Power converter

Abstract

According to the invention, the problem of how to more reliably carry out soft handover is solved. The controller (50) may perform a first control operation and a second control operation when it is determined that a resonant current each passing through a respective switch of the two or more switches (8) simultaneously flows through the resonant inductor (L1). The first control operation is to enable a high-level period of the control signal of each of the two or more switches (8) to overlap a predetermined period of time with a dead-time period associated with each of the two or more switching circuits (10) respectively connected to the two or more switches (8). The second control operation is used for determining a start of a high-level period of the control signal of the at least one switch (8) by means of the load current.

Description

Technical Field

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

[0002] Patent Document 1 discloses a 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. 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 to 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] In the power converter of patent document 1, when the control component determines that multiple phase currents flow through the coil, it controls multiple auxiliary switching elements so that the current flowing through at least one phase is less than a preset amount, so the control component does not perform soft switching of the main switch corresponding to the at least one phase.

[0005] Citation List

[0006] Patent Document 1: Japanese Patent Application Publication No. 2010-233306 Summary of the invention

[0007] An object of the present disclosure is to provide a power converter having the capability of soft switching more reliably.

[0008] A power converter according to one aspect of the present disclosure includes a first DC terminal and a second DC terminal, a power conversion circuit, a plurality of AC terminals, a plurality of switches, a plurality of resonant capacitors, a resonant inductor, a regenerative capacitor, and a controller. The power conversion circuit includes a plurality of first switching elements and a plurality of second switching elements. In the power conversion circuit, a plurality of switching circuits are connected in parallel to each other, and in each of the plurality of switching circuits, a first switching element in the plurality of first switching elements and a corresponding second switching element in the plurality of second switching elements are connected in series one-to-one. In the power conversion circuit, a plurality of first switching elements are connected to the first DC terminal, and a plurality of second switching elements are connected to the second DC terminal. A plurality of AC terminals are set one-to-one for a 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 in the plurality of switching circuits. A plurality of switches are set one-to-one for a plurality of switching circuits. A first terminal of each of the plurality of switches is connected to a connection node between a first switching element and a second switching element of a corresponding switching circuit in the plurality of switching circuits. The second terminals of each of the plurality of switches are connected in common to a common connection node. A plurality of resonant capacitors are set one-to-one for a plurality of switches. Each of the plurality of resonant capacitors is connected between a first terminal and a second DC terminal of a corresponding switch in the plurality of switches. The resonant inductor has a first terminal and a second terminal. In the resonant inductor, the first terminal of the resonant inductor is connected to a common connection node. The regenerative capacitor has a third terminal and a fourth terminal. In the regenerative capacitor, the third terminal is connected to the first DC terminal or the second DC terminal. The controller applies a control signal having a potential alternating between a high level and a low level to each of the plurality of first switching elements, the plurality of second switching elements, and the plurality of switches. When it is determined that the resonant currents of the corresponding switches of two or more switches belonging to the plurality of switches flow through the resonant inductor at the same time, the controller is capable of performing a first control operation and a second control operation. The first control operation includes: enabling the high level period of the control signal of each of the two or more switches to overlap a predetermined period of the dead time period associated with each of the two or more switching circuits belonging to the plurality of switching circuits and connected to the two or more switches respectively. The second control operation includes determining a start of a high level period of a control signal of at least one of the plurality of switches by a load current flowing through at least one phase of an AC load connected to the plurality of AC terminals. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a circuit diagram of a system including a power converter according to a first embodiment;

[0010] Figure 2shows how duty ratios and load currents respectively corresponding to three-phase voltage commands in AC loads connected to a plurality of AC terminals of a power converter vary with time;

[0011] Figure 3 shows how the power converter operates in the case where its controller has performed basic operations when the load current is > 0 and its resonant capacitor has performed charging operations;

[0012] Figure 4 It also shows how the power converter operates in the case where its controller has performed basic operations when the load current is > 0 and its resonant capacitor has performed charging operations;

[0013] Figure 5 showing a first current threshold and a second current threshold used in a controller of a power converter;

[0014] Figure 6 shows how the power converter operates in the case where its controller has performed basic operation when the load current is >0 and its resonant capacitor has performed a discharge operation;

[0015] Figure 7 It also shows how the power converter operates in the case where its controller has performed basic operation when the load current is <0 and its resonant capacitor has performed a discharge operation;

[0016] Figure 8 shows how the power converter operates in the case where its controller has performed basic operations when the load current is <0 and its resonant capacitor has performed charging operations;

[0017] Fig. 9 is a timing diagram showing how the power converter operates in a situation where its controller has performed a first control operation, a second control operation, and a third control operation;

[0018] Fig.10 is a timing chart showing how the power converter operates in a case where its controller does not perform any of the first control operation, the second control operation and the third control operation;

[0019] Fig.11 is a timing diagram showing an exemplary situation in which a controller of a power converter assumes that two-phase resonant currents overlap each other;

[0020] Fig.12 is a timing diagram showing another exemplary situation in which the controller of the power converter assumes that two-phase resonant currents overlap each other;

[0021] Fig.13 is a timing diagram showing still another exemplary situation in which the controller of the power converter assumes that two-phase resonant currents overlap each other;

[0022] Fig.14 Also shown is how the duty ratio and load current respectively corresponding to the three-phase voltage commands in the AC load connected to the plurality of AC terminals of the power converter vary with time;

[0023] Fig.15 is a timing diagram showing still another exemplary situation in which the controller of the power converter assumes that two-phase resonant currents overlap each other;

[0024] Fig.16 is a timing diagram showing how the power converter operates in a situation where its controller has performed a first control operation, a second control operation, and a third control operation;

[0025] Fig.17 is a timing chart showing how the power converter operates in a case where its controller does not perform any of the first control operation, the second control operation and the third control operation;

[0026] Fig.18 is a timing diagram showing how the power converter operates in a situation where its controller has performed the first control operation and the third control operation;

[0027] Fig.19 is a timing diagram showing how the power converter operates in a situation where its controller performs neither the first control operation nor the third control operation;

[0028] Fig. 20 is a timing diagram showing still another exemplary situation in which the controller of the power converter assumes that the three-phase resonant currents overlap with each other;

[0029] Fig.21 is a timing diagram showing still another exemplary situation in which the controller of the power converter assumes that the three-phase resonant currents overlap with each other;

[0030] Fig. 22 is a timing diagram showing still another exemplary situation in which the controller of the power converter assumes that two-phase resonant currents overlap each other;

[0031] Fig.23 is a timing diagram showing still another exemplary situation in which the controller of the power converter assumes that two-phase resonant currents overlap each other;

[0032] Fig.24 is a timing diagram showing how the power converter operates in a situation where its controller has performed the first control operation and the third control operation;

[0033] Fig.25 is a timing diagram showing how the power converter operates in a situation where its controller performs neither the first control operation nor the third control operation;

[0034] Fig.26 is a timing chart showing how the power converter according to the first modification of the first embodiment operates in a situation where its controller has performed the first control operation and the second control operation;

[0035] Fig. 27 is a timing chart showing how the power converter according to the second modification of the first embodiment operates in a situation where its controller has performed the first control operation and the second control operation;

[0036] Fig.28 is a timing diagram showing how the power converter operates in a situation where its controller performs neither the first control operation nor the second control operation;

[0037] Fig.29 is a timing chart showing how the power converter according to the third modification of the first embodiment operates in a situation where its controller has performed the first control operation and the second control operation;

[0038] Fig.30 is a timing chart showing how the power converter according to the fourth modification of the first embodiment operates in a situation where its controller has performed the first control operation, the second control operation, and the third control operation;

[0039] Fig.31 is a timing chart showing how the power converter according to the fifth modification of the first embodiment operates in a situation where its controller has performed the first control operation and the second control operation;

[0040] Fig.32 is a timing diagram showing how the power converter operates in a situation where its controller has performed a first control operation and a second control operation;

[0041] Fig.33 The premise of the operation of the power converter according to the sixth modification of the first embodiment is shown;

[0042] Fig.34 is a timing diagram showing how the power converter operates in a situation where its controller has performed a first control operation, a second control operation, and a third control operation;

[0043] Fig.35 is a timing chart showing how the power converter according to the seventh modification of the first embodiment operates in a situation where its controller has performed the first control operation and the second control operation;

[0044] Fig.36 is a circuit diagram of a system including a power converter according to an eighth modification of the first embodiment;

[0045] Fig.37is a circuit diagram of a system including a power converter according to a ninth modification of the first embodiment;

[0046] Fig.38 is a circuit diagram of a system including a power converter according to a tenth modification of the first embodiment;

[0047] Fig.39 is a circuit diagram of a system including a power converter according to an eleventh modification of the first embodiment;

[0048] Fig.40 is a circuit diagram of a system including a power converter according to a twelfth modification of the first embodiment;

[0049] Fig.41 is a circuit diagram of a system including a power converter according to a thirteenth modification of the first embodiment;

[0050] Fig.42 is a circuit diagram of a system including a power converter according to a second embodiment; and

[0051] Fig.43 is a circuit diagram of a system including a power converter according to a third embodiment. DETAILED DESCRIPTION

[0052] (First embodiment)

[0053] Will refer to Figures 1 to 25 A power converter 100 according to a first embodiment is described.

[0054] (1) Overall configuration of power converter

[0055] For example, Figure 1 As shown, the power converter 100 includes a first DC terminal 31 and a second DC terminal 32 and a plurality of (e.g., three) AC terminals 41. The DC power source E1 is connected between the first DC terminal 31 and the second DC terminal 32. The AC load RA1 is connected to the plurality of AC terminals 41. The AC load RA1 may be, for example, a three-phase motor. The power converter 100 converts the DC output of the DC power source E1 into AC power and outputs the AC power to the AC load RA1. The DC power source E1 may include, for example, a solar cell or a fuel cell. The DC power source E1 may include a DC-DC converter. In the power converter 100, if the plurality of AC terminals 41 are three AC terminals 41, the AC power may be, for example, a three-phase AC power having a U phase, a V phase, and a W phase.

[0056] The power converter 100 includes a power conversion circuit 11, a plurality of (e.g., three) switches 8, a plurality of (e.g., three) resonant capacitors 9, a regenerative capacitor 15, a resonant inductor L1, and a controller 50. The power converter 100 also includes a protection circuit 17 and a capacitor C10. Each of the plurality of switches 8 may be, for example, a bidirectional switch.

[0057] 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 first switching element among the plurality of first switching elements 1 and a corresponding 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 the plurality of switching circuits 10. Each of the plurality of AC terminals 41 is connected to a connection node 3 between the first switching element 1 and the second switching element 2 of a corresponding switching circuit 10 among the plurality of switching circuits 10. A plurality of switches 8 are provided one-to-one for the plurality of switching circuits 10. A first terminal 81 of each of the plurality of switches 8 is connected to a connection node 3 between the first switching element 1 and the second switching element 2 of a corresponding switching circuit 10 among the plurality of switching circuits 10. A plurality of resonant capacitors 9 are provided one-to-one for the plurality of switches 8. Each of the plurality of resonant capacitors 9 is connected between a first terminal 81 of a corresponding switch 8 in the plurality of switches 8 and the second DC terminal 32. The resonant inductor L1 has a first terminal and a second terminal. The first terminal of the resonant inductor L1 is connected to the common connection node 25. The regenerative capacitor 15 has a third terminal 153 and a fourth terminal 154. In the regenerative capacitor 15, its third terminal 153 is connected to the second DC terminal 32, and its fourth terminal 154 is connected to the common connection node 25 via the resonant inductor L1. The controller 50 controls the plurality of first switching elements 1, the plurality of second switching elements 2, and the plurality of switches 8.

[0058] (2) Details of power converter

[0059] In the following description, for the sake of convenience, for the sake of convenience, with respect to the plurality of switching circuits 10, the switching circuits 10 for the U phase, the V phase, and the W phase will be referred to as “switching circuit 10U”, “switching circuit 10V”, and “switching circuit 10W”, respectively, hereinafter. In addition, in the following description, the first switching element 1 and the second switching element 2 of the switching circuit 10U will be referred to as “the first switching element 1U” and the “second switching element 2U”, respectively, hereinafter. Similarly, in the following description, the first switching element 1 and the second switching element 2 of the switching circuit 10V will be referred to as “the first switching element 1V” and the “second switching element 2V”, respectively, hereinafter. Similarly, in the following description, the first switching element 1 and the second switching element 2 of the switching circuit 10W will be referred to as “the first switching element 1W” and the “second switching element 2W”, respectively, hereinafter. Furthermore, in the following description, the connection node 3 between the first switching element 1U and the second switching element 2U will be referred to as “connection node 3U” hereinafter, the connection node 3 between the first switching element 1V and the second switching element 2V will be referred to as “connection node 3V” hereinafter, and the connection node 3 between the first switching element 1W and the second switching element 2W will be referred to as “connection node 3W” hereinafter. Furthermore, in the following description, the AC terminal 41 connected to the connection node 3U will be referred to as “AC terminal 41U” hereinafter, the AC terminal 41 connected to the connection node 3V will be referred to as “AC terminal 41V” hereinafter, and the AC terminal 41 connected to the connection node 3W will be referred to as “AC terminal 41W” hereinafter. Furthermore, in the following description, the resonance capacitor 9 connected in parallel to the second switching element 2U will be referred to as “resonance capacitor 9U” hereinafter, the resonance capacitor 9 connected in parallel to the second switching element 2V will be referred to as “resonance capacitor 9V” hereinafter, and the resonance capacitor 9 connected in parallel to the second switching element 2W will be referred to as “resonance capacitor 9W” hereinafter. In addition, in the following description, the switch 8 connected to the connection node 3U will be referred to as "switch 8U" below, the switch 8 connected to the connection node 3V will be referred to as "switch 8V" below, and the switch 8 connected to the connection node 3W will be referred to as "switch 8W" below.

[0060] 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, a U-phase terminal, a V-phase terminal, and a W-phase terminal of the AC load RA1 are connected to three AC terminals 41U, 41V, and 41W, respectively.

[0061] In the power conversion circuit 11, each of the plurality of (for example, three) first switching elements 1 and the plurality of (for example, three) second switching elements 2 has a control terminal, a first main terminal, and a second main terminal. Each of the control terminals of the plurality of first switching elements 1 and the plurality of second switching elements 2 is connected to the controller 50. In each of the plurality of switching circuits 10 of the power converter 100, the first main terminal of the first switching element 1 is connected to the first DC terminal 31, the second main terminal of the first switching element 1 is connected to the first main terminal of the second switching element 2, and the second main terminal of the second switching element 2 is connected to the second DC terminal 32. In each of the plurality of switching circuits 10, the first switching element 1 is a high-side switching element (P-side switching element), and the second switching element 2 is a low-side switching element (N-side switching element). Each of the plurality of first switching elements 1 and the plurality of second switching elements 2 may be, for example, an insulated gate bipolar transistor (IGBT). Thus, in each of the plurality of first switching elements 1 and the plurality of second switching elements 2 , the control terminal, the first main terminal, and the second main terminal thereof are the gate terminal, the collector terminal, and the emitter terminal, respectively.

[0062] 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.

[0063] The U-phase terminal of the AC load RA1 may be connected to the connection node 3U between the first switching element 1U and the second switching element 2U, for example, via the AC terminal 41U. The V-phase of the AC load RA1 may be connected to the connection node 3V between the first switching element 1V and the second switching element 2V, for example, via the AC terminal 41V. The W-phase of the AC load RA1 may be connected to the connection node 3W between the first switching element 1W and the second switching element 2W, for example, via the AC terminal 41W.

[0064] A plurality of resonant capacitors 9 are provided one-to-one for a plurality of 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 switch 8. The power converter 100 includes a plurality of resonant circuits. The plurality of resonant circuits include a resonant circuit having a resonant capacitor 9U and a resonant inductor L1, a resonant circuit having a resonant capacitor 9V and a resonant inductor L1, and a resonant circuit having a resonant capacitor 9W and a resonant inductor L1. The plurality of resonant circuits share the resonant inductor L1 in common.

[0065] Each of the plurality of switches 8 may include, for example, two IGBTs (i.e., a first IGBT 6 and a second IGBT 7) connected together in anti-parallel. In each of the plurality of switches 8, the collector terminal of the first IGBT 6 and the emitter terminal of the second IGBT 7 are connected to each other, and the emitter terminal of the first IGBT 6 and the collector terminal of the second IGBT 7 are connected to each other. In each of the plurality of switches 8, the emitter terminal of the first IGBT 6 is connected to the connection node 3 of the switching circuit 10 corresponding to the switch 8 including the first IGBT 6. In each of the plurality of switches 8, the collector terminal of the second IGBT 7 is connected to the connection node 3 of the switching circuit 10 corresponding to the switch 8 including the second IGBT 7. The switch 8U is connected to the connection node 3U between the first switching element 1U and the second switching element 2U. The switch 8V is connected to the connection node 3V between the first switching element 1V and the second switching element 2V. The switch 8W is connected to the connection node 3W between the first switching element 1W and the second switching element 2W. In the following description, for the sake of convenience, the first IGBT 6 and the second IGBT 7 of the switch 8U will be referred to as the "first IGBT 6U" and the "second IGBT 7U", respectively, the first IGBT 6 and the second IGBT 7 of the switch 8V will be referred to as the "first IGBT 6V" and the "second IGBT 7V", respectively, and the first IGBT 6 and the second IGBT 7 of the switch 8W will be referred to as the "first IGBT 6W" and the "second IGBT 7W", respectively.

[0066] The plurality of switches 8 are controlled by the controller 50. In other words, the first IGBT 6U, the second IGBT 7U, the first IGBT 6V, the second IGBT 7V, the first IGBT 6W, and the second IGBT 7W are controlled by the controller 50.

[0067] The resonant inductor L1 has a first terminal and a second terminal. In the resonant inductor L1 , the first terminal of the resonant inductor L1 is connected to the common connection node 25 , and the second terminal of the resonant inductor L1 is connected to the fourth terminal 154 of the regenerative capacitor 15 .

[0068] The regenerative capacitor 15 is connected between the second terminal of the resonant inductor L1 and the second DC terminal 32. The regenerative capacitor 15 may be, for example, a film capacitor.

[0069] The protection circuit 17 includes a third diode 13 and a fourth diode 14. The third diode 13 is connected between the common connection node 25 and the first DC terminal 31. In the third diode 13, the anode of the third diode 13 is connected to the common connection node 25, and the cathode of the third diode 13 is connected to the first DC terminal 31. The fourth diode 14 is connected between the common connection node 25 and the second DC terminal 32. In the fourth diode 14, the anode of the fourth diode 14 is connected to the second DC terminal 32, and the cathode of the fourth diode 14 is connected to the common connection node 25. Thus, the fourth diode 14 is connected to the third diode 13 in series.

[0070] 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.

[0071] The controller 50 controls a plurality of first switching elements 1, a plurality of second switching elements 2, and a plurality of switches 8. An agent for performing the functions of the controller 50 includes a computer system. The computer system includes a single or multiple computers. The computer system may include a processor and a memory as its main hardware components. The computer system is used as an agent for performing the functions of the controller 50 according to the present disclosure by causing the processor to execute a program stored in the memory of the computer system. The program may be pre-stored in the memory of the computer system. Alternatively, the program may also be downloaded via a telecommunications line, or distributed after being recorded in a non-transient storage medium such as a memory card, an optical disk, or a hard disk drive (disk) (any of which storage media is readable for the computer system). The processor of the computer system may be composed of a single or multiple electronic circuits including a semiconductor integrated circuit (IC) or a large-scale integrated circuit (LSI). These electronic circuits may be integrated together on a single chip or distributed on multiple chips, whichever is appropriate. These multiple chips may be aggregated together in a single device or distributed in multiple devices without limitation.

