Power conversion device and power supply device for a substation

Abstract

The present application relates to a power conversion device and a power supply device for a substation, and achieves miniaturization of the power conversion device and the power supply device. The power conversion device of the embodiment is a device electrically connected between a first DC power supply (1) and a second DC power supply (2), and includes a chopper circuit having a step-down output terminal electrically connected between a positive terminal and a negative terminal of the second DC power supply (2) via a reactor (8), and a high-frequency insulation circuit including a first inverter (INV1) having a first DC main circuit electrically connected between a positive terminal and a negative terminal of the first DC power supply (1), a second inverter (INV2) electrically connected with a high-voltage circuit side of the chopper circuit (5), and a high-frequency insulation transformer (15) electrically connected between an AC terminal of the first inverter (INV1) and an AC terminal of the second inverter (INV2).

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to a power conversion device and a power supply device for a substation. BACKGROUND

[0002] A DC feeding system as a power supply system of a DC electric railway has a characteristic that a load varies drastically and a feeding line voltage varies greatly. Further, in the DC feeding system, an AC power is generally converted into a DC power using a diode rectifier. For example, in order to perform power regeneration from the DC feeding system to an AC power system, a regeneration inverter must be provided to be able to implement, and if there is no sufficient load capable of absorbing a regenerated current from a regenerative car in the vicinity of the regenerative car, the regenerative car can be caught in a regeneration failure.

[0003] In order to cope with the above-described voltage variation and the regeneration failure, a DC feeding system provided with an electric storage unit is provided. For example, in a case where a high-output electric car is introduced, in order to cope with a decrease in catenary voltage and generation of excess regenerated power, a power supply device including an electric storage unit can be considered to be provided. The power supply device used in this case has a converter for converting a battery voltage into an arbitrary voltage to output.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT DOCUMENTS

[0006] Patent Document 1: Japanese Patent Application Publication No. 2018-98834 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] For example, when a feeding circuit and a battery circuit are insulated, the ground insulation withstand voltage of the battery can be reduced, and arbitrary power can be charged and discharged between the catenary and the battery. On the other hand, for example, in a case where DC 1500 V feeding is performed, the catenary voltage generally varies in a range of about 900 V to 1800 V, and when the difference between the battery voltage and the catenary voltage is large, the peak current value flowing in the insulation circuit (for example, a high-frequency transformer) becomes large. As a result, it is necessary to make the high-frequency insulation transformer large, and to increase the rated current of the power semiconductor element used in the power conversion device, resulting in a large device and high cost.

[0009] Embodiments of the present application are made in view of the above-described circumstances, and an object thereof is to achieve a small power conversion device and a power supply device.

[0010] MEANS FOR SOLVING THE PROBLEMS

[0011] The power conversion device of the embodiment is a device electrically connected between a first DC power supply and a second DC power supply, and includes a chopper circuit having a step-down output terminal connected between a positive terminal and a negative terminal of the second DC power supply via a reactor, and a high-frequency insulation circuit including a first inverter electrically connected between the positive terminal and the negative terminal of the first DC power supply, a second inverter electrically connected to a high-voltage circuit side of the chopper circuit, and a high-frequency insulation transformer electrically connected between an AC terminal of the first inverter and an AC terminal of the second inverter. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 FIG. 1 is a diagram schematically showing one configuration example of a power conversion device and a power supply device of a first embodiment.

[0013] Figure 2 FIG. 4 is a diagram schematically showing one configuration example of a power conversion unit of a power conversion device of a second embodiment.

[0014] Figure 3 FIG. 7 is a diagram schematically showing one configuration example of a power conversion device and a power supply device of a third embodiment. DETAILED DESCRIPTION

[0015] Hereinafter, the power conversion device and the power supply device for a substation of the embodiment will be described in detail with reference to the drawings.

[0016] Figure 1 FIG. 1 is a diagram schematically showing one configuration example of a power conversion device and a power supply device of a first embodiment.

