Power converter

Abstract

The present invention addresses the problem of improving power conversion efficiency. In a power converter (100), a controller (50) performs a first control operation including: overlapping a high level period of a control signal for each of a plurality of bidirectional switches (8) corresponding to each of a plurality of switching circuits (10) with a dead time; the start time of the high-level period is set to a point in time that is earlier than the start time of the dead time by an additional time. If the potential detected at the fourth terminal (154) of the regenerative capacitor (15) is less than a first threshold value, the controller (50) performs a second control operation for controlling the plurality of bidirectional switches (8) to raise the potential (V15) at the fourth terminal (154) of the regenerative capacitor (15). If the detected potential is greater than a second threshold value, the controller (50) controls the plurality of bidirectional switches (8) to lower the potential (V15) at the fourth terminal (154) of the regenerative capacitor (15).

Description

Technical Field

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

[0002] Patent Document 1 discloses a power converter for converting DC power into multi-phase AC power.

[0003] The power converter of patent document 1 includes a main switching component (power conversion circuit), two capacitors, a coil (resonant inductor), a plurality of auxiliary switching elements, and a control component. The main switching component includes a plurality of main switching circuits provided for each phase of the multi-phase AC power. Each of the plurality of main switching circuits is implemented as a pair of main switching elements connected in series between two terminals of a DC power supply, and the interconnection node of the pair of main switching elements is used as the output node of its associated phase. The two capacitors divide the voltage of the DC power supply. One terminal of the coil is connected to the voltage dividing node of the two capacitors. A plurality of auxiliary switching elements connect the other terminals of the coil and the output nodes of each phase. When it is determined that a plurality of phase currents flow through the coil, the control component controls the plurality of auxiliary switching elements so that the amount of current flowing through at least one phase is less than a preset amount.

[0004] When the load status changes, the power converter may cause the power conversion efficiency to decrease.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2010-233306 Summary of the invention

[0008] An object of the present disclosure is to provide a power converter that can help increase power conversion efficiency.

[0009] 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 bidirectional switches, a plurality of resonant capacitors, a regenerative capacitor, a first resonant inductor, a second resonant inductor, a third resonant inductor, 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, a first switching element among the plurality of first switching elements and a corresponding second switching element among 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. The plurality of AC terminals are respectively set one-to-one for the plurality of switching circuits. Each of the plurality of AC terminals is connected to a connection node between a first switching element and a second switching element of a corresponding switching circuit among the plurality of switching circuits. The plurality of bidirectional switches are set one-to-one for the plurality of switching circuits. The first terminal of each of the plurality of bidirectional switches is connected to a connection node between a first switching element and a second switching element of a corresponding switching circuit among the plurality of switching circuits. The plurality of resonant capacitors are respectively provided one-to-one for the plurality of bidirectional switches. Each of the plurality of resonant capacitors is connected between the first terminal of the corresponding bidirectional switch in the plurality of bidirectional switches and the second DC terminal. The regenerative capacitor has a third terminal and a fourth terminal. The third terminal of the regenerative capacitor is connected to the first DC terminal or the second DC terminal. The first resonant inductor is connected between the first bidirectional switch belonging to the plurality of bidirectional switches and the fourth terminal of the regenerative capacitor. The second resonant inductor is connected between the second bidirectional switch belonging to the plurality of bidirectional switches and the fourth terminal of the regenerative capacitor. The third resonant inductor is connected between the third bidirectional switch belonging to the plurality of bidirectional switches and the fourth terminal of the regenerative capacitor. The controller applies a PWM signal having a potential alternating between a high level and a low level to each of the plurality of first switching elements and the plurality of second switching elements. The controller performs a first control operation. The first control operation includes: for each of the plurality of switching circuits, setting a dead time between a high level time period of the PWM signal for the first switching element and a high level time period of the PWM signal for the second switching element. The first control operation also includes: making the high-level time period of the control signal for each bidirectional switch among the multiple bidirectional switches corresponding to each switching circuit among the multiple switching circuits overlap with the dead time; and setting the start time of the high-level time period to a time point that is earlier than the start time of the dead time by an additional time.The controller acquires a potential detected at a fourth terminal of the regenerative capacitor. When the detected potential is less than a first threshold value that is less than half of a voltage value applied between the first DC terminal and the second DC terminal, the controller performs a second control operation that includes increasing the potential at the fourth terminal of the regenerative capacitor. When the detected potential is greater than a second threshold value that is greater than half of a voltage value applied between the first DC terminal and the second DC terminal, the controller performs a third control operation that includes decreasing the potential at the fourth terminal of the regenerative capacitor.

[0010] According to another aspect of the present disclosure, a power converter includes a first DC terminal and a second DC terminal, a power conversion circuit, a plurality of AC terminals, a plurality of bidirectional switches, a plurality of resonant capacitors, a regenerative capacitor, a first resonant inductor, a second resonant inductor, a third resonant inductor, 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, a first switching element among the plurality of first switching elements and a corresponding second switching element among 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. The plurality of AC terminals are respectively set one-to-one for the plurality of switching circuits. Each of the plurality of AC terminals is connected to a connection node between a first switching element and a second switching element of a corresponding switching circuit among the plurality of switching circuits. The plurality of bidirectional switches are set one-to-one for the plurality of switching circuits. The first terminal of each of the plurality of bidirectional switches is connected to a connection node between a first switching element and a second switching element of a corresponding switching circuit among the plurality of switching circuits. The plurality of resonant capacitors are respectively provided one-to-one for the plurality of bidirectional switches. Each of the plurality of resonant capacitors is connected between the first terminal of the corresponding bidirectional switch in the plurality of bidirectional switches and the second DC terminal. The regenerative capacitor has a third terminal and a fourth terminal. The third terminal of the regenerative capacitor is connected to the first DC terminal or the second DC terminal. The first resonant inductor is connected between the first bidirectional switch belonging to the plurality of bidirectional switches and the fourth terminal of the regenerative capacitor. The second resonant inductor is connected between the second bidirectional switch belonging to the plurality of bidirectional switches and the fourth terminal of the regenerative capacitor. The third resonant inductor is connected between the third bidirectional switch belonging to the plurality of bidirectional switches and the fourth terminal of the regenerative capacitor. The controller applies a PWM signal having a potential alternating between a high level and a low level to each of the plurality of first switching elements and the plurality of second switching elements. The controller performs a first control operation. The first control operation includes: for each of the plurality of switching circuits, setting a dead time between a high level time period of the PWM signal for the first switching element and a high level time period of the PWM signal for the second switching element. The first control operation also includes: making the high-level time period of the control signal for each bidirectional switch among the multiple bidirectional switches corresponding to each switching circuit among the multiple switching circuits overlap with the dead time; and setting the start time of the high-level time period to a time point that is earlier than the start time of the dead time by an additional time.The controller acquires a potential detected at a fourth terminal of the regenerative capacitor. In a case where the detected potential is less than a first threshold value that is less than half of a voltage value applied between the first DC terminal and the second DC terminal, the controller performs a second control operation, the second control operation including: applying a control signal having a high level period overlapping the dead time to one bidirectional switch belonging to the plurality of bidirectional switches in one cycle of a carrier signal according to each polarity of a plurality of output currents supplied from the plurality of AC terminals, and applying a control signal having a high level period associated with a charging operation of the regenerative capacitor to the one bidirectional switch. In a case where the detected potential is greater than a second threshold value that is greater than half of a voltage value applied between the first DC terminal and the second DC terminal, the controller performs a third control operation, the third control operation including: applying a control signal having a high level period overlapping the dead time to one bidirectional switch belonging to the plurality of bidirectional switches in one cycle of a carrier signal according to each polarity of a plurality of output currents supplied from the plurality of AC terminals, and applying a control signal having a high level period associated with a discharging operation of the regenerative capacitor to the one bidirectional switch in one cycle of a carrier signal according to each polarity of a plurality of output currents supplied from the plurality of AC terminals. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a circuit diagram of a system including a power converter according to a first embodiment;

[0012] Figure 2 illustrating how the power converter may operate when its controller performs a first control operation;

[0013] Figure 3 illustrating how the power converter can also operate when its controller performs a first control operation;

[0014] Figure 4 illustrating how a controller in the power converter may operate;

[0015] Figure 5 showing how duty ratios respectively corresponding to three-phase voltage commands in AC loads connected to a plurality of AC terminals of the power converter change over time;

[0016] Figure 6 is a timing diagram illustrating how the power converter may operate in a case where its controller performs a second control operation;

[0017] Figure 7 is a timing diagram illustrating how the power converter may operate when its controller performs a third control operation;

[0018] Figure 8is a circuit diagram of a system including a power converter according to a second embodiment;

[0019] Fig. 9 is a timing diagram illustrating how the power converter may operate when its controller performs a first control operation;

[0020] Fig.10 is a timing diagram illustrating how the power converter may operate in a case where its controller performs a second control operation;

[0021] Fig.11 is a timing diagram illustrating how the power converter can also operate when its controller performs a second control operation;

[0022] Fig.12 is a timing diagram illustrating how the power converter may operate when its controller performs a third control operation;

[0023] Fig.13 is a timing diagram illustrating how the power converter can also operate when its controller performs a third control operation;

[0024] Fig.14 is a timing chart illustrating how the power converter according to the third embodiment may operate in a case where its controller performs a second control operation;

[0025] Fig.15 is a timing diagram illustrating how the power converter may operate when its controller performs a third control operation;

[0026] Fig.16 is a timing chart illustrating how the power converter according to the fourth embodiment may operate in a case where its controller performs a second control operation;

[0027] Fig.17 is a timing diagram illustrating how the power converter may operate when its controller performs a third control operation;

[0028] Fig.18 is a timing chart illustrating how the power converter according to the fifth embodiment may operate in a case where its controller performs a second control operation;

[0029] Fig.19 is a timing diagram illustrating how the power converter may operate when its controller performs a third control operation;

[0030] Fig. 20 is a timing chart illustrating how the power converter according to the sixth embodiment may operate in a case where its controller performs a second control operation;

[0031] Fig.21 is a timing diagram illustrating how the power converter may operate when its controller performs a third control operation;

[0032] Fig. 22 is a timing chart illustrating how the power converter according to the seventh embodiment may operate in a case where its controller performs a second control operation;

[0033] Fig.23 is a timing diagram illustrating how the power converter may operate when its controller performs a third control operation;

[0034] Fig.24 is a circuit diagram of a system including a power converter according to an eighth embodiment;

[0035] Fig.25 is a circuit diagram of a system including a power converter according to a ninth embodiment;

[0036] Fig.26 is a circuit diagram of a system including a power converter according to a first modification of the second embodiment;

[0037] Fig. 27 is a circuit diagram of a system including a power converter according to a second modification of the second embodiment;

[0038] Fig.28 is a circuit diagram of a system including a power converter according to a third modification of the second embodiment;

[0039] Fig.29 is a circuit diagram of a system including a power converter according to a fourth modification of the second embodiment; and

[0040] Fig.30 is a circuit diagram of a system including a power converter according to a fifth modification of the second embodiment. DETAILED DESCRIPTION

[0041] (First embodiment)

[0042] Will refer to Figures 1 to 7 A power converter 100 according to a first embodiment will be described.

[0043] (1) Overall structure of power converter

[0044] For example, Figure 1As 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.

[0045] The power converter 100 includes a power conversion circuit 11, a plurality of (e.g., three) bidirectional switches 8, a plurality of (e.g., three) resonant capacitors 9, a regenerative capacitor 15, a first resonant inductor L1, a second resonant inductor L2, a third resonant inductor L3, and a controller 50. The power converter 100 also includes a plurality of (e.g., three) protection circuits 17 and a capacitor C10.

[0046] 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 one 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, respectively. 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 bidirectional switches 8 are provided one-to-one for the plurality of switching circuits 10, respectively. A first terminal 81 of each of the plurality of bidirectional 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 bidirectional switches 8, respectively. Each resonant capacitor 9 of the plurality of resonant capacitors 9 is connected between the first terminal of the corresponding bidirectional switch 8 of the plurality of bidirectional switches 8 and the second DC terminal 32. The regenerative capacitor 15 has a third terminal 153 and a fourth terminal 154. The third terminal 153 is connected to the second DC terminal 32. The first resonant inductor L1, the second resonant inductor L2, and the third resonant inductor L3 are respectively connected between the three bidirectional switches 8 and the fourth terminal 154 of the regenerative capacitor 15. The controller 50 controls the plurality of first switching elements 1, the plurality of second switching elements 2, and the plurality of bidirectional switches 8.

[0047] (2) Details of power converter

[0048] 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. 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. 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. 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. 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 bidirectional switch 8 connected to the connection node 3U will be referred to as "bidirectional switch 8U (first bidirectional switch 8U)", the bidirectional switch 8 connected to the connection node 3V will be referred to as "bidirectional switch 8V (second bidirectional switch 8V)", and the bidirectional switch 8 connected to the connection node 3W will be referred to as "bidirectional switch 8W (third bidirectional switch 8W)".

[0049] 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, the U-phase, V-phase, and W-phase of the AC load RA1 are connected to three AC terminals 41U, 41V, and 41W, respectively.

[0050] 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 control terminal 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, its control terminal, the first main terminal, and the second main terminal are respectively a gate terminal, a collector terminal, and an emitter terminal.

[0051] 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.

[0052] The U phase 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.

[0053] The plurality of resonant capacitors 9 are provided one-to-one for the plurality of bidirectional switches 8. Each of the plurality of resonant capacitors 9 is connected between the first terminal 81 and the second DC terminal 32 of its corresponding bidirectional switch 8. The power converter 100 includes a plurality of resonant circuits. The plurality of resonant circuits include a first resonant circuit having a resonant capacitor 9U and a first resonant inductor L1, a second resonant circuit having a resonant capacitor 9V and a second resonant inductor L2, and a third resonant circuit having a resonant capacitor 9W and a third resonant inductor L3.

[0054] Each of the plurality of bidirectional 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 bidirectional 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 bidirectional 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 bidirectional switch 8 including the first IGBT 6. In each of the plurality of bidirectional 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 bidirectional switch 8 including the second IGBT 7. The bidirectional switch 8U is connected to the connection node 3U between the first switching element 1U and the second switching element 2U. The bidirectional switch 8V is connected to the connection node 3V between the first switching element 1V and the second switching element 2V. The bidirectional 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 bidirectional 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 bidirectional 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 bidirectional switch 8W will be referred to as the "first IGBT 6W" and the "second IGBT 7W" respectively.

[0055] The plurality of bidirectional 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.

[0056] The regenerative capacitor 15 is connected between the first resonant inductor L1, the second resonant inductor L2, and the third resonant inductor L3 and the second DC terminal 32. The regenerative capacitor 15 may be, for example, a film capacitor.

