Power conversion device and control program

Abstract

This electric power conversion device (10) comprises a plurality of external connection terminals (20), a plurality of bridge circuits (30) that are individually connected to the external connection terminals, an inductance element (50) that is connected between AC terminals of any two bridge circuits that are capable of transmitting electric power, and a control unit (70). A closed-loop circuit that includes the two bridge circuits and the inductance element has a capacitor (60) that is connected between the inductance element and at least one of the AC terminals of the two bridge circuits. The control unit drives a switching element at a switching frequency that is higher than the resonance frequency of the closed-loop circuit.

Description

Cross - reference to related applications

[0001] This application is based on Japanese Patent Application No. 2022 - 114433 filed in Japan on July 18, 2022, and the content of the base application is incorporated herein by reference in its entirety.

Technical Field

[0002] The disclosure in this specification relates to a power conversion device and a control program.

Background Art

[0003] Patent Document 1 discloses a power conversion device in which an inductance element such as a transformer is connected between the AC terminals of two bridge circuits. The description of the prior art document is incorporated herein by reference as an explanation of the technical elements in this specification.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] Power conversion devices mounted on moving bodies such as electric vehicles are required to be small from the perspective of mountability. In the physical size of power conversion devices, passive components such as capacitors and inductors occupy a large proportion, so miniaturization of passive components is effective.

[0006] In Patent Document 1, a snubber capacitor is connected in parallel to the switching element constituting the bridge circuit, and the charging operation of the snubber capacitor is utilized to reduce the loss during switching. When such soft switching technology is used, it is possible to achieve a higher frequency by reducing the loss and reduce the size of passive components. However, in the light load region, the charge stored in the snubber capacitor is lost, and the conversion efficiency decreases compared to a configuration without a snubber capacitor. From the above viewpoints, or from other viewpoints not mentioned, further improvements are required for the power conversion device and the control program.

[0007] One disclosed object is to provide a power conversion device and a control program with high conversion efficiency over a wide range from the light load region to the rated load region.

[0008] A power conversion device according to one disclosure is a plurality of external connection terminals, a plurality of bridge circuits individually connected to the external connection terminals, an inductance element connected between the AC terminals of any two bridge circuits capable of transmitting power, and a control unit that controls the driving of the switching elements constituting the plurality of bridge circuits. The closed-loop circuit including the two bridge circuits and the inductance element has a capacitor connected between at least one of the AC terminals of the two bridge circuits and the inductance element. The control unit drives the switching element at a switching frequency higher than the resonance frequency of the closed-loop circuit. and there are three or more external connection terminals, a plurality of bridge circuits are individually connected to the external connection terminals, the inductance elements are provided for each combination of two bridge circuits capable of power transmission, the capacitors are provided for each of the closed-loop circuits, the control unit drives the switching element at a switching frequency higher than the maximum resonance frequency among the resonance frequencies of the closed-loop circuits.

[0009] According to the disclosed power conversion device, a capacitor is provided in a closed-loop circuit, and a switching element is driven in a frequency region higher than the resonance frequency of the closed-loop circuit, that is, in an inductive region. As a result, the current waveform approaches a sine wave, and the current value at the time of switching can be reduced. As a result, a power conversion device with high conversion efficiency over a wide range can be provided.

[0010] One of the other disclosed control programs is a plurality of external connection terminals, a plurality of bridge circuits individually connected to the external connection terminals, an inductance element connected between AC terminals of any two bridge circuits capable of transmitting power, In a closed-loop circuit including two bridge circuits and an inductance element, a capacitor connected between at least one of the AC terminals of the two bridge circuits and the inductance element is provided. 、 there are three or more external connection terminals, a plurality of bridge circuits are individually connected to the external connection terminals, the inductance elements are provided for each combination of two bridge circuits capable of power transmission, the capacitors are provided for each of the closed-loop circuits A control program applied to a power conversion device having the above, causes at least one processing unit (712) to set a switching frequency higher than the resonance frequency of the closed-loop circuit among the maximum resonance frequencies and drive switching elements that make up a plurality of bridge circuits at the switching frequency.

[0011] According to the disclosed control program, a switching element is driven in a frequency region higher than the resonance frequency of the closed-loop circuit, that is, in an inductive region. As a result, the current waveform approaches a sine wave, and the current value at the time of switching can be reduced. As a result, a control program with high conversion efficiency over a wide range can be provided.

[0012] ​The multiple aspects disclosed in this specification adopt different technical means to achieve their respective purposes. The claims and the reference signs in parentheses described in this section exemplarily show the correspondence with the parts of the embodiments described later, and are not intended to limit the technical scope. The purposes, features, and effects disclosed in this specification will become clearer by referring to the subsequent detailed description and the attached drawings.

Brief Description of the Drawings

[0013]

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Embodiments for Carrying Out the Invention

[0014] Hereinafter, a plurality of embodiments will be described with reference to the drawings. In each embodiment, the corresponding components may be denoted by the same reference numerals, and redundant descriptions may be omitted. When only a part of the configuration is described in each embodiment, the configuration of other embodiments described previously can be applied to the other parts of the said configuration. Also, not only the combinations of configurations explicitly shown in the description of each embodiment, but also the configurations of a plurality of embodiments can be partially combined with each other without any problem in the combination, even if not explicitly shown.

[0015] The power conversion device of this embodiment is applied to a moving body. The moving body is, for example, an electric vehicle such as a battery electric vehicle (BEV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), a flying body such as an electric vertical take-off and landing aircraft or a drone, a ship, a construction machine, or an agricultural machine. The power conversion device can also be applied to a stationary device that requires miniaturization.

[0016] (First Embodiment) FIG. 1 shows the overall configuration of the power conversion device 10 according to this embodiment. As shown in FIG. 1, the power conversion device 10 includes a plurality of external connection terminals 20, a plurality of bridge circuits 30, an inductance element 50, a capacitor 60, and a control unit 70. The power conversion device 10 further includes a smoothing capacitor 40. The power conversion device 10 is a device that converts DC power into DC power. The power conversion device 10 may be referred to as a DC-DC conversion device.

[0017] The external connection terminal 20 is a terminal for electrically connecting the power conversion device 10 to an external device. The external connection terminal 20 inputs or outputs power. For this reason, the external connection terminal 20 may be referred to as an input / output terminal. The external device is a rechargeable secondary battery, an AC-DC conversion circuit, a load, etc. All of the external devices connected to the external connection terminal 20 may be secondary batteries or AC-DC conversion circuits. Some of the external devices connected to the external connection terminal 20 may be secondary batteries or AC-DC conversion circuits, and some of the other external devices may be loads.

[0018] As an example, the power conversion device 10 of this embodiment includes three external connection terminals 20, specifically, a first terminal 21, a second terminal 22, and a third terminal 23. Among the first terminals 21, the first terminal 21H is a high-potential side terminal, and the first terminal 21L is a low-potential side terminal. Similarly, among the second terminals 22, the second terminal 22H is a high-potential side terminal, and the second terminal 22L is a low-potential side terminal. Among the third terminals 23, the third terminal 23H is a high-potential side terminal, and the third terminal 23L is a low-potential side terminal. The voltage of the first terminal 21, that is, the potential difference between the first terminals 21H and 21L, is a high voltage of 300 V or more, for example. The same applies to the voltage of the second terminal 22 and the voltage of the third terminal 23.

[0019] The bridge circuit 30 is individually connected to the external connection terminal 20. The bridge circuit 30 is connected in parallel to the external connection terminal 20. The bridge circuit 30 has a high-potential side DC terminal, a low-potential side DC terminal, and an AC terminal. The high-potential side DC terminal is connected to the high-potential side of the external connection terminal 20, and the low-potential side DC terminal is connected to the low-potential side of the external connection terminal 20. The AC terminal is connected to the inductance element 50. The bridge circuit 30 converts DC power into AC power, or converts AC power into DC power. The bridge circuit 30 may be referred to as a power conversion circuit, an AC-DC conversion circuit, an inverter, etc.

[0020] The bridge circuit 30 includes at least one series circuit of switching elements. The series circuit may be referred to as a bridge, a switching leg, an upper and lower arm circuit, etc. The switching elements constituting the series circuit are, for example, MOSFETs, IGBTs, etc. MOSFET is an abbreviation for Metal Oxide Semiconductor Field Effect Transistor. IGBT is an abbreviation for Insulated Gate Bipolar Transistor.

