Power converter

Abstract

According to the invention, the problem of miniaturization is solved. In a power converter (100), a controller (50) performs a charge control operation including charging a regenerative capacitor (15) as a start-up operation and an inverter control operation. The controller (50) alternately performs a first control operation and a second control operation as a charge control operation. The first control operation comprises turning on at least one first switching element (1) belonging to the plurality of first switching elements (1), thereby charging the at least one resonant capacitor (9) via a path through the first DC terminal (31) and the at least one first switching element (1). The at least one resonant capacitor (9) belongs to the plurality of resonant capacitors (9) and corresponds to the at least one first switching element (1). The second control operation includes turning on a switch (8) corresponding to the at least one first switching element (1) belonging to the plurality of switches (8), thereby charging the regenerative capacitor (15) with the charge supplied from the at least one resonant capacitor (9).

Description

Technical Field

[0001] The present disclosure generally relates to a power converter. More particularly, the present disclosure relates to a power converter having the ability to convert DC power into AC power. Background Art

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

[0003] In the resonant inverter of Patent Document 1, the DC voltage of the DC voltage source is converted into an AC voltage by an inverter unit (power conversion circuit). The inverter unit has a configuration in which six main switching elements are bridged between the positive bus and the negative bus in three phases (i.e., U phase, V phase, and W phase).

[0004] Furthermore, in the resonant inverter, two voltage-dividing capacitors are connected in series between the positive bus and the negative bus. The two voltage-dividing capacitors are used not only as voltage-dividing components for dividing the DC voltage of the DC voltage source, but also as components for generating half of the DC voltage of the DC voltage source at the connection node between the two voltage-dividing capacitors. In addition, a resonant circuit section for performing a resonant operation when the main switching element is switching is also provided between the two voltage-dividing capacitors and the inverter unit. The resonant circuit section is formed by connecting a series circuit of a resonant inductor and an auxiliary switch between the connection node of the two voltage-dividing capacitors and the connection node of the upper and lower arms of each of the three phases, and connecting the resonant capacitor in parallel with the series circuit of each of the three phases.

[0005] The ON / OFF states of the respective switching elements and the respective auxiliary switches are controlled by the control unit.

[0006] It is sometimes desirable for power converters to have reduced size.

[0007] Citation List

[0008] Patent Literature

[0009] Patent Document 1: JP 2000-32775A Summary of the invention

[0010] An object of the present disclosure is to provide a power converter that can have a reduced size.

[0011] A power converter according to one aspect of the present disclosure includes a first DC terminal and a second DC terminal, a power conversion circuit, a plurality of AC terminals, a plurality of switches, a plurality of resonant capacitors, at least one resonant inductor, a regenerative capacitor, and a controller. The power conversion circuit includes a plurality of first switching elements and a plurality of second switching elements. In the power conversion circuit, a plurality of switching circuits are connected in parallel to each other, and in each of the plurality of switching circuits, one of the plurality of first switching elements and a corresponding second switching element of the plurality of second switching elements are connected in series one-to-one. In the power conversion circuit, the plurality of first switching elements are connected to the first DC terminal, and the plurality of second switching elements are connected to the second DC terminal. A plurality of AC terminals are set one-to-one for the plurality of switching circuits. Each of the plurality of AC terminals is connected to a connection node between the first switching element and the second switching element of a corresponding switching circuit in the plurality of switching circuits. A plurality of switches are set one-to-one for the plurality of switching circuits. Each of the plurality of switches has a first end and a second end. The first end of each of the plurality of switches is connected to a connection node between the first switching element and the second switching element of a corresponding switching circuit in the plurality of switching circuits. A plurality of resonant capacitors are provided one-to-one for the plurality of switches. Each of the plurality of resonant capacitors is connected between the second DC terminal and the first end of the corresponding switch of the plurality of switches. 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 of the plurality of switches. A regenerative capacitor has a fifth end and a sixth end. The fifth end of the regenerative capacitor is connected to the second DC terminal. The sixth end of the regenerative capacitor is connected to the fourth end of the at least one resonant inductor. A controller controls the on / off states of each of the plurality of first switching elements, the plurality of second switching elements, and the plurality of switches. The controller performs a charging control operation including charging the regenerative capacitor as a startup operation, and also performs an inverter control operation including causing an output current to flow through each of the plurality of AC terminals. The controller alternately performs a first control operation and a second control operation as the charging control operation. The first control operation includes turning on at least one first switching element belonging to the plurality of first switching elements, thereby charging at least one resonant capacitor via a path passing through the first DC terminal and the at least one first switching element. The at least one resonant capacitor belongs to the plurality of resonant capacitors and corresponds to the at least one first switching element. The second control operation includes turning on a switch corresponding to the at least one first switching element belonging to the plurality of switches, thereby charging the regenerative capacitor with the charge supplied from the at least one resonant capacitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a circuit diagram of a system including a power converter according to a first embodiment;

[0013] Figure 2 shows how the power converter operates in a situation where its controller has performed basic operation with load current>0 and its resonant capacitor is operated through charging;

[0014] Figure 3 Also shown is how the power converter operates in the case where its controller has performed basic operation with load current > 0 and its resonant capacitor has been operated through charging;

[0015] Figure 4 shows how duty ratios and load currents respectively corresponding to three-phase voltage commands in AC loads connected to a plurality of AC terminals of a power converter vary with time;

[0016] Figure 5 A first current threshold and a second current threshold used in a controller of a power converter are shown;

[0017] Figure 6 shows how the power converter operates in a situation where its controller has performed basic operation with load current>0 and its resonant capacitor has undergone discharge operation;

[0018] Figure 7 Also shown is how the power converter operates in the case where its controller has performed basic operation with load current < 0 and its resonant capacitor has undergone discharge operation;

[0019] Figure 8 shows how the power converter operates in a situation where its controller has performed basic operation with load current < 0 and its resonant capacitor is operated with charging;

[0020] Fig. 9 shows the voltage across a regenerative capacitor in a power converter;

[0021] Fig.10 is a timing diagram showing how the controller of the power converter performs a charging control operation;

[0022] Fig.11 shows how the power converter operates in a situation where its controller has performed a first control operation of a charging control operation;

[0023] Fig.12 shows how the power converter operates in a situation where its controller has performed a second control operation of a charging control operation;

[0024] Fig.13 is a circuit diagram of a system including a power converter according to a first modification of the first embodiment;

[0025] Fig.14 is a circuit diagram of a system including a power converter according to a second modification of the first embodiment;

[0026] Fig.15 is a circuit diagram of a system including a power converter according to a third modification of the first embodiment;

[0027] Fig.16 is a circuit diagram of a system including a power converter according to a fourth modification of the first embodiment;

[0028] Fig.17 is a circuit diagram of a system including a power converter according to a fifth modification of the first embodiment;

[0029] Fig.18 is a circuit diagram of a system including a power converter according to a sixth modification of the first embodiment; and

[0030] Fig.19 is a circuit diagram of a system including a power converter according to a second embodiment. DETAILED DESCRIPTION

[0031] (First embodiment)

[0032] Reference Figures 1 to 12 A power converter 100 according to a first embodiment is described.

[0033] (1) Overall configuration of power converter

[0034] For example, Figure 1 As shown, the power converter 100 includes a first DC terminal 31 and a second DC terminal 32 and a plurality of (e.g., three) AC terminals 41. The DC power source E1 is connected between the first DC terminal 31 and the second DC terminal 32. The AC load RA1 is connected to the plurality of AC terminals 41. The AC load RA1 may be, for example, a three-phase motor. The power converter 100 converts the DC output of the DC power source E1 into AC power and outputs the AC power to the AC load RA1. The DC power source E1 may include, for example, a solar cell or a fuel cell. The DC power source E1 may include a DC-DC converter. In the power converter 100, if the plurality of AC terminals 41 are three AC terminals 41, the AC power may be, for example, a three-phase AC power having a U phase, a V phase, and a W phase.

[0035] The power converter 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 controller 50. The power converter 100 also includes a protection circuit 17 and a capacitor C10. Each of the plurality of switches 8 may be, for example, a bidirectional switch.

[0036] The power conversion circuit 11 includes a plurality of (for example, three) first switching elements 1 and a plurality of (for example, three) second switching elements 2. In the power conversion circuit 11, a plurality of (for example, three) switching circuits 10 are connected in parallel, and in each switching circuit 10, one of the plurality of first switching elements 1 and a corresponding second switching element of the plurality of second switching elements 2 are connected in series one-to-one. 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. A plurality of AC terminals 41 are provided one-to-one for the plurality of switching circuits 10. Each of the plurality of AC terminals 41 is connected to a connection node 3 between the first switching element 1 and the second switching element 2 of a corresponding switching circuit 10 of the plurality of switching circuits 10. A plurality of switches 8 are provided one-to-one for the plurality of switching circuits 10. Each of the plurality of switches 8 has a first end 81 and a second end 82. The first end 81 of each of the plurality of switches 8 is connected to a connection node 3 between the first switching element 1 and the second switching element 2 of a corresponding switching circuit 10 of the plurality of switching circuits 10. A plurality of resonant capacitors 9 are provided one-to-one for the plurality of switches 8. Each of the plurality of resonant capacitors 9 is connected between the first end 81 of a corresponding switch 8 of the plurality of switches 8 and the second DC terminal 32. The resonant inductor L1 has a third end and a fourth end. The third end of the resonant inductor L1 is connected to a corresponding switch 8 of the plurality of switches 8 (for example, in Figure 1 The controller 50 controls the plurality of first switching elements 1, the plurality of second switching elements 2 and the plurality of switches 8.

[0037] (2) Details of the power converter

[0038] In the following description, for the sake of convenience, for the sake of convenience, with respect to the plurality of switching circuits 10, the switching circuits 10 for the U phase, the V phase, and the W phase will be referred to as “switching circuit 10U”, “switching circuit 10V”, and “switching circuit 10W”, respectively, hereinafter. In addition, in the following description, the first switching element 1 and the second switching element 2 of the switching circuit 10U will be referred to as “the first switching element 1U” and the “second switching element 2U”, respectively, hereinafter. Similarly, in the following description, the first switching element 1 and the second switching element 2 of the switching circuit 10V will be referred to as “the first switching element 1V” and the “second switching element 2V”, respectively, hereinafter. Similarly, in the following description, the first switching element 1 and the second switching element 2 of the switching circuit 10W will be referred to as “the first switching element 1W” and the “second switching element 2W”, respectively, hereinafter. Furthermore, in the following description, the connection node 3 between the first switching element 1U and the second switching element 2U will be referred to as “connection node 3U” hereinafter, the connection node 3 between the first switching element 1V and the second switching element 2V will be referred to as “connection node 3V” hereinafter, and the connection node 3 between the first switching element 1W and the second switching element 2W will be referred to as “connection node 3W” hereinafter. Furthermore, in the following description, the AC terminal 41 connected to the connection node 3U will be referred to as “AC terminal 41U” hereinafter, the AC terminal 41 connected to the connection node 3V will be referred to as “AC terminal 41V” hereinafter, and the AC terminal 41 connected to the connection node 3W will be referred to as “AC terminal 41W” hereinafter. Furthermore, in the following description, the resonance capacitor 9 connected in parallel to the second switching element 2U will be referred to as “resonance capacitor 9U” hereinafter, the resonance capacitor 9 connected in parallel to the second switching element 2V will be referred to as “resonance capacitor 9V” hereinafter, and the resonance capacitor 9 connected in parallel to the second switching element 2W will be referred to as “resonance capacitor 9W” hereinafter. In addition, in the following description, the switch 8 connected to the connection node 3U will be referred to as "switch 8U" below, the switch 8 connected to the connection node 3V will be referred to as "switch 8V" below, and the switch 8 connected to the connection node 3W will be referred to as "switch 8W" below.

[0039] In the power converter 100, a high potential output terminal (positive electrode) of the DC power source E1 is connected to the first DC terminal 31, and a low potential output terminal (negative electrode) of the DC power source E1 is connected to the second DC terminal 32. Furthermore, in the power converter 100, U-phase, V-phase, and W-phase terminals of the AC load RA1 are connected to, for example, three AC terminals 41U, 41V, and 41W, respectively.

