AC / DC power supply system with groundable power supply end

Abstract

A kind of AC power supply system for power supply end can be grounded, in the scheme, the input end of power electronic transformer is connected with medium-high voltage network, and the output end is connected with the low-voltage DC bus;The input end of the low-voltage inverter DC / AC device is connected with the low-voltage DC bus, and the output end is connected with low-voltage AC load and grounded;Multiple non-isolated DC / DC device input end is connected in parallel to the low-voltage DC bus, and the output end is respectively connected with low-voltage DC load.In the scheme, three-phase four-wire or three-phase five-wire system is constructed in AC power supply side, the problem of lack of ground line system when three-phase three-wire system inverter is powered is solved.In addition, star-connected capacitor is installed on the output side of low-voltage inverter DC / AC device and connected with the input side of non-isolated DC / DC device, low-impedance loop of common-mode voltage is constructed, common-mode voltage from DC side to AC side can be effectively suppressed, and the problem of common-mode voltage of non-isolated AC power supply circuit being too large to interfere with power supply process is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of AC / DC power supply, in particular to an AC / DC power supply system with groundable power supply end. BACKGROUND

[0002] The AC / DC power supply system is the core part of the future emerging AC / DC distribution network, and plays an important role in power conversion (including voltage level conversion, frequency conversion, AC / DC power supply mode conversion, etc.) and power supply. The 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 considering other design factors, the low-voltage AC side of the equipment usually adopts a large-power three-phase three-wire non-isolated inverter to supply power to the low-voltage AC load, and the low-voltage DC side of the equipment usually adopts a large-power non-isolated DC / DC converter to supply power to the low-voltage DC load.

[0003] However, in most cases, the power supply wiring mode required by the low-voltage AC load is three-phase four-wire (or three-phase five-wire) system, and the grounding mode of the low-voltage DC load is usually IT (I=power supply end not grounded or grounded through high impedance; T=the exposed conductive part of the electrical device is directly grounded, and the grounding point is independent of the grounding point of the power supply end) grounding form. In this case, if the wiring mode of the AC / 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, and the three-phase three-wire power supply mode cannot realize the grounding of the non-isolated AC / DC power supply system. SUMMARY

[0004] In order to solve the problem that the existing system cannot supply power in three-phase four-wire or three-phase five-wire mode and the power supply end cannot be grounded in the prior art, the present application provides an AC / DC power supply system with a groundable power supply end.

[0005] The technical scheme provided by the present application is as follows:

[0006] An AC / DC power supply system with a groundable power supply end, the system comprising:

[0007] a power electronic transformer, a low-voltage DC bus, a low-voltage inverter DC / AC device, and a non-isolated DC / DC device;

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

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

[0010] A plurality of the non-isolated DC / DC devices are connected in parallel to the low-voltage DC bus, and the output ends are connected to low-voltage DC loads respectively.

[0011] Preferably, the low-voltage inverter DC / AC device comprises:

[0012] a DC side DC support capacitor, a power semiconductor switch and an LC filter;

[0013] The DC side DC support capacitor and the power semiconductor switch are connected in series to the low-voltage DC bus;

[0014] The LC filter is connected between the power semiconductor switch and a low-voltage AC load.

[0015] Preferably, the LC filter comprises three reactances and three capacitors.

[0016] The three reactances are connected in series to the output end of the power semiconductor switch.

[0017] The three capacitors are connected in parallel to the three reactances to form a three-phase three-wire output end.

[0018] Preferably, the system further comprises:

[0019] a Z-type grounding transformer, a grounding transformer coupling voltage filter capacitor, an AC switch, a low-voltage AC power supply and a neutral line;

[0020] 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.

[0021] The AC switch is connected to the low-voltage AC power supply.

[0022] 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.

[0023] The neutral line is connected to the low-voltage AC load to form a three-phase four-wire circuit.

[0024] The neutral line is grounded to form a three-phase five-wire circuit.

[0025] Preferably, the LC filter comprises three reactances and three capacitors.

[0026] The three reactances are connected in series to the output end of the power semiconductor switch respectively.

[0027] The three capacitors are connected in parallel to the three reactances to form a three-phase three-wire output end.

[0028] Preferably, the system further comprises:

[0029] AC switch, low-voltage AC power supply and zero line;

[0030] The low-voltage AC power supply is connected with the three-phase three-wire output end through the AC switch;

[0031] The midpoint of the DC side DC support capacitor, the capacitor common connection point of the second LC filter and the low-voltage AC power supply are connected with the zero line;

[0032] The zero line is connected with the low-voltage AC load to form a three-phase four-wire system circuit;

[0033] The zero line is grounded to form a three-phase five-wire system circuit.

