Power converter

Abstract

The present invention more reliably performs soft switching for a power converter. A power converter (100) includes a power conversion circuit (11), a plurality of switches (8), a plurality of resonant capacitors (9), a resonant inductor (L1), a regenerative capacitor (15), and a controller (50). A power conversion circuit (11) includes a plurality of first switching elements (1) and a plurality of second switching elements (2). In a power converter (100), when it is determined that resonance currents respectively passing through two or more switches (8) belonging to a plurality of switches (8) will simultaneously flow through a resonance inductor (L1), a controller (50) performs shift control for shifting a high-level period of a control signal for at least one switch (8) of the two or more switches (8), the two or more switches (8) are arranged in the resonant inductor (L1) so as to prevent resonant currents respectively passing through the two or more switches (8) from simultaneously flowing through the resonant inductor (L1).

Description

Technical Field

[0001] The present disclosure relates generally to power converters. More particularly, the present disclosure relates to power converters having the capability of converting 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. The two capacitors divide the voltage of the DC power supply. One end of the coil is connected to the voltage dividing node of the two capacitors. The plurality of auxiliary switching elements connects the other end of the coil to the output node of each phase. When it is determined that multiple phase currents will 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] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2010-233306 Summary of the Invention

[0007] In the power converter of Patent Document 1, when the control component determines that multiple phase currents will 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.

[0008] An object of the present disclosure is to provide a power converter having the capability of soft switching more reliably.

[0009] According to one aspect of the present disclosure, a power converter includes first and second DC terminals, a power conversion circuit, multiple AC terminals, multiple switches, multiple resonant capacitors, a resonant inductor, a regenerative capacitor, and a controller. The power conversion circuit includes multiple first switching elements and multiple second switching elements. In the power conversion circuit, the multiple switching circuits are connected in parallel with each other, and in each of the multiple switching circuits, one of the multiple first switching elements and a corresponding second switching element of the multiple second switching elements are connected in series on a one-to-one basis. In the power conversion circuit, the multiple first switching elements are connected to the first DC terminal, and the multiple second switching elements are connected to the second DC terminal. The multiple AC terminals are provided one-to-one for each of the multiple switching circuits. Each of the multiple AC terminals is connected to a connection node between a first switching element and a second switching element of a corresponding switching circuit of the multiple switching circuits. The multiple switches are provided one-to-one for each of the multiple switching circuits. A first end of each of the multiple switches is connected to a connection node between the first switching element and the second switching element of the corresponding switching circuit of the multiple switching circuits. A second end of each of the multiple switches is commonly connected to a common connection node. The multiple resonant capacitors are provided one-to-one for each of the multiple switches. Each of the plurality of resonant capacitors is connected between the second DC terminal and the first end of a corresponding switch among the plurality of switches. The resonant inductor has a first end and a second end, and in the resonant inductor, the first end of the resonant inductor is connected to the common connection node. The regenerative capacitor has a third end and a fourth end. In the regenerative capacitor, the third end 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 resonant currents respectively passing through two or more switches belonging to the plurality of switches will flow through the resonant inductor simultaneously, the controller performs shift control to shift a high-level period of the control signal for at least one of the two or more switches to prevent the resonant currents respectively passing through the two or more switches from flowing through the resonant inductor simultaneously.

[0010] The power converter according to the present disclosure achieves the advantage of enabling soft switching to be performed more reliably. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0012] Figure 2illustrates how the power converter operates under the condition that its controller has performed basic operations when the load current is >0 and its resonant capacitor undergoes a charging operation;

[0013] Figure 3 It also illustrates how the power converter operates in a situation where its controller has performed basic operations when the load current is >0 and its resonant capacitor undergoes a charging operation;

[0014] Figure 4 shows how duty ratios and load currents corresponding to three-phase voltage commands in AC loads connected to a plurality of AC terminals of the power converter vary with time;

[0015] Figure 5 showing a first current threshold and a second current threshold for use in a controller of the power converter;

[0016] Figure 6 illustrates how the power converter operates under the condition that its controller has performed basic operation when the load current is >0 and its resonant capacitor undergoes a discharge operation;

[0017] Figure 7 illustrates how the power converter operates under the condition that its controller has performed basic operation when the load current is <0 and its resonant capacitor undergoes a discharge operation;

[0018] Figure 8 illustrates how the power converter operates under the condition that its controller has performed basic operations when the load current is <0 and its resonant capacitor undergoes a charging operation;

[0019] Figure 9 is a timing diagram illustrating how the controller in the power converter operates;

[0020] Figure 10 is a timing diagram illustrating how the controller in the power converter operates;

[0021] Figure 11 is a timing diagram illustrating how the controller in the power converter operates;

[0022] Figure 12 is a timing chart illustrating how the controller thereof operates in the power converter according to the second embodiment;

[0023] Figure 13 is a timing diagram illustrating how the controller in the power converter operates;

[0024] Figure 14 is a timing diagram illustrating how the controller in the power converter operates;

[0025] Figure 15 is a timing chart illustrating a case where the controller thereof has performed shift control in the power converter according to the third embodiment;

[0026] Figure 16 is a timing chart illustrating a case where the controller of the power converter does not perform shift control;

[0027] Figure 17 is a timing diagram illustrating a situation in which the controller of the power converter performs shift control;

[0028] Figure 18 is a timing chart illustrating a case where the controller of the power converter does not perform shift control;

[0029] Figure 19 is a timing chart illustrating a case where the controller thereof has performed shift control in the power converter according to the fourth embodiment;

[0030] Figure 20 is a timing chart illustrating a case where the controller thereof has performed shift control in the power converter according to the fifth embodiment;

[0031] Figure 21 is a timing chart illustrating a case where the controller of the power converter does not perform shift control;

[0032] Figure 22 is a circuit diagram of a system including a power converter according to a sixth embodiment;

[0033] Figure 23 is a circuit diagram of a system including a power converter according to a seventh embodiment;

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

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

[0036] Figure 26 is a circuit diagram of a system including a power converter according to a tenth embodiment;

[0037] Figure 27 is a circuit diagram of a system including a power converter according to an eleventh embodiment;

[0038] Figure 28 is a circuit diagram of a system including a power converter according to a twelfth embodiment; and

[0039] Figure 29 is a circuit diagram of a system including a power converter according to a thirteenth embodiment. DETAILED DESCRIPTION

[0040] (First embodiment)

[0041] Will refer to Figures 1 to 11 A power converter 100 according to a first embodiment will be described.

[0042] (1) Overall configuration of power converter

[0043] 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. A DC power source E1 is connected between the first DC terminal 31 and the second DC terminal 32. An 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, three-phase AC power having a U phase, a V phase, and a W phase.

[0044] Power converter 100 includes power conversion circuit 11, multiple (e.g., three) switches 8, multiple (e.g., three) resonant capacitors 9, regenerative capacitor 15, resonant inductor L1, and controller 50. Power converter 100 also includes protection circuit 17 and capacitor C10. Each of the multiple switches 8 can be, for example, a bidirectional switch.

[0045] The power conversion circuit 11 includes a plurality (e.g., three) of first switching elements 1 and a plurality (e.g., three) of second switching elements 2. In the power conversion circuit 11, a plurality (e.g., three) of switching circuits 10 are connected in parallel. In each switching circuit 10, one of the plurality of first switching elements 1 and a corresponding second switching element of the plurality of second switching elements 2 are connected in series on a one-to-one basis. In the power conversion circuit 11, the plurality of first switching elements 1 are connected to a first DC terminal 31, and the plurality of second switching elements 2 are connected to a second DC terminal 32. A plurality of AC terminals 41 are provided for each of the plurality of switching circuits 10. Each of the plurality of AC terminals 41 is connected to a connection node 3 between the first switching element 1 and the second switching element 2 of a corresponding switching circuit 10. A plurality of switches 8 are provided for each of the plurality of switching circuits 10. A first end 81 of each of the plurality of switches 8 is connected to a connection node 3 between the first switching element 1 and the second switching element 2 of a corresponding switching circuit 10. A plurality of resonant capacitors 9 are provided for each of the plurality of switches 8. Each resonant capacitor in the plurality of resonant capacitors 9 is connected between the first end 81 of a corresponding switch in the plurality of switches 8 and the second DC terminal 32. The resonant inductor L1 has a first end and a second end. The first end of the resonant inductor L1 is connected to the common connection node 25. The regenerative capacitor 15 has a third end 153 and a fourth end 154. In the regenerative capacitor 15, its third end is connected to the second DC terminal 32, and its fourth end 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.

[0046] (2) Details of power converter

[0047] In the following description, for the sake of convenience, with respect to a plurality of switching circuits 10, the switching circuits 10 for the U-phase, V-phase, and 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 “first switching element 1U” and “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 “first switching element 1V” and “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 “first switching element 1W” and “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," the connection node 3 between the first switching element 1V and the second switching element 2V will be referred to as "connection node 3V," 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." Furthermore, in the following description, the AC terminal 41 connected to the connection node 3U will be referred to as "AC terminal 41U," the AC terminal 41 connected to the connection node 3V will be referred to as "AC terminal 41V," and the AC terminal 41 connected to the connection node 3W will be referred to as "AC terminal 41W." Furthermore, in the following description, the resonant capacitor 9 connected in parallel to the second switching element 2U will be referred to as "resonant capacitor 9U," the resonant capacitor 9 connected in parallel to the second switching element 2V will be referred to as "resonant capacitor 9V," and the resonant capacitor 9 connected in parallel to the second switching element 2W will be referred to as "resonant capacitor 9W." In 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.

[0048] In the power converter 100, the high potential output terminal (positive electrode) of the DC power source E1 is connected to the first DC terminal 31, and the low potential output terminal (negative electrode) of the DC power source E1 is connected to the second DC terminal 32. In addition, in the power converter 100, the U-phase terminal, the V-phase terminal, and the W-phase terminal of the AC load RA1 are connected to the three AC terminals 41U, 41V, and 41W, respectively.

[0049] In the power conversion circuit 11, each of the plurality (e.g., three) first switching elements 1 and the plurality (e.g., three) second switching elements 2 has a control terminal, a first main terminal, and a second main terminal. The control terminals of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 are 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 can be, for example, an insulated gate bipolar transistor (IGBT). Thus, in each of the plurality of first switching elements 1 and the plurality of second switching elements 2, its control terminal, first main terminal, and second main terminal are, respectively, the gate terminal, collector terminal, and emitter terminal.

[0050] The power conversion circuit 11 also includes: a plurality of (e.g., three) first diodes 4, which are connected in anti-parallel to the plurality of (e.g., three) first switching elements 1 in a one-to-one manner; and a plurality of (e.g., three) second diodes 5, which are connected in anti-parallel to the plurality of (e.g., three) second switching elements 2 in a one-to-one manner. 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.

[0051] The U-phase terminal of the AC load RA1 may be connected to a connection node 3U between the first switching element 1U and the second switching element 2U via, for example, an AC terminal 41U. The V-phase terminal of the AC load RA1 may be connected to a connection node 3V between the first switching element 1V and the second switching element 2V via, for example, an AC terminal 41V. The W-phase terminal of the AC load RA1 may be connected to a connection node 3W between the first switching element 1W and the second switching element 2W via, for example, an AC terminal 41W.

[0052] Multiple resonant capacitors 9 are provided one-to-one with each of the multiple switches 8. Each of the multiple resonant capacitors 9 is connected between the first end 81 of its corresponding switch 8 and the second DC terminal 32. The power converter 100 includes multiple resonant circuits. The multiple resonant circuits include a resonant circuit including a resonant capacitor 9U and a resonant inductor L1, a resonant circuit including a resonant capacitor 9V and a resonant inductor L1, and a resonant circuit including a resonant capacitor 9W and a resonant inductor L1. The multiple resonant circuits share the resonant inductor L1.

[0053] Each of the plurality of switches 8 may, for example, include two IGBTs (i.e., a first IGBT 6 and a second IGBT 7) connected 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. Switch 8U is connected to the connection node 3U between the first switching element 1U and the second switching element 2U. Switch 8V is connected to the connection node 3V between the first switching element 1V and the second switching element 2V. 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 convenience of explanation, 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.

[0054] 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.

[0055] The resonant inductor L1 has a first end and a second end. In the resonant inductor L1 , the first end of the resonant inductor L1 is connected to the common connection node 25 , and the second end of the resonant inductor L1 is connected to the fourth end 154 of the regenerative capacitor 15 .

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

[0057] Protection circuit 17 includes a third diode 13 and a fourth diode 14. Third diode 13 is connected between common connection node 25 and first DC terminal 31. The anode of third diode 13 is connected to common connection node 25, and the cathode of third diode 13 is connected to first DC terminal 31. Fourth diode 14 is connected between common connection node 25 and second DC terminal 32. The anode of fourth diode 14 is connected to second DC terminal 32, and the cathode of fourth diode 14 is connected to common connection node 25. Thus, fourth diode 14 is connected in series to third diode 13.

[0058] 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.

[0059] 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-transitory storage medium such as a memory card, an optical disc or a hard disk drive (disk) (any of which is readable by the computer system). The processor of the computer system may be composed of a single or multiple electronic circuits including a semiconductor integrated circuit (IC) or a large-scale integrated circuit (LSI). These electronic circuits may be integrated together on a single chip or distributed on multiple chips, whichever is appropriate. These multiple chips may be aggregated together in a single device or distributed in multiple devices without limitation.

[0060] The controller 50 outputs control signals SU1, SV1, and SW1 for controlling the on / off states of the plurality of first switching elements 1U, 1V, and 1W, respectively. Each of the control signals SU1, SV1, and SW1 may be, for example, a pulse-width modulated (PWM) signal having a potential level that alternates between a first potential level (hereinafter referred to as a "low level") and a second potential level (hereinafter referred to as a "high level") that is higher than the first potential level. The first switching elements 1U, 1V, and 1W are turned on when the control signals SU1, SV1, and SW1 are at a high level, and are turned off when the control signals SU1, SV1, and SW1 are at a low level. Furthermore, the controller 50 outputs control signals SU2, SV2, and SW2 for controlling the on / off states of the plurality of second switching elements 2U, 2V, and 2W, respectively. Each of the control signals SU2, SV2, and SW2 may be, for example, a PWM signal having a potential level that alternates between a first potential level (hereinafter referred to as a "low level") and a second potential level (hereinafter referred to as a "high level") that is higher than the first potential level. The second switching elements 2U, 2V, and 2W are turned on when the control signals SU2, SV2, and SW2 are at a high level, respectively, and are turned off when the control signals SU2, SV2, and SW2 are at a low level, respectively.

[0061] The controller 50 uses a carrier signal having a sawtooth waveform (reference Figure 2 ) to generate control signals SU1, SV1, SW1 for multiple first switching elements 1U, 1V, 1W and control signals SU2, SV2, SW2 for multiple second switching elements 2U, 2V, 2W. More specifically, the controller 50 generates control signals SU1, SU2 to be applied to the first switching element 1U and the second switching element 2U, respectively, based at least on the carrier signal and the U-phase voltage instruction. 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 instruction. 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 instruction. The U-phase voltage instruction, the V-phase voltage instruction and the W-phase voltage instruction can be, for example, sinusoidal wave signals whose phases differ by 120 degrees from each other and whose amplitudes (voltage instruction values) vary with time. Note that the waveform of the carrier signal does not have to be a sawtooth waveform, but can also be a triangular waveform or Figure 2 The sawtooth waveform shown is a mirror-inverted version. 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, the cycle of the U-phase voltage command, the V-phase voltage command, and the W-phase voltage command is longer than the cycle of the carrier signal.

[0062] The duty ratios of the control signals SU1, SU2 to be applied from the controller 50 to the first switching element 1U and the second switching element 2U, respectively, vary according to the U-phase voltage command. Figure 4 In FIG. 5 , the duty cycle of the control signal SU1 is shown as “U-phase duty cycle”. The controller 50 (refer to FIG. 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 band period Td (reference period) between the high level period of the control signal SU1 and the high level period of the control signal SU2. Figure 2 ).

[0063] 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 “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 band period Td (reference period) between the high level period of the control signal SV1 and the high level period of the control signal SV2. Figure 2 ).

[0064] The duty ratios of the control signals SW1, SW2 to be applied from the controller 50 to the first switching element 1W and the second switching element 2W, respectively, vary according to the W-phase voltage command. Figure 4 In FIG. 5 , 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 on-periods of the first switching element 1W and the second switching element 2W from overlapping each other, the controller 50 sets a dead band period Td (reference period) between the high-level period of the control signal SW1 and the high-level period of the control signal SW2. Figure 3 ).

[0065] 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 by 120 degrees from each other and whose amplitudes vary with time. Figure 4 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. Similarly, 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.

[0066] Controller 50 generates control signals SU1, SU2, SV1, SV2, SW1, and SW2 based on the carrier signal, the voltage commands, and information about the state of AC load RA1. For example, if AC load RA1 is a three-phase motor, the information about the state of AC load RA1 may include detection values ​​provided by a plurality of current sensors for detecting output currents iU, iV, and iW, respectively, flowing through the U-phase, V-phase, and W-phase of AC load RA1 (hereinafter referred to as "load currents").

[0067] 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 .

[0068] 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 .

[0069] 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 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.