[0040] In the power conversion circuit 11, each of the plurality of (for example, three) first switching elements 1 and the plurality of (for example, three) second switching elements 2 has a control terminal, a first main terminal, and a second main terminal. Each of the control terminals of the plurality of first switching elements 1 and the plurality of second switching elements 2 is connected to the controller 50. In each of the plurality of switching circuits 10 of the power converter 100, the first main terminal of the first switching element 1 is connected to the first DC terminal 31, the second main terminal of the first switching element 1 is connected to the first main terminal of the second switching element 2, and the second main terminal of the second switching element 2 is connected to the second DC terminal 32. In each of the 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 may be, for example, an insulated gate bipolar transistor (IGBT). Thus, in each of the plurality of first switching elements 1 and the plurality of second switching elements 2 , the control terminal, the first main terminal, and the second main terminal thereof are the gate terminal, the collector terminal, and the emitter terminal, respectively.

[0041] The power conversion circuit 11 also includes: a plurality of (for example, three) first diodes 4, which are connected in anti-parallel to the plurality of (for example, three) first switching elements 1 in one-to-one; and a plurality of (for example, three) second diodes 5, which are connected in anti-parallel to the plurality of (for example, three) second switching elements 2 in one-to-one. 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.

[0042] The U-phase terminal of the AC load RA1 may be connected to the connection node 3U between the first switching element 1U and the second switching element 2U, for example, via the AC terminal 41U. The V-phase of the AC load RA1 may be connected to the connection node 3V between the first switching element 1V and the second switching element 2V, for example, via the AC terminal 41V. The W-phase of the AC load RA1 may be connected to the connection node 3W between the first switching element 1W and the second switching element 2W, for example, via the AC terminal 41W.

[0043] A plurality of resonant capacitors 9 are provided one by one for a plurality of switches 8. Each of the plurality of resonant capacitors 9 is connected between the first end 81 and the second DC terminal 32 of its corresponding switch 8. The power converter 100 includes a plurality of resonant circuits. The plurality of 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 plurality of resonant circuits share the resonant inductor L1 in common.

[0044] Each of the plurality of switches 8 may include, for example, two IGBTs (i.e., a first IGBT 6 and a second IGBT 7) connected together in anti-parallel. In each of the plurality of switches 8, the collector terminal of the first IGBT 6 and the emitter terminal of the second IGBT 7 are connected to each other, and the emitter terminal of the first IGBT 6 and the collector terminal of the second IGBT 7 are connected to each other. In each of the plurality of switches 8, the emitter terminal of the first IGBT 6 is connected to the connection node 3 of the switching circuit 10 corresponding to the switch 8 including the first IGBT 6. In each of the plurality of switches 8, the collector terminal of the second IGBT 7 is connected to the connection node 3 of the switching circuit 10 corresponding to the switch 8 including the second IGBT 7. The switch 8U is connected to the connection node 3U between the first switching element 1U and the second switching element 2U. The switch 8V is connected to the connection node 3V between the first switching element 1V and the second switching element 2V. The switch 8W is connected to the connection node 3W between the first switching element 1W and the second switching element 2W. In the following description, for the sake of convenience, the first IGBT 6 and the second IGBT 7 of the switch 8U will be referred to as the "first IGBT 6U" and the "second IGBT 7U", respectively, the first IGBT 6 and the second IGBT 7 of the switch 8V will be referred to as the "first IGBT 6V" and the "second IGBT 7V", respectively, and the first IGBT 6 and the second IGBT 7 of the switch 8W will be referred to as the "first IGBT 6W" and the "second IGBT 7W", respectively.

[0045] The plurality of switches 8 are controlled by the controller 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 controller 50.

[0046] The resonant inductor L1 has a third end and a fourth end. In the resonant inductor L1, the third end of the resonant inductor L1 is connected to the common connection node 25 to which the respective second ends 82 of the plurality of switches 8 are commonly connected. The fourth end of the resonant inductor L1 is connected to the sixth end 154 of the regenerative capacitor 15.

[0047] The regeneration capacitor 15 is connected between the fourth end of the resonance inductor L1 and the second DC terminal 32. The regeneration capacitor 15 may be, for example, a film capacitor.

[0048] The protection circuit 17 includes a third diode 13 and a fourth diode 14. The third diode 13 is connected between the common connection node 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 node 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 node 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 node 25. Thus, the fourth diode 14 is connected in series to the third diode 13.

[0049] 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 may be, for example, an electrolytic capacitor.

[0050] The controller 50 controls a plurality of first switching elements 1, a plurality of second switching elements 2, and a plurality of switches 8. An agent for performing the functions of the controller 50 includes a computer system. The computer system includes a single or multiple computers. The computer system may include a processor and a memory as its main hardware components. The computer system is used as an agent for performing the functions of the controller 50 according to the present disclosure by causing the processor to execute a program stored in the memory of the computer system. The program may be pre-stored in the memory of the computer system. Alternatively, the program may also be downloaded via a telecommunications line, or distributed after being recorded in a non-transient storage medium such as a memory card, an optical disk, or a hard disk drive (disk) (any of which storage media is readable for the computer system). The processor of the computer system may be composed of a single or multiple electronic circuits including a semiconductor integrated circuit (IC) or a large-scale integrated circuit (LSI). These electronic circuits may be integrated together on a single chip or distributed on multiple chips, whichever is appropriate. These multiple chips may be aggregated together in a single device or distributed in multiple devices without limitation.

[0051] The controller 50 outputs control signals SU1, SV1, SW1 for controlling the ON / OFF states of the plurality of first switching elements 1U, 1V, 1W, respectively. Each of the control signals SU1, SV1, SW1 may be, for example, a pulse width modulation (PWM) signal having a potential level that alternates between, for example, a first potential level (hereinafter referred to as a "low level") and a second potential level (hereinafter referred to as a "high level") higher than the first potential level. The first switching elements 1U, 1V, 1W each turn on when their control signals SU1, SV1, SW1 have a high level, and each turn off when their control signals SU1, SV1, SW1 have a low level. In addition, the controller 50 also outputs control signals SU2, SV2, SW2 for controlling the ON / OFF states of the plurality of second switching elements 2U, 2V, 2W, respectively. Each of the control signals SU2, SV2, SW2 may be, for example, a PWM signal having a potential level that alternates between a first potential level (hereinafter referred to as a "low level") and a second potential level (hereinafter referred to as a "high level") higher than the first potential level. The second switching elements 2U, 2V, 2W each become conductive when the control signals SU2, SV2, SW2 thereof have a high level, and each become off when the control signals SU2, SV2, SW2 thereof have a low level.

[0052] The controller 50 uses a carrier signal having a sawtooth waveform (reference Figure 2 ) to generate control signals SU1, SV1, SW1 for multiple first switching elements 1U, 1V, 1W and control signals SU2, SV2, SW2 for multiple second switching elements 2U, 2V, 2W. More specifically, the controller 50 generates control signals SU1, SU2 to be applied to the first switching element 1U and the second switching element 2U, respectively, based at least on the carrier signal and the U-phase voltage command. In addition, the controller 50 generates control signals SV1, SV2 to be applied to the first switching element 1V and the second switching element 2V, respectively, based at least on the carrier signal and the V-phase voltage command. In addition, the controller 50 generates control signals SW1, SW2 to be applied to the first switching element 1W and the second switching element 2W, respectively, based at least on the carrier signal and the W-phase voltage command. The U-phase voltage command, the V-phase voltage command and the W-phase voltage command can, for example, be sinusoidal wave signals whose phases differ by 120 degrees from each other and whose values ​​(voltage command values) vary with time. Note that the waveform of the carrier signal does not have to be a sawtooth waveform, but can also be a triangular waveform or Figure 2 The sawtooth waveform shown is a mirror-inverted form. In addition, the U-phase voltage command, the V-phase voltage command, and the W-phase voltage command each have a cycle of the same length. In addition, one cycle of the U-phase voltage command, the V-phase voltage command, and the W-phase voltage command is longer than one cycle of the carrier signal.

[0053] The duty ratios of the control signals SU1, SU2 to be applied from the controller 50 to the first switching element 1U and the second switching element 2U, respectively, vary according to the U-phase voltage command. Figure 4 In FIG. 5 , the duty cycle of the control signal SU1 is shown as “U-phase duty cycle”. Figure 1 ) generates a control signal SU1 to be applied to the first switching element 1U by comparing the U-phase voltage command with the carrier signal. The controller 50 generates a control signal SU2 to be applied to the second switching element 2U by inverting the control signal SU1 to be applied to the first switching element 1U. In addition, in order to prevent the respective conduction periods of the first switching element 1U and the second switching element 2U from overlapping each other, the controller 50 sets a dead zone period Td (reference period Td) between the high level period of the control signal SU1 and the high level period of the control signal SU2. Figure 2 ).

[0054] The duty ratios of the control signals SV1, SV2 to be applied from the controller 50 to the first switching element 1V and the second switching element 2V, respectively, vary according to the V-phase voltage command. Figure 4 In FIG. 5 , the duty cycle of the control signal SV1 is shown as the “V-phase duty cycle”. Figure 1 ) generates a control signal SV1 to be applied to the first switching element 1V by comparing the V-phase voltage command with the carrier signal. The controller 50 also generates a control signal SV2 to be applied to the second switching element 2V by inverting the control signal SV1 to be applied to the first switching element 1V. In addition, in order to prevent the respective conduction periods of the first switching element 1V and the second switching element 2V from overlapping each other, the controller 50 sets a dead zone period Td (reference period Td) between the high level period of the control signal SV1 and the high level period of the control signal SV2. Figure 2 ).

[0055] The duty ratios of the control signals SW1, SW2 to be applied from the controller 50 to the first switching element 1W and the second switching element 2W, respectively, vary according to the W-phase voltage command. Figure 4 , the duty cycle of the control signal SW1 is shown as the "W-phase duty cycle". Figure 1 ) generates a control signal SW1 to be applied to the first switching element 1W by comparing the W-phase voltage command with the carrier signal. The controller 50 generates a control signal SW2 to be applied to the second switching element 2W by inverting the control signal SW1 to be applied to the first switching element 1W. In addition, in order to prevent the respective conduction periods of the first switching element 1W and the second switching element 2W from overlapping each other, the controller 50 sets a dead zone period Td (reference period Td) between the high level period of the control signal SW1 and the high level period of the control signal SW2. Figure 3 ).

[0056] The U-phase voltage command, the V-phase voltage command, and the W-phase voltage command may be, for example, sinusoidal wave signals whose phases differ from each other by 120 degrees and whose values ​​vary with time. Figure 4 As shown, the duty ratios of the control signals SU1, SV1, and SW1 (i.e., the U-phase, V-phase, and W-phase duty ratios) vary in the form of sinusoidal waves that are 120 degrees out of phase with each other. In the same manner, the duty ratios of the control signals SU2, SV2, and SW2 also vary in the form of sinusoidal waves that are 120 degrees out of phase with each other.

[0057] The controller 50 generates the respective control signals SU1, SU2, SV1, SV2, SW1, SW2 based on the carrier signal, the respective voltage commands, and the information related to the state of the AC load RA1. For example, if the AC load RA1 is a three-phase motor, the information related to the state of the AC load RA1 may include, for example, detection values ​​provided by a plurality of current sensors for respectively detecting output currents iU, iV, iW of the U-phase, V-phase, and W-phase, respectively, flowing through the AC load RA1.

[0058] A plurality of switches 8 , a resonant inductor L1 , a plurality of resonant capacitors 9 , and a regenerative capacitor 15 are provided to perform zero-voltage soft switching of a plurality of first switching elements 1 and a plurality of second switching elements 2 .

[0059] In this power converter 100 , the controller 50 controls not only the plurality of first switching elements 1 and the plurality of second switching elements 2 of the power conversion circuit 11 , but also the plurality of switches 8 .

[0060] The controller 50 generates control signals SU6, SU7, SV6, SV7, SW6, SW7 for respectively controlling the on / off states of 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, and outputs the control signals SU6, SU7, SV6, SV7, SW6, SW7 to the respective gate terminals of 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.

[0061] If the first IGBT 6U is turned on and the second IGBT 7U is turned off, the switch 8U enables a charging current that flows through the regenerative capacitor 15, the resonant inductor L1, the switch 8U, and the resonant capacitor 9U in sequence to pass. The charging current is a current for charging the resonant capacitor 9U. On the other hand, if the first IGBT 6U is turned off and the second IGBT 7U is turned on, the switch 8U enables a discharging current that flows through the resonant capacitor 9U, the switch 8U, the resonant inductor L1, and the regenerative capacitor 15 in sequence to pass. The discharging current is a current for discharging (i.e., removing charge) from the resonant capacitor 9U.