[0034] Preferably, the third LC filter comprises three reactances, three capacitors and a zero line branch reactance;

[0035] The three reactances and the zero line branch reactance are connected in series on the output end of the power semiconductor switch;

[0036] The three reactances are connected with the zero line branch reactance through the capacitors respectively to form a three-phase three-wire output end.

[0037] Preferably, the system further comprises:

[0038] AC switch, low-voltage AC power supply and zero line;

[0039] The low-voltage AC power supply is connected with the three-phase three-wire output end through the AC switch;

[0040] The zero line branch reactance and the low-voltage AC power supply are connected with the zero line;

[0041] The zero line is connected with the low-voltage AC load to form a three-phase four-wire system circuit;

[0042] The zero line is grounded to form a three-phase five-wire system circuit.

[0043] Preferably, the non-isolated DC / DC device comprises:

[0044] Input side DC support capacitor, power semiconductor switch device and output side LC filter;

[0045] The input side DC support capacitor is connected with the power semiconductor switch device;

[0046] The output end of the output side LC filter is connected with the low-voltage DC load.

[0047] Preferably, the system further comprises:

[0048] The common-mode resistance impedance is connected in parallel with the AC side common-mode capacitance, the ground common-mode capacitance and the star capacitor;

[0049] The input end of the common-mode resistance impedance is connected in parallel with the low-voltage DC bus;

[0050] The AC side common-mode capacitance and the ground common-mode capacitance are connected in parallel with the low-voltage DC bus;

[0051] The star capacitor is connected with the three-phase three-wire output end, and the neutral point of the star capacitor is connected with the neutral point of the AC side common-mode capacitance to form a common-mode voltage low-impedance loop;

[0052] The ground common-mode capacitance is grounded.

[0053] Preferably, the star capacitor comprises:

[0054] Three capacitors in a star connection relationship.

[0055] Preferably, the power electronic transformer comprises:

[0056] A high-voltage AC reactor, a high-voltage DC reactor, a high-voltage AC unit, a high-voltage DC unit, a high-frequency transformer isolation unit and a low-voltage DC unit;

[0057] One end of the high-voltage AC reactor is connected with a high-voltage AC power supply, and the other end is connected with the high-voltage AC unit;

[0058] One end of the high-voltage DC reactor is connected with a high-voltage DC power supply, and the other end is connected with the high-voltage DC unit;

[0059] The high-voltage AC unit and the high-voltage DC power supply are connected with the low-voltage DC unit through the high-frequency transformer isolation unit;

[0060] The low-voltage DC unit is connected in parallel with the low-voltage DC bus.

[0061] Compared with the prior art, the present application has the following advantages:

[0062] The technical scheme provided by the application comprises: 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 with a medium-high voltage power grid, and the output end is connected with the low-voltage DC bus; the input end of the low-voltage inverter DC / AC device is connected with the low-voltage DC bus, and the output end is connected with a low-voltage AC load and grounded; the input ends of a plurality of non-isolated DC / DC devices are connected in parallel to the low-voltage DC bus, and the output ends are respectively connected with low-voltage DC loads. The low-voltage inverter DC / AC device in the scheme can construct a three-phase four-wire or three-phase five-wire power supply mode to supply power to the low-voltage AC load, the non-isolated DC / DC device in the scheme can construct a three-phase four-wire or three-phase five-wire power supply mode to supply power to the low-voltage DC load, and the power supply demand of the low-voltage AC load is solved; the three-phase five-wire power supply mode provided by the low-voltage inverter DC / AC device and the non-isolated DC / DC device can realize the grounding of the non-isolated AC / DC power supply system, and the problem of lacking a grounding system while supplying power after AC / DC conversion or voltage level conversion is solved.

[0063] In addition, the scheme is provided with a star-connected capacitor on the output side of the low-voltage inverter DC / AC device, which is connected with the input side of the non-isolated DC / DC device to construct a low-impedance loop of common-mode voltage, so that the common-mode voltage from the DC side to the AC side can be effectively suppressed, and the problem of interference in the power supply process caused by the excessive common-mode voltage of the non-isolated AC / DC power supply circuit is solved. BRIEF DESCRIPTION OF DRAWINGS

[0064] Figure 1 FIG. 1 is a schematic diagram of an AC / DC power supply system with a groundable power supply end according to the application;

[0065] Figure 2 FIG. 2 is a second ground connection schematic diagram of the AC / DC power supply system with a groundable power supply end according to the application;

[0066] Figure 3 FIG. 3 is a third ground connection schematic diagram of the AC / DC power supply system with a groundable power supply end according to the application. DETAILED DESCRIPTION

[0067] In order to better understand the application, the content of the application will be further described below in combination with the drawings and examples in the specification.

