Power converter

Abstract

In the present invention, a switching state in a power conversion circuit is detected. A power converter (100) includes a first DC terminal (31) and a second DC terminal (32), a power conversion circuit (11), a plurality of AC terminals (41), a plurality of switches (8), a plurality of resonant capacitors (9), at least one resonant inductor (L1), a regenerative capacitor (15), and a controller (50). A power conversion circuit (11) includes a plurality of first switching elements (1) and a plurality of second switching elements (2). Each of the plurality of switches (8) is connected to a connection node (3) between a respective one of the first switching elements (1) and a respective one of the second switching elements (2). The controller (50) includes a determination section (54) for determining a switching state in the power conversion circuit (11) on the basis of a ripple voltage included in the voltage (V15) across the regenerative capacitor (15) and a plurality of load currents (iU, iV, iW) supplied from the plurality of AC terminals (41).

Description

Technical Field

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

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

[0003] In the resonant inverter of Patent Document 1, the DC voltage of a DC voltage source is converted into an AC voltage by an inverter unit (power conversion circuit). The inverter unit has the following configuration: Six main switching elements (composed of three first switching elements and three second switching elements) are connected in a three-phase (i.e., U-phase, V-phase, and W-phase) bridge between a positive bus and a negative bus.

[0004] In addition, in the resonant inverter, two voltage-dividing capacitors are connected in series between the positive bus and the negative bus. These two voltage-dividing capacitors not only function as voltage-dividing components for dividing the DC voltage of the DC voltage source, but also function as components for generating half of the DC voltage of the DC voltage source at the connection node between the two voltage-dividing capacitors. Further, a resonant circuit section for performing a resonant operation when the main switching elements are being switched is provided between the two voltage-dividing capacitors and the inverter unit. The resonant circuit section is formed by connecting a series circuit of a resonant reactor (resonant inductor) and an auxiliary switch (switch) between the connection node of the two voltage-dividing capacitors and the connection nodes of the upper arm and the lower arm in each of the three phases, and by connecting a resonant capacitor in parallel to each of the series circuits for the three phases.

[0005] The on / off (ON / OFF) states of each switching element and each auxiliary switch are controlled by a control unit.

[0006] In the power converter of Patent Document 1, for example, if a switch connected to the resonant inductor fails, then in some cases, each switching element among the first switching element and the second switching element connected to the auxiliary switch in the power conversion circuit is hard-switched.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 2000-32775 Summary of the Invention

[0010] An object of the present disclosure is to provide a power converter having the ability to detect the switching state in a power conversion circuit.

[0011] A power converter according to one aspect of the present disclosure includes a first DC terminal and a second DC terminal, a power conversion circuit, a plurality of AC terminals, a plurality of switches, a plurality of resonant capacitors, at least one resonant inductor, a regenerative capacitor, and a controller. The power conversion circuit includes a plurality of first switching elements and a plurality of second switching elements. In the power conversion circuit, a plurality of switching circuits are connected in parallel with each other. In each of the plurality of switching circuits, one first switching element among the plurality of first switching elements and a corresponding second switching element among the plurality of second switching elements are connected in series one-to-one. In the power conversion circuit, the plurality of first switching elements are connected to the first DC terminal, and the plurality of second switching elements are connected to the second DC terminal. The plurality of AC terminals are provided one-to-one for the plurality of switching circuits. Each of the plurality of AC terminals is connected to a connection node between the first switching element and the second switching element of the corresponding switching circuit among the plurality of switching circuits. The plurality of switches are provided one-to-one for the plurality of switching circuits. Each of the plurality of switches has a first end and a second end. The first end of each of the plurality of switches is connected to the connection node between the first switching element and the second switching element of the corresponding switching circuit among the plurality of switching circuits. The plurality of resonant capacitors are provided one-to-one for the plurality of switches. Each of the plurality of resonant capacitors is connected between the second DC terminal and the first end of the corresponding switch among the plurality of switches. The at least one resonant inductor has a third end and a fourth end. The third end of the at least one resonant inductor is connected to the second end of the corresponding switch among the plurality of switches. The regenerative capacitor has a fifth end and a sixth end. The fifth end of the regenerative capacitor is connected to the second DC terminal. The sixth end of the regenerative capacitor is connected to the fourth end of the at least one resonant inductor. The controller controls the on / off states of the plurality of first switching elements, the plurality of second switching elements, and the plurality of switches respectively. The controller includes a determination unit. The determination unit determines a switching state in the power conversion circuit based on a ripple voltage included in a voltage across the regenerative capacitor and a plurality of load currents supplied from the plurality of AC terminals. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0013] Figure 2 FIG. A is a waveform diagram illustrating the relationship between a load current and a voltage across a regenerative capacitor in a case where the power converter is operating normally;

[0014] Figure 2Waveform diagram B illustrates the relationship between the load current and the voltage across the regenerative capacitor when the power converter is operating abnormally;

[0015] Figure 3 Illustrates how the power converter operates when the load current > 0 and its resonant capacitor is undergoing a charging operation, and its controller has performed basic operations;

[0016] Figure 4 Also illustrates how the power converter operates when the load current > 0 and its resonant capacitor is undergoing a charging operation, and its controller has performed basic operations;

[0017] Figure 5 Shows how the duty ratio and the load current corresponding to the three-phase voltage commands in the AC loads connected to the multiple AC terminals of the power converter change over time;

[0018] Figure 6 Shows the first current threshold and the second current threshold for use in the controller of the power converter;

[0019] Figure 7 Illustrates how the power converter operates when the load current > 0 and its resonant capacitor is undergoing a discharging operation, and its controller has performed basic operations;

[0020] Figure 8 Also illustrates how the power converter operates when the load current < 0 and its resonant capacitor is undergoing a discharging operation, and its controller has performed basic operations;

[0021] Figure 9 Illustrates how the power converter operates when the load current < 0 and its resonant capacitor is undergoing a charging operation, and its controller has performed basic operations;

[0022] Figure 10 Waveform diagram A illustrates the relationship between the load current and the voltage across the regenerative capacitor when the power converter according to the first modification of the first embodiment is operating normally;

[0023] Figure 10 Waveform diagram B illustrates the relationship between the load current and the voltage across the regenerative capacitor when the power converter is operating abnormally;

[0024] Figure 11 Waveform diagram A illustrates the relationship between the load current and the voltage across the regenerative capacitor when the power converter according to the second modification of the first embodiment is operating normally;

[0025] Figure 11Waveform B illustrates the relationship between the load current and the voltage across the regenerative capacitor when the power converter is operating abnormally;

[0026] Figure 12 is a circuit diagram of a system including a power converter according to the second embodiment;

[0027] Figure 13 is a circuit diagram of a system including a power converter according to the third embodiment;

[0028] Figure 14 is a circuit diagram of a system including a power converter according to the first modification of the third embodiment;

[0029] Figure 15 is a circuit diagram of a system including a power converter according to the second modification of the third embodiment;

[0030] Figure 16 is a circuit diagram of a system including a power converter according to the third modification of the third embodiment;

[0031] Figure 17 is a circuit diagram of a system including a power converter according to the fourth modification of the third embodiment;

[0032] Figure 18 is a circuit diagram of a system including a power converter according to the fifth modification of the third embodiment;

[0033] Figure 19 is a circuit diagram of a system including a power converter according to the sixth modification of the third embodiment; and

[0034] Figure 20 is a circuit diagram of a system including a power converter according to the fourth embodiment. Detailed Description

[0035] (First Embodiment)

[0036] Reference will be made to Figures 1 to 9 to describe the power converter 100 according to the first embodiment.

[0037] (1) Overall Configuration of Power Converter

[0038] For example, as Figure 1As shown, the power converter 100 includes a first DC terminal 31, a second DC terminal 32, and a plurality (e.g., three) of AC terminals 41. A DC power supply 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 can be, for example, a three-phase motor. The power converter 100 converts the DC output of the DC power supply E1 into AC power and outputs the AC power to the AC load RA1. The DC power supply E1 can include, for example, a solar cell or a fuel cell. The DC power supply E1 can 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 can be, for example, three-phase AC power having a U phase, a V phase, and a W phase.

[0039] The power converter 100 includes a power conversion circuit 11, a plurality (e.g., three) of switches 8, a plurality (e.g., three) of resonance capacitors 9, a regeneration capacitor 15, a plurality (e.g., three) of resonance inductors L1, and a controller 50. The power converter 100 further includes a protection circuit 17. Each of the plurality of switches 8 can be, for example, a bidirectional switch.

[0040] The power conversion circuit 11 includes a plurality of (e.g., three) first switching elements 1 and a plurality of (e.g., three) second switching elements 2. In the power conversion circuit 11, a plurality of (e.g., three) switching circuits 10 are connected in parallel with each other. In each switching circuit 10, one of the plurality of first switching elements 1 and a corresponding second switching element among the plurality of second switching elements 2 are connected in series one-to-one. In the power conversion circuit 11, the plurality of first switching elements 1 are connected to 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 one-to-one for the plurality of switching circuits 10. Each of the plurality of AC terminals 41 is connected to a connection node 3 between the first switching element 1 and the second switching element 2 of the corresponding switching circuit among the plurality of switching circuits 10. A plurality of switches 8 are provided one-to-one for the plurality of switching circuits 10. Each of the plurality of switches 8 has a first end 81 and a second end 82. The first end 81 of each of the plurality of switches 8 is connected to the connection node 3 between the first switching element 1 and the second switching element 2 of the corresponding switching circuit among the plurality of switching circuits 10. A plurality of resonant capacitors 9 are provided one-to-one for the plurality of switches 8. Each of the plurality of resonant capacitors 9 is connected between the first end 81 of the corresponding switch among the plurality of switches 8 and the second DC terminal 32. Each of the plurality of resonant inductors L1 has a third end and a fourth end. In each resonant inductor L1, its fourth end is connected to a regenerative capacitor 15. In each of the plurality of resonant inductors L1, its third end is connected to the second end 82 of the corresponding switch among the plurality of switches 8. The regenerative capacitor 15 has a fifth end 153 and a sixth end 154. The fifth end 153 of the regenerative capacitor 15 is connected to the second DC terminal 32. The sixth end 154 of the regenerative capacitor 15 is connected to the fourth end of the corresponding resonant inductor among the resonant inductors 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.

[0041] (2) Details of the power converter

[0042] In the following description, for the sake of convenience, among the plurality of switching circuits 10, the switching circuits 10 for the U-phase, V-phase, and W-phase will be hereinafter referred to as "switching circuit 10U", "switching circuit 10V", and "switching circuit 10W", respectively. Further, in the following description, the first switching element 1 and the second switching element 2 of the switching circuit 10U will be hereinafter referred to as "first switching element 1U" and "second switching element 2U", respectively. Similarly, in the following description, the first switching element 1 and the second switching element 2 of the switching circuit 10V will be hereinafter referred to as "first switching element 1V" and "second switching element 2V", respectively. Similarly, in the following description, the first switching element 1 and the second switching element 2 of the switching circuit 10W will be hereinafter referred to as "first switching element 1W" and "second switching element 2W", respectively. Further, in the following description, the connection node 3 between the first switching element 1U and the second switching element 2U will be hereinafter referred to as "connection node 3U", the connection node 3 between the first switching element 1V and the second switching element 2V will be hereinafter 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 hereinafter referred to as "connection node 3W". Further, in the following description, the AC terminal 41 connected to the connection node 3U will be hereinafter referred to as "AC terminal 41U", the AC terminal 41 connected to the connection node 3V will be hereinafter referred to as "AC terminal 41V", and the AC terminal 41 connected to the connection node 3W will be hereinafter referred to as "AC terminal 41W". Further, in the following description, the resonance capacitor 9 connected in parallel to the second switching element 2U will be hereinafter referred to as "resonance capacitor 9U", the resonance capacitor 9 connected in parallel to the second switching element 2V will be hereinafter referred to as "resonance capacitor 9V", and the resonance capacitor 9 connected in parallel to the second switching element 2W will be hereinafter referred to as "resonance capacitor 9W". Further, in the following description, the switch 8 connected to the connection node 3U will be hereinafter referred to as "switch 8U", the switch 8 connected to the connection node 3V will be hereinafter referred to as "switch 8V", and the switch 8 connected to the connection node 3W will be hereinafter referred to as "switch 8W".

[0043] In the power converter 100, the high-potential output terminal (positive electrode) of the DC power supply E1 is connected to the first DC terminal 31, for example, and the low-potential output terminal (negative electrode) of the DC power supply E1 is connected to the second DC terminal 32, for example. Further, in the power converter 100, for example, the U-phase terminal, V-phase terminal, and W-phase terminal of the AC load RA1 are connected to the three AC terminals 41U, 41V, and 41W, respectively.