[0021] As an example, the power conversion device 10 of this embodiment includes three bridge circuits 30, specifically, a first bridge circuit 31, a second bridge circuit 32, and a third bridge circuit 33. The power conversion device 10 includes the same number of bridge circuits 30 as the external connection terminals 20. Each bridge circuit 30 is a full-bridge circuit including two series circuits. The switching elements constituting the series circuit are all n-channel type MOSFETs. The diodes shown in the figure are parasitic diodes of the MOSFETs and allow current reflux.

[0022] The first bridge circuit 31 has four switching elements Q11, Q12, Q13, Q14. Two switching elements Q11, Q12 form a series circuit with switching element Q11 on the high side. The source of switching element Q11 and the drain of switching element Q12 are connected to each other. Two switching elements Q13, Q14 form a series circuit with switching element Q13 on the high side. The source of switching element Q13 and the drain of switching element Q14 are connected to each other.

[0023] The drains of the high-side switching elements Q11, Q13 are connected to the high-potential side DC terminal of the first bridge circuit 31. The sources of the low-side switching elements Q12, Q14 are connected to the low-potential side DC terminal of the first bridge circuit 31. The midpoint (connection point) of the series circuit is connected to the AC terminal of the first bridge circuit 31.

[0024] The second bridge circuit 32 has the same configuration as the first bridge circuit 31. The second bridge circuit 32 has four switching elements Q21, Q22, Q23, and Q24. Two switching elements Q21 and Q22 form a series circuit with the switching element Q21 on the high side. Two switching elements Q23 and Q24 form a series circuit with the switching element Q23 on the high side. The drains of the high-side switching elements Q21 and Q23 are connected to the high-potential side DC terminal of the second bridge circuit 32. The sources of the low-side switching elements Q22 and Q24 are connected to the low-potential side DC terminal of the second bridge circuit 32. The midpoint (connection point) of the series circuit is connected to the AC terminal of the second bridge circuit 32.

[0025] The third bridge circuit 33 also has the same configuration as the first bridge circuit 31. The third bridge circuit 33 has four switching elements Q31, Q32, Q33, and Q34. Two switching elements Q31 and Q32 form a series circuit with the switching element Q31 on the high side. Two switching elements Q33 and Q34 form a series circuit with the switching element Q33 on the high side. The drains of the high-side switching elements Q31 and Q33 are connected to the high-potential side DC terminal of the third bridge circuit 33. The sources of the low-side switching elements Q32 and Q34 are connected to the low-potential side DC terminal of the third bridge circuit 33. The midpoint (connection point) of the series circuit is connected to the AC terminal of the third bridge circuit 33.

[0026] The smoothing capacitor 40 is provided between the external connection terminal 20 and the bridge circuit 30. The smoothing capacitor 40 is connected in parallel with the external connection terminal 20. The smoothing capacitor 40 is connected in parallel with the bridge circuit 30. As the smoothing capacitor 40, for example, a film capacitor, an electrolytic capacitor, etc. can be adopted. The power conversion device 10 is provided with the same number of smoothing capacitors 40 as the bridge circuit 30.

[0027] As an example, the power conversion device 10 of the present embodiment includes three smoothing capacitors 40, specifically, a first smoothing capacitor 41, a second smoothing capacitor 42, and a third smoothing capacitor 43. The positive terminal of the first smoothing capacitor 41 is connected to the first terminal 21H on the high potential side, and the negative terminal is connected to the first terminal 21L on the low potential side. The positive terminal of the second smoothing capacitor 42 is connected to the second terminal 22H on the high potential side, and the negative terminal is connected to the second terminal 22L on the low potential side. The positive terminal of the third smoothing capacitor 43 is connected to the third terminal 23H on the high potential side, and the negative terminal is connected to the third terminal 23L on the low potential side. The positive terminal of the smoothing capacitor 40 is connected to the DC terminal on the high potential side of the bridge circuit 30, and the negative terminal is connected to the DC terminal on the low potential side.

[0028] The smoothing capacitor 40 may be referred to as a power conversion circuit together with the bridge circuit 30. The first bridge circuit 31 performs power conversion between the AC terminal of the first bridge circuit 31 and the first smoothing capacitor 41. The DC voltage Vdc1 is the voltage across the first smoothing capacitor 41. The first bridge circuit 31 converts the DC voltage Vdc1 into an AC voltage, for example. The second bridge circuit 32 performs power conversion between the AC terminal of the second bridge circuit 32 and the second smoothing capacitor 42. The DC voltage Vdc2 is the voltage across the second smoothing capacitor 42. The third bridge circuit 33 performs power conversion between the AC terminal of the third bridge circuit 33 and the third smoothing capacitor 43. The DC voltage Vdc3 is the voltage across the third smoothing capacitor 43.

[0029] The inductance element 50 is connected between the AC terminals of any two bridge circuits 30 capable of transmitting power. The power conversion device 10 can perform power conversion for freely transmitting and receiving power between two bridge circuits 30 sandwiching the inductance element 50. The direction of power can also be freely controlled. In the circuit sandwiching the inductance element 50, the power transmission side may be referred to as the primary side and the power reception side may be referred to as the secondary side.

[0030] As an example, the inductance element 50 of the present embodiment is a transformer. The transformer electrically insulates two bridge circuits 30. The power conversion device 10 includes two inductance elements 50, specifically, a first transformer 51 and a second transformer 52.

[0031] The first transformer 51 is connected between the AC terminals of the first bridge circuit 31 and the AC terminals of the second bridge circuit 32. The first transformer 51 has a first coil 511 and a second coil 512. The first coil 511 and the second coil 512 are magnetically coupled to each other through a core (not shown) provided in the first transformer 51, for example. The first coil 511 is connected to the AC terminals of the first bridge circuit 31. One end of the first coil 511 is connected to the AC terminals of a series circuit formed by switching elements Q11 and Q12, and the other end is connected to the AC terminals of a series circuit formed by switching elements Q13 and Q14. The second coil 512 is connected to the AC terminals of the second bridge circuit 32. One end of the second coil 512 is connected to the AC terminals of a series circuit formed by switching elements Q21 and Q22, and the other end is connected to the AC terminals of a series circuit formed by switching elements Q23 and Q24.

[0032] The number of turns of the winding of the first coil 511 is N12, and the number of turns of the winding of the second coil 512 is N21. Assuming the first bridge circuit 31 side as the primary side, a voltage Vt2 corresponding to the multiplication value of the voltage Vt1 between the AC terminals of the first bridge circuit 31 and the turn ratio N21 / N12 is generated between the AC terminals of the second bridge circuit 32, which is the secondary side. The voltage Vt1 may be referred to as the output voltage of the first bridge circuit 31. The voltage Vt2 may be referred to as the output voltage of the second bridge circuit 32.

[0033] The second transformer 52 is connected between the AC terminals of the first bridge circuit 31 and the AC terminals of the third bridge circuit 33. The second transformer 52 has the same configuration as the first transformer 51. The second transformer 52 has a first coil 521 and a second coil 522. The first coil 521 and the second coil 522 are magnetically coupled to each other through a core (not shown) provided in the second transformer 52, for example. The first coil 521 is connected to the AC terminals of the first bridge circuit 31. One end of the first coil 521 is connected to the AC terminals of a series circuit formed by switching elements Q11 and Q12, and the other end is connected to the AC terminals of a series circuit formed by switching elements Q13 and Q14. The second coil 522 is connected to the AC terminals of the third bridge circuit 33. One end of the second coil 522 is connected to the AC terminals of a series circuit formed by switching elements Q31 and Q32, and the other end is connected to the AC terminals of a series circuit formed by switching elements Q33 and Q34.

[0034] The number of turns of the winding of the first coil 521 is N13, and the number of turns of the winding of the second coil 522 is N31. Assuming the first bridge circuit 31 side as the primary side, a voltage Vt3 corresponding to the multiplication value of the voltage Vt1 between the AC terminals of the first bridge circuit 31 and the turns ratio N31 / N13 is generated between the AC terminals of the third bridge circuit 33, which is the secondary side. The voltage Vt3 may be referred to as the output voltage of the third bridge circuit 33.

[0035] The inductances L12 and L21 shown in FIG. 1 are the leakage inductances of the first transformer 51. The inductances L12 and L21 are equivalent. The inductances L13 and L31 are the leakage inductances of the second transformer 52. The inductances L13 and L31 are equivalent. The inductances L12, L13, L21, and L31 are equal to each other. The inductance is not limited to only the leakage inductance. An additional inductor may be connected to the first transformer 51 or the second transformer 52.