[0068] Embodiment 1

[0069] The embodiment provides an AC / DC power supply system with a groundable power supply end, which is usually composed of a power electronic transformer device, an inverter DC / AC device and a DC / DC device, etc. Figure 1

[0070] ​The power electronic transformer device in the figure is usually composed of a high-voltage alternating current unit, a high-voltage direct current unit, a high-frequency transformer isolation unit, a low-voltage direct current unit, a high-voltage alternating current reactor L ac , a high-voltage direct current reactor L dc ; the power electronic transformer is connected with a high-voltage alternating current power source through a reactor L ac , an alternating current switch QF1, and connected with a high-voltage direct current power source through a smoothing reactor L dc , a direct current switch QS1; the low-voltage direct current unit is connected with a low-voltage direct current bus. The power electronic transformer is responsible for the transformation of voltage levels and the transformation of alternating current and direct current forms, and the energy flow among the high-voltage alternating current, the high-voltage direct current and the low-voltage direct current can flow mutually.

[0071] The low-voltage inverter DC / AC device in the figure is usually composed of a direct current support capacitor, a power semiconductor switch device combination and an LC type filter (the low-voltage inverter DC / AC in this place is a three-phase three-wire system), responsible for the transformation of low-voltage power supply alternating current and direct current forms, and the electric energy can flow mutually between the alternating current side and the direct current side. The alternating current side of the low-voltage inverter DC / AC device is constructed through a Z-type grounding transformer to form a neutral line N, and the neutral line N and the three-phase live lines A, B and C output by the low-voltage inverter DC / AC form a three-phase four-wire power supply mode, and if the neutral line N is connected with the ground wire, a three-phase five-wire power supply mode is formed; the low-voltage inverter DC / AC device can also be connected with a low-voltage alternating current power source through an alternating current switch QF2 to operate in parallel.

[0072] The non-isolated DC / DC device is usually composed of a direct current support capacitor on the input side, a power semiconductor switch device combination and an LC type filter on the output side, responsible for the transformation of low-voltage direct current power supply voltage levels, and the electric energy can flow unilaterally or bidirectionally.

[0073] The application firstly adds a set of Z-type grounding transformers (the input end of the transformer is connected with three-phase low-voltage alternating current buses A, B and C, and the output end is connected with a neutral line N and the ground) and a set of voltage filter capacitors C f (three-phase capacitors are respectively connected in parallel with the input and output ends of the Z-type grounding transformer, used for filtering the induced voltage caused by the input and output coupling leakage inductance of the Z-type grounding transformer) on the alternating current output side of the low-voltage inverter DC / AC device, and adds a set of common-mode filter capacitors (C a , C b , C c ) on the direct current side, and additionally connects a common-mode inductor Ln, a set of common-mode capacitors C n1 , C n2 and a set of common-mode capacitors C n3 , C n4 in series on the low-voltage direct current bus on the input side of each non-isolated DC / DC device; wherein the capacitors C a , Cb , C c After star connection, the neutral point O is connected with the capacitor C n1 , C n2 added on the low-voltage DC bus at the input side of each isolated DC / DC device; in addition, the common-mode capacitor C n3 , C n4 added on the low-voltage DC bus at the input side of each isolated DC / DC device is directly connected with the ground wire.

[0074] The connection relationship thus formed first meets the requirements of the access mode (three-phase four-wire or three-phase five-wire system) of the low-voltage AC load, and provides a ground reference potential N for the AC / DC power supply system. In addition, the connection relationship can establish a low-impedance circulation loop for the common-mode current caused by the common-mode voltage from the DC side to the AC side, because the common-mode reactor Ln is additionally added in the loop, so that most of the common-mode voltage from the DC side to the AC side can be dropped on the reactor of the common-mode reactor and the LC filter at the AC side, thereby ensuring the suppression effect of the input and output buses of the non-isolated DC / DC device on the common-mode voltage at the AC side; in addition, the common-mode capacitor C n3 , C n4 parallelly connected with the input and output of the Z-type grounding transformer f also constitutes a low-impedance loop, which can drop most of the common-mode voltage of the low-voltage DC bus to the ground on the common-mode reactor Ln and the reactor of the LC filter at the AC side, further ensuring the suppression effect of the input and output sides of the non-isolated DC / DC device on the common-mode voltage to the ground.