[0044] In the power conversion circuit 11, each of the plurality of (e.g., three) first switching elements 1 and the plurality of (e.g., three) second switching elements 2 has a control terminal, a first main terminal, and a second main terminal. The control terminals of the plurality of first switching elements 1 and the plurality of second switching elements 2 are connected to the controller 50. In each of the plurality of switching circuits 10 of the power converter 100, the first main terminal of the first switching element 1 is connected to the first DC terminal 31, the second main terminal of the first switching element 1 is connected to the first main terminal of the second switching element 2, and the second main terminal of the second switching element 2 is connected to the second DC terminal 32. In each of the plurality of switching circuits 10, the first switching element 1 is a high-side switching element (P-side switching element), and the second switching element 2 is a low-side switching element (N-side switching element). Each of the plurality of first switching elements 1 and the plurality of second switching elements 2 may be, for example, an insulated gate bipolar transistor (IGBT). Thus, in each of the plurality of first switching elements 1 and the plurality of second switching elements 2, its control terminal, first main terminal, and second main terminal are the gate terminal, collector terminal, and emitter terminal, respectively.

[0045] The power conversion circuit 11 further includes: a plurality of (e.g., three) first diodes 4, which are anti-parallel connected to the plurality of (e.g., three) first switching elements 1 one-to-one; and a plurality of (e.g., three) second diodes 5, which are anti-parallel connected to the plurality of (e.g., three) second switching elements 2 one-to-one. In each of the plurality of first diodes 4, the anode of the first diode 4 is connected to the second main terminal (emitter terminal) of the first switching element 1 corresponding to the first diode 4, and the cathode of the first diode 4 is connected to the first main terminal (collector terminal) of the first switching element 1 corresponding to the first diode 4. In each of the plurality of second diodes 5, the anode of the second diode 5 is connected to the second main terminal (emitter terminal) of the second switching element 2 corresponding to the second diode 5, and the cathode of the second diode 5 is connected to the first main terminal (collector terminal) of the second switching element 2 corresponding to the second diode 5.

[0046] The U-phase terminal of the AC load RA1 may be connected to the connection node 3U between the first switching element 1U and the second switching element 2U via the AC terminal 41U, for example. The V-phase of the AC load RA1 may be connected to the connection node 3V between the first switching element 1V and the second switching element 2V via the AC terminal 41V, for example. The W-phase of the AC load RA1 may be connected to the connection node 3W between the first switching element 1W and the second switching element 2W via the AC terminal 41W, for example.

[0047] A plurality of resonant capacitors 9 are provided one-to-one corresponding to a plurality of switches 8. Each of the plurality of resonant capacitors 9 is connected between a first end 81 of a corresponding one of the plurality of switches 8 and a second DC terminal 32. The power converter 100 includes a plurality of resonant circuits. Each of the plurality of resonant circuits includes a corresponding one of the resonant capacitors 9 and a corresponding one of the resonant inductors L1.

[0048] Each of the plurality of switches 8 may include, for example, two IGBTs (i.e., a first IGBT 6 and a second IGBT 7) connected 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 a connection node 3 of a 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 a connection node 3 of a switching circuit 10 corresponding to the switch 8 including the second IGBT 7. The switch 8U is connected to a connection node 3U between the first switching element 1U and the second switching element 2U. The switch 8V is connected to a connection node 3V between the first switching element 1V and the second switching element 2V. The switch 8W is connected to a connection node 3W between the first switching element 1W and the second switching element 2W. In the following description, for the sake of convenience, the first IGBT 6 and the second IGBT 7 of the switch 8U will be hereinafter referred to as "first IGBT 6U" and "second IGBT 7U" respectively, the first IGBT 6 and the second IGBT 7 of the switch 8V will be hereinafter referred to as "first IGBT 6V" and "second IGBT 7V" respectively, and the first IGBT 6 and the second IGBT 7 of the switch 8W will be hereinafter referred to as "first IGBT 6W" and "second IGBT 7W" respectively.

[0049] The plurality of switches 8 are controlled by a 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.

[0050] Each of the plurality of resonant inductors L1 has a third terminal and a fourth terminal. In each of the plurality of resonant inductors L1, its third terminal is connected to the second terminal 82 of the corresponding switch among the plurality of switches 8. The fourth terminal of each of the plurality of resonant inductors L1 is connected to the sixth terminal 154 of the regenerative capacitor 15. The inductances of the plurality of resonant inductors L1 are equal to each other. That is, the inductances of the three resonant inductors L1 are equal to each other. As used herein, the statement "the inductances of the three resonant inductors L1 are equal to each other" not only refers to the case where the inductances of two of the three resonant inductors L1 are exactly equal to the inductance of the other resonant inductor L1, but also refers to the case where the inductance of each of the two resonant inductors L1 is equal to or greater than 95% and equal to or less than 105% of the inductance of the other resonant inductor L1.

[0051] The regenerative capacitor 15 is connected between the fourth terminal of each of the plurality of resonant inductors L1 and the second DC terminal 32. The regenerative capacitor 15 can be, for example, a thin film capacitor.

[0052] Each of the plurality of protection circuits 17 includes a third diode 13 and a fourth diode 14. In each of the plurality of protection circuits 17, the third diode 13 is connected between the connection node where its corresponding resonant inductor L1 and its corresponding switch 8 are connected to each other and the first DC terminal 31. In the third diode 13, the anode of the third diode 13 is connected to the connection node between the resonant inductor L1 and the switch 8. In the third diode 13, the cathode of the third diode 13 is connected to the first DC terminal 31. The fourth diode 14 is connected between the connection node where its corresponding resonant inductor L1 and its corresponding switch 8 are connected to each other and the second DC terminal 32. In the fourth diode 14, the anode of the fourth diode 14 is connected to the second DC terminal 32. In the fourth diode 14, the cathode of the fourth diode 14 is connected to the connection node between the resonant inductor L1 and the switch 8. Thus, in each of the plurality of protection circuits 17, the fourth diode 14 is connected in series to the third diode 13.

[0053] The controller 50 controls the plurality of first switching elements 1, the plurality of second switching elements 2, and the plurality of switches 8.

[0054] The controller 50 outputs control signals SU1, SV1, and SW1 for respectively controlling the on / off states of a plurality of first switching elements 1U, 1V, and 1W. Each of the control signals SU1, SV1, and SW1 can be, for example, a pulse width modulation (PWM) signal having a potential level that alternates between a first potential level (hereinafter referred to as "low level") and a second potential level higher than the first potential level (hereinafter referred to as "high level"). Each of the first switching elements 1U, 1V, and 1W becomes conductive when its control signal SU1, SV1, or SW1 has a high level, and becomes non-conductive when its control signal SU1, SV1, or SW1 has a low level. In addition, the controller 50 also outputs control signals SU2, SV2, and SW2 for respectively controlling the on / off states of a plurality of second switching elements 2U, 2V, and 2W. Each of the control signals SU2, SV2, and SW2 can be, for example, a PWM signal having a potential level that alternates between a first potential level (hereinafter referred to as "low level") and a second potential level higher than the first potential level (hereinafter referred to as "high level"). Each of the second switching elements 2U, 2V, and 2W becomes conductive when its control signal SU2, SV2, or SW2 has a high level, and becomes non-conductive when its control signal SU2, SV2, or SW2 has a low level.

[0055] The controller 50 uses a carrier signal having a sawtooth waveform (refer to Figure 3 ) to generate the control signals SU1, SV1, and SW1 for the plurality of first switching elements 1U, 1V, and 1W respectively, and the control signals SU2, SV2, and SW2 for the plurality of second switching elements 2U, 2V, and 2W respectively. More specifically, the controller 50 generates the control signals SU1 and SU2 to be respectively applied to the first switching element 1U and the second switching element 2U based on at least the carrier signal and the U-phase voltage command. In addition, the controller 50 generates the control signals SV1 and SV2 to be respectively applied to the first switching element 1V and the second switching element 2V based on at least the carrier signal and the V-phase voltage command. In addition, the controller 50 generates the control signals SW1 and SW2 to be respectively applied to the first switching element 1W and the second switching element 2W based on at least the carrier signal and the W-phase voltage command. The U-phase voltage command, the V-phase voltage command, and the W-phase voltage command can be, for example, sine wave signals whose phases differ from each other by 120 degrees and whose values (voltage command values) change over time. Note that the waveform of the carrier signal does not necessarily have to be a sawtooth waveform, but can also be a triangular waveform or Figure 3 a mirror-inverted version of the sawtooth waveform shown. In addition, each of the U-phase voltage command, the V-phase voltage command, and the W-phase voltage command has a cycle of the same length. In addition, a cycle of the U-phase voltage command, the V-phase voltage command, and the W-phase voltage command is longer than a cycle of the carrier signal.

[0056] The duty ratios of the control signals SU1 and SU2 to be respectively applied from the controller 50 to the first switching element 1U and the second switching element 2U vary according to the U-phase voltage command. In Figure 5 , the duty ratio of the control signal SU1 is shown as the "U-phase duty ratio". The controller 50 (refer to Figure 1 ) generates the 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 the 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 conduction periods of the first switching element 1U and the second switching element 2U from overlapping with each other, the controller 50 sets a dead time period Td between the high-level period of the control signal SU1 and the high-level period of the control signal SU2 (refer to Figure 3 ).

[0057] The duty ratios of the control signals SV1 and SV2 to be respectively applied from the controller 50 to the first switching element 1V and the second switching element 2V vary according to the V-phase voltage command. In Figure 5 , the duty ratio of the control signal SV1 is shown as the "V-phase duty ratio". The controller 50 (refer to Figure 1 ) generates the 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 the 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 conduction periods of the first switching element 1V and the second switching element 2V from overlapping with each other, the controller 50 sets a dead time period Td between the high-level period of the control signal SV1 and the high-level period of the control signal SV2 (refer to Figure 3 ).

[0058] The duty ratios of the control signals SW1 and SW2 to be respectively applied from the controller 50 to the first switching element 1W and the second switching element 2W vary according to the W-phase voltage command. In Figure 5 , the duty ratio of the control signal SW1 is shown as the "W-phase duty ratio". The controller 50 (refer to Figure 1 ) generates the 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 the 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 conduction periods of the first switching element 1W and the second switching element 2W from overlapping with each other, the controller 50 sets a dead time period Td between the high-level period of the control signal SW1 and the high-level period of the control signal SW2 (refer to Figure 4 ).

[0059] The U-phase voltage command, V-phase voltage command, and W-phase voltage command can be, for example, sine wave signals with phases differing from each other by 120 degrees and whose values change over time. Thus, for example, as Figure 5 shown, the duty ratios of the control signals SU1, SV1, SW1 (i.e., the U-phase duty ratio, V-phase duty ratio, and W-phase duty ratio) change in the form of sine waves with phases differing from each other by 120 degrees. In the same manner, the duty ratios of the control signals SU2, SV2, SW2 also change in the form of sine waves with phases differing from each other by 120 degrees.

[0060] The controller 50 generates the respective control signals SU1, SU2, SV1, SV2, SW1, SW2 based on a carrier signal, each voltage command, and information related to the state of the AC load RA1. For example, if the AC load RA1 is a three-phase motor, the information related to the state of the AC load RA1 can include, for example, the detection values provided by a plurality of current sensors for respectively detecting the output currents (hereinafter referred to as "load currents") iU, iV, iW flowing through the U-phase, V-phase, and W-phase of the AC load RA1, respectively.

[0061] A plurality of switches 8, a plurality of resonant inductors 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.

[0062] 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.

[0063] The controller 50 generates control signals SU6, SU7, SV6, SV7, SW6, SW7 for respectively controlling the on / off states of the first IGBT 6U, second IGBT 7U, first IGBT 6V, second IGBT 7V, first IGBT 6W, and second IGBT 7W, and outputs the control signals SU6, SU7, SV6, SV7, SW6, SW7 to the gate terminals of the first IGBT 6U, second IGBT 7U, first IGBT 6V, second IGBT 7V, first IGBT 6W, and second IGBT 7W, respectively.

[0064] If the first IGBT 6U is turned on and the second IGBT 7U is turned off, the switch 8U allows the charging current flowing through the regenerative capacitor 15, the resonant inductor L1, the switch 8U, and the resonant capacitor 9U in sequence to pass. The charging current is the current for charging the resonant capacitor 9U. On the other hand, if the first IGBT 6U is turned off and the second IGBT 7U is turned on, the switch 8U allows the discharging current flowing through the resonant capacitor 9U, the switch 8U, the resonant inductor L1, and the regenerative capacitor 15 in sequence to pass. The discharging current is the current for discharging (i.e., removing charge) from the resonant capacitor 9U.