[0072] The controller 50 outputs control signals SU1, SV1, SW1 for controlling the ON / OFF states of the plurality of first switching elements 1U, 1V, 1W, respectively. Each of the control signals SU1, SV1, SW1 may be, for example, a pulse width modulation (PWM) signal, which has, for example, a potential level that alternates between a first potential level (hereinafter referred to as a "low level") and a second potential level (hereinafter referred to as a "high level") higher than the first potential level. The first switching elements 1U, 1V, 1W become turned on when the control signals SU1, SV1, SW1 have a high level, respectively, and become turned off when the control signals SU1, SV1, SW1 have a low level, respectively. In addition, the controller 50 also outputs control signals SU2, SV2, SW2 for controlling the ON / OFF states of the plurality of second switching elements 2U, 2V, 2W, respectively. Each of the control signals SU2, SV2, SW2 may be, for example, a PWM signal having, for example, a potential level that alternates between a first potential level (hereinafter referred to as a "low level") and a second potential level (hereinafter referred to as a "high level") higher than the first potential level. The second switching elements 2U, 2V, 2W become conductive when the control signals SU2, SV2, SW2 have a high level, respectively, and become off when the control signals SU2, SV2, SW2 have a low level, respectively.

[0073] The controller 50 uses a carrier signal having a sawtooth waveform (reference Figure 3 ) to generate control signals SU1, SV1, SW1 for multiple first switching elements 1U, 1V, 1W and control signals SU2, SV2, SW2 for multiple second switching elements 2U, 2V, 2W. More specifically, the controller 50 generates control signals SU1, SU2 to be applied to the first switching element 1U and the second switching element 2U, respectively, based at least on the carrier signal and the U-phase voltage command. In addition, the controller 50 generates control signals SV1, SV2 to be applied to the first switching element 1V and the second switching element 2V, respectively, based at least on the carrier signal and the V-phase voltage command. In addition, the controller 50 generates control signals SW1, SW2 to be applied to the first switching element 1W and the second switching element 2W, respectively, based at least on the carrier signal and the W-phase voltage command. The U-phase voltage command, the V-phase voltage command and the W-phase voltage command can, for example, be sinusoidal wave signals whose phases differ by 120 degrees from each other and whose amplitudes (voltage command values) vary with time. Note that the waveform of the carrier signal does not have to be a sawtooth waveform, but can also be a triangular waveform or Figure 3 The sawtooth waveform shown is a mirror-inverted wave. 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.

[0074] The duty ratios of the control signals SU1, SU2 to be applied from the controller 50 to the first switching element 1U and the second switching element 2U, respectively, vary according to the U-phase voltage command. Figure 2 In FIG. 5 , the duty cycle of the control signal SU1 is shown as “U-phase duty cycle”. Figure 1 ) generates a control signal SU1 to be applied to the first switching element 1U by comparing the U-phase voltage command with the carrier signal. The controller 50 generates a control signal SU2 to be applied to the second switching element 2U by inverting the control signal SU1 to be applied to the first switching element 1U. In addition, in order to prevent the respective conduction periods of the first switching element 1U and the second switching element 2U from overlapping each other, the controller 50 sets a dead zone period Td (reference period Td) between the high level period of the control signal SU1 and the high level period of the control signal SU2. Figure 3 ).

[0075] The duty ratios of the control signals SV1, SV2 to be applied from the controller 50 to the first switching element 1V and the second switching element 2V, respectively, vary according to the V-phase voltage command. Figure 2 In FIG. 5 , the duty cycle of the control signal SV1 is shown as the “V-phase duty cycle”. Figure 1 ) generates a control signal SV1 to be applied to the first switching element 1V by comparing the V-phase voltage command with the carrier signal. The controller 50 also generates a control signal SV2 to be applied to the second switching element 2V by inverting the control signal SV1 to be applied to the first switching element 1V. In addition, in order to prevent the respective conduction periods of the first switching element 1V and the second switching element 2V from overlapping each other, the controller 50 sets a dead zone period Td (reference period Td) between the high level period of the control signal SV1 and the high level period of the control signal SV2. Figure 3 ).

[0076] The duty ratios of the control signals SW1, SW2 to be applied from the controller 50 to the first switching element 1W and the second switching element 2W, respectively, vary according to the W-phase voltage command. Figure 2 , the duty cycle of the control signal SW1 is shown as "W-phase duty cycle". Figure 1 ) generates a control signal SW1 to be applied to the first switching element 1W by comparing the W-phase voltage command with the carrier signal. The controller 50 generates a control signal SW2 to be applied to the second switching element 2W by inverting the control signal SW1 to be applied to the first switching element 1W. In addition, in order to prevent the respective conduction periods of the first switching element 1W and the second switching element 2W from overlapping each other, the controller 50 sets a dead zone period Td (reference period Td) between the high level period of the control signal SW1 and the high level period of the control signal SW2. Figure 4 ).

[0077] The U-phase voltage command, the V-phase voltage command, and the W-phase voltage command may be, for example, sinusoidal signals whose phases differ from each other by 120 degrees and whose amplitudes vary with time. Figure 2 As shown, the duty ratios of the control signals SU1, SV1, and SW1 (i.e., the U-phase duty ratio, the V-phase duty ratio, and the W-phase duty ratio) vary in the form of sinusoidal waves that are 120 degrees out of phase with each other. In the same manner, the duty ratios of the control signals SU2, SV2, and SW2 also vary in the form of sinusoidal waves that are 120 degrees out of phase with each other.

[0078] The controller 50 generates the respective control signals SU1, SU2, SV1, SV2, SW1, SW2 based on the carrier signal, the respective voltage commands, and the information related to the state of the AC load RA1. For example, if the AC load RA1 is a three-phase motor, the information related to the state of the AC load RA1 may include, for example, detection values ​​provided by a plurality of current sensors for respectively detecting output currents iU, iV, iW of the U-phase, V-phase, and W-phase, respectively, flowing through the AC load RA1.

[0079] A plurality of switches 8 , a resonant inductor L1 , a plurality of resonant capacitors 9 , and a regenerative capacitor 15 are provided to perform zero-voltage soft switching of the plurality of first switching elements 1 and the plurality of second switching elements 2 .

[0080] In this power converter 100 , the controller 50 controls not only the plurality of first switching elements 1 and the plurality of second switching elements 2 of the power conversion circuit 11 , but also the plurality of switches 8 .

[0081] 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.

[0082] If the first IGBT 6U is turned on and the second IGBT 7U is turned off, the switch 8U enables a charging current that flows through the regenerative capacitor 15, the resonant inductor L1, the switch 8U, and the resonant capacitor 9U in sequence to pass. The charging current is a current for charging the resonant capacitor 9U. On the other hand, if the first IGBT 6U is turned off and the second IGBT 7U is turned on, the switch 8U enables a discharging current that flows through the resonant capacitor 9U, the switch 8U, the resonant inductor L1, and the regenerative capacitor 15 in sequence to pass. The discharging current is a current for discharging from the resonant capacitor 9U.

[0083] If the first IGBT 6V is turned on and the second IGBT 7V is turned off, the switch 8V enables a charging current to flow through the regenerative capacitor 15, the resonant inductor L1, the switch 8V, and the resonant capacitor 9V in sequence. The charging current is a current for charging the resonant capacitor 9V. On the other hand, if the first IGBT 6V is turned off and the second IGBT 7V is turned on, the switch 8V enables a discharging current to flow through the resonant capacitor 9V, the switch 8V, the resonant inductor L1, and the regenerative capacitor 15 in sequence. The discharging current is a current for discharging from the resonant capacitor 9V.

[0084] If the first IGBT 6W is turned on and the second IGBT 7W is turned off, the switch 8W enables a charging current to flow through the regenerative capacitor 15, the resonant inductor L1, the switch 8W, and the resonant capacitor 9W in sequence. The charging current is a current for charging the resonant capacitor 9W. On the other hand, if the first IGBT 6W is turned off and the second IGBT 7W is turned on, the switch 8W enables a discharging current to flow through the resonant capacitor 9W, the switch 8W, the resonant inductor L1, and the regenerative capacitor 15 in sequence. The discharging current is a current for discharging from the resonant capacitor 9W.

[0085] (3) Operation of power converter

[0086] In the following description, for the current iL1 flowing through the resonant inductor L1, if the current is Figure 1 If the current iL1 flows in the direction indicated by the arrow shown in FIG. 1 , the polarity of the current iL1 is assumed to be positive. On the other hand, if the current iL1 flows in the direction indicated by the arrow shown in FIG. Figure 1 If the current iL1 flows in the direction opposite to the direction indicated by the arrow shown in FIG. 1 , the polarity of the current iL1 is assumed to be negative. In addition, in the following description, for each of the load currents iU, iV, iW flowing through the U phase, V phase, and W phase of the AC load RA1, if the load currents iU, iV, iW are Figure 1 If the load current iU, iV, iW flows in the direction indicated by the corresponding arrow in the arrows shown, it is assumed that the polarity of the load current iU, iV, iW is positive. On the other hand, if the load current iU, iV, iW flows in the direction indicated by the corresponding arrow in the arrows shown, it is assumed that the polarity of the load current iU, iV, iW is positive. Figure 1 If the load current iU, iV, iW flows in the direction opposite to the direction indicated by the arrow shown in FIG. 1 , the polarity of the load current iU, iV, iW is assumed to be negative. In addition, for each of the currents i9U, i9V, i9W flowing through the resonant capacitors 9U, 9V, 9W, respectively, if the currents i9U, i9V, i9W are Figure 1 If the currents i9U, i9V, i9W flow in the direction indicated by the corresponding arrows in the arrows shown, the polarity of the currents i9U, i9V, i9W is assumed to be positive. On the other hand, if the currents i9U, i9V, i9W flow in the direction indicated by the corresponding arrows in the arrows shown, the polarity of the currents i9U, i9V, i9W is assumed to be positive. Figure 1 If the current i9U, i9V, i9W flows in a direction opposite to the direction indicated by the arrow shown in FIG. 1 , the polarity of the current i9U, i9V, i9W is assumed to be negative. Therefore, in the case of a discharge operation of discharging from the resonance capacitor 9U, 9V, 9W, the polarity of the current i9U, i9V, i9W is positive. On the other hand, in the case of a charging operation of charging the resonance capacitor 9U, 9V, 9W, the polarity of the current i9U, i9V, i9W is negative.

[0087] In the power converter 100, for example, in a state where the first IGBT 6U of the switch 8U is turned on and the positive current iL1 is flowing through the resonant inductor L1, the first IGBT 6U of the switch 8U can be turned off. In this case, the current iL1 flowing through the resonant inductor L1 is regenerated to the power conversion circuit 11 via the third diode 13 until the current iL1 becomes zero due to the energy consumption of the resonant inductor L1. In addition, in the power converter 100, for example, in a state where the second IGBT 7U of the switch 8U is turned on and the negative current iL1 is flowing through the resonant inductor L1, the second IGBT 7U of the switch 8U can be turned off. In this case, the current iL1 flows through the resonant inductor L1 along a path that passes through the fourth diode 14, the resonant inductor L1, and the regeneration capacitor 15 in sequence until the current iL1 becomes zero due to the energy consumption of the resonant inductor L1.

[0088] Furthermore, in the power converter 100, for example, in a state where the first IGBT 6V of the switch 8V is turned on and the positive current iL1 is flowing through the resonant inductor L1, the first IGBT 6V of the switch 8V can be turned off. In this case, the current iL1 flowing through the resonant inductor L1 is regenerated to the power conversion circuit 11 via the third diode 13 until the current iL1 becomes zero due to the energy consumption of the resonant inductor L1. Furthermore, in the power converter 100, for example, in a state where the second IGBT 7V of the switch 8V is turned on and the negative current iL1 is flowing through the resonant inductor L1, the second IGBT 7V of the switch 8V can be turned off. In this case, the current iL1 flows through the resonant inductor L1 along a path that passes through the fourth diode 14, the resonant inductor L1, and the regeneration capacitor 15 in sequence until the current iL1 becomes zero due to the energy consumption of the resonant inductor L1.

[0089] Furthermore, in the power converter 100, for example, in a state where the first IGBT 6W of the switch 8W is turned on and the positive current iL1 is flowing through the resonant inductor L1, the first IGBT 6W of the switch 8W can be turned off. In this case, the current iL1 flowing through the resonant inductor L1 is regenerated to the power conversion circuit 11 via the third diode 13 until the current iL1 becomes zero due to the energy consumption of the resonant inductor L1. Furthermore, in the power converter 100, for example, in a state where the second IGBT 7W of the switch 8W is turned on and the negative current iL1 is flowing through the resonant inductor L1, the second IGBT 7W of the switch 8W can be turned off. In this case, the current iL1 flows through the resonant inductor L1 along a path that passes through the fourth diode 14, the resonant inductor L1, and the regeneration capacitor 15 in sequence until the current iL1 becomes zero due to the energy consumption of the resonant inductor L1.

[0090] The controller 50 sets a dead time period Td between the high level period of the control signal SU1, SV1, SW1 for the first switching element 1U, 1V, 1W and the high level period of the control signal SU2, SV2, SW2 for the second switching element 2U, 2V, 2W for each switching circuit 10 among the multiple switching circuits 10.

[0091] Next, we will refer to Figure 1 and Figure 2The basic operation of zero voltage soft switching to be performed on each of the plurality of first switching elements 1 and the plurality of second switching elements 2 is described. As used herein, "basic operation" refers to an operation to be performed when the resonant current through each of the two or more switches 8 belonging to the plurality of switches 8 does not flow through the resonant inductor L1 at the same time. After the basic operation is described, how the power converter 100 operates when the controller 50 determines that the resonant current through each of the two or more switches 8 belonging to the plurality of switches 8 flows at the same time will be described.

[0092] (3.1) Basic operations

[0093] When the first switching element 1 is subjected to zero voltage soft switching, the voltage across the first switching element 1 needs to be reduced to zero just before the first switching element 1, which is the object of the zero voltage soft switching, becomes conductive. When the second switching element 2 is subjected to zero voltage soft switching, the voltage across the second switching element 2 needs to be reduced to zero just before the second switching element 2, which is the object of the zero voltage soft switching, becomes conductive. In the following description, the switching element, which is the object of the zero voltage soft switching (which is the first switching element 1 or the second switching element 2), will be referred to as the "object switching element" hereinafter.

[0094] The basic operation of the controller 50 varies according to the polarity (i.e., positive or negative) of the load current flowing through the AC terminal 41 connected to the object switching element and according to whether the resonant capacitor 9 connected in series or in parallel to the object switching element is undergoing a charging operation or a discharging operation. The load current has a positive polarity when flowing from the AC terminal 41 toward the AC load RA1, and has a negative polarity when flowing from the AC load RA1 toward the AC terminal 41. During the period when the resonant capacitor 9 is undergoing a charging operation, the voltage across the resonant capacitor 9 increases. On the other hand, during the period when the resonant capacitor 9 is undergoing a discharging operation, the voltage across the resonant capacitor 9 decreases. The voltage across each of the plurality of second switching elements 2 is the same as the voltage across the resonant capacitor 9 connected in parallel to the second switching element 2.

[0095] (3.1.1) When the load current is greater than 0, the soft switching operation of the first switching element is performed

[0096] If the object of soft switching is the first switching element 1 (hereinafter referred to as "the object first switching element 1") and the polarity of the load current flowing through the AC terminal 41 connected to the object first switching element 1 is positive, the controller 50 turns on the first IGBT 6 corresponding to the object first switching element 1. In this way, the controller 50 causes the resonant inductor L1 and the resonant capacitor 9 connected to the object first switching element 1 to resonate, thereby charging the resonant capacitor 9 with the charge removed from the regenerative capacitor 15 and reducing the voltage across the object first switching element 1 to zero. This enables the power converter 100 to perform zero-voltage soft switching of the object first switching element 1.

[0097] Figure 3 , control signals SU1 and SU2 to be applied from the controller 50 to the first switching element 1U and the second switching element 2U of the switching circuit 10U, respectively, are shown in FIG. Figure 3 Also shown are the control signal SU6 to be applied from the controller 50 to the first IGBT 6U of the switch 8U, the load current iU of the U phase flowing through the AC load RA1, the current iL1 flowing through the resonant inductor L1, the voltage V across the first switching element 1U, and the 1U and the voltage V across the second switching element 2U 2U .also, Figure 3 , control signals SV1 and SV2 to be applied from the controller 50 to the first switching element 1V and the second switching element 2V of the switching circuit 10V, respectively, are also shown in FIG. Figure 3 Also shown are the control signal SV6 to be applied from the controller 50 to the first IGBT 6V of the switch 8V, the load current iV of the V phase flowing through the AC load RA1, the current iL1 flowing through the resonant inductor L1, the voltage V across the first switching element 1V, and the 1V and the voltage V across the second switching element 2V 2V .

[0098] also, Figure 3 4 also shows the dead time period Td set by the controller 50 to prevent the first switching element 1 and the second switching element 2 of the same phase from becoming conductive at the same time. Figure 3 Also shown in FIG. 5 are the additional time Tau set by the controller 50 for the control signal SU6 of the first IGBT 6U of the switch 8U and the additional time Tav set by the controller 50 for the control signal SV6 of the first IGBT 6V of the switch 8V. The additional time Tau and the additional time Tav will be described later.

[0099] Figure 4 shown are control signals SW1 and SW2 that are to be applied from a controller 50 to a first switching element 1W and a second switching element 2W of a switching circuit 10W, respectively, in a case where the first switching element 1 of an object is the first switching element 1W of the switching circuit 10W. In addition, Figure 4 shown is also a control signal SW6 that is to be applied from the controller 50 to a first IGBT 6W of a switch 8W and a load current iW of a W-phase flowing through an AC load RA1. Figure 4 shown is also a current iL1 flowing through a resonance inductor L1. Figure 4 shown is also a voltage V across the first switching element 1W. 1W and a voltage V across the second switching element 2W. 2W . In Figure 4 the voltage value of a DC power supply E1 is specified by Vd.

[0100] In addition, Figure 4 shown is also a dead time period Td that is set by the controller 50 to prevent the first switching element 1W and the second switching element 2W from becoming conductive simultaneously. In addition, Figure 4 shown is also an additional time Taw that is set by the controller 50 for the control signal SW6 of the first IGBT 6W of the switch 8W. The additional time Taw will be described later.