[0062] If the first IGBT 6V is turned on and the second IGBT 7V is turned off, the switch 8V enables a charging current to flow through the regenerative capacitor 15, the resonant inductor L1, the switch 8V, and the resonant capacitor 9V in sequence. The charging current is a current for charging the resonant capacitor 9V. On the other hand, if the first IGBT 6V is turned off and the second IGBT 7V is turned on, the switch 8V enables a discharging current to flow through the resonant capacitor 9V, the switch 8V, the resonant inductor L1, and the regenerative capacitor 15 in sequence. The discharging current is a current for discharging (i.e., removing charge) from the resonant capacitor 9V.

[0063] If the first IGBT 6W is turned on and the second IGBT 7W is turned off, the switch 8W enables a charging current to flow through the regenerative capacitor 15, the resonant inductor L1, the switch 8W, and the resonant capacitor 9W in sequence. The charging current is a current for charging the resonant capacitor 9W. On the other hand, if the first IGBT 6W is turned off and the second IGBT 7W is turned on, the switch 8W enables a discharging current to flow through the resonant capacitor 9W, the switch 8W, the resonant inductor L1, and the regenerative capacitor 15 in sequence. The discharging current is a current for discharging (i.e., removing charge) from the resonant capacitor 9W.

[0064] (3) Operation of power converter

[0065] In the following description, for the current iL1 flowing through the resonant inductor L1, if the current is Figure 1 If the current iL1 flows in the direction indicated by the arrow shown in FIG. 1 , the polarity of the current iL1 is assumed to be positive. On the other hand, if the current iL1 flows in the direction indicated by the arrow shown in FIG. Figure 1 If the current iL1 flows in the direction opposite to the direction indicated by the arrow shown in FIG. 1 , the polarity of the current iL1 is assumed to be negative. In addition, in the following description, for each of the load currents iU, iV, iW flowing through the U phase, V phase, and W phase of the AC load RA1, if the load currents iU, iV, iW are Figure 1If the load current iU, iV, iW flows in the direction indicated by the corresponding arrow in the arrows shown, it is assumed that the polarity of the load current iU, iV, iW is positive. On the other hand, if the load current iU, iV, iW flows in the direction indicated by the corresponding arrow in the arrows shown, it is assumed that the polarity of the load current iU, iV, iW is positive. Figure 1 If the load current iU, iV, iW flows in the direction opposite to the direction indicated by the arrow shown in FIG. 1 , the polarity of the load current iU, iV, iW is assumed to be negative. In addition, for each of the currents i9U, i9V, i9W flowing through the resonant capacitors 9U, 9V, 9W, respectively, if the currents i9U, i9V, i9W are Figure 1 If the currents i9U, i9V, i9W flow in the direction indicated by the corresponding arrows in the arrows shown, the polarity of the currents i9U, i9V, i9W is assumed to be positive. On the other hand, if the currents i9U, i9V, i9W flow in the direction indicated by the corresponding arrows in the arrows shown, the polarity of the currents i9U, i9V, i9W is assumed to be positive. Figure 1 If the current i9U, i9V, i9W flows in a direction opposite to the direction indicated by the arrow shown in FIG. 1 , the polarity of the current i9U, i9V, i9W is assumed to be negative. Therefore, in the case of a discharge operation of discharging from the resonance capacitor 9U, 9V, 9W, the polarity of the current i9U, i9V, i9W is positive. On the other hand, in the case of a charging operation of charging the resonance capacitor 9U, 9V, 9W, the polarity of the current i9U, i9V, i9W is negative.

[0066] The controller 50 performs a charging control operation including charging the regenerative capacitor 15 as a startup operation of the power converter 100 , and also performs an inverter control operation including causing output currents iU, iV, iW to flow through each of the plurality of AC terminals 41 as a steady-state operation of the power converter 100 .

[0067] In the following description, it will be first described how the power converter 100 operates in a case where the controller 50 performs an inverter control operation. Thereafter, it will be described how the power converter 100 operates in a case where the controller 50 performs a charging control operation.

[0068] (3.1) How the power converter operates when the controller performs inverter control operation

[0069] In the power converter 100, for example, in a state where the first IGBT 6U of the switch 8U is turned on and the positive current iL1 is flowing through the resonant inductor L1, the first IGBT 6U of the switch 8U can be turned 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 current iL1 becomes zero due to the energy consumption of the resonant inductor L1. In addition, in the power converter 100, for example, in a state where the second IGBT 7U of the switch 8U is turned on and the negative current iL1 is flowing through the resonant inductor L1, the second IGBT 7U of the switch 8U can be turned off. In this case, the current iL1 flows through the resonant inductor L1 along a path that passes through the fourth diode 14, the resonant inductor L1, and the regeneration capacitor 15 in sequence until the current iL1 becomes zero due to the energy consumption of the resonant inductor L1.

[0070] Furthermore, in the power converter 100, for example, in a state where the first IGBT 6V of the switch 8V is turned on and the positive current iL1 is flowing through the resonant inductor L1, the first IGBT 6V of the switch 8V can be turned 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 current iL1 becomes zero due to the energy consumption of the resonant inductor L1. Furthermore, in the power converter 100, for example, in a state where the second IGBT 7V of the switch 8V is turned on and the negative current iL1 is flowing through the resonant inductor L1, the second IGBT 7V of the switch 8V can be turned off. In this case, the current iL1 flows through the resonant inductor L1 along a path that passes through the fourth diode 14, the resonant inductor L1, and the regeneration capacitor 15 in sequence until the current iL1 becomes zero due to the energy consumption of the resonant inductor L1.

[0071] Furthermore, in the power converter 100, for example, in a state where the first IGBT 6W of the switch 8W is turned on and the positive current iL1 is flowing through the resonant inductor L1, the first IGBT 6W of the switch 8W can be turned 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 current iL1 becomes zero due to the energy consumption of the resonant inductor L1. Furthermore, in the power converter 100, for example, in a state where the second IGBT 7W of the switch 8W is turned on and the negative current iL1 is flowing through the resonant inductor L1, the second IGBT 7W of the switch 8W can be turned off. In this case, the current iL1 flows through the resonant inductor L1 along a path that passes through the fourth diode 14, the resonant inductor L1, and the regeneration capacitor 15 in sequence until the current iL1 becomes zero due to the energy consumption of the resonant inductor L1.

[0072] The controller 50 sets a dead time period Td between the high level period of the control signal SU1, SV1, SW1 of the first switching element 1U, 1V, 1W and the high level period of the control signal SU2, SV2, SW2 of the second switching element 2U, 2V, 2W for each switching circuit 10 among the multiple switching circuits 10.

[0073] Next, we will refer to Figures 1 to 8 A basic operation of zero voltage soft switching to be performed on each of the plurality of first switching elements 1 and the plurality of second switching elements 2 is described. As used herein, "basic operation" refers to an operation to be performed when the resonant current through two or more switches 8 belonging to the plurality of switches 8 does not flow through the resonant inductor L1 at the same time. After describing the basic operation, how the power converter 100 operates when the controller 50 determines that the resonant current through two or more switches 8 belonging to the plurality of switches 8 flows at the same time will be described.

[0074] (3.1.1) Basic operations

[0075] When the first switching element 1 is subjected to zero voltage soft switching, the voltage across the first switching element 1, which is the object of zero voltage soft switching, needs to be reduced to zero immediately before the first switching element 1 becomes conductive. When the second switching element 2 is subjected to zero voltage soft switching, the voltage across the second switching element 2, which is the object of zero voltage soft switching, needs to be reduced to zero immediately before the second switching element 2 becomes conductive. In the following description, the switching element, which is the object of zero voltage soft switching (which is the first switching element 1 or the second switching element 2), will be referred to as the "object switching element" hereinafter.

[0076] The basic operation of the controller 50 changes according to the polarity (i.e., positive or negative) of the load current flowing through the AC terminal 41 connected to the object switching element and depending on whether the resonant capacitor 9 connected in series or in parallel to the object switching element is undergoing a charging operation or a discharging operation. The load current has a positive polarity when flowing from the AC terminal 41 toward the AC load RA1, and has a negative polarity when flowing from the AC load RA1 toward the AC terminal 41. When the resonant capacitor 9 is undergoing a charging operation, the voltage across the resonant capacitor 9 increases. On the other hand, when the resonant capacitor 9 is undergoing a discharging operation, the voltage across the resonant capacitor 9 decreases. The voltage across each of the plurality of second switching elements 2 is the same as the voltage across the resonant capacitor 9 connected in parallel to the second switching element 2.

[0077] (3.1.1.1) Soft switching of the first switching element when the load current is greater than 0

[0078] If the object of soft switching is the first switching element 1 (hereinafter referred to as "the object first switching element 1"), and the polarity of the load current flowing through the AC terminal 41 connected to the object first switching element 1 is positive, the controller 50 turns on the first IGBT 6 corresponding to the object first switching element 1. In this way, the controller 50 causes the resonant inductor L1 and the resonant capacitor 9 connected to the object first switching element 1 to resonate, thereby charging the resonant capacitor 9 with the charge supplied from the regenerative capacitor 15 and reducing the voltage across the object first switching element 1 to zero. This enables the power converter 100 to perform zero-voltage soft switching of the object first switching element 1.

[0079] Figure 2 , control signals SU1 and SU2 to be applied from the controller 50 to the first switching element 1U and the second switching element 2U of the switching circuit 10U, respectively, are shown in FIG. Figure 2 Also shown in FIG. 5 are the control signal SU6 to be applied from the controller 50 to the first IGBT 6U of the switch 8U, the load current iU of the U phase flowing through the AC load RA1, the current iL1 flowing through the resonant inductor L1, the voltage V1u across the first switching element 1U, and the voltage V2u across the second switching element 2U. In addition, Figure 2 , control signals SV1 and SV2 to be applied from the controller 50 to the first switching element 1V and the second switching element 2V of the switching circuit 10V, respectively, are also shown in FIG. Figure 2 Also shown are the control signal SV6 to be applied from the controller 50 to the first IGBT 6V of the switch 8V, the load current iV of the V phase flowing through 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.

[0080] also, Figure 2 4 also shows the dead time period Td set by the controller 50 to prevent the first switching element 1 and the second switching element 2 of the same phase from becoming conductive at the same time. Figure 2 Also shown in FIG. 5 are the additional time Tau set by the controller 50 for the control signal SU6 of the first IGBT 6U of the switch 8U and the additional time Tav set by the controller 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.

[0081] Figure 3Shown is a case where the first switching element of the object is the first switching element 1W of the switching circuit 10W, and control signals SW1 and SW2 to be respectively applied from the controller 50 to the first switching element 1W and the second switching element 2W of the switching circuit 10W. Additionally, Figure 3 Shown is also a control signal SW6 to be applied from the controller 50 to the first IGBT 6W of the switch 8W and a load current iW of the W-phase flowing through the AC load RA1. Figure 3 Shown is also a current iL1 flowing through the resonant inductor L1. Figure 3 Shown is also a voltage V1w across the first switching element 1W and a voltage V2w across the second switching element 2W. In Figure 3 the voltage value of the DC power supply E1 is specified by Vd.

[0082] Furthermore, Figure 3 shown is also a dead time period Td set by the controller 50 to prevent the first switching element 1W and the second switching element 2W from becoming conductive simultaneously. Furthermore, Figure 3 shown is also an additional time Taw set by the controller 50 for the control signal SW6 of the first IGBT 6W of the switch 8W. The additional time Taw will be described later.