[0036] The current IL12 is the current flowing through the inductance L12, that is, the first coil 511. The current IL21 is the current flowing through the inductance L21, that is, the second coil 512. The current IL13 is the current flowing through the inductance L13, that is, the first coil 521. The current IL31 is the current flowing through the inductance L31, that is, the second coil 522. These currents IL12, IL21, IL13, IL31 may be referred to as transformer currents, port currents, etc.

[0037] The capacitor 60 is arranged in a closed-loop circuit including any two bridge circuits 30 and an inductance element 50 connected between the AC terminals of any two bridge circuits 30. The capacitor 60 is connected in the closed-loop circuit between at least one of the AC terminals of the two bridge circuits 30 and the inductance element 50. The closed-loop circuit has the capacitor 60. The capacitor 60 is a capacitor for resonance.

[0038] As an example, the power conversion device 10 of this embodiment includes two capacitors 60, specifically, a first capacitor 61 and a second capacitor 62. The first capacitor 61 is arranged in a closed-loop circuit including the first bridge circuit 31, the first transformer 51, and the second bridge circuit 32. This closed-loop circuit may be hereinafter referred to as the first closed-loop circuit. The first capacitor 61 is connected between the AC terminal on the switching element Q11, Q12 side in the first bridge circuit 31 and the first coil 511. The first capacitor 61 forms an LC series resonance circuit with the leakage inductances L12, L21 of the first transformer 51.

[0039] The second capacitor 62 is arranged in a closed-loop circuit including the first bridge circuit 31, the second transformer 52, and the third bridge circuit 33. This closed-loop circuit may be hereinafter referred to as the second closed-loop circuit. The second capacitor 62 is connected between the AC terminals on the switching element Q11, Q12 side in the first bridge circuit 31 and the first coil 521. The second capacitor 62 forms an LC series resonance circuit with the inductances L13, L31 which are the leakage inductances of the second transformer 52.

[0040] As an example, the capacitance value of the first capacitor 61 and the capacitance value of the second capacitor 62 are equal to each other. Therefore, the resonance frequency of the first closed-loop circuit and the resonance frequency of the second closed-loop circuit are equal to each other. Note that a closed-loop circuit (the third closed-loop circuit) is formed by the second bridge circuit 32, the first transformer 51, the second transformer 52, and the third bridge circuit 33. Based on the first closed-loop circuit, the combined inductance in the third closed-loop circuit is doubled and the combined capacitance is halved. Therefore, the resonance frequency of the third closed-loop circuit is equal to the resonance frequency of the first closed-loop circuit and the resonance frequency of the second closed-loop circuit.

[0041] The control unit 70 controls the driving of the switching elements constituting each bridge circuit 30, specifically, on driving and off driving. Thereby, the control unit 70 converts a DC voltage into an AC voltage and then converts the AC voltage into a DC voltage. The control unit 70 controls the power transmitted and received between the primary side and the secondary side. The control unit 70 of the present embodiment controls the driving of the switching elements Q11~Q14, Q21~Q24, Q31~Q34. The control unit 70 includes a control circuit 71 and a driving circuit 72. The control circuit 71 generates a driving command for operating the switching elements Q11~Q14, Q21~Q24, Q31~Q34 and outputs it to the driving circuit 72. The control circuit 71 outputs a PWM signal as the driving command. PWM is an abbreviation for Pulse Width Modulation.

[0042] As an example, the control circuit 71 of the present embodiment includes a dedicated computer. The dedicated computer has at least one memory 711 and at least one processor 712. The memory 711 is a non-transitory tangible storage medium that stores a program 713 and data that can be read by a computer. The program 713 includes computer-readable instructions that cause the processor 712 to execute various functions when executed by the processor 712. The processor 712 constructs a plurality of functional units by executing a plurality of instructions included in the program 713. The processor 712 is a processing unit that executes a predetermined process by executing the instructions of the program 713.

[0043] The memory 711 is at least one type of storage medium among, for example, semiconductor memories, magnetic media, and optical media. The memory 711 can adopt various storage media such as RAM, ROM, HDD, and SSD. RAM is an abbreviation for Random Access Memory. ROM is an abbreviation for Read Only Memory. HDD is an abbreviation for Hard-disk Drive. SSD is an abbreviation for Solid State Drive.

[0044] The processor 712 includes at least one type among, for example, a CPU, MPU, GPU, and DFP as a core. CPU is an abbreviation for Central Processing Unit. MPU is an abbreviation for Micro-Processing Unit. GPU is an abbreviation for Graphics Processing Unit. DFP is an abbreviation for Data Flow Processor. The control circuit 71 may be realized by combining a plurality of types of arithmetic processing units such as a CPU, MPU, and GPU.

[0045] The dedicated computer that constitutes the control circuit 71 may be implemented as a SoC. SoC is an abbreviation for System on Chip. At least a part of the dedicated computer may be implemented using an ASIC or an FPGA. ASIC is an abbreviation for Application Specific Integrated Circuit. FPGA is an abbreviation for Field-Programmable Gate Array.

[0046] The drive circuit 72 supplies drive voltages to the gates of the switching elements Q11 to Q14, Q21 to Q24, and Q31 to Q34 based on the drive commands from the control circuit 71. The drive circuit 72 drives the switching elements Q11 to Q14, Q21 to Q24, and Q31 to Q34 by applying the drive voltages, that is, turns them on and off. The drive circuit 72 may be referred to as a driver.

[0047] The control unit 70 drives the switching elements that constitute the bridge circuit 30 at a switching frequency fsw higher than the resonance frequency fr of the closed-loop circuit. When the power conversion device 10 includes a plurality of closed-loop circuits, the control unit 70 drives the switching elements at a switching frequency fsw higher than the maximum resonance frequency frmax among the resonance frequencies fr of the plurality of closed-loop circuits. In the present embodiment, as described above, the power conversion device 10 includes three closed-loop circuits, and the resonance frequencies fr of the three closed-loop circuits are equal to each other. Therefore, the control unit 70 drives the switching elements Q11 to Q14, Q21 to Q24, and Q31 to Q34 at a switching frequency fsw higher than the resonance frequency fr common to the three closed-loop circuits.

[0048] <Control Method> The following shows an example in which the control circuit 71 controls the first bridge circuit 31 and the second bridge circuit 32. Note that the same applies to the control of the first bridge circuit 31 and the third bridge circuit 33, and the second bridge circuit 32 and the third bridge circuit 33, respectively. The control circuit 71 controls the driving of the switching elements Q11, Q12, Q13, Q14, Q21, Q22, Q23, Q24 by, for example, the method disclosed in Japanese Patent Application Laid-Open No. 2021-145407. The description of Japanese Patent Application Laid-Open No. 2021-145407 is incorporated herein by reference as the explanation of the technical elements in this specification.

[0049] The control circuit 71 acquires the commanded power on the second bridge circuit 32 side and the detection signals of the respective sensors. When the commanded power is positive, the control circuit 71 divides the input commanded power by the voltage Vdc2 acquired from the voltage sensor, and calculates a commanded current that is the commanded value of the current flowing through the second terminal 22H. The commanded current is set to supply power to an external device connected to the second terminal 22 by constant power control. The control circuit 71 acquires the current flowing through the second terminal 22H from the current sensor, and calculates a current deviation by subtracting the acquired current from the above-described commanded current. The control circuit 71 calculates a commanded phase difference φ as an operation amount for feedback control to zero the current deviation. The feedback control is, for example, proportional integral (PI) control or proportional integral derivative (PID) control. The control circuit 71 generates drive commands (PWM signals) for the switching elements Q11, Q12, Q13, Q14, Q21, Q22, Q23, Q24 based on the commanded phase difference.

[0050] Figure 2 shows the switching operation and current-voltage waveforms. In Figure 2, the switching states of the switching elements Q11, Q12, Q13, Q14, Q21, Q22, Q23, Q24, the voltages Vt1, Vt2, and the current IL1 are shown. For the sake of convenience, the dead time provided to prevent a short circuit in the series circuit is omitted in Figure 2. In Figure 2, the operations of the switching elements Q11, Q13, Q21, Q23 are shown by solid lines, and the operations of the switching elements Q12, Q14, Q22, Q24 are shown by broken lines.

[0051] In the first bridge circuit 31, the switching elements Q11 and Q12 that form a series circuit are turned on alternately. The switching elements Q13 and Q14 that form a series circuit are turned on alternately. The on-period of the switching element Q11 and the on-period of the switching element Q14 are synchronized. The on-period of the switching element Q12 and the on-period of the switching element Q13 are synchronized. That is, the switching elements Q11 and Q14 operate in the same switching state as each other, and the switching elements Q12 and Q13 operate in the same switching state as each other.

