the length of the dead time period Td, the control device 50 estimates that resonant currents corresponding to the two phases of the switching circuit 10V and the switching circuit 10W flow simultaneously in the resonant inductor L1. Furthermore, the method for calculating the time difference used to determine whether the 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 the two-phase resonant currents flow simultaneously may be the time difference between the end point of the high-level period of the control signal SV2 (time t6) and the end point of the high-level period of the control signal SW2 (time t10).

[0081] (3.1.2.1.2) 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.

[0082] 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).

[0083] 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).

[0084] 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).

[0085] (3.1.2.2) 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 do not flow simultaneously through the resonant inductor L1.

[0086] 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.

[0087] In the power conversion device 100, 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 100, when the control device 50 executes shift control, the switching of the first switching elements 1U and 1V becomes zero-voltage soft switching.

[0088] 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.

[0089] Furthermore, in the power conversion device 100, 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 100, when the control device 50 executes shift control, the switching of the second switching elements 2U and 2V becomes zero-voltage soft switching.

[0090] 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.

[0091] (3.2) Operation of the Power Conversion Device When the Control Device Performs a Charge Control Operation as a Startup Operation When the power conversion device 100 is started, the control device 50 performs a charge control operation to charge the regenerative capacitor 15 in order to shorten the time Ts required for the voltage V15 across the regenerative capacitor 15 to rise from 0 V to the threshold Vth, as shown in FIG. 9 . The threshold Vth is, for example, Vd / 2, but is not limited thereto. It may be a value between 90% and 110% of Vd / 2, and more preferably between 95% and 105% of Vd / 2. The power conversion device 100 according to the first embodiment can shorten the time Ts required for the voltage V15 across the regenerative capacitor 15 to rise from 0 V to the threshold Vth, compared to when the control device 50 performs an inverter control operation without performing a charge control operation. The power conversion device 100 according to the first embodiment can shorten the time Ts from 13.5 ms to 2.8 ms, for example. It should be noted that the DC bus voltage in FIG. 9 is the voltage between the first DC terminal 31 and the second DC terminal 32 .

[0092] In the charge control operation, the control device 50 alternately performs a first control operation and a second control operation.

[0093] In the first control operation, the control device 50 turns on the multiple (three) first switching elements 1 to charge the multiple (three) resonant capacitors 9 through paths passing through the first DC terminal 31 and each of the multiple (three) first switching elements 1. In the second control operation, the control device 50 turns on the multiple (three) switches 8 to charge the regenerative capacitor 15 from the multiple (three) resonant capacitors 9.

[0094] The first control operation and the second control operation will be described in more detail below with reference to Figures 10 to 12. Note that Figures 11 and 12 omit some of the circuit diagram from Figure 1 and simplify the diagram, and each of the three first switching elements 1, three second switching elements 2, and three switches 8 is represented by a switch symbol.

[0095] In the first control operation, the control device 50 controls the three first switching elements 1 to the ON state, the three second switching elements 2 to the OFF state, and the three switches 8 to the OFF state.

[0096] More specifically, in the first control operation, the control device 50 sets each of the three control signals SU1, SV1, and SW1 to a high level, each of the three control signals SU2, SV2, and SW2 to a low level, each of the three control signals SU6, SV6, and SW6 (not shown in FIG. 10) to a low level, and each of the three control signals SU7, SV7, and SW7 to a low level, as shown in FIG. 11 . As a result, as shown in FIG. 11 , the three resonant capacitors 9U, 9V, and 9W are charged by currents (the current paths are indicated by arrows in FIG. 11 ) flowing from the DC power supply E1 through the three first switching elements 1. The “resonant capacitor charging current” in FIG. 10 indicates the current waveforms of the currents (charging currents) flowing from the DC power supply E1 to each of the three resonant capacitors 9U, 9V, and 9W.

[0097] In addition, in the second control operation, the control device 50 controls the three first switching elements 1 to the OFF state, the three second switching elements 2 to the OFF state, and the three switches 8 to the ON state.

