A common mode voltage suppression system

Abstract

A common-mode voltage suppression system, in which the input end of the power electronic transformer is connected to a medium- and high-voltage power grid, and the output end is connected to the low-voltage DC bus; the input end of the low-voltage inverter DC / AC device is connected to the low-voltage DC bus, and the output end is connected to a low-voltage AC load; the input end of the non-isolated DC / DC device is connected in parallel to the low-voltage DC bus, and the output end is respectively connected to the low-voltage DC load; the output side of the low-voltage inverter DC / AC device is connected to the input side of the non-isolated DC / DC device to construct a low-impedance loop for the common-mode voltage. In this solution, by constructing a low-impedance loop for the common-mode voltage on the output side of the low-voltage inverter DC / AC device and the input side of the non-isolated DC / DC device, the common-mode voltage on the AC side can be effectively suppressed by the DC side, solving the problem of excessive common-mode voltage in the non-isolated AC / DC power supply circuit interfering with the power supply process.

Description

Technical Field

[0001] The invention relates to the technical field of AC and DC power supply and utilization, and in particular to a common mode voltage suppression system. Background Art

[0002] The AC / DC power supply system is the core part of the AC / DC distribution network that will emerge in the future. It plays an important role in power conversion (including voltage level conversion, frequency conversion, AC / DC power supply mode conversion, etc.) and power supply. Its core technology is power electronic equipment technology. In actual application design, in order to improve the power density of the equipment, reduce the manufacturing cost of the equipment or take other design factors into consideration, the low-voltage AC side of the equipment usually uses a high-power three-phase three-wire non-isolated inverter to power the low-voltage AC load, and the low-voltage DC side of the equipment often uses a high-power non-isolated DC / DC (DC / DC) converter to power the low-voltage DC load.

[0003] However, in most cases, the power supply wiring method required for low-voltage AC loads is mostly three-phase four-wire (or three-phase five-wire), and the grounding method of low-voltage DC loads is mostly IT (I = the power supply end is not grounded or grounded via high impedance; T = the exposed conductive part of the electrical device is directly grounded, and this grounding point is electrically independent of the grounding point at the power supply end). In this case, if the wiring method of the AC and DC power supply system is not processed, it will result in the inability to supply power to the low-voltage three-phase four-phase (or three-phase five-wire) AC load. In addition, if the common-mode voltage generated by the converter device using PWM (pulse width modulation) technology on the low-voltage AC and DC bus is not processed, the excessive common-mode voltage will damage the low-voltage AC and DC load. Summary of the invention

[0004] In order to solve the problem in the prior art that the existing system cannot perform three-phase four-wire or three-phase five-wire power supply and there is common mode interference on the AC and DC sides, the present invention provides a common mode voltage suppression system.

[0005] The technical solution provided by the present invention is:

[0006] A common mode voltage suppression system, the system comprising:

[0007] Power electronic transformers, low voltage DC busbars, low voltage inverter DC / AC devices and non-isolated DC / DC devices;

[0008] The input end of the power electronic transformer is connected to the medium and high voltage power grid, and the output end is connected to the low voltage DC bus;

[0009] The input end of the low-voltage inverter DC / AC device is connected to the low-voltage DC bus, and the output end is connected to the low-voltage AC load;

[0010] The input end of the non-isolated DC / DC device is connected in parallel to the low-voltage DC bus, and the output end is connected to the low-voltage DC load respectively;

[0011] The output side of the low voltage inverter DC / AC device is connected to the input side of the non-isolated DC / DC device to construct a low impedance loop of the common mode voltage.

[0012] Preferably, the inverter DC / AC device comprises:

[0013] DC support capacitors, power semiconductor switches and LC filters on the DC side;

[0014] The DC side DC support capacitor and the power semiconductor switch are sequentially connected in parallel to the low voltage DC bus;

[0015] The AC side LC filter is connected between the power semiconductor switch and the low voltage AC load;

[0016] The AC side LC filter is also connected to the input side of the non-isolated DC / DC device to construct a low impedance loop of the common mode voltage.