[0070] When the first IGBT 6U is on and the second IGBT 7U is off, the switch 8U allows a charging current to flow sequentially through the regenerative capacitor 15, the resonant inductor L1, the switch 8U, and the resonant capacitor 9U. The charging current is the current used to charge the resonant capacitor 9U. On the other hand, when the first IGBT 6U is off and the second IGBT 7U is on, the switch 8U allows a discharging current to flow sequentially through the resonant capacitor 9U, the switch 8U, the resonant inductor L1, and the regenerative capacitor 15. The discharging current is the current used to discharge the resonant capacitor 9U.

[0071] When the first IGBT 6V is on and the second IGBT 7V is off, the switch 8V allows a charging current to flow sequentially through the regenerative capacitor 15, the resonant inductor L1, the switch 8V, and the resonant capacitor 9V. The charging current is the current used to charge the resonant capacitor 9V. On the other hand, when the first IGBT 6V is off and the second IGBT 7V is on, the switch 8V allows a discharging current to flow sequentially through the resonant capacitor 9V, the switch 8V, the resonant inductor L1, and the regenerative capacitor 15. The discharging current is the current used to discharge the resonant capacitor 9V.

[0072] When the first IGBT 6W is on and the second IGBT 7W is off, the switch 8W allows a charging current to flow sequentially through the regenerative capacitor 15, the resonant inductor L1, the switch 8W, and the resonant capacitor 9W. The charging current is the current used to charge the resonant capacitor 9W. On the other hand, when the first IGBT 6W is off and the second IGBT 7W is on, the switch 8W allows a discharging current to flow sequentially through the resonant capacitor 9W, the switch 8W, the resonant inductor L1, and the regenerative capacitor 15. The discharging current is the current used to discharge the resonant capacitor 9W.

[0073] (3) Operation of power converter

[0074] 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, 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, the polarity of the current iL1 is assumed to be positive. 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 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 in the direction indicated by the arrow shown in FIG. Figure 1If the load currents iU, iV, iW flow in the direction indicated by the corresponding arrows in the arrows shown, the polarity of the load currents iU, iV, iW is assumed to be positive. On the other hand, if the load currents iU, iV, iW flow in the direction indicated by the corresponding arrows in the arrows shown, the polarity of the load currents iU, iV, iW is assumed to be positive. Figure 1 If the load currents iU, iV, and iW flow in the direction opposite to the direction indicated by the arrow shown in FIG. 1 , the polarity of the load currents iU, iV, and iW is assumed to be negative. In addition, for each of the currents i9U, i9V, and i9W flowing through the resonant capacitors 9U, 9V, and 9W, respectively, if the currents i9U, i9V, and 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 currents i9U, i9V, and i9W flow in a direction opposite to the direction indicated by the arrows shown in FIG. 1 , the polarity of the currents i9U, i9V, and i9W is negative. Therefore, during a discharge operation (discharging the resonant capacitors 9U, 9V, and 9W), the polarity of the currents i9U, i9V, and i9W is positive. On the other hand, during a charge operation (charging the resonant capacitors 9U, 9V, and 9W), the polarity of the currents i9U, i9V, and i9W is negative.

[0075] In this power converter 100, for example, when the first IGBT 6U of the switch 8U is on and a 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 reaches zero due to energy dissipation in the resonant inductor L1. Furthermore, in this power converter 100, for example, when the second IGBT 7U of the switch 8U is on and a 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 this order until the current iL1 reaches zero due to energy dissipation in the resonant inductor L1.

[0076] Furthermore, in this power converter 100, for example, when the first IGBT 6V of the switch 8V is on and a 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 reaches zero due to energy dissipation in the resonant inductor L1. Furthermore, in this power converter 100, for example, when the second IGBT 7V of the switch 8V is on and a 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 this order until the current iL1 reaches zero due to energy dissipation in the resonant inductor L1.

[0077] Furthermore, in this power converter 100, for example, when the first IGBT 6W of the switch 8W is on and a 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 reaches zero due to energy dissipation in the resonant inductor L1. Furthermore, in this power converter 100, for example, when the second IGBT 7W of the switch 8W is on and a 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 this order until the current iL1 reaches zero due to energy dissipation in the resonant inductor L1.

[0078] The controller 50 sets a dead zone period Td for each switching circuit in the plurality of switching circuits 10 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.

[0079] Next, refer to Figures 1 to 8The 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 will be described. As used herein, "basic operation" refers to the operation to be performed when the resonant currents flowing through each of two or more switches 8 belonging to the plurality of switches 8 do not flow through the resonant inductor L1 at the same time. After the basic operation has been described, how the power converter 100 operates when the controller 50 determines that the resonant currents flowing through two or more switches 8 belonging to the plurality of switches 8 will flow simultaneously will be described.

[0080] (3.1) Basic operations

[0081] When performing zero-voltage soft switching on the first switching element 1, the voltage across the first switching element 1 needs to be reduced to zero immediately before the first switching element 1, which is the target of zero-voltage soft switching, becomes conductive. When performing zero-voltage soft switching on the second switching element 2, the voltage across the second switching element 2 needs to be reduced to zero immediately before the second switching element 2, which is the target of zero-voltage soft switching, becomes conductive. In the following description, the switching element that is the target of zero-voltage soft switching (whether it is the first switching element 1 or the second switching element 2) will be referred to as the "target switching element" below.

[0082] The basic operation of the controller 50 changes depending on the polarity (i.e., positive or negative) of the load current flowing through the AC terminal 41 connected to the target switching element, and whether the resonant capacitor 9 connected in series or parallel to the target switching element is performing a charging operation or a discharging operation. The load current has a positive polarity when flowing from the AC terminal 41 toward the AC load RA1, and has a negative polarity when flowing from the AC load RA1 toward the AC terminal 41. When the resonant capacitor 9 is performing a charging operation, the voltage across the resonant capacitor 9 increases. On the other hand, when the resonant capacitor 9 is performing 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.

[0083] (3.1.1) Soft Switching Operation of the First Switching Element When Load Current > 0

[0084] If the target of soft switching is the first switching element 1 (hereinafter referred to as "target first switching element 1") and the polarity of the load current flowing through the AC terminal 41 connected to the target first switching element 1 is positive, the controller 50 turns on the first IGBT 6 corresponding to the target first switching element 1. In this way, the controller 50 causes the resonant inductor L1 and the resonant capacitor 9 connected to the target first switching element 1 to resonate, thereby charging the resonant capacitor 9 with the charge supplied from the regenerative capacitor 15 and reducing the voltage across the target first switching element 1 to zero. This enables the power converter 100 to perform zero-voltage soft switching of the target first switching element 1.

[0085] exist Figure 2 , which shows 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, when the target first switching element is the first switching element 1U of the switching circuit 10U. Figure 2 Also shown in FIG. 5 are the control signal SU6 to be applied from the controller 50 to the first IGBT 6U of the switch 8U, the load current iU of the U phase flowing through the AC load RA1, the current iL1 flowing through the resonant inductor L1, the voltage V1u across the first switching element 1U, and the voltage V2u across the second switching element 2U. Figure 2 , control signals SV1 and SV2 to be applied from the controller 50 to the first switching element 1V and the second switching element 2V of the switching circuit 10V, respectively, are also shown in FIG. Figure 2 Also shown are the control signal SV6 to be applied from the controller 50 to the first IGBT 6V of the switch 8V, the load current iV of the V phase flowing through the AC load RA1, the current iL1 flowing through the resonant inductor L1, the voltage V1v across the first switching element 1V, and the voltage V2v across the second switching element 2V.

[0086] In addition, Figure 2 The dead zone 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 being turned on at the same time is also shown in FIG. Figure 2 8U and the additional time Tau and Tav are also shown. The additional time Tau and Tav are set by the controller 50 for the control signal SV6 for the first IGBT 6V of the switch 8V. The additional time Tau and Tav will be described later.

[0087] exist Figure 3FIG. shows control signals SW1 and SW2 that are to be applied from controller 50 to the first switching element 1W and the second switching element 2W of switching circuit 10W, respectively, in a case where the first switching element of the object is the first switching element 1W of switching circuit 10W. Further, in Figure 3 FIG. also shows the control signal SW6 applied from controller 50 to the first IGBT 6W of switch 8W and the load current iW of the W-phase flowing through AC load RA1. In Figure 3 FIG. also shows the current iL1 flowing through resonance inductor L1. In Figure 3 FIG. also shows the voltage V1w across the first switching element 1W and the voltage V2w across the second switching element 2W. In Figure 3 FIG., the voltage value of DC power supply E1 is specified by Vd.

[0088] In addition, in Figure 3 FIG. also shows the dead time period Td set by controller 50 to prevent the first switching element 1W and the second switching element 2W from becoming conductive simultaneously. In addition, in Figure 3 FIG. also shows the additional time Taw set by controller 50 for the control signal SW6 of the first IGBT 6W for switch 8W. The additional time Taw will be described later.

[0089] As Figure 2 shown, the additional time Tau is the amount of time in which controller 50 sets this time amount to make the high-level period of control signal SU6 longer than the dead time period Td by setting the start time t1 of the high-level period of control signal SU6 to a time point earlier than the start time t2 of the dead time period Td. The length of the additional time Tau is determined by the value of the load current iU. In order to generate LC resonance starting from the start time 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 AC load RA1, and thus the resonance capacitor 9U cannot be charged. The end time of the high-level period of control signal SU6 can be the same as or later than the end time t3 of the dead time period Td. In Figure 2 the example shown, the end time of the high-level period of control signal SU6 is set to be the same as the end time t3 of the dead time period Td. Controller 50 sets the high-level period of control signal SU6 to Tau + Td. In switching circuit 10U, the voltage V2u across the second switching element 2U becomes Vd at the end time t3 of the dead time period Td, and the voltage V1u across the first switching element 1U becomes zero at the end time t3 of the dead time period Td. In Figure 2In the example shown, the current iL1 starts to flow through the resonant inductor L1 at the start time t1 of the high level period of the control signal SU6, and becomes zero at the time t4 after the additional time Tau has passed since the end time t3 of the dead time period Td. With respect to the current iL1, from the start time t2 of the dead time period Td, the current iL1 satisfies iL1 ≥ iU, and thus Figure 2 From the top of the current waveform, the current iL1 in the shaded portion of the fifth waveform flows into the resonant capacitor 9U, generating LC resonance. From the end time t3 of the dead time period Td, the current iL1 is regenerated to the power conversion circuit 11 via the third diode 13 directly connected to the resonant inductor L1.

[0090] As described above, in order to initiate LC resonance at the start time t2 of the dead-band period Td and to end the resonant half-cycle at the end time of the dead-band period Td, the controller 50 determines the additional time Tau based on the load current iU so that iL1 = iU at the start time t2 of the dead-band period Td. More specifically, for example, using the detection result of the load current iU using a current sensor or its signal-processed value, or an estimated value of the current iU, the pre-stored inductance L of the resonant inductor L1, and the potential V15 at the regenerative capacitor 15, the controller 50 determines the additional time Tau using the equation Tau = iU × (L / V15). In this case, the detection result of the load current iU or its signal-processed value can be a detection value at the carrier cycle to which the additional time Tau is added, or a detection value at a timing closest to the carrier cycle. Furthermore, in this case, the estimated value of the load current iU can be, for example, a value estimated at the carrier cycle to which the additional time Tau is added. 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 The controller 50 sets the resonance half period in the case of the basic operation to make the resonance half period as long as the length of the dead zone period Td, for example.

[0091] like Figure 2As shown, the additional time Tav is the amount of time during which the controller 50 sets the start time t5 of the high-level period of the control signal SV6 to a time point earlier than the start time t6 of the dead time 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 time of the high-level period of the control signal SV6 can be the same as or later than the end time t7 of the dead time period Td. In Figure 2 the example shown, the end time of the high-level period of the control signal SV6 is set to be the same as 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 V1v across the first switching element 1V becomes zero at the end time t7 of the dead time period Td. In Figure 2 the example shown, the current iL1 starts flowing through the resonance inductor L1 at the start time t5 of the high-level period of the control signal SV6, and becomes zero at the time t8 after the additional time Tav has elapsed since the end time t7 of the dead time period Td. Regarding 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 iL in the shaded portion of the current waveform shown as the tenth waveform from the top Figure 2 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.

[0092] As described above, in order to start generating the 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, using the detection result of the load current iV by the current sensor or its signal processing value, or the estimated value of the current iV, the detection result of the inductance L of the resonance inductor L1 stored in advance, and the potential V15 at the regenerative capacitor 15, the controller 50 determines the additional time Tav by the formula Tav = iV × (L / V15). In this case, as the detection result of the load current iV or its signal processing value, the detection value according to the carrier period plus the additional time Tav or the detection value according to the timing closest to the carrier period can be used. Further, in this case, as the estimated value of the load current iV, for example, the value of the load current iV estimated according to the carrier period plus the additional time Tav can be used.

[0093] As Figure 3 shown, the additional time Taw is the amount of time in which the controller 50 sets this time amount to make the high-level period of the control signal SW6 longer than the dead time period Td by setting the start time t9 of the high-level period of the control signal SW6 to a time point earlier than the start time t10 of the dead time period Td. The length of the additional time Taw is determined by the value of the load current iW. In order to start generating the LC resonance 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 time of the high-level period of the control signal SW6 can be the same as or later than the end time t11 of the dead time period Td. In Figure 3 the example shown, the end time of the high-level period of the control signal SW6 is set to be the same as the end time 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 V1w across the first switching element 1W becomes zero at the end time t11 of the dead time period Td. In Figure 3 the example shown, the current iL1 starts flowing through the resonance inductor L1 at the start time t9 of the high-level period of the control signal SW6 and becomes zero at the time t12 after the additional time Taw has elapsed since the end time t11 of the dead time period Td. Regarding the current iL1, from the start time t10 of the dead time period Td, iL1 ≥ iW is satisfied for the current iL1, and thus from Figure 3From the top of the fourth waveform, the current iL1 in the shaded portion of the current waveform flows into the resonant capacitor 9W to generate LC resonance. From the end time t11 of the dead time period Td, the current iL1 is regenerated to the power conversion circuit 11 via the third diode 13 directly connected to the resonant inductor L1.

[0094] 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 using the current sensor, the pre-stored inductance L of the resonant inductor L1, and the potential V15 at the regenerative capacitor 15 to determine the additional time Taw using the equation Taw = iW × (L / V15). In this case, the detection result of the load current iW or its signal-processed value can be a detection value at a carrier cycle to which the additional time Taw is added, or a detection value at a timing closest to the carrier cycle. Furthermore, in this case, the estimated value of the load current iW can be, for example, a value estimated at a carrier cycle to which the additional time Taw is added.

[0095] (3.1.2) Soft switching operation of the second switching element when the load current is greater than 0

[0096] 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 ). If the current value of the load current is greater than the first current threshold 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 I1, the controller 50 turns on the switch 8 during 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 I1, the controller 50 can use the load current iU to discharge the resonant capacitor 9U connected in parallel with the second switching element 2, without turning on the switch 8 corresponding to the second switching element 2. This enables the power converter 100 to perform zero-voltage soft switching of the second switching element 2.

[0097] exist Figure 6 In FIG. 1 , regarding the case where the 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, the control signals SU1, SU2, and SU7, the load current iU, the current i9U flowing from the resonant capacitor 9U, and the voltage V2u across the second switching element 2U are shown. Figure 6 Also shown in FIG. 8 are a dead-band period Td and an additional time Tau set by the controller 50 for the control signal SU7 for the second IGBT 7U of the switch 8U.

[0098] If the current value of the load current iU is greater than the first current threshold I1, the controller 50 does not set any high-level period for the control signal SU7. In this case, in the power converter 100, the current i9U begins to flow from the resonant capacitor 9U at the start time t22 of the dead time period Td, and the current i9U decreases to zero before the end time t23 of the dead time period Td. Furthermore, the voltage V2u across the second switching element 2U becomes zero before the end time t23 of the dead time period Td. Thus, in the power converter 100, when the control signal SU2 changes from a low level to a high level at the end time t23 of the dead time period Td, zero-voltage soft switching is performed on the second switching element 2U.

[0099] If the current value of the load current iU is less than the first current threshold I1, then, for example, Figure 6 The double-dotted chain line in FIG indicates that the controller 50 sets a high-level period for the control signal SU7. In this case, the start time of the high-level period of the control signal SU7 may coincide with the start time t22 of the dead time period Td. Furthermore, the end time of the high-level period of the control signal SU7 coincides with the end time t23 of the dead time period Td. Therefore, in the power converter 100, the voltage V2u across the second switching element 2U reaches 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, zero-voltage soft switching is performed on the second switching element 2U. Alternatively, the start time of the high-level period of the control signal SU7 may be time t21, which is earlier than the start time of the dead time period Td by an additional time Tau. The end time of the high-level period of the control signal SU7 may be time t24, which is later than the end time t23 of the dead time period Td by an additional time Tau. Note that the time before or after the high level period overlaps with the dead band period Td does not necessarily have to be the additional time Tau, but may be any other preset time.

[0100] (3.1.3) Soft switching operation of the second switching element when the load current is less than 0

[0101] If the polarity of the load current (which is load current iU, load current iV, or load current iW) flowing through the AC terminal 41 connected to the second switching element 2 is negative, the controller 50 turns on the second IGBT 7 corresponding to the second switching element 2. In this way, the controller 50 causes the resonant capacitor 9 and the resonant inductor L1 connected to the second switching element 2 to resonate, thereby discharging the resonant capacitor 9 and reducing the voltage across the second switching element 2 to zero. This enables the power converter 100 to perform zero-voltage soft switching of the second switching element 2.