[0098] More specifically, in the second control operation, the control device 50 sets each of the three control signals SU1, SV1, and SW1 to a low level, sets each of the three control signals SU2, SV2, and SW2 to a low level, sets each of the three control signals SU6, SV6, and SW6 (not shown in FIG. 10) to a low level, and sets each of the three control signals SU7, SV7, and SW7 to a high level, as shown in FIG. 12. As a result, the regenerative capacitor 15 is charged by currents flowing from the three resonant capacitors 9U, 9V, and 9W through the three switches 8U, 8V, and 8W, respectively. In other words, by performing the second control operation, the control device 50 discharges the resonant capacitors 9U, 9V, and 9W and charges the regenerative capacitor 15. 10 shows the current waveform of the current (discharge current) flowing from each of the three resonance capacitors 9U, 9V, and 9W to the regeneration capacitor 15.

[0099] In the power conversion device 100 according to the first embodiment, the control device 50 also sets a dead time period Td between the high-level periods of the three control signals SU1, SV1, and SW1 and the high-level periods of the three control signals SU2, SV2, and SW2 during the charge control operation. In the first control operation, the control device 50 complementarily turns on and off the three first switching elements 1 and the three second switching elements 2. In the second control operation, the control device 50 turns on the multiple switches 8 during the second period T2, during which the dead time period Td during which both the three first switching elements 1 and the three second switching elements 2 are turned off is set as the second period T2.

[0100] 10 , the control device 50 provides a dead time period Td between the high-level period of the control signal SU1 to the first switching element 1U and the high-level period of the control signal SU2 to the second switching element 2U, and provides a high-level period of the control signal SU7 to the second IGBT 7U of the switch 8U during the dead time period Td. Similarly, the control device 50 provides a dead time period Td between the high-level period of the control signal SV1 to the first switching element 1V and the high-level period of the control signal SV2 to the second switching element 2V, and provides a high-level period of the control signal SV7 to the second IGBT 7V of the switch 8V during the dead time period Td. Similarly, the control device 50 provides a dead time period Td between the high-level period of the control signal SW1 to the first switching element 1W and the high-level period of the control signal SW2 to the second switching element 2W, and provides a high-level period of the control signal SW7 to the second IGBT 7W of the switch 8W during the dead time period Td.

[0101] (4) Summary In the power conversion device 100 according to the first embodiment, the control device 50 performs, as a startup operation, a charge control operation for charging the regenerative capacitor 15 and an inverter control operation for causing output currents iU, iV, and iW to flow through each of the multiple AC terminals 41. In the charge control operation, a first control operation and a second control operation are alternately performed. In the first control operation, the multiple (three) first switching elements 1 are turned on to charge the multiple (three) resonant capacitors 9 via paths passing through the first DC terminal 31 and each of the multiple (three) first switching elements 1. In the second control operation, the multiple (three) switches 8 are turned on to charge the regenerative capacitor 15 from the multiple (three) resonant capacitors 9.

[0102] The power conversion device 100 according to the first embodiment can be made smaller. More specifically, the power conversion device 100 according to the first embodiment can reduce the number of regenerative capacitors 15 to one, thereby making it possible to make the device smaller.

[0103] The power conversion device 100 according to the first embodiment employs a configuration using one regenerative capacitor 15 to generate a voltage of Vd / 2. Therefore, when the power conversion device 100 is started, the voltage V15 across the regenerative capacitor 15 transiently rises to Vd / 2. Therefore, if the control device 50 of the power conversion device 100 performs an inverter control operation without performing a charge control operation, the switching of each of the first switching elements 1 and the second switching elements 2 may become hard switching during the inverter control operation. In contrast, the power conversion device 100 according to the first embodiment uses the control device 50 to perform a charge control operation, thereby shortening the time required to raise the voltage V15 across the regenerative capacitor 15 to Vd / 2 and preventing hard switching of each of the first switching elements 1 and the second switching elements 2 during the inverter control operation.