[0101] As Figure 3 shown, the additional time Tau is an amount of time that the controller 50 sets such that a start (time t1) of a high level period of a control signal SU6 is set earlier than a start (time t2) of the dead time period Td so that the high level period of the control signal SU6 is longer than the dead time period Td. The length of the additional time Tau is determined by a value of the load current iU. In order to generate LC resonance starting from the start (time t2) of the dead time period Td, it is preferable that the value of the current iL1 coincides with the value of the load current iU at the start (time t2) of the dead time period Td. This is because as long as iL1 < iU, all of the current iL1 flows through the AC load RA1, and thus the resonance capacitor 9U cannot be charged. An end of the high level period of the control signal SU6 may be simultaneous with or later than an end (time t3) of the dead time period Td. In Figure 3 the example shown, the end of the high level period of the control signal SU6 is set to be simultaneous with the end (time t3) of the dead time period Td. The controller 50 sets the high level period of the control signal SU6 to be Tau + Td. In the switching circuit 10U, the voltage V 2U across the second switching element 2U becomes Vd at the end (time t3) of the dead time period Td, and the voltage V 1Ubecomes zero at the end of the dead time period Td (time t3). Figure 3 In the example shown, the current iL1 starts to flow through the resonant inductor L1 at the beginning of the high level period of the control signal SU6 (time t1), and becomes zero at time t4 after the additional time Tau has passed from the end of the dead time period Td (time t3). For the current iL1, from the beginning of the dead time period Td (time t2), the current iL1 satisfies iL1 ≥ iU, so from Figure 3 The current iL1 in the shaded portion of the current waveform shown in the fifth waveform from the top flows into the resonant capacitor 9U to generate LC resonance. From the end of the dead time period Td (time t3), the current iL1 will be regenerated to the power conversion circuit 11 via the third diode 13 directly connected to the resonant inductor L1.

[0102] As described above, in order to start generating LC resonance at the beginning (time t2) of the dead time period Td and end the resonant half cycle at the end of the dead time period Td, the controller 50 determines the additional time Tau based on the load current iU so that iL1=iU is satisfied at the beginning (time t2) of the dead time period Td. More specifically, for example, the controller 50 uses the detection result of the load current iU by the current sensor or its signal processing value, or the estimated value of the load current iU, the inductance L of the resonant inductor L1 that has been stored in advance, and the detection result of the potential V15 at the regenerative capacitor 15, and determines the additional time Tau by the formula Tau=iU×(L / V15). In this case, as the detection result of the load current iU or its signal processing value, the detection value according to the carrier cycle to which the additional time Tau is added or the detection value according to the timing closest to the carrier cycle can be used. In addition, in this case, as the estimated value of the load current iU, for example, the value of the load current iU estimated according to the carrier cycle to which the additional time Tau is added can be used. The resonant half period in the basic operation case is half of the resonant period which is the inverse of the resonant frequency of the resonant circuit including the resonant inductor L1 and one resonant capacitor 9. Thus, if the inductance of the resonant inductor L1 is L and the capacitance of the resonant capacitor 9 is C, the resonant half period is π×(L·C) 1 / 2 For example, the controller 50 sets the resonance half period in the case of the basic operation so that the resonance half period is as long as the length of the dead time period Td.

[0103] like Figure 3As shown, the additional time Tav is the amount of time that the controller 50 sets to make the start (time t5) of the high-level period of the control signal SV6 earlier than the start (time t6) of the dead time period Td so that the high-level period of the control signal SV6 is longer than the dead time period Td. The length of the additional time Tav is determined by the value of the load current iV. In order to generate LC resonance starting from the start (time t6) of the dead time period Td, it is preferable that the value of the current iL1 coincides with the value of the load current iV at the start (time t6) of the dead time period Td. This is because as long as iL1 < iV, all of the current iL1 flows through the AC load RA1, and thus the resonance capacitor 9V cannot be charged. The end of the high-level period of the control signal SV6 can be simultaneous with or later than the end (time t7) of the dead time period Td. In Figure 3 the example shown, the end of the high-level period of the control signal SV6 is set to be simultaneous with the end (time t7) of the dead time period Td. The controller 50 sets the high-level period of the control signal SV6 to Tav + Td. The voltage V across the first switching element 1V 1V becomes zero at the end (time t7) of the dead time period Td. In Figure 3 the example shown, the current iL1 starts flowing through the resonance inductor L1 at the start (time t5) of the high-level period of the control signal SV6 and becomes zero at time t8 which is the additional time Tav after the end (time t7) of the dead time period Td. For the current iL1, starting from the start (time t6) of the dead time period Td, the current iL1 satisfies iL1 ≥ iV, and thus the current iL1 in the shaded portion of the current waveform shown by the tenth waveform from the top of Figure 3 flows into the resonance capacitor 9V to generate LC resonance. Starting from the end (time t7) of the dead time period Td, the current iL1 will be regenerated to the power conversion circuit 11 via the third diode 13 directly connected to the resonance inductor L1.

[0104] As described above, in order to start generating LC resonance at the start (time t6) of the dead time period Td, the controller 50 determines an additional time Tav based on the load current iV such that iL1 = iV is satisfied at the start (time t6) of the dead time period Td. More specifically, for example, the controller 50 uses the detection result of the load current iV by the current sensor or its signal processing value, or the estimated value of the load current iV, the inductance L of the resonance inductor L1 stored in advance, and the detection result of the potential V15 at the regenerative capacitor 15, and determines the additional time Tav by the formula Tav = iV × (L / V15). In this case, as the detection result of the load current iV or its signal processing value, the detection value according to the carrier period added with the additional time Tav or the detection value according to the timing closest to the carrier period can be used. Further, in this case, as the estimated value of the load current iV, for example, the value of the load current iV estimated according to the carrier period added with the additional time Tav can be used.

[0105] As Figure 4 shown, the additional time Taw is the time amount that the controller 50 sets to make the start (time t9) of the high level period of the control signal SW6 earlier than the start (time t10) of the dead time period Td so that the high level period of the control signal SW6 is longer than the dead time period Td. The length of the additional time Taw is determined by the value of the load current iW. In order to generate LC resonance starting from the start (time t10) of the dead time period Td, it is preferable that the value of the current iL1 coincides with the value of the load current iW at the start (time t10) of the dead time period Td. This is because as long as iL1 < iW is satisfied, all of the current iL1 flows through the AC load RA1, and thus the resonance capacitor 9W cannot be charged. The end of the high level period of the control signal SW6 may be simultaneous with or later than the end (time t11) of the dead time period Td. In Figure 4 the example shown, the end of the high level period of the control signal SW6 is set to be simultaneous with the end (time t11) of the dead time period 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 period Td. In Figure 4 the example shown, the current iL1 starts flowing through the resonance inductor L1 at the start (time t9) of the high level period of the control signal SW6, and becomes zero at the time t12 when the additional time Taw has elapsed from the end (time t11) of the dead time period Td. For the current iL1, starting from the start (time t10) of the dead time period Td, iL1 ≥ iW is satisfied for the current iL1, and thus from Figure 4The current iL1 in the shaded portion of the current waveform shown in the fourth waveform from the top flows into the resonant capacitor 9W to generate LC resonance. From the end of the dead time period Td (time t11), the current iL1 will be regenerated to the power conversion circuit 11 via the third diode 13 directly connected to the resonant inductor L1.

[0106] The controller 50 determines the additional time Taw based on the load current iW. More specifically, for example, the controller 50 uses the detection result of the load current iW by the current sensor, the inductance L of the resonant inductor L1 that has been stored in advance, and the detection result of the potential V15 at the regenerative capacitor 15 to determine the additional time Taw by the formula Taw=iW×(L / V15). In this case, as the detection result of the load current iW or its signal processing value, a detection value according to the carrier cycle to which the additional time Taw is added or a detection value according to the timing closest to the carrier cycle can be used. In addition, in this case, as the estimated value of the load current iW, for example, the value of the load current iW estimated according to the carrier cycle to which the additional time Taw is added can be used.

[0107] (3.1.2) When the load current is greater than 0, the second switching element performs soft switching.

[0108] If the object of soft switching is the second switching element 2 (hereinafter referred to as "the object second switching element 2") and the polarity of the load current (which is the load current iU, the load current iV or the load current iW) flowing through the AC terminal 41 connected to the object second switching element 2 is positive, the controller 50 compares the current value of the load current with the first current threshold value I1 (=Ith, reference Figure 5 ) is compared. If the current value of the load current is greater than the first current threshold value I1, the controller 50 does not turn on the switch 8. On the other hand, if the current value of the load current is less than the first current threshold value I1, the controller 50 turns on the switch 8 in the dead time period Td. In the power converter 100, if the current value of the load current is greater than the first current threshold value I1, the controller 50 can use the load current iU to discharge the resonant capacitor 9U connected in parallel to the object second switching element 2 without turning on the switch 8 corresponding to the object second switching element 2. This enables the power converter 100 to perform zero voltage soft switching of the object second switching element 2.

[0109] exist Figure 6 , for a case where the target second switching element 2 is the second switching element 2U of the switching circuit 10U and the current value of the load current is greater than the first current threshold value I1, control signals SU1, SU2, SU7, load current iU, current i9U flowing from the resonant capacitor 9U, and voltage V across the second switching element 2 are shown. 2UIn addition, Figure 6 Also shown in FIG. 8 are the dead time period Td and the additional time Tau set by the controller 50 for the control signal SU7 of the second IGBT 7U of the switch 8U.

[0110] If the current value of the load current iU is greater than the first current threshold value I1, the controller 50 does not set any high level period to the control signal SU7. In this case, in the power converter 100, the current iU9 starts to flow from the resonant capacitor 9U at the beginning of the dead time period Td (time t22), the current i9U decreases to zero before the end of the dead time period Td (time t23), and the voltage V across the second switching element 2 is 2U Thus, in the power converter 100, when the control signal SU2 changes from low level to high level at the end of the dead time period Td (time t23), the second switching element 2 performs zero voltage soft switching.

[0111] For example, if the current value of the load current iU is less than the first current threshold I1, then Figure 6 As shown by the double-dotted line in FIG. 1 , the controller 50 sets a high level period to the control signal SU7. In this case, the start of the high level period of the control signal SU7 may be, for example, simultaneous with the start of the dead time period Td (time t22). In addition, the end of the high level period of the control signal SU7 is simultaneous with the end of the dead time period Td (time t23). Thus, in the power converter 100, the voltage V across the second switching element 2U is 2U It becomes zero before the end (time t23) of the dead time period Td. Therefore, in the power converter 100, when the control signal SU2 changes from a low level to a high level at the end (time t23) of the dead time period Td, the second switching element 2 is subjected to zero voltage soft switching. Alternatively, the start of the high level period of the control signal SU7 may be a time t21 that is earlier than the start of the dead time period Td by the additional time Tau. The end of the high level period of the control signal SU7 may be a time t24 that is later than the end (time t23) of the dead time period Td by the additional time Tau. Note that the time before or after the high level period overlaps with the dead time period Td does not necessarily have to be the additional time Tau, but may also be any other preset time.

[0112] (3.1.3) When the load current is less than 0, the soft switching operation of the second switching element is performed

[0113] If the polarity of the load current (which is the load current iU, the load current iV, or the load current iW) flowing through the AC terminal 41 connected to the object second switching element 2 is negative, the controller 50 turns on the second IGBT 7 corresponding to the object second switching element 2. In this way, the controller 50 causes the resonant capacitor 9 and the resonant inductor L1 connected to the object second switching element 2 to resonate, thereby discharging from the resonant capacitor 9 and reducing the voltage across the object second switching element 2 to zero. This enables the power converter 100 to perform zero-voltage soft switching of the object second switching element 2.

[0114] exist Figure 7 , for the case where the second switching element 2 is the second switching element 2U of the switching circuit 10U, the control signals SU1, SU2, SU7, the load current iU, the current iL1 flowing through the resonant inductor L1, and the voltage V across the second switching element 2 are shown. 2U .

[0115] In addition, Figure 7 The figure also shows the dead time period Td set by the controller 50 to prevent the first switching element 1 and the second switching element 2 of the same phase from becoming conductive at the same time. Figure 7 8U, the additional time Tau set by the controller 50 for the control signal SU7 of the second IGBT 7U of the switch 8U is also shown. The end of the high level period of the control signal SU7 may be simultaneous with the end of the dead time period Td (time t33), or may be later than the end of the dead time period Td (time t33). Figure 7 In the example shown, the end of the high level period of the control signal SU7 is set to coincide with the end of the dead time period Td (time t33). The controller 50 sets the high level period of the control signal SU7 to Tau+Td. In the switching circuit 10U, the voltage V across the second switching element 2U is 2U becomes zero at the end of the dead time period Td (time t33). Figure 7 In the example shown, the current iL1 starts to flow through the resonant inductor L1 at the beginning (time t31) of the high level period of the control signal SU7, and becomes zero at time t34 after the additional time Tau has passed from the end (time t33) of the dead time period Td. For the current iL1, from the beginning (time t32) of the dead time period Td, the current iL1 satisfies iL1≥iU, and thus LC resonance is generated so that the resonant current (i.e., the discharge current from the resonant capacitor 9U) flows from the resonant capacitor 9U toward the resonant inductor L1. From the end (time t33) of the dead time period Td, the current iL1 will be regenerated to the power conversion circuit 11 via the fourth diode 14 directly connected to the resonant inductor L1.

[0116] In order to start generating LC resonance at the beginning (time t32) of the dead time period Td and end the resonant half cycle at the end (time t33) of the dead time period Td, the controller 50 determines the additional time Tau based on the load current iU so that iL1=iU is satisfied at the beginning (time t32) of the dead time period Td. More specifically, for example, the controller 50 uses the detection result of the output current iU by the current sensor or its signal processing value, or the estimated value of the load current iU, the inductance L of the resonant inductor L1 that has been stored in advance, and the detection result of the potential V15 at the regenerative capacitor 15, and determines the additional time Tau by the formula Tau=iU×(L / V15). In this case, as the detection result of the load current iU or its signal processing value, the detection value according to the carrier cycle to which the additional time Tau is added or the detection value according to the timing closest to the carrier cycle can be used. In addition, in this case, as the estimated value of the load current iU, for example, the value of the load current iU estimated according to the carrier cycle to which the additional time Tau is added can be used. The resonant half period in the case of basic operation is half of the resonant period which is the inverse of the resonant frequency of the resonant circuit including the resonant inductor L1 and the resonant capacitor 9. Thus, if the inductance of the resonant inductor L1 is L and the capacitance of the resonant capacitor 9 is C, the resonant half period is π×(L·C) 1 / 2 For example, the controller 50 sets the resonance half period in the case of the basic operation so that the resonance half period is as long as the length of the dead time period Td.

[0117] (3.1.4) When the load current is less than 0, the soft switching operation of the first switching element is performed

[0118] If the polarity of the load current (which is the load current iU, the load current iV or the load current iW) flowing through the AC terminal 41 connected to the object first switching element 1 is negative, the controller 50 compares the current value of the load current with the second current threshold value I2 (=−Ith, reference Figure 5 ) is compared. If the current value of the load current is less than the second current threshold value I2, the controller 50 does not turn on the switch 8. On the other hand, if the current value of the load current is greater than the second current threshold value I2, the controller 50 turns on the switch 8 in the dead time period Td. In the power converter 100, if the current value of the load current is less than the second current threshold value I2, the controller 50 can charge the resonant capacitor 9U connected in series to the object first switching element 1 with the load current without turning on the switch 8 corresponding to the object first switching element 1. This enables the power converter 100 to perform zero voltage soft switching of the object first switching element 1.

[0119] exist Figure 8, for a case where the object first switching element 1 is the first switching element 1U of the switching circuit 10U and the current value of the load current is greater than the second current threshold value I2 (in other words, a case where the absolute value of the current value of the load current is less than the absolute value of the second current threshold value I2), control signals SU1, SU2, SU6, the load current iU, the current i9U flowing from the resonant capacitor 9U, and the voltage V across the second switching element 2U are shown. 2U .in addition, Figure 8 A dead time period Td is also shown in FIG.

[0120] If the current value of the load current is less than the second current threshold value I2 (in other words, if the absolute value of the load current is greater than the absolute value of the second current threshold value I2), the controller 50 does not set any high level period to the control signal SU6. In this case, in the power converter 100, the current iU9 starts to flow through the resonant capacitor 9U at the beginning (time t41) of the dead time period Td. As a result, in the power converter 100, the resonant capacitor 9U is charged so that the voltage V across the second switching element 2U is 2U The current i9U becomes zero before the end of the dead time period Td (time t23), and the voltage V across the first switching element 1 increases. 1U Thus, in the power converter 100, when the control signal SU1 changes from low level to high level at the end of the dead time period Td (time t42), the first switching element 1 is subjected to zero voltage soft switching.

[0121] For example, if the current value of the load current is greater than the second current threshold value I2 (in other words, if the absolute value of the load current is less than the absolute value of the second current threshold value), then Figure 8 As shown by the double-dotted line in FIG. 1 , the controller 50 sets a high-level period to the control signal SU6. In this case, the start of the high-level period of the control signal SU6 may be simultaneous with, for example, the start of the dead time period Td (time t41). In addition, the end of the high-level period of the control signal SU6 is simultaneous with the end of the dead time period Td (time t42). Thus, in the power converter 100, the voltage V across the first switching element 1U is 1U Therefore, in the power converter 100, when the control signal SU1 changes from low level to high level at the end of the dead time period Td (time t42), the first switching element 1 is subjected to zero voltage soft switching.

[0122] (3.2) Operations to be performed when it is determined that two-phase resonant currents flow simultaneously

[0123] When it is determined that the resonant currents respectively passing through two switches 8 among the plurality of switches 8 flow through the resonant inductor L1 at the same time, the controller 50 may perform the first control operation, the second control operation, and the third control operation. As used herein, the expression "when it is determined that the resonant currents respectively passing through two switches 8 among the plurality of switches 8 flow at the same time" refers to a situation where it has been pre-assumed that the resonant currents respectively passing through the two switches 8 will flow through the resonant inductor L1 at the same time.

[0124] (3.2.1) Determine whether the resonant current flows simultaneously

[0125] In the power converter 100, the phases of the three-phase (i.e., U-phase, V-phase, and W-phase) voltage commands are different from each other by 120 degrees, but the command values ​​of the two-phase voltage commands are close to each other every 60 degrees in electrical angle, and the duty ratios of the two-phase control signals are close to each other (refer to Figure 2 Specifically, in the areas A1 and A2 shown in FIG. Figure 2 In the region A1 shown in FIG. 1 , the duty ratio of the U-phase control signal and the duty ratio of the V-phase control signal become approximately 0.75. Figure 2 In the region A2 shown, the duty ratio of the U-phase control signal and the duty ratio of the V-phase control signal become about 0.25. The polarity of the resonant current is the same as the polarity of the current iL1. In the region A1, the polarity of the resonant current is positive. In the region A2, the polarity of the resonant current is negative. In the region A1, within one cycle time of the carrier signal, the start of the high level period of the control signal SU6 to be applied to the first IGBT 6U (time t1; reference numeral t2) is equal to the start of the high level period of the control signal SU6 to be applied to the first IGBT 6U. Figure 3 ) and the start of the high level period of the control signal SV6 to be applied to the first IGBT 6V (time t5; refer to Figure 3 ) becomes so short that the U-phase resonant current and the V-phase resonant current may flow through the resonant inductor L1 at the same time. In the power converter 100, the direction of the resonant current in the region A2 is opposite to the direction of the resonant current in the region A1, but the U-phase resonant current and the V-phase resonant current may flow through the resonant inductor L1 at the same time.

[0126] Assuming that the capacitance of each of the plurality of resonant capacitors 9U, 9V, and 9W is C, if the U-phase current and the V-phase current flow through the resonant inductor L1 at the same time, in the equivalent circuit, a capacitor having a combined capacitance (=2×C) of the resonant capacitor 9U and the resonant capacitor 9V is connected in series to the resonant inductor L1. Thus, in the power converter 100, if two-phase currents flow through the resonant inductor L1 at the same time, the resonant frequency of the resonant circuit including the resonant inductor L1 changes compared to the case where a single-phase current flows through the resonant inductor L1. Therefore, the power converter 100 may not be able to perform zero-voltage soft switching.