[0065] If the first IGBT 6V is turned on and the second IGBT 7V is turned off, the switch 8V allows the charging current flowing through the regenerative capacitor 15, the resonant inductor L1, the switch 8V, and the resonant capacitor 9V in sequence to pass. The charging current is the current for charging the resonant capacitor 9V. On the other hand, if the first IGBT 6V is turned off and the second IGBT 7V is turned on, the switch 8V allows the discharging current flowing through the resonant capacitor 9V, the switch 8V, the resonant inductor L1, and the regenerative capacitor 15 in sequence to pass. The discharging current is the current for discharging (i.e., removing charge) from the resonant capacitor 9V.

[0066] If the first IGBT 6W is turned on and the second IGBT 7W is turned off, the switch 8W allows the charging current flowing through the regenerative capacitor 15, the resonant inductor L1, the switch 8W, and the resonant capacitor 9W in sequence to pass. The charging current is the current for charging the resonant capacitor 9W. On the other hand, if the first IGBT 6W is turned off and the second IGBT 7W is turned on, the switch 8W allows the discharging current flowing through the resonant capacitor 9W, the switch 8W, the resonant inductor L1, and the regenerative capacitor 15 in sequence to pass. The discharging current is the current for discharging (i.e., removing charge) from the resonant capacitor 9W.

[0067] The controller 50 includes a control unit 51, a first acquisition unit 52, a second acquisition unit 53, and a determination unit 54.

[0068] The control unit 51 has a function of controlling the on / off states of the plurality of first switching elements 1, the plurality of second switching elements 2, and the plurality of switches 8. In the controller 50, the control unit 51 has a function of generating respective control signals SU1, SU2, SV1, SV2, SW1, SW2 based on a carrier signal, respective voltage commands, and information related to the state of the AC load RA1. The information related to the state of the AC load RA1 may include, for example, detection values provided by a plurality of current sensors for respectively detecting the load currents iU, iV, iW.

[0069] The first acquisition unit 52 has a function of acquiring a detection value of a voltage sensor 20 that detects a voltage V15 across the regenerative capacitor 15.

[0070] The second acquisition unit 53 has a function of acquiring detection values from a plurality of current sensors. That is, the second acquisition unit 53 has a function of acquiring detection values of a plurality of load currents iU, iV, and iW supplied from a plurality of AC terminals 41. Each of the plurality of load currents iU, iV, and iW can be, for example, an AC current having a sine waveform. The phases of the plurality of load currents iU, iV, and iW differ from each other by, for example, 120 degrees.

[0071] The determination unit 54 determines a switching state in the power conversion circuit 11 based on a ripple voltage included in the voltage V15 across the regenerative capacitor 15 and the plurality of load currents iU, iV, and iW supplied from the plurality of AC terminals 41. The switching state in the power conversion circuit 11 includes at least one of the switching states of the plurality of first switching elements 1 and the plurality of second switching elements 2. How the determination unit 54 operates will be further described in detail in the section of “(3.2) Operation of the determination unit”.

[0072] The agent for performing the functions of the controller 50 includes a computer system. The computer system includes one or more computers. The computer system may include a processor and a memory as its main hardware components. The computer system serves as an agent that performs the functions of the controller 50 according to the present disclosure by causing the processor to execute a program stored in the memory of the computer system. The program may be pre-stored in the memory of the computer system. Alternatively, the program may also be downloaded via a telecommunication 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 (magnetic disk) (any of which is readable by the computer system). The processor of the computer system may be constituted by one or more 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, either of which is appropriate. These multiple chips may be aggregated together in a single device or distributed in multiple devices without limitation.

[0073] (3) Operation of the power converter

[0074] In the following description, for the current iL1 flowing through each resonance inductor L1, if the current iL1 flows in the direction indicated by the arrow shown by Figure 1 it is assumed that the polarity of the current iL1 is positive. On the other hand, if the current iL1 is in the direction opposite to that indicated by Figure 1If it flows in the direction opposite to the direction indicated by the arrow shown, the polarity of the current iL1 is assumed to be negative. In the following description, for each of the load currents iU, iV, and iW flowing through the U-phase, V-phase, and W-phase of the AC load RA1, respectively, if the load currents iU, iV, and iW flow in the direction indicated by the corresponding arrow in the arrow shown by Figure 1 the polarity of the load currents iU, iV, and iW is assumed to be positive. On the other hand, if the load currents iU, iV, and iW flow in the direction opposite to the direction indicated by the arrow shown by Figure 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 resonance capacitors 9U, 9V, and 9W, respectively, if the currents i9U, i9V, and i9W flow in the direction indicated by the corresponding arrow in the arrow shown by Figure 1 the polarity of the currents i9U, i9V, and i9W is assumed to be positive. On the other hand, if the currents i9U, i9V, and i9W flow in the direction opposite to the direction indicated by the arrow shown by Figure 1 the polarity of the currents i9U, i9V, and i9W is assumed to be negative. Thus, in the case of the discharge operation of discharging from the resonance capacitors 9U, 9V, and 9W, the polarity of the currents i9U, i9V, and i9W is positive. On the other hand, in the case of the charging operation of charging the resonance capacitors 9U, 9V, and 9W, the polarity of the currents i9U, i9V, and i9W is negative.

[0075] The controller 50 sets a dead time period Td between the high-level periods of the control signals SU1, SV1, and SW1 for the first switching elements 1U, 1V, and 1W and the high-level periods of the control signals SU2, SV2, and SW2 for the second switching elements 2U, 2V, and 2W for each of the plurality of switching circuits 10.

[0076] Next, the basic operation of the controller 50 for performing zero-voltage soft switching of each of the plurality of first switching elements 1 and the plurality of second switching elements 2 will be described with reference to Figure 1 and Figures 3 to 9 After that, how the determination unit 54 operates will be described with reference to Figure 2 A of Figure 2 and B of

[0077] (3.1) Basic operation

[0078] When performing zero-voltage soft switching on the first switching element 1, it is necessary to reduce the voltage across the first switching element 1 to zero immediately before the first switching element 1, which is the object of zero-voltage soft switching, becomes conductive. When performing zero-voltage soft switching on the second switching element 2, it is necessary to reduce the voltage across the second switching element 2 to zero immediately before the second switching element 2, which is the object of zero-voltage soft switching, becomes conductive. In the following description, the switching element that is the object of zero-voltage soft switching (which is the first switching element 1 or the second switching element 2) will be referred to as the "object switching element" hereinafter.

[0079] The basic operation of the controller 50 changes according to the polarity of the load current flowing through the AC terminal 41 connected to the object switching element (i.e., positive or negative) and according to whether the resonant capacitor 9 connected in series or in parallel with the object switching element is performing a charging operation or a discharging operation. The load currents iU, iV, iW have a positive polarity when flowing from the AC terminal 41 toward the AC load RA1, and have 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 second switching elements among 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. Note that the basic operation of the controller 50 is performed by the control unit 51.

[0080] (3.1.1) Operation of performing soft switching of the first switching element when the load current > 0

[0081] If the object of soft switching is the first switching element 1 (hereinafter referred to as "object first switching element 1") and the polarity of the load current flowing through the AC terminal 41 connected to the object first switching element 1 is positive, the controller 50 turns on the first IGBT 6 corresponding to the object first switching element 1. In this way, the controller 50 causes the resonant inductor L1 and the resonant capacitor 9 connected to the object first switching element 1 to resonate, thereby charging the resonant capacitor 9 with the charge removed from the regeneration capacitor 15 and reducing the voltage across the object first switching element 1 to zero. This enables the power converter 100 to perform zero-voltage soft switching of the object first switching element 1.

[0082] In Figure 3 shows the control signals SU1, 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, in the case where the object first switching element is the first switching element 1U of the switching circuit 10U. Additionally, in Figure 3Also shown is 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 resonance inductor L1, the voltage V1u across the first switching element 1U, and the voltage V2u across the second switching element 2U. In addition, in Figure 3 Also shown are the control signals SV1 and SV2 to be respectively applied from the controller 50 to the first switching element 1V and the second switching element 2V of the switching circuit 10V in the case where the object first switching element is the first switching element 1V of the switching circuit 10V. Additionally, in Figure 3 Also shown is 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 resonance inductor L1, the voltage V1v across the first switching element 1V, and the voltage V2v across the second switching element 2V.

[0083] In addition, in Figure 3 Also shown is the dead time period Td set by the controller 50 to prevent the first switching element 1 and the second switching element 2 of the same phase from becoming conductive simultaneously. In addition, in Figure 3 Also shown are the additional time Tau set by the controller 50 for the control signal SU6 for the first IGBT 6U of the switch 8U and the additional time Tav set by the controller 50 for the control signal SV6 for the first IGBT 6V of the switch 8V. The additional time Tau and the additional time Tav will be described later.

[0084] In Figure 4 Also shown are the control signals SW1 and SW2 to be respectively applied from the controller 50 to the first switching element 1W and the second switching element 2W of the switching circuit 10W in the case where the object first switching element is the first switching element 1W of the switching circuit 10W. Additionally, in Figure 4 Also shown is the control signal SW6 to be applied from the controller 50 to the first IGBT 6W of the switch 8W and the load current iW of the W-phase flowing through the AC load RA1. In Figure 4 Also shown is the current iL1 flowing through the resonance inductor L1. In Figure 4 Also shown are the voltage V1w across the first switching element 1W and the voltage V2w across the second switching element 2W. In Figure 4 In, the voltage value of the DC power supply E1 is specified by Vd.

[0085] In addition, in Figure 4 Also shown is the dead time period Td set by the controller 50 to prevent the first switching element 1W and the second switching element 2W from becoming conductive simultaneously. In addition, in Figure 4Also shown is an additional time Taw set by the controller 50 for the control signal SW6 of the first IGBT 6W for the switch 8W. The additional time Taw will be described later.

[0086] As Figure 3 shown, the additional time Tau is an amount of time during which the controller 50 sets the start time t1 of the high-level period of the control signal SU6 to an earlier time point than the start time t2 of the dead time period Td (hereinafter also referred to as "start time t2") so that the high-level period of the control signal SU6 is longer than the dead time period Td. The length of the additional time Tau is determined by the value of the load current iU. In order to generate LC resonance starting from the start time t2 of the dead time period Td, it is preferable that the value of the current iL1 coincides with the value of the load current iU at the start time t2 of the dead time period Td. This is because as long as iL1 < iU, all of the current iL1 flows through the AC load RA1, and thus the resonance capacitor 9U cannot be charged. The end time of the high-level period of the control signal SU6 can be the same as or later than the time t3 (hereinafter referred to as "end time t3") at which the dead time period Td ends. In Figure 3 the example shown, the end time of the high-level period of the control signal SU6 is set to be the same as the end time t3 of the dead time period Td. The controller 50 sets the length of the high-level period of the control signal SU6 to Tau + Td. In the switching circuit 10U, the voltage V2u across the second switching element 2U becomes Vd at the end 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 3 the example shown, the current iL1 starts flowing through the resonance 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 an additional time Tau has elapsed since the end time t3 of the dead time period Td. Regarding the current iL1, starting from the start time t2 of the dead time period Td, the current iL1 satisfies iL1 ≥ iU, and thus the current iL1 in the shaded portion of the current waveform shown as the fifth waveform from the top of Figure 3 flows into the resonance capacitor 9U to generate LC resonance. Starting from the end time t3 of the dead time period Td, the current iL1 will be regenerated to the power conversion circuit 11 via the third diode 13 directly connected to the resonance inductor L1.

[0087] As described above, in order to start generating LC resonance at the start time t2 of the dead time period Td and end the resonance half cycle at the end time of the dead time period Td, the controller 50 determines an additional time Tau based on the load current iU such that iL1 = iU is satisfied at the start time t2 of the dead time period Td. More specifically, for example, using the detection result of the load current iU by the current sensor or its signal processing value, or the estimated value of the current iU, and the detection result of the inductance L of the resonance inductor L1 and the voltage V15 across the regenerative capacitor 15 that have been pre-stored, the controller 50 determines the additional time Tau by the formula Tau = iU × (L / V15). In this case, as the detection result of the load current iU or its signal processing value, for example, the detection value according to the carrier period plus the additional time Tau or the detection value at the timing closest to the carrier period can be used. Further, in this case, as the estimated value of the load current iU, for example, the value of the load current iU estimated according to the carrier period plus the additional time Tau can be used. The resonance half cycle is half of the resonance period, which is the reciprocal of the resonance frequency of a resonance circuit including a resonance inductor L1 and a resonance capacitor 9. The controller 50 sets the resonance half cycle so that the resonance half cycle is equal to or shorter than the dead time period Td (for example, as long as the length of the dead time period Td).