[0017] Preferably, the AC side LC filter comprises:

[0018] Three filter reactances, three filter capacitors and loop capacitors;

[0019] The filter reactor is connected to the semiconductor switch;

[0020] The filter capacitor is connected in star shape and then connected in parallel with the filter reactance;

[0021] The neutral point of the star-connected filter capacitor is connected to the input end of the non-isolated DC / DC device through the loop capacitor.

[0022] Preferably, the non-isolated DC / DC device comprises:

[0023] Input side DC support capacitor, power semiconductor switch device and output side LC filter;

[0024] The power semiconductor switch device is connected in parallel to the input-side DC support capacitor;

[0025] The input end of the output-side LC filter is connected to the power semiconductor switch device, and the output end is connected to the low-voltage DC load.

[0026] Preferably, the system further comprises:

[0027] Common mode reactance, common mode capacitance to AC side and common mode capacitance to ground;

[0028] The input end of the common mode reactor is connected in parallel to the low voltage DC bus, and the output end is connected in parallel to the AC side common mode capacitor and the ground common mode capacitor in sequence;

[0029] The pair of AC side common mode capacitors are connected to the neutral point via the loop capacitor to construct a low impedance loop of the common mode voltage;

[0030] The common mode capacitor to ground is grounded.

[0031] Preferably, the pair of AC side common mode capacitors include:

[0032] a first common-mode capacitor and a second common-mode capacitor;

[0033] The first common-mode capacitor and the second common-mode capacitor are connected in series and connected in parallel to the output end of the common-mode reactance;

[0034] The midpoint of the pair of AC-side common-mode capacitors is connected to the neutral point to construct a low-impedance loop of the common-mode voltage.

[0035] Preferably, the common-mode capacitor to ground includes:

[0036] a first common-mode capacitor to ground and a second common-mode capacitor to ground;

[0037] The first common-mode capacitor to ground and the second common-mode capacitor to ground are connected in series, and the whole is connected in parallel with the pair of AC-side common-mode capacitors;

[0038] A connection midpoint between the first common-mode capacitor to ground and the second common-mode capacitor to ground is grounded.

[0039] Preferably, the system further comprises:

[0040] Z-type grounding transformer, grounding transformer coupling voltage filter capacitor, AC switch, low voltage AC power supply and neutral wire;

[0041] The Z-type grounding transformer, the grounding transformer coupling voltage filter capacitor and the AC switch are connected in parallel to the three-phase three-wire output terminal;

[0042] The AC switch is connected to the low-voltage AC power supply;

[0043] The Z-type grounding transformer, the grounding transformer coupling voltage filter capacitor and the low-voltage AC power supply are connected to the neutral line;

[0044] The neutral line is connected to the low-voltage AC load to form a three-phase four-wire circuit;

[0045] The neutral line can also be grounded to form a three-phase five-wire circuit.

[0046] Preferably, the ground-variable coupling voltage filter capacitor comprises:

[0047] Three capacitors;

[0048] After the capacitor is connected in star shape, it is connected in parallel with the output end of the AC side LC filter;

[0049] The neutral point of the capacitor star connection is connected to the zero line.

[0050] Preferably, the power electronic transformer device comprises:

[0051] High voltage AC reactors, high voltage DC reactors, high voltage AC units, high voltage DC units, high frequency transformer isolation units and low voltage DC units;

[0052] One end of the high-voltage AC reactor is connected to the high-voltage AC power supply, and the other end is connected to the high-voltage AC unit;

[0053] One end of the high-voltage DC reactor is connected to the high-voltage DC power supply, and the other end is connected to the high-voltage DC unit;

[0054] The high-voltage AC unit and the high-voltage DC power supply are connected to the low-voltage DC unit via the high-frequency transformer isolation unit;