[0017] The power supply device of the embodiment is, for example, a device provided in a substation, and includes a first DC power supply 1, a resistor R, and a power conversion device 3, and is electrically connected with a second DC power supply 2. The second DC power supply 2 is a DC power supply including a DC feeder circuit, and is, for example, an overhead line. The second DC power supply 2 performs, for example, DC 1500 V feeding.

[0018] The power conversion device 3 includes a plurality of power conversion units 4, reactors 6, 8, a capacitor 7, and a control circuit CTR.

[0019] The first DC power supply 1 is, for example, a DC power supply including a storage battery. Alternatively, the first DC power supply 1 can include a power converter that converts AC power into DC power and outputs the same.

[0020] In the present embodiment, the first DC power supply 1 is grounded via a resistor R at a neutral point between the high-potential side power supply 1P and the low-potential side power supply 1N. Thus, the ground potential of the storage battery of the first DC power supply 1 can be reduced. In addition, when the insulation withstand voltage of the storage battery of the first DC power supply 1 is sufficient, the first DC power supply 1 can be grounded at the low-potential side instead of the neutral point, or the circuit on the first DC power supply 1 side of the insulation circuit (high-frequency insulation transformer 15) can be made electrically floating.

[0021] In Figure 1 In the example shown, the power conversion device 3 has three power conversion units 4. The power conversion units 4 each have a chopper circuit 5 and a resonance type high-frequency insulation circuit. The resonance type high-frequency insulation circuit has a capacitor 12, 13, a first inverter INV1, a resonance capacitor 14, a high-frequency insulation transformer 15, and a second inverter INV2.

[0022] The first inverter INV1 is a full-bridge circuit having two branches electrically connected between the first DC main circuit. Each branch of the first inverter INV1 has an upper arm and a lower arm. The upper arm and the lower arm of the first inverter INV1 each have a power semiconductor element 10 such as an insulated gate bipolar transistor (IGBT). By using the power semiconductor element 10 such as an IGBT, the conduction loss of the first inverter INV1 can be reduced.

[0023] The capacitor 13 is connected between the DC terminal on the high-potential side and the DC terminal on the low-potential side of the first inverter INV1.

[0024] The second inverter INV2 is a full-bridge circuit having two branches electrically connected between the second DC main circuit. Each branch of the second inverter INV2 has an upper arm and a lower arm. The upper arm and the lower arm of the second inverter INV2 each have a power semiconductor element 11 such as an IGBT. By using the power semiconductor element 11 such as an IGBT, the conduction loss of the second inverter INV2 can be reduced.

[0025] The capacitor 12 is connected between the DC terminal on the high-potential side and the DC terminal on the low-potential side of the second inverter INV2.

[0026] The high-frequency insulation transformer 15 is connected between the AC terminals of the first inverter INV1 and the AC terminals of the second inverter INV2. The high-frequency insulation transformer 15 is, for example, a high-frequency transformer circuit having a first winding connected between the AC terminals of the two branches of the first inverter INV1 and a second winding connected between the AC terminals of the two branches of the second inverter INV2. The number of turns of the first winding and the number of turns of the second winding of the high-frequency insulation transformer 15 are set in accordance with the ratio of the voltages of the capacitor 12 and the capacitor 13 and the voltage of the direct-current power supply 1.

[0027] The resonance capacitor 14 is provided on an AC line electrically connecting the second winding of the high-frequency insulation transformer 15 and the AC terminal of one branch of the second inverter INV2. The resonance capacitor 14 can also be provided on an AC line between the first winding and the first inverter INV1.

[0028] The high-voltage circuit side of the chopper circuit 5 is electrically connected to the second direct-current main circuit of the second inverter INV2. The chopper circuit 5 is a half-bridge circuit having two switching elements 9 connected in series between the second direct-current main circuit. The switching elements 9 of the chopper circuit 5 preferably use, for example, a wide-bandgap semiconductor element such as a SiC (Silicon Carbide)-MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). The wide-bandgap semiconductor includes, for example, a III-V group semiconductor. Since the chopper circuit 5 performs hard switching, the use of the above-described wide-bandgap semiconductor can reduce switching loss in the chopper circuit 5.