[0102] exist Figure 7 , for the case where the target second switching element 2 is the second switching element 2U of the switching circuit 10U, control signals SU1, SU2, SU7, load current iU, current iL1 flowing through the resonant inductor L1, and voltage V2u across the second switching element 2U are shown.

[0103] In addition, Figure 7 The dead zone 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 being turned on at the same time is also shown in FIG. Figure 7 8U. The additional time Tau set by the controller 50 for the control signal SU7 of the second IGBT 7U for the switch 8U is also shown in FIG. The end time of the high level period of the control signal SU7 may be simultaneous with or later than the end time t33 of the dead time period Td. Figure 7 In the example shown, the end time of the high level period of the control signal SU7 is set to coincide with the end time t33 of the dead time period Td. The controller 50 sets the high level period of the control signal SU7 to Tau+Td. In the switching circuit 10U, the voltage V2u across the second switching element 2U becomes zero at the end time t33 of the dead time period Td. Figure 7 In the example shown, current iL1 begins flowing through resonant inductor L1 at time t31, the start of the high-level period of control signal SU7, and becomes zero at time t34, after an additional time Tau has elapsed since time t33, the end of dead-band period Td. Regarding current iL1, from time t32, the start of dead-band period Td, current iL1 satisfies iL1 ≤ iU, thus generating LC resonance and causing a resonant current (i.e., a discharge current from resonant capacitor 9U) to flow from resonant capacitor 9U toward resonant inductor L1. From time t33, the end of dead-band period Td, current iL1 is regenerated to power conversion circuit 11 via fourth diode 14, which is directly connected to resonant inductor L1.

[0104] To start LC resonance at the start time t32 of the dead-band period Td and end the resonant half-cycle at the end time t33 of the dead-band period Td, the controller 50 determines the additional time Tau based on the load current iU so that iL1 = iU is satisfied at the start time t32 of the dead-band period Td. More specifically, for example, the controller 50 uses the detection result of the output current iU using the current sensor or its signal-processed value, or an estimated value of the load current iU, the pre-stored inductance L of the resonant inductor L1, and the potential V15 at the regenerative capacitor 15 to determine the additional time Tau using the equation Tau = |iU| × (L / V15). In this case, the detection result of the load current iU or its signal-processed value can be a detection value at the carrier cycle to which the additional time Tau is added, or a detection value at a timing closest to the carrier cycle. Furthermore, in this case, the estimated value of the load current iU can be, for example, a value estimated at the carrier cycle to which the additional time Tau is added. 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 The controller 50 sets the resonance half period in the case of the basic operation to make the resonance half period as long as the length of the dead zone period Td, for example.

[0105] (3.1.4) Soft switching operation of the first switching element when the load current is less than 0

[0106] 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 subject 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 ). If the current value of the load current is less than the second current threshold 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 I2, the controller 50 turns on the switch 8 during 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 I2, the controller 50 can use the load current to charge the resonant capacitor 9U connected in series with the first switching element 1, without turning on the switch 8 corresponding to the first switching element 1. This enables the power converter 100 to perform zero-voltage soft switching of the first switching element 1.

[0107] exist Figure 8, regarding the case where the target first switching element 1 is the first switching element 1U of the switching circuit 10U and the current value of the load current is greater than the second current threshold value I2 (in other words, the 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), the control signals SU1, SU2, and SU6, the load current iU, the current i9U flowing from the resonant capacitor 9U, and the voltage V2u across the second switching element 2U are also shown. Figure 8 Also shown in FIG. 1 is a dead-band period Td.

[0108] 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 provide any high-level period for the control signal SU6. In this case, in the power converter 100, the current i9U begins to flow through the resonant capacitor 9U at the start time t41 of the dead time period Td. As a result, in the power converter 100, the resonant capacitor 9U is charged, causing the voltage V2u across the second switching element 2U to increase. The current i9U becomes zero before the end time t23 of the dead time period Td, and the voltage V1u across the first switching element 1U becomes zero before the end time t42 of the dead time period Td. Thus, in the power converter 100, when the control signal SU1 changes from a low level to a high level at the end time t42 of the dead time period Td, zero-voltage soft switching is performed on the first switching element 1U.

[0109] If the current value of the load current is greater than the second current threshold value I2 (in other words, if the absolute value of the load current is less than the absolute value of the second current threshold value), then, for example, as given by Figure 8 The double-dotted chain line in FIG indicates that the controller 50 provides a high-level period for the control signal SU6. In this case, the start time of the high-level period of the control signal SU6 may coincide with the start time t41 of the dead time period Td, for example. Furthermore, the end time of the high-level period of the control signal SU6 coincides with the end time t42 of the dead time period Td. Thus, in the power converter 100, the voltage V1u across the first switching element 1U reaches zero before the end time t42 of the dead time period Td. Therefore, in the power converter 100, when the control signal SU1 changes from a low level to a high level at the end time t42 of the dead time period Td, zero-voltage soft switching is performed on the first switching element 1U.

[0110] (3.2) Shift control operation

[0111] When the controller 50 determines that the resonant currents flowing through two or more switches 8 belonging to the plurality of switches 8 will flow simultaneously through the resonant inductor L1, the controller 50 performs a shift control to shift the high-level period of the control signal for at least one of the two or more switches 8, thereby preventing the resonant currents flowing through the two or more switches 8 from flowing simultaneously through the resonant inductor L1. As used herein, the expression "when it is determined that the resonant currents flowing through two or more switches 8 belonging to the plurality of switches 8 will flow simultaneously" refers to a situation where it has been previously estimated that the resonant currents flowing through the two or more switches 8 will flow simultaneously through the resonant inductor L1.

[0112] (3.2.1) Determine whether the two-phase resonant current will flow simultaneously

[0113] 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 FIG. Figure 4 Specifically, in the areas A1 and A2 shown in FIG. Figure 4 In the region A1 shown, the duty ratio of the U-phase control signal and the duty ratio of the V-phase control signal are around 0.75. Figure 4 In the region A2 shown, the duty ratio of the U-phase control signal and the duty ratio of the V-phase control signal are around 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, for example, the start time t1 of the high level period of the control signal SU6 to be applied to the first IGBT 6U (refer to Figure 2 ) and the start time t5 of the high level period of the control signal SV6 to be applied to the first IGBT 6V (reference Figure 2 ) becomes so short within one cycle of the carrier signal 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.

[0114] 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 simultaneously flow through the resonant inductor L1, then in the equivalent circuit, a capacitor having a combined capacitance (=2×C) of the resonant capacitors 9U and 9V is connected in series to the resonant inductor L1. Therefore, in power converter 100, if two-phase currents simultaneously flow through resonant inductor L1, the resonant frequency of the resonant circuit including resonant inductor L1 will change compared to the case where a single-phase current flows through resonant inductor L1. Consequently, power converter 100 may be unable to perform zero-voltage soft switching.

[0115] (3.2.1.1) Charging the resonant capacitor

[0116] Figure 2 Exemplary boundary conditions between the case where the U-phase resonant current and the V-phase resonant current do not overlap with each other (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) are shown. Figure 2 To illustrate this boundary condition.

[0117] In the power converter 100, if the time lag ΔTuv between the start time t3 of the high-level period of the control signal SU1 and the start time t7 of the high-level period of the control signal SV1 is equal to or greater than (Tau + Tav + Td), the U-phase resonant current and the V-phase resonant current do not overlap with each other. On the other hand, if the time lag ΔTuv is less than (Tau + Tav + Td), the U-phase resonant current and the V-phase resonant current overlap with each other. That is, when the threshold value for the time lag ΔTuv is set to (Tau + Tav + Td), if the time lag ΔTuv is less than the threshold value, the controller 50 estimates that the resonant currents 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 simultaneously through the resonant inductor L1. Note that this threshold value is merely an example, and the threshold value may also be set to any other value. For example, in consideration of the error in the additional time Tau and the error in the additional time Tav, the threshold value may also be set to a value even greater than (Tau + Tav + Td). The above-described method for calculating the time lag ΔTuv to determine whether the two-phase resonant currents flow simultaneously is merely an example. Instead, any other calculation method may be employed as long as a time lag corresponding to the above-described time lag can be calculated. For example, the time lag between the end time t2 of the high-level period of the control signal SU2 and the end time t6 of the high-level period of the control signal SV2 may be used as the time lag ΔTuv used to determine whether the two-phase resonant currents flow simultaneously.

[0118] In the power converter 100, if the time lag between the start time t3 of the high-level period of the control signal SU1 and the start time t11 of the high-level period of the control signal SW1 is equal to or greater than (Tau + Taw + Td), the U-phase resonant current and the W-phase resonant current do not overlap with each other. On the other hand, if the time lag is less than (Tau + Taw + Td), the U-phase resonant current and the W-phase resonant current overlap with each other. That is, when the threshold value for this time lag is set to (Tau + Taw + Td), if the time lag is less than the threshold value, the controller 50 infers that the resonant currents 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 simultaneously through the resonant inductor L1. Note that this threshold value is merely an example, and the threshold value may also be set to any other value. For example, in the case of taking into account the error of the additional time Tau and the error of the additional time Taw, the threshold value may also be set to a value even greater than (Tau + Taw + Td). In addition, the above-mentioned method for calculating the time lag to determine whether the two-phase resonant currents flow simultaneously is merely an example. On the contrary, any other calculation method may be used as long as a time lag corresponding to the above-mentioned time lag can be calculated. For example, as the time lag for determining whether the two-phase resonant currents flow simultaneously, the time lag between the end time t2 of the high-level period of the control signal SU2 and the end time t10 of the high-level period of the control signal SW2 may be used.

[0119] In the power converter 100, if the time lag between the start time t7 of the high-level period of the control signal SV1 to be applied to the first switching element 1V of the switching circuit 10V and the start time t11 of the high-level period of the control signal SW1 to be applied to the first switching element 1W of the switching circuit 10W is equal to or greater than (Tav+Taw+Td), the V-phase resonant current and the W-phase resonant current do not overlap with each other. On the other hand, if the time lag is less than (Tav+Taw+Td), the V-phase resonant current and the W-phase resonant current overlap with each other. That is, when 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 estimates that the resonant currents 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 this threshold value is merely an example, and the threshold value may also be set to any other value. For example, taking into account the error of the additional time Tav and the error of the additional time Taw, the threshold value can also be set to a value even greater than (Tav+Taw+Td). In addition, the above-mentioned 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 can be used as long as the time lag corresponding to the above-mentioned time lag can be calculated. For example, as the time lag for determining whether the two-phase resonant current flows simultaneously, the time lag between the end time t6 of the high level period of the control signal SV2 and the end time t10 of the high level period of the control signal SW2 can also be used.

[0120] (3.2.1.2) Discharging the resonant capacitor

[0121] In the discharge operation of the resonance capacitor 9 , the controller 50 can also use the same time lag and threshold value as in the case of the charging operation of the resonance capacitor 9 to determine whether the two-phase resonance currents will flow simultaneously.

[0122] For example, if the time lag between the start time of the high level period of the control signal SU2 and the start time of the high level period of the control signal SV2 is less than a threshold value (e.g., Tau+Tav+Td), the controller 50 estimates that the U-phase resonant current and the V-phase resonant current will overlap with each other.

[0123] In addition, if the time lag between the start time of the high level period of the control signal SU2 and the start time of the high level period of the control signal SW2 is less than the threshold value (for example, Tau+Taw+Td), the controller 50 estimates that the U-phase resonant current and the W-phase resonant current will overlap with each other.

[0124] In addition, if the time lag between the start time of the high level period of the control signal SV2 and the start time of the high level period of the control signal SW2 is less than the threshold value (for example, Tav+Taw+Td), the controller 50 estimates that the V-phase resonant current and the W-phase resonant current will overlap with each other.

[0125] (3.2.2) Shift control to be performed when it is determined that two-phase resonant currents flow simultaneously

[0126] The controller 50 performs, for example, a shift control of shifting the high-level periods of the control signals for the two switches 8 to prevent the resonant currents respectively passing through the two switches 8 from flowing through the resonant inductor L1 at the same time.

[0127] When performing shift control, the controller 50 shifts the high-level periods of the control signals for the two switches 8 to prevent changes in the length of the high-level periods of the control signals applied to the first switching element 1 and the second switching element 2 in each of the two switching circuits 10 corresponding to the two switches 8. For example, when shifting the high-level period of the control signal SU6 or SU7 applied to the switch 8U, the controller 50 shifts the high-level periods of the control signals SU1 and SU2, respectively, without changing the duty cycle of either control signal SU1 or SU2 within a single cycle of the carrier signal. Similarly, when shifting the high-level period of the control signal SV6 or SV7 applied to the switch 8V, the controller 50 shifts the high-level period of the control signals SV1 and SV2, respectively, without changing the duty cycle of either control signal SV1 or SV22 within a single cycle of the carrier signal. In the same manner, when shifting the high-level period of control signal SW6 or SW7 to be applied to switch 8W, controller 50 shifts the high-level period of each of control signals SW1 and SW2, but does not change the duty cycle of any control signal in control signal SW1 or SW2 within one cycle of the carrier signal. In the following description, for ease of explanation, when shifting the high-level period of control signal SU6 or SU7 for switch 8U, the amount of time the high-level period of control signal SU6 or SU7 is shifted (hereinafter referred to as "shift time") will be designated as Tus. Furthermore, when shifting the high-level period of control signal SV6 or SV7 for switch 8V, the shift time of the high-level period of control signal SV6 or SV7 will be designated as Tvs. Furthermore, when shifting the high-level period of control signal SW6 or SW7 for switch 8W, the shift time of the high-level period of control signal SW6 or SW7 will be designated as Tws.

[0128] (3.2.2.1) Soft Switching Operation of the First Switching Element

[0129] When performing shift control, the controller 50 shifts the high-level periods of the control signals for the two switches 8 in different directions. When performing shift control, if the polarity of the load current flowing through the two AC terminals 41 connected to the two switches 8 is positive, the controller 50 compares the duty cycles of the control signals for the two first switching elements 1 corresponding to the two switches 8, among the plurality of first switching elements 1. The controller 50 then shifts the high-level periods of the control signals for the switches 8 corresponding to the first switching elements 1 with a relatively high duty cycle, among the two switches 8, in a direction that advances the high-level periods of the control signals. On the other hand, the controller 50 shifts the high-level periods of the control signals for the switches 8 corresponding to the first switching elements 1 with a relatively low duty cycle, among the two switches 8, in a direction that delays the high-level periods of the control signals.

[0130] Figure 9 The example controller 50 is in Figure 4 How to operate when shift control is performed in the period corresponding to area A1 shown. Figure 9 The upper portion is a timing chart showing the waveforms of the control signals SU1, SU2, SV1, SV2, the control signals SU6, SV6, the load currents iU, iV, and the current iL1 before the shift (i.e., when the shift notification is not performed) when the controller 50 determines that the U-phase current and the V-phase current will flow simultaneously. On the other hand, Figure 9 The lower part is a timing chart showing the waveforms of the control signals SU1, SU2, SV1, SV2, the control signals SU6, SV6, the load currents iU, iV, and the current iL1 in the case where the control signals SU6, SV6 are shifted so that the total shift time amount (which is the sum of the shift time of the high level period of the control signal SU6 and the shift time of the high level period of the control signal SV6) is equal to the predetermined period. Figure 9 In the illustrated example, the controller 50 shifts the start timing of the high-level period of the control signal SU6 for the switch 8U by the shift time Tus, and shifts the high-level period of the control signal SV6 for the switch 8V by the shift time Tvs.

[0131] When it is determined that the two-phase resonant current will flow simultaneously, the controller 50 sets the length of the predetermined period to be equal to or greater than the length of the overlap time Tov of the two-phase resonant current. Figure 10 To illustrate the overlapping time Tov. Figure 10 The waveform of the resonant current is illustrated in the case where the resonant inductor L1 is not used in common (i.e., in the case where three resonant inductors L1 are provided corresponding to three resonant capacitors on a one-to-one basis). The U-phase resonant current (whose waveform is shown as Figure 10The fourth waveform from the top of Figure 10 The overlapping time Tov between the eighth waveform from the top of the waveform is calculated by the formula Tov = (Tau + Tav + Td) - ΔTuv. If the resonance period of the resonant circuit formed by the inductance L of the resonant inductor L1 and the capacitance C of the resonant capacitor 9 is Tres, then Tres = 1 / {2π(L·C) 1 / 2} and Td = Tres / 2. The resonant current (whose waveform is shown as Figure 10 The twelfth waveform from the top of FIG) shows that the control signals SV1, SV2 and SV6 (whose waveforms are shown as Figure 10 The fifth waveform, the sixth waveform and the seventh waveform from the top of the V phase resonant current are shifted so that the high level period thereof is delayed by the waveform of the V phase resonant current when the overlapping time Tov is exceeded. Figure 10 It can be seen that the waveform is shown as Figure 10 The resonant current waveform of the twelfth waveform from the top is shown as Figure 10 The resonant current of the fourth waveform from the top does not overlap. Figure 10 The case where the U-phase resonant current and the V-phase resonant current overlap with each other is illustrated, but even when the U-phase resonant current and the W-phase resonant current overlap with each other and when the V-phase resonant current and the W-phase resonant current overlap with each other, the overlapping time Tov and the shift direction of the control signal can be determined in the same manner.