[0052] In the second bridge circuit 32, the switching elements Q21 and Q22 that form a series circuit are turned on alternately. The switching elements Q23 and Q24 that form a series circuit are turned on alternately. The on-period of the switching element Q21 and the on-period of the switching element Q24 are synchronized. The on-period of the switching element Q22 and the on-period of the switching element Q23 are synchronized. That is, the switching elements Q21 and Q24 operate in the same switching state as each other, and the switching elements Q22 and Q23 operate in the same switching state as each other.

[0053] When the command phase difference φ is positive, the switching timing of the switching elements Q21 and Q24 to turn on lags behind the switching timing of the switching elements Q11 and Q14 to turn on by the command phase difference φ. During this period of the command phase difference φ, the current IL12 changes and has a current waveform as shown in FIG. 2. When the command phase difference φ is positive, the switching timing of the voltage Vt2 to change from the negative polarity to the positive polarity lags behind the switching timing of the voltage Vt1 to change from the negative polarity to the positive polarity by the command phase difference φ. The control circuit 71 controls the power by controlling the current IL12 according to the command phase difference φ.

[0054] In the example shown in FIG. 2, the command phase difference φ (phase difference φ) is positive, and the phase of voltage Vt2 lags behind that of voltage Vt1. Therefore, power is transmitted from the first bridge circuit 31 to the second bridge circuit 32 by the switching operation. Both voltages Vt1 and Vt2 are two-level voltages of positive and negative values. Voltage Vt1 outputs a positive value when switching elements Q11 and Q14 are turned on, and outputs a negative value when switching elements Q12 and Q13 are turned on. Similarly, voltage Vt2 outputs a positive value when switching elements Q21 and Q24 are turned on, and outputs a negative value when switching elements Q22 and Q23 are turned on. The control circuit 71 controls the power transmission amount from the first bridge circuit 31 to the second bridge circuit 32 by changing the delay amount of the switching timing of the second bridge circuit 32 with respect to the switching timing of the first bridge circuit 31.

[0055] FIG. 3 shows the current flow in each operation mode. In MODE1, switching elements Q11 and Q14 are off, and switching elements Q12 and Q13 remain on. Switching elements Q21 and Q24 turn from on to off, and switching elements Q22 and Q23 turn from off to on. The polarity of current IL12 is negative, and current flows through the parasitic diodes of switching elements Q22 and Q23. Voltage Vt2 drops from a positive value to a negative value. Note that although current also flows through switching elements Q22 and Q23 in MODE1 due to their being turned on, it is omitted in FIG. 3 for the sake of simplicity.

[0056] Next, in MODE2, switching elements Q11 and Q14 turn from off to on, and switching elements Q12 and Q13 turn from on to off. Switching elements Q22 and Q23 are on, and switching elements Q21 and Q24 remain off. Since the polarity of current IL12 is positive, current flows through switching elements Q22 and Q23. Voltage Vt1 rises from a negative value to a positive value.

[0057] Next, in MODE3, the switching elements Q11 and Q14 are turned on, and the switching elements Q12 and Q13 remain off. The switching elements Q21 and Q24 switch from off to on, and the switching elements Q22 and Q23 switch from on to off. The polarity of the current IL12 is positive, and current flows through the parasitic diodes of the switching elements Q22 and Q23. The voltage Vt2 rises from a negative value to a positive value. Note that when the switching elements Q21 and Q24 are turned on, current also flows through the switching elements Q21 and Q24 in MODE3, but this is omitted for simplicity.

[0058] Next, in MODE4, the switching elements Q11 and Q14 switch from on to off, and the switching elements Q12 and Q13 switch from off to on. The switching elements Q21 and Q24 are turned on, and the switching elements Q22 and Q23 remain off. Since the polarity of the current IL12 is negative, current flows through the switching elements Q21 and Q24. The voltage Vt1 drops from a positive value to a negative value.

[0059] Although an example in which the control circuit 71 controls the phase of the voltage Vt2 to be lagging with respect to the voltage Vt1 has been shown, the present invention is not limited to this. The control circuit 71 may control the phase of the voltage Vt2 to be leading or in phase with respect to the voltage Vt1.

[0060] Although an example in which the power command is a positive value has been shown, the present invention is not limited to this. The power command may be a negative value or zero. In the case of a negative value, it is also possible to transmit power from the second bridge circuit 32 to the first bridge circuit 31 via the inductance element 50.

[0061] <Summary of the First Embodiment> Figure 4 shows the relationship between the switching frequency fsw and the impedance ZLC of the LC circuit. As shown in Figure 4, the region with a frequency lower than the resonance frequency fr is the capacitive region, and the region with a frequency higher than the resonance frequency fr is the inductive region. The impedance ZLC of the LC circuit decreases with an increase in the switching frequency fsw in the capacitive region and reaches a minimum at the resonance frequency fr. The impedance ZLC increases with an increase in the switching frequency fsw in the inductive region.

[0062] As shown in Figure 4, in the inductive region, the waveform of the transformer current approaches a sine wave. Especially, the closer it is to the resonance frequency fr, the closer the waveform is to a sine wave. The control unit 70 (control circuit 71) of the present embodiment drives the switching elements Q11~Q14, Q21~Q24, Q31~Q34 at a switching frequency fsw higher than the resonance frequency fr of the closed-loop circuit. In this way, by driving the switching elements Q11~Q14, Q21~Q24, Q31~Q34 in the inductive region, the current waveform approaches a sine waveform.

[0063] Figure 5 shows the relationship between the switching frequency fsw and the reduction amount of switching loss in a configuration including the capacitor 60. Figure 5 shows the simulation results. As shown in Figure 5, by setting the switching frequency fsw higher than the resonance frequency fr, the switching loss can be reduced. The reduction amount of the switching loss decreases with an increase in the switching frequency fsw. The reduction amount of the switching loss is larger the closer it is to the resonance frequency fr. Therefore, it is preferable to set the switching frequency fsw in the range of 1.3 times or more and 2 times or less the resonance frequency fr.

[0064] Figure 6 shows the simulation results of the port current waveforms. Figure 6 shows the port current waveforms during the power transmission operation from the second terminal 22 to the third terminal 23. In Figure 6, a reference example and this example (an example of the present embodiment) are compared. The reference example is different from this example in that it does not include the capacitor 60, and other configurations are the same as this example. The solid line shown in Figure 6 indicates the port current IL21 of the second bridge circuit 32, and the dashed line indicates the port current IL31 of the third bridge circuit 33. The dashed-dotted line indicates the port current of the first bridge circuit 31, that is, the sum of the current IL13 and the current IL12. The dashed-dotted line is the current flowing through the connection point A1 in Figure 1. As shown in Figure 6, in the reference example, the peak value of the port current of the first bridge circuit 31 is large. In this example, the peak value of the port current of the first bridge circuit 31 can be reduced by approximately 60% compared to the reference example.

[0065] Figure 7 shows the simulation results of the semiconductor losses. Figure 7 shows the semiconductor losses of the first bridge circuit 31 during the power transmission operation from the second terminal 22 to the third terminal 23, similar to Figure 6. Also in Figure 7, this example with the configuration including the capacitor 60 and the reference example without the capacitor 60 are compared. In the reference example, the semiconductor losses of the first bridge circuit 31 are large. In this example, the semiconductor losses of the first bridge circuit 31 can be reduced by approximately 78% compared to the reference example.

[0066] In the present embodiment, a capacitor 60 is connected between at least one of the AC terminals of the two bridge circuits 30 and the inductance element 50 in the closed-loop circuit. As an example, the power conversion device 10 includes three bridge circuits 30, and a capacitor 60 is provided in each of the closed-loop circuits. Then, the control unit 70 drives the switching elements Q11~Q14, Q21~Q24, Q31~Q34 at a switching frequency fsw higher than the resonance frequency fr of the closed-loop circuit. Thereby, as shown in Figures 4 and 6, the current waveform approaches a sine waveform. Therefore, the current value during switching, and thus the semiconductor losses, can be reduced. Since the current value during switching becomes small, the conversion efficiency can be increased over a wide range from the light load region to the rated load region.

[0067] Similarly, the program 713 (control program) stored in the memory 711 causes at least one processor 712 (processing unit) to set a switching frequency fsw higher than the resonance frequency fr of the closed-loop circuit. The program 713 causes the processor 712 to drive the switching elements Q11 to Q14, Q21 to Q24, and Q31 to Q34 at the set switching frequency. As a result, the current waveform approaches a sine wave as described above. Therefore, the current value at the time of switching can be reduced. As a result, the conversion efficiency of the power conversion device 10 can be increased over a wide range from the light load region to the rated load region.