[0029] The capacitors 13 of the three power conversion units 4 are connected in series between the positive terminal and the negative terminal of the first direct-current power supply 1. That is, the high-potential side first direct-current main circuit of the power conversion unit 4 on the highest-potential side is electrically connected to the positive terminal of the first direct-current power supply 1. The low-potential side first direct-current main circuit of the power conversion unit 4 on the highest-potential side is electrically connected to the high-potential side first direct-current main circuit of the power conversion unit 4 on the next stage (connected to the low-potential side). The high-potential side first direct-current main circuit of the power conversion unit 4 on the lowest-potential side is electrically connected to the low-potential side first direct-current main circuit of the power conversion unit 4 on the previous stage (connected to the high-potential side). The low-potential side first direct-current main circuit of the power conversion unit 4 on the lowest-potential side is electrically connected to the negative terminal of the first direct-current power supply 1.

[0030] The chopper circuits 5 of the three power conversion units 4 are electrically connected to each other at the step-down output terminals. That is, the low-potential side second DC main circuit of the power conversion unit 4 is electrically connected between the two switching elements 9 of the power conversion unit 4 of the next stage (connected to the low-potential side). The two switching elements 9 of the chopper circuit 5 of the power conversion unit 4 of the highest-potential side are electrically connected to the positive terminal of the second DC power supply 2 via the reactor 8 and the reactor 6. The low-potential side second DC main circuit of the power conversion unit 4 of the lowest-potential side is electrically connected to the negative terminal of the second DC power supply 2. That is, as shown in FIG. 1, the chopper circuit 5 side of the three power conversion units 5 is connected in cascade. Figure 1

[0031] The reactor 6 and the reactor 8 are connected in series between the positive terminal of the second DC power supply 2 and the two switching elements 9 of the power conversion unit 4 of the highest-potential side. The capacitor 7 is connected in series with the reactor 6 between the positive terminal and the negative terminal of the second DC power supply 2. The reactor 6 and the capacitor 7 constitute an LC filter, and can suppress the flow of high-order harmonic currents to the second DC power supply 2.

[0032] The control circuit CTR is, for example, an arithmetic circuit provided with at least one processor such as a CPU (central processing unit) or an MPU (microprocessing unit), and a memory capable of recording a program executed by the processor.

[0033] The control circuit CTR controls the operation of the chopper circuit 5 to control the current flowing in the reactor 8, and performs voltage control to make the voltage of the capacitor 7 a predetermined value. In addition, the control circuit CTR can acquire values detected by a voltage sensor that detects the voltage of the capacitor 7 and various sensors (not shown) included in the power conversion device 3 as needed, and use them for arithmetic operations.

[0034] Next, an example of the operation of the power supply device and the power conversion device according to the present embodiment will be described.

[0035] For example, when power is supplied from the first DC power supply 1 to the second DC power supply 2, the first inverter INV1 stops switching operation. That is, the four power semiconductor elements 11 of the first inverter INV1 become in an off state. The second inverter INV2 outputs a high-frequency current as a high-frequency inverter.

[0036] The voltages of the capacitors 12 and 13 are determined by the turns ratio of the first winding and the second winding of the high-frequency insulation transformer 15. Here, the value obtained by adding the voltages of the capacitors 12 of the number of series stages (three) is set to be greater than the voltage of the second DC power supply 2.