[0057] The first resonant inductor L1 is connected between the fourth terminal 154 of the regenerative capacitor 15 and the second terminal 82 of the bidirectional switch 8U. The second resonant inductor L2 is connected between the fourth terminal 154 of the regenerative capacitor 15 and the second terminal 82 of the bidirectional switch 8V. The third resonant inductor L3 is connected between the fourth terminal 154 of the regenerative capacitor 15 and the second terminal 82 of the bidirectional switch 8W.

[0058] As described above, the power converter 100 includes a plurality of (eg, three) protection circuits 17. The plurality of protection circuits 17 are provided one-to-one for the U-phase, the V-phase, and the W-phase of the AC load RA1, respectively.

[0059] A plurality of protection circuits 17 are connected between the first DC terminal 31 and the second DC terminal 32. Each of the plurality of protection circuits 17 includes a third diode 13 and a fourth diode 14 connected in series with the third diode 13. The plurality of protection circuits 17 are provided one-to-one for the plurality of bidirectional switches 8. In each of the plurality of protection circuits 17, a connection node between the third diode 13 and the fourth diode 14 is connected to a second terminal 82 of a corresponding bidirectional switch 8 in the bidirectional switch 8. An anode of the third diode 13 is connected to the second terminal 82 of the bidirectional switch 8, and a cathode thereof is connected to the first DC terminal 31. An anode of the fourth diode 14 is connected to the second DC terminal 32, and a cathode thereof is connected to the second terminal 82 of the bidirectional switch 8.

[0060] 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.

[0061] The controller 50 controls a plurality of first switching elements 1, a plurality of second switching elements 2, and a plurality of bidirectional switches 8. The intelligent body that performs 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 intelligent body that performs 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 is readable by 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.

[0062] The controller 50 outputs pulse width modulation (PWM) signals SU1, SV1, SW1 for controlling the on / off state of the plurality of first switching elements 1U, 1V, 1W, respectively. The PWM signals SU1, SV1, SW1 are each a signal having a potential level that alternates between, for example, a first potential level (hereinafter referred to as "low level") and a second potential level (hereinafter referred to as "high level") higher than the first potential level. The first switching elements 1U, 1V, 1W are each turned on when the PWM signals SU1, SV1, SW1 have a high level, and are each turned off when the PWM signals SU1, SV1, SW1 have a low level. In addition, the controller 50 also outputs PWM signals SU2, SV2, SW2 for controlling the on / off state of the plurality of second switching elements 2U, 2V, 2W, respectively. The PWM signals SU2, SV2, SW2 are each a signal having a potential level that alternates between, for example, a first potential level (hereinafter referred to as "low level") and a second potential level (hereinafter referred to as "high level") higher than the first potential level. The second switching elements 2U, 2V, 2W respectively become conductive when the PWM signals SU2, SV2, SW2 have a high level, and respectively become off when the PWM signals SU2, SV2, SW2 have a low level.

[0063] The controller 50 uses a carrier signal having a sawtooth waveform (reference Figure 2) to generate PWM signals SU1, SV1, SW1 to be applied to a plurality of first switching elements 1U, 1V, 1W, respectively, and PWM signals SU2, SV2, SW2 to be applied to a plurality of second switching elements 2U, 2V, 2W, respectively. More specifically, the controller 50 generates PWM 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 PWM 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 PWM 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, for example, can be sinusoidal wave signals whose phases differ by 120 degrees from each other and whose amplitudes (voltage command values) change over time. 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.

[0064] The duty ratios of the PWM signals SU1 and 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. The controller 50 generates the PWM 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 the PWM signal SU2 to be applied to the second switching element 2U by inverting the PWM signal SU1 to be applied to the first switching element 1U. In addition, in order to prevent the respective on-time periods of the first switching element 1U and the second switching element 2U from overlapping each other, the controller 50 sets a dead time Td (reference time Td) between the high-level time period of the PWM signal SU1 and the high-level time period of the PWM signal SU2. Figure 2 ).

[0065] The duty ratios of the PWM signals SV1 and 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. The controller 50 generates the PWM 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 generates the PWM signal SV2 to be applied to the second switching element 2V by inverting the PWM signal SV1 to be applied to the first switching element 1V. In addition, in order to prevent the respective on-time periods of the first switching element 1V and the second switching element 2V from overlapping each other, the controller 50 sets a dead time Td (reference time Td) between the high-level time period of the PWM signal SV1 and the high-level time period of the PWM signal SV2. Figure 2 ).

[0066] The duty ratios of the PWM signals SW1 and 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. The controller 50 generates the PWM 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 the PWM signal SW2 to be applied to the second switching element 2W by inverting the PWM signal SW1 to be applied to the first switching element 1W. In addition, in order to prevent the respective on-time periods of the first switching element 1W and the second switching element 2W from overlapping each other, the controller 50 sets a dead time Td (reference time Td) between the high-level time period of the PWM signal SW1 and the high-level time period of the PWM signal SW2. Figure 3 ).

[0067] 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 amplitudes vary with time. Figure 5 As shown, the respective duty ratios of the PWM signals SU1, SV1, SW1 (i.e., the U-phase duty ratio, the V-phase duty ratio, and the W-phase duty ratio) are changed in the form of sine waves with phases different from each other by 120 degrees. Similarly, the respective duty ratios of the PWM signals SU2, SV2, SW2 are also changed in the form of sine waves with phases different from each other by 120 degrees.

[0068] The controller 50 generates the respective PWM 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 the output currents iU, iV, and iW of the U-phase, V-phase, and W-phase flowing through the AC load RA1.

[0069] A plurality of bidirectional switches 8 , a first resonant inductor L1 , a second resonant inductor L2 , a third resonant inductor L3 , a plurality of resonant capacitors 9 , and a regenerative capacitor 15 are provided to perform zero voltage soft switching on a plurality of first switching elements 1 and a plurality of second switching elements 2 .

[0070] 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 bidirectional switches 8 .

[0071] 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.

[0072] If the first IGBT 6U is turned on and the second IGBT 7U is turned off, the bidirectional switch 8U allows a charging current to flow through the regenerative capacitor 15, the first resonant inductor L1, the bidirectional switch 8U, the connection node 3U, and the resonant capacitor 9U in order to charge 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 bidirectional switch 8U allows a discharging current to flow through the resonant capacitor 9U, the connection node 3U, the bidirectional switch 8U, the first resonant inductor L1, and the regenerative capacitor 15 in order to remove the charge from the resonant capacitor 9U.

[0073] If the first IGBT 6V is on and the second IGBT 7V is off, the bidirectional switch 8V allows a charging current to flow through the regenerative capacitor 15, the second resonant inductor L2, the bidirectional switch 8V, the connection node 3V, and the resonant capacitor 9V in order to charge the resonant capacitor 9V. On the other hand, if the first IGBT 6V is off and the second IGBT 7V is on, the bidirectional switch 8V allows a discharging current to flow through the resonant capacitor 9V, the connection node 3V, the bidirectional switch 8V, the second resonant inductor L2, and the regenerative capacitor 15 in order to remove the charge from the resonant capacitor 9V.

[0074] If the first IGBT 6W is on and the second IGBT 7W is off, the bidirectional switch 8W allows a charging current to flow through the regenerative capacitor 15, the third resonant inductor L3, the bidirectional switch 8W, the connection node 3W, and the resonant capacitor 9W in order to charge the resonant capacitor 9W. On the other hand, if the first IGBT 6W is off and the second IGBT 7W is on, the bidirectional switch 8W allows a discharging current to flow through the resonant capacitor 9W, the connection node 3W, the bidirectional switch 8W, the third resonant inductor L3, and the regenerative capacitor 15 in order to remove the charge from the resonant capacitor 9W.

[0075] (3) Operation of power converter

[0076] In the following description, regarding each of the currents iL1, iL2, iL3 flowing through the first resonant inductor L1, the second resonant inductor L2, and the third resonant inductor L3, if the currents iL1, iL2, iL3 are Figure 1 If the currents iL1, iL2, iL3 flow in the direction indicated by the corresponding arrows in the arrows shown in FIG. 1 , the polarity of the currents iL1, iL2, iL3 is assumed to be positive. On the other hand, if the currents iL1, iL2, iL3 flow in the direction indicated by the corresponding arrows in the arrows shown in FIG. Figure 1 If the currents iL1, iL2, and iL3 flow in the direction opposite to the direction indicated by the arrows shown in FIG. 1 , the polarity of the currents iL1, iL2, and iL3 is assumed to be negative. In addition, in the following description, regarding each of the output currents iU, iV, and iW flowing through the U-phase, V-phase, and W-phase of the AC load RA1, if the currents iU, iV, and iW are in the direction indicated by Figure 1 If the current iU, iV, iW flows in the direction indicated by the corresponding arrow in the arrows shown, the polarity of the current iU, iV, iW is assumed to be positive. On the other hand, if the current iU, iV, iW flows in the direction indicated by the corresponding arrow in the arrows shown Figure 1 If the current iU, iV, iW flows in the direction opposite to the direction indicated by the arrow shown, the polarity of the current iU, iV, iW is assumed to be negative.

[0077] In the power converter 100, for example, in a state where the first IGBT 6U of the bidirectional switch 8U is on and the positive current iL1 is flowing through the first resonant inductor L1, the first IGBT 6U of the bidirectional switch 8U may be turned off. In this case, the current iL1 flowing through the first resonant inductor L1 is regenerated to the power conversion circuit 11 via the third diode 13 until the current iL1 flowing through the first resonant inductor L1 becomes zero due to the energy consumption of the first resonant inductor L1. In addition, in the power converter 100, for example, in a state where the second IGBT 7U of the bidirectional switch 8U is on and the negative current iL1 is flowing through the resonant inductor L1, the second IGBT 7U of the bidirectional switch 8U may be turned off. In this case, the current flows through the first resonant inductor L1 along a path that passes through the fourth diode 14, the first resonant inductor L1, and the regeneration capacitor 15 in sequence until the current iL1 becomes zero due to the energy consumption of the first resonant inductor L1.

[0078] In addition, in the power converter 100, for example, in a state where the first IGBT 6V of the bidirectional switch 8V is turned on and the positive current iL2 is flowing through the second resonant inductor L2, the first IGBT 6V of the bidirectional switch 8V may be turned off. In this case, the current iL2 flowing through the second resonant inductor L2 is regenerated to the power conversion circuit 11 via the third diode 13 until the current iL2 flowing through the second resonant inductor L2 becomes zero due to the energy consumption of the second resonant inductor L2. In addition, in the power converter 100, for example, in a state where the second IGBT 7V of the bidirectional switch 8V is turned on and the negative current iL2 is flowing through the second resonant inductor L2, the second IGBT 7V of the bidirectional switch 8V may be turned off. In this case, the current iL2 flows through the second resonant inductor L2 along a path that passes through the fourth diode 14, the second resonant inductor L2, and the regeneration capacitor 15 in sequence until the current iL2 becomes zero due to the energy consumption of the second resonant inductor L2.

[0079] In addition, in the power converter 100, for example, in a state where the first IGBT 6W of the bidirectional switch 8W is on and the positive current iL1 is flowing through the third resonant inductor L3, the first IGBT 6W of the bidirectional switch 8W may be turned off. In this case, the current iL3 flowing through the third resonant inductor L3 is regenerated to the power conversion circuit 11 via the third diode 13 until the current iL3 flowing through the third resonant inductor L3 becomes zero due to the energy consumption of the third resonant inductor L3. In addition, in the power converter 100, for example, in a state where the second IGBT 7W of the bidirectional switch 8W is on and the negative current iL3 is flowing through the third resonant inductor L3, the second IGBT 7W of the bidirectional switch 8W may be turned off. In this case, the current iL3 flows through the third resonant inductor L3 along a path that passes through the fourth diode 14, the third resonant inductor L3, and the regeneration capacitor 15 in sequence until the current iL3 becomes zero due to the energy consumption of the third resonant inductor L3.

[0080] Next, refer to Figures 1 to 3 It will be described how the controller 50 performs the first control operation for performing zero voltage soft switching control on each of the plurality of first switching elements 1 and the plurality of second switching elements 2 .

[0081] The controller 50 performs the first control operation by setting a dead time Td between the high level time period of the PWM signal SU1, SV1, SW1 for the first switching element 1U, 1V, 1W and the high level time period of the PWM signal SU2, SV2, SW2 for the second switching element 2U, 2V, 2W for each of the plurality of switching circuits 10. In addition, the controller 50 also performs the first control operation by making the high level time period of the control signal for each of the plurality of bidirectional switches 8 corresponding to each of the plurality of switching circuits 10 overlap with the dead time Td, and setting the start time of the high level time period at a time point earlier than the start time of the dead time Td by an additional time.

[0082] The first control operation will now be described in more detail.

[0083] When the first switching element 1 is subjected to zero voltage soft switching control, it is necessary to reduce the voltage across the first switching element 1 to zero immediately before the first switching element 1, which is the object of zero voltage soft switching, becomes conductive. Therefore, the controller 50 turns on the first IGBT 6 corresponding to the first switching element 1, which is the object of zero voltage soft switching control. In this way, the controller 50 causes the resonant inductor and the resonant capacitor 9 connected to the first switching element 1 to resonate, and charges the resonant capacitor 9 with the charge stored in the regenerative capacitor 15, thereby reducing the voltage across the first switching element 1 to zero. In this case, the resonant inductor may be the first resonant inductor L1, the second resonant inductor L2, or the third resonant inductor L3.

[0084] On the other hand, when the second switching element 2 is subjected to zero voltage soft switching control, it is necessary to reduce the voltage across the second switching element 2 to zero immediately before the second switching element 2, which is the object of the zero voltage soft switching control, becomes conductive. Therefore, the controller 50 turns on the second IGBT 7 corresponding to the second switching element 2, which is the object of the zero voltage soft switching control. In this way, the controller 50 causes the resonant inductor and the resonant capacitor 9 connected to the second switching element 2 to resonate, and discharges from the resonant capacitor 9 to the regenerative capacitor 15, thereby reducing the voltage across the second switching element 2 to zero. The controller 50 charges and discharges the resonant capacitor 9 via the bidirectional switch 8 so that the dead time Td is equal to the half cycle of the LC resonance. This allows the power converter 100 to perform zero voltage soft switching.

[0085] exist Figure 2 PWM 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 are shown in FIG. Figure 2Also shown are the control signal SU6 to be supplied from the controller 50 to the first IGBT 6U of the bidirectional switch 8U, the output current iU of the U phase flowing through the AC load RA1, the current iL1 flowing through the first resonant inductor L1, and the voltage V across the first switching element 1U. 1U In addition, Figure 2 PWM 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 are shown in FIG. Figure 2 Also shown are the control signal SV6 to be supplied from the controller 50 to the first IGBT 6V of the bidirectional switch 8V, the V-phase output current iV flowing through the AC load RA1, the current iL2 flowing through the second resonant inductor L2, and the voltage V across the first switching element 1V. 1V .