[0068] As shown in FIG. 5, the switching frequency fsw only needs to be higher than the resonance frequency fr. Preferably, the switching frequency fsw is set within a range of 1.3 times or more and 2 times or less the resonance frequency fr. As shown in FIG. 4, the closer the current waveform is to the resonance frequency fr, the closer it is to a sine wave. That is, the current value at the time of switching can be reduced. By setting the switching frequency fsw within a range of 1.3 times or more and 2 times or less the resonance frequency fr, power conversion can be stably performed, and switching losses (semiconductor losses) can be effectively reduced.

[0069] <Modification Example> In the configuration including three or more bridge circuits 30, an example in which the resonance frequencies of the closed-loop circuits are equal to each other has been shown, but the present invention is not limited thereto. For example, in the configuration shown in FIG. 1, the capacitance values of the capacitors 61 and 62 may be made different, and thereby the resonance frequencies of the closed-loop circuits may be made different. The control unit 70 may drive the switching elements Q11 to Q14, Q21 to Q24, and Q31 to Q34 at a switching frequency fsw higher than the maximum resonance frequency among the resonance frequencies fr of the closed-loop circuits.

[0070] The arrangement of the capacitor 60 is not limited to the above example. In a closed-loop circuit, it can be arranged between the AC terminal and the inductance element 50. For example, the first capacitor 61 may be provided between the AC terminal on the side of the switching elements Q13, Q14 and the end of the first coil 511. It may also be provided between the AC terminal on the side of the switching elements Q21, Q22 and the end of the second coil 512. It may also be provided between the AC terminal on the side of the switching elements Q23, Q24 and the end of the second coil 512. The same applies to the second capacitor 62.

[0071] (Second Embodiment) This embodiment is a modification based on the preceding embodiment, and the description of the preceding embodiment can be incorporated by reference. In the preceding embodiment, each of the bridge circuits 30 had two series circuits. Instead, the number of series circuits may be other than two.

[0072] FIG. 8 shows the power conversion device 10 according to this embodiment. Similar to the preceding embodiment, the power conversion device 10 includes three bridge circuits 30. Each of the bridge circuits 30 has only one series circuit. The bridge circuit 30 is sometimes referred to as a half-bridge circuit.

[0073] The first bridge circuit 31 has only a series circuit of the switching elements Q11, Q12. A first capacitor 61 is connected between the AC terminal on the side of the switching elements Q11, Q12 and one end of the first coil 511 of the first transformer 51. The other end of the first coil 511 is connected to the source of the switching element Q12 on the low side.

[0074] The second bridge circuit 32 has only a series circuit of the switching elements Q21, Q22. One end of the second coil 512 of the first transformer 51 is connected to the AC terminal on the side of the switching elements Q21, Q22, and the other end is connected to the source of the switching element Q22 on the low side.

[0075] The third bridge circuit 33 has only a series circuit of switching elements Q31 and Q32. One end of the second coil 522 of the second transformer 52 is connected to the AC terminal on the side of the switching elements Q31 and Q32. A second capacitor 62 is connected between one end of the first coil 521 and the AC terminal on the side of the switching elements Q11 and Q12. The other end of the first coil 521 is connected to the source of the low-side switching element Q12.

[0076] In the above-described configuration, the control unit 70 drives the switching elements Q11 to Q14, Q21 to Q24, and Q31 to Q34 at a switching frequency fsw higher than the resonance frequency fr of the closed-loop circuit. Other configurations are the same as those of the power conversion device 10 described in the previous embodiment.

[0077] <Summary of the Second Embodiment> Also in this embodiment, the power conversion device 10 includes three bridge circuits 30, and a capacitor 60 is provided in each of the closed-loop circuits. Then, the control unit 70 drives the switching elements Q11 to Q14, Q21 to Q24, and Q31 to Q34 at a switching frequency fsw higher than the resonance frequency fr of the closed-loop circuit. Therefore, the same effects as those of the configuration described in the previous embodiment can be achieved. Specifically, since the current waveform approaches a sine waveform, the current value at the time of switching can be reduced. And the conversion efficiency can be increased over a wide range from the light load region to the rated load region.

[0078] Although an example in which each of the bridge circuits 30 has one series circuit has been shown, each of them may have three series circuits.

[0079] (Third Embodiment) This embodiment is a modification example based on the preceding embodiment, and the description of the preceding embodiment can be incorporated. In the preceding embodiment, the power conversion device 10 included two inductance elements 50. Instead of this, the number of inductance elements 50 may be three or more.

[0080] FIG. 9 shows the power conversion device 10 according to the present embodiment. In FIG. 9, for convenience, the communication lines of the control unit 70 are simplified and illustrated. Similar to the first embodiment, the power conversion device 10 includes three bridge circuits 30 having a full-bridge configuration. The power conversion device 10 includes three inductance elements, specifically, a first transformer 51, a second transformer 52, and a third transformer 53. The power conversion device 10 includes three capacitors 60, specifically, a first capacitor 61, a second capacitor 62, and a third capacitor 63.

[0081] The first transformer 51, the second transformer 52, and the first capacitor 61 are arranged in the same manner as in the first embodiment. The second capacitor 62 is connected between the end of the second coil 522 of the second transformer 52 and the AC terminals on the switching element Q31, Q32 side of the third bridge circuit 33.

[0082] The third transformer 53 is connected between the AC terminals of the second bridge circuit 32 and the AC terminals of the third bridge circuit 33. The third transformer 53 has the same configuration as the first transformer 51 and the second transformer 52. The first coil 531 of the third transformer 53 is connected to the AC terminal of the second bridge circuit 32. One end of the first coil 531 is connected to the AC terminal of the series circuit formed by the switching elements Q21, Q22, and the other end is connected to the AC terminal of the series circuit formed by the switching elements Q23, Q24. The second coil 532 is connected to the AC terminal of the third bridge circuit 33. One end of the second coil 532 is connected to the AC terminal of the series circuit formed by the switching elements Q31, Q32, and the other end is connected to the AC terminal of the series circuit formed by the switching elements Q33, Q34.

[0083] The inductances L23 and L32 shown in FIG. 9 are the leakage inductances of the third transformer 53. The inductances L23 and L32 are equivalent. The inductances L12, L13, L21, L23, L31, and L32 are equal to each other. The current IL23 is the current flowing through the inductance L23, that is, the first coil 531. The current IL32 is the current flowing through the inductance L32, that is, the second coil 532.

[0084] The third capacitor 63 is connected between the AC terminals on the switching element Q21, Q22 side in the second bridge circuit 32 and the first coil 531. The third capacitor 63 forms an LC series resonance circuit with the inductances L23 and L32, which are the leakage inductances of the third transformer 53. As an example, the capacitance values of the first capacitor 61, the second capacitor 62, and the third capacitor 63 are equal to each other. Therefore, in all the closed-loop circuits of the power conversion device 10, the resonance frequencies are equal to each other.

[0085] The power conversion device 10 has six closed-loop circuits. One of the closed-loop circuits includes the first bridge circuit 31, the first transformer 51, and the second bridge circuit 32. Another one of the closed-loop circuits includes the first bridge circuit 31, the second transformer 52, and the third bridge circuit 33. Another one of the closed-loop circuits includes the second bridge circuit 32, the third transformer 53, and the third bridge circuit 33. Another one of the closed-loop circuits includes the first bridge circuit 31, the second transformer 52, the third transformer 53, and the second bridge circuit 32. Another one of the closed-loop circuits includes the first bridge circuit 31, the first transformer 51, the third transformer 53, and the third bridge circuit 33. Another one of the closed-loop circuits includes the second bridge circuit 32, the first transformer 51, the second transformer 52, and the third bridge circuit 33. As an example, similar to the previous embodiment, the resonance frequencies of all the closed-loop circuits are equal to each other.

[0086] In the above-described configuration, the control unit 70 drives the switching elements Q11~Q14, Q21~Q24, Q31~Q34 at a switching frequency fsw higher than the resonance frequency fr of the closed-loop circuit. The other configurations are the same as those of the power conversion device 10 described in the first embodiment.

[0087] <Summary of the Third Embodiment> Also in this embodiment, the power conversion device 10 includes three bridge circuits 30, and a capacitor 60 is provided in each of the closed-loop circuits. Then, the control unit 70 drives the switching elements Q11 to Q14, Q21 to Q24, Q31 to Q34 at a switching frequency fsw higher than the resonance frequency fr of the closed-loop circuit. Therefore, the same effects as those of the configuration described in the previous embodiment can be achieved. Specifically, since the current waveform approaches a sine wave, the current value at the time of switching can be reduced. And the conversion efficiency can be increased over a wide range from the light load region to the rated load region.