[0132] Figure 9 The example in which the controller 50 defines the predetermined period as Tov+ΔT is shown. Figure 9 In the illustrated example, the controller 50 defines the predetermined period as Tov+ΔT=Tus+Tvs.

[0133] exist Figure 9 In the illustrated example, the polarity of the load currents iU and iV flowing through the two AC terminals 41U and 41V connected to the two switches 8U and 8V, respectively, is positive. In this case, the controller 50 compares the duty cycles of the control signals SU1 and SV1 for the two first switching elements 1U and 1V corresponding one-to-one to the two switches 8U and 8V. The controller 50 shifts the high-level period of the control signal SV6 applied to the switch 8V corresponding to the first switching element 1V to which the control signal SV1 with a relatively high duty cycle is applied, in a direction that advances the high-level period of the control signal SV6 by a shift time Tvs. On the other hand, the controller 50 shifts the high-level period of the control signal SU6 applied to the switch 8U corresponding to the first switching element 1U to which the control signal SU1 with a relatively low duty cycle is applied, in a direction that delays the high-level period of the control signal SU6 by a shift time Tus.

[0134] As from Figure 9 As can be seen from the waveform of the current iL1 shown, when the controller 50 predetermines that the two-phase resonant current (i.e., the U-phase resonant current and the V-phase resonant current) will flow simultaneously, the power converter 100 can avoid the overlap between the U-phase resonant current and the V-phase resonant current by performing shift control (refer to Figure 9 ). In the same way, when the controller 50 predetermines that the two-phase resonant current (i.e., the U-phase resonant current and the W-phase resonant current) will flow simultaneously, the power converter 100 can avoid overlap between the U-phase resonant current and the W-phase resonant current by performing shift control. In addition, when the controller 50 predetermines that the two-phase resonant current (i.e., the V-phase resonant current and the W-phase resonant current) will flow simultaneously, the power converter 100 can avoid overlap between the V-phase resonant current and the W-phase resonant current by performing shift control. Note that the upper limit value (maximum value) of the shift time in the case where the high-level period of the control signal for the switch 8 is shifted to advance is the shift time in the case where the time lag between the start time of one cycle of the carrier signal and the start time of the high-level period of the shifted control signal (i.e., the shifted control signal for the switch 8) becomes equal to the minimum value (e.g., zero) without changing the length of the high-level period. On the other hand, the upper limit value (maximum value) of the shift time in the case where the high-level period of the control signal for switch 8 is shifted to be delayed is the shift time in the case where the time lag between the end time of one cycle of the carrier signal and the end time of the high-level period of the shifted control signal (i.e., the shifted control signal for switch 8) becomes equal to the minimum value (for example, zero) without changing the length of the high-level period.

[0135] In the power converter 100, if the controller 50 does not perform shift control, the voltages V2u and V2v across the second switching elements 2U and 2V do not rise to Vd at the time when the control signals SU1 and SV1 transition from a low-level period to a high-level period (i.e., at the end of the dead-band period Td corresponding to each of the U and V phases). In other words, if the controller 50 does not perform shift control, the resonant capacitors 9U and 9V are not fully charged at the end of the dead-band period Td corresponding to each of the U and V phases. Therefore, if the controller 50 does not perform shift control, the voltages across the first switching elements 1U and 1V do not drop to zero at the end of the dead-band period Td corresponding to each of the U and V phases. Consequently, in the power converter 100, the first switching elements 1U and 1V are hard-switched.

[0136] On the other hand, if the controller 50 has performed the shift control, then Figure 9As shown, at the point in time when the control signals SU1 and SV1 transition from a low-level period to a high-level period (i.e., at the end of the dead-band period Td corresponding to each of the U-phase and V-phase), the voltages V2u and V2v across the second switching elements 2U and 2V rise to Vd. That is, if the controller 50 has performed shift control, then at the end of the dead-band period Td corresponding to each of the U-phase and V-phase, the resonant capacitors 9U and 9V have already been charged. Therefore, in the power converter 100, if the controller 50 has performed shift control, the first switching elements 1U and 1V are switched using zero-voltage soft switching.

[0137] Figure 9 The following illustrates how shift control can be performed when the controller 50 has predetermined that the U-phase resonant current and the V-phase resonant current will flow through the resonant inductor L1 at the same time. However, this is merely an example and should not be construed as limiting. For example, even if the controller 50 has predetermined that the V-phase resonant current and the W-phase resonant current will flow through the resonant inductor L1 at the same time, and even if the controller 50 has predetermined that the W-phase resonant current and the U-phase resonant current will flow through the resonant inductor L1 at the same time, zero-voltage soft switching can be performed by having the controller 50 perform shift control.

[0138] (3.2.2.2) Soft Switching Operation of the Second Switching Element

[0139] When performing shift control, the controller 50 shifts the high-level periods of the control signals for the two switches 8 in different directions. When performing shift control, if the polarity of the load current flowing through the two AC terminals 41 connected to the two switches 8 is negative, the controller 50 compares the duty cycles of the control signals for the two first switching elements 1 corresponding to the two switches 8, among the plurality of first switching elements 1. The controller 50 then shifts the high-level periods of the control signals for the switches 8 corresponding to the first switching elements 1 with a relatively high duty cycle, among the two switches 8, in a direction that delays the high-level periods of the control signals. On the other hand, the controller 50 shifts the high-level periods of the control signals for the switches 8 corresponding to the first switching elements 1 with a relatively low duty cycle, among the two switches 8, in a direction that advances the high-level periods of the control signals.

[0140] Figure 11 Example when with Figure 4 How the controller 50 may operate when performing shift control in the period corresponding to the area A2 is shown. Figure 11The upper portion is a timing chart showing the waveforms of the control signals SU1, SU2, SV1, SV2, the control signals SU7, SV7, the load currents iU, iV, and the current iL1 before the shift (i.e., in the case where the shift control is not performed) when the controller 50 has determined that the two-phase resonant current (i.e., the U-phase current and the V-phase current) will flow simultaneously. On the other hand, Figure 11 The lower part is a timing chart showing the waveforms of the control signals SU1, SU2, SV1, SV2, the control signals SU7, SV7, the load currents iU, iV, and the current iL1 in the case where the control signals SU7, SV7 are shifted so that the total shift time amount (which is the sum of the shift time of the high level period of the control signal SU7 and the shift time of the high level period of the control signal SV7) is equal to the predetermined period. Figure 11 In the illustrated example, the controller 50 shifts the start timing of the high-level period of the control signal SU7 for the switch 8U by the shift time Tus, and shifts the high-level period of the control signal SV7 for the switch 8V by the shift time Tvs.

[0141] When determining that the two-phase resonant currents will flow simultaneously, the controller 50 sets the length of the predetermined period to be equal to or longer than the length of the overlapping time Tov of the two-phase resonant currents.

[0142] Figure 11 The example in which the controller 50 defines the predetermined period as Tov+ΔT is shown. Figure 11 In the illustrated example, the controller 50 defines the predetermined period as Tov+ΔT=Tus+Tvs.

[0143] exist Figure 11 In the illustrated example, the polarity of the load currents iU and iV flowing through the two AC terminals 41U and 41V connected to the two switches 8U and 8V, respectively, is negative. In this case, the controller 50 compares the duty cycles of the control signals SU1 and SV1 for the two first switching elements 1U and 1V corresponding one-to-one to the two switches 8U and 8V. The controller 50 shifts the high-level period of the control signal SV7 applied to the switch 8V corresponding to the first switching element 1V to which the control signal SV1 with a relatively high duty cycle is applied, in a direction that delays the high-level period of the control signal SV7 by a shift time Tvs. On the other hand, the controller 50 shifts the high-level period of the control signal SU7 applied to the switch 8U corresponding to the first switching element 1U to which the control signal SU1 with a relatively low duty cycle is applied, in a direction that advances the high-level period of the control signal SU7 by a shift time Tus.

[0144] As from Figure 11As can be seen from the waveform of the current iL1 shown, when the controller 50 has predetermined that the two-phase resonant current (i.e., the U-phase resonant current and the V-phase resonant current) will flow simultaneously, the power converter 100 can avoid the overlap between the U-phase resonant current and the V-phase resonant current by performing shift control (refer to FIG. Figure 11 ). In the same manner, when the controller 50 has predetermined that the two-phase resonant currents (i.e., the U-phase resonant current and the W-phase resonant current) will flow simultaneously, the power converter 100 can avoid overlap between the U-phase resonant current and the W-phase resonant current by performing shift control. Furthermore, when the controller 50 has predetermined that the two-phase resonant currents (i.e., the V-phase resonant current and the W-phase resonant current) will flow simultaneously, the power converter 100 can avoid overlap between the V-phase resonant current and the W-phase resonant current by performing shift control.

[0145] In the power converter 100, if the controller 50 does not perform shift control, the voltages V1u and V1v across the first switching elements 1U and 1V do not rise to Vd at the time when the control signals SU2 and SV2 transition from a low-level period to a high-level period (i.e., at the end of the dead-band period Td corresponding to each of the U and V phases). In other words, if the controller 50 does not perform shift control, the resonant capacitors 9U and 9V are not fully charged at the end of the dead-band period Td corresponding to each of the U and V phases. Therefore, if the controller 50 does not perform shift control, the voltages across the second switching elements 2U and 2V do not drop to zero at the end of the dead-band period Td corresponding to each of the U and V phases. Consequently, in the power converter 100, the second switching elements 2U and 2V are hard-switched.

[0146] On the other hand, if the controller 50 has performed the shift control, then Figure 11 As shown, at the point in time when the control signals SU2 and SV2 transition from a low-level period to a high-level period (i.e., at the end of the dead-band period Td corresponding to each of the U-phase and V-phase), the voltages V1u and V1v across the first switching elements 1U and 1V rise to Vd. That is, if the controller 50 has performed shift control, then at the end of the dead-band period Td corresponding to each of the U-phase and V-phase, the discharge from the resonant capacitors 9U and 9V has already been completed. Therefore, in the power converter 100, if the controller 50 has performed shift control, the second switching elements 2U and 2V are switched by zero-voltage soft switching.

[0147] The above referenced Figure 11The following illustrates how shift control can be performed when the controller 50 has predetermined that the U-phase resonant current and the V-phase resonant current will flow through the resonant inductor L1 at the same time. However, this is merely an example and should not be construed as limiting. For example, even if the controller 50 has predetermined that the V-phase resonant current and the W-phase resonant current will flow through the resonant inductor L1 at the same time, and even if the controller 50 has predetermined that the W-phase resonant current and the U-phase resonant current will flow through the resonant inductor L1 at the same time, zero-voltage soft switching can be performed by having the controller 50 perform shift control.

[0148] (4) Summary

[0149] In the power converter 100 according to the first embodiment, when it is determined that the resonant currents respectively passing through two switches 8 belonging to the plurality of switches 8 will flow simultaneously through the resonant inductor L1, the controller 50 performs control for shifting the high-level period of the control signal for each of the two switches 8 to prevent the resonant currents respectively passing through the two switches 8 from flowing simultaneously through the resonant inductor L1. This enables the power converter 100 to perform soft switching more reliably.

[0150] Furthermore, in the power converter 100 according to the first embodiment, when performing shift control, the controller 50 shifts the high-level period of the control signal for each of the two switches 8 to prevent changes in the length of the high-level period of the control signal to be applied to the first switching element 1 and the second switching element 2 of one switching circuit 10 connected to the two switches 8, which belongs to the plurality of switching circuits 10. This enables the power converter 100 according to the first embodiment to suppress variations in the line voltage.

[0151] In the power converter 100 according to the first embodiment, the controller 50 shifts the high-level periods of the control signals for the two switches 8 in different directions when performing shift control. This allows the power converter 100 according to the first embodiment to contribute to increasing the operating frequency.

[0152] Furthermore, in the power converter 100 according to the first embodiment, when performing shift control, if the polarity of the load current flowing through the two AC terminals 41 connected to the two switches 8 is positive, the controller 50 compares the duty ratios of the control signals for the two first switching elements 1 corresponding to the two switches 8. The controller 50 then shifts the high-level period of the control signal applied to the switch 8 corresponding to the first switching element 1 to which the control signal with a relatively high duty ratio is applied, thereby advancing the high-level period of the control signal. On the other hand, the controller 50 shifts the high-level period of the control signal applied to the switch 8 corresponding to the first switching element 1 to which the control signal with a relatively low duty ratio is applied, thereby delaying the high-level period of the control signal. If the polarity of the load current flowing through the two AC terminals 41 connected to the two switches 8 is negative, the controller 50 compares the duty ratios of the control signals for the two first switching elements 1 corresponding to the two switches 8. Then, the controller 50 shifts the high-level period of the control signal applied to the switch 8 corresponding to the first switching element 1 to which the control signal with a relatively large duty cycle is applied, in a direction to postpone the high-level period of the control signal, and shifts the high-level period of the control signal applied to the switch 8 corresponding to the first switching element 1 to which the control signal with a relatively small duty cycle is applied, in a direction to advance the high-level period of the control signal. This enables the power converter 100 according to the first embodiment to contribute to an increase in the operating frequency.

[0153] (Second embodiment)

[0154] The power converter 100 according to the second embodiment has the same features as the power converter 100 according to the first embodiment described above (refer to Figure 1 ) has the same circuit structure, so its illustration and description will be omitted in this article.

[0155] In the power converter 100 according to the second embodiment, when it is determined that the two-phase resonant currents will overlap each other, the controller 50 performs shift control in a manner different from that of the controller 50 according to the first embodiment.

[0156] In the following description, reference will be made to Figure 12 and Figure 13 To illustrate how the controller 50 operates to perform soft switching of the first switching element 1 when it is determined that the two-phase resonant current will flow through the resonant inductor L1 at the same time. Figure 14 1 and 2. It will be described how the controller 50 operates to perform soft switching of the second switching element 2 when it is determined that the two-phase resonant current will flow through the resonant inductor L1 at the same time.

[0157] (1.1) Soft switching operation of the first switching element

[0158] When performing shift control, the controller 50 shifts the high-level periods of the control signals for the two switches 8 in different directions. When performing shift control, if the polarity of the load current flowing through the two AC terminals 41 connected to the two switches 8 is positive, the controller 50 compares the duty cycles of the control signals for the two first switching elements 1 corresponding to the two switches 8, among the plurality of first switching elements 1. The controller 50 then shifts the high-level periods of the control signals applied to the switches 8 corresponding to the first switching elements 1 with a relatively high duty cycle in a direction that delays the high-level periods of the control signals. On the other hand, the controller 50 shifts the high-level periods of the control signals applied to the switches 8 corresponding to the first switching elements 1 with a relatively low duty cycle in a direction that advances the high-level periods of the control signals.

[0159] Figure 12 Example when with Figure 4 How the controller 50 may operate when performing shift control in the period corresponding to the area A1 is shown. Figure 12 The upper portion is a timing chart showing the waveforms of the control signals SU1, SU2, SV1, SV2, the control signals SU6, SV6, the load currents iU, iV, and the current iL1 before the shift (i.e., in the case where the shift control is not performed) when the controller 50 has determined that the two-phase resonant current (i.e., the U-phase resonant current and the V-phase resonant current) flow simultaneously. On the other hand, Figure 12 The lower part is a timing chart showing the waveforms of the control signals SU1, SU2, SV1, SV2, the control signals SU6, SV6, the load currents iU, iV, and the current iL1 in the case where the control signals SU6, SV6 are shifted so that the total shift time amount (which is the sum of the shift time of the high level period of the control signal SU6 and the shift time of the high level period of the control signal SV6) is equal to the predetermined period. Figure 12 In the illustrated example, the controller 50 shifts the start timing of the high-level period of the control signal SU6 for the switch 8U by the shift time Tus, and shifts the high-level period of the control signal SV6 for the switch 8V by the shift time Tvs.

[0160] Assuming that the resonant current time is Ti and the time margin is ΔT, the controller 50 defines the predetermined period as ΔTuv + Ti + ΔT. If the additional time of the high level period of one of the two switches 8 connected to the AC terminal 41 with the larger absolute value of the load current is Ta, the resonant current time Ti is calculated by the formula 2×Ta+Tres / 2. Figure 12 The resonance current time Tiu of the U phase and the resonance current time Tiv of the V phase are shown. Figure 12 In the example shown, the absolute value of the V-phase load current iV is greater than the absolute value of the U-phase load current iU, so the resonant current time Ti is assumed to be the V-phase resonant current time Tiv and the additional time Ta is assumed to be the additional time Tav of the high level period of the switch 8V. Figure 12 The case where the U-phase resonant current and the V-phase resonant current overlap with each other is illustrated, but even when the U-phase resonant current and the W-phase resonant current overlap with each other and when the V-phase resonant current and the W-phase resonant current overlap with each other, the predetermined period and the shift direction of the control signal can be determined in the same manner.

[0161] exist Figure 12 In the illustrated example, the controller 50 defines the predetermined period as ΔTuv+(2×Tav+Tres / 2)+ΔT. That is, Figure 12 In the illustrated example, the controller 50 defines the predetermined period as ΔTuv+(2×Tav+Tres / 2)+ΔT.

