A circuit and method for improving the safety of photovoltaic power grid

Abstract

A circuit and method for improving the safety of a photovoltaic power grid, including the coils of the first, second, and third contactors controlling the normally closed contacts of the corresponding contactors to open and the normally open contacts to close, so that the corresponding first zinc oxide varistor, the second zinc oxide varistor, and the third zinc oxide varistor are connected in series to the power grid loop, and the elimination characteristics of the varistor are used to make the AC voltage and current waveform zero for 1-3 milliseconds, so as to extinguish the arc at the fault point of the power grid; the corresponding first compensation capacitor, the second compensation capacitor, and the third compensation capacitor are connected to the power grid loop to increase the reactive output of the power grid; the first DC bus support capacitor and the second DC bus support capacitor are connected to the AC power grid N to form a compressed rectifier circuit to provide power output. The present invention can simultaneously ensure that the power grid can remove faults without interrupting power transmission, greatly reducing the potential hidden dangers of new energy converters to the safety of the power grid.

Description

Technical Field

[0001] The present invention belongs to the technical field of power grid safety, and more specifically, relates to a circuit and method for improving the safety of a photovoltaic power grid. Background Art

[0002] Photovoltaic is the main new energy source for the future power grid. The existing photovoltaic inverter has a serious contradiction with the power grid. When a short circuit fault occurs in the power grid, if the photovoltaic inverter immediately shuts down the output, it can cooperate with the power grid circuit breaker to completely cut off the arc at the fault point, so that the insulation of the fault point can be restored and the circuit breaker can be reclosed to resume operation with a high probability. However, this will cause the power grid to instantly lose a large amount of photovoltaic power support when a fault occurs, causing the power grid frequency to fluctuate, and even the transient stability to be destroyed, causing serious power grid accidents.

[0003] The patent with the publication number CN118611188A provides a droop inverter fault ride-through method and system considering the influence of reactive droop coefficient. The method considers the influence of reactive-voltage loop, proposes a control strategy for dynamically adjusting the reference power of droop inverter to realize low voltage ride-through, and the control strategy is combined with the relationship between the inverter output active power and the grid connection point voltage, and dynamically adjusts the reference active power to control the power angle before and after the fault to maintain near the rated value. The present invention also dynamically adjusts the reference reactive power to limit the output current of the droop inverter to a safe threshold according to the influence of the reactive power output of the droop inverter on the line current. However, the patent keeps the power output from being shut down when the power grid fails, that is, the low voltage ride-through mode. However, in this way, the active power continues to be output when the power grid fails. Although the power of the power grid is maintained stable, the arc at the fault point cannot be extinguished, that is, the fault point cannot be isolated, resulting in the failure of reclosing and even the fire at the fault point, and the elimination of the grid fault of the photovoltaic system and the maintenance of the low voltage ride-through power cannot be achieved. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the present invention provides a photovoltaic power grid security improvement circuit.

[0005] The present invention adopts the following technical solution.

[0006] The first aspect of the present invention proposes a photovoltaic power grid safety improvement circuit, a photovoltaic power grid safety improvement circuit, comprising: a photovoltaic inverter 3, a first zinc oxide varistor 71, a second zinc oxide varistor 72, a third zinc oxide varistor 73, a coil 8A of a first contactor, a coil 8B of a second contactor, a coil 8C of a third contactor, a normally closed contact 8A-1 of the first contactor, a normally closed contact 8B-1 of the second contactor and a normally closed contact 8C-1 of the third contactor, a first compensation capacitor 91, a second compensation capacitor 92, a third compensation capacitor 93, a first group of normally open contacts 8A-2 of the first contactor, a first group of normally open contacts 8B-2 of the second contactor and a first group of normally open contacts 8C-2 of the third contactor, characterized in that:

[0007] The A, B, and C phase output terminals of the photovoltaic inverter 3 are respectively connected to one end of the first, second, and third zinc oxide varistors; and the A, B, and C phase output terminals of the photovoltaic inverter 3 are also connected to one end of the normally closed contacts of the first, second, and third contactors;

[0008] The other end of the first zinc oxide varistor 71, the other end of the normally closed contact 8A-1 of the first contactor, and one end of the coil 8A of the first contactor are connected to the AC grid A; the other end of the second zinc oxide varistor 72, the other end of the normally closed contact 8B-1 of the second contactor, and one end of the coil 8B of the second contactor are connected to the AC grid B; the other end of the third zinc oxide varistor 73, the other end of the normally closed contact 8C-1 of the third contactor, and one end of the coil 8C of the third contactor are connected to the AC grid C;

[0009] The other end of the coil 8A of the first contactor, the other end of the coil 8B of the second contactor, and the other end of the coil 8C of the third contactor are connected to the N phase on the AC grid side.