[0088] As Figure 3 shown, the additional time Tav is a time quantity where the controller 50 sets this time quantity to make the high-level period of the control signal SV6 longer than the dead time period Td by setting the start time t5 of the high-level period of the control signal SV6 to a time point earlier than the start time t6 of the dead time period Td (hereinafter referred to as "start time t6"). The length of the additional time Tav is determined by the value of the load current iV. In order to start generating LC resonance from the start time t6 of the dead time period Td, it is preferable that the value of the current iL1 is consistent 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 is satisfied, 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 (hereinafter referred to as "end time t7") of the dead time period Td. In Figure 3 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 length of 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 3In the example shown, the current iL1 starts flowing through the resonant inductor L1 at the start time t5 of the high-level period of the control signal SV6, and becomes zero at the time t8 which is at an additional time Tav after 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, so the current iL1 in the shaded part of the current waveform shown as the tenth waveform from the top of Figure 3 flows into the resonant 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 resonant inductor L1.

[0089] As described above, in order to start generating LC resonance at the start time t6 of the dead time period Td, the controller 50 determines the 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, and the detection result of the inductance L of the pre-stored resonant inductor L1 and the voltage V15 across the regeneration 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, for example, 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. In addition, 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.

[0090] As Figure 4 shown, the additional time Taw is a time amount where 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 (hereinafter referred to as "start time t10") when the dead time period Td starts. The length of the additional time Taw is determined by the value of the load current iW. In order to start generating LC resonance from the start time t10 of the dead time period Td, it is preferable that the value of the current iL1 is consistent 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, all of the current iL1 flows through the AC load RA1, so the resonant 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 time t11 (hereinafter referred to as "end time t11") when the dead time period Td ends. In Figure 4In the example shown, the end time of the high-level period of the control signal SW6 is set to be simultaneous with the end time t11 of the dead time period Td. The controller 50 sets the length of 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. At Figure 4 In 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 which is after the additional time Taw from 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, the current iL1 satisfies iL1 ≥ iW, so from Figure 4 the top, the current iL1 in the shaded part of the current waveform shown as the fourth waveform flows into the resonance capacitor 9W to generate LC resonance. From the end time t11 of the dead time period Td, the current iL1 will be regenerated to the power conversion circuit 11 via the third diode 13 directly connected to the resonance inductor L1.

[0091] The controller 50 determines the additional time Taw based on the load current iW. More specifically, for example, using the detection result of the load current iW by the current sensor, the inductance L of the resonance inductor L1 pre-stored, and the detection result of the voltage V15 across the regeneration capacitor 15, the controller 50 determines the additional time Taw by the formula Taw = iW × (L / V15). In this case, as the detection result of the load current iW or its signal processing value, for example, the detection value according to the carrier period plus the additional time Taw or the detection value according to the timing closest to the carrier period can be used. In addition, in this case, as the estimated value of the load current iW, for example, the value of the load current iw estimated according to the carrier period plus the additional time Taw can be used.

[0092] (3.1.2) Operation of soft-switching the second switching element when the load current > 0

[0093] If the object of soft-switching is the second switching element 2 (hereinafter referred to as "object second switching element 2"), and the polarity of the load current (which is the load current iU, load current iV or load current iW) flowing through the AC terminal 41 connected to the object second switching element 2 is positive, then the controller 50 compares the current value of the load current with the first current threshold I1 (= Ith, reference Figure 6)Compare. 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 within 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 discharge the resonant capacitor 9U connected in parallel with the target second switching element 2 using the load current iU without turning on the switch 8 corresponding to the target second switching element 2. This enables the power converter 100 to perform zero-voltage soft switching of the target second switching element 2.

[0094] In Figure 7 , for the case where the target second switching element 2 is the second switching element 2U of the switching circuit 10U and the current value of the load current iU is greater than the first current threshold I1, the control signals SU1, SU2, 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. Additionally, in Figure 7 , the dead time period Td and the additional time Tau set by the controller 50 for the control signal SU7 for the second IGBT 7U of the switch 8U are also shown.

[0095] 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 time period for the control signal SU7. In this case, in the power converter 100, the current i9U starts to flow from the resonant capacitor 9U at the start time t22 of the dead time period Td, the current i9U decreases to zero before the end time t23 of the dead time period Td, and 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 low level to high level at the end time t23 of the dead time period Td, zero-voltage soft switching of the second switching element 2U is performed.

[0096] If the current value of the load current iU is less than the first current threshold I1, for example, as shown by Figure 7The double-dot chain line in [Fig. 0] 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 can be, for example, simultaneous with the start time t22 of the dead time period Td. In addition, the end time of the high-level period of the control signal SU7 is simultaneous with the end time t23 of the dead time period Td. Thus, in the power converter 100, before the end time t23 of the dead time period Td, the voltage V2u across the second switching element 2U becomes zero. As a result, in the power converter 100, when the control signal SU2 changes from low level to 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 can be the time t21 that is earlier than the start time t22 of the dead time period Td by an additional time Tau. The end time of the high-level period of the control signal SU7 can be the time t24 that 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 of the control signal SU7 overlaps with the dead time period Td does not necessarily have to be the additional time Tau, but can also be any other preset time.

[0097] (3.1.3) Operation of soft-switching the second switching element when the load current < 0

[0098] If the polarity of the load current (which is the load current iU, load current iV, or load current iW) flowing through the AC terminal 41 connected to the target second switching element 2 is negative, the controller 50 turns on the second IGBT 7 corresponding to the target second switching element 2. In this way, the controller 50 causes the resonant capacitor 9 and the resonant inductor L1 connected to the target second switching element 2 to resonate, thereby discharging from the resonant capacitor 9 and reducing the voltage across the target second switching element 2 to zero. This enables the power converter 100 to perform zero-voltage soft switching of the target second switching element 2.

[0099] In Figure 8 , for the case where the target second switching element 2 is the second switching element 2U of the switching circuit 10U, the control signals SU1, SU2, SU7, the load current iU, the current iL1 flowing through the resonant inductor L1, and the voltage V2u across the second switching element 2U are shown.

[0100] In addition, in Figure 8 the dead time period Td set by the controller 50 to prevent the first switching element 1 and the second switching element 2 of the same phase from being turned on simultaneously is also shown. In addition, in Figure 8Also shown is an additional time Tau set by the controller 50 for the control signal SU7 of the second IGBT 7U for the switch 8U. The end time of the high-level period of the control signal SU7 can be the same as or later than the end time t33 of the dead time period Td. In Figure 8 the example shown, the end time of the high-level period of the control signal SU7 is set to be the same as the end time t33 of the dead time period Td. The controller 50 sets the length of 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. In Figure 8 the example shown, the current iL1 starts flowing through the resonant inductor L1 at the start time t31 of the high-level period of the control signal SU7 and becomes zero at the time t34 which is an additional time Tau after the end time t33 of the dead time period Td. Regarding the current iL1, starting from the start time t32 of the dead time period Td, the current iL1 satisfies iL1 ≤ iU, so LC resonance is generated such that the resonant current (i.e., the discharge current from the resonant capacitor 9U) flows from the resonant capacitor 9U towards the resonant inductor L1. Starting from the end time t33 of the dead time period Td, the current iL1 will be regenerated to the power conversion circuit 11 via the fourth diode 14 directly connected to the resonant inductor L1.

[0101] In order to start generating LC resonance at the start time t32 of the dead time period Td and end the resonant half-cycle at the end time t33 of the dead time period Td, the controller 50 determines the additional time Tau based on the load current iU such that iL1 = iU is satisfied at the start time t32 of the dead time period Td. More specifically, for example, using the detection result of the load current iU by the current sensor or its signal processing value, or the estimated value of the load current iU, and the detection result of the inductance L of the pre-stored resonant inductor L1 and the voltage V15 across the regeneration capacitor 15, the controller 50 determines the additional time Tau by the formula Tau = |iU| × (L / V15). In this case, as the detection result of the load current iU or its signal processing value, for example, the detection value according to the carrier period plus the additional time Tau or the detection value at the timing closest to the carrier period can be used. In addition, in this case, as the estimated value of the load current iU, for example, the value of the load current iU estimated according to the carrier period plus the additional time Tau can be used.

[0102] (3.1.4) Operation of soft-switching the first switching element when the load current < 0

[0103] 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 first switching element 1 of the object is negative, the controller 50 compares the current value of the load current with a second current threshold I2 (= -Ith, reference Figure 6 ). 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 within 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 charge the resonant capacitor 9U connected in series with the first switching element 1 of the object using the load current without having to turn on the switch 8 corresponding to the first switching element 1 of the object. This enables the power converter 100 to perform zero-voltage soft switching of the first switching element 1 of the object.

[0104] In Figure 9 , for the case where the first switching element 1 of the object is the first switching element 1U of the switching circuit 10U and the current value of the load current iU is greater than the second current threshold I2 (in other words, the absolute value of the current value of the load current iU is less than the absolute value of the second current threshold I2), the control signals SU1, SU2, 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. Additionally, the dead time period Td is also shown in Figure 9 .

[0105] If the current value of the load current iU is less than the second current threshold I2 (in other words, if the absolute value of the load current iU is greater than the absolute value of the second current threshold 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 starts flowing 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 to increase the voltage V2u across the second switching element 2U. 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 low level to high level at the end time t42 of the dead time period Td, zero-voltage soft switching of the first switching element 1 is performed.

[0106] If the current value of the load current iU is greater than the second current threshold I2 (in other words, if the absolute value of the load current iU is less than the absolute value of the second current threshold I2), then for example as shown by Figure 9The double-dot chain line in [description] 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 can be, for example, simultaneous with the start time t41 of the dead time period Td. In addition, the end time of the high-level period of the control signal SU6 is simultaneous with the end time t42 of the dead time period Td. Thus, in the power converter 100, the voltage V1u across the first switching element 1U becomes zero before the end time t42 of the dead time period Td. As a result, in the power converter 100, when the control signal SU1 changes from low level to 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.

[0107] (3.2) Operation of the determination unit

[0108] In the controller 50, even when the control unit 51 is performing the above-described basic operation, the determination unit 54 is operating.

[0109] In Figure 2 A of Figure 2 and B of Figure 2 A of Figure 2 and B of Figure 2 for example, the load current iU, the load current iV, the load current iW, and the voltage V15 across the regenerative capacitor 15 are shown to illustrate how the determination unit 54 operates when a fault has occurred in the U-phase switch 8U. Note that in Figure 2 A of Figure 2 and B of

[0110] In the following description, reference will be made to Figure 2 B of FIG. 3 to describe how the determination unit 54 operates in the case where a failure has occurred in the U-phase switch 8U. It should be understood that the determination unit 54 operates in the same manner even in the case where a failure has occurred in the V-phase switch 8V and in the case where a failure has occurred in the W-phase switch 8W.

[0111] As described above, the determination unit 54 determines the switching state in the power conversion circuit 11 based on the ripple voltage included in the voltage V15 across the regenerative capacitor 15 and the plurality of load currents iU, iV, iW supplied from the plurality of AC terminals 41. The switching state in the power conversion circuit 11 includes the switching states of the respective switching elements among the plurality of first switching elements 1 and the plurality of second switching elements 2.

[0112] If a predetermined condition (hereinafter referred to as "first predetermined condition") is satisfied, the determination unit 54 determines that a hard switching has occurred in the power conversion circuit 11. As used herein, the expression "a hard switching has occurred in the power conversion circuit 11" means that a hard switching has occurred in at least one of the plurality of first switching elements 1 and the plurality of second switching elements 2. The first predetermined condition is as follows: the number of intersection points B1 between any two of the plurality of load currents iU, iV, iW during a specified period Ts is greater than a predefined value (for example, two). The specified period Ts is a period between the first generation timing tg1 of the first peak P1 of the ripple voltage and the second generation timing tg2 of the second peak P2 of the ripple voltage. In the first embodiment, as Figure 2 shown in FIG. 3A and Figure 2 FIG. 3B, the first peak P1 is a maximum peak at which the ripple voltage reaches the maximum value Vmax, and the second peak P2 is another maximum peak at which the ripple voltage reaches the maximum value Vmax after the first peak P1 (for example, in the first embodiment, the second peak P2 immediately follows the first peak P1). That is, the first peak P1 is one of the plurality of maximum peaks at which the ripple voltage reaches the maximum value Vmax, and the second peak P2 is one of the plurality of maximum peaks that immediately follows the one maximum peak. In this case, the specified period Ts is as long as one period of the ripple voltage. At each intersection point B1, the two load currents have the same polarity and the same magnitude.

[0113] In Figure 2 FIG. 3A, the number of intersection points B1 during the specified period Ts is 2. On the other hand, in Figure 2 FIG. 3B, the number of intersection points B1 during the specified period Ts is 7, which is greater than 2.