[0083] As Figure 2 shown, the additional time Tau is an amount of time that the controller 50 sets such that the start time (time t1) of the high-level period of the control signal SU6 is set earlier than the start time (time t2) of the dead time period Td so that the high-level period of the control signal SU6 is longer than the dead time period Td. The length of the additional time Tau is determined by the value of the load current iU. In order to generate LC resonance starting from the start time (time t2) of the dead time period Td, it is preferable that the value of the current iL1 coincides with the value of the load current iU at the start time (time t2) of the dead time period Td. This is because as long as iL1 < iU, all of the current iL1 flows through the AC load RA1, and thus the resonant capacitor 9U cannot be charged. The end time of the high-level period of the control signal SU6 can be the same as or later than the end time (time t3) of the dead time period Td. In Figure 2 the example shown, the end time of the high-level period of the control signal SU6 is set to be the same as the end time (time t3) of the dead time period Td. The controller 50 sets the high-level period of the control signal SU6 to be Tau + Td. In the switching circuit 10U, the voltage V2u across the second switching element 2U becomes Vd at the end time (time t3) of the dead time period Td, and the voltage V1u across the first switching element 1U becomes zero at the end time (time t3) of the dead time period Td. In Figure 2In the example shown, the current iL1 starts to flow through the resonant inductor L1 at the start time (time t1) of the high level period of the control signal SU6, and becomes zero at time t4 after the additional time Tau has passed from the end time (time t3) of the dead time period Td. As for the current iL1, from the start time (time t2) of the dead time period Td, the current iL1 satisfies iL1 ≥ iU, so from Figure 2 The current iL1 in the shaded portion of the current waveform shown in the fifth waveform from the top flows into the resonant capacitor 9U to generate LC resonance. From the end time (time t3) of the dead time period Td, the current iL1 will be regenerated to the power conversion circuit 11 via the third diode 13 directly connected to the resonant inductor L1.

[0084] As described above, in order to start generating LC resonance at the start time (time t2) of the dead time period Td and end the resonant half cycle at the end time of the dead time period Td, the controller 50 determines the additional time Tau based on the load current iU so that iL1=iU is satisfied at the start time (time t2) of the dead time period Td. More specifically, for example, the controller 50 uses the detection result of the load current iU by the current sensor or its signal processing value, or the estimated value of the load current iU, the inductance L of the resonant inductor L1 that has been stored in advance, and the detection result of the voltage V15 across the regenerative capacitor 15, and determines the additional time Tau by the formula Tau=iU×(L / V15). In this case, as the detection result of the load current iU or its signal processing value, the detection value according to the carrier cycle to which the additional time Tau is added or the detection value according to the timing closest to the carrier cycle can be used. In addition, in this case, as the estimated value of the load current iU, for example, the value of the load current iU estimated according to the carrier cycle to which the additional time Tau is added can be used. The resonant half period in the case of basic operation is half of the resonant period, where the resonant period is the inverse of the resonant frequency of the resonant circuit including the resonant inductor L1 and the resonant capacitor 9. Thus, if the inductance of the resonant inductor L1 is L and the capacitance of the resonant capacitor 9 is C, the resonant half period is π×(L·C) 1 / 2 For example, the controller 50 sets the resonance half period in the case of the basic operation so that the resonance half period is as long as the length of the dead time period Td.

[0085] like Figure 2As shown, the additional time Tav is the amount of time by which the controller 50 sets the start time (time t5) of the high-level period of the control signal SV6 to be earlier than the start time (time t6) of the dead time period Td so that the high-level period of the control signal SV6 is longer than the dead time period Td. The length of the additional time Tav is determined by the value of the load current iV. In order to generate LC resonance starting from the start time (time t6) of the dead time period Td, it is preferable that the value of the current iL1 coincides with the value of the load current iV at the start time (time t6) of the dead time period Td. This is because as long as iL1 < iV, all of the current iL1 flows through the AC load RA1, and thus the resonance capacitor 9V cannot be charged. The end time of the high-level period of the control signal SV6 can be simultaneous with or later than the end time (time t7) of the dead time period Td. In Figure 2 the example shown, the end time of the high-level period of the control signal SV6 is set to be simultaneous with the end time (time t7) of the dead time period Td. The controller 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 time (time t7) of the dead time period Td. In Figure 2 the example shown, the current iL1 starts flowing through the resonance inductor L1 at the start time (time t5) of the high-level period of the control signal SV6, and becomes zero at time t8 which is the additional time Tav after the end time (time t7) of the dead time period Td. Regarding the current iL1, starting from the start time (time t6) of the dead time period Td, the current iL1 satisfies iL1 ≥ iV, and thus the current iL1 in the shaded portion of the current waveform shown by the tenth waveform from the top of Figure 2 flows into the resonance capacitor 9V to generate LC resonance. Starting from the end time (time t7) of the dead time period Td, the current iL1 will be regenerated to the power conversion circuit 11 via the third diode 13 directly connected to the resonance inductor L1.

[0086] As described above, in order to start generating the LC resonance at the start time (time t6) of the dead time period Td, the controller 50 determines the additional time Tav based on the load current iV such that iL1 = iV is satisfied at the start time (time t6) of the dead time period Td. More specifically, for example, the controller 50 uses the detection result of the load current iV by the current sensor or its signal processing value, or the estimated value of the load current iV, the inductance L of the resonance inductor L1 stored in advance, and the detection result of the voltage V15 across the regenerative capacitor 15, and determines the additional time Tav by the formula Tav = iV × (L / V15). In this case, as the detection result of the load current iV or its signal processing value, the detection value according to the carrier period plus the additional time Tav or the detection value according to the timing closest to the carrier period can be used. Further, in this case, as the estimated value of the load current iV, for example, the value of the load current iV estimated according to the carrier period plus the additional time Tav can be used.

[0087] As Figure 3 shown, the additional time Taw is the time amount that the controller 50 sets to make the start time (time t9) of the high level period of the control signal SW6 earlier than the start time (time t10) of the dead time period Td so that the high level period of the control signal SW6 is longer than the dead time period Td. The length of the additional time Taw is determined by the value of the load current iW. In order to generate the LC resonance from the start time (time t10) of the dead time period Td, it is preferable that the value of the current iL1 coincides with the value of the load current iW at the start time (time t10) of the dead time period Td. This is because as long as iL1 < iW is satisfied, all of the current iL1 flows through the AC load RA1, and thus the resonance capacitor 9W cannot be charged. The end time of the high level period of the control signal SW6 may be the same as or later than the end time (time t11) of the dead time period Td. In Figure 3 the example shown, the end time of the high level period of the control signal SW6 is set to be the same as the end time (time t11) of the dead time period Td. The controller 50 sets the high level period of the control signal SW6 to be Taw + Td. The voltage V1w across the first switching element 1W becomes zero at the end time (time t11) of the dead time period Td. In Figure 3 the example shown, the current iL1 starts flowing through the resonance inductor L1 at the start time (time t9) of the high level period of the control signal SW6, and becomes zero at the time t12 which is the additional time Taw after the end time (time t11) of the dead time period Td. Regarding the current iL1, starting from the start time (time t10) of the dead time period Td, iL1 satisfies iL1 ≥ iW, so from Figure 3The current iL1 in the shaded portion of the current waveform shown in the fourth waveform from the top flows into the resonant capacitor 9W to generate LC resonance. From the end time (time t11) of the dead time period Td, the current iL1 will be regenerated to the power conversion circuit 11 via the third diode 13 directly connected to the resonant inductor L1.

[0088] The controller 50 determines the additional time Taw based on the load current iW. More specifically, for example, the controller 50 uses the detection result of the load current iW by the current sensor, the inductance L of the resonant inductor L1 that has been stored in advance, and the detection result of the voltage V15 across the regenerative capacitor 15, and determines the additional time Taw by the formula Taw=iW×(L / V15). In this case, as the detection result of the load current iW or its signal processing value, a detection value according to the carrier cycle to which the additional time Taw is added or a detection value according to the timing closest to the carrier cycle can be used. In addition, in this case, as the estimated value of the load current iW, for example, the value of the load current iW estimated according to the carrier cycle to which the additional time Taw is added can be used.

[0089] (3.1.1.2) Soft switching of the second switching element when the load current is greater than 0

[0090] If the object of soft switching is the second switching element 2 (hereinafter referred to as "the object second switching element 2"), and the polarity of the load current (which is the load current iU, the load current iV, or the load current iW) flowing through the AC terminal 41 connected to the object second switching element 2 is positive, the controller 50 compares the current value of the load current with the first current threshold value I1 (=Ith, reference Figure 5 ) is compared. If the current value of the load current is greater than the first current threshold value I1, the controller 50 does not turn on the switch 8. On the other hand, if the current value of the load current is less than the first current threshold value I1, the controller 50 turns on the switch 8 in the dead time period Td. In the power converter 100, if the current value of the load current is greater than the first current threshold value I1, the controller 50 can use the load current iU to discharge the resonant capacitor 9U connected in parallel to the object second switching element 2 without turning on the switch 8 corresponding to the object second switching element 2. This enables the power converter 100 to perform zero voltage soft switching of the object second switching element 2.

[0091] exist Figure 6, for the case where 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 value I1, control signals SU1, SU2, SU7, load current iU, current i9U flowing from the resonant capacitor 9U, and voltage V2u across the second switching element 2 are shown. In addition, Figure 6 Also shown in FIG. 8 are the dead time period Td and the additional time Tau set by the controller 50 for the control signal SU7 of the second IGBT 7U of the switch 8U.

[0092] If the current value of the load current iU is greater than the first current threshold value I1, the controller 50 does not set any high level period to the control signal SU7. In this case, in the power converter 100, the current i9U starts to flow from the resonant capacitor 9U at the start time (time t22) of the dead time period Td, the current i9U decreases to zero before the end time (time t23) of the dead time period Td, and the voltage V2u across the second switching element 2U becomes zero before the end time (time t23) of the dead time period Td. Thus, in the power converter 100, when the control signal SU2 changes from a low level to a high level at the end time (time t23) of the dead time period Td, the second switching element 2U undergoes zero voltage soft switching.

[0093] If the current value of the load current iU is less than the first current threshold I1, then for example Figure 6 As shown in the double dotted line, the controller 50 sets a high level period to the control signal SU7. In this case, the start time of the high level period of the control signal SU7 may be simultaneous with, for example, the start time (time t22) of the dead time period Td. In addition, the end time of the high level period of the control signal SU7 is simultaneous with the end time (time t23) of the dead time period Td. Thus, in the power converter 100, the voltage V2u across the second switching element 2U becomes zero before the end time (time t23) of the dead time period Td. Therefore, in the power converter 100, when the control signal SU2 changes from a low level to a high level at the end time (time t23) of the dead time period Td, the second switching element 2U undergoes zero voltage soft switching. Alternatively, the start time of the high level period of the control signal SU7 may be time t21 earlier than the start time of the dead time period Td by an additional time Tau. The end time of the high level period of the control signal SU7 may be time t24 later than the end time (time t23) of the dead time period Td by an additional time Tau. Note that the time before or after the high level period overlaps with the dead time period Td does not necessarily have to be the additional time Tau, but may also be any other preset time.

[0094] (3.1.1.3) Soft switching operation of the second switching element when the load current is less than 0

[0095] If the polarity of the load current (which is the load current iU, the load current iV, or the load current iW) flowing through the AC terminal 41 connected to the object second switching element 2 is negative, the controller 50 turns on the second IGBT 7 corresponding to the object second switching element 2. In this way, the controller 50 causes the resonant capacitor 9 and the resonant inductor L1 connected to the object second switching element 2 to resonate, thereby discharging from the resonant capacitor 9 and reducing the voltage across the object second switching element 2 to zero. This enables the power converter 100 to perform zero-voltage soft switching of the object second switching element 2.

[0096] exist Figure 7 , for the case where the target second switching element 2 is the second switching element 2U of the switching circuit 10U, control signals SU1, SU2, SU7, load current iU, current iL1 flowing through the resonant inductor L1, and voltage V2u across the second switching element 2U are shown.

[0097] In addition, Figure 7 4 also shows the dead time period Td set by the controller 50 to prevent the first switching element 1 and the second switching element 2 of the same phase from becoming conductive at the same time. Figure 7 8U also shows the additional time Tau set by the controller 50 for the control signal SU7 of the second IGBT 7U of the switch 8U. The end time of the high level period of the control signal SU7 may be simultaneous with or later than the end time (time t33) of the dead time period Td. Figure 7 In the example shown, the end time of the high level period of the control signal SU7 is set to coincide with the end time (time t33) of the dead time period Td. The controller 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 time (time t33) of the dead time period Td. Figure 7In the example shown, the current iL1 starts to flow through the resonant inductor L1 at the start time (time t31) of the high level period of the control signal SU7, and becomes zero at time t34 after the additional time Tau has passed from the end time (time t33) of the dead time period Td. As for the current iL1, from the start time (time t32) of the dead time period Td, the current iL1 satisfies iL1≤iU, and thus LC resonance is generated so that the resonant current (i.e., the discharge current from the resonant capacitor 9U) flows from the resonant capacitor 9U toward the resonant inductor L1. From the end time (time t33) of the dead time period Td, the current iL1 will be regenerated to the power conversion circuit 11 via the fourth diode 14 directly connected to the resonant inductor L1.