[0104] Furthermore, in the power conversion device 100 according to the first embodiment, the control device 50 performs the inverter control operation after the voltage V15 across the regenerative capacitor 15 becomes equal to or greater than the threshold value Vth. This allows the power conversion device 100 to suppress hard switching of each of the first switching elements 1 and the second switching elements 2 while performing the inverter control operation. In other words, the power conversion device 100 can more reliably achieve soft switching. This allows the power conversion device 100 to use elements with lower withstand voltages and lower allowable currents for each of the first switching elements 1 and the second switching elements 2, thereby enabling cost reduction.

[0105] Furthermore, in the power conversion device 100 according to the first embodiment, when the control device 50 determines that resonant currents passing through two of the multiple switches 8 respectively flow through the 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 resonant inductor L1 simultaneously. This enables the power conversion device 100 to more reliably achieve soft switching.

[0106] (5) Modifications of First Embodiment (5.1) Modification 1 A power conversion device 100 according to Modification 1 will be described with reference to Fig. 13. Regarding the power conversion device 100 according to Modification 1, components that are the same as those of the power conversion device 100 according to the first embodiment (see Fig. 1) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0107] In the power conversion device 100 according to the first modification, the first IGBT 6 and the second IGBT 7 are connected in anti-series in each of the plurality of switches 8. In the power conversion device 100 according to the first modification, the collector terminal of the first IGBT 6 and the collector terminal of the second IGBT 7 are connected in each of the plurality of switches 8, the emitter terminal of the first IGBT 6 is connected to the connection point 3 of a corresponding one of the plurality of switching circuits 10, and the emitter terminal of the second IGBT 7 is connected to the 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.

[0108] In the power conversion device 100 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. 13 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 100 according to the first modification, the diode 61 and the diode 71 are not limited to being externally connected to the first IGBT 6 and the second IGBT 7, but may also be an element built into the chip.

[0109] The operation of the control device 50 is the same as that of the control device 50 of the first embodiment, for example.

[0110] (5.2) Modification 2 A power conversion device 100 according to Modification 2 will be described with reference to Fig. 14. With regard to the power conversion device 100 according to Modification 2, components that are the same as those of the power conversion device 100 according to the first embodiment (see Fig. 1) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0111] In the power conversion device 100 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 100 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 second IGBT 7 is connected to the connection point 3 of a corresponding one of the multiple switching circuits 10, and the collector terminal of the first IGBT 6 is connected to the common connection point 25. 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.

[0112] In the power conversion device 100 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. 14 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 100 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.

[0113] The operation of the control device 50 is the same as that of the control device 50 of the first embodiment, for example.

[0114] (5.3) Modification 3 A power conversion device 100 according to Modification 3 will be described with reference to Fig. 15. Regarding the power conversion device 100 according to Modification 3, components that are the same as those of the power conversion device 100 according to the first embodiment (see Fig. 1) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0115] In the power conversion device 100 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 100 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 the 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.

[0116] The operation of the control device 50 is similar to that of the control device 50 of the first embodiment, for example.

[0117] (5.4) Modification 4 A power conversion device 100 according to Modification 4 will be described with reference to Fig. 16. With regard to the power conversion device 100 according to Modification 4, components that are the same as those of the power conversion device 100 according to the first embodiment (see Fig. 1) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0118] In the power conversion device 100 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 100 according to the fourth modification, the series circuit of the first MOSFET 6A and the diode 63 and the series circuit of the second MOSFET 7A and the diode 73 are connected in anti-parallel.

[0119] The operation of the control device 50 is similar to that of the control device 50 of the first embodiment, for example.

[0120] (5.5) Modification 5 A power conversion device 100 according to Modification 5 will be described with reference to Fig. 17. With regard to the power conversion device 100 according to Modification 5, components that are the same as those of the power conversion device 100 according to the first embodiment (see Fig. 1) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0121] In the power conversion device 100 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.

[0122] 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.

[0123] 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 100, 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 100, 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.

[0124] In the power conversion device 100 according to the fifth modification, each of the plurality of MOSFETs 80 may be replaced with an IGBT. Furthermore, in the power conversion device 100 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.

[0125] The operation of the control device 50 is similar to that of the control device 50 of the first embodiment, for example.