[0010] One end of the first group of normally open contacts of the first, second and third contactors is respectively connected to one end of the first, second and third zinc oxide varistors, and the other end of the first group of normally open contacts of the first, second and third contactors is respectively connected to the N phase on the AC power grid side through the first, second and third compensation capacitors in series.

[0011] Preferably, the photovoltaic power grid safety improvement circuit includes a first DC bus support capacitor 5, a second DC bus support capacitor 6, a second group of normally open contacts 8A-3 of the first contactor, a second group of normally open contacts 8B-3 of the second contactor, a second group of normally open contacts 8C-3 of the third contactor, and a DC bus neutral point terminal 4;

[0012] The negative input terminal of the DC bus of the photovoltaic inverter 3 is connected to one end of the first DC bus support capacitor 5, and the positive input terminal of the DC bus of the photovoltaic inverter 3 is connected to the second DC bus support capacitor 6. The other end of the first DC bus support capacitor 5 and the other end of the second DC bus support capacitor 6 are both connected through the DC bus neutral point terminal 4 inside the photovoltaic inverter;

[0013] One end of the second group of normally open contacts 8A-3 of the first contactor, one end of the second group of normally open contacts 8B-3 of the second contactor, and one end of the second group of normally open contacts 8C-3 of the third contactor are all connected to the neutral point terminal 4 of the DC bus inside the photovoltaic inverter, and the other end of the second group of normally open contacts 8A-3 of the first contactor, the other end of the second group of normally open contacts 8B-3 of the second contactor, and the other end of the second group of normally open contacts 8C-3 of the third contactor are all connected to the N phase on the AC grid side.

[0014] Preferably, the first zinc oxide varistor 71 , the second zinc oxide varistor 72 , and the third zinc oxide varistor 73 are identical zinc oxide varistors, and their breakdown voltages are all 25% of the grid power supply voltage.

[0015] Preferably, the first compensation capacitor 91, the second compensation capacitor 92, and the third compensation capacitor 93 are capacitors of the same specification, and the capacitance value is 50 microfarads.

[0016] Preferably, the first DC bus supporting capacitor 5 and the second DC bus supporting capacitor 6 are capacitors of the same specification.

[0017] Preferably, when the voltage of the coil 8C of the first contactor, the coil 8C of the second contactor or the coil 8C of the third contactor drops to a set threshold, the corresponding normally closed contacts open and the corresponding normally open contacts close; the set threshold is specifically 0.7-0.8 times the grid power supply voltage.

[0018] The second aspect of the present invention provides a method for improving the safety of a photovoltaic power grid using the circuit described in the first aspect of the present invention, comprising:

[0019] When a phase of the power grid fails, the voltage of the power grid decreases, and the coil voltage of the contactor of the corresponding phase decreases to the set threshold value, so that all normally open contacts corresponding to the contactor are closed and all normally closed contacts are opened;

[0020] The normally closed contact 8A-1 of the first contactor, the normally closed contact 8B-1 of the second contactor and the normally closed contact 8C-1 of the third contactor are opened, so that the corresponding first zinc oxide varistor 71, the second zinc oxide varistor 71 and the third zinc oxide varistor 71 are connected in series to the power grid loop, and the AC voltage and current waveforms are made to be zero for 1-3 milliseconds by utilizing the elimination characteristics of the varistor, so that the arc at the fault point of the power grid is extinguished;

[0021] The first group of normally open contacts 8A-2 of the first contactor, the first group of normally open contacts 8B-2 of the second contactor and the first group of normally open contacts 8C-2 of the third contactor are closed, and the corresponding first compensation capacitor 91, second compensation capacitor 92 and third compensation capacitor 93 are connected to the power grid loop to increase the reactive power output of the power grid;

[0022] The second group of normally open contacts 8A-3 of the first contactor, the second group of normally open contacts 8B-3 of the second contactor and the second group of normally open contacts 8C-3 of the third contactor are closed; the first DC bus support capacitor 5 and the second DC bus support capacitor 6 are connected to the AC power grid N to form a compressed rectifier circuit to provide power output.

[0023] The third aspect of the present invention provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program, when loaded into the processor, implements the method for improving the safety of a photovoltaic power grid according to the second aspect of the present invention.

[0024] A fourth aspect of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method for improving the safety of a photovoltaic power grid according to the second aspect of the present invention is implemented.