[0114] The determination unit 54 can, for example, reset the value of the variable to zero, increment the value of the variable by 1 each time the intersection point B1 is detected, and decrement the value of the variable by 2 each time the maximum peak is detected. If the intersection point B1 and the maximum peak are detected at the same timing, the value of the variable is +1 - 2 = -1. If the value of the variable becomes negative, the determination unit 54 resets the value of the variable to zero. Thus, if each of the three switches 8U, 8V, and 8W is operating normally, the determination unit 54 sets the value of the variable to a value equal to or less than 2. On the other hand, for example, if the switch 8U has caused a failure, the determination unit 54 sets the value of the variable to 4 which is greater than 2.

[0115] The second peak P2 used by the determination unit 54 to set the first predetermined condition only needs to be a maximum peak at which the ripple voltage reaches the maximum value Vmax after the first peak P1. Thus, the second peak P2 can be, for example, a maximum peak at which the ripple voltage reaches the maximum value Vmax and is the second one immediately after the first peak P1. In this case, the specified period Ts is twice as long as one period of the ripple voltage, and the specified value used in the determination unit 54 can be a value twice as large as the value in the case where the specified period Ts is as long as one period of the ripple voltage. That is to say, the specified value can be 4 (= 2 multiplied by 2). Alternatively, the second peak P2 used by the determination unit 54 to set the first predetermined condition can be, for example, a maximum peak at which the ripple voltage reaches the maximum value Vmax and is the third one immediately after the first peak P1. In this case, the specified period Ts is three times as long as one period of the ripple voltage, and the specified value used in the determination unit 54 can be a value three times as large as the value in the case where the specified period Ts is as long as one period of the ripple voltage. That is to say, the specified value can be 6 (= 2 multiplied by 3). In short, the specified value used in the determination unit 54 can be appropriately determined according to the length of the specified period Ts. More generally, if the specified period Ts is as long as n periods of the ripple voltage (where n is a natural number), the specified value can be n × 2.

[0116] To determine whether the first predetermined condition is satisfied, the determination unit 54 uses a moving average as a signal processing value representing the detection results of the respective load currents iU, iV, iW and the voltage V15 across the regenerative capacitor 15. Unless each period for obtaining the moving average is exactly the same length as one cycle of the change in the respective load currents iU, iV, iW and the voltage V15 across the regenerative capacitor 15, this period can be set arbitrarily. This reduces the possibility that the determination made by the determination unit 54 is affected by noise included in the respective detection values of the load currents iU, iV, iW and the voltage V15 across the regenerative capacitor 15, thereby contributing to improving the accuracy of the determination. That is to say, the determination unit 54 can improve the detection accuracy of the first peak P1, the second peak P2 and each intersection point B1, and can more accurately determine whether hard switching has occurred in the power conversion circuit 11.

[0117] In the power converter 100, if the determination unit 54 determines that hard switching has occurred in the power conversion circuit 11, the controller 50 deactivates the power conversion circuit 11.

[0118] If a predetermined condition (hereinafter referred to as "second predetermined condition") is satisfied, the determination unit 54 can determine that each switching element among the plurality of first switching elements 1 and the plurality of second switching elements 2 has been soft-switched. As used herein, if each switching element among the plurality of first switching elements 1 and the plurality of second switching elements 2 has been soft-switched, then in other words, this means that hard switching has not occurred in the power conversion circuit 11. The second predetermined condition is as follows: the number of intersection points B1 between any two of the plurality of load currents iU, iV, iW during a specified period Ts is equal to or less than a predefined value. The specified period Ts is the period between the first generation timing tg1 of the first peak of the ripple voltage and the second generation timing tg2 of the second peak P2 of the ripple voltage.

[0119] If the determination unit 54 has determined that hard switching has occurred in the power conversion circuit 11, the controller 50 deactivates the power conversion circuit 11. In the controller 50, the control unit 51 deactivates the power conversion circuit 11 according to the determination made by the determination unit 54. To deactivate the power conversion circuit 11, the control unit 51 can, for example, cause each of the control signals SU1, SV1, SW1, SU2, SV2, SW2 to drop to a low level, or stop outputting the control signals SU1, SV1, SW1, SU2, SV2, SW2.

[0120] (4) Summary

[0121] In the power converter 100 according to the first embodiment, the controller 50 includes a determination unit 54 that determines the switching state in the power conversion circuit 11 based on the ripple voltage included in the voltage V15 across the regenerative capacitor 15 and the plurality of load currents iU, iV, iW supplied from the plurality of AC terminals 41.

[0122] The power converter 100 according to the first embodiment can detect the switching state in the power conversion circuit 11.

[0123] In addition, compared with the case where six voltage sensors are provided to detect the voltages across each of the three first switching elements 1 and the three second switching elements 2 in the power conversion circuit 11, the power converter 100 according to the first embodiment can not only reduce costs by reducing the number of required components, but also reduce the number of input ports required for the computer system (processor) of the controller 50.

[0124] Furthermore, in the power converter 100 according to the first embodiment, if a first predetermined condition is satisfied, the determination unit 54 determines that a hard switching has occurred in the power conversion circuit 11. The predetermined condition is as follows: the number of intersection points B1 between any two of the plurality of load currents iU, iV, iW during a specified period Ts is greater than a predefined value. The specified period Ts is the period between the first generation timing tg1 of the first peak P1 of the ripple voltage and the second generation timing tg2 of the second peak P2 of the ripple voltage. Thus, if a hard switching has occurred in at least one of the plurality of first switching elements 1 and the plurality of second switching elements 2, the power converter 100 according to the first embodiment can detect that a hard switching has occurred in the power conversion circuit 11.

[0125] Moreover, in the power converter 100 according to the first embodiment, when the determination unit 54 determines that a hard switching has occurred in the power conversion circuit 11, the controller 50 deactivates the power conversion circuit 11. This enables the power converter 100 to reduce the temperature rise of the power conversion circuit 11 caused by the hard switching in the power conversion circuit 11.

[0126] In addition, in the power converter 100 according to the first embodiment, when a predetermined condition is satisfied, the determination unit 54 determines that each of the plurality of first switching elements 1 and the plurality of second switching elements 2 has been soft-switched. The predetermined condition is as follows: the number of intersection points B1 between any two of the plurality of load currents iU, iV, and iW during a specified period Ts is equal to or less than a predefined value. The specified period Ts is the period between the first generation timing tg1 of the first peak P1 of the ripple voltage and the second generation timing tg2 of the second peak P2 of the ripple voltage. Thus, the power converter 100 according to the first embodiment can detect that each of the plurality of first switching elements 1 and the plurality of second switching elements 2 has been soft-switched.

[0127] (5) Variation of the First Embodiment

[0128] (5.1) First Variation

[0129] The power converter 100 according to the first variation of the first embodiment has the same configuration as the power converter 100 according to the first embodiment, and thus its illustration and description will be omitted herein.

[0130] The first peak P1 and the second peak P2 used in the determination unit 54 according to the first variation are different from the first peak P1 and the second peak P2 used in the determination unit 54 according to the first embodiment.

[0131] Reference will be made to Figure 10 A of Figure 10 and B of

[0132] The first peak P1 used in the determination unit 54 according to the first variation is a minimum peak at which the ripple voltage included in the voltage V15 across the regenerative capacitor 15 reaches the minimum value Vmin. The second peak P2 used in the determination unit 54 according to the first variation is another minimum peak at which the ripple voltage reaches the minimum value Vmin after the first peak P1. In the examples shown in Figure 10 A of Figure 10 and B of

[0133] (5.2) Second Variation

[0134] The power converter 100 according to the second modification of the first embodiment has the same configuration as the power converter 100 according to the first embodiment, and thus its illustration and description will be omitted herein.

[0135] The first peak P1 and the second peak P2 used in combination in the determination unit 54 according to the second modification are different from the first peak P1 and the second peak P2 used in combination in the determination unit 54 according to the first embodiment.

[0136] Reference will be made to Figure 11 A of Figure 11 B of

[0137] The first peak P1 used in the determination unit 54 according to the second modification is a maximum peak at which the ripple voltage included in the voltage V15 across the regenerative capacitor 15 reaches the maximum value Vmax. The second peak P2 is a minimum peak at which the ripple voltage reaches the minimum value Vmin after the first peak P1. In the example shown in Figure 11 A of Figure 11 B of

[0138] The second peak P2 is the minimum peak immediately following the first peak P1, and thus the specified period Ts is half a cycle of the ripple voltage and the predefined value is 1. Note that in the second modification, the specified period Ts does not necessarily have to be half a cycle of the ripple voltage, and for example, it can also be two-thirds or two-fifths of a cycle of the ripple voltage. The predefined value can be determined according to the length of the specified period Ts. That is, if the specified period Ts is as long as two-nths of a cycle of the ripple voltage (where n is a natural number), the predefined value can be n×1.

[0139] (Second Embodiment)

[0140] Reference will be made to Figure 12 to describe the power converter 100A according to the second embodiment. In the following description, any constituent element in the power converter 100B according to the second embodiment that has the same function as the corresponding part of the power converter 100 according to the first embodiment described above will be designated by the same reference numeral as that corresponding part, and its description will be omitted herein.

[0141] The power converter 100A according to the second embodiment further includes another regenerative capacitor 16 (hereinafter referred to as "second regenerative capacitor 16") connected between the sixth terminal 154 of the regenerative capacitor 15 (hereinafter referred to as "first regenerative capacitor 15") and the first DC terminal 31, which is different from the power converter 100 according to the first embodiment described above.

[0142] The second regenerative capacitor 16 is connected in series to the first regenerative capacitor 15. Thus, in this power converter 100A, the series circuit of the second regenerative capacitor 16 and the first regenerative capacitor 15 is connected between the first DC terminal 31 and the second DC terminal 32. The capacitance of the second regenerative capacitor 16 is the same as the capacitance of the first regenerative capacitor 15. As used herein, the expression "the capacitance of the second regenerative capacitor 16 is the same as the capacitance of the first regenerative capacitor 15" not only refers to the case where the capacitance of the second regenerative capacitor 16 is exactly equal to the capacitance of the first regenerative capacitor 15, but also includes the case where the capacitance of the second regenerative capacitor 16 is equal to or greater than 95% and equal to or less than 105% of the capacitance of the first regenerative capacitor 15.

[0143] In the power converter 100A according to the second embodiment, the voltage V15 across the first regenerative capacitor 15 (i.e., the potential at the sixth terminal 154 of the first 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 second regenerative capacitor 16 and the first regenerative capacitor 15). Thus, the voltage V15 across the first regenerative capacitor 15 is approximately equal to Vd / 2 while changing transiently, but includes a ripple voltage caused by the resonant currents of the U-phase, V-phase, and W-phase.

[0144] The controller 50 of the power converter 100A according to the second embodiment operates in the same manner as the controller 50 of the power converter 100 according to the first embodiment. Thus, the power converter 100A according to the second embodiment can detect the switching state in the power conversion circuit 11 in the same way as the power converter 100 according to the first embodiment.

[0145] (Third Embodiment)

[0146] Reference will be made to Figure 13 to describe the power converter 100B according to the third embodiment. In the following description, any component in the power converter 100B according to the third embodiment that has the same function as the corresponding part of the power converter 100 according to the first embodiment described above will be designated by the same reference numeral as that corresponding part, and its description will be omitted herein.

[0147] (1) Configuration

[0148] The power converter 100B includes only one resonant inductor L1, which is different from the power converter 100 according to the first embodiment. In the power converter 100B, the resonant inductor L1 is commonly shared by a plurality of resonant circuits. In the power converter 100B, the third end of the resonant inductor L1 is connected to the common connection node 25. The second ends 82 of the plurality of switches 8 are commonly connected to the common connection node 25.

[0149] In the power converter 100B, the third end of the resonant inductor L1 is connected to the common connection node 25. The second ends 82 of the plurality of switches 8 are commonly connected to the common connection node 25.

[0150] In addition, the power converter 100B includes only one protection circuit 17, which is another difference from the power converter 100 according to the first embodiment.

[0151] In the power converter 100B, the third diode 13 of the protection circuit 17 is connected between the common connection node 25 and the first DC terminal 31. In the third diode 13, the anode of the third diode 13 is connected to the common connection node 25. In the third diode 13, the cathode of the third diode 13 is connected to the first DC terminal 31. The fourth diode 14 of the protection circuit 17 is connected between the common connection node 25 and the second DC terminal 32. In the fourth diode 14, the anode of the fourth diode 14 is connected to the second DC terminal 32. In the fourth diode 14, the cathode of the fourth diode 14 is connected to the common connection node 25. Thus, the fourth diode 14 is connected in series with the third diode 13.