[0126] (5.6) Modification 6 A power conversion device 100 according to Modification 6 will be described with reference to Fig. 18. With regard to the power conversion device 100 according to Modification 6, components that are the same as those of the power conversion device 100 according to the first embodiment (see Fig. 1) are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0127] In the power conversion device 100 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 100 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.

[0128] The operation of the control device 50 is similar to that of the control device 50 of the first embodiment, for example.

[0129] (Embodiment 2) A power conversion device 100A according to embodiment 2 will be described with reference to Fig. 19. Regarding the power conversion device 100A according to embodiment 2, components similar to those of the power conversion device 100 according to embodiment 1 (see Fig. 1) are denoted by the same reference numerals, and description thereof will be omitted.

[0130] The power conversion device 100A includes a plurality of (three in the illustrated example) resonant inductors L1, and the plurality of (three) resonant inductors L1 correspond one-to-one to the plurality of (three) switches 8. A third end of each of the plurality of resonant inductors L1 is connected to a second end 82 of a corresponding one of the plurality of switches 8. A fourth end of each of the plurality of resonant inductors L1 is connected to a sixth end 154 of the regenerative capacitor 15. The inductances of the plurality of resonant inductors L1 are the same as each other. That is, the inductances of the three resonant inductors L1 are the same as each other. The phrase "the inductances of the three resonant inductors L1 are the same as each other" 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 inductance of each of the two resonant inductors L1 is within a range of 95% to 105% of the inductance of the remaining resonant inductor L1.

[0131] In the power conversion device 100A according to the second embodiment, the control device 50 performs a charge control operation as an operation at the start-up of the power conversion device 100A, similar to the power conversion device 100 according to the first embodiment. Furthermore, the control device 50 performs an inverter control operation after the charge control operation.

[0132] The power conversion device 100A according to the second embodiment can reduce the number of regenerative capacitors 15 to one, similar to the power conversion device 100 according to the first embodiment, and therefore can be made smaller.

[0133] (Other Modifications) The above-described first and second embodiments are merely examples of various embodiments of the present disclosure. The above-described first and second embodiments can be modified in various ways depending on the design, etc., as long as the object of the present disclosure can be achieved.

[0134] For example, in the first control operation, the control device 50 turns on at least one first switching element 1 (e.g., first switching element 1U) among the plurality of first switching elements 1, and charges at least one resonant capacitor 9 (e.g., resonant capacitor 9U) among the plurality of resonant capacitors 9 that corresponds to the at least one first switching element 1, via a path passing through the first DC terminal 31 and the at least one first switching element 1.

[0135] In addition, in the second control operation, the control device 50 simply turns on a switch 8 (e.g., switch 8U) among the multiple switches 8 that corresponds to at least one of the first switching elements 1, thereby charging the regenerative capacitor 15 from the at least one resonant capacitor 9.

[0136] In addition, in the second control operation, the control device 50 only needs to turn on a switch 8 among the multiple switches 8 that corresponds to the at least one first switching element 1 during a dead time period Td in which both the at least one first switching element 1 and the at least one second switching element 2 (e.g., second switching element 2U) that corresponds one-to-one to the at least one first switching element 1 are turned off.

[0137] As an example, in the first control operation, the control device 50 may turn on the first switching element 1U to charge the resonant capacitor 9U via a path passing through the first DC terminal 31 and the first switching element 1U. In this case, in the second control operation, the control device 50 may turn on the switch 8U to charge the regenerative capacitor 15 from the resonant capacitor 9U. In this case, in the second control operation, the control device 50 may turn on the switch 8U during the dead time period Td in which both the first switching element 1U and the second switching element 2U are turned off.

[0138] Furthermore, in the control device 50, 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 is less than the threshold value described in embodiment 1.

[0139] 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.

[0140] 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).

[0141] 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.

[0142] Furthermore, in the power conversion devices 100 and 100A, 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.

[0143] The length of the dead time period Td is not limited to being set to be the same as the resonance half cycle, but may be set to a length different from the resonance half cycle. In either case, however, it is preferable that the end point of the dead time period Td coincides with the end point of the resonance half cycle.