[0086] In addition, Figure 2 , the dead time Td set by the controller 50 to prevent the first switching element 1 and the second switching element 2 of the same phase from being turned on at the same time is also shown. Figure 2 Also shown in FIG. 5 are additional time Tau set by the controller 50 for the control signal SU6 for the first IGBT 6U of the bidirectional switch 8U and additional time Tav set by the controller 50 for the control signal SV6 for the first IGBT 6V of the bidirectional switch 8V. The additional time Tau and the additional time Tav will be described later.

[0087] exist Figure 3 PWM signals SW1 and SW2 to be applied from the controller 50 to the first switching element 1W and the second switching element 2W of the switching circuit 10W are shown in FIG. Figure 3 Also shown in FIG. 5 are the control signal SW6 to be supplied from the controller 50 to the first IGBT 6W of the bidirectional switch 8W and the output current iW of the W phase flowing through the AC load RA1. Figure 3 Also shown in FIG. 1 is a current iL3 flowing through the third resonant inductor L3. Figure 3 The voltage V across the first switching element 1W is also shown in FIG. 1W .

[0088] In addition, Figure 3 , the controller 50 also shows the dead time Td set to prevent the first switching element 1W and the second switching element 2W from being turned on at the same time. Figure 3 4 also shows an additional time Taw set by the controller 50 for the control signal SW6 for the first IGBT 6W of the bidirectional switch 8W. The additional time Taw will be described later.

[0089] like Figure 2As shown, the additional time Tau is the amount of time provided by the controller 50 to make the high-level time period of the control signal SU6 longer than the dead time Td by setting the start time t1 of the high-level time period of the control signal SU6 to a time point earlier than the start time t2 of the dead time Td. The length of the additional time Tau is determined by the value of the output current iU. In order to generate LC resonance starting from the start time t2 of the dead time Td, it is preferable that the value of the current iL1 at the start time t2 of the dead time Td is the same as the value of the output current iU. This is because as long as iL1 < iU, all the current flows through the AC load RA1, and thus the resonance capacitor 9U cannot be charged. The end time of the high-level time period of the control signal SU6 can be the same as or later than the end time t3 of the dead time Td. In Figure 2 the example shown, the end time of the high-level time period of the control signal SU6 is set to be the same as the end time t3 of the dead time Td. The controller 50 sets the high-level time period of the control signal SU6 to Tau + Td. The voltage V across the first switching element 1U 1U becomes zero at the end time t3 of the dead time Td. In Figure 2 the example shown, the current iL1 starts flowing through the first resonance inductor L1 at the start time t1 of the high-level time period of the control signal SU6 and becomes zero at the time t4 after the additional time Tau has elapsed since the end time t3 of the dead time Td. At this time, starting from the start time t2 of the dead time Td, the current iL1 satisfies iL1 ≥ iU, and thus, as shown by the shaded part of the current waveform which is the fifth waveform from the top of Figure 2 , the current iL1 flows into the resonance capacitor 9U to generate LC resonance. Starting from the end time t3 of the dead time Td, the current iL1 will be regenerated to the power conversion circuit 11 via the third diode 13 directly connected to the first resonance inductor L1.

[0090] In order to start generating LC resonance at the start time t2 of the dead time Td as described above, the controller 50 determines an additional time Tau based on the output current iU such that iL1 = iU at the start time t2 of the dead time Td. More specifically, for example, using the detection result of the output current iU by the current sensor or its signal processing value, or the estimated value of the current iU, the inductance L1 of the pre-stored first resonant inductor L1, and the detection result of the voltage across the regenerative capacitor 15 (for example, the potential V15 at the fourth terminal 154 of the regenerative capacitor 15), the controller 50 determines the additional time Tau by the following formula: Tau = iU × (L1 / V15). In this case, as the detection result of the output current iU or its signal processing value, the detected value of the carrier period plus the additional time Tau or the detected value at the timing closest to the carrier period can be used. Further, in this case, as the estimated value of the output current iU, for example, the value of the output current iU estimated according to the carrier period plus the additional time Tau can be used.

[0091] Note that if, as Figure 4 shown, the polarity of the output current iU is negative, the power converter 100 can charge the resonant capacitor 9U and perform zero-voltage soft switching of the first switching element 1U without turning on the first IGBT 6U of the bidirectional switch 8U. In Figure 4 , the voltage V across the first switching element 1U is also shown 1U and the voltage V across the second switching element 2U 2U . Additionally, in Figure 4 , the charging current for the resonant capacitor 9U is also shown.

[0092] As Figure 2 shown, the additional time Tav is the amount of time provided by the controller 50 to make the high-level period of the control signal SV6 longer than the dead time Td by setting the start time t5 of the high-level period of the control signal SV6 to a time point earlier than the start time t6 of the dead time Td. The length of the additional time Tav is determined by the value of the output current iV. In order to start generating LC resonance from the start time t6 of the dead time Td, it is preferable that the value of the current iL2 be consistent with the value of the output current iV at the start time t6 of the dead time Td. This is because as long as iL2 < iV, all the current flows through the AC load RA1, and thus the resonant capacitor 9V cannot be charged. The end time of the high-level period of the control signal SV6 can be the same as or later than the end time t7 of the dead time Td. In Figure 2In the example shown, the end time of the high level period of the control signal SV6 is set to coincide with the end time t7 of the dead time Td. The controller 50 sets the high level period of the control signal SV6 to Tav+Td. The voltage V across the first switching element 1V is 1V It becomes zero at the end time t7 of the dead time Td. Figure 2 In the example shown, the current iL2 starts to flow through the second resonant inductor L2 at the start time t5 of the high level period of the control signal SV6, and becomes zero at the time t8 after the additional time Tav has passed since the end time t7 of the dead time Td. At this time, from the start time t6 of the dead time Td, the current iL2 satisfies iL2 ≥ iV, and therefore, as Figure 2 The current iL2 in the shaded portion of the current waveform shown in the tenth waveform from the top flows into the resonant capacitor 9V to generate LC resonance. From the end time t7 of the dead time Td, the current iL2 will be regenerated to the power conversion circuit 11 via the third diode 13 directly connected to the second resonant inductor L2.

[0093] In order to start generating LC resonance at the start time t6 of the dead time Td as described above, the controller 50 determines the additional time Tav based on the output current iV so that iL2=iV is satisfied at the start time of the dead time Td. More specifically, for example, by using the detection result of the output current iV using the current sensor or its signal processing value or the estimated value of the current iV, the pre-stored inductance L2 of the second resonant inductor L2, and the detection result of the voltage across the regenerative capacitor 15 (i.e., the potential V15 at the fourth terminal 154 of the regenerative capacitor 15), the controller 50 determines the additional time Tav by the following formula: Tav=iV×(L2 / V15). In this case, as the detection result of the output current iV or its signal processing value, the detection value of the carrier cycle to which the additional time Tav is added or the detection value at the timing closest to the carrier cycle can be used. In addition, in this case, as the estimated value of the output current iV, for example, the value of the output current iV estimated according to the carrier cycle to which the additional time Tav is added can be used.

[0094] Note that if the polarity of the output current iV is negative, the power converter 100 can charge the resonance capacitor 9V and perform zero-voltage soft switching of the first switching element 1 without turning the bidirectional switch 8V conductive.

[0095] like Figure 3As shown, the additional time Taw is the amount of time provided by the controller 50 to make the high-level period of the control signal SW6 longer than the dead time Td by setting the start time t9 of the high-level period of the control signal SW6 to a time point earlier than the start time t10 of the dead time Td. The length of the additional time Taw is determined by the value of the output current iW. To generate the LC resonance starting from the start time t10 of the dead time Td, it is preferable that the value of the current iL3 at the start time t10 of the dead time Td is consistent with the value of the output current iW. This is because as long as iL3 < iW, all the current 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 can be the same as or later than the end time t11 of the dead time 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 t11 of the dead time Td. The controller 50 sets the high-level period of the control signal SW6 to Taw + Td. The voltage V across the first switching element 1W 1W becomes zero at the end time t11 of the dead time Td. In Figure 3 the example shown, the current iL3 starts flowing through the third resonance inductor L3 at the start time t9 of the high-level period of the control signal SW6 and becomes zero at the time point t12 after the additional time Taw has elapsed since the end time t11 of the dead time Td. At this time, starting from the start time t10 of the dead time Td, the current iL3 satisfies iL3 ≥ iW, and thus, as the current iL3 in the shaded part of the current waveform shown as the fourth waveform from the top of Figure 3 flows into the resonance capacitor 9W to generate the LC resonance. Starting from the end time t11 of the dead time Td, the current iL3 will be regenerated to the power conversion circuit 11 via the third diode 13 directly connected to the third resonance inductor L3.

[0096] The controller 50 determines the additional time Taw based on the output current iW. More specifically, for example, by using the detection result of the output current iW using the current sensor, the inductance L3 of the pre-stored third resonance inductor L3, and the detection result of the voltage across the regeneration capacitor 15 (i.e., the potential V15 at the fourth terminal 154 of the regeneration capacitor 15), the controller 50 determines the additional time Taw by the following formula: Taw = iW × (L3 / V15). In this case, as the detection result of the output current iW or its signal processing value, the detected value of the carrier period plus the additional time Taw or the detected value at the timing closest to the carrier period can be used. In addition, in this case, as the estimated value of the output current iW, for example, the value of the output current iW estimated according to the carrier period plus the additional time Taw can be used.

[0097] Note that if the polarity of the output current iW is negative, the power converter 100 can charge the resonance capacitor 9W and perform zero-voltage soft switching of the first switching element 1 without turning the bidirectional switch 8W conductive.

[0098] The power converter 100 causes the resonance capacitor 9 and the resonance inductor associated with the switching elements that are the target of zero voltage soft switching, which belong to the plurality of first switching elements 1 and the plurality of second switching elements 2, to resonate. In this case, the voltage across the resonance capacitor 9 associated with the switching elements that are the target of zero voltage soft switching varies according to the amplitude of the resonance voltage centered on the potential V15 at the fourth terminal 154 of the regenerative capacitor 15. At this time, by causing the voltage across the switching elements to change from the voltage value Vd (reference voltage Vd) of the DC power source E1 applied between the first DC terminal 31 and the second DC terminal 32, the voltage across the switching elements is changed to the value Vd (reference voltage Vd) of the DC power source E1 applied between the first DC terminal 31 and the second DC terminal 32. Figure 2 and Figure 3 ) is changed to zero to perform zero voltage soft switching. In addition, whenever the resonant capacitor 9 and the resonant inductor resonate, the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 also changes according to the amount of charge stored in or removed from the regenerative capacitor 15. In addition, the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 also changes according to the amount of charge stored in or removed from the regenerative capacitor 15 in each carrier cycle. The amount of charge stored in or removed from the regenerative capacitor 15 in association with the output currents iU, iV, iW of the U phase, the V phase, and the W phase is determined for each carrier cycle. In this case, the amount of charge stored or removed becomes the maximum in association with the output current having the largest absolute value among the output currents iU, iV, iW of the U phase, the V phase, and the W phase. Thus, in the power converter 100, the amount of charge stored in or removed from the regenerative capacitor 15 changes for each carrier cycle. If the motor serving as the AC load RA1 is operating normally, the output currents iU, iV, iW in each phase have sinusoidal waves and their phases differ from each other by 120 degrees, thereby achieving a charge / discharge balance at the regeneration capacitor 15 and reducing the change in the potential V15 at the fourth terminal 154 of the regeneration capacitor 15.

[0099] The controller 50 performs the first control operation by setting a dead time Td between the high level time period of the PWM signal SU1, SV1, SW1 for the first switching element 1U, 1V, 1W and the high level time period of the PWM signal SU2, SV2, SW2 for the second switching element 2U, 2V, 2W for each of the plurality of switching circuits 10. In addition, the controller 50 also performs the first control operation by making the high level time period of the control signal for each of the plurality of bidirectional switches 8 corresponding to each of the plurality of switching circuits 10 overlap with the dead time Td, and setting the start time of the high level time period to a time point earlier than the start time of the dead time Td by an additional time.

[0100] In the power converter 100, if the controller 50 performs only the first control operation, any change in the condition of the load (such as locking of the motor used as the AC load RA1, etc.) will cause the output current in each phase to have a correspondingly different constant value. Then, in the power converter 100, the difference between the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 for the ground potential and half (Vd / 2) of the voltage value Vd of the DC power supply E1 will be enlarged. In this case, in the power converter 100, when the resonant capacitors 9U, 9V, 9W and the first to third resonant inductors L1 to L3 are made to resonate to perform zero voltage soft switching, the amplitude of the resonant voltage will be reduced too much to perform zero voltage soft switching.

[0101] Thus, the controller 50 of the power converter 100 is configured to be capable of performing not only the above-described first control operation but also operations to be described below.

[0102] In the power converter 100, the controller 50 acquires the potential V15 detected at the fourth terminal 154 of the regenerative capacitor 15 with respect to the ground potential. For example, the controller 50 may acquire the detection potential at each cycle of the carrier signal. The controller 50 may, for example, pre-store the voltage value Vd of the DC voltage applied between the first DC terminal 31 and the second DC terminal 32, or acquire the detection result of the voltage value Vd, whichever is appropriate. The controller 50 determines the details of the control operation based on the detection potential, the value of Vd / 2, and the detection results of the output currents iU, iV, iW.

[0103] The controller 50 performs a first control operation when the detection potential of the regenerative capacitor 15 is equal to or greater than the first threshold value Vth1 and equal to or less than the second threshold value Vth2, performs a second control operation when the detection potential of the regenerative capacitor 15 is less than the first threshold value Vth1, and performs a third control operation when the detection potential is greater than the second threshold value Vth2. The first threshold value Vth1 is less than Vd / 2. The second threshold value Vth2 is greater than Vd / 2. The first threshold value Vth1 may be, for example, 90% of Vd / 2. The second threshold value Vth2 may be, for example, 110% of Vd / 2. The second control operation is an operation of controlling the plurality of bidirectional switches 8 so that the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 rises. The third control operation is an operation of controlling the plurality of bidirectional switches 8 so that the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 drops.