[0127] (3.2.1.1) When charging the resonant capacitor

[0128] Figure 3 An exemplary boundary condition between the case where the U-phase resonant current and the V-phase resonant current do not overlap with each other (ie, do not flow simultaneously) and the case where the U-phase resonant current and the V-phase resonant current overlap with each other (ie, flow simultaneously) is shown. Figure 3 Describe the boundary conditions.

[0129] In the power converter 100, if the time lag ΔT between the start of the high level period of the control signal SU1 (time t3) and the start of the high level period of the control signal SV1 (time t7) is equal to or greater than (Tau+Tav+Td), the U-phase resonant current and the V-phase resonant current do not overlap with each other. On the other hand, if the time lag ΔT is less than (Tau+Tav+Td), the U-phase resonant current and the V-phase resonant current overlap with each other. That is, in the case where the threshold of the time lag ΔT is set to (Tau+Tav+Td), if the time lag ΔT is less than the threshold, the controller 50 assumes that the resonant current corresponding to the two phases of the switching circuit 10U and the switching circuit 10V belonging to the plurality of switching circuits 10 will flow through the resonant inductor L1 at the same time. Note that the threshold is only an example, and the threshold may also be set to any other value. For example, in the case where the error of the additional time Tau and the error of the additional time Tav are taken into account, the threshold may also be set to a value even greater than (Tau+Tav+Td). Optionally, the controller 50 may also set the threshold for the time lag ΔT to, for example, the same value as the resonant half-cycle (in this embodiment, the resonant half-cycle = the dead time period Td). In this case, if the time lag ΔT is less than the length of the dead time period Td, the controller 50 assumes that the resonant currents corresponding to the two phases of the switching circuits 10U and 10V will flow through the resonant inductor L1 at the same time. In addition, the above method for calculating the time lag to determine whether the two-phase resonant currents flow simultaneously is only an example. On the contrary, any other calculation method may be used as long as a time lag equivalent to the above-mentioned time lag can be calculated. For example, as a time lag for determining whether the two-phase resonant currents flow simultaneously, the time lag between the end of the high level period of the control signal SU2 (time t2) and the end of the high level period of the control signal SV2 (time t6) may also be used.

[0130] In the power converter 100, if the time lag between the start of the high level period of the control signal SU1 (time t3) and the start of the high level period of the control signal SW1 (time t11) is equal to or greater than (Tau+Taw+Td), the U-phase resonant current and the W-phase resonant current do not overlap with each other. On the other hand, if the time lag is less than (Tau+Taw+Td), the U-phase resonant current and the W-phase resonant current overlap with each other. That is, in the case where the threshold for the time lag is set to (Tau+Taw+Td), if the time lag is less than the threshold, the controller 50 assumes that the resonant current corresponding to the two phases of the switching circuit 10U and the switching circuit 10W belonging to the plurality of switching circuits 10 will flow through the resonant inductor L1 at the same time. Note that the threshold is only an example, and the threshold may also be set to any other value. For example, in the case where the error of the additional time Tau and the error of the additional time Taw are taken into account, the threshold may also be set to a value even greater than (Tau+Taw+Td). In addition, the controller 50 can set the threshold value for the time lag to the same value as the resonant half-cycle (in this embodiment, the resonant half-cycle = the dead time period Td). In this case, if the time lag is less than the length of the dead time period Td, the controller 50 assumes that the resonant currents corresponding to the two phases of the switching circuits 10U and 10V will flow through the resonant inductor L1 at the same time. In addition, the above method for calculating the time lag to determine whether the two-phase resonant currents flow simultaneously is only an example. On the contrary, any other calculation method can also be used as long as the time lag equivalent to the above-mentioned time lag can be calculated. For example, as a time lag for determining whether the two-phase resonant currents flow simultaneously, the time lag between the end of the high level period of the control signal SU2 (time t2) and the end of the high level period of the control signal SW2 (time t10) can also be used.

[0131] In the power converter 100, if the time lag between the start of the high level period of the control signal SV1 of the first switching element 1V to be applied to the switching circuit 10V (time t7) and the start of the high level period of the control signal SW1 of the first switching element 1W to be applied to the switching circuit 10W (time t11) is equal to or greater than (Tav+Taw+Td), the V-phase resonant current and the W-phase resonant current do not overlap with each other. On the other hand, if the time lag is less than (Tav+Taw+Td), the V-phase resonant current and the W-phase resonant current overlap with each other. That is, in the case where the threshold value for the time lag is set to (Tav+Taw+Td), if the time lag is less than the threshold value, the controller 50 assumes that the resonant current corresponding to the two phases of the switching circuit 10V and the switching circuit 10W belonging to the plurality of switching circuits 10 will flow through the resonant inductor L1 at the same time. Note that the threshold value is only an example, and the threshold value may also be set to any other value. For example, the threshold value may also be set to a value even greater than (Tav+Taw+Td) in consideration of the error of the additional time Tav and the error of the additional time Taw. In addition, the controller 50 may set the threshold value for the time lag to the same value as the resonant half cycle (in this embodiment, the resonant half cycle = the dead time period Td). In this case, if the time lag is less than the length of the dead time period Td, the controller 50 assumes that the resonant current corresponding to the two phases of the switching circuit 10V and 10W will flow through the resonant inductor L1 at the same time. In addition, the above method for calculating the time lag to determine whether the two-phase resonant current flows simultaneously is only an example. On the contrary, any other calculation method may be used as long as a time lag equivalent to the above time lag can be calculated. For example, as a time lag for determining whether the two-phase resonant current flows simultaneously, the time lag between the end of the high level period of the control signal SV2 (time t6) and the end of the high level period of the control signal SW2 (time t10) may also be used.

[0132] (3.2.1.2) When discharging the resonant capacitor

[0133] When performing the discharge operation on the resonance capacitor 9 , the controller 50 can also judge whether the two-phase resonance currents flow simultaneously using the same time lag and threshold as in the case of performing the charging operation on the resonance capacitor 9 .

[0134] For example, if the time lag between the start of the high level period of the control signal SU2 and the start of the high level period of the control signal SV2 is less than a threshold value (e.g., Tau+Tav+Td), the controller 50 assumes that the U-phase resonant current and the V-phase resonant current will overlap each other.

[0135] Furthermore, if the time lag between the start of the high level period of the control signal SU2 and the start of the high level period of the control signal SW2 is less than a threshold value (eg, Tau+Taw+Td), the controller 50 assumes that the U-phase resonant current and the W-phase resonant current will overlap with each other.

[0136] Furthermore, if the time lag between the start of the high level period of the control signal SV2 and the start of the high level period of the control signal SW2 is less than a threshold value (eg, Tav+Taw+Td), the controller 50 assumes that the V-phase resonant current and the W-phase resonant current will overlap each other.

[0137] (3.2.2) First Control Operation, Second Control Operation, and Third Control Operation

[0138] (3.2.2.1) Operations for Soft Switching of the First Switching Element

[0139] The controller 50 performs the first control operation by enabling the high level period of the control signal of each of the two switches 8 to overlap with the dead time period Td corresponding to each of the two switching circuits 10 connected to the two switches 8 for a predetermined period.

[0140] The controller 50 performs the second control operation by determining the start of the high level period of the control signal of at least one of the plurality of switches 8 according to the load current flowing through the AC load RA1. In this case, the controller 50 performs the second control operation by shifting the start of the high level period of each of the two control signals of the two switches 8 according to the total value of the two-phase load current flowing through the two AC terminals 41 connected to the two switches 8 belonging to the plurality of switches 8, respectively. Fig. 9 In the example shown, the start of each high level period of the control signals SU6 , SV6 of the two switches 8 is shifted according to the total value of the U-phase load current iU flowing through the AC terminal 41U and the V-phase load current iV flowing through the AC terminal 41V.

[0141] The controller 50 may perform the third control operation by making the dead time periods Td1, Td2 respectively corresponding to two or more switching circuits 10 connected to two or more switches 8 belonging to the plurality of switching circuits 10 longer than a predetermined dead time period Td by an additional time Tad. The predetermined dead time period Td is the dead time period Td in the case of the basic operation.

[0142] Fig. 9 1 is a timing chart showing how the power converter 100 operates if the controller 50 has performed the first control operation, the second control operation, and the third control operation. Fig.10is a timing diagram showing how the power converter 100 operates when the controller 50 does not perform the first control operation, the second control operation, or the third control operation. As used herein, the predetermined period may form at least a portion of a resonant half-cycle of a resonant circuit, which includes, for example, a resonant inductor L1 and two resonant capacitors 9 (e.g., resonant capacitors 9U, 9V in this example). Assuming that the resonant half-cycle in the case where the resonant circuit includes two resonant capacitors 9 (in other words, in the case where the current iL1 flowing through the resonant inductor L1 includes a two-phase resonant current) is Tr2, the resonant half-cycle Tr2 is half of the resonant cycle that is the inverse of the resonant frequency of the resonant circuit including the resonant inductor L1 and the two resonant capacitors 9. If the resonant circuit includes two resonant capacitors 9, the resonant half-cycle Tr2 of the resonant circuit is given by Tr2=2 1 / 2 ×π×(L·C) 1 / 2 Given as, where L is the inductance of the resonant inductor L1 and C is the capacitance of each of the two resonant capacitors 9. Fig. 9 In the example shown, the predetermined period is the entirety of the resonance half period Tr2. In other words, the length of the predetermined period is 100% of the resonance half period Tr2.

[0143] Next, how the controller 50 operates will be described in further detail.

[0144] When it is determined that the two-phase resonant currents overlap each other, the controller 50 performs the first step, the second step, and the third step in sequence. In the following description, the case where the resonant current flowing through the U-phase switch 8U and the resonant current flowing through the V-phase switch 8V overlap each other in the resonant inductor L1 will be described as an example. The same statement also applies to the combination of the U-phase and the W-phase and the combination of the V-phase and the W-phase.

[0145] The first step includes synchronizing the U-phase control signals SU1, SU2 with the V-phase control signals SV1, SV2. Fig. 9 In the example shown, Fig.10 Compared with the example shown, the U-phase control signals SU1 and SU2 are synchronized with the V-phase control signals SV1 and SV2 by shifting (advancing) the start of the high-level period of the V-phase control signal SV1 and the end of the high-level period of the V-phase control signal SV2 by ΔT1. In the power converter 100 according to the first embodiment, the first step corresponds to the first control operation to be performed by the controller 50. Fig.10In the example shown, ΔT1 is the time lag between the start of the high level period of the control signal SU1 and the start of the high level period of the control signal SV1, or the time lag between the end of the high level period of the control signal SU2 and the end of the high level period of the control signal SV2. Alternatively, the first step may include synchronizing the U-phase control signals SU1, SU2 with the V-phase control signals SV1, SV2 by shifting (postponing) the high level period of each of the U-phase control signals SU1, SU2 by ΔT1. Still alternatively, the first step may include synchronizing the U-phase control signals SU1, SU2 with the V-phase control signals SV1, SV2 by shifting the total of the U-phase control signals SU1, SU2 and the V-phase control signals SV1, SV2 by ΔT1.

[0146] The second step includes adding an additional time Tad corresponding to the total current value |iU+iV| of the two-phase load currents iU, iV to the two-phase dead time periods Td (see Fig.10 ) respectively high level periods of the control signals SU6 and SV6 of the two-phase switch 8 corresponding to the current sensor. More specifically, for example, the controller 50 uses the respective detection results of the load currents iU and iV or their signal processed values, or the estimated values ​​of the load currents iU and iV, the inductance L of the resonant inductor L1 stored in advance, and the detection results of the potential V15 at the regenerative capacitor 15 to determine the additional time Tad by the formula Tad=L×|iU+iV| / V15. In the power converter 100 according to the first embodiment, the second step corresponds to the second control operation to be performed by the controller 50.

[0147] The third step includes: 1 / 2 ×π×(L·C) 1 / 2 ) to change the length of the high level period and the dead time period Td of each of the control signals SU6 and SV6. More specifically, the controller 50 subtracts the additional time Tad from the high level period of each of the control signals SU6 and SV6 and sets the length of the remaining period to the resonant half period Tr2 of the resonant circuit, and changes the dead time period Td to a dead time period Td1 equal to the resonant half period Tr2 of the resonant circuit. In the power converter 100 according to the first embodiment, the third step corresponds to the third control operation to be performed by the controller 50. Note that the end of the control signals SU6 and SV6 may be simultaneous with the end of the resonant half period Tr2, or may be later than the end of the resonant half period Tr2.

[0148] In the power converter 100, if the controller 50 does not perform any of the first control operation, the second control operation, and the third control operation, Fig.10As shown, at the time point when the control signals SU1 and SV1 change from the low level period to the high level period (i.e., at the end of the dead time period Td corresponding to each of the U phase and the V phase), the voltage V across the second switching element 2U and 2V is 2U 、V 2V has not risen to Vd. That is, if the controller 50 does not perform any of the first control operation, the second control operation, and the third control operation, at the end of the dead time period Td corresponding to each of the U phase and the V phase, the resonant capacitors 9U, 9V have not been fully charged. Therefore, if the controller 50 does not perform any of the first control operation, the second control operation, and the third control operation, at the end of the dead time period Td corresponding to each of the U phase and the V phase, the voltage across each of the first switching elements 1U, 1V has not been reduced to zero. As a result, in the power converter 100, the first switching elements 1U, 1V are switched by hard switching.

[0149] On the other hand, if the controller 50 has performed the first control operation, the second control operation, and the third control operation, then Fig. 9 As shown, at the time point when the control signals SU1 and SV1 change from the low level period to the high level period (i.e., at the end of the dead time period Td corresponding to each of the U phase and the V phase), the voltage V across the second switching element 2U and 2V is 2U 、V 2V That is, if the controller 50 has performed the first control operation, the second control operation, and the third control operation, the resonant capacitors 9U, 9V are fully charged at the end of the dead time period Td corresponding to each of the U phase and the V phase. Thus, in the power converter 100, if the controller 50 has performed the first control operation, the second control operation, and the third control operation, the first switching elements 1U, 1V are switched by zero voltage soft switching.

[0150] Notice, Fig.10 The relationship between the control signals SU1, SU2, SV1, SV2, SU6, SV6 and other physical quantities in an exemplary case where the control signal SU6 of the U-phase switch 8 and the control signal SV6 of the V-phase switch 8 overlap each other is shown. However, this is only an example and should not be construed as limiting. On the contrary, for example, regardless of whether the V-phase and the W-phase overlap each other or whether the W-phase and the U-phase overlap each other, zero voltage soft switching can also be performed by causing the controller 50 to perform the first control operation, the second control operation, and the third control operation. Fig.11 An exemplary relationship among the respective control signals SV1 , SV2 , SW1 , SW2 , SV6 , SW6 in an exemplary case where the control signal SV6 of the V-phase switch 8 and the control signal SW6 of the W-phase switch 8 overlap each other is shown.

[0151] Furthermore, if it is determined that the two-phase resonant currents overlap each other, the two control signals of the two switches 8 need to at least partially overlap each other. In this case, the time relationship between the control signals of the first switching element 1 and the time relationship between the control signals of the second switching element 2 are not particularly limited. For example, Fig.12 As shown, the start of the high level period of the control signal SV1 may be earlier than the start of the high level period of the control signal SU1, and the start of the high level period of the control signal SV6 may be earlier than the start of the high level period of the control signal SU6. Fig.13 As shown, the dead time period Td between the control signals SU1 and SU2 does not necessarily overlap with the dead time period Td between the control signals SV1 and SV2, but the high level periods of the control signals SU6 and SV6 may partially overlap with each other.

[0152] In addition, in the case where the two-phase resonant currents overlap each other, the relationship between the polarity and magnitude of the two-phase load currents is not limited to Figure 2 The relationship iU>iV>0 in the region A1 of the example shown can also be Fig.14 The relationship iU>0>iV in the region A1 of the example shown. In this case, for example, Fig.15 As shown, the control signals SU6 and SV6 overlap each other and the two-phase resonant currents overlap each other.

[0153] (3.2.2.2) Operations for Soft Switching of the Second Switching Element

[0154] The controller 50 controls the switching circuit 10 by making the high level period of the control signal of each of the two or more switches 8 coincide with the dead time period Td (for example, reference 1 to FIG. 1 ) corresponding to each of the two switching circuits 10 respectively connected to the two switches 8 belonging to the plurality of switching circuits 10. Fig.17 ) overlaps a predetermined period of time to perform a first control operation. Fig.16 1 is a timing chart showing how the power converter 100 operates if the controller 50 has performed the first control operation, the second control operation, and the third control operation. Fig.17 1 is a timing diagram showing how the power converter 100 operates when the controller 50 does not perform the first control operation, the second control operation, or the third control operation. As used herein, the predetermined period may form at least a portion of one resonant half-cycle Tr2 of a resonant circuit, which includes, for example, a resonant inductor L1 and two resonant capacitors 9 connected to two switches 8, respectively. The resonant half-cycle Tr2 is given by Tr2=2 1 / 2 ×π×(L·C) 1 / 2 Given. Fig.16In the example shown, the predetermined period is the entirety of the resonance half period Tr2. In other words, the length of the predetermined period is 100% of the length of the resonance half period.

[0155] Next, how the controller 50 operates will be described in further detail.

[0156] When it is determined that the resonant currents overlap each other, the controller 5 performs the first step, the second step, and the third step in sequence. In the following description, the case where the resonant current flowing through the U-phase switch 8U and the resonant current flowing through the V-phase switch 8V overlap each other in the resonant inductor L1 will be described as an example. The same statement also applies to the combination of the U-phase and the W-phase and the combination of the V-phase and the W-phase.

[0157] The first step includes synchronizing the U-phase control signals SU1, SU2 with the V-phase control signals SV1, SV2. Fig.16 In the example shown, Fig.17 Compared with the example shown, the U-phase control signals SU1 and SU2 are synchronized with the V-phase control signals SV1 and SV2 by offsetting (advancing) the end of the high-level period of the V-phase control signal SV1 and the start of the high-level period of the V-phase control signal SV2 by ΔT1. In the power converter 100 according to the first embodiment, the first step corresponds to the first control operation to be performed by the controller 50. Alternatively, the first step may include synchronizing the U-phase control signals SU1 and SU2 with the V-phase control signals SV1 and SV2 by offsetting (postponing) the high-level periods of the U-phase control signals SU1 and SU2, respectively. Still alternatively, the first step may include synchronizing the U-phase control signals SU1 and SU2 with the V-phase control signals SV1 and SV2 by offsetting the total of the U-phase control signals SU1 and SU2 and the V-phase control signals SV1 and SV2 by ΔT1.

[0158] The second step includes adding an additional time Tad corresponding to the total current value of the two-phase load currents iU, iV to the high level periods of the control signals SU7, SV7 of the two-phase switches 8 respectively corresponding to the two-phase dead time periods Td. More specifically, for example, the controller 50 uses the respective detection results of the load currents iU, iV by the current sensor or their signal processing values, or the estimated values ​​of the load currents iU, iV, the inductance L of the resonant inductor L1 that has been stored in advance, and the detection results of the potential V15 at the regenerative capacitor 15, and determines the additional time Tad by the formula Tad = L × | iU + iV | / V15. In the power converter 100 according to the first embodiment, the second step corresponds to the second control operation to be performed by the controller 50.