[0152] (2) Operation of the power converter

[0153] In the power converter 100B, as in the power converter 100, the controller 50 also controls a plurality of (e.g., three) first switching elements 1, a plurality of (e.g., three) second switching elements 2, and a plurality of (e.g., three) switches 8. The controller 50 (control unit 51 thereof) performs a basic operation and a shift control operation.

[0154] (2.1) Basic operation

[0155] The basic operation performed by the controller 50 is the same as the operation performed by the controller 50 in the power converter 100 according to the first embodiment. The basic operation is an operation performed when the resonant currents respectively flowing through two or more switches 8 belonging to the plurality of switches 8 do not flow through the resonant inductor L1 at the same time.

[0156] (2.2) Shift control operation

[0157] The shift control operation is an operation performed when the controller 50 determines that the resonance currents respectively passing through two or more than two switches 8 belonging to a plurality of switches 8 flow simultaneously.

[0158] When it is determined that the resonance currents respectively passing through two switches 8 belonging to a plurality of switches 8 flow through the resonance inductor L1 simultaneously, the controller 50 performs a shift control operation for shifting the high-level period of the control signal for one of the two switches 8 to prevent the resonance currents respectively passing through the two switches 8 from flowing through the resonance inductor L1 simultaneously. As used herein, the expression "when it is determined that the resonance currents respectively passing through two switches 8 belonging to a plurality of switches 8 flow through simultaneously" means that it has been previously presumed that the resonance currents respectively passing through the two switches 8 will flow through the resonance inductor L1 simultaneously.

[0159] (2.2.1) Determine whether two-phase resonance currents flow simultaneously

[0160] In the power converter 100B, the phases of the three-phase (i.e., U-phase, V-phase, and W-phase) voltage commands are 120 degrees apart from each other, but the command values of the two-phase voltage commands are close to each other every 60 degrees of electrical angle, and the duty ratios of the two-phase control signals are close to each other (refer to Figure 5 the shown regions A1, A2). Specifically, in Figure 5 the shown region A1, the duty ratios of the U-phase control signal and the V-phase control signal become around 0.75. In Figure 5 the shown region A2, the duty ratios of the U-phase control signal and the V-phase control signal become around 0.25. The polarity of the resonance current is the same as the polarity of the current iL1. In region A1, the polarity of the resonance current is positive. In region A2, the polarity of the resonance current is negative. In region A1, the start time t1 (refer to Figure 3 ) of the high-level period of the control signal SU6 to be applied to the first IGBT 6U and the start time t5 (refer to Figure 3 ) of the high-level period of the control signal SV6 to be applied to the first IGBT 6V have such a short time lag within one cycle time of the carrier signal that the U-phase resonance current and the V-phase resonance current may flow through the resonance inductor L1 simultaneously. In the power converter 100B, the direction of the resonance current in region A2 is opposite to the direction of the resonance current in region A1, but the U-phase resonance current and the V-phase resonance current may flow through the resonance inductor L1 simultaneously.

[0161] Assuming that the capacitance of each of the plurality of resonant capacitors 9U, 9U, and 9W is Cr, if the U-phase current and the V-phase current flow through the resonant inductor L1 simultaneously, then in the equivalent circuit, a capacitor having a combined capacitance (= 2×Cr) of the resonant capacitor 9U and the resonant capacitor 9V is connected in series to the resonant inductor L1. Thus, in the power converter 100B, if two-phase currents flow through the resonant inductor L1 simultaneously, the resonant frequency of the resonant circuit including the resonant inductor L1 changes compared to the case where a single-phase current flows through the resonant inductor L1. As a result, the power converter 100B may not be able to perform zero-voltage soft switching.

[0162] (2.2.2) Case of charging the resonant capacitor

[0163] Reference will be made Figure 3 to illustrate exemplary boundary conditions between a case where the U-phase resonant current and the V-phase resonant current do not overlap (i.e., do not flow simultaneously) and a case where the U-phase resonant current and the V-phase resonant current overlap (i.e., flow simultaneously).

[0164] In the power converter 100B (reference Figure 13 ), if the time lag ΔTuv between the start time t3 of the high-level period of the control signal SU1 (hereinafter referred to as "start time t3") and the start time t7 of the high-level period of the control signal SV1 (hereinafter referred to as "start time t7") is equal to or greater than (Tau + Tav + Td), then the U-phase resonant current and the V-phase resonant current do not overlap. On the other hand, if the time lag ΔTuv is less than (Tau + Tav + Td), then the U-phase resonant current and the V-phase resonant current overlap. That is, in the case where the threshold for the time lag ΔTuv is set to (Tau + Tav + Td), if the time lag ΔTuv is less than the threshold, the controller 50 presumes that the resonant currents corresponding to the two phases belonging to the switching circuits 10U and 10V of the plurality of switching circuits 10 will flow through the resonant inductor L1 simultaneously. Note that this threshold is merely an example, and the threshold can also be set to any other value. For example, in consideration of the error of the additional time Tau and the error of the additional time Tav, the threshold can also be set to a value even larger than (Tau + Tav + Td). In addition, the above method for calculating the time lag ΔTuv to determine whether two-phase resonant currents flow simultaneously is merely an example and should not be construed as restrictive. Instead, any other calculation method can be adopted as long as the time lag corresponding to the above time lag can be calculated. For example, as the time lag ΔTuv for determining whether two-phase resonant currents flow simultaneously, the time lag between the end time t2 of the high-level period of the control signal SU2 (hereinafter referred to as "end time t2") and the end time t6 of the high-level period of the control signal SV2 (hereinafter referred to as "end time t6") can also be used.

[0165] In the power converter 100B, if the time lag between the start time t3 of the high-level period of the control signal SU1 and the start time t11 (hereinafter referred to as "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 to say, in the case where 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 presumes that the resonant currents corresponding to the two phases of the switching circuits 10U and 10W belonging to the plurality of switching circuits 10 will flow through the resonant inductor L1 simultaneously. Note that this threshold value is only an example, and the threshold value can also be set to any other value. For example, in consideration of the error of the additional time Tau and the error of the additional time Taw, the threshold value can also be set to a value even larger than (Tau + Taw + Td). In addition, the above method for calculating the time lag to determine whether the two-phase resonant currents flow simultaneously is only an example and should not be construed as restrictive. On the contrary, any other calculation method can also be adopted as long as the time lag corresponding to the above 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 (hereinafter referred to as "end time t10") of the high-level period of the control signal SW2 can also be used.

[0166] In the power converter 100B, 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 to say, in the case where the threshold value for this time lag is set to (Tav + Taw + Td), if the time lag is less than the threshold value, the controller 50 presumes 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 simultaneously. Note that this threshold value is only an example, and the threshold value can also be set to any other value. For example, in consideration of 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 larger than (Tav + Taw + Td). In addition, the above method for calculating the time lag to determine whether the two-phase resonant currents flow simultaneously is only an example and should not be construed as restrictive. On the contrary, any other calculation method can also be adopted as long as the time lag corresponding to the above 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 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.

[0167] (2.2.3) Case of discharging the resonant capacitor

[0168] When discharging the resonant capacitor 9, the controller 50 can also use the same time lag and threshold value as in the case of charging the resonant capacitor 9 to determine whether the two-phase resonant currents flow simultaneously.

[0169] 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 the threshold value (for example, Tau + Tav + Td), the controller 50 presumes that the U-phase resonant current and the V-phase resonant current will overlap with each other.

[0170] 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 presumes that the U-phase resonant current and the W-phase resonant current will overlap with each other.

[0171] Further, if the time lag between the start time of the high-level period of the control signal SV2 and the start time of the high-level period of the control signal SW2 is less than a threshold value (e.g., Tav + Taw + Td), the controller 50 presumes that the V-phase resonant current and the W-phase resonant current will overlap each other.

[0172] (2.2.4) Shift control to be performed when it is determined that two-phase resonant currents flow simultaneously

[0173] For example, in order to prevent the resonant currents respectively passing through the two switches 8 from flowing through the resonant inductor L1 simultaneously, the controller 50 performs shift control including shifting the high-level period of the control signal for one of the two switches 8.

[0174] When performing the shift control, the controller 50 shifts the high-level period of the control signal for one of the two switches 8 to prevent the length of the high-level period of the control signal to be respectively applied to the first switching element 1 and the second switching element 2 of one switching circuit 10 corresponding to the one switch 8 from changing. For example, when shifting the high-level period of the control signal SU6 or SU7 to be applied to the switch 8U, the controller 50 shifts the high-level periods of the control signals SU1 and SU2 respectively, but does not change the duty ratio of each of the control signals SU1 and SU2 in one period of the carrier signal. Similarly, for example, when shifting the high-level period of the control signal SV6 or SV7 to be applied to the switch 8V, the controller 50 shifts the high-level periods of the control signals SV1 and SV2 respectively, but does not change the duty ratio of each of the control signals SV1 and SV2 in one period of the carrier signal. In the same manner, for example, when shifting the high-level period of the control signal SW6 or SW7 to be applied to the switch 8W, the controller 50 shifts the high-level periods of the control signals SW1 and SW2 respectively, but does not change the duty ratio of each of the control signals SW1 and SW2 in one period of the carrier signal.

[0175] In the power converter 100B, if the controller 50 has performed shift control for soft switching of the first switching element 1, for example, at the moment when each of the control signals in the control signals SU1 and SV1 changes from the low-level period to the high-level period (i.e., at the end of the dead time period Td corresponding to each of the U phase and the V phase), the voltages V2u and V2v across the second switching elements 2U and 2V increase to Vd respectively. That is to say, if the controller 50 has performed shift control, at the end of the dead time period Td corresponding to each of the U phase and the V phase, the charging of the resonant capacitors 9U and 9V is completed. Thus, in the power converter 100B, if the controller 50 has performed shift control, the first switching elements 1U and 1V are switched by zero-voltage soft switching.

[0176] In the above example, an exemplary shift control to be performed by the controller 50 has been described in the case where the controller 50 has previously estimated 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 restrictive. For example, even in the case where the controller 50 has previously estimated that the V-phase resonant current and the W-phase resonant current will flow through the resonant inductor L1 simultaneously, or in the case where the controller 50 has previously estimated 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 causing the controller 50 to perform shift control.

[0177] In the power converter 100B, if the controller 50 has performed shift control to perform soft switching of the second switching element 2, then for example, at the moment when each of the control signals in the control signals SU2 and SV2 changes from the low-level period to the high-level period (i.e., at the end of the dead time period Td corresponding to each of the U-phase and the V-phase), each of the voltages V1u and V1v across the first switching elements 1U and 1V increases to Vd. That is to say, if the controller 50 has performed shift control, then at the end of the dead time period Td corresponding to each of the U-phase and the V-phase, the discharge of the resonant capacitors 9U and 9V is completed. Thus, in the power converter 100B, if the controller 50 has performed shift control, then the second switching elements 2U and 2V are switched by zero-voltage soft switching.

[0178] In the above example, an exemplary shift control to be performed by the controller 50 has been described in the case where the controller 50 has previously estimated 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 restrictive. For example, even in the case where the controller 50 has previously estimated that the V-phase resonant current and the W-phase resonant current will flow through the resonant inductor L1 simultaneously, or in the case where the controller 50 has previously estimated 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 causing the controller 50 to execute shift control.

[0179] (2.3) Operation of the determination unit

[0180] The determination unit 54 operates in the same manner as the determination unit 54 of the controller 50 in the power converter 100 according to the first embodiment described above. Thus, the determination unit 54 determines the switching state in the power conversion circuit 11 based on the ripple voltage included in the voltage V15 across the regenerative capacitor 15 and the plurality of load currents iU, iV, and iW supplied from the plurality of AC terminals 41.

[0181] (3) Summary

[0182] The power converter 100B according to the third embodiment includes a determination unit 54 that determines the switching state in the power conversion circuit 11 based on the ripple voltage included in the voltage V15 across the regeneration capacitor 15 and the plurality of load currents iU, iV, iW supplied from the plurality of AC terminals 41. Thus, the power converter 100B according to the third embodiment can detect the switching state in the power conversion circuit 11.

[0183] In addition, in the power converter 100B according to the third embodiment, the number of the provided resonance inductors L1 is one, and the second ends 82 of the plurality of switches 8 are commonly connected to a single resonance inductor L1. Thus, the power converter 100B according to the third embodiment can contribute to reducing the number of required components and miniaturization.