[0037] ​In the above state, the control circuit CTR controls so that the chopper circuits 5 perform the step-down operation and output the current from the power conversion device 3 to the second DC power supply 2. At this time, the control circuit CTR causes the plurality of chopper circuits 5 to perform the interleaved operation. For example, in the power conversion device 3 shown in FIG. 1, since the three chopper circuits 5 are connected in series, the control circuit CTR generates the gate signals for the switching elements 9 of the three chopper circuits 5 so that the phases are shifted from each other by 120°. Thereby, for example, when the switching frequency in one power conversion unit 4 is 1 kHz, the switching frequency in the entire power conversion device 3 is equivalent to 3 kHz. As a result, it is possible to make the current output from the power conversion device 3 high-frequency, to suppress the inductance value of the reactor 8, and to reduce the size of the reactor 8. Figure 1 In the power conversion device 3 shown in FIG. 1, since the three chopper circuits 5 are connected in series, the control circuit CTR generates the gate signals for the switching elements 9 of the three chopper circuits 5 so that the phases are shifted from each other by 120°. Thereby, for example, when the switching frequency in one power conversion unit 4 is 1 kHz, the switching frequency in the entire power conversion device 3 is equivalent to 3 kHz. As a result, it is possible to make the current output from the power conversion device 3 high-frequency, to suppress the inductance value of the reactor 8, and to reduce the size of the reactor 8.

[0038] Further, the power conversion unit 4 of the present embodiment is a resonance type high-frequency isolation circuit, and therefore, for example, compared with a conventional dual active bridge (DAB) circuit, the peak current value flowing in the high-frequency isolation transformer 15 does not increase. Therefore, it is possible to suppress an increase in the rated current of the high-frequency isolation transformer 15, and to suppress the peak current of the power semiconductor elements 10 and 11 of the first and second inverters INV1 and INV2, and to make the power supply device and the power conversion device small.

[0039] In addition, when the power is supplied from the second DC power supply 2 to the first power supply 2, in contrast to the above operation, the second inverter INV2 stops the switching operation, and the first inverter INV1 operates as a high-frequency inverter to output the high-frequency current. The control circuit CTR generates the gate signals for the switching elements 9 of the chopper circuits 5 in the above state so that the arbitrary current flows in the reactor 8.

[0040] As described above, according to the present embodiment, it is possible to achieve the miniaturization of the power conversion device and the power supply device.

[0041] Next, the power conversion device and the power supply device of the second embodiment will be described in detail with reference to the drawings. In the following description, the same symbols are attached to the same configurations as those of the power conversion device and the power supply device of the above first embodiment, and the description thereof will be omitted.

[0042] Figure 2 is a view schematically showing one configuration example of the power conversion unit of the power conversion device of the second embodiment.

[0043] The power conversion device of the present embodiment differs from the above first embodiment in the configuration of the first and second inverters INV1 and INV2 of the power conversion unit 4.

[0044] The first inverter INV1 is configured of leg lines (first leg lines) each of which has the power semiconductor element 10 in the upper arm and the lower arm, and leg lines (second leg lines) each of which has the resonance capacitor 21 in the upper arm and the lower arm.

[0045] The second inverter INV2 is configured of leg lines (first leg lines) each of which has the power semiconductor element 11 in the upper arm and the lower arm, and leg lines (second leg lines) each of which has the resonance capacitor 22 in the upper arm and the lower arm.

[0046] In the power conversion device of the present embodiment, the first inverter INV1 and the second inverter INV2 are configured with the resonance capacitors 21 and 22, and therefore the resonance capacitor 14 in the power conversion unit 4 of the first embodiment described above is omitted.

[0047] The power conversion unit 4 of the power conversion device of the present embodiment is the same as that of the first embodiment described above except for the above configuration. Further, the operation of the power conversion device and the power supply device of the present embodiment is the same as that of the first embodiment described above.

[0048] That is, according to the power conversion device and the power supply device of the present embodiment, the rated current of the high-frequency isolation transformer 15 can be suppressed from increasing, and the peak current of the power semiconductor elements 10 and 11 of the first inverter INV1 and the second inverter INV2 can be suppressed. Thus, according to the present embodiment, the power conversion device and the power supply device can be miniaturized.

[0049] Next, the power conversion device and the power supply device of the third embodiment will be described in detail with reference to the drawings.

[0050] Figure 3 is a diagram schematically showing one configuration example of the power conversion device and the power supply device of the third embodiment.

[0051] The power supply device of the present embodiment is provided with the first direct-current power supply 1, the resistor R, and the power conversion device 3, and is electrically connected to the second direct-current power supply 2. The second direct-current power supply 2 is a direct-current power supply provided with a direct-current feeding circuit, and is, for example, an overhead line. The second direct-current power supply 2 is, for example, DC 3000 V feeding.