[0159] The third step includes: 1 / 2 ×π×(L·C)1 / 2 ) to change the length of the high level period and the dead time period Td of each of the control signals SU7 and SV7. More specifically, the controller 50 subtracts the additional time Tad from the high level period of each of the control signals SU7 and SV7 and sets the length of the remaining period to the resonant half period Tr2 of the resonant circuit, and changes the dead time period Td to a dead time period Td1 equal to the resonant half period Tr2 of the resonant circuit. In the power converter 100 according to the first embodiment, the third step corresponds to the third control operation to be performed by the controller 50. Note that the end of the control signals SU7 and SV7 may be simultaneous with the end of the resonant half period Tr2, or may be later than the end of the resonant half period Tr2.

[0160] In the power converter 100, if the controller 50 does not perform any of the first control operation, the second control operation, and the third control operation, Fig.17 As shown, at the time point when the control signals SU2 and SV2 change from the low level period to the high level period (i.e., at the end of the dead time period Td corresponding to each of the U phase and the V phase), the voltage V across the second switching element 2U and 2V is 2U 、V 2V That is, in the power converter 100, if the controller 50 does not perform any of the first control operation, the second control operation, and the third control operation, the discharge of the resonant capacitors 9U, 9V is not yet completed at the end of the dead time period Td corresponding to each of the U phase and the V phase. Thus, in the power converter 100, if the controller 50 does not perform any of the first control operation, the second control operation, and the third control operation, the second switching elements 2U, 2V are switched by hard switching.

[0161] On the other hand, if the controller 50 has performed the first control operation, the second control operation, and the third control operation, then Fig.16 As shown, at the time point when the control signals SU2 and SV2 change from the low level period to the high level period (i.e., at the end of the dead time period Td corresponding to each of the U phase and the V phase), the voltage V across the second switching element 2U and 2V is 2U 、V 2V That is, if the controller 50 has performed the first control operation, the second control operation, and the third control operation, the discharge of the resonant capacitors 9U, 9V is completed at the end of the dead time period Td1 corresponding to each of the U phase and the V phase. Thus, in the power converter 100, if the controller 50 has performed the first control operation, the second control operation, and the third control operation, the second switching elements 2U, 2V are switched by zero voltage soft switching.

[0162] (3.3) Operations to be performed when it is determined that three-phase resonant currents flow simultaneously

[0163] Next, we will refer to Fig.18 How the controller 50 operates when it is determined that the resonant currents respectively passing through the three switches 8 belonging to the plurality of switches 8 flow through the resonant inductor L1 at the same time is described. When it is determined that the resonant currents respectively passing through the three switches 8 belonging to the plurality of switches 8 flow through the resonant inductor L1 at the same time, the controller 50 performs a first control operation. As used herein, the expression "when it is determined that the resonant currents respectively passing through the three switches 8 belonging to the plurality of switches 8 flow at the same time" refers to a situation where it has been pre-assumed that the resonant currents respectively passing through the three switches 8 will flow through the resonant inductor L1 at the same time. It is assumed that in the case where the state of the AC load RA1 is a light load and iU=0, iV=0, and iW=0, the three-phase resonant currents overlap with each other. For example, when the AC load RA1 is a motor (particularly when the motor is running at a low speed or when the rotation speed of the motor is zero (for example, when the motor is locked)), this state occurs. Thus, for example, when the rotation speed (for example, the number of revolutions (rpm)) of the motor is less than the rotation speed threshold, the controller 50 determines that the three-phase resonant currents should flow at the same time. In this case, for example, if the speed determined by calculation or the estimated speed based on the sensor information provided by a sensor device for detecting the number of revolutions of the motor (such as an encoder or a resolver, etc.) is less than the speed threshold, the controller 50 determines that the three-phase resonant current should flow simultaneously.

[0164] Assuming that the capacitance of each of the plurality of resonant capacitors 9U, 9V, and 9W is C, if the U-phase current, the V-phase current, and the W-phase current simultaneously flow through the resonant inductor L1, in the equivalent circuit, a capacitor having a combined capacitance (=3×C) of the resonant capacitor 9U, the resonant capacitor 9V, and the resonant capacitor 9W is connected in series to the resonant inductor L1. Thus, in the power converter 100, if the three-phase current simultaneously flows through the resonant inductor L1, the resonant frequency of the resonant circuit including the resonant inductor L1 changes compared to the case where a single-phase current flows through the resonant inductor L1. Therefore, the power converter 100 may not be able to perform zero-voltage soft switching.

[0165] (3.3.1) First control operation

[0166] (3.3.1.1) Operations for Soft Switching of the First Switching Element

[0167] The controller 50 enables the high level periods of the control signals of the three switches 8 to be respectively connected to the three switches 8 and the dead time periods Td (for example, reference time periods Td) corresponding to the three switching circuits 10 respectively connected to the three switches 8 belonging to the same plurality of switching circuits 10. Fig.19) overlaps a predetermined period of time to perform a first control operation. Fig.18 is a timing chart showing how the power converter 100 operates in a situation where the controller 50 thereof has performed the first control operation. Fig.19 1 is a timing diagram showing how the power converter 100 operates in a case where its controller 50 does not perform the first control operation. As used herein, the predetermined period may form at least a portion of one resonant half-cycle of a resonant circuit, which includes, for example, a resonant inductor L1 and three resonant capacitors 9 respectively connected to three switches 8. In the case where it is assumed that the resonant half-cycle in a case where the resonant circuit includes three resonant capacitors 9 (in other words, in a case where the current iL1 flowing through the resonant inductor L1 includes a three-phase resonant current) is Tr3, the resonant half-cycle Tr3 is half of the resonant cycle, which is the resonant frequency of the resonant circuit including the resonant inductor L1 and the three resonant capacitors 9. If the resonant circuit includes three resonant capacitors 9, the resonant half-cycle Tr3 of the resonant circuit is given by Tr3=3 1 / 2 ×π×(L·C) 1 / 2 Given as, where L is the inductance of the resonant inductor L1 and C is the capacitance of each of the three resonant capacitors 9. Fig.18 In the example shown, the predetermined period is the entirety of the resonance half period Tr3. In other words, the length of the predetermined period is 100% of the resonance half period.

[0168] When performing the first control operation, the controller 50 makes the dead time period Td2 as long as the resonance half period Tr3. Thus, when performing the first control operation, the controller 50 sets the length of the dead time period Td2 to 3 times the length of the dead time period Td in the case of the basic operation. 1 / 2 In addition, the controller 50 also synchronizes not only the start of the high level periods of the control signals SU6, SV6, SW6 of the first IGBTs 6U, 6V, 6W of the three switches 8 through which the resonant current flows, but also the end of the high level periods thereof.

[0169] Next, how the controller 50 operates will be described in further detail.

[0170] When determining that the three-phase resonant currents overlap with each other, the controller 50 performs the first step and the second step in sequence.

[0171] The first step includes synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2, and the W-phase control signals SW1, SW2 with each other. Fig.18 In the example shown, Fig.19Compared to the example shown in FIG. 1 , the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2, and the W-phase control signals SW1, SW2 are synchronized with each other by shifting (advancing) the start of the high-level period of the V-phase control signal SV1 and the end of the high-level period of the V-phase control signal SV2 and shifting (advancing) the start of the high-level period of the W-phase control signal SW1 and the end of the high-level period of the W-phase control signal SW2. Alternatively, the first step may include synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2, and the W-phase control signals SW1, SW2 with each other by shifting (postponing) the high-level period of each of the U-phase control signals SU1, SU2 and shifting (advancing) the high-level period of each of the W-phase control signals SW1, SW2. Still alternatively, the first step may also include synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2, and the W-phase control signals SW1, SW2 with each other by shifting (postponing) the high-level periods of the U-phase control signals SU1, SU2, and shifting (postponing) the high-level periods of the V-phase control signals SV1, SV2. Still alternatively, the first step may also include synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2, and the W-phase control signals SW1, SW2 with each other by shifting (postponing) the high-level periods of the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2, and the W-phase control signals SW1, SW2.

[0172] The second step includes the following steps: 1 / 2 ×π×(L·C) 1 / 2 ) changes the high level period and dead time period Td of each of the control signals SU6, SV6, SW6. More specifically, the controller 50 sets the length of the high level period of each of the control signals SU6, SV6, SW6 to the resonant half period Tr3 of the resonant circuit, and sets the dead time period Td to be equal to the dead time period Td2 of the resonant half period Tr3 of the resonant circuit. Note that if the load current iU=0, the load current iV=0 and the load current iW=0, the controller 50 sets the additional times Tau, Tav, Taw to zero respectively.

[0173] In the power converter 100, if the controller 50 does not perform the first control operation, Fig.19 As shown, at the time point when the control signals SU1, SV1, SW1 transition from the low level period to the high level period (i.e., at the end of the dead time period Td corresponding to each of the U phase, the V phase, and the W phase), the voltage V across the second switching elements 2U, 2V, 2W is 2U 、V2V 、V 2W It has not risen to Vd. That is, in the power converter 100, if the controller 50 does not perform the first control operation, at the end of the dead time period Td corresponding to each of the U phase, the V phase and the W phase, the resonant capacitors 9U, 9V, 9W have not been fully charged. Therefore, in the power converter 100, if the controller 50 does not perform the first control operation, at the end of the dead time period Td corresponding to each of the U phase, the V phase and the W phase, the voltage across each of the first switching elements 1U, 1V, 1W has not been reduced to zero. As a result, in the power converter 100, the first switching elements 1U, 1V, 1W are switched by hard switching.

[0174] On the other hand, in the power converter 100, if the controller 50 has performed the first control operation, then Fig.18 As shown, at the time point when the control signals SU1, SV1, SW1 transition from the low level period to the high level period (i.e., at the end of the dead time period Td2 corresponding to each of the U phase, the V phase, and the W phase), the voltage V across the second switching elements 2U, 2V, 2W is 2U 、V 2V 、V 2W That is, in the power converter 100, if the controller 50 has performed the first control operation, the resonant capacitors 9U, 9V, 9W are fully charged at the end of the dead time period Td2 corresponding to each of the U phase, the V phase, and the W phase. Thus, in the power converter 100, if the controller 50 has performed the first control operation, the first switching elements 1U, 1V, 1W are switched by zero voltage soft switching.

[0175] In addition, in the case where it is determined that the three-phase resonant currents overlap each other, the polarity and magnitude relationship between the three-phase load currents are not limited to Fig.19 The relationship iU=0, iV=0 and iW=0 in the example shown may also be, for example Fig. 20 The relationship shown is iU>0>iV or for example Fig.21 The relationship shown is iW>iV>0>iU.

[0176] In addition, the three control signals of the three switches 8 need to overlap each other at least partially. In this case, the time relationship between the control signals of the first switching element 1 and the relationship between the control signals of the second switching element 2 are not restricted. Fig. 22As shown, the start of the high level period of the control signal SV1 may be earlier than the start of the high level period of the control signal SU1, the start of the high level period of the control signal SU1 may be earlier than the start of the high level period of the control signal SW1, the start of the high level period of the control signal SV6 may be earlier than the start of the high level period of the control signal SU6, and the start of the high level period of the control signal SU6 may be earlier than the start of the high level period of the control signal SW6. In addition, as Fig.23 As shown, the dead time period Td between the control signals SU1 and SU2 does not necessarily overlap with the dead time period Td between the control signals SV1 and SV2, but the high level periods of the control signals SU6, SV6, and SW may partially overlap with each other. Note that in the case of performing the soft switching operation of the first switching element 1 (i.e., in the case of performing the charging operation of the resonant capacitor 9), in the case where the three-phase resonant current flows simultaneously, when the load current is positive and when the basic operation is performed, it is preferred to add the additional time Tau, Tav, and Taw to the high level period of the switch 8 associated with the phase through which the positive load current flows.

[0177] (3.3.1.2) Operations for Soft Switching of the Second Switching Element

[0178] The first control operation includes enabling the high level periods of the control signals SU7, SV7, SW7 of the three switches 8 to be aligned with the dead time periods Td2 (for example, reference 1 to FIG. 1 ) corresponding to the respective switching circuits 10 of the three switching circuits 10. Fig.24 ) overlaps the scheduled time period. Fig.24 is a timing chart showing how the power converter 100 operates in a case where the controller 50 has performed the first control operation. Fig.25 is a timing chart showing how the power converter 100 operates in a case where the controller 50 does not perform the first control operation. Fig.24 and Fig.25 Each shows a timing diagram in the case where there is a period of time when the resonant circuit includes the resonant capacitors 9U, 9V, 9W. As used herein, the predetermined period may form at least a portion of a resonant half-cycle Tr3 of a resonant circuit, for example, including the resonant inductor L1 and the three resonant capacitors 9. The resonant half-cycle Tr3 is given by Tr3=3 1 / 2 ×π×(L·C) 1 / 2 Given. Fig.24 In the example shown, the predetermined period is the entirety of the resonance half period Tr3. In other words, the length of the predetermined period is 100% of the resonance half period Tr3.

[0179] When performing the first control operation, the controller 50 makes the dead time period Td2 as long as the resonance half period Tr3. Thus, when performing the first control operation, the controller 50 sets the length of the dead time period Td2 to 3 times the length of the dead time period Td in the case of the basic operation. 1 / 2 In addition, the controller 50 synchronizes not only the start of the high level period of each of the control signals SU7, SV7, SW7 of the three second IGBTs 7U, 7V, 7W but also the end of the high level period of each of them.

[0180] Next, how the controller 50 operates will be described in further detail.

[0181] When it is determined that the three-phase resonant currents overlap with each other, the controller 50 performs the first step and the second step in sequence.

[0182] The first step includes synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2, and the W-phase control signals SW1, SW2 with each other. Fig.24 In the example shown, Fig.25 Compared to the example shown in FIG. 1 , the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2, and the W-phase control signals SW1, SW2 are synchronized with each other by shifting (advancing) the end of the high-level period of the V-phase control signal SV1 and the start of the high-level period of the V-phase control signal SV2, and shifting (advancing) the end of the high-level period of the W-phase control signal SW1 and the start of the high-level period of the W-phase control signal SW2. Alternatively, the first step may include synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2, and the W-phase control signals SW1, SW2 with each other by shifting (postponing) the high-level periods of the U-phase control signals SU1, SU2, and shifting (advancing) the high-level periods of the W-phase control signals SW1, SW2. Still alternatively, the first step may also include synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2, and the W-phase control signals SW1, SW2 with each other by shifting (postponing) the high-level periods of the U-phase control signals SU1, SU2, and shifting (postponing) the high-level periods of the V-phase control signals SV1, SV2. Still alternatively, the first step may also include synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2, and the W-phase control signals SW1, SW2 with each other by shifting (postponing) the high-level periods of the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2, and the W-phase control signals SW1, SW2.

[0183] The second step includes the following steps: 1 / 2 ×π×(L·C) 1 / 2 ) to change the high level period and dead time period Td of each of the control signals SU6, SV6, and SW6. More specifically, the controller 50 sets the length of the high level period of each of the control signals SU6, SV6, and SW6 to the resonant half period Tr3 of the resonant circuit, and sets the dead time period Td to be equal to the dead time period Td2 of the resonant half period Tr3 of the resonant circuit. Note that if the load current iU=0, the load current iV=0, and the load current iW=0, the controller 50 sets the additional times Tau, Tav, and Taw to zero respectively.

[0184] If the controller 50 does not perform the first control operation, Fig.25 As shown, at the time point when the control signals SU2, SV2, SW2 transition from the low level period to the high level period (i.e., at the end of the dead time period Td corresponding to each of the U phase, the V phase, and the W phase), the voltage V across the second switching elements 2U, 2V, 2W is 2U 、V 2V 、V 2W That is, in the power converter 100, if the controller 50 does not perform the first control operation, at the end of the dead time period Td corresponding to each of the U phase, the V phase, and the W phase, the resonant capacitors 9U, 9V, 9W have not yet been completely discharged. Thus, in the power converter 100, if the controller 50 does not perform the first control operation, the second switching elements 2U, 2V, 2W are switched by hard switching.

[0185] On the other hand, in the power converter 100, if the controller 50 has performed the first control operation, then Fig.24 As shown, at the time point when the control signals SU2, SV2, SW2 transition from the low level period to the high level period (i.e., at the end of the dead time period Td2 corresponding to each of the U phase, the V phase, and the W phase), the voltage V across the second switching elements 2U, 2V, 2W is 2U 、V 2V 、V 2W That is, in the power converter 100, if the controller 50 has performed the first control operation, the discharge of the resonant capacitors 9U, 9V, 9W is completed at the end of the dead time period Td2. Thus, in the power converter 100, if the controller 50 has performed the first control operation, the second switching elements 2U, 2V, 2W are switched by soft switching.

[0186] (4) Summary

[0187] In the power converter 100 according to the first embodiment, when it is determined that the resonant currents respectively passing through the corresponding switches 8 among the two or more switches 8 belonging to the plurality of switches 8 flow through the resonant inductor L1 at the same time, the controller 50 can perform the first control operation and the second control operation. The first control operation includes enabling the high level period of the control signal of each of the two or more switches 8 to overlap with the dead time period (Td1, Td2) associated with each of the two or more switching circuits 10 connected to the two or more switches 8 belonging to the same plurality of switching circuits 10 by a predetermined period. The second control operation includes determining the start of the high level period of the control signal of at least one of the plurality of switches 8 by the load current of at least one phase of the AC load RA1 connected to the plurality of AC terminals 41. This enables the power converter 100 to perform soft switching more reliably.

[0188] In addition, in the power converter 100 according to the first embodiment, the predetermined period is the entirety of the resonance half cycle. This enables the power converter 100 according to the first embodiment to perform zero voltage soft switching more reliably.

[0189] Furthermore, in the power converter 100 according to the first embodiment, the controller 50 performs the second control operation by shifting the start of the high level period of the control signal of at least one switch 8 among the plurality of switches 8 according to the total amount of the load currents respectively flowing through the two or more phases of the two or more AC terminals 41 connected to the two or more switches 8 belonging to the plurality of AC terminals 41. This enables the power converter 100 to start generating resonance at the start of the dead time periods Td1, Td2.

[0190] Furthermore, in the power converter 100 according to the first embodiment, the controller 50 may perform a third control operation including making the dead time period Td1, Td2 associated with each of the two or more switching circuits 10 connected to the two or more switches 8 belonging to the plurality of switching circuits 10 longer by an additional time Tad than the predefined dead time period Td. This enables the power converter 100 to perform zero voltage soft switching even if the resonant half periods Tr2, Tr3 are longer than the dead time period Td.

[0191] (First Modification)

[0192] The power converter 100 according to the first modification of the first embodiment has the same features as the power converter 100 according to the first embodiment (see Figure 1 ) has the same circuit configuration, so its illustration and description will be omitted in this article.

[0193] In the power converter 100 according to the first modification, when it is determined that the two-phase resonant currents overlap each other, the controller 50 operates in a manner that is partially different from the controller 50 according to the first embodiment. Fig.26 2 and other figures illustrate how the controller 50 operates to perform soft switching of the first switching element 1 .

[0194] The controller 50 enables the high level period of the control signal of each of the two or more switches 8 to be connected to the dead time period Td (for example, reference 1 to FIG. 1 ) corresponding to each of the two switching circuits 10 respectively connected to the two switches 8 belonging to the same plurality of switching circuits 10. Fig.26 ) overlaps a predetermined period of time to perform a first control operation. Fig.26 1 is a timing diagram showing how the power converter 100 operates when the controller 50 has performed the first control operation and the second control operation. As used herein, the predetermined period may form a portion of one resonant half cycle Tr2 of a resonant circuit including, for example, a resonant inductor L1 and two resonant capacitors 9 connected to two switches 8, respectively. Fig.26 In the example shown, the predetermined period occupies 60% of the resonance half period Tr2. In other words, the length of the predetermined period is 60% of the length of the resonance half period.