[0098] In order to start generating LC resonance at the start time (time t32) of the dead time period Td and end the resonant half cycle at the end time (time t33) of the dead time period Td, the controller 50 determines the additional time Tau based on the load current iU so that iL1=iU is satisfied at the start time (time t32) of the dead time period Td. More specifically, the controller 50 uses, for example, the detection result of the output current iU by the current sensor or its signal processing value, or the estimated value of the load current iU, the inductance L of the resonant inductor L1 that has been stored in advance, and the detection result of the voltage V15 across the regenerative capacitor 15, and determines the additional time Tau by the formula Tau=|iU|×(L / V15). In this case, as the detection result of the load current iU or its signal processing value, the detection value according to the carrier cycle to which the additional time Tau is added or the detection value according to the timing closest to the carrier cycle can be used. In addition, in this case, as the estimated value of the load current iU, for example, the value of the load current iU estimated according to the carrier cycle to which the additional time Tau is added can be used. The resonant half period in the case of basic operation is half of the resonant period, where the resonant period is the inverse of the resonant frequency of the resonant circuit including the resonant inductor L1 and the resonant capacitor 9. Thus, if the inductance of the resonant inductor L1 is L and the capacitance of the resonant capacitor 9 is C, the resonant half period is π×(L·C) 1 / 2 For example, the controller 50 sets the resonance half period in the case of the basic operation so that the resonance half period is as long as the length of the dead time period Td.

[0099] (3.1.1.4) Soft switching of the first switching element when the load current is less than 0

[0100] If the polarity of the load current (which is the load current iU, the load current iV or the load current iW) flowing through the AC terminal 41 connected to the object first switching element 1 is negative, the controller 50 compares the current value of the load current with the second current threshold value I2 (=−Ith, reference Figure 5 ) is compared. If the current value of the load current is less than the second current threshold value I2, the controller 50 does not turn on the switch 8. On the other hand, if the current value of the load current is greater than the second current threshold value I2, the controller 50 turns on the switch 8 in the dead time period Td. In the power converter 100, if the current value of the load current is less than the second current threshold value I2, the controller 50 can charge the resonant capacitor 9U connected in series to the object first switching element 1 with the load current without turning on the switch 8 corresponding to the object first switching element 1. This enables the power converter 100 to perform zero voltage soft switching of the object first switching element 1.

[0101] exist Figure 8 , for the case where 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 value I2 (in other words, the absolute value of the current value of the load current is less than the absolute value of the second current threshold value I2), control signals SU1, SU2, SU6, load current iU, current i9U flowing from the resonant capacitor 9U, and voltage V2u across the second switching element 2U are shown. In addition, Figure 8 A dead time period Td is also shown in FIG.

[0102] If the current value of the load current is less than the second current threshold value I2 (in other words, if the absolute value of the load current is greater than the absolute value of the second current threshold value I2), the controller 50 does not set any high level period to the control signal SU6. In this case, in the power converter 100, the current i9U starts to flow through the resonant capacitor 9U at the start time (time t41) of the dead time period Td. As a result, in the power converter 100, the resonant capacitor 9U is charged so that the voltage V2u across the second switching element 2U increases. The current i9U becomes zero before the end time (time t42) of the dead time period Td, and the voltage V1u across the first switching element 1 becomes zero before the end time (time t42) of the dead time period Td. Thus, in the power converter 100, when the control signal SU1 changes from a low level to a high level at the end time (time t42) of the dead time period Td, the first switching element 1 undergoes zero voltage soft switching.

[0103] If the current value of the load current is greater than the second current threshold value I2 (in other words, if the absolute value of the load current is less than the absolute value of the second current threshold value), then, for example, Figure 8As shown in the double dotted line, the controller 50 sets a high level period to the control signal SU6. In this case, the start time of the high level period of the control signal SU6 can be simultaneous with, for example, the start time (time t41) of the dead time period Td. In addition, the end time of the high level period of the control signal SU6 is simultaneous with the end time (time t42) of the dead time period Td. Thus, in the power converter 100, the voltage V1u across the first switching element 1U becomes zero before the end time (time t42) of the dead time period Td. Therefore, in the power converter 100, when the control signal SU1 changes from a low level to a high level at the end time (time t42) of the dead time period Td, the first switching element 1 undergoes zero voltage soft switching.

[0104] (3.1.2) Offset control operation

[0105] When it is determined that the resonant currents respectively passing through two switches among the plurality of switches 8 flow through the resonant inductor L1 at the same time, the controller 50 performs offset control that offsets the high level period of the control signal for one of the two switches 8 to prevent the resonant currents respectively passing through the two switches 8 from flowing through the resonant inductor L1 at the same time. As used herein, the expression “when it is determined that the resonant currents respectively passing through two switches among the plurality of switches 8 flow at the same time” refers to a situation where it has been pre-assumed that the resonant currents respectively passing through the two switches 8 will flow through the resonant inductor L1 at the same time.

[0106] (3.1.2.1) Determine whether the two-phase resonant current flows simultaneously

[0107] In the power converter 100, the phases of the three-phase (i.e., U-phase, V-phase, and W-phase) voltage commands are different from each other by 120 degrees, but the command values ​​of the two-phase voltage commands are close to each other every 60 degrees in electrical angle, and the duty ratios of the two-phase control signals are close to each other (refer to Figure 4 Specifically, in the area A1, A2 shown in Figure 4 In the region A1 shown in FIG. 1 , the duty ratio of the U-phase control signal and the duty ratio of the V-phase control signal become approximately 0.75. Figure 4 In the region A2 shown, the duty ratio of the U-phase control signal and the duty ratio of the V-phase control signal become about 0.25. The polarity of the resonant current is the same as the polarity of the current iL1. In the region A1, the polarity of the resonant current is positive. In the region A2, the polarity of the resonant current is negative. In the region A1, the start time of the high level period of the control signal SU6 to be applied to the first IGBT 6U (time t1; reference numeral t2) is t3. Figure 2 ) and the start time of the high level period of the control signal SV6 to be applied to the first IGBT 6V (time t5; refer to Figure 2) The time lag between them becomes so short, for example, within one cycle time of the carrier signal, that the U-phase resonant current and the V-phase resonant current can flow through the resonant inductor L1 simultaneously. In the power converter 100, the direction of the resonant current in region A2 is opposite to that in region A1, but the U-phase resonant current and the V-phase resonant current can flow through the resonant inductor L1 simultaneously.

[0108] Assume that the capacitance of each of the plurality of resonant capacitors 9U, 9V, and 9W is C. If the U-phase current and the V-phase current flow through the resonant inductor L1 simultaneously, then in the equivalent circuit, a capacitor having a combined capacitance (=2×C) of the resonant capacitor 9U and the resonant capacitor 9V is connected in series to the resonant inductor L1. Thus, in the power converter 100, if two-phase currents flow through the resonant inductor L1 simultaneously, the resonant frequency of the resonant circuit including the resonant inductor L1 changes compared with the case where a single-phase current flows through the resonant inductor L1. Therefore, the power converter 100 may not be able to perform zero-voltage soft switching.

[0109] (3.1.2.1.1) When performing a charging operation on the resonant capacitor

[0110] Figure 2 Exemplary boundary conditions between the case where the U-phase resonant current and the V-phase resonant current do not overlap with each other (i.e., do not flow simultaneously) and the case where the U-phase resonant current and the V-phase resonant current overlap with each other (i.e., flow simultaneously) are shown. Reference will be made to Figure 2 describe the boundary conditions.

[0111] In the power converter 100, if the time lag ΔTuv between the start time (time t3) of the high level period of the control signal SU1 and the start time (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 with each other. On the other hand, if the time lag ΔTuv is less than (Tau+Tav+Td), the U-phase resonant current and the V-phase resonant current overlap with each other. That is, in the case where the threshold value for the time lag ΔTuv is set to (Tau+Tav+Td), if the time lag ΔTuv is less than the threshold value, the controller 50 assumes that the resonant current corresponding to the two phases of the switching circuit 10U and the switching circuit 10V belonging to the plurality of switching circuits 10 will flow through the resonant inductor L1 at the same time. Note that the threshold value is only an example, and the threshold value may also be set to any other value. For example, in the case where the error of the additional time Tau and the error of the additional time Tav are taken into account, the threshold value may also be set to a value even greater than (Tau+Tav+Td). Alternatively, the controller 50 may also set the threshold for the time lag ΔTuv to be the same value as, for example, the resonant half-cycle (in this embodiment, the resonant half-cycle = the dead time period Td). In this case, if the time lag ΔTuv is less than the length of the dead time period Td, the controller 50 assumes that the resonant currents corresponding to the two phases of the switching circuits 10U and 10V will flow through the resonant inductor L1 at the same time. In addition, the above method for calculating the time lag ΔTuv to determine whether the two-phase resonant currents flow simultaneously is only an example. On the contrary, any other calculation method may be used as long as the time lag corresponding to the above-mentioned time lag can be calculated. For example, as the time lag ΔTuv used to determine whether the two-phase resonant currents flow simultaneously, the time lag between the end time (time t2) of the high level period of the control signal SU2 and the end time (time t6) of the high level period of the control signal SV2 may also be used.

[0112] In the power converter 100, if the time lag between the start time (time t3) of the high level period of the control signal SU1 and the start time (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 with each other. On the other hand, if the time lag is less than (Tau+Taw+Td), the U-phase resonant current and the W-phase resonant current overlap with each other. That is, in the case where the threshold for the time lag is set to (Tau+Taw+Td), if the time lag is less than the threshold, the controller 50 assumes that the resonant current corresponding to the two phases of the switching circuit 10U and the switching circuit 10W belonging to the plurality of switching circuits 10 will flow through the resonant inductor L1 at the same time. Note that the threshold is only an example, and the threshold may also be set to any other value. For example, in the case where the error of the additional time Tau and the error of the additional time Taw are taken into account, the threshold may also be set to a value even greater than (Tau+Taw+Td). In addition, the controller 50 can set the threshold value for the time lag to the same value as, for example, the resonant half cycle (in this embodiment, the resonant half cycle = the dead time period Td). In this case, if the time lag is less than the length of the dead time period Td, the controller 50 assumes that the resonant currents corresponding to the two phases of the switching circuits 10U and 10W will flow through the resonant inductor L1 at the same time. In addition, the above method for calculating the time lag to determine whether the two-phase resonant currents flow simultaneously is only an example. On the contrary, any other calculation method can also be used as long as the time lag corresponding to the above-mentioned time lag can be calculated. For example, as a time lag for determining whether the two-phase resonant currents flow simultaneously, the time lag between the end time (time t2) of the high level period of the control signal SU2 and the end time (time t10) of the high level period of the control signal SW2 can also be used.

[0113] In the power converter 100, if the time lag between the start time (time t7) of the high level period of the control signal SV1 to be applied to the first switching element 1V of the switching circuit 10V and the start time (time t11) of the high level period of the control signal SW1 to be applied to the first switching element 1W of the switching circuit 10W is equal to or greater than (Tav+Taw+Td), the V-phase resonant current and the W-phase resonant current do not overlap with each other. On the other hand, if the time lag is less than (Tav+Taw+Td), the V-phase resonant current and the W-phase resonant current overlap with each other. That is, in the case where the threshold value for the time lag is set to (Tav+Taw+Td), if the time lag is less than the threshold value, the controller 50 assumes that the resonant current corresponding to the two phases of the switching circuit 10V and the switching circuit 10W belonging to the plurality of switching circuits 10 will flow through the resonant inductor L1 at the same time. Note that the threshold value is only an example, and the threshold value may also be set to any other value. For example, the threshold value may also be set to a value even greater than (Tav+Taw+Td) in consideration of the error of the additional time Tav and the error of the additional time Taw. In addition, the controller 50 may set the threshold value for the time lag to the same value as, for example, the resonant half cycle (in this embodiment, the resonant half cycle = the dead time period Td). In this case, if the time lag is less than the length of the dead time period Td, the controller 50 assumes that the resonant current corresponding to the two phases of the switching circuit 10V and 10W will flow through the resonant inductor L1 at the same time. In addition, the above method for calculating the time lag to determine whether the two-phase resonant current flows simultaneously is only an example. On the contrary, any other calculation method may be used as long as the time lag corresponding to the above time lag can be calculated. For example, as a time lag for determining whether the two-phase resonant current flows simultaneously, the time lag between the end time (time t6) of the high level period of the control signal SV2 and the end time (time t10) of the high level period of the control signal SW2 may also be used.