[0052] The power conversion device 3 of the present embodiment is provided with a plurality of power conversion units 4 each of which includes the chopper circuit 5 and the resonance-type high-frequency isolation circuit. At least a part of the first direct-current main circuit of the plurality of first inverters INV1 is connected in parallel to the first direct-current power supply 1. The step-down output terminals of the plurality of chopper circuits 5 are connected in series between the positive terminal and the negative terminal of the second direct-current power supply 2.

[0053] In Figure 3In the example shown, the power conversion device 3 includes a first conversion section 31, a second conversion section 32, a capacitor 7, and reactors 6 and 8.

[0054] The first DC power supply 1 is, for example, a DC power supply including a storage battery. Alternatively, the first DC power supply 1 can be a power converter that converts AC power into DC power and outputs the DC power.

[0055] In the present embodiment, the first DC power supply 1 is grounded via a resistor R at a neutral point between a high-potential side power supply IP and a low-potential side power supply IN. Thus, the ground potential of the storage battery of the first DC power supply 1 can be reduced. Alternatively, when the insulation withstand voltage of the storage battery of the first DC power supply 1 is sufficient, the first DC power supply 1 can be grounded at the low-potential side instead of at the neutral point, or the circuit on the first DC power supply 1 side can be insulated to be in an electrically floating state.

[0056] The first conversion section 31 and the second conversion section 32 each include three power conversion units 4. The first conversion section 31 and the second conversion section 32 are connected in parallel to the first DC power supply 1 and are connected in series between the positive terminal and the negative terminal of the second DC power supply 2.

[0057] In each of the first conversion section 31 and the second conversion section 32, the capacitors 13 of the three power conversion units 4 are connected in series between the positive terminal and the negative terminal of the first DC power supply 1. That is, the high-potential side first DC main circuit of the power conversion unit 4 on the highest-potential side is electrically connected to the positive terminal of the first DC power supply 1. The high-potential side first DC main circuit of the power conversion unit 4 on the next highest-potential side (connected to the low-potential side) is electrically connected to the low-potential side first DC main circuit of the power conversion unit 4 on the highest-potential side. The low-potential side first DC main circuit of the power conversion unit 4 on the next lowest-potential side (connected to the high-potential side) is electrically connected to the high-potential side first DC main circuit of the power conversion unit 4 on the next highest-potential side. The low-potential side first DC main circuit of the power conversion unit 4 on the lowest-potential side is electrically connected to the negative terminal of the first DC power supply 1.

[0058] The step-down output terminals of the chopper circuits 5 of the three power conversion units 4 of the first conversion section 31 and the step-down output terminals of the chopper circuits 5 of the three power conversion units 4 of the second conversion section 32 are connected in series between the positive terminal and the negative terminal of the second DC power supply 2. That is, the low-potential side second DC main circuit of the power conversion unit 4 is electrically connected between the two switching elements 9 of the power conversion unit 4 on the next lowest-potential side (connected to the low-potential side). The two switching elements 9 of the chopper circuit 5 of the power conversion unit 4 on the highest-potential side are electrically connected to the positive terminal of the second DC power supply 2 via the reactor 8 and the reactor 6. The low-potential side second DC main circuit of the power conversion unit 4 on the lowest-potential side is electrically connected to the negative terminal of the second DC power supply 2.

[0059] The reactor 6 and the reactor 8 are connected in series between the positive terminal of the second DC power supply 2 and the two switching elements 9 of the power conversion unit 4 on the highest potential side. The capacitor 7 is connected in series with the reactor 6 between the positive terminal and the negative terminal of the second DC power supply 2. The reactor 6 and the capacitor 7 constitute an LC filter that suppresses the flow of high-order harmonic currents to the second DC power supply 2.

[0060] The control circuit CTR is, for example, an arithmetic circuit that has at least one processor such as a CPU (central processing unit) or an MPU (microprocessing unit), and a memory capable of recording a program executed by the processor.