[0195] In addition, the controller 50 synchronizes not only the start of the high level periods of the two control signals of the first IGBTs 6 of the two switches 8 through which the resonant current flows, but also the end of the high level periods of the two control signals of the first IGBTs 6 of the two switches 8 through which the resonant current flows. Fig.26 In the example shown, the controller 50 synchronizes not only the start of the respective high level periods of the control signals SU6 , SV6 of the first IGBTs 6U, 6V with each other but also the end of the respective high level periods with each other.

[0196] Next, how the controller 50 operates will be described in further detail.

[0197] When it is determined that the two-phase resonant currents overlap each other, the controller 50 performs the first step, the second step, and the third step in sequence. In the following description, the case where the resonant current flowing through the U-phase switch 8U and the resonant current flowing through the V-phase switch 8V overlap each other in the resonant inductor L1 will be described as an example. The same statement also applies to the combination of the U-phase and the W-phase and the combination of the V-phase and the W-phase.

[0198] The first step includes synchronizing the U-phase control signals SU1, SU2 with the V-phase control signals SV1, SV2. Fig.26 In the example shown, Fig.10Compared with the example shown, the U-phase control signals SU1 and SU2 are synchronized with the V-phase control signals SV1 and SV2 by shifting (advancing) the high-level periods of the V-phase control signals SV1 and SV2 by ΔT1. The first step corresponds to the first control operation to be performed by the controller 50. Alternatively, the first step may include synchronizing the U-phase control signals SU1 and SU2 with the V-phase control signals SV1 and SV2 by shifting (delaying) the high-level periods of the U-phase control signals SU1 and SU2 by ΔT1. Still alternatively, the first step may include synchronizing the U-phase control signals SU1 and SU2 with the V-phase control signals SV1 and SV2 by shifting the total of the U-phase control signals SU1 and SU2 and the V-phase control signals SV1 and SV2 by ΔT1.

[0199] The second step includes adding an additional time Tad corresponding to the total current value of the two-phase load currents iU, iV to the high level periods of the control signals SU6, SV6 of the two-phase switches 8 respectively corresponding to the two-phase dead time periods Td. More specifically, for example, the controller 50 uses the respective detection results of the load currents iU, iV by the current sensor or their signal processing values, or the estimated values ​​of the load currents iU, iV, the inductance L of the resonant inductor L1 that has been stored in advance, and the detection results of the potential V15 at the regenerative capacitor 15, and determines the additional time Tad by the formula Tad = L × |iU + iV| / V15. The second step corresponds to the second control operation to be performed by the controller 50.

[0200] The third step includes: 1 / 2 ×π×(L·C) 1 / 2 ) to change the length of the high level period of each of the control signals SU6 and SV6. More specifically, the controller 50 subtracts the additional time Tad from the high level period of each of the control signals SU6 and SV6, and sets the length of the remaining period to 60% of the resonance half period Tr2 of the resonance circuit. Note that the end of the control signals SU6 and SV6 may be simultaneous with the end of the resonance half period Tr2, or may be later than the end of the resonance half period Tr2.

[0201] In the power converter 100 according to the first embodiment, if the controller 50 does not perform any of the first control operation and the second control operation, Fig.10 As shown, at the time point when the control signals SU1 and SV1 change from the low level period to the high level period (ie, at the end of the dead time period Td), the voltage V across the second switching element 2U and 2V is 2U 、V 2VThat is, if the controller 50 does not perform any of the first control operation and the second control operation, the resonant capacitors 9U, 9V are not fully charged at the end of the dead time period Td. Therefore, if the controller 50 does not perform any of the first control operation and the second control operation, the voltage across each of the first switching elements 1U, 1V does not decrease to zero at the end of the dead time period Td, and thus the first switching elements 1U, 1V are switched by hard switching.

[0202] On the other hand, in the power converter 100 according to the first modification, if the controller 50 has performed the first control operation and the second control operation, then Fig.26 As shown, at the time point when the control signals SU1 and SV1 change from the low level period to the high level period (ie, at the end of the dead time period Td), the voltage V across the second switching element 2U and 2V is 2U 、V 2V That is, in the power converter 100 according to the first modification, if the controller 50 has performed the first control operation and the second control operation, the first switching elements 1U, 1V are switched by slightly incomplete soft switching, but the loss and noise can still be reduced compared to the complete hard switching.

[0203] (Second Modification)

[0204] The power converter 100 according to the second modification of the first embodiment has the same features as the power converter 100 according to the first embodiment (see Figure 1 ) has the same circuit configuration, so its illustration and description will be omitted in this article. In the following description, reference will be made to Fig. 27 and other figures to illustrate how the controller 50 operates.

[0205] In the power converter 100 according to the second variant, the resonant half cycle in the case of basic operation is half as long as the dead time period Td in the case of basic operation, and when it is determined that the two-phase resonant currents should overlap with each other, the controller 50 operates in a partially different manner from the controller 50 according to the first embodiment.

[0206] The controller 50 performs the first control operation by allowing the high level periods of the control signals of two or more switches 8 to overlap for a predetermined period with the dead time period Td corresponding to each of the two switching circuits 10 respectively connected to the two switches 8 belonging to the same plurality of switching circuits 10 . Fig. 27 1 is a timing chart showing how the power converter 100 operates in a case where the controller 50 has performed the first control operation and the second control operation. Fig.281 is a timing diagram showing how the power converter 100 operates when the controller 50 does not perform any of the first control operation and the second control operation. In this second modification, the resonant half period in the case of the basic operation is Td / 2. As used herein, the predetermined period is the entirety of one resonant half period Tr2 of a resonant circuit including, for example, a resonant inductor L1 and two resonant capacitors 9 connected to two switches 8, respectively. The resonant half period Tr2 has been set to satisfy the following formula: Tr2=2 1 / 2 ×Td / 2. Fig. 27 In the example shown, the length of the resonance half period Tr2 is shorter than the length of the dead time period Td, and the high level period of each of the control signals SU6, SV6 except for the additional time Tad completely overlaps with the resonance half period Tr2. According to the second modification, if the resonance half period Tr2 is equal to or shorter than the dead time period Td in the case of the basic operation, it is not necessary to make the dead time period Td longer than the dead time period Td in the case of the basic operation in the first control operation.

[0207] Next, how the controller 50 operates will be described in further detail.

[0208] When it is determined that the resonant currents overlap each other, the controller 50 performs the first step, the second step, and the third step in sequence. In the following description, the case where the resonant current flowing through the U-phase switch 8U and the resonant current flowing through the V-phase switch 8V overlap each other in the resonant inductor L1 will be described as an example. The same statement also applies to the combination of the U-phase and the W-phase and the combination of the V-phase and the W-phase.

[0209] The first step includes synchronizing the U-phase control signals SU1, SU2 with the V-phase control signals SV1, SV2. Fig. 27 In the example shown, Fig.28 Compared to the example shown, the U-phase control signals SU1 and SU2 are synchronized with the V-phase control signals SV1 and SV2 by offsetting (advancing) the start of the high-level period of the V-phase control signal SV1 and the end of the high-level period of the control signal SV2 by ΔT1. The first step corresponds to the first control operation to be performed by the controller 50. Alternatively, the first step may include synchronizing the U-phase control signals SU1 and SU2 with the V-phase control signals SV1 and SV2 by offsetting (postponing) the high-level period of the U-phase control signals SU1 and SU2 by ΔT1. Still alternatively, the first step may include synchronizing the U-phase control signals SU1 and SU2 with the V-phase control signals SV1 and SV2 by offsetting the total of the U-phase control signals SU1 and SU2 and the V-phase control signals SV1 and SV2 by ΔT1.

[0210] The second step includes adding an additional time Tad corresponding to the total current value of the two-phase load currents iU, iV to the high level periods of the control signals SU7, SV7 of the two-phase switches 8 respectively corresponding to the two-phase dead time periods Td. More specifically, for example, the controller 50 uses the respective detection results of the load currents iU, iV by the current sensor or their signal processing values, or the estimated values ​​of the load currents iU, iV, the inductance L of the resonant inductor L1 that has been stored in advance, and the detection results of the potential V15 at the regenerative capacitor 15, and determines the additional time Tad by the formula Tad = L × |iU + iV| / V15. The second step corresponds to the second control operation to be performed by the controller 50.

[0211] The third step includes: 1 / 2 ×Td / 2) to change the length of the high level period of each of the control signals SU7 and SV7. More specifically, the controller 50 subtracts the additional time Tad from the high level period of each of the control signals SU7 and SV7, and sets the length of the remaining period to the resonance half period Tr2 of the resonance circuit. Note that the end of the control signals SU7 and SV7 may be simultaneous with the end of the resonance half period Tr2, or may be later than the end of the resonance half period Tr2.

[0212] If the controller 50 does not perform any of the first control operation and the second control operation, Fig.28 As shown, at the time point when the control signals SU1 and SV1 change from the low level period to the high level period (ie, at the end of the dead time period Td), the voltage V across the second switching element 2U and 2V is 2U 、V 2V has not risen to Vd. That is, if the controller 50 does not perform any of the first control operation and the second control operation, at the end of the dead time period Td, the resonant capacitors 9U, 9V are not fully charged. Thus, in the power converter 100 according to the second modification, if the controller 50 does not perform any of the first control operation and the second control operation, the first switching elements 1U, 1V are switched by hard switching.

[0213] On the other hand, in the power converter 100 according to the second modification, if the controller 50 has performed the first control operation and the second control operation, then Fig. 27 As shown, at the time point when the control signals SU1 and SV1 change from the low level period to the high level period (ie, at the end of the dead time period Td), the voltage V across the first switching element 1U and 1V is 1U 、V 1VThat is, in the power converter 100 according to the second modification, if the controller 50 has performed the first control operation and the second control operation, at the end of the dead time period Td, the resonant capacitors 9U, 9V are fully charged. Thus, in the power converter 100 according to the second modification, if the controller 50 has performed the first control operation and the second control operation, the first switching elements 1U, 1V are switched by zero voltage soft switching.

[0214] (Third Modification)

[0215] The power converter 100 according to the third modification of the first embodiment has the same features as the power converter 100 according to the first embodiment (see Figure 1 ) has the same circuit configuration, so its illustration and description will be omitted in this article. In the following description, reference will be made to Fig.29 2 and other figures illustrate how the controller 50 operates to perform soft switching of the first switching element 1 .

[0216] In the power converter 100 according to the third variant, the resonant half cycle in the case of basic operation is half as long as the dead time period Td in the case of basic operation, and when it is determined that the three-phase resonant currents should overlap with each other, the controller 50 operates in a partially different manner from the controller 50 according to the first embodiment.

[0217] The controller 50 performs the first control operation by allowing the high level period of each of the control signals of the three switches 8 to overlap with the dead time period Td corresponding to each of the three switching circuits 10 connected to the three switches 8 by a predetermined period. Fig.29 1 is a timing diagram showing how the power converter 100 operates when the controller 50 has performed the first control operation and the second control operation. As used herein, the predetermined period may form a portion of one resonant half cycle Tr3 of a resonant circuit including, for example, a resonant inductor L1 and three resonant capacitors 9. Fig.29 In the example shown, the predetermined period occupies 60% of the resonance half period Tr2. In other words, the length of the predetermined period is 60% of the length of the resonance half period Tr2.

[0218] In addition, the controller 50 synchronizes not only the start of the respective high level periods of the three control signals SU6 , SV6 , SW6 of the first IGBTs 6 of the three switches 8 through which the resonant current flows, but also the end of the respective high level periods.

[0219] Next, how the controller 50 operates will be described in further detail.

[0220] When it is determined that the three-phase resonant currents overlap with each other, the controller 50 performs the first step and the second step in sequence.

[0221] The first step includes synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2, and the W-phase control signals SW1, SW2 with each other. Fig.29 In the example shown, Fig.19 Compared to the example shown, the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2 and the W-phase control signals SW1, SW2 are synchronized with each other by shifting (advancing) the high-level periods of the V-phase control signals SV1, SV2 and shifting (advancing) the high-level periods of the W-phase control signals SW1, SW2. Alternatively, the first step may include synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2 and the W-phase control signals SW1, SW2 with each other by shifting (postponing) the high-level periods of the U-phase control signals SU1, SU2 and shifting (advancing) the high-level periods of the W-phase control signals SW1, SW2. Still alternatively, the first step may also include synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2 and the W-phase control signals SW1, SW2 with each other by shifting (postponing) the high-level periods of the U-phase control signals SU1, SU2 and shifting (postponing) the high-level periods of the V-phase control signals SV1, SV2. Alternatively, the first step may also include synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2 and the W-phase control signals SW1, SW2 with each other by offsetting (delaying) the high-level period of each of the U-phase control signals SU1, SU2, offsetting (delaying) the high-level period of each of the V-phase control signals SV1, SV2 and offsetting (advancing) the high-level period of each of the W-phase control signals SW1, SW2.

[0222] The second step includes the following steps: 1 / 2 ×π×(L·C) 1 / 2 ) to change the high level period and dead time period Td of each of the control signals SU6, SV6, and SW6. More specifically, the controller 50 sets the predetermined period of the high level period of each of the control signals SU6, SV6, and SW6 overlapping with the dead time period Td to 60% of the resonance half period Tr3 of the resonance circuit for each of the high level periods of the control signals SU6, SV6, and SW6. Note that if the load current iU=0, the load current iV=0, and the load current iW=0, the controller 50 sets the additional time Tau, Tav, and Taw to zero.

[0223] If the controller 50 does not perform any of the first control operation and the second control operation, Fig.19 As shown, at the time point when the control signals SU1, SV1, SW1 transition from the low level period to the high level period (i.e., at the end of the dead time period Td corresponding to each of the U phase, the V phase, and the W phase), the voltage V across the second switching elements 2U, 2V, 2W is 2U 、V 2V 、V 2W That is, in the power converter 100, if the controller 50 does not perform any of the first control operation and the second control operation, at the end of the dead time period Td corresponding to each of the U phase, the V phase and the W phase, the resonant capacitors 9U, 9V, 9W are not fully charged. Therefore, in the power converter 100, if the controller 50 does not perform any of the first control operation and the second control operation, the first switching elements 1U, 1V, 1W are switched by hard switching.

[0224] On the other hand, in the power converter 100, if the controller 50 has performed the first control operation and the second control operation, then Fig.29 As shown, at the time point when the control signals SU1, SV1, SW1 change from the low level period to the high level period (i.e., at the end of the dead time period Td of each of the U phase, the V phase, and the W phase), the voltage V across the first switching elements 1U, 1V, 1W is 1U 、V 1V 、V 1W That is, in the power converter 100 according to the third modification, if the controller 50 has performed the first control operation and the second control operation, the first switching elements 1U, 1V are switched by slightly incomplete soft switching, but the loss and noise can still be reduced compared to the complete hard switching.

[0225] (Fourth Modification)

[0226] The power converter 100 according to the fourth modification of the first embodiment has the same features as the power converter 100 according to the first embodiment (see Figure 1 ) has the same circuit configuration, so its illustration and description will be omitted in this article. In the following description, reference will be made to Fig.30 2 and other figures illustrate how the controller 50 operates to perform soft switching of the first switching element 1 .

[0227] In the power converter 100 according to the fourth variant, the resonant half cycle in the case of basic operation is half as long as the dead time period Td in the case of basic operation, and when it is determined that the three-phase resonant currents should overlap with each other, the controller 50 operates in a partially different manner from the controller 50 according to the first embodiment.

[0228] The controller 50 performs the first control operation by allowing the high level period of each of the control signals of the three switches 8 to overlap with the dead time period Td corresponding to each of the three switching circuits 10 connected to the three switches 8 by a predetermined period. Fig.30 1 is a timing diagram showing how the power converter 100 operates when its controller 50 has performed the first control operation, the second control operation and the third control operation. The predetermined period may be, for example, the entirety of the resonant half period Tr3 of the resonant circuit including the resonant inductor L1 and the three resonant capacitors 9. Fig.30 In the example shown, the length of the predetermined period is 100% of the resonance half period Tr3.

[0229] In addition, the controller 50 synchronizes not only the start of the respective high level periods of the three control signals SU6 , SV6 , SW6 of the first IGBTs 6 of the three switches 8 through which the resonant current flows, but also the end of the respective high level periods.

[0230] Next, how the controller 50 operates will be described in further detail.

[0231] When it is determined that the three-phase resonant currents overlap with each other, the controller 50 performs the first step, the second step, and the third step in sequence.

[0232] The first step includes synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2, and the W-phase control signals SW1, SW2 with each other. Fig.30 In the example shown, Fig.19Compared to the example shown, in the case where iU≠0, iV≠0, iW=0 and iU>0>iV, the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2 and the W-phase control signals SW1, SW2 are synchronized with each other by shifting (advancing) the high-level periods of the V-phase control signals SV1, SV2 and shifting (advancing) the high-level periods of the W-phase control signals SW1, SW2. Alternatively, the first step may include synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2 and the W-phase control signals SW1, SW2 with each other by shifting (postponing) the high-level periods of the U-phase control signals SU1, SU2 and shifting (advancing) the high-level periods of the W-phase control signals SW1, SW2. Still alternatively, the first step may also include synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2, and the W-phase control signals SW1, SW2 with each other by shifting (postponing) the high-level periods of the U-phase control signals SU1, SU2, and shifting (postponing) the high-level periods of the V-phase control signals SV1, SV2. Still alternatively, the first step may also include synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2, and the W-phase control signals SW1, SW2 with each other by shifting (postponing) the high-level periods of the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2, and the W-phase control signals SW1, SW2.

[0233] The second step includes changing the additional time Tad of the high level period of each of the control signals SU6, SV6, and SW6 to a value using the total load current (for example, Fig.30 In the example shown, it is zero) a value calculated by the formula Tad = |iU + iV + iW | / V15.

[0234] The third step includes: 1 / 2 ×π×(L·C) 1 / 2 ) to change the high level period and dead time period Td of each of the control signals SU6, SV6, and SW6. More specifically, the controller 50 sets the length of the high level period of each of the control signals SU6, SV6, and SW6 to the resonance half period Tr3 of the resonance circuit, and sets the dead time period Td to be equal to the dead time period Td2 of the resonance half period Tr3 of the resonance circuit.

[0235] If the controller 50 does not perform any of the first, second, and third control operations, at a point in time when the control signals SU1, SV1, SW1 transition from a low level period to a high level period (i.e., at the end of a dead time period Td corresponding to each of the U phase, the V phase, and the W phase), the voltage V across the second switching elements 2U, 2V, 2W is 1U 、V 1V 、V 1W That is, in the power converter 100, if the controller 50 does not perform any of the first control operation, the second control operation, and the third control operation, at the end of the dead time period Td corresponding to each of the U phase, the V phase, and the W phase, the resonant capacitors 9U, 9V, 9W are not fully charged. Thus, in the power converter 100, if the controller 50 does not perform any of the first control operation, the second control operation, and the third control operation, the first switching elements 1U, 1V, 1W are switched by hard switching.