[0162] exist Figure 12 In the illustrated example, the polarity of the load current iU, iV flowing through the two AC terminals 41U, 41V connected to the two switches 8U, 8V, respectively, is positive. In this case, the controller 50 compares the duty cycles of the control signals SU1, SV1 for the two first switching elements 1U, 1V corresponding one-to-one to the two switches 8U, 8V with each other. The controller 50 shifts the high-level period of the control signal SV6 to be applied to the switch 8V corresponding to the first switching element 1V to which the control signal SV1 with a relatively large duty cycle is applied, in a direction that delays the high-level period of the control signal SV6 by the shift time Tvs. On the other hand, the controller 50 shifts the high-level period of the control signal SU6 to be applied to the switch 8U corresponding to the first switching element 1U to which the control signal SU1 with a relatively small duty cycle is applied, in a direction that advances the high-level period of the control signal SU6 by the shift time Tus. Note that, Figure 13 It is shown that: assuming that the total time amount (which is the sum of the shift time for shifting the high-level period of the control signal SU6 in the direction of advancing its high-level period and the shift time for shifting the high-level period of the control signal SV6 in the direction of delaying its high-level period) is ΔTuv, if the end time of the high-level period of the control signal SU6 and the end time of the high-level period of the control signal SV6 are synchronized with each other, the U-phase resonant current and the V-phase resonant current overlap with each other.

[0163] As from Figure 12As can be seen from the waveform of the current iL1 shown, when the controller 50 has predetermined that the two-phase resonant current (i.e., the U-phase resonant current and the V-phase resonant current) will flow simultaneously, the power converter 100 can avoid the overlap between the U-phase resonant current and the V-phase resonant current by performing shift control (refer to FIG. Figure 12 ). In the same way, when the controller 50 has predetermined that the two-phase resonant current (i.e., the U-phase resonant current and the W-phase resonant current) will flow simultaneously, the power converter 100 can avoid overlap between the U-phase resonant current and the W-phase resonant current by performing shift control. When the controller 50 has determined that the two-phase resonant current (i.e., the V-phase resonant current and the W-phase resonant current) will flow simultaneously, the power converter 100 can avoid overlap between the V-phase resonant current and the W-phase resonant current by performing shift control. Note that the upper limit value (maximum value) of the shift time in the case where the high-level period of the control signal for the switch 8 is shifted to be delayed is the shift time in the case where the time lag between the end time of one cycle of the carrier signal and the end time of the high-level period of the shifted control signal (i.e., the shifted control signal for the switch 8) becomes equal to zero. On the other hand, the upper limit value (maximum value) of the shift time in the case where the high-level period of the control signal for switch 8 is shifted to be advanced is the shift time in the case where the time lag between the start time of one cycle of the carrier signal and the start time of the high-level period of the shifted control signal (i.e., the shifted control signal for switch 8) becomes equal to zero.

[0164] In the power converter 100 according to the second embodiment, if the controller 50 performs shift control by determining that the two-phase resonant currents will flow through the resonant inductor L1 at the same time, then Figure 12 As shown, overlap between the resonant currents can be avoided. Thus, at the end of the dead time period Td corresponding to each of the U-phase and V-phase, charging of the resonant capacitors 9U, 9V is complete. Therefore, in the power converter 100, if the controller 50 performs shift control, the first switching elements 1U, 1V are switched using zero-voltage soft switching.

[0165] The above referenced Figure 12 The following illustrates how to perform shift control in a case where the controller 50 has predetermined that the U-phase resonant current and the V-phase resonant current will flow through the resonant inductor L1 simultaneously. However, this is merely an example and should not be construed as limiting. For example, even if the controller 50 has predetermined that the V-phase resonant current and the W-phase resonant current will flow through the resonant inductor L1 simultaneously, and even if the controller 50 has predetermined that the W-phase resonant current and the U-phase resonant current will flow through the resonant inductor L1 simultaneously, zero-voltage soft switching can be performed by having the controller 50 perform shift control.

[0166] (1.2) Soft switching operation of the second switching element

[0167] When performing shift control, the controller 50 shifts the high-level periods of the control signals for the two switches 8 in different directions. When performing shift control, if the polarity of the load current flowing through the two AC terminals 41 connected to the two switches 8 is negative, the controller 50 compares the duty cycles of the control signals for the two first switching elements 1 corresponding to the two switches 8. The controller 50 then shifts the high-level period of the control signal applied to the switch 8 corresponding to the first switching element 1 with a relatively high duty cycle, thereby advancing the high-level period of the control signal. On the other hand, the controller 50 shifts the high-level period of the control signal applied to the switch 8 corresponding to the first switching element 1 with a relatively low duty cycle, thereby delaying the high-level period of the control signal.

[0168] Figure 14 Example when with Figure 4 How the controller 50 may operate when performing shift control in the period corresponding to the area A2 is shown. Figure 14 The upper portion is a timing chart showing the waveforms of the control signals SU1, SU2, SV1, SV2, the control signals SU7, SV7, the load currents iU, iV, and the current iL1 before the shift (i.e., in the case where the shift control is not performed) when the controller 50 has determined that the two-phase resonant current (i.e., the U-phase resonant current and the V-phase resonant current) flow simultaneously. On the other hand, Figure 14 The lower part is a timing chart showing the waveforms of the control signals SU1, SU2, SV1, SV2, the control signals SU7, SV7, the load currents iU, iV, and the current iL1 in the case where the control signals SU7, SV7 are shifted so that the total shift time amount (which is the sum of the shift time of the high level period of the control signal SU7 and the shift time of the high level period of the control signal SV7) is equal to the predetermined period. Figure 14 In the illustrated example, the controller 50 shifts the start timing of the high-level period of the control signal SU7 for the switch 8U by the shift time Tus, and shifts the high-level period of the control signal SV7 for the switch 8V by the shift time Tvs.

[0169] exist Figure 14 In the illustrated example, the controller 50 defines the predetermined period as ΔTuv+(2×Tau+Tres / 2)+ΔT.

[0170] exist Figure 14In the illustrated example, the polarity of the load currents iU and iV flowing through the two AC terminals 41U and 41V connected to the two switches 8U and 8V, respectively, is negative. In this case, the controller 50 compares the duty cycles of the control signals SU1 and SV1 for the two first switching elements 1U and 1V corresponding one-to-one to the two switches 8U and 8V. The controller 50 shifts the high-level period of the control signal SV7 applied to the switch 8V corresponding to the first switching element 1V to which the control signal SV1 with a relatively high duty cycle is applied, in a direction that advances the high-level period of the control signal SV7 by a shift time Tvs. On the other hand, the controller 50 shifts the high-level period of the control signal SU7 applied to the switch 8U corresponding to the first switching element 1U to which the control signal SU1 with a relatively low duty cycle is applied, in a direction that delays the high-level period of the control signal SU7 by a shift time Tus.

[0171] As from Figure 14 As can be seen from the waveform of the current iL1 shown, when the controller 50 has predetermined that the two-phase resonant current (i.e., the U-phase resonant current and the V-phase resonant current) will flow simultaneously, the power converter 100 can avoid the overlap between the U-phase resonant current and the V-phase resonant current by performing shift control (refer to FIG. Figure 14 ). In the same manner, when the controller 50 has previously determined that the two-phase resonant currents (i.e., the U-phase resonant current and the W-phase resonant current) will flow simultaneously, the power converter 100 can avoid overlap between the U-phase resonant current and the W-phase resonant current by performing shift control. Furthermore, when the controller 50 has previously determined that the two-phase resonant currents (i.e., the V-phase resonant current and the W-phase resonant current) will flow simultaneously, the power converter 100 can avoid overlap between the V-phase resonant current and the W-phase resonant current by performing shift control.

[0172] In the power converter 100, if the controller 50 has performed the shift control, then Figure 14 As shown, at the time point when the control signals SU2 and SV2 transition from the low-level period to the high-level period (i.e., at the end of the dead-band period Td corresponding to each of the U-phase and the V-phase), the discharge from the resonant capacitors 9U and 9V is completed. Therefore, in the power converter 100, if the controller 50 has performed the shift control, the second switching elements 2U and 2V are switched by zero-voltage soft switching.

[0173] The above referenced Figure 14The following illustrates how shift control can be performed when the controller 50 has predetermined that the U-phase resonant current and the V-phase resonant current will flow through the resonant inductor L1 at the same time. However, this is merely an example and should not be construed as limiting. For example, even if the controller 50 has predetermined that the V-phase resonant current and the W-phase resonant current will flow through the resonant inductor L1 at the same time, and even if the controller 50 has predetermined that the W-phase resonant current and the U-phase resonant current will flow through the resonant inductor L1 at the same time, zero-voltage soft switching can be performed by having the controller 50 perform shift control.

[0174] (Variation of the Second Embodiment)

[0175] In the power converter 100 according to the modified example of the second embodiment, the controller 50 is configured to perform the shift control of the controller 50 according to the second embodiment and the shift control of the controller 50 according to the first embodiment alternately or at an arbitrary ratio by combining the shift control of the controller 50 according to the second embodiment and the shift control of the controller 50 according to the first embodiment. This enables the power converter 100 according to this modified example to more significantly reduce the deviation of the ripple variation of the line voltage compared to the power converter 100 according to the first embodiment or the power converter 100 according to the second embodiment. In addition, the power converter 100 according to this modified example can more widely disperse the period during which the resonant current flows through the resonant inductor L1 compared to the power converter 100 according to the first embodiment or the power converter 100 according to the second embodiment, thereby reducing the thermal load on the resonant inductor L1.

[0176] (Third embodiment)

[0177] The power converter 100 according to the third embodiment has the same features as the power converter 100 according to the first embodiment described above (refer to Figure 1 ) has the same circuit structure, so its illustration and description will be omitted in this article.

[0178] In the power converter 100 according to the third embodiment, the shift control operation performed by the controller 50 that has determined that the three-phase resonant currents will overlap with each other is different from the shift control operation performed by the controller 50 according to the first embodiment.

[0179] Next, refer to Figure 15 and Figure 17The following describes how the controller 50 operates when it is determined that the resonant currents flowing through the three switches 8 belonging to the plurality of switches 8 will flow simultaneously through the resonant inductor L1. When it is determined that the resonant currents flowing through the three switches 8 belonging to the plurality of switches 8 will flow simultaneously through the resonant inductor L1, the controller 50 performs a shift control operation. As used herein, the expression "when it is determined that the resonant currents flowing through the three switches 8 belonging to the plurality of switches 8 will flow simultaneously" refers to a situation where it has been previously estimated that the resonant currents flowing through the three switches 8 will flow simultaneously through the resonant inductor L1. When the AC load RA1 is lightly loaded and iU = 0, iV = 0, and iW = 0, it is assumed that the three-phase resonant currents overlap. For example, when the AC load RA1 is a motor, such a situation occurs, particularly when the motor is operating at a low speed or when the motor's rotational speed is zero (for example, when the motor is locked). Thus, for example, when the motor's rotational speed (for example, number of revolutions [rpm]) is less than a rotational speed threshold, the controller 50 determines that the three-phase resonant currents will flow simultaneously. In this case, for example, if the rotation speed 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 rotary transformer, etc.) or estimated based on the sensor information is less than the rotation speed threshold, the controller 50 determines that the three-phase resonant current will flow simultaneously.

[0180] 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, then in the equivalent circuit, a capacitor having a combined capacitance (=3×C) of the resonant capacitors 9U, 9V, and 9W is connected in series with the resonant inductor L1. Therefore, in power converter 100, if the three-phase current simultaneously flows through resonant inductor L1, the resonant frequency of the resonant circuit including resonant inductor L1 changes compared to the case where a single-phase current flows through resonant inductor L1. Consequently, power converter 100 may be unable to perform zero-voltage soft switching.

[0181] When it is determined that the resonant currents passing through the three switches 8 will flow through the resonant inductor L1 at the same time, the controller 50 performs shift control for shifting the high level periods of the control signals for two of the three switches 8 to prevent the resonant currents passing through the three switches 8 from flowing through the resonant inductor L1 at the same time.

[0182] In addition, when performing shift control, the controller 50 shifts the high level periods of the control signals for the two switches 8 to prevent the lengths of the high level periods of the control signals applied to the first switching element 1 and the second switching element 2 of a switching circuit 10 connected to the two switches 8 belonging to a plurality of switching circuits 10 from changing.

[0183] In addition, when performing shift control, the controller 50 selects control signals for any two switches 8 from the control signals for the three switches 8 as shift objects, and shifts the high-level periods of the control signals for the two switches 8 as shift objects in different directions to prevent the resonant currents passing through the three switches 8 respectively from flowing through the resonant inductor L1 at the same time.

[0184] (1) Operation of power converter

[0185] (1.1) Basic operations

[0186] The basic operation of the controller 50 is the same as that already described for the first embodiment, and therefore description thereof will be omitted herein.

[0187] (1.2) Shift control

[0188] (1.2.1) Soft Switching Operation of the First Switching Element

[0189] Figure 15 1 is a timing diagram illustrating how the power converter 100 operates when the controller 50 has determined that the three-phase resonant current (i.e., the U-phase resonant current, the V-phase resonant current, and the W-phase resonant current) will flow simultaneously when the polarity of the current iL1 is positive and has performed shift control. Figure 16 is a timing chart illustrating how the power converter 100 operates when the controller 50 does not perform shift control. Figure 15 and Figure 16 The timing diagrams shown each show a waveform in only a portion of one cycle of the carrier signal.

[0190] Figure 15 and Figure 16 Each is a timing diagram illustrating the waveforms of the control signals SU1, SU2, SV1, SV2, SW1, SW2, SU6, SV6, SW6, the load current iU, iV, the current iL1, and the voltages V2u, V2v, V2w across the second switching elements 2U, 2V, 2W. The controller 50 sets the length of the high-level period of each of the control signals SU6, SV6, SW6 to the resonance half cycle (Tre / 2), and sets the dead time period Td to the same length as the resonance half cycle. Note that, as Figure 15 and Figure 16 As shown, 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, which have been explained for the first embodiment, to zero.

[0191] exist Figure 15In the example shown, the controller 50 regards the control signals SU6, SW6 to be applied to the two switches 8U, 8W, respectively, as shift objects. However, this is merely an example and should not be construed as limiting. Figure 15 In the example shown, the controller 50 shifts the high-level period of the control signal SU6 by a first shift time T1 in a direction that advances the start time of the high-level period of the control signal SU6 for the switch 8U, so as to prevent the resonant current from overlapping between one of the two switches 8 that are shift objects and the other switch 8 that is not a shift object (for example, in this example, the U-phase resonant current and the V-phase resonant current are prevented from flowing simultaneously). In addition, the controller 50 shifts the high-level period of the control signal SW6 by a second shift time T2 in a direction that delays the start time of the high-level period of the control signal SW6 for the switch 8W, so as to prevent the resonant current from overlapping between the other switch of the two switches 8 that are shift objects and the other two switches 8 (for example, in this example, the W-phase resonant current is prevented from flowing simultaneously with any resonant current of the U-phase resonant current and the V-phase resonant current). Figure 15 , the state of the control signals SU6, SW6 before shifting their high level periods (ie, Figure 16 The state shown) is indicated by a two-dot chain line, and the state of the control signals SU6, SW6 after the high level period has been shifted is indicated by a solid line.

[0192] Figure 15 The example in which the controller 50 defines the first shift time T1 as T1=Tres / 2+Δ is shown. Figure 15 The case where T2=Tres / 2+Δ is shown in FIG, where Δ is the time margin left to more reliably avoid the overlap between the two-phase resonant currents. Figure 15 In the example shown, the high-level period of control signal SU6 for switch 8U is shifted by a first shift time T1 in a direction that advances the start time of the high-level period of control signal SU6, and the high-level period of control signal SW6 for switch 8W is shifted by a second shift time T2 in a direction that delays the start time of the high-level period of control signal SW6. However, this is merely an example and should not be construed as limiting. Alternatively, the high-level period of control signal SW6 for switch 8W may be shifted by a first shift time T1 in a direction that advances the start time of the high-level period of control signal SW6, and the high-level period of control signal SU6 for switch 8U may be shifted by a second shift time T2 in a direction that delays the start time of the high-level period of control signal SU6. Furthermore, the combination of the two switches 8 to be shifted does not necessarily have to be a combination of switches 8U and 8W, but may also be a combination of switches 8U and 8V, or a combination of switches 8V and 8W.

[0193] In the power converter 100 according to the third embodiment, each of the first shift time T1 and the second shift time T2 is a predetermined period. Note that the upper limit value (maximum value) of the first shift time T1 when the high-level period of the control signal for switch 8 is shifted to an earlier time is the shift time when the time lag between the start time of one cycle of the carrier signal and the start time of the high-level period of the shifted control signal (i.e., the shifted control signal for switch 8) becomes equal to a minimum value (e.g., zero) without changing the length of the high-level period. On the other hand, the upper limit value (maximum value) of the second shift time T2 when the high-level period of the control signal for switch 8 is shifted to a later time is the shift time when the time lag between the end time of one cycle of the carrier signal and the end time of the high-level period of the shifted control signal (i.e., the shifted control signal for switch 8) becomes equal to a minimum value (e.g., zero) without changing the length of the high-level period.