[0104] As described above, the first control operation is an operation of causing the high level period of the control signal for each of the plurality of bidirectional switches 8 corresponding to each of the plurality of switching circuits 10 to overlap with the dead time Td, and setting the start time of the high level period to a time point earlier than the start time of the dead time Td by an additional time. The high level period of the control signal for the bidirectional switch 8U is a period in which the potential level of the control signal SU6 for the first IGBT 6U has a high level, or a period in which the potential level of the control signal SU7 for the second IGBT 7U has a high level. The high level period of the control signal for the bidirectional switch 8V is a period in which the potential level of the control signal SV6 for the first IGBT 6V has a high level, or a period in which the potential level of the control signal SV7 for the second IGBT 7V has a high level. The high level period of the control signal for the bidirectional switch 8W is a period in which the potential level of the control signal SW6 for the first IGBT 6W has a high level, or a period in which the potential level of the control signal SW7 for the second IGBT 7W has a high level. The additional time used to start the high level period of the control signal for the bidirectional switch 8U earlier than the start time of the dead time Td is the additional time Tau mentioned above. The additional time used to start the high level period of the control signal for the bidirectional switch 8V earlier than the start time of the dead time Td is the additional time Tav mentioned above. The additional time used to start the high level period of the control signal for the bidirectional switch 8W earlier than the start time of the dead time Td is the additional time Taw mentioned above.

[0105] The second control operation is an operation of controlling the plurality of bidirectional switches 8 to increase the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 according to the respective polarities of the plurality of output currents iU, iV, iW supplied from the plurality of AC terminals 41. The third control operation is an operation of controlling the plurality of bidirectional switches 8 to decrease the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 according to the respective polarities of the plurality of output currents iU, iV, iW supplied from the plurality of AC terminals 41.

[0106] The controller 50 performs the second control operation by setting the high level period of one bidirectional switch 8 participating in the discharge operation of the regenerative capacitor 15 among the plurality of bidirectional switches 8 to zero according to the respective polarities of the plurality of output currents iU, iV, iW supplied from the plurality of AC terminals 41. Figure 6 An exemplary operation in such a situation will be described.

[0107] Figure 6 The figure shows how the carrier signal, the control signals SU6, SV7, SW7, the plurality of output currents iU, iV, iW, the current iL1 flowing through the first resonant inductor L1, the current iL2 flowing through the second resonant inductor L2, and the current iL3 flowing through the third resonant inductor L3 change when the locking of the motor as the exemplary AC load RA1 causes the output currents iU, iV, iW to have respectively different constant values. Figure 6 In the case of , the absolute value of the output current iU>the absolute value of the output current iW>the absolute value of the output current iV. Figure 6 In the example, the high level time period of the control signal SU6>the high level time period of the control signal SW7>the high level time period of the control signal SV7. The greater the absolute value of the output currents iU, iV, iW corresponding to the currents iL1, iL2, iL3, the greater the amplitude of the currents iL1, iL2, iL3. Figure 6 The voltage V across the second switching elements 2U, 2V, 2W is also shown. 2U 、V 2V 、V 2W and the potential V15 at the fourth terminal 154 of the regenerative capacitor 15. The voltage V across the second switching elements 2U, 2V, 2W 2U 、V 2V 、V 2W The voltages at both ends of the resonant capacitors 9U, 9V, and 9W are the same. Figure 6 , the timing for acquiring the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 at each carrier cycle is indicated by an arrow.

[0108] In the power converter 100, if Figure 6The polarities of the output currents iU, iV, iW are positive, negative, and negative, respectively, and the bidirectional switches 8U, 8V, and 8W respectively participate in the discharge operation, the charge operation, and the charge operation of the regeneration capacitor 15. This allows the controller 50 to set the high level time period of the control signal for one of the plurality of bidirectional switches 8 that participates in the discharge operation of the regeneration capacitor 15 to zero according to the respective polarities of the output currents iU, iV, and iW by performing the second control operation. Figure 6 As shown, the controller 50 performs a Figure 6 The potential V15 detected at the regeneration capacitor 15 is acquired at the timing indicated by the upward arrow shown below the time axis in FIG. 1 , and if the detected potential is less than the first threshold value Vth1, the high level period of the control signal SU6 for the first IGBT 6U participating in the discharge operation of the regeneration capacitor 15 is set to zero. As a result, zero voltage soft switching involving the discharge operation of the regeneration capacitor 15 is not performed to make the potential V15 at the regeneration capacitor 15 in the next carrier cycle greater than the first threshold value Vth1. Figure 6 In FIG. 1 , the control signal SU6 and its corresponding current iL1 before the high level period changes to zero are indicated by a double dot chain line. In the power converter 100, when the high level period of the control signal SU6 for the first IGBT 6U becomes zero, as shown in FIG. Figure 6 As shown, the voltage V across the second switching element 2U 2U At this time, in the power converter 100 , the zero voltage soft switching of the first switching element 1U is not performed but hard switching thereof occurs, and the first switching element 1V and the first switching element 1W are softly switched.

[0109] The controller 50 performs the third control operation by setting the high level period of one bidirectional switch 8 participating in the charging operation of the regenerative capacitor 15 among the plurality of bidirectional switches 8 to zero according to the respective polarities of the plurality of output currents iU, iV, iW supplied from the plurality of AC terminals 41. Figure 7 To illustrate an exemplary operation in such a situation. Figure 6 Explain in the same way Figure 7 .

[0110] In the power converter 100, if Figure 7 The polarities of the output currents iU, iV, iW are negative, positive, and positive, respectively, and the bidirectional switches 8U, 8V, 8W respectively participate in the charging operation, discharging operation, and discharging operation of the regenerative capacitor 15. This allows the controller 50 to set the high level period of the control signal for one of the plurality of bidirectional switches 8 that participates in the charging operation of the regenerative capacitor 15 to zero according to the respective polarities of the output currents iU, iV, iW by performing the third control operation. Figure 7As shown, the controller 50 acquires the potential V15 detected at the regeneration capacitor 15 in each carrier cycle, and if the detected potential is greater than the second threshold value Vth2, the high level period of the control signal SU7 for the second IGBT 7U participating in the charging operation of the regeneration capacitor 15 is set to zero. As a result, zero voltage soft switching involving the charging operation of the regeneration capacitor 15 is not performed to make the potential V15 at the regeneration capacitor 15 in the next carrier cycle less than the second threshold value Vth2. Figure 7 , the control signal SU7 and its corresponding current iL1 before the high level period changes to zero are indicated by a double-dot chain line.

[0111] (4) Summary

[0112] In the power converter 100 according to the first embodiment, the controller 50 performs a first control operation including overlapping a high level period of a control signal for each of the plurality of bidirectional switches 8 corresponding to each of the plurality of switching circuits 10 with a dead time Td, and setting the start time of the high level period to a time point earlier than the start time of the dead time Td by an additional time. This allows the power converter 100 to perform zero voltage soft switching on each of the plurality of first switching elements 1 and the plurality of second switching elements 2. In addition, the controller 50 of the power converter 100 acquires the potential detected at the fourth terminal 154 of the regenerative capacitor 15 per carrier cycle. In the case where the detected potential is less than a first threshold value Vth1 less than Vd / 2, the controller 50 performs a second control operation including increasing the potential V15 at the fourth terminal 154 of the regenerative capacitor 15. In the case where the detected potential is greater than a second threshold value Vth2 greater than Vd / 2, the controller 50 performs a third control operation including decreasing the potential V15 at the fourth terminal 154 of the regenerative capacitor 15. This allows the power converter 100 to reduce changes in the potential V15 at the regeneration capacitor 15 and increase the proportion of soft switching compared to a case where no operation is performed in response to changes in the potential V15 at the regeneration capacitor 15, thereby helping to increase power conversion efficiency and reduce noise.

[0113] In addition, in the power converter 100 according to the first embodiment, the controller 50 acquires the potential detected at the fourth terminal 154 of the regenerative capacitor 15 at each cycle of the carrier signal. The second control operation is an operation of controlling the plurality of bidirectional switches 8 to increase the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 according to the respective polarities of the plurality of output currents iU, iV, iW supplied from the plurality of AC terminals 41. The third control operation is an operation of controlling the plurality of bidirectional switches 8 to decrease the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 according to the respective polarities of the plurality of output currents iU, iV, iW supplied from the plurality of AC terminals 41. This allows the power converter 100 according to the first embodiment to more quickly reduce the change in the potential at the fourth terminal 154 of the regenerative capacitor 15.

[0114] In addition, the controller 50 of the power converter 100 according to the first embodiment performs a second control operation by setting a high-level period of a control signal for one of the plurality of bidirectional switches 8 participating in the discharge operation of the regenerative capacitor 15 to zero according to the respective polarities of the plurality of output currents iU, iV, iW supplied from the plurality of AC terminals 41. The controller 50 performs a third control operation by setting a high-level period of a control signal for one of the plurality of bidirectional switches 8 participating in the charge operation of the regenerative capacitor 15 to zero according to the respective polarities of the plurality of output currents iU, iV, iW supplied from the plurality of AC terminals 41. This allows the power converter 100 according to the first embodiment to perform the second control operation and the third control operation by making a simple change from the first control operation.

[0115] (Second embodiment)

[0116] Next, refer to Figures 8 to 13 In the following description, any constituent element in the power converter 100A according to the second embodiment having the same function as the corresponding part of the power converter 100 according to the first embodiment described above will be designated by the same reference numeral as the reference numeral of the corresponding part, and the description thereof will be omitted herein.

[0117] (1) Structure of power converter

[0118] In the power converter 100A according to the second embodiment, as Figure 8 As shown, the power converter 100 according to the first embodiment (refer to Figure 1) is implemented as a single resonant inductor L0. Thus, in the power converter 100A, the resonant inductor L0 is a resonant inductor for common use in a plurality of resonant capacitors 9. In the power converter 100A, the resonant circuit used for the U phase is formed by the resonant inductor L0 and the resonant capacitor 9U, the resonant circuit used for the V phase is formed by the resonant inductor L0 and the resonant capacitor 9V, and the resonant circuit used for the W phase is formed by the resonant inductor L0 and the resonant capacitor 9W. From a different perspective, in the power converter 100A, the resonant inductor L0 is used as the first resonant inductor L1, the second resonant inductor L2, and the third resonant inductor L3, thereby making it possible to reduce the number of resonant inductors provided. In addition, the power converter 100A can also reduce the number of protection circuits 17 provided.

[0119] In the power converter 100A, as in the power converter 100, the plurality of bidirectional switches 8 are provided one-to-one for the plurality of switching circuits 10. In each of the plurality of bidirectional switches 8, the first terminal 81 thereof is connected to the connection node 3 between the first switching element 1 and the second switching element 2 of the switching circuit 10 corresponding to the bidirectional switch 8.

[0120] In the power converter 100A, the respective second terminals 82 of the plurality of bidirectional switches 8 are connected to a single common connection node 25 .

[0121] The resonant inductor L0 has a first terminal and a second terminal. The first terminal of the resonant inductor L0 is connected to the common connection node 25. The regeneration capacitor 15 is connected between the second terminal of the resonant inductor L0 and the second DC terminal 32.

[0122] (2) Operation of power converter

[0123] When the controller 50 determines that the two-phase resonant currents corresponding to the two switching circuits 10 belonging to the plurality of switching circuits 10 flow through the resonant inductor L0 at the same time during the first control operation, the controller 50 synchronizes the start and end times of the high-level time periods of the two control signals for the two bidirectional switches 8 corresponding to the two switching circuits 10, respectively, among the plurality of bidirectional switches 8. In the power converter 100A, if the controller 50 overlaps the high-level time periods of the two control signals for the two bidirectional switches 8, one cycle of the LC resonance increases by 100% compared to the case where the two control signals do not overlap. times and the amount of current flowing through the resonant inductor L0 increases. Therefore, the controller 50 synchronizes the start and end times of the high-level time periods of the two control signals for the two bidirectional switches 8 by extending each high-level time period of the two control signals. At this time, in order to perform zero-voltage soft switching on the two switching circuits 10, the controller 50 determines the high-level time period so that the dead time increases In this case, the controller 50 synchronizes the start and end times of the high-level time periods of the two control signals for the two bidirectional switches 8 corresponding to the two switching circuits 10 with each other by performing control to offset at least one of the start and end times of the high-level time periods of the two control signals for the two bidirectional switches 8. Fig. 9 In FIG. 5 , the PWM signals SV1, SV2, SW1, SW2 and the control signals SV7, SW7 are indicated by double-dot chain lines before the respective high-level time periods of the two control signals SV6, SW6 are extended to completely overlap each other when the controller 50 determines that the U-phase resonant current and the W-phase resonant current flow simultaneously. Fig. 9 In FIG. 5 , the PWM signals SU1, SU2, SV1, SV2, SW1, SW2 and the control signals SU6, SV7, SW7 when the respective high-level time periods of the two control signals SV7, SW7 are extended to completely overlap each other are indicated by solid lines. Fig. 9 In FIG. 1 , the current iL0 flowing in each high level period of the control signals SV7 and SW7 before the control signals SV7 and SW7 are completely overlapped with each other is indicated by a double dot chain line, and the current iL0 flowing when the control signals SV7 and SW7 are completely overlapped with each other is indicated by a solid line. Fig. 9 In order to make the PWM signal and the control signal indicated by the double-dot chain line easily compared with the PWM signal and the control signal represented by the solid line, their high-level time periods have different potential levels, but their potential levels during the high-level time periods are actually the same.

[0124] The controller 50 performs the second control operation by setting the high level period of the control signal for at least one of the two bidirectional switches 8 participating in the discharge operation of the regenerative capacitor 15 among the plurality of bidirectional switches 8 to zero according to the respective polarities of the plurality of output currents iU, iV, iW supplied from the plurality of AC terminals 41. Fig.10 and Fig.11 To illustrate an exemplary operation in such a situation. Figure 6 Explain in the same way Fig.10 and Fig.11 .

[0125] In the power converter 100A, if Fig.10 The polarities of the output currents iU, iV, iW shown are negative, positive, and positive, respectively, and the bidirectional switches 8U, 8V, 8W respectively participate in the charging operation, discharging operation, and discharging operation of the regenerative capacitor 15. This allows the controller 50 to set the high level period of the control signal SV6 for one of the two bidirectional switches 8V, 8W participating in the discharging operation of the regenerative capacitor 15 (bidirectional switch 8V) of the plurality of bidirectional switches 8 to zero according to the respective polarities of the output currents iU, iV, iW by performing the second control operation. Fig.10 As shown, the controller 50 acquires the potential V15 detected at the regeneration capacitor 15 in each carrier cycle, and if the detected potential is less than the first threshold value Vth1, the high level period of the control signal SV6 for the first IGBT 6V participating in the discharge operation of the regeneration capacitor 15 is set to zero. In this way, the high level period of the control signal SW6 for the first IGBT 6W is shortened. This makes the potential V15 of the regeneration capacitor 15 in the next carrier cycle greater than the first threshold value Vth1. Fig.10 , the control signal SV6 and its corresponding current iL0 before the high level period changes to zero are indicated by a double-dot chain line.