[0088] Note that the power conversion device 10 requires an inductance element 50 (transformer) in a number obtained by subtracting 1 from at least the number of the bridge circuits 30. As in this embodiment, an inductance element 50 having a number equal to or more than the number of the bridge circuits 30 may be arranged.

[0089] The configuration described in this embodiment can be combined with either the configuration described in the first embodiment or the configuration described in the second embodiment.

[0090] (Fourth Embodiment) This embodiment is a modified example based on the preceding embodiment, and the description of the preceding embodiment can be incorporated by reference. In the preceding embodiment, the power conversion device 10 included three external connection terminals 20 and bridge circuits 30. Instead, four or more external connection terminals 20 and bridge circuits 30 may be provided. That is, a configuration with four ports or more may be adopted.

[0091] FIG. 10 shows a power conversion device 10 according to the present embodiment. In FIG. 10, for convenience, the communication lines of the control unit 70 are omitted. The power conversion device 10 includes four external connection terminals 20 and four bridge circuits 30 configured in a full-bridge configuration. The power conversion device 10 further includes a fourth terminal 24, a fourth smoothing capacitor 44, and a fourth bridge circuit 34 with respect to the configuration of the previous embodiment. The fourth terminal 24 includes a fourth terminal 24H on the high potential side and a fourth terminal 24L on the low potential side. The fourth bridge circuit 34 has switching elements Q41, Q42, Q43, and Q44. The switching elements Q41 and Q42 form a series circuit with the switching element Q41 on the high side. The switching elements Q43 and Q44 form a series circuit with the switching element Q43 on the high side.

[0092] The power conversion device 10 includes three inductance elements, specifically, a first transformer 51, a second transformer 52, and a third transformer 53. The power conversion device 10 includes three capacitors 60, specifically, a first capacitor 61, a second capacitor 62, and a third capacitor 63.

[0093] The first transformer 51 is connected between the AC terminals of the first bridge circuit 31 and the AC terminals of the second bridge circuit 32. The first capacitor 61 is connected between the AC terminals on the side of the switching elements Q11 and Q12 and the end of the first coil 511.

[0094] The second transformer 52 is connected between the AC terminals of the second bridge circuit 32 and the AC terminals of the second bridge circuit 32. The second capacitor 62 is connected between the AC terminals on the side of the switching elements Q21 and Q22 and the end of the first coil 521.

[0095] The third transformer 53 is connected between the AC terminals of the third bridge circuit 33 and the AC terminals of the fourth bridge circuit 34. The third capacitor 63 is connected between the AC terminals on the side of the switching elements Q31 and Q32 and the end of the first coil 531.

[0096] The inductances L23 and L32 shown in FIG. 10 are the leakage inductances of the second transformer 52. The inductances L34 and L43 are the leakage inductances of the third transformer 53. The inductances L12, L21, L23, L32, L34, and L43 are equal to each other. The current IL34 is the current flowing through the inductance L34. The current IL43 is the current flowing through the inductance L43.

[0097] The power conversion device 10 has six closed-loop circuits. One of the closed-loop circuits includes the first bridge circuit 31, the first transformer 51, and the second bridge circuit 32. Another one of the closed-loop circuits includes the second bridge circuit 32, the second transformer 52, and the third bridge circuit 33. Another one of the closed-loop circuits includes the third bridge circuit 33, the third transformer 53, and the fourth bridge circuit 34. Another one of the closed-loop circuits includes the first bridge circuit 31, the first transformer 51, the second transformer 52, and the third bridge circuit 33. Another one of the closed-loop circuits includes the second bridge circuit 32, the second transformer 52, the third transformer 53, and the fourth bridge circuit 34. Another one of the closed-loop circuits includes the first bridge circuit 31, the first transformer 51, the second transformer 52, the third transformer 53, and the fourth bridge circuit 34. As an example, similar to the previous embodiment, the resonance frequencies of all the closed-loop circuits are equal to each other.

[0098] In the above-described configuration, the control unit 70 drives the switching elements Q11 to Q14, Q21 to Q24, Q31 to Q34, and Q41 to Q44 at a switching frequency fsw higher than the resonance frequency fr of the closed-loop circuit. Other configurations are the same as those of the power conversion device 10 described in the first embodiment.

[0099] <Summary of the Fourth Embodiment> In this embodiment, the power conversion device 10 includes four bridge circuits 30, and a capacitor 60 is provided in each of the closed-loop circuits. Then, the control unit 70 drives the switching elements Q11 to Q14, Q21 to Q24, Q31 to Q34, and Q41 to Q44 at a switching frequency fsw higher than the resonance frequency fr of the closed-loop circuit. Therefore, the same effects as those of the configuration described in the previous embodiment can be achieved. Specifically, since the current waveform approaches a sine waveform, the current value at the time of switching can be reduced. And the conversion efficiency can be increased over a wide range from the light load region to the rated load region.

[0100] The configuration described in this embodiment can be combined with any of the configurations described in the first embodiment, the second embodiment, and the third embodiment.

[0101] (Fifth Embodiment) This embodiment is a modification based on the preceding embodiment, and the description of the preceding embodiment can be incorporated by reference. In the preceding embodiment, the AC voltages output by each bridge circuit 30, for example, the voltages Vt1 and Vt2, were two-level voltages of positive and negative values. Instead, the output voltage of the bridge circuit 30 may be a three-level voltage of positive, zero, and negative values.

[0102] FIG. 11 shows the switching operation and current-voltage waveforms in the power conversion device 10 according to this embodiment. FIG. 11 corresponds to FIG. 2. Also in FIG. 11, the phase of the output voltage Vt2 of the second bridge circuit 32 lags behind the output voltage Vt1 of the first bridge circuit 31. FIG. 11 shows the operation of transmitting power from the first bridge circuit 31 to the second bridge circuit 32.

[0103] The output voltage Vt1 is a three-level voltage of a positive value, a zero value, and a negative value. The output voltage Vt2 is a two-level voltage of a positive value and a negative value. The output voltage Vt1 outputs a positive value when the switching elements Q11, Q14, Q21, and Q24 are turned on. The output voltage Vt1 outputs a negative value when the switching elements Q12, Q13, Q22, and Q23 are turned on. The output voltage Vt1 outputs a zero value when the switching elements Q11 and Q13 are turned on. Alternatively, the output voltage Vt1 may output a zero value when the switching elements Q22 and Q24 are turned on.

[0104] Similar to the previous embodiment, the control unit 70 controls the power transmission amount between the first bridge circuit 31 and the second bridge circuit 32 by changing the phase difference φ. Other configurations are the same as those described in the first embodiment, for example.

[0105] <Summary of the Fifth Embodiment> Also in this embodiment, the control unit 70 drives the switching elements Q11 to Q14, Q21 to Q24, and Q31 to Q34 at a switching frequency fsw higher than the resonance frequency fr of the closed-loop circuit. Therefore, the same effects as those of the configuration described in the previous embodiment can be achieved.

[0106] The configuration described in this embodiment can be combined with any of the configurations described in the first embodiment, the second embodiment, the third embodiment, and the fourth embodiment.

[0107] Although an example in which the output voltage Vt1 is a three-level voltage is shown, the present invention is not limited to this. The output voltage Vt2 may be a three-level voltage. The output voltages Vt1 and Vt2 may be three-level voltages.

[0108] (Sixth Embodiment) This embodiment is a modified example based on the preceding embodiment, and the description of the preceding embodiment can be incorporated by reference. In the preceding embodiment, the power conversion device 10 included three or more external connection terminals 20 and a bridge circuit 30. Instead, it may include two external connection terminals 20 and a bridge circuit 30. That is, a two-port configuration may be adopted.

[0109] FIG. 12 shows a power conversion device 10 according to this embodiment. The power conversion device 10 includes two external connection terminals 20, specifically, a first terminal 21 and a second terminal 22. The power conversion device 10 includes two bridge circuits 30, specifically, a first bridge circuit 31 and a second bridge circuit 32.

[0110] The power conversion device 10 has a configuration obtained by excluding a third terminal 23, a third bridge circuit 33, a third smoothing capacitor 43, a second transformer 52, and a second capacitor 62 from the configuration described in the first embodiment (see FIG. 1). The power conversion device 10 includes a first transformer 51 and a first capacitor 61. Hereinafter, the first transformer 51 may be denoted as transformer 51, and the first capacitor 61 may be denoted as capacitor 61.