[0184] Furthermore, in the power converter 100B according to the third embodiment, when it is determined that the resonance currents respectively passing through two switches 8 belonging to the plurality of switches 8 flow through the single resonance inductor L1 simultaneously, the controller 50 performs control to shift the high-level periods of the control signals for each of the two switches 8 to prevent the resonance currents respectively passing through the two switches 8 from flowing through the single resonance inductor L1 simultaneously. This enables the power converter 100B according to the third embodiment to perform soft switching more reliably.

[0185] (4) Variation of the Third Embodiment

[0186] (4.1) First Variation

[0187] Reference will be made to Figure 14 to describe the power converter 100B according to the first variation. In the following description, any component in the power converter 100B according to the first variation that has the same function as the corresponding part of the power converter 100B according to the above third embodiment will be designated by the same reference numeral as that corresponding part, and its description will be omitted herein.

[0188] In the power converter 100B according to the first variation, in each of the plurality of switches 8, its first IGBT 6 and second IGBT 7 are connected in anti-series. In the power converter 100B according to the first variation, in each of the plurality of switches 8, the collector terminals of the first IGBT 6 and 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 among 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.

[0189] In the power converter 100B according to the first modification example, 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 14 the shown diodes 61 and 71 can each be replaced with, for example, a parasitic diode of a replacement element or an element built in one chip of the replacement element. Further, in the power converter 100B according to the first modification example, the diodes 61 and 71 do not necessarily have to be provided as external elements for the first IGBT 6 and the second IGBT 7, respectively, and may also be elements built in one chip.

[0190] The controller 50 can operate in the same manner as, for example, the controller 50 according to the third embodiment.

[0191] (4.2) Second modification example

[0192] Reference will be made to Figure 15 to describe the power converter 100B according to the second modification example. In the following description, any constituent elements in the power converter 100B according to the second modification example that have the same functions as the corresponding parts of the power converter 100B according to the third embodiment described above will be designated by the same reference numerals as those of the corresponding parts, and the description thereof will be omitted herein.

[0193] In the power converter 100B according to the second modification example, 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 100B according to the second modification example, in each of the plurality of switches 8, the emitter terminals of the first IGBT 6 and the second IGBT 7 are connected to each other, the collector terminal of the first IGBT 6 is connected to the common connection node 25, and 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. Further, each of the plurality of switches 8 also 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.

[0194] In the power converter 100B according to the second modification example, 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 15The shown diodes 61 and 71 can each be replaced by, for example, parasitic diodes of replacement elements or elements built in one chip of the replacement elements. Further, in the power converter 100B according to the second modification example, the diodes 61 and 71 do not necessarily have to be externally provided elements for the first IGBT 6 and the second IGBT 7, respectively, but may also be elements built in one chip.

[0195] The controller 50 can operate in the same manner as, for example, the controller 50 according to the third embodiment.

[0196] (4.3) Third modification example

[0197] will be described with reference to Figure 16 the power converter 100B according to the third modification example. In the following description, any constituent element having the same function as the corresponding part of the power converter 100B according to the third embodiment described above in the power converter 100B according to the third modification example will be designated by the same reference numeral as that of the corresponding part, and its description will be omitted herein.

[0198] In the power converter 100B according to the third modification example, 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 100B according to the third modification example, in each of the plurality of switches 8, the drain terminals of the first MOSFET 6A and the second MOSFET 7A are connected to each other. Further, each of the plurality of switches 8 further includes a diode 61 connected in anti - parallel to the first MOSFET 6A and a diode 71 connected in anti - parallel to the second MOSFET 7A. In each of the plurality of switches 8, the source terminal of the second MOSFET 7A is connected to the common connection node 25. In each of the plurality of switches 8, the source terminal of the first MOSFET 6A is connected to the connection node 3 of the switching circuit 10 corresponding to the switch 8 including the first MOSFET 6A. The control signals SU6, SU7 are respectively applied from the controller 50 to the first MOSFET 6A and the second MOSFET 7A of the switch 8U. The control signals SV6, SV7 are respectively applied from the controller 50 to the first MOSFET 6A and the second MOSFET 7A of the switch 8V. The control signals SW6, SW7 are respectively applied from the controller 50 to the first MOSFET 6A and the second MOSFET 7A of the switch 8W.

[0199] The controller 50 can operate in the same manner as, for example, the controller 50 according to the third embodiment.

[0200] (4.4) Fourth modification example

[0201] will be described with reference to Figure 17 the power converter 100B according to the fourth modification example. In the following description, any component in the power converter 100B according to the fourth modification example that has the same function as the corresponding part of the power converter 100B according to the third embodiment described above will be designated by the same reference numeral as that corresponding part, and its description will be omitted herein.

[0202] In the power converter 100B according to the fourth modification example, in each of the plurality of switches 8, a diode 63 is connected in series to the first MOSFET 6A, and a diode 73 is connected in series to the second MOSFET 7A. In the power converter 100B according to the fourth modification example, the series circuit of the first MOSFET 6A and the diode 63 and the series circuit of the second MOSFET 7A and the diode 73 are connected in anti-parallel with each other.

[0203] The controller 50 can operate in the same manner as, for example, the controller 50 according to the third embodiment.

[0204] (4.5) Fifth modification example

[0205] will be described with reference to Figure 18 the power converter 100B according to the fifth modification example. In the following description, any component in the power converter 100B according to the fifth modification example that has the same function as the corresponding part of the power converter 100B according to the third embodiment described above will be designated by the same reference numeral as that corresponding part, and its description will be omitted herein.

[0206] In the power converter 100B according to the fifth modification example, each of the plurality of switches 8 includes: a MOSFET 80; a diode 83 that is connected in anti-parallel to the MOSFET 80; a series circuit of two diodes 84, 85 that is connected in anti-parallel to the MOSFET 80; and a series circuit of two diodes 86, 87 that is connected in anti-parallel to the MOSFET 80. In each of the plurality of switches 8, the connection node between the diodes 84, 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 among the plurality of switching circuits 10, and the connection node between the diodes 86, 87 (i.e., the second end 82 of the switch 8) is connected to the common connection node 25. In each switch 8, when the MOSFET 80 is turned on, the switch 8 is turned on. On the other hand, when the MOSFET 80 is turned off, the switch 8 is turned off.

[0207] 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.

[0208] In each of the switches 8, when its MOSFET 80 is turned on, a resonance current generated by a resonance circuit including the resonance inductor L1 and the resonance capacitor 9 flows through the switch 8. In the power converter 100B, during the charging operation of the resonance capacitor 9, when one of the plurality of switches 8 is turned on, a charging current including the resonance current flows along a path sequentially passing through the regeneration capacitor 15, the resonance inductor L1, the diode 86, the MOSFET 80, the diode 85, and the resonance capacitor 9. Further, in the power converter 100B, during the discharging operation of the resonance capacitor 9, when one of the plurality of switches 8 is turned on, a discharging current including the resonance current flows along a path sequentially passing through the resonance capacitor 9, the diode 84, the MOSFET 80, the diode 87, the resonance inductor L1, and the regeneration capacitor 15.

[0209] In the power converter 100B according to the fifth modification example, each of the plurality of MOSFETs 80 can be replaced with an IGBT. Further, in the power converter 100B according to the fifth modification example, each of the plurality of switches 8 can include, for example, a bipolar transistor or a GaN-based gate injection transistor (GIT) instead of the MOSFET 80.

[0210] The controller 50 can operate in the same manner as the controller 50 according to, for example, the third embodiment.

[0211] (4.6) Sixth modification example

[0212] Reference will be made to Figure 19 to describe the power converter 100B according to the sixth modification example. In the following description, any component of the power converter 100B according to the sixth modification example that has the same function as the corresponding part of the power converter 100B according to the third embodiment described above will be designated by the same reference numeral as that of the corresponding part, and its description will be omitted herein.

[0213] In the power converter 100B according to the sixth modification, each of the plurality of switches 8 is a dual-gate GaN-based GIT including a first source terminal, a first gate terminal, a second gate terminal, and a second source terminal. In the power converter 100B according to the sixth modification, a control signal SU6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT serving as the switch 8U, and a control signal SU7 is applied between the second gate terminal and the second source terminal thereof. In addition, a control signal SV6 is applied between the first gate terminal and the first source terminal of the dual-gate GaN-based GIT serving as the switch 8V, and a control signal SV7 is applied between the second gate terminal and the second source terminal thereof. Further, 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 the switch 8W, and a control signal SW7 is applied between the second gate terminal and the second source terminal thereof.

[0214] The controller 50 can operate in the same manner as the controller 50 according to, for example, the third embodiment.

[0215] (Fourth Embodiment)

[0216] Reference will be made to Figure 20 to describe the power converter 100C according to the fourth embodiment. In the following description, any component in the power converter 100C according to the fourth embodiment having the same function as the corresponding part of the power converter 100B according to the above-described third embodiment will be designated by the same reference numeral as that of the corresponding part, and the description thereof will be omitted herein.

[0217] The power converter 100C according to the fourth embodiment further includes another regenerative capacitor 16 (hereinafter referred to as "second regenerative capacitor 16") connected between the sixth terminal 154 of the regenerative capacitor 15 (hereinafter referred to as "first regenerative capacitor 15") and the first DC terminal 31, which is different from the power converter 100B according to the third embodiment.

[0218] The second regenerative capacitor 16 is connected in series to the first regenerative capacitor 15. Thus, in this power converter 100C, the series circuit of the second regenerative capacitor 16 and the first regenerative capacitor 15 is connected between the first DC terminal 31 and the second DC terminal 32. The capacitance of the second regenerative capacitor 16 is equal to the capacitance of the first regenerative capacitor 15. As used herein, the expression "the capacitance of the second regenerative capacitor 16 is equal to the capacitance of the first regenerative capacitor 15" refers not only to the case where the capacitance of the second regenerative capacitor 16 is exactly equal to the capacitance of the first regenerative capacitor 15, but also to the case where the capacitance of the second regenerative capacitor 16 is equal to or greater than 95% and equal to or less than 105% of the capacitance of the first regenerative capacitor 15.

[0219] In the power converter 100C according to the fourth embodiment, the voltage V15 across the first regenerative capacitor 15 (i.e., the potential at the sixth terminal 154 of the first 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 second regenerative capacitor 16 and the first regenerative capacitor 15). Thus, the voltage V15 across the first regenerative capacitor 15 is approximately equal to Vd / 2, but includes some ripple voltage. This ripple voltage is generated along with the operation of charging the resonance capacitor 9 using the charge removed from the first regenerative capacitor 15 and the operation of charging the first regenerative capacitor 15 using the charge removed from the resonance capacitor 9.

[0220] The controller 50 of the power converter 100C according to the fourth embodiment operates in the same manner as the controller 50 of the power converter 100B according to the third embodiment. Thus, the power converter 100C according to the fourth embodiment can detect the switching state in the power conversion circuit 11 in the same way as the power converter 100B according to the third embodiment.

[0221] (Other modification examples)

[0222] Note that the above-described first to fourth embodiments and their modification examples are merely exemplary embodiments among the various embodiments and their modification examples of the present disclosure, and should not be construed as restrictive. On the contrary, without departing from the scope of the present disclosure, the first to fourth exemplary embodiments and their modification examples can be easily modified in various ways according to design choices or any other factors.

[0223] For example, the operation of "determining that two-phase resonance currents flow simultaneously" performed by the controller 50 of the power converter 100B according to the third embodiment is not limited to the operation of "determining that two-phase resonance currents flow simultaneously" when the time lag described for the third embodiment is less than the threshold value.

[0224] Alternatively, for example, if any one of the current differences between the U-phase load current iU and the V-phase load current iV, between the V-phase load current iV and the W-phase load current iW, and between the W-phase load current iW and the U-phase load current iU is less than the current difference threshold value, the controller 50 can also determine that two-phase resonance currents flow simultaneously.

[0225] Alternatively, if the electrical angle determined by calculation or the estimated electrical angle based on sensor information provided by a sensor device (such as an encoder or a resolver, etc.) for detecting the number of revolutions of the motor falls within a first rotation angle range (for example, equal to or greater than 55 degrees and equal to or less than 65 degrees), or a second rotation angle range (for example, equal to or greater than 115 degrees and equal to or less than 125 degrees), or a third rotation angle range (for example, equal to or greater than 175 degrees and equal to or less than 185 degrees), or a fourth rotation angle range (for example, equal to or greater than 235 degrees and equal to or less than 245 degrees), or a fifth rotation angle range (for example, equal to or greater than 295 degrees and equal to or less than 305 degrees), or a sixth rotation angle range (for example, equal to or greater than 355 degrees and equal to or less than 365 degrees), then the controller 50 can also determine that "two-phase resonant currents flow simultaneously".