[0126] In the power converter 100A, if the potential V15 detected at the regenerative capacitor 15 is smaller than the first threshold value Vth1, and the difference between the detected potential and the first threshold value Vth1 is larger than a predetermined value, then Fig.11 As shown, each high level period of the control signal SV6, SW6 for the first IGBT 6V, 6W participating in the discharge operation of the regeneration capacitor 15 is set to zero. This makes the potential V15 at the regeneration capacitor 15 in the next carrier cycle greater than the first threshold Vth1.

[0127] The controller 50 performs a third control operation by setting a high level period of a control signal for at least one of two bidirectional switches 8 participating in the charging operation of the regenerative capacitor 15 among the plurality of bidirectional switches 8 to zero according to the respective polarities of the plurality of output currents iU, iV, iW supplied from the plurality of AC terminals 41. Fig.12 and Fig.13 To illustrate an exemplary operation in such a situation. Figure 6 Explain in the same way Fig.12 and Fig.13 .

[0128] In the power converter 100A, if Fig.12The polarities of the output currents iU, iV, iW shown are positive, negative, and negative, respectively, and the bidirectional switches 8U, 8V, and 8W respectively participate in the discharge operation, the charge operation, and the charging operation of the regeneration capacitor 15. This allows the controller 50 to set the high level period of the control signal SV7 for one of the two bidirectional switches 8V and 8W participating in the charging operation of the regeneration capacitor 15 (bidirectional switch 8V) among the multiple bidirectional switches 8 to zero according to the respective polarities of the output currents iU, iV, and iW by performing the second control operation. Fig.12 As shown, the controller 50 acquires the potential V15 detected at the regeneration capacitor 15 in each carrier cycle, and if the detected potential is greater than the second threshold value Vth2, the high level period of the control signal SV7 for the second IGBT 7V participating in the charging operation of the regeneration capacitor 15 is set to zero, thereby shortening the high level period of the control signal SW7 for the second IGBT 7W. This makes the potential V15 of the regeneration capacitor 15 in the next carrier cycle less than the second threshold value Vth2. Fig.12 , the control signal SV7 and its corresponding current iL0 before the high level period changes to zero are indicated by a double-dot chain line.

[0129] In the power converter 100A, if the potential V15 detected at the regenerative capacitor 15 is greater than the second threshold value Vth2, and the difference between the detected potential and the second threshold value Vth2 is greater than a predetermined value, then Fig.13 As shown, each high level period of the control signal SV7, SW7 for the second IGBT 7V, 7W participating in the charging operation of the regeneration capacitor 15 is set to zero. This makes the potential V15 of the regeneration capacitor 15 in the next carrier cycle smaller than the second threshold value Vth2.

[0130] (3) Summary

[0131] In the power converter 100A according to the second embodiment, when the controller 50 determines that the two-phase resonant current flows through the resonant inductor L0 at the same time during the first control operation, the start time and the end time of the high-level time period of each of the two control signals are synchronized with each other by extending the high-level time periods of the two control signals for the two bidirectional switches 8 through which the two-phase resonant current flows respectively. This allows the power converter 100A to perform zero-voltage soft switching on each of the plurality of first switching elements 1 and the plurality of second switching elements 2 in a structure in which only one resonant inductor L0 is provided. In addition, the controller 50 of the power converter 100A performs the second control operation by setting the high-level time period of the control signal for at least one of the two bidirectional switches 8 participating in the discharge operation of the regenerative capacitor 15 among the plurality of bidirectional switches 8 to zero according to the respective polarities of the plurality of output currents iU, iV, iW. In addition, the controller 50 performs the third control operation by setting the high-level time period of the control signal for at least one of the two bidirectional switches 8 participating in the charging operation of the regenerative capacitor 15 among the plurality of bidirectional switches 8 to zero according to the respective polarities of the plurality of output currents iU, iV, iW. This allows the power converter 100A according to the second embodiment to increase power conversion efficiency and reduce noise in a structure in which only one resonance inductor L0 is provided.

[0132] (Third Embodiment)

[0133] The power converter 100 according to the third embodiment has the same features as the power converter 100 according to the first embodiment (see Figure 1 ) has the same circuit structure, so the circuit diagram thereof will be omitted. Figure 1 , Fig.14 and Fig.15 How the power converter 100 according to the third embodiment operates will be described.

[0134] In the power converter 100 according to the third embodiment, the second control operation and the third control operation performed by the controller 50 are different from the second control operation and the third control operation performed by the controller 50 of the power converter 100 according to the first embodiment.

[0135] The controller 50 according to the present embodiment performs the second control operation by shortening the high level period of the control signal for the bidirectional switch 8 participating in the discharge operation of the regenerative capacitor 15 among the plurality of bidirectional switches 8 according to the respective polarities of the plurality of output currents iU, iV, iW so that the integral value of the current flowing through the regenerative capacitor 15 in one cycle of the carrier signal is equal to zero. Fig.14 To illustrate an exemplary operation in such a situation. Figure 6 Explain in the same way Fig.14 .

[0136] In the power converter 100 according to the third embodiment, if Fig.14 The polarities of the output currents iU, iV, iW shown are positive, negative, and negative, respectively, and the bidirectional switches 8U, 8V, and 8W respectively participate in the discharge operation, the charge operation, and the charge operation of the regeneration capacitor 15. This allows the controller 50 to shorten the high level period of the control signal SU6 for one of the plurality of bidirectional switches 8 that participates in the discharge operation of the regeneration capacitor 15 according to the respective polarities of the output currents iU, iV, and iW by performing the second control operation. Fig.14 As shown, the controller 50 acquires the potential V15 detected at the regeneration capacitor 15 at each carrier cycle, and if the detected potential is less than the first threshold value Vth1, shortens the high level period of the control signal SU6 for the first IGBT 6U participating in the discharge operation of the regeneration capacitor 15. The shortened high level period of the control signal SU6 is a period longer than zero.

[0137] The controller 50 according to the present embodiment performs the third control operation by shortening the high level period of the control signal for the bidirectional switch 8 participating in the charging operation of the regenerative capacitor 15 among the plurality of bidirectional switches 8 according to the respective polarities of the plurality of output currents iU, iV, iW so that the integral value of the current flowing through the regenerative capacitor 15 in one cycle of the carrier signal is equal to zero. Fig.15 To illustrate an exemplary operation in such a situation. Figure 6 Explain in the same way Fig.15 .

[0138] In the power converter 100 according to the third embodiment, if Fig.15 The polarities of the output currents iU, iV, iW shown are negative, positive, and positive, respectively, and the bidirectional switches 8U, 8V, 8W respectively participate in the charging operation, discharging operation, and discharging operation of the regenerative capacitor 15. This allows the controller 50 to shorten the high level period of the control signal SU7 for one bidirectional switch 8U of the plurality of bidirectional switches 8 that participates in the charging operation of the regenerative capacitor 15 according to the respective polarities of the output currents iU, iV, iW by performing the third control operation. Fig.15 As shown, the controller 50 acquires the potential V15 detected at the regeneration capacitor 15 at each carrier cycle, and if the detected potential is greater than the second threshold value Vth2, shortens the high level period of the control signal SU7 for the second IGBT 7U participating in the charging operation of the regeneration capacitor 15 to a period longer than zero. The shortened high level period of the control signal SU7 is a period longer than zero.

[0139] The power converter 100 according to the third embodiment can reduce the possibility of causing ripples in the output current when performing the second control operation and the third control operation compared to the power converter 100 according to the first embodiment. In addition, the power converter 100 according to the third embodiment can also reduce the switching loss involved in the second control operation and the third control operation compared to the power converter 100 according to the first embodiment, thereby making it possible to further increase the power conversion efficiency.

[0140] (Fourth embodiment)

[0141] The power converter 100A according to the fourth embodiment has the same features as the power converter 100A of the second embodiment (see Figure 8 ) has the same circuit structure, so the circuit diagram thereof will be omitted. Figure 8 , Fig.16 and Fig.17 How the power converter 100A according to the fourth embodiment operates will be described.

[0142] In the power converter 100A according to the fourth embodiment, the second control operation and the third control operation performed by the controller 50 are different from the second control operation and the third control operation performed by the controller 50 of the power converter 100A according to the second embodiment.

[0143] According to the fourth embodiment, when the controller 50 of the power converter 100A determines during the first control operation that the two-phase resonant currents corresponding to two switching circuits 10 belonging to a plurality of switching circuits 10 flow through the resonant inductor L0 at the same time, the start time and the end time of the high level time periods of the two control signals for the two bidirectional switches 8 respectively corresponding to the two switching circuits 10 among the plurality of bidirectional switches 8 are synchronized with each other by extending the high level time periods of the two control signals.

[0144] The controller 50 according to the present embodiment performs the second control operation by shortening the high level period of the control signal for two bidirectional switches 8 participating in the charging operation of the regenerative capacitor 15 among the plurality of bidirectional switches 8 according to the respective polarities of the plurality of output currents iU, iV, iW. Fig.16 To illustrate an exemplary operation in such a situation. Figure 6 Explain in the same way Fig.16 .

[0145] In the power converter 100 according to the fourth embodiment, if Fig.16The polarities of the output currents iU, iV, iW are negative, positive, and positive, respectively, and the bidirectional switches 8U, 8V, 8W respectively participate in the charging operation, discharging operation, and discharging operation of the regenerative capacitor 15. This allows the controller 50 to shorten the high level time period of the control signals SV6, SW6 for the bidirectional switches 8V, 8W respectively participating in the discharging operation of the regenerative capacitor 15 among the plurality of bidirectional switches 8 according to the respective polarities of the output currents iU, iV, iW by performing the second control operation. Fig.16 As shown, the controller 50 acquires the potential V15 detected at the regeneration capacitor 15 per carrier cycle, and if the detected potential is less than the first threshold value Vth1, shortens the high level period of the control signal SV6, SW6 for the first IGBT 6V, 6W participating in the discharge operation of the regeneration capacitor 15 by the same amount of time. The shortened high level period of the control signal SV6, SW6 is a period longer than zero.

[0146] The controller 50 according to the present embodiment performs the third control operation by shortening the high level period of the control signal for two bidirectional switches 8 participating in the charging operation of the regenerative capacitor 15 among the plurality of bidirectional switches 8 according to the respective polarities of the plurality of output currents iU, iV, iW. Fig.17 To illustrate an exemplary operation in such a situation. Figure 6 Explain in the same way Fig.17 .

[0147] In the power converter 100 according to the fourth embodiment, if Fig.17 The polarities of the output currents iU, iV, iW shown are positive, negative, and negative, respectively, and the bidirectional switches 8U, 8V, and 8W respectively participate in the discharge operation, the charge operation, and the charging operation of the regeneration capacitor 15. This allows the controller 50 to shorten the high level time period of the control signals SV7 and SW7 for the bidirectional switches 8V and 8W respectively participating in the charging operation of the regeneration capacitor 15 among the plurality of bidirectional switches 8 according to the respective polarities of the output currents iU, iV, and iW by performing the third control operation. Fig.17 As shown, the controller 50 acquires the potential V15 detected at the regeneration capacitor 15 per carrier cycle, and if the detected potential is greater than the second threshold value Vth2, shortens the high level period of the control signal SV7, SW7 for the second IGBT 7V, 7W participating in the discharge operation of the regeneration capacitor 15 by the same amount of time. The shortened high level period of the control signal SV7, SW7 is a period longer than zero.

[0148] The power converter 100A according to the fourth embodiment can reduce the possibility of causing ripples in the output current when performing the second control operation and the third control operation compared to the power converter 100A according to the second embodiment. In addition, the power converter 100A according to the fourth embodiment can also reduce the switching loss involved in the second control operation and the third control operation compared to the power converter 100A according to the second embodiment, thereby enabling the power conversion efficiency to be further increased.

[0149] (Fifth Embodiment)

[0150] The power converter 100 according to the fifth embodiment has the same features as the power converter 100 according to the first embodiment (see Figure 1 ) has the same circuit structure, so the circuit diagram thereof will be omitted. Figure 1 , Fig.18 and Fig.19 How the power converter 100 according to the fifth embodiment operates will be described.

[0151] In the power converter 100 according to the fifth embodiment, the second control operation and the third control operation performed by the controller 50 are different from the second control operation and the third control operation performed by the controller 50 of the power converter 100 according to the first embodiment.

[0152] The controller 50 according to the present embodiment performs the second control operation by extending the high level period of the control signal for the bidirectional switch 8 participating in the charging operation of the regenerative capacitor 15 among the plurality of bidirectional switches 8 according to the respective polarities of the plurality of output currents iU, iV, iW so that the integral value of the current flowing through the regenerative capacitor 15 in one cycle of the carrier signal is equal to zero. Fig.18 To illustrate an exemplary operation in such a situation. Figure 6 Explain in the same way Fig.18 .

[0153] In the power converter 100 according to the fifth embodiment, if Fig.18 The polarities of the output currents iU, iV, iW are respectively positive, negative, and negative, and the bidirectional switches 8U, 8V, 8W respectively participate in the discharge operation, the charge operation, and the charging operation of the regeneration capacitor 15. This allows the controller 50 to extend the control signal with the shortest high level period (i.e., the control signal of the bidirectional switch 8 participating in the charging operation of the regeneration capacitor 15) among the plurality of bidirectional switches 8 by performing the second control operation according to the respective polarities of the output currents iU, iV, iW. Fig.18 The high level period of the control signal SV7 in the carrier signal is controlled so that the integral value of the current flowing through the regeneration capacitor 15 in one cycle of the carrier signal is equal to zero. Fig.18As shown, the controller 50 acquires the potential V15 detected at the regeneration capacitor 15 at each carrier cycle, and if the detected potential is less than the first threshold value Vth1, extends the high level period of the control signal SV7 for the second IGBT 7V participating in the charging operation of the regeneration capacitor 15. When extending the high level period of the control signal SV7, the controller 50 sets the start time of the high level period to an earlier time point, and sets the end time of the high level period to a later time point.

[0154] The controller 50 according to the present embodiment performs the third control operation by extending the high level period of the control signal for the bidirectional switch 8 participating in the discharge operation of the regeneration capacitor 15 among the plurality of bidirectional switches 8 according to the respective polarities of the plurality of output currents iU, iV, iW so that the integral value of the current flowing through the regeneration capacitor 15 in one cycle of the carrier signal is equal to zero. Fig.19 To illustrate an exemplary operation in such a situation. Figure 6 Explain in the same way Fig.19 .