[0075] In addition, the AC power supply mode and grounding form of the low-voltage inverter DC / AC device should also include the forms as shown in Figure 2 and Figure 3 . Among them, Figure 2 in which the neutral line is extracted from the midpoint of the two DC support capacitors, connected with the midpoint of the three capacitors of the LC filter at the AC side and the grounding point to form the zero line N; Figure 3 in which the fourth bridge arm of the four-bridge-arm inverter is used to extract the line, which is connected with the grounding point through the LC filter to form the zero line N. Figure 2 and Figure 3 The capacitor C a , C b , C c in Figure 1 plays the same role as the capacitor C a , C b , C c .

[0076] Example Two:

[0077] The embodiment provides a power supply system with a groundable power supply end, and the system comprises the following:

[0078] a power electronic transformer, a low-voltage DC bus, a low-voltage inverter DC / AC device and a non-isolated DC / DC device;

[0079] The input end of the power electronic transformer is connected with a medium-high voltage power grid, and the output end is connected with the low-voltage DC bus;

[0080] The input end of the low-voltage inverter DC / AC device is connected with the low-voltage DC bus, and the output end is connected with a low-voltage AC load and grounded;

[0081] The input ends of a plurality of the non-isolated DC / DC devices are connected in parallel to the low-voltage DC bus, and the output ends are respectively connected with low-voltage DC loads.

[0082] The low-voltage inverter DC / AC device comprises the following:

[0083] a DC side DC support capacitor, a power semiconductor switch and an LC filter;

[0084] The DC side DC support capacitor and the power semiconductor switch are connected in parallel to the low-voltage DC bus in sequence;

[0085] The LC filter is connected between the power semiconductor switch and a low-voltage AC load.

[0086] The LC filter comprises three reactances and three capacitors;

[0087] The three reactances are connected in series on the output end of the power semiconductor switch;

[0088] The three capacitors are connected in delta and connected in parallel with the three reactances to form a three-phase three-wire output end.

[0089] The system further comprises the following:

[0090] a Z-type grounding transformer, a grounding transformer coupled voltage filter capacitor, an AC switch, a low-voltage AC power supply and a zero line;

[0091] The Z-type grounding transformer, the grounding transformer coupled voltage filter capacitor and the AC switch are connected in parallel on the three-phase three-wire output end;

[0092] The AC switch is connected with the low-voltage AC power supply;

[0093] The Z-type grounding transformer, the grounding transformer coupled voltage filter capacitor and the low-voltage AC power supply are connected with the zero line together;

[0094] The zero line is connected with the low-voltage AC load to form a three-phase four-wire circuit.

[0095] The zero line is grounded, forming a three-phase five-wire circuit.

[0096] The LC filter comprises three reactances and three capacitors.

[0097] The three reactances are respectively connected in series at the output end of the power semiconductor switch.

[0098] The capacitors are connected in parallel with the three reactances, forming a three-phase three-wire output end.

[0099] The system further comprises:

[0100] An AC switch, a low-voltage AC power supply, and a zero line.

[0101] The low-voltage AC power supply is connected to the three-phase three-wire output end through the AC switch.

[0102] The midpoint of the DC side DC support capacitor, the common connection point of the capacitors of the second LC filter, and the low-voltage AC power supply are collectively connected to the zero line.

[0103] The zero line is connected to the low-voltage AC load, forming a three-phase four-wire circuit.

[0104] The zero line is grounded, forming a three-phase five-wire circuit.

[0105] The third LC filter comprises three reactances, three capacitors, and a zero line branch reactance.

[0106] The three reactances and the zero line branch reactance are connected in series at the output end of the power semiconductor switch.

[0107] The three reactances are respectively connected in parallel with the capacitors and the zero line branch reactance, forming a three-phase three-wire output end.

[0108] The system further comprises:

[0109] An AC switch, a low-voltage AC power supply, and a zero line.

[0110] The low-voltage AC power supply is connected to the three-phase three-wire output end through the AC switch.

[0111] The zero line branch reactance and the low-voltage AC power supply are collectively connected to the zero line.

[0112] The zero line is connected to the low-voltage AC load, forming a three-phase four-wire circuit.

[0113] The zero line is grounded, forming a three-phase five-wire circuit.