[0114] (3.1.2.1.2) When discharging the resonant capacitor

[0115] When performing the discharge operation on the resonance capacitor 9 , the controller 50 can also judge whether the two-phase resonance currents flow simultaneously using the same time lag and threshold as in the case of performing the charging operation on the resonance capacitor 9 .

[0116] For example, if the time lag between the start time of the high level period of the control signal SU2 and the start time of the high level period of the control signal SV2 is less than a threshold value (e.g., Tau+Tav+Td), the controller 50 assumes that the U-phase resonant current and the V-phase resonant current will overlap with each other.

[0117] In addition, if the time lag between the start time of the high level period of the control signal SU2 and the start time of the high level period of the control signal SW2 is less than a threshold value (e.g., Tau+Taw+Td), the controller 50 assumes that the U-phase resonant current and the W-phase resonant current will overlap with each other.

[0118] Furthermore, if the time lag between the start time of the high level period of the control signal SV2 and the start time of the high level period of the control signal SW2 is less than a threshold value (eg, Tav+Taw+Td), the controller 50 assumes that the V-phase resonant current and the W-phase resonant current will overlap with each other.

[0119] (3.1.2.2) Offset control to be performed when it is determined that two-phase resonant currents flow simultaneously

[0120] The controller 50 performs offset control that offsets a high level period of a control signal for one of the two switches 8 to prevent the resonant currents respectively passing through the two switches 8 from flowing through the resonant inductor L1 at the same time, for example.

[0121] When performing the offset control, the controller 50 offsets the high level period of the control signal for one of the two switches 8 to prevent the length of the high level period of the control signal to be applied to each of the first switching element 1 and the second switching element 2 of the switching circuit 10 corresponding to the one switch 8 from changing. For example, when the high level period of the control signal SU6 or SU7 to be applied to the switch 8U is offset, the controller 50 offsets the respective high level periods of the control signals SU1 and SU2, but does not change the duty cycle of any one of the control signals SU1 and SU2 in one cycle of the carrier signal. Similarly, when the high level period of the control signal SV6 or SV7 to be applied to the switch 8V is offset, the controller 50 offsets the respective high level periods of the control signals SV1 and SV2, but does not change the duty cycle of any one of the control signals SV1 and SV2 in one cycle of the carrier signal. In the same manner, when shifting the high level period of the control signal SW6 or SW7 to be applied to the switch 8W, the controller 50 shifts the respective high level periods of the control signals SW1, SW2, but does not change the duty cycle of either of the control signals SW1, SW2 in one cycle of the carrier signal.

[0122] In the power converter 100, if the controller 50 has performed offset control to perform soft switching of the first switching element 1, the voltage V2u, V2v across the second switching element 2U, 2V increases to Vd at a time point when, for example, the control signal SU1, SV1 changes from a low level period to a high level period (i.e., the end of the dead time period Td corresponding to each of the U phase and the V phase). That is, if the controller 50 has performed offset control, the resonant capacitor 9U, 9V is fully charged at the end of the dead time period Td corresponding to each of the U phase and the V phase. Thus, in the power converter 100, if the controller 50 has performed offset control, the first switching element 1U, 1V is switched by zero voltage soft switching.

[0123] In this example, it is described how the controller 50 performs offset control when it is pre-determined that the U-phase resonant current and the V-phase resonant current will flow through the resonant inductor L1 at the same time. However, this is only an example and should not be interpreted as limiting. For example, even when the controller 50 pre-determines that the V-phase resonant current and the W-phase resonant current will flow through the resonant inductor L1 at the same time or the W-phase resonant current and the U-phase resonant current will flow through the resonant inductor L1 at the same time, the controller 50 can perform zero voltage soft switching by performing offset control.

[0124] In the power converter 100, if the controller 50 has performed offset control to perform soft switching of the second switching element 2, for example, at the time point when the control signals SU2, SV2 change from the low level period to the high level period (i.e., the dead time period Td corresponding to each of the U phase and the V phase ends), the voltage V1u, V1v across the first switching element 1U, 1V increases to Vd. That is, if the controller 50 has performed offset control, at the end of the dead time period Td corresponding to each of the U phase and the V phase, the resonant capacitor 9U, 9V is completely discharged. Thus, in the power converter 100, if the controller 50 has performed offset control, the second switching element 2U, 2V is switched by zero voltage soft switching.

[0125] In this example, it is described how the controller 50 performs offset control when it is pre-determined that the U-phase resonant current and the V-phase resonant current will flow through the resonant inductor L1 at the same time. However, this is only an example and should not be interpreted as limiting. For example, even when the controller 50 pre-determines that the V-phase resonant current and the W-phase resonant current will flow through the resonant inductor L1 at the same time or the W-phase resonant current and the U-phase resonant current will flow through the resonant inductor L1 at the same time, the controller 50 can perform zero voltage soft switching by performing offset control.

[0126] (3.2) How the power converter operates when the controller performs charging control operation as a startup operation

[0127] When the power converter 100 is started, the controller 50 charges the regenerative capacitor 15 to shorten the time. Fig. 9 The charging control operation of the regeneration capacitor 15 shown is for the amount of time Ts it takes for the voltage V15 across the regeneration capacitor 15 to increase from 0V to the threshold value Vth. For example, the threshold value Vth may be Vd / 2. However, this is merely an example and should not be construed as limiting. Alternatively, the threshold value Vth may also be equal to or greater than 90% of Vd / 2 and equal to or less than 110% of Vd / 2, and preferably equal to or greater than 95% of Vd / 2 and equal to or less than 105% of Vd / 2. In the power converter 100 according to the first embodiment, the controller 50 can shorten the amount of time Ts it takes for the voltage V15 across the regeneration capacitor 15 to increase from 0V to the threshold value Vth, compared to a situation where the controller 50 has performed an inverter control operation without performing a charging control operation. For example, the power converter 100 according to this embodiment can shorten the time Ts from 13.5ms to 2.8ms. Note that, Fig. 9 The DC bus voltage shown is the voltage between the first DC terminal 31 and the second DC terminal 32 .

[0128] As the charging control operation, the controller 50 performs the first control operation and the second control operation alternately.

[0129] When performing the first control operation, the controller 50 turns on the plurality of (for example, three) first switching elements 1 to charge the plurality of (for example, three) resonance capacitors 9 via the path passing through the first DC terminal 31 and the plurality of (three) first switching elements 1. On the other hand, when performing the second control operation, the controller 50 turns on the plurality of (for example, three) switches 8 to charge the regenerative capacitor 15 with the charge supplied from the plurality of (for example, three) resonance capacitors 9.

[0130] Next, we will refer to Figures 10 to 12 The first control operation and the second control operation are described in more detail. Fig.11 and Fig.12 middle, Figure 1 The circuit diagram of FIG. 1 is in a partially omitted and simplified form, and each of the three first switching elements 1 , the three second switching elements 2 , and the three switches 8 is designated by a circuit symbol of the switch.

[0131] When performing the first control operation, the controller 50 controls the three first switching elements 1 toward the on state, controls the three second switching elements 2 toward the off state, and controls the three switches 8 toward the off state.

[0132] More specifically, the controller 50 performs the following operations, for example: Fig.10As in the first period T1 shown in FIG. 1 , each of the three control signals SU1, SV1, and SW1 has a high level, each of the three control signals SU2, SV2, and SW2 has a low level, and the three control signals SU6, SV6, and SW6 ( Fig.10 Each of the three control signals SU7, SV7, and SW7 has a low level, and each of the three control signals SU7, SV7, and SW7 has a low level to perform the first control operation. This enables the three resonant capacitors 9U, 9V, and 9W to utilize the Fig.11 The currents flowing from the DC power source E1 through the three first switching elements 1 are shown in FIG. Fig.11 to charge. Fig.10 In FIG. 1 , “charging current of the resonance capacitor” indicates the current waveform of the current (charging current) flowing from the DC power supply E1 through the three resonance capacitors 9U, 9V, 9W, respectively.

[0133] On the other hand, the controller 50 performs the second control operation by controlling the three first switching elements 1 toward the OFF state, the three second switching elements 2 toward the OFF state, and the three switches 8 toward the ON state.

[0134] More specifically, the controller 50 performs the following operations, for example: Fig.10 As in the second period T2 shown in FIG. 1 , each of the three control signals SU1, SV1, and SW1 has a low level, each of the three control signals SU2, SV2, and SW2 has a low level, and the three control signals SU6, SV6, and SW6 ( Fig.10 Each of the three control signals SU7, SV7, and SW7 has a low level, and each of the three control signals SU7, SV7, and SW7 has a high level to perform the second control operation. This enables the regenerative capacitor 15 to utilize the Fig.12 As shown, the three resonant capacitors 9U, 9V, 9W are charged by current flowing through the three switches 8U, 8V, 8W, respectively. That is, the controller 50 discharges the resonant capacitors 9U, 9V, 9W and charges the regenerative capacitor 15 by performing the second control operation. Fig.10 In FIG. 1 , “discharge current of the resonant capacitor” indicates the current waveform of the current (discharge current) flowing through the regenerative capacitor 15 from the three resonant capacitors 9U, 9V, 9W, respectively.

[0135] In the power converter 100 according to the first embodiment, even when the charging control operation is performed, the controller 50 sets a dead time period Td between the high level period of each of the three control signals SU1, SV1, SW1 and the high level period of the corresponding control signal in the control signals SU2, SV2, SW2. In this case, the controller 50 performs the first control operation by complementarily turning on and off the three first switching elements 1 and the three second switching elements 2. In addition, in the case where the dead time period Td in which both the three first switching elements 1 and the three second switching elements 2 are turned off is defined as the second time period T2, the controller 50 performs the second control operation by turning on the plurality of switches 8.

[0136] That is, the controller 50 sets the dead time period Td between the high level period of the control signal SU1 of the first switching element 1U and the high level period of the control signal SU2 of the second switching element 2U, and sets the high level period of the control signal SU7 of the second IGBT 7U of the switch 8U in the dead time period Td. In the same way, the controller 50 sets the dead time period Td between the high level period of the control signal SV1 of the first switching element 1V and the high level period of the control signal SV2 of the second switching element 2V, and sets the high level period of the control signal SV7 of the second IGBT 7V of the switch 8V in the dead time period Td. In the same way, the controller 50 sets the dead time period Td between the high level period of the control signal SW1 of the first switching element 1W and the high level period of the control signal SW2 of the second switching element 2W, and sets the high level period of the control signal SW7 of the second IGBT 7W of the switch 8W in the dead time period Td.

[0137] (4) Overview

[0138] In the power converter 100 according to the first embodiment, the controller 50 performs a charging control operation including charging the regenerative capacitor 15 as a startup operation, and also performs an inverter control operation including causing the output current iU, iV, iW to flow through each of the plurality of AC terminals 41. The controller 50 alternately performs a first control operation and a second control operation as a charging control operation. The first control operation includes turning on a plurality of (e.g., three) first switching elements 1, thereby charging a plurality of (e.g., three) resonant capacitors 9 via a path passing through the first DC terminal 31 and each of the plurality of (e.g., three) first switching elements 1. The second control operation includes turning on a plurality of (e.g., three) switches 8, thereby charging the regenerative capacitor 15 with the charge supplied from the plurality of (e.g., three) resonant capacitors 9.

[0139] The power converter 100 according to the first embodiment can contribute to miniaturization. More specifically, the power converter 100 according to the first embodiment can reduce the number of regenerative capacitors 15 to be used to one, thereby contributing to miniaturization.

[0140] On the other hand, the power converter 100 according to the first embodiment adopts a configuration that uses a single regenerative capacitor 15 to generate a voltage of Vd / 2. Therefore, when the power converter 100 is started, the voltage V15 across the regenerative capacitor 15 is transiently increased to Vd / 2. Thus, in the power converter 100, if the controller 50 performs an inverter control operation without performing a charging control operation, each of the plurality of first switching elements 1 and the plurality of second switching elements 2 can be switched by hard switching during the inverter control operation. In contrast, in the power converter 100 according to the first embodiment, the controller 50 can not only shorten the time taken to increase the voltage V15 across the regenerative capacitor 15 to Vd / 2 by performing a charging control operation, but also prevent each of the plurality of first switching elements 1 and the plurality of second switching elements 2 from switching by hard switching during the inverter control operation.