[0155] In the power converter 100 according to the fifth embodiment, if Fig.19 The polarities of the output currents iU, iV, iW are negative, positive, and positive, respectively, and the bidirectional switches 8U, 8V, 8W respectively participate in the charging operation, discharging operation, and discharging operation of the regenerative capacitor 15. This allows the controller 50 to extend the control signal with the shortest high level period (i.e., the control signal of the bidirectional switch 8 participating in the discharging operation of the regenerative capacitor 15) among the plurality of bidirectional switches 8 by performing the third control operation according to the respective polarities of the output currents iU, iV, iW. Fig.19 The high level period of the control signal SV6 in the carrier signal is controlled so that the integral value of the current flowing through the regeneration capacitor 15 in one cycle of the carrier signal is equal to zero. Fig.19 As shown, the controller 50 acquires the potential V15 detected at the regeneration capacitor 15 at each carrier cycle, and if the detected potential is greater than the second threshold value Vth2, extends the high level period of the control signal SV6 for the first IGBT 6V participating in the discharge operation of the regeneration capacitor 15. When extending the high level period of the control signal SV6, the controller 50 sets the start time of the high level period to an earlier time point, and sets the end time of the high level period to a later time point.

[0156] The power converter 100 according to the fifth embodiment can reduce the possibility of causing ripples in the output current when performing the second control operation and the third control operation compared to the power converter 100 according to the first embodiment. In addition, the power converter 100 according to the fifth embodiment can also reduce the switching loss involved in the second control operation and the third control operation compared to the power converter 100 according to the first embodiment, thereby making it possible to further increase the power conversion efficiency.

[0157] (Sixth embodiment)

[0158] The power converter 100A according to the sixth embodiment has the same features as the power converter 100A according to the second embodiment (see Figure 8 ) has the same circuit structure, so the circuit diagram thereof will be omitted. Figure 8 , Fig. 20 and Fig.21 How the power converter 100A according to the sixth embodiment operates will be described.

[0159] In the power converter 100A according to the sixth embodiment, the second control operation and the third control operation performed by the controller 50 thereof are different from the second control operation and the third control operation performed by the controller 50 of the power converter 100A according to the second embodiment.

[0160] According to the controller 50 of this embodiment, when it is determined during the first control operation that the two-phase resonant currents corresponding to two switching circuits 10 belonging to a plurality of switching circuits 10 flow through the resonant inductor L0 at the same time, the start and end times of the high-level time periods of the two control signals for the two bidirectional switches 8 respectively corresponding to the two switching circuits 10 among the plurality of bidirectional switches 8 are synchronized with each other by extending the high-level time periods of the two control signals respectively.

[0161] The controller 50 according to the present embodiment performs the second control operation by extending the high level period of the control signal for the bidirectional switch 8 different from the two bidirectional switches 8 so that the integral value of the current flowing through the regeneration capacitor 15 in one cycle of the carrier signal is equal to zero. Fig. 20 To illustrate an exemplary operation in such a situation. Figure 6 Explain in the same way Fig. 20 .

[0162] In the power converter 100A according to the sixth embodiment, if Fig. 20 The polarities of the output currents iU, iV, and iW are respectively positive, negative, and negative, and the bidirectional switches 8U, 8V, and 8W respectively participate in the discharge operation, the charge operation, and the recharge operation of the regenerative capacitor 15. Fig. 20As shown, the controller 50 acquires the potential V15 detected at the regenerative capacitor 15 at each carrier cycle, and if the detected potential is less than the first threshold value Vth1, extends the high level period of the control signal SU6 for the first IGBT 6U of the bidirectional switch 8U different from the two bidirectional switches 8V, 8W whose high level periods will overlap with each other. When extending the high level period of the control signal SU6, the controller 50 sets the start timing of the high level period to an earlier time point.

[0163] The controller 50 according to the present embodiment performs the third control operation by extending the high level period of the control signal for the bidirectional switch 8 different from the two bidirectional switches 8 so that the integrated value of the current flowing through the regeneration capacitor 15 in one cycle of the carrier signal is equal to zero. Fig.21 To illustrate an exemplary operation in such a situation. Figure 6 Explain in the same way Fig.21 .

[0164] In the power converter 100A according to the sixth embodiment, if Fig.21 The polarities of the output currents iU, iV, and iW are negative, positive, and positive, respectively, and the bidirectional switches 8U, 8V, and 8W respectively participate in the charging operation, the discharging operation, and the discharging operation of the regenerative capacitor 15. Fig.21 As shown, the controller 50 acquires the potential V15 detected at the regenerative capacitor 15 at each carrier cycle, and if the detected potential is greater than the second threshold value Vth2, extends the high level period of the control signal SU7 for the second IGBT 7U of the bidirectional switch 8U different from the two bidirectional switches 8V, 8W whose high level periods will overlap with each other. When extending the high level period, the controller 50 sets the start timing of the high level period to an earlier time point.

[0165] The power converter 100A according to the sixth embodiment can reduce switching losses involved in the second control operation and the third control operation as compared with the power converter 100A according to the second embodiment, thereby enabling further increase in power conversion efficiency.

[0166] (Seventh Embodiment)

[0167] The power converter 100 according to the seventh embodiment has the same features as the power converter 100 according to the first embodiment (see Figure 1 ) has the same circuit structure, so the circuit diagram thereof will be omitted. Figure 1 , Fig. 22 and Fig.23 How the power converter 100 according to the seventh embodiment operates will be described.

[0168] In the power converter 100 according to the seventh embodiment, the second control operation and the third control operation performed by the controller 50 thereof are different from the second control operation and the third control operation performed by the controller 50 of the power converter 100 according to the first embodiment.

[0169] The controller 50 performs the first control operation by setting a dead time Td between a high level time period of the PWM signal SU1, SV1, SW1 for the first switching element 1 and a high level time period of the PWM signal SU2, SV2, SW2 for the second switching element 2 for each of the plurality of switching circuits 10. The first control operation also includes causing a high level time period of the control signal for each of the plurality of bidirectional switches 8 corresponding to each of the plurality of switching circuits 10 to overlap with the dead time Td, and setting a start time of the high level time period to a time point earlier than a start time of the dead time by an additional time.

[0170] The controller 50 performs the second control operation by acquiring the potential detected at the fourth terminal 154 of the regenerative capacitor 15 in each cycle of the carrier signal. If the detected potential is less than the first threshold value Vth1, the controller 50 applies a control signal having a high level period of time associated with the charging operation of the regenerative capacitor 15 to one of the multiple bidirectional switches 8 in one cycle of the carrier signal, in addition to applying a control signal having a high level period of time overlapping with the dead time Td to one of the multiple bidirectional switches 8. Referring to Fig. 22 To illustrate an exemplary operation in such a situation. Figure 6 Explain in the same way Fig. 22 .

[0171] exist Fig. 22 In the example shown, the controller 50 acquires the detection potential of the potential V15 at the regeneration capacitor 15 at each carrier cycle. If the detection potential is less than the first threshold Vth1, the controller 50 applies the control signal SU7 having a high level period associated with the charging operation of the regeneration capacitor 15 to the bidirectional switch 8U separately from the control signal SU6 having a high level period overlapping the dead time Td.

[0172] If the detection potential is greater than the second threshold value Vth2, the controller 50 performs a third control operation by applying a control signal having a high level period of time associated with the discharge operation of the regenerative capacitor 15 to one of the multiple bidirectional switches 8 in one cycle of the carrier signal in addition to applying a control signal having a high level period of time overlapping with the dead time Td to the one bidirectional switch 8 belonging to the multiple bidirectional switches 8 according to the respective polarities of the multiple output currents iU, iV, iW. Fig.23 To illustrate an exemplary operation in such a situation. Figure 6 Explain in the same way Fig.23 .

[0173] exist Fig.23 In the example shown, the controller 50 acquires the detection potential of the potential V15 at the regeneration capacitor 15 at each carrier cycle. If the detection potential is less than the second threshold Vth2, the controller 50 applies the control signal SU6 having a high level period associated with the discharge operation of the regeneration capacitor 15 and the control signal SU7 having a high level period overlapping the dead time Td to the bidirectional switch 8U separately.

[0174] In the power converter 100 according to the seventh embodiment, the controller 50 performs a first control operation, which includes: overlapping the high level period of the control signal for each of the plurality of bidirectional switches 8 corresponding to each of the plurality of switching circuits 10 with the dead time Td, and setting the start time of the high level period to a time point earlier than the dead time Td by an additional time. This allows the power converter 100 to perform zero voltage soft switching on each of the plurality of first switching elements 1 and the plurality of second switching elements 2. In addition, the controller 50 of the power converter 100 acquires the potential detected at the fourth terminal 154 of the regenerative capacitor 15 per carrier cycle. If the detected potential is less than the first threshold value Vth1 less than Vd / 2, the controller 50 of the power converter 100 performs a second control operation including increasing the potential V15 at the fourth terminal 154 of the regenerative capacitor 15. If the detected potential is greater than the second threshold value Vth2 greater than Vd / 2, the controller 50 of the power converter 100 performs a third control operation including decreasing the potential V15 at the fourth terminal 154 of the regenerative capacitor 15. This allows the power converter 100 to reduce changes in the potential V15 at the regeneration capacitor 15 and increase the proportion of soft switching compared to a case where no operation is performed in response to changes in the potential V15 at the regeneration capacitor 15, thereby helping to increase power conversion efficiency and reduce noise.

[0175] In addition, in the power converter 100 according to the seventh embodiment, the controller 50 acquires the potential detected at the fourth terminal 154 of the regenerative capacitor 15 at each cycle of the carrier signal. The second control operation performed by the controller 50 is an operation of controlling the plurality of bidirectional switches 8 to increase the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 according to the respective polarities of the plurality of output currents iU, iV, iW supplied from the plurality of AC terminals 41. The third control operation performed by the controller 50 is an operation of controlling the plurality of bidirectional switches 8 to decrease the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 according to the respective polarities of the plurality of output currents iU, iV, iW supplied from the plurality of AC terminals 41. This allows the power converter 100 according to the seventh embodiment to more quickly reduce the change in the potential at the fourth terminal 154 of the regenerative capacitor 15.

[0176] In addition, the controller 50 of the power converter 100 according to the seventh embodiment can perform each of the second control operation and the third control operation by simply adding a control signal compared to the case of performing the first control operation, so the second control operation and the third control operation can be performed by making a simple change from the first control operation.

[0177] (Eighth Embodiment)

[0178] Next, refer to Fig.24 The power converter 100B according to the eighth embodiment is described below. The power converter 100B according to the eighth embodiment further includes a capacitor 16 connected between the second terminal of the resonant inductor L0 and the first DC terminal 31, which is different from the power converter 100A according to the second embodiment (refer to Figure 8 In the following description, any constituent element in the power converter 100B according to the eighth embodiment having the same function as the corresponding portion of the power converter 100A according to the second embodiment described above will be designated by the same reference numeral as that of the corresponding portion, and description thereof will be omitted herein.

[0179] The power converter 100B does not include the capacitor C10 of the power converter 100A according to the second embodiment. The capacitor 16 is connected in series to the regenerative capacitor 15. Thus, in this power converter 100B, a series circuit of the capacitor 16 and the regenerative capacitor 15 is connected between the first DC terminal 31 and the second DC terminal 32. The capacitance of the capacitor 16 is the same as the capacitance of the regenerative capacitor 15. As used herein, the expression "the capacitance of the capacitor 16 is the same as the capacitance of the regenerative capacitor 15" refers not only to the case where the capacitance of the capacitor 16 is completely equal to the capacitance of the regenerative capacitor 15, but also to the case where the capacitance of the capacitor 16 is equal to or greater than 95% and equal to or less than 105% of the capacitance of the regenerative capacitor 15.

[0180] In the power converter 100B according to the eighth embodiment, the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 has a value calculated by dividing the voltage value Vd of the DC power supply E1 by 2 (2 is the number of capacitors (i.e., the capacitor 16 and the regenerative capacitor 15)). Thus, the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 is Vd / 2. In the power converter 100B according to the eighth embodiment, the controller 50 may store the value of the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 in advance.

[0181] The controller 50 of the power converter 100B according to the eighth embodiment performs the first control operation, the second control operation, and the third control operation like the controller 50 of the power converter 100A according to the second embodiment. Thus, the power converter 100B according to the eighth embodiment can contribute to increasing the power conversion efficiency like the power converter 100A according to the second embodiment.

[0182] (Ninth Embodiment)

[0183] Reference Fig.25 In the power converter 100C according to the ninth embodiment, the regenerative capacitor 15 is connected between the second terminal of the resonant inductor L0 and the first DC terminal 31, which is different from the power converter 100A according to the second embodiment (refer to Figure 8 In the following description, any constituent element in the power converter 100C according to this ninth embodiment having the same function as the corresponding portion of the power converter 100A according to the second embodiment described above will be designated by the same reference numeral as that of the corresponding portion, and description thereof will be omitted herein.

[0184] The controller 50 of the power converter 100C according to the ninth embodiment performs the first control operation, the second control operation, and the third control operation like the controller 50 of the power converter 100A according to the second embodiment. Thus, the power converter 100C according to the ninth embodiment can contribute to increasing the power conversion efficiency like the power converter 100A according to the second embodiment.

[0185] (Variation Example)

[0186] Note that the first to ninth embodiments and their variants described above are merely typical embodiments and their variants among the various embodiments of the present disclosure and should not be interpreted as limiting. On the contrary, the first to ninth exemplary embodiments and their variants can be easily modified in various ways according to design choices or any other factors without departing from the scope of the present disclosure.

[0187] For example, each switching element in 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 metal oxide semiconductor field effect transistor (MOSFET). In this case, each first diode in 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 second diode in 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. MOSFET may be, for example, a Si-based MOSFET or a SiC-based MOSFET. Each switching element in 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 gate injection transistor (GIT).

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

[0189] For example, each of the plurality of bidirectional switches 8 in the power converter 100A according to the second embodiment may have Figures 26 to 30 Any exemplary alternative structures shown.

[0190] exist Fig.26 In the illustrated example, in each of the plurality of bidirectional switches 8, the first IGBT 6 and the second IGBT 7 are connected in anti-series. Fig.26 In the illustrated example, in each of the plurality of bidirectional 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 of the second IGBT 7 is connected to the common connection node 25. In addition, each of the plurality of bidirectional 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.

[0191] exist Fig.26 In the illustrated example, 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.26 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 a chip of the replacement element. Fig.26The diode 61 and the diode 71 shown do not necessarily need to be provided as external elements for the first IGBT 6 and the second IGBT 7, respectively, but may be elements built in one chip.

[0192] exist Fig. 27 In the illustrated example, in each of the plurality of bidirectional switches 8, the first MOSFET 6A and the second MOSFET 7A are connected in anti-series. Fig. 27 In the illustrated example, in each of the plurality of bidirectional 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 bidirectional 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 bidirectional switches 8, the source terminal of the second MOSFET 7A is connected to the common connection node 25. In each of the plurality of bidirectional 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 bidirectional switch 8 including the first MOSFET 6A. PWM signals SU1 and SU2 are applied from the controller 50 to the first MOSFET 6A and the second MOSFET 7A of the bidirectional switch 8U, respectively. PWM signals SV1 and SV2 are applied from the controller 50 to the first MOSFET 6A and the second MOSFET 7A of the bidirectional switch 8V, respectively. PWM signals SW1 and SW2 are applied from the controller 50 to the first MOSFET 6A and the second MOSFET 7A of the bidirectional switch 8W, respectively.