[0144] 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.

[0145] Furthermore, the power conversion devices 100 and 100A are not limited to a configuration that outputs three-phase AC, but may be configured to output polyphase AC with three or more phases.

[0146] (Aspects) The following aspects are disclosed in this specification.

[0147] A power conversion device (100; 100A) according to a first aspect includes a first DC terminal (31) and a second DC terminal (32), a power conversion circuit (11), a plurality of AC terminals (41), a plurality of switches (8), a plurality of resonant capacitors (9), at least one resonant inductor (L1), a regenerative capacitor (15), and a control device (50). The power conversion circuit (11) has a plurality of first switching elements (1) and a plurality of second switching elements (2). In the power conversion circuit (11), a plurality of switching circuits (10) are connected in parallel to each other, each of which has a plurality of first switching elements (1) and a plurality of second switching elements (2) connected in series in a one-to-one relationship. In the power conversion circuit (11), the plurality of first switching elements (1) are connected to the first DC terminal (31), and the plurality of second switching elements (2) are connected to the second DC terminal (32). The plurality of AC terminals (41) correspond one-to-one to the plurality of switching circuits (10). Each of the plurality of AC terminals (41) is connected to a connection point (3) between a first switching element (1) and a second switching element (2) in 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) 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 resonant capacitors (9) correspond one-to-one to the plurality of switches (8). Each of the plurality of resonant capacitors (9) is connected between a first end (81) of a corresponding one of the plurality of switches (8) and a second DC terminal (32). At least one resonant inductor (L1) has a third end and a fourth end. The third end of the at least one resonant inductor (L1) is connected to the second end (82) of a corresponding one of 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 a fourth terminal of at least one resonant inductor (L1). The control device (50) controls the on / off of each of the first switching elements (1), the second switching elements (2), and the switches (8). The control device (50) performs a charge control operation as a startup operation to charge the regenerative capacitor (15) and an inverter control operation to cause output currents (iU, iV, iW) to flow through the AC terminals (41), respectively. In the charge control operation, a first control operation and a second control operation are alternately performed. In a first control operation, at least one first switching element (1) among the plurality of first switching elements (1) is turned on, and at least one resonant capacitor (9) among the plurality of resonant capacitors (9) corresponding to the at least one first switching element (1) is charged through a path passing through a first DC terminal (31) and the at least one first switching element (1). In a second control operation, a switch (8) among the plurality of switches (8) corresponding to the at least one first switching element (1) is turned on, and the regenerative capacitor (15) is charged from the at least one resonant capacitor (9).

[0148] According to this aspect, it is possible to achieve miniaturization.

[0149] A power conversion device (100; 100A) according to a second aspect is based on the first aspect. In the charge control operation, the control device (50) charges the regenerative capacitor (15) until a voltage (V15) across the regenerative capacitor (15) becomes equal to or greater than a threshold (Vth).

[0150] According to this aspect, the voltage (V15) across the regenerative capacitor (15) can be made equal to or higher than the threshold value (Vth) in a shorter time.

[0151] In the power conversion device (100; 100A) according to the third aspect, in the second aspect, the control device (50) performs the inverter control operation after the voltage (V15) across the regenerative capacitor (15) becomes equal to or greater than the threshold value (Vth).

[0152] According to this aspect, when the inverter control operation is being performed, it is possible to prevent the plurality of first switching elements (1) and the plurality of second switching elements (2) from being hard-switched.

[0153] A power conversion device (100; 100A) according to a fourth aspect is based on any one of the first to third aspects. In a first control operation, a control device (50) complementarily turns on and off at least one first switching element (1) and at least one second switching element (2) among a plurality of second switching elements (2) corresponding to the at least one first switching element (1). In a second control operation, a switch (8) among a plurality of switches (8) corresponding to the at least one first switching element (1) is turned on during a dead time period (Td) in which both the at least one first switching element (1) and the at least one second switching element (2) are turned off.

[0154] A power conversion device (100; 100A) according to a fifth aspect is based on any one of the first to fourth aspects. In a first control operation, a control device (50) turns on a plurality of first switching elements (1).