[0226] For example, each switching element among the plurality of first switching elements 1 and the plurality of second switching elements 2 does not necessarily have to be an IGBT, but can also be a MOSFET. In this case, each first diode among the plurality of first diodes 4 can be replaced by, for example, the parasitic diode of the MOSFET serving as its corresponding first switching element 1. Additionally, each second diode among the plurality of second diodes 5 can be replaced by, for example, the parasitic diode of the MOSFET serving as its corresponding second switching element 2. The MOSFET can be, for example, an Si-based MOSFET or an SiC-based MOSFET. Each switching element among the plurality of first switching elements 1 and the plurality of second switching elements 2 can also be, for example, a bipolar transistor or a GaN-based GIT.

[0227] Optionally, in the power converters 100, 100A, 100B, 100C, if each of the plurality of resonant capacitors 9 has a relatively small capacitance, instead of setting the plurality of resonant capacitors 9 as separate elements, the parasitic capacitors across the plurality of second switching elements 2 can also be used as the plurality of resonant capacitors 9.

[0228] Furthermore, the length of the dead time period Td does not necessarily have to be set to be as long as one resonant half-cycle, but can also be set to be different from one resonant half-cycle.

[0229] The dead time period Td can also be set by a dead time generation circuit included in a gate driver integrated circuit (IC) separately provided from the controller 50. Alternatively, the controller 50 can include a gate driver IC, and the dead time generation circuit included in the gate driver IC can set the dead time period Td.

[0230] In addition, the power converters 100, 100A, 100B, 100C do not necessarily have to be configured to output three-phase AC power, but may also be configured to output polyphase AC power having more than three phases. A specified value used in the determination unit 54 can be appropriately determined according to the number of switching circuits 10 included in the power conversion circuit 11, and the number of switching circuits 10 included in the power conversion circuit 11 is in turn determined by the number of phases of the polyphase AC power.

[0231] (Each aspect)

[0232] The foregoing description provides specific implementations of the following aspects of the present disclosure.

[0233] A power converter (100; 100A; 100B; 100C) according to a first aspect includes a first DC terminal (31) and a second DC terminal (32), a power conversion circuit (11), a plurality of AC terminals (41), a plurality of switches (8), a plurality of resonant capacitors (9), at least one resonant inductor (L1), a regeneration 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 with each other. In each of the plurality of switching circuits (10), one first switching element among the plurality of first switching elements (1) is connected in series with a corresponding second switching element among the plurality of second switching elements (2) in a one-to-one manner. 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 in a one-to-one manner for the plurality of switching circuits (10). Each AC terminal among 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 the corresponding switching circuit among the plurality of switching circuits (10). The plurality of switches (8) are provided in a one-to-one manner for the plurality of switching circuits (10). Each switch among the plurality of switches (8) has a first end (81) and a second end (82). The first end (81) of each switch among the plurality of switches (8) is connected to the connection node (3) between the first switching element (1) and the second switching element (2) of the corresponding switching circuit among the plurality of switching circuits (10). The plurality of resonant capacitors (9) are provided in a one-to-one manner for the plurality of switches (8). Each resonant capacitor among the plurality of resonant capacitors (9) is connected between the first end (81) of the corresponding switch among the plurality of switches (8) and the second DC terminal (32). The at least one resonant inductor (L1) has a third end and a fourth end. The third end of the at least one resonant inductor (L1) is connected to the second end (82) of the corresponding switch among the plurality of switches (8). The regeneration capacitor (15) has a fifth end (153) and a sixth end (154). The fifth end (153) of the regeneration capacitor (15) is connected to the second DC terminal (32). The sixth end (154) of the regeneration capacitor (15) is connected to the fourth end of the at least one resonant inductor (L1). The controller (50) controls the on / off states of the plurality of first switching elements (1), the plurality of second switching elements (2), and the plurality of switches (8) respectively. The controller (50) includes a determination unit (54). The determination unit (54) determines the switching state in the power conversion circuit (11) based on the ripple voltage included in the voltage (V15) across the regeneration capacitor (15) and the plurality of load currents (iU, iV, iW) supplied from the plurality of AC terminals (41).

[0234] This aspect allows the detection of the switching state in the power conversion circuit (11).

[0235] In a power converter (100; 100A; 100B; 100C) according to a second aspect that can be implemented in combination with the first aspect, when a predetermined condition is satisfied, the determination unit (54) determines that a hard switching has occurred in the power conversion circuit (11). The predetermined condition is as follows: the number of intersections (B1) between any two of the plurality of load currents (iU, iV, iW) during a specified period (Ts) is greater than a predefined value. The specified period (Ts) is the period between the first generation timing (tg1) of the first peak (P1) of the ripple voltage and the second generation timing (tg2) of the second peak (P2) of the ripple voltage.

[0236] This aspect allows the detection of the occurrence of hard switching in the power conversion circuit (11) when hard switching has occurred in at least one of the plurality of first switching elements (1) and the plurality of second switching elements (2).

[0237] In a power converter (100; 100A; 100B; 100C) according to a third aspect that can be implemented in combination with the second aspect, when the determination unit (54) has determined that a hard switching has occurred in the power conversion circuit (11), the controller (50) deactivates the power conversion circuit (11).

[0238] This aspect can reduce the temperature rise of the power conversion circuit (11) caused by hard switching in the power conversion circuit (11).

[0239] In a power converter (100; 100A; 100B; 100C) according to a fourth aspect that can be implemented in combination with the first aspect, when a predetermined condition is satisfied, the determination unit (54) determines that each of the plurality of first switching elements (1) and the plurality of second switching elements (2) has been soft-switched. The predetermined condition is as follows: the number of intersections (B1) between any two of the plurality of load currents (iU, iV, iW) during a specified period (Ts) is equal to or less than a predefined value. The specified period (Ts) is the period between the first generation timing (tg1) of the first peak (P1) of the ripple voltage and the second generation timing (tg2) of the second peak (P2) of the ripple voltage.

[0240] This aspect allows the detection that each of the plurality of first switching elements (1) and the plurality of second switching elements (2) has been soft-switched.

[0241] In the power converter (100; 100A; 100B; 100C) according to the fifth aspect, which can be implemented in combination with any one of the second to fourth aspects, the first peak (P1) is a maximum peak at which the ripple voltage reaches the maximum value (Vmax), and the second peak (P2) is another maximum peak at which the ripple voltage reaches the maximum value (Vmax) after the first peak (P1).

[0242] In the power converter (100; 100A; 100B; 100C) according to the sixth aspect, which can be implemented in combination with any one of the second to fourth aspects, the first peak (P1) is a minimum peak at which the ripple voltage reaches the minimum value (Vmin), and the second peak (P2) is another minimum peak at which the ripple voltage reaches the minimum value (Vmin) after the first peak (P1).

[0243] In the power converter (100; 100A; 100B; 100C) according to the seventh aspect, which can be implemented in combination with any one of the first to seventh aspects, the first peak (P1) is a maximum peak at which the ripple voltage reaches the maximum value (Vmax) or a minimum peak at which the ripple voltage reaches the minimum value (Vmin). When the first peak (P1) is a maximum peak, the second peak (P2) is a minimum peak at which the ripple voltage reaches the minimum value (Vmin) after the first peak (P1). When the first peak (P1) is a minimum peak, the second peak (P2) is a maximum peak at which the ripple voltage reaches the maximum value (Vmax) after the first peak (P1).

[0244] In the power converter (100B; 100C) according to the eighth aspect, which can be implemented in combination with any one of the first to seventh aspects, at least one resonant inductor (L1) is a single resonant inductor (L1), and the second ends (82) of the plurality of switches (8) are commonly connected to the single resonant inductor (L1).

[0245] This aspect enables the number of the provided resonant inductors (L1) to be reduced to one, thereby contributing to miniaturization.

[0246] Description of Reference Numerals

[0247] 1 First switching element

[0248] 2 Second switching element

[0249] 3 Connection node

[0250] 8 Switch

[0251] 81 First end

[0252] 82 Second end

[0253] 9 Resonant capacitor

[0254] 10 Switching Circuit

[0255] 11 Power Conversion Circuit

[0256] 15 Regenerative Capacitor

[0257] 153 Fifth Terminal

[0258] 154 Sixth Terminal

[0259] 31 First DC Terminal

[0260] 32 Second DC Terminal

[0261] 41 AC Terminal

[0262] 50 Controller

[0263] 54 Determination Unit

[0264] 100, 100A, 100B, 100C Power Converter

[0265] B1 Intersection Point

[0266] iU, iV, iW Output Current (Load Current)

[0267] L1 Resonant Inductor

[0268] P1 First Peak

[0269] P2 Second Peak

[0270] RA1 AC Load

[0271] SU1, SU2, SU6, SU7 Control Signals

[0272] SV1, SV2, SV6, SV7 Control Signals

[0273] SW1, SW2, SW6, SW7 Control Signals

[0274] Ts Specified Time Period

[0275] tg1 First Generation Timing

[0276] tg2 Second Generation Timing

[0277] V15 Voltage

Claims

1. A power converter, comprising: a first DC terminal and a second DC terminal; a power conversion circuit including a plurality of first switching elements and a plurality of second switching elements, the power conversion circuit being implemented as a parallel connection of a plurality of switching circuits, in each of the plurality of switching circuits, one first switching element among the plurality of first switching elements and a corresponding second switching element among the plurality of second switching elements are connected in series one-to-one, the plurality of first switching elements are connected to the first DC terminal, and the plurality of second switching elements are connected to the second DC terminal; a plurality of AC terminals provided one-to-one for the plurality of switching circuits, each AC terminal among the plurality of AC terminals being connected to a connection node between the first switching element and the second switching element of the corresponding switching circuit among the plurality of switching circuits; a plurality of switches provided one-to-one for the plurality of switching circuits, each switch among the plurality of switches having a first end and a second end, the first end of each switch among the plurality of switches being connected to a connection node between the first switching element and the second switching element of the corresponding switching circuit among the plurality of switching circuits; a plurality of resonance capacitors provided one-to-one for the plurality of switches, each resonance capacitor among the plurality of resonance capacitors being connected between the second DC terminal and the first end of the corresponding switch among the plurality of switches; at least one resonance inductor having a third end and a fourth end, the third end of the at least one resonance inductor being connected to the second end of the corresponding switch among the plurality of switches; a regeneration capacitor having a fifth end and a sixth end, the fifth end of the regeneration capacitor being connected to the second DC terminal, and the sixth end of the regeneration capacitor being connected to the fourth end of the at least one resonance inductor; and a controller configured to control the on / off states of the plurality of first switching elements, the plurality of second switching elements, and the plurality of switches respectively, wherein the controller includes a determination unit configured to determine a switching state in the power conversion circuit based on a ripple voltage included in a voltage across the regeneration capacitor and a plurality of load currents supplied from the plurality of AC terminals.

2. The power converter according to claim 1, wherein the determination unit is configured to determine that hard switching has occurred in the power conversion circuit when a predetermined condition is satisfied, the predetermined condition being as follows: the number of intersections between any two load currents belonging to the plurality of load currents during a specified period is greater than a predefined value, and the specified period is a period between a first generation timing of a first peak of the ripple voltage and a second generation timing of a second peak of the ripple voltage.

3. The power converter according to claim 2, wherein the controller is configured to deactivate the power conversion circuit when the determination unit has determined that hard switching has occurred in the power conversion circuit.

4. The power converter according to claim 1, wherein The determination unit is configured to determine that each of the plurality of first switching elements and the plurality of second switching elements has been soft-switched when a predetermined condition is satisfied. The predetermined condition is as follows: the number of intersections between any two load currents belonging to the plurality of load currents during a specified period is equal to or less than a predefined value, and the specified period is a period between a first generation timing of a first peak of the ripple voltage and a second generation timing of a second peak of the ripple voltage.

5. The power converter according to any one of claims 2 to 4, wherein, the first peak is a maximum peak at which the ripple voltage reaches a maximum value, and the second peak is another maximum peak at which the ripple voltage reaches a maximum value after the first peak.

6. The power converter according to any one of claims 2 to 4, wherein, the first peak is a minimum peak at which the ripple voltage reaches a minimum value, and the second peak is another minimum peak at which the ripple voltage reaches a minimum value after the first peak.

7. The power converter according to any one of claims 2 to 4, wherein, the first peak is a maximum peak at which the ripple voltage reaches a maximum value or a minimum peak at which the ripple voltage reaches a minimum value, in a case where the first peak is a maximum peak, the second peak is a minimum peak at which the ripple voltage reaches a minimum value after the first peak, and in a case where the first peak is a minimum peak, the second peak is a maximum peak at which the ripple voltage reaches a maximum value after the first peak.

8. The power converter according to any one of claims 1 to 7, wherein, the at least one resonant inductor is a single resonant inductor, and second ends of the plurality of switches are commonly connected to the single resonant inductor.

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