[0194] In the power converter 100, if the controller 50 does not perform the shift control, Figure 16 As shown, at the point in time when the control signals SU1, SV1, and SW1 transition from a low-level period to a high-level period (i.e., at the end of the dead time period Td corresponding to each of the U-phase, V-phase, and W-phase), the voltages V2u, V2v, and V2w across the second switching elements 2U, 2V, and 2W do not rise to Vd. That is, in the power converter 100, if the controller 50 does not perform shift control, the resonant capacitors 9U, 9V, and 9W are not fully charged at the end of the dead time period Td corresponding to each of the U-phase, V-phase, and W-phase. Therefore, in the power converter 100, if the controller 50 does not perform shift control, the voltages across the first switching elements 1U, 1V, and 1W do not drop to zero at the end of the dead time period Td corresponding to each of the U-phase, V-phase, and W-phase. Consequently, in the power converter 100, the first switching elements 1U, 1V, and 1W are hard-switched.

[0195] On the other hand, in the power converter 100, if the controller 50 has performed the shift control, then Figure 15As shown, at the point in time when the control signals SU1, SV1, and SW1 transition from a low-level period to a high-level period (i.e., at the end of the dead-band period Td corresponding to each of the U-phase, V-phase, and W-phase), the voltages V2u, V2v, and V2w across the second switching elements 2U, 2V, and 2W rise to Vd. That is, in the power converter 100, if the controller 50 has already performed shift control, then at the end of the dead-band period Td corresponding to each of the U-phase, V-phase, and W-phase, the resonant capacitors 9U, 9V, and 9W have already been charged. Therefore, in the power converter 100, if the controller 50 has already performed shift control, the first switching elements 1U, 1V, and 1W are switched using zero-voltage soft switching.

[0196] Note that if the controller 50 determines that the three-phase resonant currents will overlap with each other, the relationship between the polarity and magnitude of the three-phase load currents does not necessarily have to be defined as satisfying iU=0, iV=0 and iW=0, but can also be defined as satisfying iU>0>iV or iW>iV>0>iU, whichever is appropriate.

[0197] In addition, as long as the control signals for the three switches 8 at least partially overlap with each other, the time relationship between the control signals for the first switching element 1 or the time relationship between the control signals for the second switching element 2 is not limited to any specific time relationship. For example, the start time of the high-level period of the control signal SV6 can be earlier than the start time of the high-level period of the control signal SU6, and the start time of the control signal SU6 can be earlier than the start time of the control signal SW6. In addition, in the operation of soft switching of the first switching element (i.e., the operation of charging the resonant capacitor 9), if the three-phase resonant current flows simultaneously and the load current is positive, as in the basic example described above, it is preferable to add additional times Tau, Tav, and Taw to the high-level period of the switch 8 corresponding to the phase in which the positive load current flows.

[0198] (1.2.2) Soft Switching Operation of the Second Switching Element

[0199] Figure 17 1 is a timing diagram illustrating how the power converter 100 operates when the controller 50 has determined that the three-phase resonant current (i.e., the U-phase resonant current, the V-phase resonant current, and the W-phase resonant current) will flow simultaneously when the polarity of the current iL1 is negative and has performed shift control. Figure 18 is a timing chart illustrating how the power converter 100 operates when the controller 50 does not perform shift control. Figure 17 and Figure 18 The timing diagrams shown each show a waveform in only a portion of one cycle of the carrier signal.

[0200] Figure 17 and Figure 18 Each is a timing diagram showing the waveforms of the control signals SU1, SU2, SV1, SV2, SW1, SW2, SU7, SV7, SW7, the load current iU, iV, the current iL1, and the voltages V2u, V2v, V2w across the second switching elements 2U, 2V, 2W. The controller 50 sets the length of the high-level period of each of the control signals SU7, SV7, SW7 to the resonance half cycle (Tre / 2), and sets the dead time period Td to the same length as the resonance half cycle. Note that, as Figure 17 and Figure 18 As shown, 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, which have been explained for the first embodiment, to zero.

[0201] exist Figure 17 In the example shown, the controller 50 regards the control signals SU7, SW7 to be applied to the two switches 8U, 8W, respectively, as shift objects. However, this is merely an example and should not be construed as limiting. Figure 17 In the example shown, the controller 50 shifts the high-level period of the control signal SU7 for the switch 8U by a first shift time T1 in a direction that advances the start time of the high-level period of the control signal SU7, so as to prevent the resonant current from overlapping between one of the two switches 8 that are shift objects and the other switch 8 that is not a shift object (for example, in this example, the U-phase resonant current and the V-phase resonant current are prevented from flowing simultaneously). In addition, the controller 50 shifts the high-level period of the control signal SW7 for the switch 8W by a second shift time T2 in a direction that delays the start time of the high-level period of the control signal SW7, so as to prevent the resonant current from overlapping between the other switch of the two switches 8 that are shift objects and the other two switches 8 (for example, in this example, the W-phase resonant current is prevented from flowing simultaneously with any resonant current of the U-phase resonant current and the V-phase resonant current). Figure 17 , the states of the control signals SU7, SW7 before shifting their high level periods (ie, Figure 18 The state shown) is indicated by a two-dot chain line, and the state of the control signals SU6, SW6 after shifting their high level periods is indicated by a solid line.

[0202] Figure 17 The example in which the controller 50 defines the first shift time T1 as T1=Tres / 2+Δ is shown. Figure 17 The case where T2=Tres / 2+Δ is shown in FIG, where Δ is the time margin left to more reliably avoid the overlap between the two-phase resonant currents. Figure 17 In the example shown, the high-level period of control signal SU7 for switch 8U is shifted by a first shift time T1 in a direction that advances the start time of the high-level period of control signal SU7, and the high-level period of control signal SW7 for switch 8W is shifted by a second shift time T2 in a direction that delays the start time of the high-level period of control signal SW7. However, this is merely an example and should not be construed as limiting. Alternatively, the high-level period of control signal SW7 for switch 8W may be shifted by a first shift time T1 in a direction that advances the start time of the high-level period of control signal SW7, and the high-level period of control signal SU7 for switch 8U may be shifted by a second shift time T2 in a direction that delays the start time of the high-level period of control signal SU7. Furthermore, the combination of the two switches 8 to be shifted does not necessarily have to be a combination of switches 8U and 8W, but may also be a combination of switches 8U and 8V, or a combination of switches 8V and 8W.

[0203] In the power converter 100, if the controller 50 does not perform the shift control, Figure 18 As shown, at the point in time when the control signals SU2, SV2, and SW2 transition from a low-level period to a high-level period (i.e., at the end of the dead time period Td corresponding to each of the U-phase, V-phase, and W-phase), the voltages V2u, V2v, and V2w across the second switching elements 2U, 2V, and 2W do not drop to zero. That is, in the power converter 100, if the controller 50 does not perform shift control, then at the end of the dead time period Td corresponding to each of the U-phase, V-phase, and W-phase, the discharge from the resonant capacitors 9U, 9V, and 9W is not yet complete. Therefore, in the power converter 100, if the controller 50 does not perform shift control, then at the end of the dead time period Td corresponding to each of the U-phase, V-phase, and W-phase, the voltages V2u, V2v, and V2w across the second switching elements 2U, 2V, and 2W do not drop to zero. Therefore, in the power converter 100, the second switching elements 2U, 2V, and 2W are hard-switched.

[0204] On the other hand, in the power converter 100, if the controller 50 has performed the shift control, then Figure 17As shown, at the point in time when the control signals SU2, SV2, and SW2 transition from a low-level period to a high-level period (i.e., at the end of the dead-band period Td corresponding to each of the U-phase, V-phase, and W-phase), the voltages V2u, V2v, and V2w across the second switching elements 2U, 2V, and 2W drop to zero. That is, in the power converter 100, if the controller 50 has performed shift control, then at the end of the dead-band period Td corresponding to each of the U-phase, V-phase, and W-phase, discharge from the resonant capacitors 9U, 9V, and 9W has completed. Therefore, in the power converter 100, if the controller 50 has performed shift control, the second switching elements 2U, 2V, and 2W are switched by zero-voltage soft switching.

[0205] (2) Summary

[0206] In the power converter 100 according to the third embodiment, when it is determined that the resonant currents passing through the three switches 8 will flow simultaneously through the resonant inductor L1, the controller 50 controls the high-level periods of the control signals for two of the three switches 8 to be shifted, thereby preventing the resonant currents passing through the three switches 8 from flowing simultaneously through the resonant inductor L1. This enables the power converter 100 to perform soft switching more reliably.

[0207] (Fourth embodiment)

[0208] The power converter 100 according to the fourth embodiment has the same features as the power converter 100 according to the first embodiment described above (see Figure 1 ) has the same circuit structure, so its illustration and description will be omitted in this article.

[0209] In the power converter 100 according to the fourth embodiment, the shift control operation performed by the controller 50 that has determined that the three-phase resonant currents will overlap with each other is different from the shift control operation performed by the controller 50 according to the third embodiment.

[0210] Will refer to Figure 19 The following describes how the controller 50 operates when it is determined that the resonant currents flowing through the three switches 8 belonging to the plurality of switches 8 will flow simultaneously through the resonant inductor L1. When it is determined that the resonant currents flowing through the three switches 8 belonging to the plurality of switches 8 will flow simultaneously through the resonant inductor L1, the controller 50 performs a shift control operation.

[0211] As in the third embodiment described above, when performing shift control, the controller 50 shifts the high-level periods of the control signals for the two switches 8 to prevent the lengths of the high-level periods of the control signals applied to the first switching element 1 and the second switching element 2 of a switching circuit 10 connected to the two switches 8 belonging to a plurality of switching circuits 10 from changing.

[0212] In addition, in the fourth embodiment, when performing shift control, the controller 50 selects any two switches 8 from the three switches 8 as shift objects, and shifts the high level periods of the two switches 8 as shift objects in the same direction to prevent the resonant currents passing through the three switches 8 respectively from flowing through the resonant inductor L1 at the same time.

[0213] Figure 19 is a timing chart illustrating how the power converter 100 operates when the controller 50 has determined that the three-phase resonant current (i.e., the U-phase resonant current, the V-phase resonant current, and the W-phase resonant current) will flow simultaneously when the polarity of the current iL1 is positive and has performed shift control. Figure 16 is a timing chart illustrating how the power converter 100 operates when the controller 50 does not perform shift control. Figure 19 The timing diagram shown shows the waveform in only a portion of one cycle of the carrier signal.

[0214] Figure 19 and Figure 16 1 is a timing diagram illustrating the waveforms of the control signals SU1, SU2, SV1, SV2, SW1, SW2, SU6, SV6, SW6, the load currents iU, iV, the current iL1, and the voltages V2u, V2v, V2w across the second switching elements 2U, 2V, 2W. The controller 50 sets the length of the high-level period of each of the control signals SU6, SV6, SW6 to the resonance half cycle (Tre / 2), and sets the dead time period Td to the same length as the resonance half cycle. Note that, as Figure 19 As shown, 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, which have been explained for the first embodiment, to zero.

[0215] exist Figure 19 In the example shown, the controller 50 regards the control signals SV6, SW6 to be applied to the two switches 8V, 8W, respectively, as shift objects. However, this is merely an example and should not be construed as limiting. Figure 19In the example shown, the controller 50 shifts the high-level period of the control signal SV6 for the switch 8V by a first shift time T1 in a direction that postpones the start moment of the high-level period of the control signal SV6 for the switch 8V, so as to prevent the resonant current from overlapping between one of the two switches 8 that are the shift objects and the other switch 8 that is not the shift object (for example, in this example, the U-phase resonant current and the V-phase resonant current are prevented from flowing simultaneously). In addition, the controller 50 also shifts the high-level period of the control signal SW6 for the switch 8W by a second shift time T2 in a direction that postpones the start moment of the high-level period of the control signal SW6 for the switch 8W, so as to prevent the resonant current from overlapping between the other switch of the two switches 8 that are the shift objects and the other two switches 8 (for example, in this example, the W-phase resonant current is prevented from flowing simultaneously with any resonant current of the U-phase resonant current and the V-phase resonant current). Figure 19 , the state of the control signals SV6, SW6 before shifting their high level period (ie, Figure 16 The state shown) is indicated by a two-dot chain line, and the state of the control signals SV6, SW6 after shifting their high level periods is indicated by a solid line.

[0216] Figure 19 The example in which the controller 50 defines the first shift time T1 as T1=Tres / 2+Δ is shown. Figure 19 , where T2=2×(Tres / 2)+Δ is a time margin left to more reliably avoid overlap between the two-phase resonant currents.

[0217] In the power converter 100 according to the fourth embodiment, if the controller 50 has performed the shift control, then Figure 19 As shown, at the point in time when the control signals SU1, SV1, and SW1 transition from a low-level period to a high-level period (i.e., at the end of the dead-band period Td corresponding to each of the U-phase, V-phase, and W-phase), the voltages V2u, V2v, and V2w across the second switching elements 2U, 2V, and 2W rise to Vd. That is, in the power converter 100, if the controller 50 has already performed shift control, then at the end of the dead-band period Td corresponding to each of the U-phase, V-phase, and W-phase, the resonant capacitors 9U, 9V, and 9W have already been charged. Therefore, in the power converter 100, if the controller 50 has already performed shift control, the first switching elements 1U, 1V, and 1W are switched using zero-voltage soft switching.

[0218] In the power converter 100 according to the fourth embodiment, when it is determined that the resonant currents passing through the three switches 8 will flow simultaneously through the resonant inductor L1, the controller 50 controls the high-level periods of the control signals for two of the three switches 8 to be shifted, thereby preventing the resonant currents passing through the three switches 8 from flowing simultaneously through the resonant inductor L1. This enables the power converter 100 to perform soft switching more reliably.

[0219] Note that in Figure 19 In the example shown, the high-level period of control signal SV6 for switch 8V is shifted by a first shift time T1 in a direction that delays the start of the high-level period of control signal SU6, and the high-level period of control signal SW6 for switch 8W is shifted by a second shift time T2 in a direction that delays the start of the high-level period of control signal SW6. However, this is merely an example and should not be construed as limiting. Alternatively, the high-level period of control signal SW6 for switch 8W may be shifted by a first shift time T1 in a direction that delays the start of the high-level period of control signal SW6 for switch 8W, and the high-level period of control signal SV6 for switch 8V may be shifted by a second shift time T2 in a direction that delays the start of the high-level period of control signal SV6. Furthermore, the combination of the two switches 8 to be shifted does not necessarily have to be a combination of switches 8V and 8W, but may also be a combination of switches 8U and 8V, or a combination of switches 8U and 8W. Furthermore, the shift direction does not necessarily need to be a direction that postpones the high-level period of the control signals for the two switches 8, but may also be a direction that advances the high-level period of the control signals for the two switches 8. Figure 19 In the example shown, the second shift time T2 is longer than the first shift time T1. However, this is merely an example and should not be construed as limiting. Alternatively, the first shift time T1 may be longer than the second shift time T2.

[0220] although Figure 19 The operation of performing soft switching on the first switching elements 1U, 1V, and 1W is exemplified, but the shift control operation can be performed in the same manner when performing soft switching on the second switching elements 2U, 2V, and 2W.

[0221] The power converter 100 according to the modified example of the fourth embodiment can reduce the deviation of the ripple variation of the line voltage by, for example, causing the controller 50 to appropriately change the combination of the two switches 8 that are the targets of shift control.

[0222] (Fifth embodiment)

[0223] The power converter 100 according to the fifth embodiment has the same features as the power converter 100 according to the first embodiment described above (refer to Figure 1 ) has the same circuit structure, so its illustration and description will be omitted in this article.

[0224] In the power converter 100 according to the fifth embodiment, the shift control operation performed by the controller 50 that has determined that the three-phase resonant currents will overlap with each other is different from the shift control operation performed by the controller 50 according to the third embodiment. In the fifth embodiment, the controller 50 performs shift control to prevent the resonant currents from overlapping with each other in any combination of one switch 8 and the other two switches 8 of the three switches 8.

[0225] In the fifth embodiment, when it is determined that the resonant currents respectively passing through the three switches 8 will flow through the resonant inductor L1 at the same time, the controller 50 performs a first shift control as a shift control when a first condition is satisfied when a charging operation for charging the plurality of resonant capacitors 9 is to be performed, and performs a second shift control as a shift control when a second condition is satisfied when a discharging operation for discharging from the plurality of resonant capacitors 9 is to be performed.

[0226] The first condition is that the time lag between the start of the high-level period of the control signal with the longest high-level period among the control signals SU1, SV1, and SW1 applied to the three first switching elements 1 and the start of the high-level period of the control signal with the shortest high-level period among the control signals SU1, SV1, and SW1 applied to the three first switching elements 1 is longer than the resonance half-period Tres. The resonance half-period Tres is a value that is half of the resonance period determined by the inverse of the resonance frequency of the resonant circuit including the resonant inductor L1 and one of the plurality of resonant capacitors 9. The first shift control includes control for shifting the high-level period of the control signal for the switch 8 corresponding to the first switching element 1 to which the control signal with the second longest high-level period among the control signals SU1, SV1, and SW1 applied to the three first switching elements 1 is applied. The second condition is a condition in which the time lag between the start time of the high-level period of the control signal with the longest high-level period among the control signals SU2, SV2, and SW2 to be applied to the three second switching elements 2 and the start time of the high-level period of the control signal with the shortest high-level period among the control signals SU2, SV2, and SW2 to be applied to the three second switching elements 2 is longer than the resonance half-period Tres. The second shift control includes a control for shifting the high-level period of the control signal for the switch 8 corresponding to the second switching element 2 to which the control signal with the second longest high-level period among the control signals SU2, SV2, and SW2 to be applied to the three second switching elements 2 is applied. When performing the shift control (the first shift control or the second shift control), the controller 50 shifts the high-level period of the control signal for the switch 8 to prevent the length of the high-level period of the control signal to be applied to the switch 8 from changing.