[0155] According to this aspect, it is possible to increase the voltage (V15) across the regenerative capacitor (15) in a shorter time.

[0156] In the power conversion device (100) according to the sixth aspect, in any one of the first to fifth 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).

[0157] According to this aspect, the number of resonance inductors (L1) can be reduced to one, which allows further miniaturization.

[0158] 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 31 First DC terminal 32 Second DC terminal 41 AC terminal 50 Control device 100, 100A Power conversion device iU, iV, iW Output current (load current) L1 Resonant inductor RA1 AC load SU1, SU2, SU6, SU7 Control signal SV1, SV2, SV6, SV7 Control signal SW1, SW2, SW6, SW7 Control signal Td Dead time period V15 Voltage across both ends Vth Threshold value

Claims

Claim 1 a first DC terminal and a second DC terminal; a power conversion circuit having a plurality of first switching elements and a plurality of second switching elements, wherein a plurality of switching circuits in which the plurality of first switching elements and the plurality of second switching elements are connected in series one-to-one are connected in parallel to each other, the plurality of first switching elements are connected to the first DC terminal, and the plurality of second switching elements are connected to the second DC terminal; a plurality of AC terminals corresponding one-to-one to the plurality of switching circuits, each connected to 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 on / off of the plurality of first switching elements, the plurality of second switching elements, and the plurality of switches; the control device: performs a charging control operation of charging the regeneration capacitor as an operation at startup; performs an inverter control operation of causing an output current to flow through each of the plurality of AC terminals; in the charging control operation: a first control operation of turning on at least one first switching element among the plurality of first switching elements and charging at least one resonance capacitor corresponding to the at least one first switching element among the plurality of resonance capacitors through a path passing through the first DC terminal and the at least one first switching element; A second control operation of turning on a switch corresponding to the at least one first switching element among the plurality of switches to charge the regeneration capacitor from the at least one resonance capacitor, and the like are alternately performed. Power conversion device.

2. The control device is In the charging control operation, the regeneration capacitor is charged until the voltage across the regeneration capacitor becomes equal to or higher than a threshold value. The power conversion device according to claim 1.

3. The control device performs the inverter control operation after the voltage across the regeneration capacitor becomes equal to or higher than the threshold value. The power conversion device according to claim 2.

4. The control device is In the first control operation, The at least one first switching element and at least one second switching element corresponding to the at least one first switching element among the plurality of second switching elements are complementarily turned on and off. In the second control operation, During a dead time period in which both the at least one first switching element and the at least one second switching element are turned off, a switch corresponding to the at least one first switching element among the plurality of switches is turned on. The power conversion device according to claim 1 or 2.

5. The control device is In the first control operation, The at least one first switching element and at least one second switching element corresponding to the at least one first switching element among the plurality of second switching elements are complementarily turned on and off. In the second control operation, During a dead time period in which both the at least one first switching element and the at least one second switching element are turned off, a switch corresponding to the at least one first switching element among the plurality of switches is turned on. The power conversion device according to claim 3.

6. The control device is In the first control operation, the plurality of first switching elements are turned on. The power conversion device according to claim 1 or 2.

7. The control device is In the first control operation, the plurality of first switching elements are turned on. The power conversion device according to claim 3.

8. The control device is In the first control operation, the plurality of first switching elements are turned on. The power conversion device according to claim 4. Claim 9. The at least one resonance inductor is one resonance inductor, and the second ends of the plurality of switches are commonly connected to the one resonance inductor. The power conversion device according to claim 1 or 2. Claim 10. The at least one resonance inductor is one resonance inductor, and the second ends of the plurality of switches are commonly connected to the one resonance inductor. The power conversion device according to claim 3. Claim 11. The at least one resonance inductor is one resonance inductor, and the second ends of the plurality of switches are commonly connected to the one resonance inductor. The power conversion device according to claim 4. Claim 12. The at least one resonance inductor is one resonance inductor, and the second ends of the plurality of switches are commonly connected to the one resonance inductor. The power conversion device according to claim 6.