[0236] On the other hand, in the power converter 100 according to the fourth modification, if the controller 50 has performed the first control operation, the second control operation, and the third control operation, then Fig.30 As shown, at the time point when the control signals SU1, SV1, SW1 change from the low level period to the high level period (i.e., at the end of the dead time period Td of each of the U phase, the V phase, and the W phase), the voltage V across the second switching elements 2U, 2V, 2W is 2U 、V 2V 、V 2W That is, in the power converter 100 according to the fourth modification, if the controller 50 has performed the first control operation, the second control operation, and the third control operation, the first switching elements 1U, 1V can be switched by zero voltage soft switching.

[0237] (Fifth Modification)

[0238] The power converter 100 according to the fifth modification of the first embodiment has the same features as the power converter 100 according to the first embodiment (see Figure 1 ) has the same circuit configuration, so its illustration and description will be omitted in this article. In the following description, reference will be made to Fig.31 2 and other figures illustrate how the controller 50 operates to perform soft switching of the first switching element 1 .

[0239] In the power converter 100 according to the fifth variant, the resonant half cycle in the case of basic operation is half as long as the dead time period Td in the case of basic operation, and when it is determined that the three-phase resonant currents should overlap with each other, the controller 50 operates in a partially different manner from the controller 50 according to the first embodiment.

[0240] The controller 50 performs the first control operation by allowing the high level period of each of the control signals of the three switches 8 to overlap with the dead time period Td corresponding to each of the three switching circuits 10 respectively connected to the three switches 8 by a predetermined period. Fig.31 1 is a timing chart showing how the power converter 100 operates in a situation where the controller 50 thereof has performed the first control operation and the second control operation. Fig.32 is a timing chart showing how the power converter 100 operates in a case where its controller 50 does not perform any of the first and second control operations. The predetermined period is, for example, the entirety of the resonance half period Tr3 of the resonance circuit including the resonance inductor L1 and the three resonance capacitors 9 .

[0241] In addition, the controller 50 synchronizes not only the start of the respective high level periods of the three control signals SU6 , SV6 , SW6 of the first IGBTs 6 of the three switches 8 through which the resonant current flows, but also the end of the respective high level periods.

[0242] Next, how the controller 50 operates will be described in further detail.

[0243] When it is determined that the three-phase resonant currents overlap with each other, the controller 50 performs the first step and the second step in sequence.

[0244] The first step includes synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2, and the W-phase control signals SW1, SW2 with each other. Fig.31 In the example shown, Fig.32Compared to the example shown, the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2 and the W-phase control signals SW1, SW2 are synchronized with each other by shifting (advancing) the high-level periods of the V-phase control signals SV1, SV2 and shifting (advancing) the high-level periods of the W-phase control signals SW1, SW2. Alternatively, the first step may include synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2 and the W-phase control signals SW1, SW2 with each other by shifting (postponing) the high-level periods of the U-phase control signals SU1, SU2 and shifting (advancing) the high-level periods of the W-phase control signals SW1, SW2. Still alternatively, the first step may also include synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2 and the W-phase control signals SW1, SW2 with each other by shifting (postponing) the high-level periods of the U-phase control signals SU1, SU2 and shifting (postponing) the high-level periods of the V-phase control signals SV1, SV2. Alternatively, the first step may also include synchronizing the U-phase control signals SU1, SU2, the V-phase control signals SV1, SV2 and the W-phase control signals SW1, SW2 with each other by offsetting (delaying) the high-level period of each of the U-phase control signals SU1, SU2, offsetting (delaying) the high-level period of each of the V-phase control signals SV1, SV2 and offsetting (advancing) the high-level period of each of the W-phase control signals SW1, SW2.

[0245] The second step includes setting the length of the high level period of each of the control signals SU6, SV6, SW6 to the resonance half period Tr3 (=3 1 / 2 ×Td / 2).

[0246] In the power converter 100 according to the fifth modification, if the controller 50 does not perform any of the first control operation and the second control operation, Fig.32 As shown, at the time point when the control signals SU1, SV1, SW1 transition from the low level period to the high level period (i.e., at the end of the dead time period Td corresponding to each of the U phase, the V phase, and the W phase), the voltage V across the second switching elements 2U, 2V, 2W is 2U 、V 2V 、V 2WThat is, in the power converter 100, if the controller 50 does not perform any of the first control operation and the second control operation, at the end of the dead time period Td corresponding to each of the U phase, the V phase and the W phase, the resonant capacitors 9U, 9V, 9W are not fully charged. Therefore, in the power converter 100, if the controller 50 does not perform any of the first control operation and the second control operation, the first switching elements 1U, 1V, 1W are switched by hard switching.

[0247] On the other hand, in the power converter 100 according to the fifth modification, if the controller 50 has performed the first control operation and the second control operation, then Fig.31 As shown, at the time point when the control signals SU1, SV1, SW1 change from the low level period to the high level period (i.e., at the end of the dead time period Td of each of the U phase, the V phase, and the W phase), the voltage V across the second switching elements 2U, 2V, 2W is 2U 、V 2V 、V 2W Rising to Vd. Thus, in the power converter 100 according to the fifth modification, if the controller 50 has performed the first control operation and the second control operation, the first switching elements 1U, 1V can be switched by zero-voltage soft switching.

[0248] (Sixth Modification)

[0249] The power converter 100 according to the sixth modification of the first embodiment has the same features as the power converter 100 according to the first embodiment (see Figure 1 ) has the same circuit configuration, so its illustration and description will be omitted in this article. In the following description, reference will be made to Fig.33 and Fig.34 and other figures to illustrate how the controller 50 operates.

[0250] In the power converter 100, when the controller 50 determines that the two-phase resonant currents overlap each other, it is not necessary to completely overlap the high-level periods of the control signals of the two-phase switches 8. Fig.33 As shown, for example, the control signal SV6, SW6 for turning on one of the two-phase switches 8 may be output until the current iL1 flowing through the resonant inductor L1 reaches iV+iW, which is the total value of the two-phase load current. Fig.33 An exemplary case where the V-phase resonant current and the W-phase resonant current overlap with each other is shown. However, this is merely an example and should not be construed as limiting. The same statement also applies to the case where the U-phase resonant current and the V-phase resonant current overlap with each other and the case where the U-phase resonant current and the W-phase resonant current overlap with each other.

[0251] In power converter 100 according to the sixth modification, when it is determined that two-phase resonant currents should overlap each other, controller 50 operates in a partially different manner from controller 50 according to the first embodiment.

[0252] The controller 50 performs the first control operation by allowing the high level period of each of the control signals of the two switches 8 to overlap with the dead time period Td corresponding to each of the two switching circuits 10 respectively connected to the two switches 8 by a predetermined period. Fig.34 1 is a timing chart showing how the power converter 100 operates when the controller 50 has performed the first control operation, the second control operation, and the third control operation. In this sixth modification, the resonance half cycle in the case of the basic operation is equal to the dead time period Td in length, and the predetermined period is the entirety of the resonance half cycle Tr2 of the following resonance circuit, which includes, for example, the resonance inductor L1 and the two resonance capacitors 9 respectively connected to the two switches 8. The resonance half cycle Tr2 is given by the formula Tr2=2 1 / 2 ×Td / 2. Fig.34 In the example shown, the dead time period Td is as long as the resonance half period Tr2, and the high level period of each of the control signals SU6, SV6 completely overlaps the entire resonance half period Tr2.

[0253] Next, how the controller 50 operates will be described in further detail.

[0254] When it is determined that the resonant currents overlap each other, the controller 50 performs the first step, the second step, and the third step in sequence. In the following description, the case where the resonant current flowing through the U-phase switch 8U and the resonant current flowing through the V-phase switch 8V overlap each other in the resonant inductor L1 will be described as an example. The same statement also applies to the combination of the U-phase and the W-phase and the combination of the V-phase and the W-phase.

[0255] The first step includes synchronizing the U-phase control signals SU1, SU2 with the V-phase control signals SV1, SV2. Fig.34 In the example shown, the U-phase control signals SU1 and SU2 are synchronized with the V-phase control signals SV1 and SV2 by shifting (advancing) the high-level periods of the V-phase control signals SV1 and SV2 by ΔT1. Alternatively, the first step may include synchronizing the U-phase control signals SU1 and SU2 with the V-phase control signals SV1 and SV2 by shifting (delaying) the high-level periods of the U-phase control signals SU1 and SU2 by ΔT1. Still alternatively, the first step may include synchronizing the U-phase control signals SU1 and SU2 with the V-phase control signals SV1 and SV2 by shifting the total of the U-phase control signals SU1 and SU2 and the V-phase control signals SV1 and SV2 by ΔT1.

[0256] The second step includes adding an additional time Tad corresponding to the total current value of the two-phase load currents iU, iV to the high level period of the control signal SU6 of the U-phase switch 8. More specifically, for example, the controller 50 uses the respective detection results of the load currents iU, iV by the current sensor or their signal processed values, or the estimated values ​​of the load currents iU, iV, the inductance L of the resonant inductor L1 that has been stored in advance, and the detection results of the potential V15 at the regenerative capacitor 15, and determines the additional time Tad by the formula Tad = L × |iU + iV| / V15.

[0257] The third step includes: 1 / 2 × Td) to change the length of the high level period and the dead time period Td of the control signals SU6 and SV6. More specifically, the controller 50 subtracts the additional time Tad from the high level period of the control signal SU6, sets the length of the remaining period to the resonance half period Tr2, sets the length of the high level period of the control signal SV6 to the resonance half period Tr2, and uses the formula Td1=2 1 / 2 ×Td determines the dead time period Td1. Note that the end of the control signals SU6, SV6 may be simultaneous with the end of the resonance half period Tr2, or may be later than the end of the resonance half period Tr2.

[0258] If the controller 50 does not perform any of the first control operation, the second control operation, and the third control operation, then Fig.10 As shown, at the time point when the control signals SU1 and SV1 change from the low level period to the high level period (ie, at the end of the dead time period Td), the voltage V across the second switching element 2U and 2V is 2U 、V 2V has not risen to Vd. That is, if the controller 50 does not perform any of the first control operation, the second control operation, and the third control operation, at the end of the dead time period Td, the resonant capacitors 9U, 9V are not fully charged. Thus, in the power converter 100 according to the sixth modification, if the controller 50 does not perform any of the first control operation, the second control operation, and the third control operation, the first switching elements 1U, 1V are switched by hard switching.

[0259] On the other hand, in the power converter 100 according to the sixth modification, if the controller 50 has performed the first control operation, the second control operation, and the third control operation, then Fig.34 As shown, at the time point when the control signals SU1 and SV1 change from the low level period to the high level period (ie, at the end of the dead time period Td), the voltage V across the first switching element 1U and 1V is 1U 、V 1Vbecomes zero. That is, in the power converter 100 according to the sixth modification, if the controller 50 has performed the first control operation, the second control operation, and the third control operation, at the end of the dead time period Td, the resonant capacitors 9U, 9V are fully charged. Therefore, in the power converter 100 according to the sixth modification, if the controller 50 has performed the first control operation, the second control operation, and the third control operation, the first switching elements 1U, 1V are switched by zero voltage soft switching.

[0260] (Seventh Modification)

[0261] The power converter 100 according to the seventh modification of the first embodiment has the same features as the power converter 100 according to the first embodiment (see Figure 1 ) has the same circuit configuration, so its illustration and description will be omitted in this article. In the following description, reference will be made to Fig.35 and other figures to illustrate how the controller 50 operates.

[0262] In the power converter 100 according to the seventh variant, the resonant half cycle in the case of basic operation is half as long as the dead time period Td in the case of basic operation, and when it is determined that the two-phase resonant currents should overlap with each other, the controller 50 operates in a partially different manner from the controller 50 according to the first embodiment.

[0263] The controller 50 performs the first control operation by allowing the high level period of each of the control signals of the two switches 8 to overlap with the dead time period Td corresponding to each of the two switching circuits 10 respectively connected to the two switches 8 by a predetermined period. Fig.35 1 is a timing chart showing how the power converter 100 operates when the controller 50 has performed the first control operation, the second control operation, and the third control operation. In this seventh modification, the resonance half period in the case of the basic operation is as long as half of the dead time period Td, and the predetermined period is the entirety of the resonance half period Tr2 of the following resonance circuit, which includes, for example, the resonance inductor L1 and the two resonance capacitors 9 respectively connected to the two switches 8. The resonance half period Tr2 is given by the formula Tr2=2 1 / 2 ×Td / 2. Fig.35 In the example shown, the resonance half period Tr2 is shorter in length than the dead time period Td, the entire high level period of the control signal SU6 excluding the additional time Tad completely overlaps the entire resonance half period Tr2, and the entire high level period of the control signal SV6 completely overlaps the entire resonance half period Tr2. According to the seventh modification, if the resonance half period Tr2 is equal to or shorter than the dead time period Td in the case of the basic operation, it is not necessary to make the dead time period Td longer than the dead time period Td in the case of the basic operation in the first control operation.

[0264] Next, how the controller 50 operates will be described in further detail.

[0265] When it is determined that the resonant currents overlap each other, the controller 50 performs the first step, the second step, and the third step in sequence. In the following description, the case where the resonant current flowing through the U-phase switch 8U and the resonant current flowing through the V-phase switch 8V overlap each other in the resonant inductor L1 will be described as an example. The same statement also applies to the combination of the U-phase and the W-phase and the combination of the V-phase and the W-phase.

[0266] The first step involves synchronizing the end of each of the U-phase control signal SU6 and the V-phase control signal SV6 with each other. Fig.35 In the example shown, Fig.28 Compared with the illustrated example, the U-phase control signal SU6 is synchronized with the V-phase control signal SV6 by shifting (advancing) the High-level period of the V-phase control signal SV6 by ΔT1.

[0267] The second step includes adding an additional time Tad corresponding to the total current value of the two-phase load currents iU, iV to the high level period of the control signal SU6 of the U-phase switch 8. More specifically, for example, the controller 50 uses the respective detection results of the load currents iU, iV by the current sensor or their signal processed values, or the estimated values ​​of the load currents iU, iV, the inductance L of the resonant inductor L1 that has been stored in advance, and the detection results of the potential V15 at the regenerative capacitor 15, and determines the additional time Tad by the formula Tad = L × |iU + iV| / V15.

[0268] The third step includes: 1 / 2 ×Td) to change the length of the high level period of each of the control signals SU6 and SV6. More specifically, the controller 50 subtracts the additional time Tad from the high level period of the control signal SU6, sets the length of the remaining period to the resonance half period Tr2, and sets the length of the high level period of the control signal SV6 to the resonance half period Tr2. Note that the end of the control signals SU6 and SV6 may be simultaneous with the end of the resonance half period Tr2, or may be later than the end of the resonance half period Tr2.

[0269] If the controller 50 does not perform any of the first control operation, the second control operation, and the third control operation, then Fig.28 As shown, at the time point when the control signals SU1 and SV1 change from the low level period to the high level period (ie, at the end of the dead time period Td), the voltage V across the second switching element 2U and 2V is 2U 、V 2Vhas not risen to Vd. That is, if the controller 50 does not perform any of the first control operation, the second control operation, and the third control operation, at the end of the dead time period Td, the resonant capacitors 9U, 9V are not fully charged. Thus, in the power converter 100 according to the seventh modification, if the controller 50 does not perform any of the first control operation, the second control operation, and the third control operation, the first switching elements 1U, 1V are switched by hard switching.

[0270] On the other hand, in the power converter 100 according to the seventh modification, if the controller 50 has performed the first control operation, the second control operation, and the third control operation, then Fig.35 As shown, at the time point when the control signals SU1 and SV1 change from the low level period to the high level period (ie, at the end of the dead time period Td), the voltage V across the first switching element 1U and 1V is 1U 、V 1V becomes zero. That is, in the power converter 100 according to the seventh modification, if the controller 50 has performed the first control operation, the second control operation, and the third control operation, at the end of the dead time period Td, the resonant capacitors 9U, 9V are fully charged. Thus, in the power converter 100 according to the seventh modification, if the controller 50 has performed the first control operation, the second control operation, and the third control operation, the first switching elements 1U, 1V are switched by zero voltage soft switching.

[0271] (Eighth Modification)

[0272] Reference Fig.36 Description of a power converter 100A according to an eighth modification of the first embodiment. In the following description, any constituent element in the power converter 100A according to the eighth modification of the first embodiment having the same function as the corresponding portion 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 portion, and the description thereof will be omitted herein.

[0273] In the power converter 100A according to the eighth modification, in each of the plurality of switches 8, the first IGBT 6 and the second IGBT 7 thereof are connected in anti-series. In the power converter 100A according to the eighth modification, in each of the plurality of switches 8, the collector terminal of the first IGBT 6 and the collector terminal of the second IGBT 7 are connected to each other, the emitter terminal of the first IGBT 6 is connected to the connection node 3 of the corresponding switching circuit 10 in the plurality of switching circuits 10, and the emitter terminal of the second IGBT 7 is connected to the common connection node 25. In addition, each of the plurality of switches 8 further includes a diode 61 connected in anti-parallel to the first IGBT 6 and a diode 71 connected in anti-parallel to the second IGBT 7.

[0274] In the power converter 100A according to the eighth modification, each of the first IGBT 6 and the second IGBT 7 may be replaced by a MOSFET or a bipolar transistor. In this case, Fig.36 The diode 61 and the diode 71 shown can be replaced by, for example, a parasitic diode of a replacement element or an element built into one chip of the replacement element. In addition, in the power converter 100A according to the first modification, the diode 61 and the diode 71 do not necessarily have to be provided as external elements of the first IGBT 6 and the second IGBT 7, respectively, but can also be elements built into one chip.

[0275] (Ninth Modification)

[0276] Reference Fig.37 A power converter 100A according to a ninth variation of the first embodiment is described. In the following description, any constituent element in the power converter 100A according to the tenth variation of the first embodiment having the same function as the corresponding portion 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 portion, and the description thereof will be omitted herein.

[0277] In the power converter 100A according to the ninth modification, in each of the plurality of switches 8, the first IGBT 6 and the second IGBT 7 thereof are connected in anti-series. In the power converter 100A according to the ninth modification, in each of the plurality of switches 8, the emitter terminal of the first IGBT 6 and the emitter terminal of the second IGBT 7 are connected to each other, the collector terminal of the 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 collector terminal of the second IGBT 7 is connected to the common connection node 25. In addition, each of the plurality of switches 8 further includes a diode 61 connected in anti-parallel to the first IGBT 6 and a diode 71 connected in anti-parallel to the second IGBT 7.

[0278] In the power converter 100A according to the ninth modification, each of the first IGBT 6 and the second IGBT 7 may be replaced by a MOSFET or a bipolar transistor. In this case, Fig.37 The diode 61 and the diode 71 shown can be replaced by, for example, a parasitic diode of a replacement element or an element built into one chip of the replacement element. In addition, in the power converter 100A according to the ninth modification, the diode 61 and the diode 71 do not necessarily have to be set as external elements of the first IGBT 6 and the second IGBT 7, respectively, but can also be elements built into one chip.

[0279] (Tenth Modification)

[0280] Reference Fig.38 A power converter 100A according to a tenth variation of the first embodiment is described. In the following description, any constituent element in the power converter 100A according to the tenth variation of the first embodiment having the same function as the corresponding portion 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 portion, and the description thereof will be omitted herein.