[0193] exist Fig.28 In the illustrated example, in each of the plurality of bidirectional switches 8, a diode 63 is connected in series to the first MOSFET 6A, and a diode 73 is connected in series to the second MOSFET 7A. Fig.28 In the embodiment, a series circuit of a first MOSFET 6A and a diode 63 and a series circuit of a second MOSFET 7A and a diode 73 are connected in anti-parallel to each other.

[0194] exist Fig.29In the illustrated example, each of the plurality of bidirectional 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 bidirectional switches 8, a connection node between the diodes 84, 85 in the bidirectional switch 8 (i.e., a first terminal 81 of the bidirectional 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 terminal 82 of the bidirectional switch 8) is connected to a common connection node 25. In each of the plurality of bidirectional switches 8, when the MOSFET 80 is turned on, the bidirectional switch 8 is turned on. On the other hand, when the MOSFET 80 is turned off, the bidirectional switch 8 is turned off.

[0195] The MOSFETs 80 of the plurality of bidirectional 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 bidirectional switch 8U, a control signal SV8 for controlling the on / off state of the MOSFET 80 of the bidirectional switch 8V, and a control signal SW8 for controlling the on / off state of the MOSFET 80 of the bidirectional switch 8W.

[0196] In the bidirectional switch 8, when the MOSFET 80 is turned on, a resonant current generated by the resonant circuit including the resonant inductor L0 and the resonant capacitor 9 flows. In the power converter 100A, a charging current including the resonant current flows along a path that passes through the regenerative capacitor 15, the resonant inductor L0, the diode 86, the MOSFET 80, the diode 85, the connection node 3, and the resonant capacitor 9 in sequence when one of the plurality of bidirectional switches 8 is turned on. Furthermore, in the power converter 100A, 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 L0, and the regenerative capacitor 15 in sequence when one of the plurality of bidirectional switches 8 is turned on.

[0197] exist Fig.29 In the illustrated example, each MOSFET 80 may be replaced with an IGBT. Fig.29 In the illustrated example, each of the plurality of bidirectional switches 8 may include, for example, a bipolar transistor or a GaN-based GIT instead of the MOSFET 80 .

[0198] exist Fig.30In the illustrated example, each of the plurality of bidirectional 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. Fig.30 In the illustrated example, the control signal SU6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT used as the bidirectional switch 8U, and the control signal SU7 is applied between its second gate terminal and the second source terminal. In addition, the control signal SV6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT used as the bidirectional switch 8V, and the control signal SV7 is applied between its second gate terminal and the second source terminal. In addition, the control signal SW6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT used as the bidirectional switch 8W, and the control signal SW7 is applied between its second gate terminal and the second source terminal.

[0199] Optionally, in the first embodiment and the third to ninth embodiments except the second embodiment, each of the plurality of bidirectional switches 8 may have, for example, Figures 26 to 30 Any of the structures shown in .

[0200] Furthermore, the power converters 100 , 100A, 100B, 100C do not necessarily have to be configured to output three-phase AC power, but may also be configured to output multi-phase AC power having more than three phases.

[0201] (All aspects)

[0202] The above-mentioned first to ninth embodiments and their modifications are specific implementations of the following aspects of the present disclosure.

[0203] A power converter (100; 100A; 100B; 100C) 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 bidirectional switches (8), a plurality of resonant capacitors (9), a regenerative capacitor (15), a first resonant inductor (L1), a second resonant inductor (L2), a third resonant inductor (L3), 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 switching circuit in the plurality of switching circuits (10), one first switching element among the plurality of first switching elements (1) and a corresponding one second switching element among 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 each of 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 in the plurality of switching circuits (10). A plurality of bidirectional switches (8) are provided one-to-one for each of the plurality of switching circuits (10). A first terminal (81) of each of the plurality of bidirectional switches (8) is connected to a connection node (3) between a first switching element (1) and a second switching element (2) of a corresponding switching circuit in the plurality of switching circuits (10). A plurality of resonant capacitors (9) are provided one-to-one for each of the plurality of bidirectional switches (8). Each of the plurality of resonant capacitors (9) is connected between a first terminal (81) of a corresponding bidirectional switch in the plurality of bidirectional switches (8) and a second DC terminal (32). The regenerative capacitor (15) has a third terminal (153) and a fourth terminal (154). The third terminal (153) of the regenerative capacitor (15) is connected to the first DC terminal (31) or the second DC terminal (32). The first resonant inductor (L1) is connected between a first bidirectional switch (bidirectional switch 8U) belonging to the plurality of bidirectional switches (8) and a fourth terminal (154) of the regenerative capacitor (15). The second resonant inductor (L2) is connected between a second bidirectional switch (bidirectional switch 8V) belonging to the plurality of bidirectional switches (8) and a fourth terminal (154) of the regenerative capacitor (15). The third resonant inductor (L3) is connected between a third bidirectional switch (bidirectional switch 8W) belonging to the plurality of bidirectional switches (8) and a fourth terminal (154) of the regenerative capacitor (15).The controller (50) applies a PWM signal (SU1, SV1, SW1, SU2, SV2, SW2) having a potential alternating between a high level and a low level to each of the plurality of first switching elements (1) and the plurality of second switching elements (2). The controller (50) performs a first control operation. The first control operation includes: for each of the plurality of switching circuits (10), setting a dead time (Td) between a high level time period of the PWM signal (SU1, SV1, SW1) for the first switching element (1) and a high level time period of the PWM signal (SU2, SV2, SW2) for the second switching element (2). The first control operation also includes: making a high level time period of a control signal for each of the plurality of bidirectional switches (8) corresponding to each of the plurality of switching circuits (10) overlap with the dead time (Td), and setting a start time of the high level time period to a time point earlier than a start time of the dead time (Td) by an additional time. The controller (50) acquires a potential detected at a fourth terminal (154) of the regenerative capacitor (15). When the detected potential is less than a first threshold value (Vth1) smaller than half of the voltage value (Vd) applied between the first DC terminal (31) and the second DC terminal (32), the controller (50) performs a second control operation including increasing the potential at the fourth terminal (154) of the regenerative capacitor (15). When the detected potential is greater than a second threshold value (Vth2) greater than half of the voltage value (Vd) applied between the first DC terminal (31) and the second DC terminal (32), the controller (50) performs a third control operation including decreasing the potential at the fourth terminal (154) of the regenerative capacitor (15).

[0204] This aspect can help increase power conversion efficiency.

[0205] In a power converter (100; 100A; 100B; 100C) according to the second aspect which can be implemented in combination with the first aspect, a controller (50) acquires a potential detected at a fourth terminal (154) of a regenerative capacitor (15) at each cycle of a carrier signal. A second control operation is an operation of controlling a plurality of bidirectional switches (8) to increase a potential (V15) at the fourth terminal (154) of the regenerative capacitor (15) according to respective polarities of a plurality of output currents (iU, iV, iW) supplied from a plurality of AC terminals (41). A third control operation is an operation of controlling a plurality of bidirectional switches (8) to decrease a potential (V15) at the fourth terminal (154) of the regenerative capacitor (15) according to respective polarities of a plurality of output currents (iU, iV, iW) supplied from a plurality of AC terminals (41).

[0206] This aspect allows the change in potential at the fourth terminal (154) of the regeneration capacitor (15) to be reduced more quickly.

[0207] In a power converter (100; 100A; 100B; 100C) according to a third aspect that can be implemented in combination with the second aspect, a controller (50) performs a second control operation by setting a high level time period of one of the plurality of bidirectional switches (8) participating in a discharge operation of a regenerative capacitor (15) to zero according to each polarity of a plurality of output currents (iU, iV, iW) supplied from a plurality of AC terminals (41). The controller (50) performs a third control operation by setting a high level time period of one of the plurality of bidirectional switches (8) participating in a charge operation of a regenerative capacitor (15) to zero according to each polarity of a plurality of output currents (iU, iV, iW) supplied from a plurality of AC terminals (41).

[0208] This aspect allows the second control operation and the third control operation to be performed by making a simple change from the first control operation.

[0209] In a power converter (100A; 100B; 100C) according to a fourth aspect that can be implemented in combination with the third aspect, a first resonant inductor (L1), a second resonant inductor (L2), and a third resonant inductor (L3) are implemented as a single resonant inductor (L0). When a controller (50) determines that two-phase resonant currents corresponding to two switching circuits (10) belonging to a plurality of switching circuits (10) flow through the single resonant inductor (L0) at the same time during a first control operation, the controller (50) synchronizes the start and end times of the high-level time periods of the two control signals for two bidirectional switches (8) corresponding to the two switching circuits (10) among the plurality of bidirectional switches (8) respectively. The controller (50) performs a second control operation by setting the high-level time period of the control signal for at least one of the two bidirectional switches (8) participating in the discharge operation of the regenerative capacitor (15) among the plurality of bidirectional switches (8) to zero according to the respective polarities of the plurality of output currents (iU, iV, iW) supplied from the plurality of AC terminals (41). The controller (50) performs a third control operation by setting a high level time period of a control signal for at least one of two bidirectional switches (8) among a plurality of bidirectional switches (8) participating in a charging operation of a regenerative capacitor (15) to zero according to respective polarities of a plurality of output currents (iU, iV, iW) supplied from a plurality of AC terminals (41).

[0210] This aspect can contribute to increasing power conversion efficiency and reducing noise in a structure in which only one resonant inductor (L0) is provided.

[0211] In a power converter (100; 100A; 100B; 100C) according to a fifth aspect that can be implemented in combination with the second aspect, a controller (50) performs a second control operation by shortening a high level period of a control signal for a bidirectional switch (8) among a plurality of bidirectional switches (8) that participates in a discharge operation of a regenerative capacitor (15) according to respective polarities of a plurality of output currents (iU, iV, iW) supplied from a plurality of AC terminals (41) so that an integral value of a current flowing through the regenerative capacitor (15) in one cycle of a carrier signal is equal to zero. The controller (50) performs a third control operation by shortening a high level period of a control signal for a bidirectional switch (8) among a plurality of bidirectional switches (8) that participates in a charge operation of the regenerative capacitor (15) according to respective polarities of a plurality of output currents (iU, iV, iW) supplied from a plurality of AC terminals (41) so that an integral value of a current flowing through the regenerative capacitor (15) in one cycle of a carrier signal is equal to zero.

[0212] This aspect can reduce switching losses involved in the second control operation and the third control operation, thereby enabling further increase in power conversion efficiency.

[0213] In a power converter (100; 100A; 100B; 100C) according to the sixth aspect which can be implemented in combination with the fifth aspect, the first resonant inductor (L1), the second resonant inductor (L2) and the third resonant inductor (L3) are implemented as a single resonant inductor (L0). When the controller (50) determines that two-phase resonant currents corresponding to two switching circuits (10) belonging to the plurality of switching circuits (10) flow through the single resonant inductor (L0) at the same time during the first control operation, the controller (50) synchronizes the start time and the end time of the high level time period of each of the two control signals by extending the high level time period of the two control signals for two bidirectional switches (8) respectively corresponding to the two switching circuits (10) among the plurality of bidirectional switches (8). The controller (50) performs the second control operation by shortening the high level time period of the control signal for each of the two bidirectional switches (8) so that the integrated value of the current flowing through the regenerative capacitor (15) in one cycle of the carrier signal is equal to zero. The controller (50) performs a third control operation by shortening a high level period of a control signal for each of the two bidirectional switches (8) so that an integral value of a current flowing through the regenerative capacitor (15) in one cycle of a carrier signal is equal to zero.

[0214] This aspect can contribute to increasing power conversion efficiency and reducing noise in a structure in which only one resonant inductor (L0) is provided.

[0215] In a power converter (100; 100A; 100B; 100C) according to a seventh aspect that can be implemented in combination with the second aspect, a controller (50) performs a second control operation by extending the shortest high level time period among high level time periods of a control signal for a bidirectional switch (8) participating in a charging operation of a regenerative capacitor (15) among a plurality of bidirectional switches (8) according to respective polarities of a plurality of output currents (iU, iV, iW) supplied from a plurality of AC terminals (41) so that an integral value of a current flowing through the regenerative capacitor (15) in one cycle of a carrier signal is equal to zero. The controller (50) performs a third control operation by extending the shortest high level time period among high level time periods of a control signal for a bidirectional switch (8) participating in a discharging operation of the regenerative capacitor (15) among a plurality of bidirectional switches (8) according to respective polarities of a plurality of output currents (iU, iV, iW) supplied from a plurality of AC terminals (41) so that an integral value of a current flowing through the regenerative capacitor (15) in one cycle of a carrier signal is equal to zero.

[0216] This aspect can reduce switching losses involved in the second control operation and the third control operation, thereby enabling further increase in power conversion efficiency.

[0217] In a power converter (100A; 100B; 100C) according to the eighth aspect which can be implemented in combination with the seventh aspect, the first resonant inductor (L1), the second resonant inductor (L2) and the third resonant inductor (L3) are implemented as a single resonant inductor (L0). When the controller (50) determines that two-phase resonant currents corresponding to two switching circuits (10) belonging to the plurality of switching circuits (10) flow through the single resonant inductor (L0) at the same time during the first control operation, the controller (50) synchronizes the start time and the end time of the high level time period of each of the two control signals by extending the high level time period of the two control signals for two bidirectional switches (8) respectively corresponding to the two switching circuits (10) among the plurality of bidirectional switches (8). The controller (50) performs the second control operation by extending the high level time period of the control signal for the bidirectional switch (8) different from the two bidirectional switches (8) so that the integral value of the current flowing through the regenerative capacitor (15) in one cycle of the carrier signal is equal to zero. The controller (50) performs a third control operation by extending a high level period of a control signal for a bidirectional switch (8) different from the two bidirectional switches (8) so that an integral value of a current flowing through a regenerative capacitor (15) in one cycle of a carrier signal is equal to zero.

[0218] This aspect can reduce switching losses involved in the second control operation and the third control operation, thereby enabling further increase in power conversion efficiency.