[0111] The transformer 51, which is an inductance element 50, is connected between the AC terminals of the first bridge circuit 31 and the AC terminals of the second bridge circuit 32. The capacitor 61 is connected between the AC terminals on the switching element Q11, Q12 side and the first coil 511.

[0112] The power conversion device 10 has a closed-loop circuit including the first bridge circuit 31, the transformer 51, and the second bridge circuit 32. The capacitor 61 is provided in this closed-loop circuit. The control unit 70 drives the switching elements Q11 to Q14, Q21 to Q24 in the same manner as in the first embodiment (see FIGS. 2 and 3). The control unit 70 drives the switching elements Q11 to Q14, Q21 to Q24 at a switching frequency fsw higher than the resonance frequency fr of the closed-loop circuit. Other configurations are the same as those described in the first embodiment.

[0113] <Summary of the Sixth Embodiment> In this embodiment, the power conversion device 10 includes two bridge circuits 30, and a capacitor 61 is connected between the AC terminals of the bridge circuit 30 and the transformer 51 in a closed-loop circuit. Then, the control unit 70 drives the switching elements Q11 to Q14 and Q21 to Q24 at a switching frequency fsw higher than the resonance frequency fr of the closed-loop circuit. Thereby, the same effect as that of the previous embodiment can be achieved. Specifically, the current waveform approaches a sine waveform. Therefore, the current value at the time of switching, and thus the semiconductor loss, can be reduced. Since the current value at the time of switching becomes small, the conversion efficiency can be increased over a wide range from the light load region to the rated load region.

[0114] Also, the program 713 (control program) stored in the memory 711 causes at least one processor 712 (processing unit) to set a switching frequency fsw higher than the resonance frequency fr of the closed-loop circuit. The program 713 causes the processor 712 to drive the switching elements Q11 to Q14 and Q21 to Q24 at the set switching frequency. Thereby, similarly to the above, the current waveform approaches a sine waveform. Therefore, the current value at the time of switching can be reduced. As a result, the conversion efficiency of the power conversion device 10 can be increased over a wide range from the light load region to the rated load region.

[0115] Similar to the previous embodiment, in this embodiment, it is preferable to set the switching frequency fsw within a range of 1.3 times or more and 2 times or less the resonance frequency fr. Thereby, power conversion can be stably performed, and the switching loss (semiconductor loss) can be effectively reduced.

[0116] <Modification Example> The arrangement of the capacitor 61 is not limited to the above example. The first capacitor 61 may be provided between the AC terminal on the switching element Q13, Q14 side and the end of the first coil 511. It may be provided between the AC terminal on the switching element Q21, Q22 side and the end of the second coil 512. It may be provided between the AC terminal on the switching element Q23, Q24 side and the end of the second coil 512.

[0117] The configuration of the two bridge circuits 30 is not limited to a full bridge. For example, as shown in FIG. 13, a bridge circuit 30 having a half-bridge configuration may be employed. The first bridge circuit 31 has only a series circuit of the switching elements Q11, Q12. The second bridge circuit 32 has only a series circuit of the switching elements Q21, Q22. One end of the first coil 511 is connected to the source of the switching element Q12. One end of the second coil 512 is connected to the source of the switching element Q22.

[0118] As shown in FIG. 14, the bridge circuit 30 may have three or more series circuits. The first bridge circuit 31 has a series circuit of the switching elements Q11, Q12, a series circuit of the switching elements Q13, Q14, and a series circuit of the switching elements Q15, Q16. The second bridge circuit 32 has a series circuit of the switching elements Q21, Q22, a series circuit of the switching elements Q23, Q24, and a series circuit of the switching elements Q25, Q26. Such a bridge circuit 30 is sometimes referred to as a three-leg circuit. The transformer 51 replaces a single phase with three phases. The capacitors 61 are respectively provided between the three AC terminals and the transformer 51. In the modified examples of FIGS. 13 and 14, the control unit 70 is omitted for convenience.

[0119] The configuration described in this embodiment can be combined with the configuration described in the fifth embodiment. The number of transformers 51 is not limited to one. Two or more transformers 51 may be provided.

[0120] (Seventh Embodiment) This embodiment is a modification based on the preceding embodiment, and the description of the preceding embodiment can be incorporated. In the preceding embodiment, in the two bridge circuits 30 and the inductance element 50 that constitute a closed-loop circuit, a capacitor 60 was provided between the AC terminal of one bridge circuit 30 and the inductance element 50. Instead of this, a capacitor 60 may be provided between each of the bridge circuits 30 and the inductance element 50.

[0121] FIG. 15 shows the power conversion device 10 according to this embodiment. For convenience, in FIG. 15, the communication lines of the control unit 70 are simplified. The basic configuration of the power conversion device 10 is the same as the configuration described in the sixth embodiment (see FIG. 12). The power conversion device 10 has two capacitors 611 and 612 as the capacitor 61 provided in the closed-loop circuit including the first bridge circuit 31, the transformer 51, and the second bridge circuit 32. The capacitor 611 is connected between the AC terminals on the switching element Q11, Q12 side and the transformer 51. The capacitor 612 is connected between the AC terminals on the switching element Q21, Q22 side and the transformer 51.

[0122] In this way, two capacitors 61 (611, 612) are arranged in series in the closed-loop circuit. The control unit 70 drives the switching elements Q11 to Q14, Q21 to Q24 at a switching frequency fsw higher than the resonance frequency fr of the closed-loop circuit.

[0123] <Summary of the Seventh Embodiment> In this embodiment, capacitors 61 are provided on both sides of the transformer 51, respectively. Thereby, in addition to the effects described in the preceding embodiment, a transformer bias magnetic field suppression effect can be achieved. Therefore, it becomes possible to perform the power conversion operation more stably.

[0124] FIG. 16 is a diagram showing the transformer bias suppression effect. FIG. 16 shows the simulation results. The reference example shown in FIG. 16 shows the result of a configuration in which a capacitor 61 is provided on one side (for example, the primary side) of the transformer 51. That is, it shows the result of the configuration described in the sixth embodiment (see FIG. 12). This example shows the result of the configuration of this embodiment, that is, the configuration in which capacitors 61 are provided on both sides of the transformer 51.

[0125] In the reference example, the exciting current increases after a DC voltage is superimposed on the transformer 51. And finally, the transformer 51 saturates. In this example, by providing the capacitors 61 on both sides of the transformer 51, DC components in both directions can be canceled. Thereby, an increase in the exciting current can be suppressed, and thus saturation of the transformer 51 can be suppressed.

[0126] <Modification example> At least one capacitor 61 may be arranged between an AC terminal of one of the two bridge circuits 30 and the inductance element 50, and at least one may be arranged between an AC terminal of the other of the two bridge circuits 30 and the inductance element 50.

[0127] For example, in the example shown in FIG. 17, a capacitor 613 is added to the configuration shown in FIG. 15. The capacitor 613 is connected between the AC terminals on the switching element Q13, Q14 side and the transformer 51. Thus, a plurality of capacitors 61 may be arranged on the first bridge circuit 31 side. Of course, a plurality of capacitors 61 may be arranged on the second bridge circuit 32 side, or a plurality of capacitors 61 may be arranged on both sides of the transformer 51 respectively. That is, the number of capacitors 61 arranged in series in the closed-loop circuit may be three or more. Even in such a configuration, a transformer bias suppression effect equivalent to that of the configuration shown in FIG. 15 can be achieved.

[0128] In the example shown in FIG. 18, a capacitor 613 added to the configuration shown in FIG. 15 is connected in parallel to the capacitor 611. Of course, a parallel circuit of the capacitor 61 may be arranged on the second bridge circuit 32 side, or parallel circuits of the capacitor 61 may be arranged on both sides of the transformer 51. Even in such a configuration, a transformer bias magnetic suppression effect equivalent to the configuration shown in FIG. 15 can be achieved. In the modified examples shown in FIGS. 17 and 18, the control unit 70 is omitted for convenience.

[0129] The configuration described in this embodiment can be combined with any of the configurations described in the first embodiment, the second embodiment, the third embodiment, the fourth embodiment, the fifth embodiment, and the sixth embodiment.

[0130] (Eighth Embodiment) This embodiment is a modified example based on the preceding embodiments, and the descriptions of the preceding embodiments can be incorporated by reference. In the preceding embodiments, the power conversion device 10 included a transformer as the inductance element 50. Instead, an inductor may be provided.