[0141] In addition, in the power converter 100 according to the first embodiment, the controller 50 does not perform the inverter control operation until the voltage V15 across the regenerative capacitor 15 has become equal to or greater than the threshold value Vth. Thus, the power converter 100 can reduce the possibility that each of the plurality of first switching elements 1 and the plurality of second switching elements 2 is hard-switched during the inverter control operation. In other words, the power converter 100 can perform soft switching more reliably. Thus, the power converter 100 enables an element with a lower breakdown voltage and a lower allowable current to be used as each of the plurality of first switching elements 1 and the plurality of second switching elements 2, thereby contributing to cost reduction.

[0142] Furthermore, in the power converter 100 according to the first embodiment, when it is determined that the resonant currents respectively passing through two switches 8 belonging to the plurality of switches 8 will flow through the resonant inductor L1 at the same time, the controller 50 performs control to shift the high level period of the control signal of each of the two switches 8 to prevent the resonant currents respectively passing through the two switches 8 from flowing through the resonant inductor L1 at the same time. This enables the power converter 100 to perform soft switching more reliably.

[0143] (5) Modification of the First Embodiment

[0144] (5.1) First Modification

[0145] Reference Fig.13A power converter 100 according to a first modification example is described. In the following description, the power converter 100 according to the first modification example has the same features as the power converter 100 according to the first embodiment described above (refer to Figure 1 ) will be designated by the same figure mark as the figure mark of the corresponding part, and its description will be omitted herein.

[0146] In the power converter 100 according to the first modification, in each of the plurality of switches 8, the first IGBT 6 and the second IGBT 7 thereof are connected in anti-series. In the power converter 100 according to the first modification, in each of the plurality of switches 8, the collector terminal of the first IGBT 6 and the collector terminal of the second IGBT 7 are connected to each other, the emitter terminal of the first IGBT 6 is connected to the connection node 3 of the corresponding switching circuit 10 in the plurality of switching circuits 10, and the emitter terminal of the second IGBT 7 is connected to the common connection node 25. In addition, 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.

[0147] In the power converter 100 according to the first modification, each of the first IGBT 6 and the second IGBT 7 may be replaced by a MOSFET or a bipolar transistor. In this case, Fig.13 The diode 61 and the diode 71 shown can each be replaced by, for example, a parasitic diode of a replacement element or an element built into one chip of the replacement element. In addition, in the power converter 100 according to the first modification, the diode 61 and the diode 71 do not necessarily have to be provided as external elements of the first IGBT 6 and the second IGBT 7, respectively, but can also be elements built into one chip.

[0148] The controller 50 may operate in the same manner as, for example, the controller 50 according to the first embodiment.

[0149] (5.2) Second Modification

[0150] Reference Fig.14 A power converter 100 according to a second modification example will be described. In the following description, the power converter 100 according to the second modification example has the same features as the power converter 100 according to the first embodiment described above (see Figure 1 ) will be designated by the same figure mark as the figure mark of the corresponding part, and its description will be omitted herein.

[0151] In the power converter 100 according to the second modification, in each of the plurality of switches 8, the first IGBT 6 and the second IGBT 7 thereof are connected in anti-series. In the power converter 100 according to the second modification, in each of the plurality of switches 8, the emitter terminal of the first IGBT 6 and the emitter terminal of the second IGBT 7 are connected to each other, the collector terminal of the second IGBT 7 is connected to the connection node 3 of the corresponding switching circuit in the plurality of switching circuits 10, and the collector terminal of the first IGBT 6 is connected to the common connection node 25. In addition, 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.

[0152] In the power converter 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, Fig.14 The diode 61 and the diode 71 shown can each be replaced with, for example, a parasitic diode of a replacement element or an element built into one chip of the replacement element. In addition, in the power converter 100 according to the second modification, the diode 61 and the diode 71 do not necessarily have to be provided as external elements of the first IGBT 6 and the second IGBT 7, respectively, but can also be elements built into one chip.

[0153] The controller 50 may operate in the same manner as, for example, the controller 50 according to the first embodiment.

[0154] (5.3) Third Modification

[0155] Reference Fig.15 A power converter 100 according to a third modification example will be described. In the following description, the power converter 100 according to the third modification example has the same features as the power converter 100 according to the first embodiment described above (see Figure 1 ) will be designated by the same figure mark as the figure mark of the corresponding part, and its description will be omitted herein.

[0156] In the power converter 100 according to the third modification, in each of the plurality of switches 8, the first MOSFET 6A and the second MOSFET 7A are connected in anti-series. In the power converter 100 according to the third modification, in each of the plurality of switches 8, the drain terminal of the first MOSFET 6A and the drain terminal of the second MOSFET 7A are connected to each other. In addition, each of the plurality of 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 plurality of switches 8, the source terminal of the second MOSFET 7A is connected to the common connection node 25. In each of the plurality of switches 8, the source terminal of the first MOSFET 6A is connected to the connection node 3 of the switching circuit 10 corresponding to the switch 8 including the first MOSFET 6A. Control signals SU6 and SU7 are applied from the controller 50 to the first MOSFET 6A and the second MOSFET 7A of the switch 8U, respectively. Control signals SV6 and SV7 are applied from the controller 50 to the first MOSFET 6A and the second MOSFET 7A of the switch 8V, respectively. Control signals SW6, SW7 are applied from the controller 50 to the first MOSFET 6A and the second MOSFET 7A of the switch 8W, respectively.

[0157] The controller 50 may operate in the same manner as, for example, the controller 50 according to the first embodiment.

[0158] (5.4) Fourth Modification

[0159] Will refer to Fig.16 A power converter 100 according to a fourth modification will be described. In the following description, the power converter 100 according to the fourth modification has the same features as the power converter 100 according to the first embodiment described above (see Figure 1 ) will be designated by the same figure mark as the figure mark of the corresponding part, and its description will be omitted herein.

[0160] In the power converter 100 according to the fourth modification, the diode 63 is connected in series to the first MOSFET 6A, and the diode 73 is connected in series to the second MOSFET 7A in each of the plurality of switches 8. In the power converter 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 to each other.

[0161] The controller 50 may operate in the same manner as, for example, the controller 50 according to the first embodiment.

[0162] (5.5) Fifth Modification

[0163] Reference Fig.17 A power converter 100 according to a fifth modification example will be described. In the following description, the power converter 100 according to the fifth modification example has the same structure as the power converter 100 according to the first embodiment described above (refer to Figure 1 ) will be designated by the same figure mark as the figure mark of the corresponding part, and its description will be omitted herein.

[0164] In the power converter 100 according to the fifth modification, each of the plurality of switches 8 includes: a MOSFET 80; a diode 83, which is connected in anti-parallel to the MOSFET 80; a series circuit of two diodes 84, 85, which are connected in anti-parallel to the MOSFET 80; and a series circuit of two diodes 86, 87, which are connected in anti-parallel to the MOSFET 80. In each of the plurality of switches 8, a connection node between the diodes 84, 85 in the switch 8 (i.e., a first end 81 of the switch 8) is connected to a connection node 3 of a corresponding switching circuit 10 in the plurality of switching circuits 10, and a connection node between the diodes 86, 87 (i.e., a second end 82 of the switch 8) is connected to a common connection node 25. In each of the plurality of switches 8, when the MOSFET 80 is turned on, the switch 8 is turned on. On the other hand, when the MOSFET 80 is turned off, the switch 8 is turned off.

[0165] The MOSFETs 80 of the plurality of switches 8 are controlled by the controller 50. The controller 50 outputs a control signal SU8 for controlling the on / off state of the MOSFET 80 of the switch 8U, a control signal SV8 for controlling the on / off state of the MOSFET 80 of the switch 8V, and a control signal SW8 for controlling the on / off state of the MOSFET 80 of the switch 8W.

[0166] In each of the switches 8, when the MOSFET 80 thereof is turned on, a resonant current generated by the resonant circuit including the resonant inductor L1 and the resonant capacitor 9 flows. In the power converter 100, when one of the plurality of switches 8 is turned on, a charging current including the resonant current flows along a path that passes through the regenerative capacitor 15, the resonant inductor L1, the diode 86, the MOSFET 80, the diode 85, and the resonant capacitor 9 in sequence. Furthermore, in the power converter 100, when one of the plurality of switches 8 is turned on, a discharging current including the resonant current flows along a path that passes through the resonant capacitor 9, the diode 84, the MOSFET 80, the diode 87, the resonant inductor L1, and the regenerative capacitor 15 in sequence.

[0167] In the power converter 100 according to the fifth modification, each of the plurality of MOSFETs 80 may be replaced by an IGBT. In addition, in the power converter 100 according to the fifth modification, each of the plurality of switches 8 may include, for example, a bipolar transistor or a GaN-based gate injection transistor (GIT) to replace the MOSFET 80.

[0168] The controller 50 may operate in the same manner as, for example, the controller 50 according to the first embodiment.

[0169] (5.6) Sixth Modification

[0170] Reference Fig.18 A power converter 100 according to a sixth modification example will be described. In the following description, the power converter 100 according to the sixth modification example has the same features as the power converter 100 according to the first embodiment described above (refer to Figure 1 ) will be designated by the same figure mark as the figure mark of the corresponding part, and its description will be omitted herein.

[0171] In the power converter 100 according to the sixth modification, each of the plurality of switches 8 is a dual-gate GaN-based GIT including a first source terminal, a first gate terminal, a second gate terminal, and a second source terminal. In the power converter 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 used as a switch 8U, and a control signal SU7 is applied between the second gate terminal and the second source terminal of the dual-gate GaN-based GIT. In addition, a control signal SV6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT used as a switch 8V, and a control signal SV7 is applied between the second gate terminal and the second source terminal of the dual-gate GaN-based GIT. In addition, a control signal SW6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT used as a switch 8W, and a control signal SW7 is applied between the second gate terminal and the second source terminal of the dual-gate GaN-based GIT.

[0172] The controller 50 may operate in the same manner as, for example, the controller 50 according to the first embodiment.

[0173] (Second embodiment)

[0174] Reference Fig.19 A power converter 100A according to a second embodiment will be described. In the following description, the power converter 100A according to the second embodiment has the same features as the power converter 100 according to the first embodiment described above (refer to Figure 1) will be designated by the same figure mark as the figure mark of the corresponding part, and its description will be omitted herein.

[0175] The power converter 100A includes a plurality of (for example, three) switches 8 provided one-to-one. Fig.19 In the example shown, there are three) resonant inductors L1. The third end of each of the plurality of resonant inductors L1 is connected to the second end 82 of the corresponding switch in the plurality of switches 8. On the other hand, each of the fourth ends of the plurality of resonant inductors L1 is commonly connected to the sixth end 154 of the regenerative capacitor 15. The inductances of the plurality of resonant inductors L1 are equal to one another. Specifically, the respective inductances of the three resonant inductors L1 are equal to one another. As used herein, the expression "the respective inductances of the three resonant inductors L1 are equal to one another" refers not only to the case where the respective inductances of two of the three resonant inductors L1 are exactly equal to the inductance of another resonant inductor L1, but also to the case where the inductance of each of the two resonant inductors L1 is equal to or greater than 95% of the inductance of the other resonant inductor L1 and equal to or less than 105% of the inductance of the other resonant inductor L1.

[0176] In power converter 100A according to the second embodiment, controller 50 also performs a charge control operation as an operation at startup of power converter 100A as in power converter 100 according to the first embodiment. In addition, controller 50 performs an inverter control operation after having performed the charge control operation.

[0177] As with the power converter 100 according to the first embodiment, the power converter 100A according to the second embodiment can also reduce the number of regenerative capacitors 15 to one, thereby contributing to miniaturization.

[0178] (Other Modifications)

[0179] Note that the above-mentioned first embodiment and second embodiment and their variants are merely exemplary embodiments and their variants among various embodiments of the present disclosure and should not be interpreted as limiting. On the contrary, the first embodiment to the second embodiment and their variants can be easily modified in various ways according to design selection or any other factors without departing from the scope of the present disclosure.

[0180] For example, when performing the first control operation, the controller 50 can cause at least one first switching element 1 (for example, the first switching element 1U) among the multiple first switching elements 1 to become conductive so as to charge at least one resonant capacitor 9 (for example, the resonant capacitor 9U) belonging to the multiple resonant capacitors 9 and corresponding to the at least one first switching element 1 via a path through the first DC terminal 31 and the at least one first switching element 1.