[0219] A power converter (100) according to a ninth 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 bidirectional switches (8), a plurality of resonant capacitors (9), a regenerative capacitor (15), a first resonant inductor (L1), a second resonant inductor (L2), a third resonant inductor (L3), 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 switching circuit in the plurality of switching circuits (10), one first switching element among the plurality of first switching elements (1) and a corresponding one second switching element among 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), respectively. 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 in a plurality of switching circuits (10). The plurality of bidirectional switches (8) are provided one-to-one for the plurality of switching circuits (10). The first terminal (81) of each of the plurality of bidirectional switches (8) is connected to a connection node (3) between a first switching element (1) and a second switching element (2) of a corresponding switching circuit in a plurality of switching circuits (10). The plurality of resonant capacitors (9) are provided one-to-one for the plurality of bidirectional switches (8), respectively. Each of the plurality of resonant capacitors (9) is connected between a first terminal (81) of a corresponding bidirectional switch in a plurality of bidirectional switches (8) and a second DC terminal (32). The regenerative capacitor (15) has a third terminal (153) and a fourth terminal (154). The third terminal (153) of the regenerative capacitor (15) is connected to the first DC terminal (31) or the second DC terminal (32). A first resonant inductor (L1) is connected between a first bidirectional switch (bidirectional switch 8U) belonging to a plurality of bidirectional switches (8) and a fourth terminal (154) of a regenerative capacitor (15). A second resonant inductor (L2) is connected between a second bidirectional switch (bidirectional switch 8V) belonging to a plurality of bidirectional switches (8) and a fourth terminal (154) of a regenerative capacitor (15). A third resonant inductor (L3) is connected between a third bidirectional switch (bidirectional switch 8W) belonging to a plurality of bidirectional switches (8) and a fourth terminal (154) of a regenerative capacitor (15). A controller (50) applies a PWM signal (SU1, SU2, SV1, SV2, SW1, SW2) having a potential alternating between a high level and a low level to each of the plurality of first switching elements (1) and the plurality of second switching elements (2).The controller (50) performs a first control operation. The first control operation includes: for each switching circuit in the plurality of switching circuits (10), setting a dead time (Td) between a high level time period of a PWM signal (SU1, SV1, SW1) for a first switching element (1) and a high level time period of a PWM signal (SU2, SV2, SW2) for a second switching element (2). The first control operation includes: making a high level time period of a control signal for each bidirectional switch in the plurality of bidirectional switches (8) corresponding to each switching circuit in the plurality of switching circuits (10) overlap with the dead time (Td), and setting a start time of the high level time period to a time point earlier than a start time of the dead time (Td) by an additional time. The controller (50) acquires a potential detected at a fourth terminal (154) of the regenerative capacitor (15). When the detected potential is less than a first threshold value (Vth1) that is less than half of the voltage value (Vd) applied between the first DC terminal (31) and the second DC terminal (32), the controller (50) performs a second control operation, the second control operation comprising: in accordance with the respective polarities of the plurality of output currents (iU, iV, iW) supplied from the plurality of AC terminals (41), in one cycle of a carrier signal, in addition to applying a control signal having a high level time period overlapping with a dead time (Td) to one of the plurality of bidirectional switches (8), a control signal having a high level time period associated with a charging operation of a regenerative capacitor (15) is also applied to the one bidirectional switch (8). When the detection potential is greater than a second threshold value (Vth2) greater than half of the voltage value (Vd) applied between the first DC terminal (31) and the second DC terminal (32), the controller (50) performs a third control operation for applying a control signal having a high level time period associated with a discharge operation of a regenerative capacitor (15) to one bidirectional switch (8) belonging to the plurality of bidirectional switches (8) in one cycle of a carrier signal, in addition to applying a control signal having a high level time period overlapping with a dead time (Td) to the one bidirectional switch (8), according to the respective polarities of the plurality of output currents (iU, iV, iW) supplied from the plurality of AC terminals (41).

[0220] This aspect can help increase power conversion efficiency.

[0221] Description of Reference Numerals

[0222] 1First switching element

[0223] 2 Second switching element

[0224] 3 Connecting Nodes

[0225] 8 Two-way switch

[0226] 9. Resonant capacitor

[0227] 10Switching circuit

[0228] 11 Power conversion circuit

[0229] 15 Regeneration capacitor

[0230] 153 Third terminal

[0231] 154 Fourth terminal

[0232] 31 First DC terminal

[0233] 32 Second DC terminal

[0234] 41 AC terminal

[0235] 50 Controller

[0236] 100,100A,100B,100C Power Converter

[0237] iU,iV,iW output current

[0238] L0 resonant inductor

[0239] L1 First resonant inductor

[0240] L2 Second resonant inductor

[0241] L3 Third resonant inductor

[0242] Td Dead time

[0243] Vd voltage value

[0244] Vth1 First threshold

[0245] Vth2 Second threshold

Claims

1. A power converter, comprising: 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, which are respectively provided one-to-one for the plurality of switching circuits, each of the plurality of AC terminals being connected to a connection node between a first switching element and a second switching element of a corresponding switching circuit of the plurality of switching circuits; a plurality of bidirectional switches, which are provided one-to-one for the plurality of switching circuits, wherein a first terminal of each of the plurality of bidirectional switches is connected to a connection node between a first switching element and a second switching element of a corresponding switching circuit of the plurality of switching circuits; a plurality of resonant capacitors, which are respectively provided one-to-one for the plurality of bidirectional switches, each of the plurality of resonant capacitors being connected between a first terminal of a corresponding bidirectional switch of the plurality of bidirectional switches and the second DC terminal; a regeneration capacitor having a third terminal and a fourth terminal, the third terminal of the regeneration capacitor being connected to the first DC terminal or the second DC terminal; a first resonant inductor connected between a first bidirectional switch belonging to the plurality of bidirectional switches and a fourth terminal of the regenerative capacitor; a second resonant inductor connected between a second bidirectional switch belonging to the plurality of bidirectional switches and a fourth terminal of the regenerative capacitor; a third resonant inductor connected between a third bidirectional switch belonging to the plurality of bidirectional switches and a fourth terminal of the regenerative capacitor; as well as a controller configured to apply a PWM signal to each of the plurality of first switching elements and the plurality of second switching elements, the PWM signal having a potential alternating between a high level and a low level, Wherein, the controller is configured as: performing a first control operation, the first control operation being used to: for each of the plurality of switching circuits, set a dead time between a high level time period of a PWM signal for the first switching element and a high level time period of a PWM signal for the second switching element; make a high level time period of a control signal for each of the plurality of bidirectional switches corresponding to each of the plurality of switching circuits overlap with the dead time; and set a start time of the high level time period to a time point earlier than a start time of the dead time by an additional time; acquiring a potential detected at a fourth terminal of the regenerative capacitor; When the detected potential is less than a first threshold value that is less than half the value of the voltage applied between the first DC terminal and the second DC terminal, performing a second control operation for increasing the potential at the fourth terminal of the regenerative capacitor; and When the detected potential is greater than a second threshold value greater than half the value of the voltage applied between the first DC terminal and the second DC terminal, a third control operation is performed for decreasing the potential at the fourth terminal of the regenerative capacitor.

2. The power converter according to claim 1, wherein: The controller is configured to acquire a potential detected at a fourth terminal of the regeneration capacitor at each cycle of the carrier signal, The second control operation is an operation for controlling the plurality of bidirectional switches to increase the potential at the fourth terminal of the regenerative capacitor according to respective polarities of the plurality of output currents supplied from the plurality of AC terminals, and The third control operation is an operation for controlling the plurality of bidirectional switches to drop the potential at the fourth terminal of the regenerative capacitor according to the respective polarities of the plurality of output currents supplied from the plurality of AC terminals.

3. The power converter according to claim 2, wherein: The controller is configured to: performing the second control operation by setting a high level period of one bidirectional switch participating in the discharge operation of the regeneration capacitor among the plurality of bidirectional switches to zero according to respective polarities of the plurality of output currents supplied from the plurality of AC terminals, and The third control operation is performed by setting a high level period of one bidirectional switch participating in the charging operation of the regeneration capacitor among the plurality of bidirectional switches to zero according to respective polarities of the plurality of output currents supplied from the plurality of AC terminals.

4. The power converter according to claim 3, wherein: The first resonant inductor, the second resonant inductor, and the third resonant inductor are implemented as a single resonant inductor, and The controller is configured to: When it is determined during the first control operation that two-phase resonant currents corresponding to two switching circuits belonging to the plurality of switching circuits flow through the single resonant inductor at the same time, the start time and the end time of the high level time periods of the two control signals are synchronized with each other by extending the high level time periods of the two control signals for the two bidirectional switches respectively corresponding to the two switching circuits among the plurality of bidirectional switches; performing the second control operation by setting a high level period of a control signal for at least one of two bidirectional switches participating in a discharge operation of the regenerative capacitor among the plurality of bidirectional switches to zero according to respective polarities of a plurality of output currents supplied from the plurality of AC terminals; as well as The third control operation is performed by setting a high level period of a control signal for at least one of two bidirectional switches participating in a charging operation of the regeneration capacitor among the plurality of bidirectional switches to zero according to respective polarities of a plurality of output currents supplied from the plurality of AC terminals.

5. The power converter according to claim 2, wherein: The controller is configured to: The second control operation is performed by shortening a high level period of a control signal for a bidirectional switch among the plurality of bidirectional switches participating in a discharge operation of the regenerative capacitor according to respective polarities of a plurality of output currents supplied from the plurality of AC terminals so that an integrated value of a current flowing through the regenerative capacitor in one cycle of a carrier signal is equal to zero; as well as The third control operation is performed by shortening the high-level time period of the control signal for the bidirectional switch among the multiple bidirectional switches participating in the charging operation of the regeneration capacitor according to the respective polarities of the multiple output currents supplied from the multiple AC terminals so that the integrated value of the current flowing through the regeneration capacitor in one cycle of the carrier signal is equal to zero.

6. The power converter according to claim 5, wherein: The first resonant inductor, the second resonant inductor, and the third resonant inductor are implemented as a single resonant inductor, and The controller is configured to: When it is determined during the first control operation that two-phase resonant currents corresponding to two switching circuits belonging to the plurality of switching circuits flow through the single resonant inductor at the same time, the start time and the end time of the high level time periods of the two control signals are synchronized with each other by extending the high level time periods of the two control signals for the two bidirectional switches respectively corresponding to the two switching circuits among the plurality of bidirectional switches; performing the second control operation by shortening a high level period of a control signal for each of the two bidirectional switches so that an integrated value of a current flowing through the regeneration capacitor in one cycle of a carrier signal is equal to zero; as well as The third control operation is performed by shortening a high level period of a control signal for each of the two bidirectional switches so that an integrated value of a current flowing through the regeneration capacitor in one cycle of a carrier signal is equal to zero.

7. The power converter according to claim 2, wherein: The controller is configured to: The second control operation is performed by extending the shortest high-level period of the high-level period of the control signal for the bidirectional switch participating in the charging operation of the regenerative capacitor among the plurality of bidirectional switches according to the respective polarities of the plurality of output currents supplied from the plurality of AC terminals so that the integrated value of the current flowing through the regenerative capacitor in one cycle of the carrier signal is equal to zero; as well as The third control operation is performed by extending the shortest high-level time period among the high-level time periods of the control signal of the bidirectional switch among the multiple bidirectional switches participating in the discharge operation of the regeneration capacitor according to the respective polarities of the multiple output currents supplied from the multiple AC terminals so that the integrated value of the current flowing through the regeneration capacitor in one cycle of the carrier signal is equal to zero.

8. The power converter according to claim 7, wherein: The first resonant inductor, the second resonant inductor, and the third resonant inductor are implemented as a single resonant inductor, and The controller is configured to: When it is determined during the first control operation that two-phase resonant currents corresponding to two switching circuits belonging to the plurality of switching circuits flow through the single resonant inductor at the same time, the start time and the end time of the high level time periods of the two control signals are synchronized with each other by extending the high level time periods of the two control signals for the two bidirectional switches respectively corresponding to the two switching circuits among the plurality of bidirectional switches; performing the second control operation by extending a high level period of a control signal for a bidirectional switch different from the two bidirectional switches so that an integrated value of a current flowing through the regenerative capacitor in one cycle of a carrier signal is equal to zero; as well as The third control operation is performed by extending a high level period of a control signal for a bidirectional switch different from the two bidirectional switches so that an integrated value of a current flowing through the regeneration capacitor in one cycle of a carrier signal is equal to zero.

9. A power converter comprising: 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, which are respectively provided one-to-one for the plurality of switching circuits, each of the plurality of AC terminals being connected to a connection node between a first switching element and a second switching element of a corresponding switching circuit of the plurality of switching circuits; a plurality of bidirectional switches, which are provided one-to-one for the plurality of switching circuits, wherein a first terminal of each of the plurality of bidirectional switches is connected to a connection node between a first switching element and a second switching element of a corresponding switching circuit of the plurality of switching circuits; a plurality of resonant capacitors, which are respectively provided one-to-one for the plurality of bidirectional switches, each of the plurality of resonant capacitors being connected between a first terminal of a corresponding bidirectional switch of the plurality of bidirectional switches and the second DC terminal; a regeneration capacitor having a third terminal and a fourth terminal, the third terminal of the regeneration capacitor being connected to the first DC terminal or the second DC terminal; a first resonant inductor connected between a first bidirectional switch belonging to the plurality of bidirectional switches and a fourth terminal of the regenerative capacitor; a second resonant inductor connected between a second bidirectional switch belonging to the plurality of bidirectional switches and a fourth terminal of the regenerative capacitor; a third resonant inductor connected between a third bidirectional switch belonging to the plurality of bidirectional switches and a fourth terminal of the regenerative capacitor; as well as a controller configured to apply a PWM signal to each of the plurality of first switching elements and the plurality of second switching elements, the PWM signal having a potential alternating between a high level and a low level, Wherein, the controller is configured as: performing a first control operation, the first control operation being used to: for each of the plurality of switching circuits, set a dead time between a high level time period of a PWM signal for the first switching element and a high level time period of a PWM signal for the second switching element; make a high level time period of a control signal for each of the plurality of bidirectional switches corresponding to each of the plurality of switching circuits overlap with the dead time; and set a start time of the high level time period to a time point earlier than a start time of the dead time by an additional time; acquiring a potential detected at a fourth terminal of the regenerative capacitor; performing a second control operation for applying a control signal having a high level period associated with a charging operation of the regenerative capacitor to one bidirectional switch belonging to the plurality of bidirectional switches in addition to applying a control signal having a high level period overlapping with the dead time in one cycle of a carrier signal, in a case where the detection potential is less than a first threshold value that is less than half of a voltage value applied between the first DC terminal and the second DC terminal, according to respective polarities of a plurality of output currents supplied from the plurality of AC terminals; and When the detection potential is greater than a second threshold value that is greater than half of the voltage value applied between the first DC terminal and the second DC terminal, a third control operation is performed, wherein the third control operation is used to apply a control signal having a high level time period associated with a discharge operation of the regenerative capacitor to one bidirectional switch belonging to the plurality of bidirectional switches in one cycle of a carrier signal, in addition to applying a control signal having a high level time period overlapping with the dead time to the one bidirectional switch according to the respective polarities of the plurality of output currents supplied from the plurality of AC terminals.

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