[0131] FIG. 19 shows a power conversion device 10 according to this embodiment. The basic configuration of the power conversion device 10 is the same as the configuration described in the sixth embodiment (see FIG. 12). The power conversion device 10 includes an inductor 54 as the inductance element 50. The inductor 54 may be referred to as a reactor.

[0132] The inductor 54 is connected to the AC terminals of the two bridge circuits 30. One of the terminals of the inductor 54 is connected to the AC terminals of the switching elements Q11 and Q12 on the first bridge circuit 31 side, and the other terminal is connected to the AC terminals of the switching elements Q21 and Q22 on the second bridge circuit 32 side. L0 indicates the inductance of the inductor 54. The AC terminals of the switching elements Q13 and Q14 on the first bridge circuit 31 side and the AC terminals of the switching elements Q23 and Q24 on the second bridge circuit 32 side are connected to each other.

[0133] The closed-loop circuit includes a first bridge circuit 31, an inductor 54, and a second bridge circuit 32. A capacitor 61 is connected between the AC terminals on the switching element Q11, Q12 side and the inductor 54 in the closed-loop circuit. The control unit 70 drives the switching elements Q11 to Q14, Q21 to Q24 at a switching frequency fsw higher than the resonance frequency fr of the closed-loop circuit.

[0134] <Summary of the Eighth Embodiment> In this embodiment, an inductor 54 is employed instead of the transformer 51. The inductor 54 does not have an insulation function like the transformer 51. However, by providing a capacitor 61 in the closed-loop circuit and driving the switching elements Q11 to Q14, Q21 to Q24 at a switching frequency fsw higher than the resonance frequency fr of the closed-loop circuit, the same effects as the previous embodiments can be achieved. Specifically, since the current waveform approaches a sine wave, the current value at the time of switching can be reduced. Thereby, the conversion efficiency can be increased over a wide range from the light load region to the rated load region.

[0135] The configuration described in this embodiment can be combined with any of the configurations described in the first embodiment, the second embodiment, the third embodiment, the fourth embodiment, the fifth embodiment, the sixth embodiment, and the seventh embodiment. For example, the transformers 51, 52, 53 may be replaced with an inductor 54.

[0136] (Other Embodiments) The disclosure in this specification, drawings, etc. is not limited to the illustrated embodiments. The disclosure includes the illustrated embodiments and modifications by those skilled in the art based thereon. For example, the disclosure is not limited to the combination of components and / or elements shown in the embodiments. The disclosure can be implemented by various combinations. The disclosure can have additional parts that can be added to the embodiments. The disclosure includes those in which components and / or elements of the embodiments are omitted. The disclosure includes the replacement or combination of components and / or elements between one embodiment and another. The disclosed technical scope is not limited to the description of the embodiments. Some of the disclosed technical scopes are indicated by the description of the claims and should be construed to include all changes within the meaning and scope equivalent to the description of the claims.

[0137] The disclosure in the specification, drawings, etc. is not limited by the description of the claims. The disclosure in the specification, drawings, etc. includes the technical idea described in the claims and extends to more diverse and extensive technical ideas than the technical idea described in the claims. Therefore, various technical ideas can be extracted from the disclosure in the specification, drawings, etc. without being restricted by the description of the claims.

[0138] When an element or layer is referred to as "above," "connected," "attached," or "coupled," it may be directly above, connected, attached, or coupled to another element or layer, and there may be intervening elements or intervening layers. In contrast, when an element is referred to as "directly above," "directly connected," "directly attached," or "directly coupled" to another element or layer, there are no intervening elements or intervening layers. Other words used to describe the relationship between elements should be interpreted in a similar manner (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.). As used in this specification, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0139] (Disclosure of Technical Ideas) This specification discloses a plurality of technical ideas described in the following listed items. Some items may be described in a multiple dependent form that alternatively cites preceding items in subsequent items. Further, some items may be described in a multiple dependent form that cites other multiple dependent form items. The items described in these multiple dependent forms define a plurality of technical ideas.

[0140] <Technical Idea 1> A plurality of external connection terminals (20), A plurality of bridge circuits (30) individually connected to the external connection terminals, An inductance element (50) connected between the AC terminals of any two of the bridge circuits capable of transmitting power, A control unit (70) for controlling the driving of the switching elements constituting the plurality of bridge circuits, The closed-loop circuit including the two bridge circuits and the inductance element has a capacitor (60) connected between at least one of the AC terminals of the two bridge circuits and the inductance element. The control unit drives the switching element at a switching frequency higher than the resonance frequency of the closed-loop circuit, and is a power conversion device.

[0141] <Technical Idea 2> There are three or more of the external connection terminals. The plurality of bridge circuits are individually connected to the external connection terminals. The inductance element is provided in each combination of two bridge circuits capable of power transmission. The capacitor is provided in each of the closed-loop circuits. The control unit drives the switching element at a switching frequency higher than the maximum resonance frequency among the resonance frequencies of the closed-loop circuits, and is the power conversion device according to Technical Idea 1.

[0142] <Technical Idea 3> The external connection terminals include a first terminal (21H, 21L) and a second terminal (22H, 22L). The bridge circuit includes a first bridge circuit (31) connected to the first terminal and a second bridge circuit (32) connected to the second terminal. The inductance element is connected between the AC terminal of the first bridge circuit and the AC terminal of the second bridge circuit. The capacitor is connected between at least one AC terminal of the first bridge circuit and the second bridge circuit and the inductance element in the closed-loop circuit including the first bridge circuit, the inductance element, and the second bridge circuit, and is the power conversion device according to Technical Idea 1.

[0143] <Technical Idea 4> The control unit drives the switching element at a switching frequency that is 1.3 times or more and 2 times or less the resonance frequency, and the power conversion device according to any one of Technical Ideas 1 to 3.

[0144] <Technical Idea 5> At least one capacitor is disposed between an AC terminal of one of the two bridge circuits connected to the common inductance element and the inductance element, and at least one is disposed between an AC terminal of the other of the two bridge circuits and the inductance element. The power conversion device according to any one of Technical Ideas 1 to 4.

[0145] <Technical Idea 6> The inductance element is a transformer, and the power conversion device according to any one of Technical Ideas 1 to 5.

[0146] <Technical Idea 7> The inductance element is an inductor, and the power conversion device according to any one of Technical Ideas 1 to 5.

Claims

1. A plurality of external connection terminals (20); A plurality of bridge circuits (30) individually connected to the external connection terminals; An inductance element (50) connected between AC terminals of any two of the bridge circuits capable of transmitting power; A control unit (70) for controlling the drive of switching elements constituting the plurality of bridge circuits, and comprising: A closed-loop circuit including two of the bridge circuits and the inductance element has a capacitor (60) connected between at least one of the AC terminals of the two bridge circuits and the inductance element; The control unit drives the switching element at a switching frequency higher than the resonance frequency of the closed-loop circuit; There are three or more of the external connection terminals; The plurality of bridge circuits are individually connected to the external connection terminals; The inductance element is provided for each combination of two of the bridge circuits capable of transmitting power; The capacitor is provided for each of the closed-loop circuits; The control unit drives the switching element at a switching frequency higher than the maximum resonance frequency among the resonance frequencies of the closed-loop circuits, a power conversion device.

2. The control unit drives the switching element at a switching frequency that is 1.3 times or more and 2 times or less the resonance frequency, the power conversion device according to claim 1.

3. The capacitor is disposed at least one between an AC terminal of one of the two bridge circuits connected to the common inductance element and the inductance element, and disposed at least one between the other AC terminal of the two bridge circuits and the inductance element, the power conversion device according to claim 1.

4. The inductance element is a transformer (51, 52, 53), the power conversion device according to claim 1.

5. The inductance element is an inductor (54), the power conversion device according to claim 1.

6. A plurality of external connection terminals (20); A plurality of bridge circuits (30) individually connected to the external connection terminals; An inductance element (50) connected between AC terminals of any two of the bridge circuits capable of transmitting power; In a closed-loop circuit including the two bridge circuits and the inductance element, a capacitor (60) connected between at least one of the AC terminals of the two bridge circuits and the inductance element is provided. The external connection terminals are three or more. The plurality of bridge circuits are individually connected to the external connection terminals. The inductance element is provided for each combination of two bridge circuits capable of power transmission. The capacitor is a control program applied to a power conversion device provided in each of the closed-loop circuits, to at least one processing unit (712), setting a switching frequency higher than the maximum resonance frequency among the resonance frequencies of the closed-loop circuit, and driving switching elements constituting the plurality of bridge circuits at the switching frequency. A control program including this.

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