[0055] The low-voltage DC unit is connected in parallel to the low-voltage DC bus.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] The technical solution provided by the present invention includes: a power electronic transformer, a low-voltage DC bus, a low-voltage inverter DC / AC device and a non-isolated DC / DC device; the input end of the power electronic transformer is connected to the medium and high voltage power grid, and the output end is connected to the low-voltage DC bus; the input end of the low-voltage inverter DC / AC device is connected to the low-voltage DC bus, and the output end is connected to the low-voltage AC load; the input end of the non-isolated DC / DC device is connected in parallel to the low-voltage DC bus, and the output end is respectively connected to the low-voltage DC load; the output side of the low-voltage inverter DC / AC device is connected to the input side of the non-isolated DC / DC device to construct a low-impedance loop of common-mode voltage. In this solution, by constructing a low-impedance loop of common-mode voltage on the output side of the low-voltage inverter DC / AC device and the input side of the non-isolated DC / DC device, the common-mode voltage of the DC side to the AC side can be effectively suppressed, solving the problem of excessive common-mode voltage of the non-isolated AC / DC power supply circuit interfering with the power supply process.

[0058] In this solution, a three-phase four-wire or three-phase five-wire power supply method is constructed through a low-voltage inverter DC / AC device to supply power to a low-voltage AC load; the non-isolated DC / DC device in this solution can construct a three-phase four-wire or three-phase five-wire power supply method to supply power to a low-voltage DC load, thereby solving the power supply demand of the low-voltage AC load. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 It is a schematic diagram of the common mode voltage suppression system of the present invention. DETAILED DESCRIPTION

[0060] In order to better understand the present invention, the content of the present invention is further described below in conjunction with the accompanying drawings and examples.

[0061] Embodiment 1:

[0062] This embodiment provides a common-mode voltage suppression system, a schematic diagram of the common-mode voltage suppression system, as shown in FIG. Figure 1 As shown, it is usually composed of a power electronic transformer device, an inverter DC / AC device and a DC / DC device.

[0063] The power electronic transformer device in the figure usually consists of a high-voltage AC unit, a high-voltage DC unit, a high-frequency transformer isolation unit, a low-voltage DC unit, and a high-voltage AC reactor L ac , High voltage DC smoothing reactor L dc etc.; the power electronic transformer is connected through the reactor L ac , AC switch QF1 is connected to the high voltage AC power supply, and through the smoothing reactor L dc , the DC switch QS1 is connected to the high voltage DC power supply; the low voltage DC unit is connected to the low voltage DC bus. The power electronic transformer is responsible for the conversion of voltage levels and the conversion of voltage AC and DC forms, and the energy flow between high voltage AC, high voltage DC and low voltage DC can flow mutually.

[0064] The low-voltage inverter DC / AC device in the figure is usually composed of a DC support capacitor, a power semiconductor switch device group and an LC filter (the low-voltage inverter DC / AC here is a three-phase three-wire system), which is responsible for the conversion of the low-voltage power supply AC and DC forms, and the electric energy can flow between the AC and DC sides. The AC side of the low-voltage inverter DC / AC device constructs a neutral line N through a Z-type grounding transformer. The neutral line N and the three-phase live wires A, B, and C output by the low-voltage inverter DC / AC form a three-phase four-wire power supply mode. If the neutral line N is connected to the ground wire, it forms a three-phase five-wire power supply mode; the low-voltage inverter DC / AC device can also be connected to the low-voltage AC power supply through the AC switch QF2 for parallel operation.

[0065] Non-isolated DC / DC devices usually consist of a DC support capacitor on the input side, a power semiconductor switching device assembly and an LC filter on the output side. They are responsible for low-voltage DC power supply voltage level conversion, and their electrical energy can flow in single-phase or bidirectional manner.