[0181] On the other hand, when performing the second control operation, the controller 50 can turn on a switch 8 (for example, switch 8U) belonging to a plurality of switches 8 corresponding to at least one first switching element 1 to charge the regeneration capacitor 15 using the charge supplied from at least one resonant capacitor 9.

[0182] In addition, when performing the second control operation, the controller 50 can turn on a switch 8 corresponding to the at least one first switching element 1 belonging to a plurality of switches 8 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 (for example, the second switching element 2U) corresponding one to the at least one first switching element 1 are turned off.

[0183] For example, when performing the first control operation, the controller 50 may turn on the first switching element 1U to charge the resonance capacitor 9U via the path passing through the first DC terminal 31 and the first switching element 1U. In this case, when performing the second control operation, the controller 50 may turn on the switch 8U to charge the regenerative capacitor 15 with the charge supplied from the resonance capacitor 9U. Furthermore, in this case, when performing the second control operation, the controller 50 may turn on the switch 8U in the dead time period Td in which both the first switching element 1U and the second switching element 2U are turned off.

[0184] The operation for “determining that two-phase resonant currents flow simultaneously” performed by the controller 50 is not limited to the operation for “determining that two-phase resonant currents flow simultaneously” when the time lag is smaller than the threshold value as has been described in the first embodiment.

[0185] For example, if 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 the current difference threshold, the controller 50 can determine that the two-phase resonant currents are flowing simultaneously.

[0186] Alternatively, if the electrical angle determined or estimated by calculation based on sensor information provided by a sensor device for checking the number of motor revolutions (such as an encoder or a rotary transformer, etc.) falls within a first rotation angle range (e.g., equal to or greater than 55 degrees and equal to or less than 65 degrees), or a second rotation angle range (e.g., equal to or greater than 115 degrees and equal to or less than 125 degrees), or a third rotation angle range (e.g., equal to or greater than 175 degrees and equal to or less than 185 degrees), or a fourth rotation angle range (e.g., equal to or greater than 235 degrees and equal to or less than 245 degrees), or a fifth rotation angle range (e.g., equal to or greater than 295 degrees and equal to or less than 305 degrees), or a sixth rotation angle range (e.g., equal to or greater than 355 degrees and equal to or less than 365 degrees), the controller 50 can determine that "two-phase resonant currents flow simultaneously."

[0187] For example, each of the plurality of first switching elements 1 and the plurality of second switching elements 2 does not necessarily have to be an IGBT, but may also be a MOSFET. In this case, each of the plurality of first diodes 4 may also be replaced by, for example, a parasitic diode of a MOSFET used as its corresponding first switching element 1. In addition, each of the plurality of second diodes 5 may also be replaced by, for example, a parasitic diode of a MOSFET used as its corresponding second switching element 2. The MOSFET may be, 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 also be, for example, a bipolar transistor or a GaN-based GIT.

[0188] Optionally, in the power converter 100, 100A, if each of the multiple resonant capacitors 9 has a relatively small capacitance, parasitic capacitors across the multiple second switching elements 2 can also be used as multiple resonant capacitors 9 instead of setting the multiple resonant capacitors 9 as separate elements.

[0189] Furthermore, the length of the dead time period Td need not necessarily be as long as one resonance half cycle, but may also be set to be different from one resonance half cycle. However, in any case, the end of the dead time period Td preferably coincides with the end of the resonance half cycle.

[0190] The dead time period Td may also be set by a dead time generator circuit included in a gate driver integrated circuit (IC) provided separately from the controller 50. Alternatively, the controller 50 may include a gate driver IC, and the dead time generator circuit included in the gate driver IC may set the dead time period Td.

[0191] Furthermore, the power converter 100 , 100A does not necessarily have to be configured to output three-phase AC power, and may be configured to output multi-phase AC power having more than three phases.

[0192] (All aspects)

[0193] The foregoing description provides specific implementations of the following aspects of the present disclosure.

[0194] A power converter (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 controller (50). The power conversion circuit (11) includes 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, and in each of the plurality of switching circuits (10), one first switching element (1) of the plurality of first switching elements (1) and a corresponding second switching element (2) of the plurality of second switching elements (2) are connected in series one-to-one. 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) are provided one-to-one for the plurality of switching circuits (10). Each of the plurality of AC terminals (41) is connected to a connection node (3) between a first switching element (1) and a second switching element (2) of a corresponding switching circuit (10) in the plurality of switching circuits (10). The plurality of switches (8) are provided one-to-one for the plurality of switching circuits (10). Each of the plurality of switches (8) has a first end (81) and a second end (82). The first end (81) of each of the plurality of switches (8) is connected to a connection node (3) between the first switching element (1) and the second switching element (2) of a corresponding switching circuit (10) in the plurality of switching circuits (10). The plurality of resonant capacitors (9) are provided one-to-one for the plurality of switches (8). Each of the plurality of resonant capacitors (9) is connected between a second DC terminal (32) and a first end (81) of a corresponding switch in the plurality of switches (8). The 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 switch in the plurality of switches (8). The regenerative capacitor (15) has a fifth end (153) and a sixth end (154). The fifth end (153) of the regenerative capacitor (15) is connected to the second DC terminal (32). The sixth end (154) of the regenerative capacitor (15) is connected to the fourth end of at least one resonant inductor (L1). The controller (50) controls the on / off state of each of the plurality of first switching elements (1), the plurality of second switching elements (2) and the plurality of switches (8). The controller (50) performs a charging control operation including charging the regenerative capacitor (15) as a startup operation, and also performs an inverter control operation including causing an output current (iU, iV, iW) to flow through each of the plurality of AC terminals (41). The controller (50) alternately performs the first control operation and the second control operation as the charging control operation.The first control operation includes turning on at least one first switching element (1) belonging to the plurality of first switching elements (1), thereby charging at least one resonant capacitor (9) via a path passing through the first DC terminal (31) and the at least one first switching element (1). The at least one resonant capacitor (9) belongs to the plurality of resonant capacitors (9) and corresponds to the at least one first switching element (1). The second control operation includes turning on a switch belonging to the plurality of switches (8) corresponding to the at least one first switching element (1), thereby charging the regeneration capacitor (15) using the charge supplied from the at least one resonant capacitor (9).

[0195] This aspect contributes to miniaturization.

[0196] In a power converter (100; 100A) according to the second aspect which can be implemented in combination with the first aspect, a controller (50) performs a charging control operation by continuously charging a regeneration capacitor (15) until a voltage (V15) across the regeneration capacitor (15) becomes equal to or greater than a threshold value (Vth).

[0197] This aspect enables the voltage (V15) across the regenerative capacitor (15) to increase to a value equal to or greater than the threshold value (Vth) in a shorter time.

[0198] In the power converter (100; 100A) according to the third aspect which can be implemented in combination with the second aspect, the controller (50) suspends the inverter control operation until the voltage (V15) across the regenerative capacitor (15) has become equal to or greater than the threshold value (Vth).

[0199] This aspect can reduce the possibility that each of the plurality of first switching elements (1) and the plurality of second switching elements (2) is hard-switched when an inverter control operation is being performed.

[0200] In a power converter (100; 100A) according to a fourth aspect that can be implemented in combination with any one of the first to third aspects, a controller (50) performs a first control operation by complementarily turning on or off at least one first switching element (1) and at least one second switching element (2) corresponding to the at least one first switching element (1) belonging to a plurality of second switching elements (2). The controller (50) performs a second control operation by turning on a switch (8) corresponding to the at least one first switching element (1) belonging to a plurality of switches (8) during a dead time period in which both the at least one first switching element (1) and the at least one second switching element (2) are turned off.

[0201] In the power converter (100; 100A) according to the fifth aspect which can be implemented in combination with any one of the first to fourth aspects, the controller (50) performs the first control operation by turning on the plurality of first switching elements (1).

[0202] This aspect enables the voltage (V15) across the regenerative capacitor (15) to increase in a shorter time.

[0203] In the power converter (100) according to the sixth aspect which can be implemented in combination with any one of the first to fifth aspects, at least one resonant inductor (L1) is a single resonant inductor (L1). The second ends (82) of the plurality of switches (8) are connected in common to the single resonant inductor (L1).

[0204] This aspect enables the number of resonant inductors (L1) to be provided to be reduced to one, thereby contributing to further miniaturization.

[0205] Description of Reference Numerals

[0206] 1First switching element

[0207] 2 Second switching element

[0208] 3 Connecting Nodes

[0209] 8 Switches

[0210] 81 First End

[0211] 82 Second End

[0212] 9. Resonant capacitor

[0213] 10Switching circuit

[0214] 11 Power conversion circuit

[0215] 15 regeneration capacitor

[0216] 153 The Fifth End

[0217] 154 The Sixth End

[0218] 31 First DC terminal

[0219] 32 Second DC terminal

[0220] 41AC terminal

[0221] 50 Controllers

[0222] 100, 100A power converter

[0223] iU, iV, iW output current (load current)

[0224] L1 resonant inductor

[0225] RA1 AC load

[0226] SU1, SU2, SU6, SU7 control signals

[0227] SV1, SV2, SV6, SV7 control signals

[0228] SW1, SW2, SW6, SW7 control signals

[0229] Td Dead Time

[0230] V15 voltage

[0231] Vth threshold

Claims

1. A power converter, include: a first DC terminal and a second DC terminal; a power conversion circuit comprising a plurality of first switching elements and a plurality of second switching elements, the power conversion circuit being implemented as a parallel connection of a plurality of switching circuits, in each of the plurality of switching circuits, a first switching element of the plurality of first switching elements and a corresponding second switching element of the plurality of second switching elements being connected in series one-to-one, the plurality of first switching elements being connected to the first DC terminal, and the plurality of second switching elements being connected to the second DC terminal; a plurality of AC terminals provided one-to-one for the plurality of switching circuits, each of the plurality of AC terminals being connected to a connection node between the first switching element and the second switching element of a corresponding switching circuit of the plurality of switching circuits; a plurality of switches, which are arranged one-to-one for the plurality of switching circuits, each of the plurality of switches having a first end and a second end, the first end of each of the plurality of switches being connected to a connection node between the first switching element and the second switching element of a corresponding switching circuit in the plurality of switching circuits; a plurality of resonant capacitors, which are provided one-to-one for the plurality of switches, each of the plurality of resonant capacitors being connected between the second DC terminal and a first end of a corresponding switch of the plurality of switches; at least one resonant inductor having a third end and a fourth end, the third end of the at least one resonant inductor being connected to the second end of a corresponding switch of the plurality of switches; a regenerative capacitor having a fifth end and a sixth end, the fifth end of the regenerative capacitor being connected to the second DC terminal, the sixth end of the regenerative capacitor being connected to the fourth end of the at least one resonant inductor; as well as a controller configured to control an on / off state of each of the plurality of first switching elements, the plurality of second switching elements, and the plurality of switches, The controller is configured to: performing a charging control operation including charging the regenerative capacitor as a startup operation, and performing an inverter control operation including causing an output current to flow through each of the plurality of AC terminals, and The controller is configured to alternately perform a first control operation and a second control operation as the charging control operation, The first control operation includes turning on at least one first switching element belonging to the plurality of first switching elements, thereby charging at least one resonant capacitor, which belongs to the plurality of resonant capacitors and corresponds 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, and The second control operation includes turning on a switch corresponding to the at least one first switching element, which belongs to the plurality of switches, thereby charging the regeneration capacitor with the charge supplied from the at least one resonant capacitor.

2. The power converter according to claim 1, in, The controller is configured to perform the charging control operation by continuously charging the regeneration capacitor until a voltage across the regeneration capacitor becomes equal to or greater than a threshold value.

3. The power converter according to claim 2, in, The controller is configured to suspend the inverter control operation until the voltage across the regeneration capacitor has become equal to or greater than the threshold value.

4. The power converter according to any one of claims 1 to 3, in, The controller is configured to perform the first control operation by complementarily turning on or off the at least one first switching element and at least one second switching element corresponding to the at least one first switching element belonging to the plurality of second switching elements, and The controller is configured to perform the second control operation by turning on a switch corresponding to the at least one first switching element belonging to the plurality of switches 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.

5. The power converter according to any one of claims 1 to 4, in, The controller is configured to perform the first control operation by turning the plurality of first switching elements conductive.

6. The power converter according to any one of claims 1 to 5, in, The at least one resonant inductor is a single resonant inductor, and The second ends of the plurality of switches are respectively connected in common to the single resonant inductor.

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