[0114] The non-isolated DC / DC device comprises:

[0115] an input side DC support capacitor, a power semiconductor switching device and an output side LC filter;

[0116] the input side DC support capacitor is connected in parallel with the power semiconductor switching device;

[0117] an input end of the output side LC filter is connected with the power semiconductor switching device, and an output end is connected with the low-voltage DC load.

[0118] the system further comprises:

[0119] a common mode resistance impedance and a common mode capacitance to AC side, a common mode capacitance to ground, a star capacitor;

[0120] an input end of the common mode resistance impedance is connected in parallel on the low-voltage DC bus;

[0121] the common mode capacitance to AC side and the common mode capacitance to ground are connected in parallel on the low-voltage DC bus;

[0122] the star capacitor is connected with the three-phase three-wire output end, a neutral point of the star capacitor is connected with a neutral point of the common mode capacitance to AC side, to form a common mode voltage low impedance loop;

[0123] the common mode capacitance to ground is grounded.

[0124] the star capacitor comprises:

[0125] three capacitors in a star connection relationship.

[0126] the power electronic transformer comprises:

[0127] a high-voltage AC reactor, a high-voltage DC reactor, a high-voltage AC unit, a high-voltage DC unit, a high-frequency transformer isolation unit and a low-voltage DC unit;

[0128] one end of the high-voltage AC reactor is connected with a high-voltage AC power supply, and the other end is connected with the high-voltage AC unit;

[0129] one end of the high-voltage DC reactor is connected with a high-voltage DC power supply, and the other end is connected with the high-voltage DC unit;

[0130] the high-voltage AC unit and the high-voltage DC power supply are connected with the low-voltage DC unit through the high-frequency transformer isolation unit;

[0131] the low-voltage DC unit is connected in parallel on the low-voltage DC bus.

[0132] Obviously, the described embodiments are only a part of the embodiments of the present application, but not all of them. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should belong to the protection scope of the present application.

[0133] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0134] The embodiments of the present application are 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 flow and / or block in the flowcharts and / or block diagrams, and the combination of the flows and / or blocks in the flowcharts and / or block diagrams 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 apparatus to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing apparatus generate a means for implementing the functions specified in the flowcharts and / or block diagrams. Figure 1 one or more flows and / or blocks Figure 1 means for carrying out the functions specified in the flowcharts and / or block diagrams.

[0135] These computer program instructions can also be stored in a computer-readable memory that can direct the computer or other programmable data processing apparatus to work in a specific manner, so that the instructions stored in the computer-readable memory produce a product including an instruction means, which implements the functions specified in the flowcharts and / or block diagrams. Figure 1 one or more flows and / or blocks Figure 1 means for carrying out the functions specified in the flowcharts and / or block diagrams.

[0136] These computer program instructions can also be loaded into a computer or other programmable data processing apparatus, so that a series of operation steps are performed on the computer or other programmable data processing apparatus to produce a computer-implemented process, so that the instructions executed on the computer or other programmable data processing apparatus provide a process for implementing the functions specified in the flowcharts and / or block diagrams. Figure 1 one or more flows and / or blocks Figure 1 means for carrying out the functions specified in the flowcharts and / or block diagrams.

[0137] The above merely illustrates the embodiments of the present application, but should not be taken as limitations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall fall into the protection scope of the present application.

Claims

1. A system for supplying AC and DC power, in which the power supply end can be grounded, characterized in that The system comprises: 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 with a medium-high voltage power grid, and the output end is connected with the low-voltage DC bus; The input end of the low-voltage inverter DC / AC device is connected with the low-voltage DC bus, and the output end is connected with a low-voltage AC load and grounded; The input ends of a plurality of non-isolated DC / DC devices are connected in parallel to the low-voltage DC bus, and the output ends are respectively connected with low-voltage DC loads; The low-voltage inverter DC / AC device comprises an LC filter and a power semiconductor switch; The LC filter comprises three reactances and three capacitors; The three reactances are connected in series at the output end of the power semiconductor switch; The three capacitors are connected in a star shape and connected in parallel with the three reactances to form a three-phase three-wire output end; The AC / DC power supply system with a groundable power supply end further comprises: Each non-isolated DC / DC device has a common-mode resistance impedance on the DC input side, and a common-mode capacitor for an AC side, a common-mode capacitor for the ground and a star capacitor; The input end of the common-mode resistance impedance is connected in parallel to the low-voltage DC bus; The common-mode capacitor for the AC side and the common-mode capacitor for the ground are connected in parallel to the low-voltage DC bus; The star capacitor is connected with the three-phase three-wire output end, the neutral point of the star capacitor is connected with the neutral point of the common-mode capacitor for the AC side to form a common-mode voltage low-impedance loop; The common-mode capacitor for the ground is grounded; The system further comprises: A Z-type grounding transformer and a grounding transformer coupled voltage filter capacitor; The input and output of the Z-type grounding transformer are connected in parallel with the grounding transformer coupled voltage filter capacitor and the common-mode capacitor to form a common-mode voltage low-impedance loop.