[0061] The control circuit CTR controls the operation of the chopper circuit 5 to control the current flowing in the reactor 8, and performs voltage control to make the voltage of the capacitor 7 a prescribed value.

[0062] The operation of the power conversion device and the power supply device according to the present embodiment is the same as that of the first embodiment described above. That is, according to the power conversion device and the power supply device according to the present embodiment, the rated current of the high-frequency isolation transformer 15 can be suppressed from increasing, and the peak current of the power semiconductor elements 10 and 11 of the first inverter INV1 and the second inverter INV2 can be suppressed. Thus, according to the present embodiment, the power conversion device and the power supply device can be made smaller.

[0063] The embodiments of the present application have been described, but these embodiments are presented as examples and are not intended to limit the scope of the application. These new embodiments can be implemented in other various ways, and various omissions, substitutions, and changes can be made within the scope of the gist of the application. These embodiments and modifications are included in the scope and gist of the application, and are included in the scope of the application and the equivalent range described in the claims.

[0064] For example, in the above-described embodiments, the plurality of capacitors 13 are connected in series between the positive terminal and the negative terminal of the first DC power supply 1, but the plurality of capacitors 13 can be connected in parallel with the first DC power supply 1. In this case, the same effects as those of the above-described embodiments can be obtained.

[0065] Further, in the above-described embodiments, the power conversion device 3 has the plurality of power conversion units 4, but the power conversion device 3 can have at least one power conversion unit 4. The number of power conversion units 4 mounted on the power conversion device 3 can be adjusted according to the switching frequency and the switching loss of the switching elements 9 of the chopper circuit 5.

Claims

1. A power conversion device electrically connected between a first DC power source and a second DC power source and provided with a plurality of power conversion units including a plurality of chopper circuits and a plurality of high-frequency insulation circuits, wherein the chopper circuit is electrically connected between a positive terminal and a negative terminal of the second DC power source via a reactor at a step-down output terminal, the high-frequency insulation circuit is provided with a first inverter electrically connected between the positive terminal and the negative terminal of the first DC power source at a first DC main circuit, a second inverter electrically connected at a high-voltage circuit side of the chopper circuit at a second DC main circuit, and a high-frequency insulation transformer electrically connected between an AC terminal of the first inverter and an AC terminal of the second inverter, a plurality of the first DC main circuits of the first inverters are connected in series between the positive terminal and the negative terminal of the first DC power source, and a plurality of the chopper circuits are connected in cascade between the positive terminal and the negative terminal of the second DC power source.

2. The power conversion device according to claim 1, wherein the first inverter and the second inverter are full-bridge circuits, the high-frequency insulation transformer is a transformer circuit provided with a first winding electrically connected between the AC terminals of the first inverter and a second winding electrically connected between the AC terminals of the second inverter, and the power conversion device is further provided with a resonance capacitor sandwiched between an AC line connected between one of the AC terminals of the second inverter and the second winding or an AC line connected between one of the AC terminals of the first inverter and the first winding.

3. The power conversion device according to claim 1, wherein the first inverter and the second inverter are provided with a first leg in which switching elements are respectively provided at upper arms and lower arms, and a second leg in which resonance capacitors are respectively provided at the upper arms and the lower arms in parallel with the first leg.

4. The power conversion device according to any one of claims 1 to 3, wherein the chopper circuit is a half-bridge circuit.

5. The power conversion device according to claim 4, wherein the chopper circuit is provided with wide-bandgap semiconductor elements at the upper arms and the lower arms, respectively.

6. The power conversion device according to any one of claims 1 to 3, wherein at least a part of the first DC main circuits of the first inverters is connected in parallel with the first DC power source.

7. The power conversion device according to claim 6, further provided with a control circuit that controls operations of the plurality of power conversion units, wherein the control circuit causes the plurality of chopper circuits to perform staggered operations among the plurality of power conversion units.

8. A power source device for a substation, provided with: the power conversion device according to any one of claims 1 to 7; and the first DC power source, wherein the first DC power source is provided with a storage battery. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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