[0227] Figure 20 1 is a timing chart illustrating how the power converter 100 operates when the controller 50 has determined that the resonant currents through the three switches 8 will flow simultaneously and has performed the first shift control in the case of a charging operation to charge the plurality of resonant capacitors 9. Figure 21 is a timing chart illustrating how the power converter 100 operates when the controller 50 does not perform the first shift control. Figure 20 and Figure 21 The timing diagrams shown each show a waveform in only a portion of one cycle of the carrier signal.

[0228] Figure 20 and Figure 21Each is a timing diagram showing the waveforms of the control signals SU1, SU2, SV1, SV2, SW1, SW2, SU6, SV6, SW6, the load currents iU, iV, iW, and the current iL1. 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 cycle (Tre / 2), and sets the dead zone period Td to the same length as the resonance half cycle. Note that, as Figure 20 and Figure 21 As shown, 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, which have been explained for the first embodiment, to zero.

[0229] exist Figure 20 In the example shown, [the length of the high-level period of the control signal SU1]>[the length of the high-level period of the control signal SV1]>[the length of the high-level period of the control signal SW1] is satisfied, so the controller 50 shifts the high-level period of the control signal SV6 for the switch 8V corresponding to the first switching element 1V to which the control signal SV1 is applied by the shift time Ts in the direction of advancing the high-level period of the control signal SV6. In the fifth embodiment, the shift time Ts is a predetermined period. Figure 20 , the state of the control signal SV6 before shifting its high level period (ie, Figure 21 The state shown in FIG1 is indicated by a double-dot chain line, and the state after its high-level period has been shifted is indicated by a solid line. Figure 20 In the example shown, the controller 50 shifts the high-level period of the control signal SV6 by a shift time Ts in a direction that advances the start time of the high-level period of the control signal SV6 for the switch 8V, thereby preventing the resonant current flowing through the switch 8V and the resonant current flowing through the switch 8U from flowing through the resonant inductor L1 at the same time, and preventing the resonant current flowing through the switch 8V and the resonant current flowing through the switch 8W from flowing through the resonant inductor L1 at the same time. The length of the predetermined period (i.e., the shift time Ts) can be, for example, 2×Tres / 2. However, the length of the predetermined period is not limited to this length and can be any other length as long as the overlap of the resonant currents can be avoided. In addition, the direction in which the high-level period of the control signal SV6 is shifted does not necessarily have to be a direction that advances the high-level period, but can also be a direction that delays the high-level period.

[0230] In the power converter 100 according to the fifth embodiment, if the controller 50 performs shift control, the voltages V2u, V2v, and V2w across the second switching elements 2U, 2V, and 2W increase to Vd at the time when the control signals SU1, SV1, and SW1 transition from a low-level period to a high-level period (i.e., at the end of the dead-band period Td corresponding to each of the U-phase, V-phase, and W-phase). That is, in the power converter 100, if the controller 50 performs shift control, the resonant capacitors 9U, 9V, and 9W are already charged at the end of the dead-band period Td corresponding to each of the U-phase, V-phase, and W-phase. Therefore, in the power converter 100, if the controller 50 performs shift control, the first switching elements 1U, 1V, and 1W are switched by zero-voltage soft switching.

[0231] Furthermore, in the power converter 100 according to the fifth embodiment, when the second condition is satisfied, by causing the controller 50 to perform the second shift control, zero-voltage soft switching can be performed on the second switching elements 2U, 2V, 2W.

[0232] As can be seen from the foregoing description, the power converter 100 according to the fifth embodiment can perform soft switching more reliably.

[0233] (Sixth embodiment)

[0234] Will refer to Figure 22 In the following description, any constituent elements of the power converter 100A according to the sixth embodiment that have the same functions as corresponding portions of the power converter 100 according to the first embodiment described above will be designated by the same reference numerals as those of the corresponding portions, and description thereof will be omitted herein.

[0235] In the power converter 100A according to the sixth embodiment, in each of the plurality of switches 8, the first IGBT 6 and the second IGBT 7 are connected in anti-series. In the power converter 100A according to the sixth embodiment, 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 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.

[0236] In the power converter 100A according to the sixth embodiment, each of the first IGBT 6 and the second IGBT 7 can be replaced with a MOSFET or a bipolar transistor. In this case, Figure 22 The diode 61 and the diode 71 shown can each be replaced with, for example, a parasitic diode of a replacement element or an element built into one chip of the replacement element. In addition, in the power converter 100A according to the sixth embodiment, the diode 61 and the diode 71 do not necessarily need to be provided as external elements for the first IGBT 6 and the second IGBT 7, respectively, but may be elements built into one chip.

[0237] The controller 50 can operate in the same manner as, for example, the controller 50 according to the first embodiment. However, this is merely an example and should not be construed as limiting. Alternatively, the controller 50 can operate in the same manner as the controller 50 according to any of the second to fifth embodiments described above, and can also perform the shift control performed by the controller 50 according to the first to fifth embodiments.

[0238] (Seventh embodiment)

[0239] Will refer to Figure 23 In the following description, any constituent elements of the power converter 100A according to the seventh embodiment that have the same functions as those of the corresponding portions of the power converter 100 according to the first embodiment described above will be designated by the same reference numerals as those of the corresponding portions, and description thereof will be omitted herein.

[0240] In the power converter 100A according to the seventh embodiment, in each of the plurality of switches 8, the first IGBT 6 and the second IGBT 7 are connected in anti-series. In the power converter 100A according to the seventh embodiment, in each of the plurality of switches 8, the emitter terminal of the first IGBT 6 and the emitter terminal of the second IGBT 7 are connected to each other, the collector terminal of the second IGBT 7 is connected to the connection node 3 of the corresponding switching circuit in the plurality of switching circuits 10, and the collector terminal of the first IGBT 6 is connected to the common connection node 25. In addition, each of the plurality of switches 8 further includes a diode 61 connected in anti-parallel to the first IGBT 6 and a diode 71 connected in anti-parallel to the second IGBT 7.

[0241] In the power converter 100A according to the seventh embodiment, each of the first IGBT 6 and the second IGBT 7 can be replaced with a MOSFET or a bipolar transistor. In this case, Figure 23The diode 61 and the diode 71 shown can each be replaced with, for example, a parasitic diode of a replacement element or an element built into one chip of the replacement element. In addition, in the power converter 100A according to the seventh embodiment, the diode 61 and the diode 71 do not necessarily need to be provided as external elements for the first IGBT 6 and the second IGBT 7, respectively, but may be elements built into one chip.

[0242] The controller 50 can operate in the same manner as, for example, the controller 50 according to the first embodiment. However, this is merely an example and should not be construed as limiting. Alternatively, the controller 50 can operate in the same manner as the controller 50 according to any of the second to fifth embodiments described above, and can also perform the shift control performed by the controller 50 according to the first to fifth embodiments.

[0243] (Eighth embodiment)

[0244] Will refer to Figure 24 In the following description, any constituent elements of the power converter 100A according to the eighth embodiment that have the same functions as corresponding portions of the power converter 100 according to the first embodiment described above will be designated by the same reference numerals as those of the corresponding portions, and description thereof will be omitted herein.

[0245] In the power converter 100A according to the eighth embodiment, 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 eighth embodiment, 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. Furthermore, each of the plurality of switches 8 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.

[0246] The controller 50 can operate in the same manner as, for example, the controller 50 according to the first embodiment. However, this is merely an example and should not be construed as limiting. Alternatively, the controller 50 can operate in the same manner as the controller 50 according to any of the second to fifth embodiments described above, and can also perform the shift control performed by the controller 50 according to the first to fifth embodiments.

[0247] (Ninth embodiment)

[0248] Will refer to Figure 25 In the following description, any constituent elements of the power converter 100A according to the ninth embodiment having the same functions as those of the corresponding portions of the power converter 100 according to the first embodiment described above will be designated by the same reference numerals as those of the corresponding portions, and description thereof will be omitted herein.

[0249] In the power converter 100A according to the ninth embodiment, a diode 63 is connected in series to the first MOSFET 6A, and a diode 73 is connected in series to the second MOSFET 7A in each of the plurality of switches 8. In the power converter 100A according to the ninth embodiment, a series circuit of the first MOSFET 6A and the diode 63 and a series circuit of the second MOSFET 7A and the diode 73 are connected in antiparallel to each other.

[0250] The controller 50 can operate in the same manner as, for example, the controller 50 according to the first embodiment. However, this is merely an example and should not be construed as limiting. Alternatively, the controller 50 can operate in the same manner as the controller 50 according to any of the second to fifth embodiments described above, and can also perform the shift control performed by the controller 50 according to the first to fifth embodiments.

[0251] (Tenth embodiment)

[0252] Will refer to Figure 26 In the following description, any constituent elements of the power converter 100A according to the tenth embodiment having the same functions as those of the corresponding portions of the power converter 100 according to the first embodiment described above will be designated by the same reference numerals as those of the corresponding portions, and description thereof will be omitted herein.

[0253] In a power converter 100A according to the tenth embodiment, each of the plurality of switches 8 includes: a MOSFET 80; a diode 83 connected in antiparallel to the MOSFET 80; a series circuit of two diodes 84 and 85 connected in antiparallel to the MOSFET 80; and a series circuit of two diodes 86 and 87 connected in antiparallel to the MOSFET 80. In each of the plurality of switches 8, the connection node between the diodes 84 and 85 in the switch 8 (i.e., the first end 81 of the switch 8) is connected to the connection node 3 of the corresponding switching circuit in the plurality of switching circuits 10, and the connection node between the diodes 86 and 87 (i.e., the second end 82 of the switch 8) is connected to the common connection node 25. In each of the plurality of switches 8, when the MOSFET 80 is on, the switch 8 is on. On the other hand, when the MOSFET 80 is off, the switch 8 is off.

[0254] 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.

[0255] In each switch 8, when its MOSFET 80 is turned on, a resonant current generated by a resonant circuit including the resonant inductor L1 and the corresponding resonant capacitor in the resonant capacitor 9 flows. In the power converter 100A, when one of the multiple switches 8 is turned on, the 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 this order. In addition, in the power converter 100A, when one of the multiple switches 8 is turned on, the 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 resonant capacitor 15 in this order.

[0256] In the power converter 100A according to the tenth embodiment, each of the plurality of MOSFETs 80 may be replaced with an IGBT. Furthermore, in the power converter 100A according to the tenth embodiment, each of the plurality of switches 8 may include, for example, a bipolar transistor or a GaN-based gate injection transistor (GIT) instead of the MOSFET 80.

[0257] The controller 50 can operate in the same manner as, for example, the controller 50 according to the first embodiment. However, this is merely an example and should not be construed as limiting. Alternatively, the controller 50 can operate in the same manner as the controller 50 according to any of the second to fifth embodiments described above, and can also perform the shift control performed by the controller 50 according to the first to fifth embodiments.

[0258] (Eleventh embodiment)

[0259] Will refer to Figure 27 In the following description, any constituent elements of the power converter 100A according to the eleventh embodiment having the same functions as those of the corresponding portions of the power converter 100 according to the first embodiment described above will be designated by the same reference numerals as those of the corresponding portions, and description thereof will be omitted herein.

[0260] In the power converter 100A according to the eleventh embodiment, 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 eleventh embodiment, a control signal SU6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT serving as switch 8U, and a control signal SU7 is applied between its second gate terminal and the second source terminal. Furthermore, a control signal SV6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT serving as switch 8V, and a control signal SV7 is applied between its second gate terminal and the second source terminal. Furthermore, a control signal SW6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT serving as switch 8W, and a control signal SW7 is applied between its second gate terminal and the second source terminal.

[0261] The controller 50 can operate in the same manner as, for example, the controller 50 according to the first embodiment. However, this is merely an example and should not be construed as limiting. Alternatively, the controller 50 can operate in the same manner as the controller 50 according to any of the second to fifth embodiments described above, and can also perform the shift control performed by the controller 50 according to the first to fifth embodiments.

[0262] (Twelfth embodiment)

[0263] Will refer to Figure 28A power converter 100B according to a twelfth embodiment will be described. The power converter 100B according to the twelfth embodiment further includes a capacitor 16 connected between the second end of the resonant inductor L1 and the first DC terminal 31, which is different from the power converter 100 according to the first embodiment. In the following description, any constituent elements in the power converter 100B according to the twelfth embodiment that have the same functions as the corresponding portions of the power converter 100 according to the first embodiment described above will be designated by the same reference numerals as those of the corresponding portions, and description thereof will be omitted herein.

[0264] Power converter 100B does not include capacitor C10 of power converter 100 according to the first embodiment. Capacitor 16 is connected in series to regenerative capacitor 15. Thus, in this power converter 100B, the series circuit of capacitor 16 and regenerative capacitor 15 is connected between first DC terminal 31 and second DC terminal 32. The capacitance of capacitor 16 is equal to the capacitance of regenerative capacitor 15. As used herein, the expression "the capacitance of capacitor 16 is equal to the capacitance of regenerative capacitor 15" refers not only to the case where the capacitance of capacitor 16 is exactly equal to the capacitance of regenerative capacitor 15, but also to the case where the capacitance of capacitor 16 is equal to or greater than 95% and equal to or less than 105% of the capacitance of regenerative capacitor 15.

[0265] In the power converter 100B according to the twelfth 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). Therefore, the potential V15 at the fourth terminal 154 of the regenerative capacitor 15 is Vd / 2. In the power converter 100B according to the twelfth embodiment, the controller 50 can pre-store the value of the potential V15 at the fourth terminal 154 of the regenerative capacitor 15.

[0266] The controller 50 of the power converter 100B according to the twelfth embodiment performs shift control in the same manner as the controller 50 of the power converter 100 according to the first embodiment. Thus, the power converter 100B according to the twelfth 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 in the same manner as the power converter 100 according to the first embodiment.

[0267] The controller 50 can operate in the same manner as, for example, the controller 50 according to the first embodiment. However, this is merely an example and should not be construed as limiting. Alternatively, the controller 50 can operate in the same manner as the controller 50 according to any of the second to fifth embodiments described above, and can also perform the shift control performed by the controller 50 according to the first to fifth embodiments.

[0268] (Thirteenth embodiment)

[0269] Will refer to Figure 29 A power converter 100C according to a thirteenth embodiment will be described. In the power converter 100C according to the thirteenth embodiment, a regenerative capacitor 15 is connected between the second end of the resonant inductor L0 and the first DC terminal 31, which is different from the power converter 100 according to the first embodiment. In the following description, any constituent elements in the power converter 100C according to this thirteenth embodiment that have the same functions as the corresponding portions of the power converter 100 according to the first embodiment described above will be designated by the same reference numerals as those of the corresponding portions, and their description will be omitted herein.

[0270] Controller 50 of power converter 100C according to the thirteenth embodiment performs shift control in the same manner as controller 50 of power converter 100 according to the first embodiment. Thus, power converter 100C according to the thirteenth embodiment can perform soft switching more reliably, as can power converter 100 according to the first embodiment.

[0271] (Other Modifications)

[0272] Note that the first to thirteenth embodiments and their modifications described above are merely exemplary embodiments among the various embodiments and their modifications of the present disclosure and should not be construed as limiting. Rather, the first to thirteenth exemplary embodiments and their modifications may be easily modified in various ways according to design choices or any other factors without departing from the scope of the present disclosure.

[0273] The operation performed by the controller 50 to "determine that multiple resonant currents will flow simultaneously" is not limited to the operation of "determining that multiple resonant currents will flow simultaneously" when the time lag described in the first embodiment is less than the threshold, and the operation of "determining that three-phase resonant currents will flow simultaneously" when the rotation speed of the motor is less than the rotation speed threshold.

[0274] For example, if the time lag between the start moment of the high-level period of the control signal corresponding to the U phase and the start moment of the high-level period of the control signal corresponding to the V phase, the time lag between the start moment of the high-level period of the control signal corresponding to the V phase and the start moment of the high-level period of the control signal corresponding to the W phase, and the time lag between the start moment of the high-level period of the control signal corresponding to the W phase and the start moment 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 current will flow simultaneously.

[0275] Alternatively, if any one of the current difference between the U-phase load current iU and the V-phase load current iV, the current difference between the V-phase load current iV and the W-phase load current iW, and the current difference between the W-phase load current iW and the U-phase load current iU is less than the current difference threshold, the controller 50 can determine that the two-phase resonant current will flow simultaneously.

[0276] Still 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 will flow simultaneously.

[0277] Alternatively, if the electrical angle determined by calculation or the estimated electrical angle based on sensor information provided by a sensor device for detecting the number of revolutions of the motor (such as an encoder or a rotary transformer, etc.) falls within a first rotation angle range (e.g., equal to or greater than 55 degrees and equal to or less than 65 degrees), or a second rotation angle range (e.g., equal to or greater than 115 degrees and equal to or less than 125 degrees), or a third rotation angle range (e.g., equal to or greater than 175 degrees and equal to or less than 185 degrees), or a fourth rotation angle range (e.g., equal to or greater than 235 degrees and equal to or less than 245 degrees), or a fifth rotation angle range (e.g., equal to or greater than 295 degrees and equal to or less than 305 degrees), or a sixth rotation angle range (e.g., equal to or greater than 355 degrees and equal to or less than 365 degrees), the controller 50 can determine that "two-phase resonant currents will flow simultaneously."