[0281] In the power converter 100A according to the tenth modification, in each of the plurality of switches 8, the first MOSFET 6A and the second MOSFET 7A are connected in anti-series. In the power converter 100A according to the tenth modification, in each of the plurality of switches 8, the drain terminal of the first MOSFET 6A and the drain terminal of the second MOSFET 7A are connected to each other. In addition, each of the plurality of switches 8 further includes a diode 61 connected in anti-parallel to the first MOSFET 6A and a diode 71 connected in anti-parallel to the second MOSFET 7A. In each of the plurality of switches 8, the source terminal of the second MOSFET 7A is connected to the common connection node 25. In each of the plurality of switches 8, the source terminal of the first MOSFET 6A is connected to the connection node 3 of the switching circuit 10 corresponding to the switch 8 including the first MOSFET 6A. Control signals SU6 and SU7 are applied from the controller 50 to the first MOSFET 6A and the second MOSFET 7A of the switch 8U, respectively. Control signals SV6 and SV7 are applied from the controller 50 to the first MOSFET 6A and the second MOSFET 7A of the switch 8V, respectively. Control signals SW6, SW7 are applied from the controller 50 to the first MOSFET 6A and the second MOSFET 7A of the switch 8W, respectively.

[0282] (Eleventh Modification)

[0283] Reference Fig.39 Description of a power converter 100A according to an eleventh variation of the first embodiment. In the following description, any constituent element in the power converter 100A according to the eleventh variation of the first embodiment having the same function as the corresponding portion 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 portion, and description thereof will be omitted herein.

[0284] In the power converter 100A according to the eleventh modification, the diode 63 is connected in series to the first MOSFET 6A, and the diode 73 is connected in series to the second MOSFET 7A in each of the plurality of switches 8. In the power converter 100A according to the eleventh modification, the series circuit of the first MOSFET 6A and the diode 63 and the series circuit of the second MOSFET 7A and the diode 73 are connected in anti-parallel to each other.

[0285] (Twelfth Modification)

[0286] Reference Fig.40 A power converter 100A according to a twelfth variation of the first embodiment is described. In the following description, any constituent element in the power converter 100A according to the twelfth variation of the first embodiment having the same function as the corresponding portion 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 portion, and the description thereof will be omitted herein.

[0287] In the power converter 100A according to the twelfth modification, each of the plurality of switches 8 includes: a MOSFET 80; a diode 83 connected in anti-parallel to the MOSFET 80; a series circuit of two diodes 84, 85 connected in anti-parallel to the MOSFET 80; and a series circuit of two diodes 86, 87 connected in anti-parallel to the MOSFET 80. In each of the plurality of switches 8, a connection node between the diodes 84, 85 in the switch 8 (i.e., a first terminal 81 of the switch 8) is connected to a connection node 3 of a corresponding switching circuit 10 in the plurality of switching circuits 10, and a connection node between the diodes 86, 87 (i.e., a second terminal 82 of the switch 8) is connected to a common connection node 25. In each of the plurality of switches 8, when the MOSFET 80 is turned on, the switch 8 is turned on. On the other hand, when the MOSFET 80 is turned off, the switch 8 is turned off.

[0288] The MOSFETs 80 of the plurality of switches 8 are controlled by the controller 50. The controller 50 outputs a control signal SU8 for controlling the on / off state of the MOSFET 80 of the switch 8U, a control signal SV8 for controlling the on / off state of the MOSFET 80 of the switch 8V, and a control signal SW8 for controlling the on / off state of the MOSFET 80 of the switch 8W.

[0289] In each switch 8, when its MOSFET 80 is turned on, a resonant current generated by the resonant circuit including the resonant inductor L1 and the resonant capacitor 9 flows. In the power converter 100A, when one switch 8 among the plurality of switches 8 is turned on, a charging current including the resonant current flows along a path that passes through the regenerative capacitor 15, the resonant inductor L1, the diode 86, the MOSFET 80, the diode 85, and the resonant capacitor 9 in sequence. In addition, in the power converter 100A, when one switch 8 among the plurality of switches 8 is turned on, a discharging current including the resonant current flows along a path that passes through the resonant capacitor 9, the diode 84, the MOSFET 80, the diode 87, the resonant inductor L1, and the regenerative capacitor 15 in sequence.

[0290] In the power converter 100A according to the twelfth modification, each of the plurality of MOSFETs 80 can be replaced by an IGBT. In addition, in the power converter 100A according to the twelfth modification, each of the plurality of switches 8 can include, for example, a bipolar transistor or a GaN-based gate injection transistor (GIT) instead of the MOSFET 80.

[0291] (Thirteenth Modification)

[0292] Reference Fig.41 A power converter 100A according to a thirteenth variation of the first embodiment is described. In the following description, any constituent element in the power converter 100A according to the thirteenth variation of the first embodiment having the same function as the corresponding portion 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 portion, and the description thereof will be omitted herein.

[0293] In the power converter 100A according to the thirteenth modification, each of the plurality of switches 8 is a dual-gate GaN-based GIT including a first source terminal, a first gate terminal, a second gate terminal, and a second source terminal. In the power converter 100A according to the thirteenth modification, 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 switch 8U, and the control signal SU7 is applied between the second gate terminal and the second source terminal of the dual-gate GaN-based GIT. 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 switch 8V, and the control signal SV7 is applied between the second gate terminal and the second source terminal of the dual-gate GaN-based GIT. 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 switch 8W, and the control signal SW7 is applied between the second gate terminal and the second source terminal of the dual-gate GaN-based GIT.

[0294] (Second embodiment)

[0295] Reference Fig.42 The power converter 100B according to the second embodiment is described. The power converter 100B according to the second embodiment further includes a capacitor 16 connected between the second terminal of the resonant inductor L1 and the first DC terminal 31, which is different from the power converter 100 according to the first embodiment (refer to Figure 1 In the following description, any constituent element in the power converter 100B according to the second embodiment having the same function as the corresponding portion of the power converter 100 according to the first embodiment described above will be designated by the same reference numeral as that of the corresponding portion, and the description thereof will be omitted herein.

[0296] The power converter 100B does not include the capacitor C10 in the power converter 100 according to the first 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% of the capacitance of the regenerative capacitor 15 and equal to or less than 105% of the capacitance of the regenerative capacitor 15.

[0297] In the power converter 100B according to the second 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, which 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 second embodiment, the controller 50 may store the value of the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 in advance.

[0298] The controller 50 of the power converter 100 according to the second embodiment performs the first control operation, the second control operation, and the third control operation, similarly to the controller 50 of the power converter 100 according to the first embodiment. Thus, similarly to the power converter 100 according to the first embodiment, the power converter 100B according to the second embodiment can perform zero voltage soft switching on each of the plurality of first switching elements 1 and the plurality of second switching elements 2.

[0299] (Third Embodiment)

[0300] Reference Fig.43 The power converter 100C according to the third embodiment is described. In the power converter 100C according to the third embodiment, the regeneration capacitor 15 is connected between the second terminal of the resonant inductor L1 and the first DC terminal 31, which is different from the power converter 100 according to the first embodiment (refer to Figure 1 In the following description, any constituent element in the power converter 100C according to the third embodiment having the same function as the corresponding portion of the power converter 100 according to the first embodiment described above will be designated by the same reference numeral as that of the corresponding portion, and the description thereof will be omitted herein.

[0301] The controller 50 of the power converter 100 according to the third embodiment performs the first control operation, the second control operation, and the third control operation, similarly to the controller 50 of the power converter 100 according to the first embodiment. Thus, the power converter 100C according to the third embodiment can perform soft switching more reliably, similarly to the power converter 100 according to the first embodiment.

[0302] (Other Modifications)

[0303] Note that the above-mentioned first to third embodiments and their variations are merely exemplary embodiments and their variations among various embodiments of the present disclosure and should not be interpreted as limiting. On the contrary, the first to third exemplary embodiments and their variations can be easily modified in various ways according to design choices or any other factors without departing from the scope of the present disclosure.

[0304] The operation performed by the controller 50 for "judging that multiple resonant currents are flowing simultaneously" is not limited to the operation of "judging that multiple resonant currents are flowing simultaneously" when the time lag is less than a threshold value and the operation of "judging that three-phase resonant currents are flowing simultaneously" when the motor speed is less than a speed threshold value.

[0305] For example, if the time lag between the start of the high-level period of the control signal corresponding to the U phase and the start of the high-level period of the control signal corresponding to the V phase, the time lag between the start of the high-level period of the control signal corresponding to the V phase and the start of the high-level period of the control signal corresponding to the W phase, and the time lag between the start of the high-level period of the control signal corresponding to the W phase and the start of the high-level period of the control signal corresponding to the U phase are all less than the threshold value, the controller 50 can determine that the three-phase resonant currents flow simultaneously.

[0306] Alternatively, if any one of the current differences between the U-phase load current iU and the V-phase load current iV, the current difference between the V-phase load current iV and the W-phase load current iW, and the current difference between the W-phase load current iW and the U-phase load current iU is less than the current difference threshold, the controller 50 can determine that the two-phase resonant currents are flowing simultaneously.

[0307] Alternatively, if the current difference between the U-phase load current iU and the V-phase load current iV, the current difference between the V-phase load current iV and the W-phase load current iW, and the current difference between the W-phase load current iW and the U-phase load current iU are all less than the current difference threshold, the controller 50 can determine that the three-phase resonant currents are flowing simultaneously.

[0308] Alternatively, if the electrical angle determined by calculation based on sensor information provided by a sensor device for detecting the number of revolutions of the motor (such as an encoder or a resolver, etc.) or the estimated electrical angle falls within a first rotation angle range (e.g., equal to or greater than 55 degrees and equal to or less than 65 degrees) or a second rotation angle range (e.g., equal to or greater than 115 degrees and equal to or less than 125 degrees) or a third rotation angle range (e.g., equal to or greater than 175 degrees and equal to or less than 185 degrees) or a fourth rotation angle range (e.g., equal to or greater than 235 degrees and equal to or less than 245 degrees) or a fifth rotation angle range (e.g., equal to or greater than 295 degrees and equal to or less than 305 degrees) or a sixth rotation angle range (e.g., equal to or greater than 355 degrees and equal to or less than 365 degrees), the controller 50 can determine that "two-phase resonant currents flow simultaneously."

[0309] For example, each of the plurality of first switching elements 1 and the plurality of second switching elements 2 does not necessarily have to be an IGBT, but may also be a MOSFET. In this case, each of the plurality of first diodes 4 may also be replaced by, for example, a parasitic diode of a MOSFET used as its corresponding first switching element 1. In addition, each of the plurality of second diodes 5 may also be replaced by, for example, a parasitic diode of a MOSFET used as its corresponding second switching element 2. The MOSFET may be, for example, a Si-based MOSFET or a SiC-based MOSFET. Each of the plurality of first switching elements 1 and the plurality of second switching elements 2 may also be, for example, a bipolar transistor or a GaN-based GIT.

[0310] Optionally, in the power converters 100, 100A, 100B, 100C, if each of the multiple resonant capacitors 9 has a relatively small capacitance, the parasitic capacitors across the multiple second switching elements 2 can also be used as multiple resonant capacitors 9, instead of setting the multiple resonant capacitors 9 as separate elements.

[0311] For example, each of the plurality of switches 8 according to the second embodiment and the third embodiment other than the first embodiment may have Figure 36 to Figure 41 Any of the exemplary alternative configurations shown.

[0312] Furthermore, the length of the dead time period Td need not necessarily be set to be the same as one resonance half cycle, and may also be set to be different from one resonance half cycle. However, in any case, the end of the dead time period Td preferably coincides with the end of the resonance half cycle.

[0313] The dead time period Td may also be set by a dead time generator circuit included in a gate driver integrated circuit (IC) provided separately from the controller 50. Alternatively, the controller 50 may include a gate driver IC, and the dead time generator circuit included in the gate driver IC may set the dead time period Td.

[0314] Furthermore, the power converters 100 , 100A, 100B, 100C are not necessarily configured to output three-phase AC power, and may be configured to output multi-phase AC power having more than three phases.

[0315] (All aspects)

[0316] The foregoing description provides specific implementations of the following aspects of the present disclosure.

[0317] 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 switches (8), a plurality of resonant capacitors (9), a resonant inductor (L1), a regenerative capacitor (15), and a controller (50). The power conversion circuit (11) includes a plurality of first switching elements (1) and a plurality of second switching elements (2). In the power conversion circuit (11), a plurality of switching circuits (10) are connected in parallel to each other, and in each of the plurality of switching circuits (10), one first switching element (1) of the plurality of first switching elements (1) and a corresponding second switching element (2) of the plurality of second switching elements (2) are connected in series one-to-one. In the power conversion circuit (11), the plurality of first switching elements (1) are connected to the first DC terminal (31), and the plurality of second switching elements (2) are connected to the second DC terminal (32). The plurality of AC terminals (41) are provided one-to-one for the plurality of switching circuits (10). Each of the plurality of AC terminals (41) is connected to a connection node (3) between a first switching element (1) and a second switching element (2) of a corresponding switching circuit in a plurality of switching circuits (10). The plurality of switches (8) are provided one-to-one for the plurality of switching circuits (10). The first terminal (81) of each of the plurality of 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 second terminals (82) of each of the plurality of switches (8) are commonly connected to a common connection node (25). The plurality of resonant capacitors (9) are provided one-to-one for the plurality of switches (8). Each of the plurality of resonant capacitors (9) is connected between a first terminal (81) and a second DC terminal (32) of a corresponding switch in a plurality of switches (8). The resonant inductor (L1) has a first terminal and a second terminal. In the resonant inductor (L1), the first terminal of the resonant inductor (L1) is connected to the common connection node (25). The regenerative capacitor (15) has a third terminal (153) and a fourth terminal (154). In the regenerative capacitor (15), the third terminal (153) of the regenerative capacitor (15) is connected to the first DC terminal (31) or the second DC terminal (32). The controller (50) applies a control signal having a potential alternating between a high level and a low level to each of the plurality of first switching elements (1), the plurality of second switching elements (2) and the plurality of switches (8). When it is determined that the resonant currents respectively passing through the corresponding switches of two or more switches (8) belonging to the plurality of switches (8) flow through the resonant inductor (L1) at the same time, the controller (50) can perform a first control operation and a second control operation.The first control operation includes enabling a high level period of a control signal of each of the two or more switches (8) to overlap a dead time period (Td) associated with each of the two or more switching circuits (10) belonging to the same plurality of switching circuits (10) and connected to the two or more switches (8) by a predetermined period. The second control operation includes determining the start of the high level period of the control signal of at least one of the plurality of switches (8) by a load current of at least one phase of an AC load (RA1) connected to the plurality of AC terminals (41).

[0318] This aspect enables soft handover to be performed more reliably.

[0319] In a power converter (100; 100A; 100B; 100C) according to the second aspect which can be implemented in combination with the first aspect, the predetermined period forms at least a part of a resonant half cycle (Tr2, Tr3) of a resonant circuit. The resonant circuit comprises a resonant inductor (L1) and two or more resonant capacitors (9) of the resonant capacitors (9). Each of the two or more resonant capacitors (9) of the resonant capacitors (9) is connected to a corresponding switch of the two or more switches (8).

[0320] In the power converter (100; 100A; 100B; 100C) according to the third aspect which can be implemented in combination with the second aspect, the predetermined period is the entirety of the resonance half period (Tr2, Tr3).

[0321] This aspect enables more reliable zero voltage soft switching.

[0322] In a power converter (100; 100A; 100B; 100C) according to a fourth aspect which can be implemented in combination with any one of the first to third aspects, a controller (50) performs a second control operation by shifting the start of a high level period of a control signal of one of the plurality of switches (8) according to a total amount of load currents of two or more phases respectively flowing through two or more AC terminals (41) belonging to the plurality of AC terminals (41) respectively connected to two or more switches (8).

[0323] This aspect enables resonance to start to be generated at the beginning of the dead time period (Td1, Td2).

[0324] In a power converter (100; 100A; 100B; 100C) according to the fifth aspect which can be implemented in combination with any one of the first to fourth aspects, the controller (50) can perform a third control operation, which includes making the dead time period (Td1, Td2) associated with each switching circuit of two or more switching circuits (10) belonging to a plurality of switching circuits (10) respectively connected to two or more switches (8) longer than a predefined dead time period (Td) by an additional time (Tad).

[0325] This aspect enables zero voltage soft switching even if the resonant half period (Tr2, Tr3) is longer than the dead time period (Td).

[0326] Description of Reference Numerals

[0327] 1First switching element

[0328] 2 Second switching element

[0329] 3 Connecting Nodes

[0330] 8 Switches

[0331] 81 First terminal

[0332] 82 Second terminal

[0333] 9. Resonant capacitor

[0334] 10Switching circuit

[0335] 11 Power conversion circuit

[0336] 15 regeneration capacitor

[0337] 153 Third terminal

[0338] 154 Fourth terminal

[0339] 25 public connection nodes

[0340] 31 First DC terminal

[0341] 32 Second DC terminal

[0342] 41AC terminal

[0343] 50 Controllers

[0344] 100, 100A, 100B, 100C power converters

[0345] iU, iV, iW output current (load current)

[0346] L1 resonant inductor

[0347] RA1 AC load

[0348] Tad additional time

[0349] Td Dead Time

[0350] Td1 Dead time period

[0351] Td2 Dead time period

[0352] Tr2 resonant half period

[0353] Tr3 resonant half period

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 provided one-to-one for the plurality of switching circuits, each of the plurality of AC terminals being connected to a connection node between the first switching element and the second switching element of a corresponding switching circuit of the plurality of switching circuits; a plurality of switches, which are arranged one-to-one for the plurality of switching circuits, wherein a first terminal of each of the plurality of switches is connected to a connection node between the first switching element and the second switching element of a corresponding switching circuit in the plurality of switching circuits, and a second terminal of each of the plurality of switches is commonly connected to a common connection node; a plurality of resonant capacitors, which are arranged one-to-one for the plurality of switches, each of the plurality of resonant capacitors being connected between the first terminal and the second DC terminal of a corresponding switch among the plurality of switches; a resonant inductor having a first terminal and a second terminal, the first terminal of the resonant inductor being connected to the common connection node; 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; as well as a controller configured to apply a control signal having a potential alternating between a high level and a low level to each of the plurality of first switching elements, the plurality of second switching elements, and the plurality of switches, wherein the controller is capable of performing a first control operation and a second control operation when it is determined that the resonant currents respectively passing through corresponding switches of two or more switches belonging to the plurality of switches flow through the resonant inductor at the same time, The first control operation is used to enable a high level period of a control signal of each of the two or more switches to overlap with a dead time period for a predetermined period, the dead time period being associated with each of two or more switching circuits belonging to the plurality of switching circuits and connected to the two or more switches, respectively; and The second control operation is for determining a start of a high level period of a control signal of at least one of the plurality of switches by a load current flowing through at least one phase of an AC load connected to the plurality of AC terminals.

2. The power converter according to claim 1, wherein: The predetermined time period forms at least a portion of a resonant half-cycle of a resonant circuit, the resonant circuit comprising the resonant inductor and two or more of the resonant capacitors, each of the two or more of the resonant capacitors being connected to a respective switch of the two or more switches.

3. The power converter according to claim 2, wherein: The predetermined period is the entirety of the resonant half cycle.

4. The power converter according to any one of claims 1 to 3, wherein: The controller is configured to perform the second control operation by shifting the start of a high level period of a control signal of one of the plurality of switches according to a total amount of load currents of two or more phases respectively flowing through two or more AC terminals belonging to the plurality of AC terminals respectively connected to the two or more switches.

5. The power converter according to any one of claims 1 to 4, wherein: The controller is capable of performing a third control operation, which is used to make the dead time period longer than the predefined dead time period by an additional time, and the dead time period is associated with each of the two or more switching circuits belonging to the multiple switching circuits and respectively connected to the two or more switches.

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