[0066] The present invention firstly installs a set of Z-type grounding transformers (the input end of the transformer is connected to the three-phase low-voltage AC busbars A, B, and C, and the output end is connected to the neutral line N and the earth) and a set of transformer coupling voltage filter capacitors C on the AC output side of the low-voltage inverter DC / AC device. f (The three-phase capacitors are connected in parallel at the input and output ends of the Z-type grounding transformer to filter out the induced voltage caused by the coupling leakage inductance of the input and output of the Z-type grounding transformer), and a capacitor C is installed at the neutral point O of the three-phase capacitor of the LC filter, and one end of the capacitor C is connected to the neutral point O; in addition, a group of common-mode inductors Ln and a group of common-mode capacitors C on the AC side are installed on the low-voltage DC bus on the input side of each non-isolated DC / DC device. n1 , C n2 And a set of common mode capacitors C to ground n3 , C n4 The other end of the capacitor C is connected to the capacitor C installed on the low-voltage DC bus on the input side of each isolated DC / DC device. n1 , C n2 In addition, the common-mode capacitor C installed on the low-voltage DC bus on the input side of each isolated DC / DC device n3 , C n4 The resulting neutral point is connected directly to the earth ground.

[0067] The connection relationship thus formed first meets the access method requirements of low-voltage AC loads (three-phase four-wire or three-phase five-wire system), and provides a ground reference potential N for the AC / DC power supply system. In addition, this connection method can establish a low-impedance flow loop for the common-mode current caused by the common-mode voltage on the DC side to the AC side. Since a common-mode reactor Ln is additionally added to this loop, most of the common-mode voltage on the DC side to the AC side can be dropped on this common-mode reactor and the AC side LC filter reactor, thereby ensuring the suppression of the common-mode voltage on the AC side by the input and output bus of the non-isolated DC / DC device; in addition, a common-mode capacitor C to ground installed on the low-voltage DC bus on the input side of each non-isolated DC / DC device n3 , C n4 It also forms a low-impedance loop with the Z-type grounding transformer, which can drop most of the common-mode voltage of the low-voltage DC bus to the ground on the common-mode inductor Ln and the AC-side LC filter inductor, further ensuring the suppression of the common-mode voltage to the ground on the input and output sides of the non-isolated DC / DC device.

[0068] Embodiment 2:

[0069] This embodiment provides a common mode voltage suppression system, the system comprising:

[0070] Power electronic transformers, low voltage DC busbars, low voltage inverter DC / AC devices and non-isolated DC / DC devices;

[0071] The input end of the power electronic transformer is connected to the medium and high voltage power grid, and the output end is connected to the low voltage DC bus;

[0072] The input end of the low-voltage inverter DC / AC device is connected to the low-voltage DC bus, and the output end is connected to the low-voltage AC load;

[0073] The input end of the non-isolated DC / DC device is connected in parallel to the low-voltage DC bus, and the output end is connected to the low-voltage DC load respectively;

[0074] The output side of the low voltage inverter DC / AC device is connected to the input side of the non-isolated DC / DC device to construct a low impedance loop of the common mode voltage;

[0075] The medium and high voltage power grid is a DC medium and high voltage power grid or an AC medium and high voltage power grid.

[0076] The inverter DC / AC device comprises:

[0077] DC support capacitors, power semiconductor switches and LC filters on the DC side;

[0078] The DC side DC support capacitor and the power semiconductor switch are sequentially connected in parallel to the low voltage DC bus;

[0079] The AC side LC filter is connected between the power semiconductor switch and the low voltage AC load;

[0080] The AC side LC filter is also connected to the input side of the non-isolated DC / DC device to construct a low impedance loop of the common mode voltage.

[0081] The AC side LC filter comprises:

[0082] Three filter reactances, three filter capacitors and loop capacitors;

[0083] The filter reactor is connected to the semiconductor switch;

[0084] The filter capacitor is connected in star shape and then connected in parallel with the filter reactance;

[0085] The neutral point of the star-connected filter capacitor is connected to the input end of the non-isolated DC / DC device through the loop capacitor.

[0086] The non-isolated DC / DC device comprises:

[0087] Input side DC support capacitor, power semiconductor switch device and output side LC filter;

[0088] The power semiconductor switch device is connected in parallel to the input-side DC support capacitor;

[0089] The input end of the output-side LC filter is connected to the power semiconductor switch device, and the output end is connected to the low-voltage DC load.