[0278] For example, each switching element in the plurality of first switching elements 1 and the plurality of second switching elements 2 does not necessarily have to be an IGBT, but may also be a MOSFET. In this case, each first diode in the plurality of first diodes 4 may be replaced by, for example, a parasitic diode of the MOSFET used as its corresponding first switching element 1. In addition, each second diode in the plurality of second diodes 5 may also be replaced by, for example, a parasitic diode of the 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 switching element in the plurality of first switching elements 1 and the plurality of second switching elements 2 may also be, for example, a bipolar transistor or a GaN-based GIT.

[0279] Optionally, in the power converters 100, 100A, 100B, 100C, if each of the multiple resonant capacitors 9 has a relatively small capacitance, instead of setting the multiple resonant capacitors 9 as separate elements, the parasitic capacitors across the multiple second switching elements 2 can also be used as the multiple resonant capacitors 9.

[0280] Furthermore, the length of the dead zone period Td does not necessarily have to be set to be as long as one resonance half cycle, but may also be set to be different from one resonance half cycle.

[0281] The dead time period Td may also be set by a dead time generation 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 generation circuit included in the gate driver IC may set the dead time period Td.

[0282] Furthermore, the power converters 100 , 100A, 100B, 100C are not necessarily configured to output three-phase AC power, but may be configured to output multi-phase AC power having more than three phases.

[0283] (all aspects)

[0284] The foregoing description provides specific implementations of the following aspects of the present disclosure.

[0285] According to the first aspect, a power converter (100; 100A; 100B; 100C) 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 switching circuit of the plurality of switching circuits (10), one first switching element of the plurality of first switching elements (1) is connected in series with a corresponding second switching element of the plurality of second switching elements (2) on a one-to-one basis. 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 on a one-to-one basis 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). A plurality of switches (8) are provided one-to-one for the plurality of switching circuits (10). A first end (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). A second end (82) of each of the plurality of switches (8) is commonly connected to a common connection node (25). 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 end (81) of a corresponding switch in a plurality of switches (8) and a second DC terminal (32). A resonant inductor (L1) has a first end and a second end. In the resonant inductor (L1), the first end 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 flowing through two or more switches (8) belonging to a plurality of switches (8) will flow through the resonant inductor (L1) at the same time, the controller (50) performs shift control for shifting the high-level period of the control signal for at least one switch (8) among the two or more switches (8) to prevent the resonant currents respectively flowing through the two or more switches (8) from flowing through the resonant inductor (L1) at the same time.

[0286] This aspect enables soft handover to be performed more reliably.

[0287] In a power converter (100; 100A; 100B; 100C) according to the second aspect that can be implemented in combination with the first aspect, when performing shift control, a controller (50) shifts a high-level period of a control signal for at least one switch (8) to prevent a change in the length of a high-level period of a control signal to be applied to a first switching element (1) and a second switching element (2) of a switching circuit (10) connected to the at least one switch (8) belonging to a plurality of switching circuits (10).

[0288] This aspect enables suppression of variations in line voltage.

[0289] In a power converter (100; 100A; 100B; 100C) according to a third aspect that can be implemented in combination with the first aspect or the second aspect, when performing shift control, a controller (50) shifts the high level periods of the control signals for two switches (8) belonging to two or more switches (8) in directions different from each other.

[0290] This aspect may help increase the frequency of operation.

[0291] In a power converter (100; 100A; 100B; 100C) according to a fourth aspect that can be implemented in combination with any one of the first to third aspects, when it is determined that resonant currents respectively flowing through two switches (8) belonging to a plurality of switches (8) will flow simultaneously through a resonant inductor (L1), if the polarity of the load current respectively flowing through two AC terminals (41) connected to the two switches (8) belonging to a plurality of AC terminals (41) is positive, a controller (50) compares the duty ratios of the control signals for two first switching elements (1) corresponding to the two switches (8) belonging to a plurality of first switching elements (1). Then, the controller (50) shifts the high-level period of the control signal for the switch (8) corresponding to the first switching element (1) to which the control signal with a relatively large duty ratio is applied in a direction that advances the high-level period of the control signal, and shifts the high-level period of the control signal for the switch (8) corresponding to the first switching element (1) to which the control signal with a relatively small duty ratio is applied in a direction that delays the high-level period of the control signal. If the polarity of the load current flowing through the two AC terminals (41) connected to the two switches (8) belonging to the plurality of AC terminals (41) is negative, the controller (50) compares the duty ratios of the control signals for the two first switching elements (1) corresponding to the two switches (8) belonging to the plurality of first switching elements (1). Then, the controller (50) shifts the high-level period of the control signal for the switch (8) corresponding to the first switching element (1) to which the control signal with a relatively large duty ratio is applied in a direction that delays the high-level period of the control signal, and shifts the high-level period of the control signal for the switch (8) corresponding to the first switching element (1) to which the control signal with a relatively small duty ratio is applied in a direction that advances the high-level period of the control signal.

[0292] This aspect enables more reliable soft switching when it is determined that resonant currents respectively passing through two switches (8) belonging to a plurality of switches (8) will flow through the resonant inductor (L1) at the same time.

[0293] In a power converter (100; 100A; 100B; 100C) according to a fifth aspect that can be implemented in combination with any one of the first to third aspects, when it is determined that resonant currents respectively flowing through two switches (8) belonging to a plurality of switches (8) will flow simultaneously through a resonant inductor (L1), if the polarity of the load current respectively flowing through two AC terminals (41) connected to the two switches (8) belonging to a plurality of AC terminals (41) is positive, a controller (50) compares the duty ratios of the control signals for two first switching elements (1) corresponding to the two switches (8) belonging to a plurality of first switching elements (1). Then, the controller (50) shifts the high-level period of the control signal for the switch (8) corresponding to the first switching element (1) to which the control signal with a relatively large duty ratio is applied in a direction to postpone the high-level period of the control signal, and shifts the high-level period of the control signal for the switch (8) corresponding to the first switching element (1) to which the control signal with a relatively small duty ratio is applied in a direction to advance the high-level period of the control signal. If the polarity of the load current flowing through the two AC terminals (41) connected to the two switches (8) belonging to the plurality of AC terminals (41) is negative, the controller (50) compares the duty ratios of the control signals for the two first switching elements (1) corresponding to the two switches (8) belonging to the plurality of first switching elements (1). Then, the controller (50) shifts the high-level period of the control signal for the switch (8) corresponding to the first switching element (1) to which the control signal with a relatively large duty ratio is applied in a direction that advances the high-level period of the control signal, and shifts the high-level period of the control signal for the switch (8) corresponding to the first switching element (1) to which the control signal with a relatively small duty ratio is applied in a direction that delays the high-level period of the control signal.

[0294] This aspect enables more reliable soft switching when it is determined that resonant currents respectively passing through two switches (8) belonging to a plurality of switches (8) will flow through the resonant inductor (L1) at the same time.

[0295] In a power converter (100; 100A; 100B; 100C) according to the sixth aspect, which can be implemented in combination with any one of the first to fifth aspects, when it is determined that resonant currents respectively passing through three switches (8) belonging to a plurality of switches (8) will flow through the resonant inductor (L1) at the same time, the controller (50) performs shift control by shifting the high-level periods of control signals to be applied to two switches (8) among the three switches (8) in a single direction.

[0296] This aspect enables more reliable soft switching when it is determined that the resonant currents respectively passing through the three switches (8) will flow simultaneously.

[0297] In a power converter (100; 100A; 100B; 100C) according to the seventh aspect, which can be implemented in combination with any one of the first to sixth aspects, the plurality of first switching elements (1) include three first switching elements (1). The plurality of second switching elements (2) include three second switching elements (2). The plurality of switches (8) include three switches (8). When it is determined that the resonant currents respectively passing through the three switches (8) will flow through the resonant inductor (L1) at the same time, the controller (50) performs a first shift control when a first condition is satisfied when a charging operation for charging the plurality of resonant capacitors (9) is about to be performed, and performs a second shift control when a second condition is satisfied when a discharging operation for discharging from the plurality of resonant capacitors (9) is about to be performed. The first condition is a condition in which a time lag between a start time of a high-level period of a control signal having the longest high-level period among the control signals (SU1, SV1, SW1) to be applied to the three first switching elements (1) and a start time of a high-level period of a control signal having the shortest high-level period among the control signals (SU1, SV1, SW1) to be applied to the three first switching elements (1) is longer than a resonance half period (Tres). The resonance half period (Tres) is a value that is half of a resonance period determined by the inverse of a resonance frequency of a resonance circuit including a resonance inductor (L1) and one of a plurality of resonance capacitors (9). The first shift control includes a control for shifting a high-level period of a control signal for a switch (8) corresponding to a first switching element (1) to which a control signal having the second longest high-level period among the control signals (SU1, SV1, SW1) to be applied to the three first switching elements (1) is applied. The second condition is a condition in which a time lag between a start time of a high-level period of a control signal having a longest high-level period among the control signals (SU2, SV2, SW2) to be applied to the three second switching elements (2) and a start time of a high-level period of a control signal having a shortest high-level period among the control signals (SU2, SV2, SW2) to be applied to the three second switching elements (2) is longer than a resonance half period (Tres). The second shift control includes a control for shifting a high-level period of a control signal for a switch (8) corresponding to the second switching element (2) to which the control signal having a second longest high-level period among the control signals (SU2, SV2, SW2) to be applied to the three second switching elements (2) is applied.

[0298] This aspect enables, in the case of a charging operation, soft switching of the three first switching elements (1) by shifting the high-level period of the control signal for one switch (8) belonging to the plurality of switches (8), and also enables, in the case of a discharging operation, soft switching of the three second switching elements (2) by shifting the high-level period of the control signal for one switch (8) belonging to the plurality of switches (8).

[0299] Industrial applicability

[0300] The power converter according to the present disclosure enables soft switching to be performed more reliably, thereby further improving the reliability of the power converter.As can be seen, the power converter according to the present disclosure is effectively applicable to various fields based on industry.

[0301] Description of Reference Numerals

[0302] 1First switching element

[0303] 2 Second switching element

[0304] 3 Connecting Nodes

[0305] 8 switches

[0306] 9 Resonant capacitor

[0307] 10Switching circuit

[0308] 11 Power conversion circuit

[0309] 15 Regeneration capacitor

[0310] 153 The Third End

[0311] 154 The Fourth End

[0312] 31 First DC terminal

[0313] 32 Second DC terminal

[0314] 41 AC terminal

[0315] 50 Controller

[0316] 100, 100A, 100B, 100C power converters

[0317] iU, iV, iW output current (load current)

[0318] L1 resonant inductor

[0319] RA1 AC load

[0320] SU1, SU2, SU6, SU7 control signals

[0321] SV1, SV2, SV6, SV7 control signals

[0322] SW1, SW2, SW6, SW7 control signals

[0323] Tres 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 the plurality of switching circuits, wherein in each of the plurality of switching circuits, one of the plurality of first switching elements and a corresponding second switching element of the plurality of second switching elements are connected in series one-to-one, 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 AC terminal of the plurality of AC terminals being connected to a connection node between a first switching element and a second switching element of a corresponding switching circuit of the plurality of switching circuits; a plurality of switches provided one-to-one for the plurality of switching circuits, wherein a first end 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 of the plurality of switching circuits, and a second end of each of the plurality of switches is commonly connected to a common connection node; a plurality of resonant capacitors provided one-to-one with respect to the plurality of switches, each resonant capacitor of the plurality of resonant capacitors being connected between the second DC terminal and a first end of a corresponding switch of the plurality of switches; a resonant inductor having a first end and a second end, the first end of the resonant inductor being connected to the common connection node; a regenerative capacitor having a third end and a fourth end, the third end of the regenerative 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, The controller is configured to, when it is determined that the resonant currents respectively passing through two or more switches belonging to the plurality of switches will flow through the resonant inductor at the same time, perform shift control for shifting the high-level period of the control signal for at least one switch of the two or more switches, so as to prevent the resonant currents respectively passing through the two or more switches from flowing through the resonant inductor at the same time.

2. The power converter according to claim 1, wherein The controller is configured to shift the high-level period of the control signal for the at least one switch when performing the shift control to prevent the length of the high-level period of the control signal applied to the first switching element and the second switching element of a switching circuit connected to the at least one switch among the multiple switching circuits from changing.

3. The power converter according to claim 1 or 2, wherein: The controller is configured to shift high-level periods of control signals for two switches belonging to the two or more switches in directions different from each other when performing the shift control.

4. The power converter according to any one of claims 1 to 3, wherein: The controller is configured to, when determining that the resonant currents respectively passing through two switches belonging to the plurality of switches will flow through the resonant inductor at the same time, comparing the duty cycles of the control signals for the two first switching elements corresponding to the two switches among the plurality of first switching elements when the polarity of the load currents respectively flowing through the two AC terminals connected to the two switches among the plurality of AC terminals is positive, so as to shift the high-level period of the control signal for the switch corresponding to the first switching element to which the control signal having a relatively large duty cycle is applied in a direction that advances the high-level period of the control signal, and shift the high-level period of the control signal for the switch corresponding to the first switching element to which the control signal having a relatively small duty cycle is applied in a direction that delays the high-level period of the control signal, and When the polarity of the load current respectively flowing through the two AC terminals connected to the two switches belonging to the plurality of AC terminals is negative, the duty cycles of the control signals for the two first switching elements corresponding to the two switches belonging to the plurality of first switching elements are compared so that the high-level period of the control signal for the switch corresponding to the first switching element to which the control signal with a relatively large duty cycle is applied is shifted in a direction that delays the high-level period of the control signal, and the high-level period of the control signal for the switch corresponding to the first switching element to which the control signal with a relatively small duty cycle is applied is shifted in a direction that advances the high-level period of the control signal.

5. The power converter according to any one of claims 1 to 3, wherein: The controller is configured to, when determining that the resonant currents respectively passing through two switches belonging to the plurality of switches will flow through the resonant inductor at the same time, comparing the duty cycles of the control signals for the two first switching elements corresponding to the two switches among the plurality of first switching elements when the polarity of the load currents respectively flowing through the two AC terminals connected to the two switches among the plurality of AC terminals is positive, so that a high-level period of the control signal for the switch corresponding to the first switching element to which the control signal having a relatively large duty cycle is applied is shifted in a direction that postpones the high-level period of the control signal, and a high-level period of the control signal for the switch corresponding to the first switching element to which the control signal having a relatively small duty cycle is applied is shifted in a direction that advances the high-level period of the control signal, and When the polarity of the load current respectively flowing through the two AC terminals connected to the two switches belonging to the plurality of AC terminals is negative, the duty cycles of the control signals for the two first switching elements corresponding to the two switches belonging to the plurality of first switching elements are compared so that the high-level period of the control signal for the switch corresponding to the first switching element to which the control signal with a relatively large duty cycle is applied is shifted in a direction that advances the high-level period of the control signal, and the high-level period of the control signal for the switch corresponding to the first switching element to which the control signal with a relatively small duty cycle is applied is shifted in a direction that delays the high-level period of the control signal.

6. The power converter according to any one of claims 1 to 5, wherein: The controller is configured to, when determining that the resonant currents respectively passing through three switches belonging to the plurality of switches will flow through the resonant inductor at the same time, The shift control is performed by shifting high-level periods of control signals to be applied to two switches among the three switches, respectively, in a single direction.

7. The power converter according to any one of claims 1 to 6, wherein: The plurality of first switching elements include three first switching elements, The plurality of second switching elements include three second switching elements, The plurality of switches includes three switches, The controller is configured to, when it is determined that the resonant currents passing through the three switches will flow through the resonant inductor at the same time, In a case where a charging operation for charging the plurality of resonant capacitors is to be performed, a first shift control is performed when a first condition is satisfied, The first condition is a condition that a time lag between a start time of a high-level period of a control signal having a longest high-level period among the control signals to be applied to the three first switching elements and a start time of a high-level period of a control signal having a shortest high-level period among the control signals to be applied to the three first switching elements is longer than a resonance half period, The resonant half period is a value that is half of a resonant period, the resonant period being determined by an inverse of a resonant frequency of a resonant circuit including the resonant inductor and one resonant capacitor among the plurality of resonant capacitors. the first shift control includes control for shifting a high level period of a control signal for a switch corresponding to a first switching element to which a control signal having a second long high level period is applied among the control signals to be applied to the three first switching elements, In a case where a discharge operation for discharging from the plurality of resonant capacitors is to be performed, a second shift control is performed when a second condition is satisfied, The second condition is a condition that a time lag between a start time of a high-level period of a control signal having a longest high-level period among the control signals to be applied to the three second switching elements and a start time of a high-level period of a control signal having a shortest high-level period among the control signals to be applied to the three second switching elements is longer than the resonance half period, and The second shift control includes control for shifting a high level period of a control signal for a switch corresponding to a second switching element to which a control signal having a second long high level period is applied, among control signals to be applied to the three second switching elements.

Images