2. The system of claim 1, wherein, The low-voltage inverter DC / AC device comprises: A DC side DC support capacitor, a power semiconductor switch and an LC filter; The DC side DC support capacitor and the power semiconductor switch are connected in parallel to the low-voltage DC bus in sequence; The LC filter is connected between the power semiconductor switch and the low-voltage AC load.

3. The system of claim 1, wherein, The system further comprises: A Z-type grounding transformer, a grounding transformer coupled voltage filter capacitor, an AC switch, a low-voltage AC power supply and a zero line; The Z-type grounding transformer, the grounding transformer coupled voltage filter capacitor and the AC switch are connected in parallel to the three-phase three-wire output end; The AC switch is connected with the low-voltage AC power supply; The Z-type grounding transformer, the grounding transformer coupled voltage filter capacitor and the low-voltage AC power supply are connected with the zero line; The zero line is connected with the low-voltage AC load to form a three-phase four-wire circuit; The zero line is grounded to form a three-phase five-wire circuit.

4. The system of claim 2, wherein, Further comprising: The LC filter is replaced by a second LC filter, and the second LC filter comprises three reactances and three capacitors; The three reactances are respectively connected in series at the output end of the power semiconductor switch; The three capacitors are connected in a star shape and connected in parallel with the three reactances to form a three-phase three-wire output end, wherein the neutral point of the star-shaped connection of the capacitors is a common connection point of the capacitors of the second LC filter.

5. The system of claim 4, wherein, The system further comprises: An AC switch, a low-voltage AC power supply and a zero line; The low-voltage alternating current power supply is connected with the three-phase three-wire output end through the alternating current switch; The midpoint of the direct current side direct current support capacitor, the capacitor common connection point of the second LC filter and the low-voltage alternating current power supply are connected with the zero line; The zero line is connected with the low-voltage alternating current load, and a three-phase four-wire system circuit is formed; The zero line is grounded, and a three-phase five-wire system circuit is formed.

6. The system of claim 2, wherein, Further comprising: The LC filter is replaced by a third LC filter, and the third LC filter comprises three reactances, three capacitors and a zero line branch reactance; The three reactances and the zero line branch reactance are connected in series on the output end of the power semiconductor switch; The three reactances are connected with the zero line branch reactance through the capacitors respectively, and a three-phase three-wire output end is formed.

7. The system of claim 6, wherein, The system further comprises: An alternating current switch, a low-voltage alternating current power supply and a zero line; The low-voltage alternating current power supply is connected with the three-phase three-wire output end through the alternating current switch; The zero line branch reactance and the low-voltage alternating current power supply are connected with the zero line; The zero line is connected with the low-voltage alternating current load, and a three-phase four-wire system circuit is formed; The zero line is grounded, and a three-phase five-wire system circuit is formed.

8. The system of any one of claims 2-7, wherein, The non-isolated DC / DC device comprises: An input side direct current support capacitor, a power semiconductor switch device and an output side LC filter; The input side direct current support capacitor is connected with the power semiconductor switch device; The output side LC filter is connected with the power semiconductor switch device at the input end and connected with the low-voltage direct current load at the output end.

9. The system of claim 1, wherein, The star type capacitor comprises: Three capacitors connected in a star type connection relationship.

10. The system of claim 1, wherein, The power electronic transformer comprises: A high-voltage alternating current reactor, a high-voltage direct current reactor, a high-voltage alternating current unit, a high-voltage direct current unit, a high-frequency transformer isolation unit and a low-voltage direct current unit; One end of the high-voltage alternating current reactor is connected with a high-voltage alternating current power supply, and the other end is connected with a high-voltage alternating current unit; One end of the high-voltage direct current reactor is connected with a high-voltage direct current power supply, and the other end is connected with a high-voltage direct current unit; The high-voltage alternating current unit and the high-voltage direct current power supply are connected with the low-voltage direct current unit through the high-frequency transformer isolation unit; The low-voltage direct current unit is connected with the low-voltage direct current bus.

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