[0090] The system further comprises:

[0091] Common mode reactance, common mode capacitance to AC side and common mode capacitance to ground;

[0092] The input end of the common mode reactor is connected in parallel to the low voltage DC bus, and the output end is connected in parallel to the AC side common mode capacitor and the ground common mode capacitor in sequence;

[0093] The pair of AC side common mode capacitors are connected to the neutral point via the loop capacitor to construct a low impedance loop of the common mode voltage;

[0094] The common mode capacitor to ground is grounded.

[0095] The pair of AC side common mode capacitors include:

[0096] a first common-mode capacitor and a second common-mode capacitor;

[0097] The first common-mode capacitor and the second common-mode capacitor are connected in series and connected in parallel to the output end of the common-mode reactance;

[0098] The midpoint of the pair of AC-side common-mode capacitors is connected to the neutral point to construct a low-impedance loop of the common-mode voltage.

[0099] The common-mode capacitor to ground includes:

[0100] a first common-mode capacitor to ground and a second common-mode capacitor to ground;

[0101] The first common-mode capacitor to ground and the second common-mode capacitor to ground are connected in series, and the whole is connected in parallel with the pair of AC-side common-mode capacitors;

[0102] A connection midpoint between the first common-mode capacitor to ground and the second common-mode capacitor to ground is grounded.

[0103] The system further comprises:

[0104] Z-type grounding transformer, grounding transformer coupling voltage filter capacitor, AC switch, low voltage AC power supply and neutral wire;

[0105] The Z-type grounding transformer, the grounding transformer coupling voltage filter capacitor and the AC switch are connected in parallel to the three-phase three-wire output terminal;

[0106] The AC switch is connected to the low-voltage AC power supply;

[0107] The Z-type grounding transformer, the grounding transformer coupling voltage filter capacitor and the low-voltage AC power supply are connected to the neutral line;

[0108] The neutral line is connected to the low-voltage AC load to form a three-phase four-wire circuit;

[0109] The neutral line can also be grounded to form a three-phase five-wire circuit.

[0110] The grounding variable coupling voltage filter capacitor comprises:

[0111] Three capacitors;

[0112] After the capacitor is connected in star shape, it is connected in parallel with the output end of the AC side LC filter;

[0113] The neutral point of the capacitor star connection is connected to the zero line.

[0114] The power electronic transformer device comprises:

[0115] High voltage AC reactors, high voltage DC reactors, high voltage AC units, high voltage DC units, high frequency transformer isolation units and low voltage DC units;

[0116] One end of the high-voltage AC reactor is connected to the high-voltage AC power supply, and the other end is connected to the high-voltage AC unit;

[0117] One end of the high-voltage DC reactor is connected to the high-voltage DC power supply, and the other end is connected to the high-voltage DC unit;

[0118] The high-voltage AC unit and the high-voltage DC power supply are connected to the low-voltage DC unit via the high-frequency transformer isolation unit;

[0119] The low-voltage DC unit is connected in parallel to the low-voltage DC bus.

[0120] Obviously, the described embodiments are only some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0121] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0122] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0123] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0124] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0125] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of the claims of the present invention to be approved.

Claims

1. A common mode voltage suppression system, characterized in that: The system comprises: Power electronic transformers, low voltage DC busbars, low voltage inverter DC / AC devices and non-isolated DC / DC devices; The input end of the power electronic transformer is connected to the medium and high voltage power grid, and the output end is connected to the low voltage DC bus; The input end of the low-voltage inverter DC / AC device is connected to the low-voltage DC bus, and the output end is connected to the low-voltage AC load; The input end of the non-isolated DC / DC device is connected in parallel to the low-voltage DC bus, and the output end is connected to the low-voltage DC load respectively; A low impedance loop of common mode voltage is constructed between the output side of the low voltage inverter DC / AC device and the input side of the non-isolated DC / DC device; The inverter DC / AC device comprises: DC support capacitors, power semiconductor switches and LC filters on the DC side; The DC side DC support capacitor and the power semiconductor switch are sequentially connected in parallel to the low voltage DC bus; The AC side LC filter is connected between the power semiconductor switch and the low voltage AC load; The AC side LC filter is also connected to the input side of the non-isolated DC / DC device to construct a low impedance loop of the common mode voltage; The AC side LC filter comprises: Three filter reactances, three filter capacitors and loop capacitors; The filter reactor is connected to the semiconductor switch; The filter capacitor is connected in star shape and then connected in parallel with the filter reactance; The neutral point of the star connection of the filter capacitor is connected to the input end of the non-isolated DC / DC device through the loop capacitor; The common mode voltage suppression system further includes: Common mode reactance, common mode capacitance to AC side and common mode capacitance to ground; The input end of the common mode reactor is connected in parallel to the low voltage DC bus, and the output end is connected in parallel to the AC side common mode capacitor and the ground common mode capacitor in sequence; The pair of AC side common mode capacitors are connected to the neutral point via the loop capacitor to construct a low impedance loop of the common mode voltage; The common mode capacitor to ground is grounded; The power electronic transformer device comprises: High voltage AC reactors, high voltage DC reactors, high voltage AC units, high voltage DC units, high frequency transformer isolation units and low voltage DC units; One end of the high-voltage AC reactor is connected to the high-voltage AC power supply, and the other end is connected to the high-voltage AC unit; One end of the high-voltage DC reactor is connected to the high-voltage DC power supply, and the other end is connected to the high-voltage DC unit; The high-voltage AC unit and the high-voltage DC power supply are connected to the low-voltage DC unit via the high-frequency transformer isolation unit; The low-voltage DC unit is connected in parallel to the low-voltage DC bus.

2. The system according to claim 1, characterized in that The non-isolated DC / DC device comprises: Input side DC support capacitor, power semiconductor switch device and output side LC filter; The power semiconductor switch device is connected in parallel to the input-side DC support capacitor; The input end of the output-side LC filter is connected to the power semiconductor switch device, and the output end is connected to the low-voltage DC load.

3. The system according to claim 1, characterized in that The pair of AC side common mode capacitors include: a first common-mode capacitor and a second common-mode capacitor; The first common-mode capacitor and the second common-mode capacitor are connected in series and connected in parallel to the output end of the common-mode reactance; The pair of AC-side common-mode capacitors are connected to the neutral point via the loop capacitor to construct a low-impedance loop of the common-mode voltage.

4. The system according to claim 1, characterized in that The common-mode capacitor to ground includes: a first common-mode capacitor to ground and a second common-mode capacitor to ground; The first common-mode capacitor to ground and the second common-mode capacitor to ground are connected in series, and the whole is connected in parallel with the pair of AC-side common-mode capacitors; A connection midpoint between the first common-mode capacitor to ground and the second common-mode capacitor to ground is grounded.

5. The system according to claim 1, wherein: The system further comprises: Z-type grounding transformer, grounding transformer coupling voltage filter capacitor, AC switch, low voltage AC power supply and neutral wire; The Z-type grounding transformer, the grounding transformer coupling voltage filter capacitor and the AC switch are connected in parallel to the three-phase three-wire output end of the inverter DC / AC device; The AC switch is connected to the low-voltage AC power supply; The Z-type grounding transformer, the grounding transformer coupling voltage filter capacitor and the low-voltage AC power supply are connected to the neutral line; The neutral line is connected to the low-voltage AC load to form a three-phase four-wire circuit; The neutral line can also be grounded to form a three-phase five-wire circuit.

6. The system according to claim 5, characterized in that The grounding variable coupling voltage filter capacitor comprises: Three capacitors; After the capacitor is connected in star shape, it is connected in parallel with the output end of the AC side LC filter; The neutral point of the capacitor star connection is connected to the zero line.

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