[0025] The beneficial effect of the present invention is that, compared with the prior art, the technical solution of the present invention can achieve both ensuring that the power grid can remove faults and not interrupt power transmission, greatly reducing the potential hidden dangers of new energy converters to the safety of the power grid. The present invention cleverly uses simple passive devices. When the power grid fails at the moment when the power grid voltage is reduced, the zinc oxide varistor is connected in series to the power grid loop through the switching of the contactor. In this way, the voltage-cutting characteristics of the varistor are used to achieve the continuous zero-point effect of the AC voltage and current waveforms, and the complete voltage and current of about 1-3 milliseconds can be achieved. Zero, which creates conditions for the extinguishing of the arc at the fault point of the power grid, so that the fault arc can be de-ionized and extinguished using a few milliseconds of complete power-off time, thereby eliminating the fault point; the switching of the other two groups of contacts of the contactor, one group is used for instantaneous The capacitor is put into use at the same time to increase the reactive output of the power grid and improve the instantaneous stability of the power grid failure, while offsetting the voltage drop caused by the series connection of the zinc oxide varistor. The other group realizes any one-phase power grid failure through the combination of the neutral point of the DC bus of the photovoltaic inverter and the two supporting capacitors. The DC side of the photovoltaic inverter can form a compressed rectifier circuit, thereby increasing the DC bus voltage inside the inverter by about 10%, so that the photovoltaic inverter maintains sufficient power output when the power grid fails and the low voltage is low, and the stability of the active output of the low voltage ride through is achieved. The present invention changes the output waveform of the photovoltaic inverter fault state through the cooperation of the above circuit, so that it maintains power output while having a long zero-crossing time period, providing conditions for the fault arc to be extinguished, and achieving both ensuring that the power grid can remove the fault and not interrupting power transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only embodiments of a part of the present invention, rather than all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0028] like Figure 1As shown, embodiment 1 of the present invention proposes a photovoltaic power grid security improvement circuit, including: the first aspect of the present invention proposes a photovoltaic power grid security improvement circuit, a photovoltaic power grid security improvement circuit, including: a photovoltaic inverter 3, a first zinc oxide varistor 71, a second zinc oxide varistor 72, a third zinc oxide varistor 73, a coil 8A of a first contactor, a coil 8B of a second contactor, a coil 8C of a third contactor, a normally closed contact 8A-1 of the first contactor, a normally closed contact 8B-1 of the second contactor and a normally closed contact 8C-1 of the third contactor, a first compensation capacitor 91, a second compensation capacitor 92, a third compensation capacitor 93, a first group of normally open contacts 8A-2 of the first contactor, a first group of normally open contacts 8B-2 of the second contactor and a first group of normally open contacts 8C-2 of the third contactor, characterized in that:

[0029] The A, B, and C phase output terminals of the photovoltaic inverter 3 are respectively connected to one end of the first, second, and third zinc oxide varistors; and the A, B, and C phase output terminals of the photovoltaic inverter 3 are also connected to one end of the normally closed contacts of the first, second, and third contactors;

[0030] The other end of the first zinc oxide varistor 71, the other end of the normally closed contact 8A-1 of the first contactor, and one end of the coil 8A of the first contactor are connected to the AC grid A; the other end of the second zinc oxide varistor 72, the other end of the normally closed contact 8B-1 of the second contactor, and one end of the coil 8B of the second contactor are connected to the AC grid B; the other end of the third zinc oxide varistor 73, the other end of the normally closed contact 8C-1 of the third contactor, and one end of the coil 8C of the third contactor are connected to the AC grid C;

[0031] The other end of the coil 8A of the first contactor, the other end of the coil 8B of the second contactor, and the other end of the coil 8C of the third contactor are connected to the N phase on the AC grid side.

[0032] One end of the first group of normally open contacts of the first, second and third contactors is respectively connected to one end of the first, second and third zinc oxide varistors, and the other end of the first group of normally open contacts of the first, second and third contactors is respectively connected to the N phase on the AC power grid side through the first, second and third compensation capacitors in series.

[0033] It should be noted that the photovoltaic power grid safety improvement circuit also includes an A-phase terminal 11 on the AC power grid side, a B-phase terminal 12 on the AC power grid side, a C-phase terminal 13 on the AC power grid side, an N-phase terminal 14 on the AC power grid side, an A-phase AC power grid terminal 21 on the photovoltaic inverter side, a B-phase AC power grid terminal 22 on the photovoltaic inverter side, and a C-phase AC power grid terminal 23 on the photovoltaic inverter side; the above terminals are all used to output corresponding voltages to external circuits or loads, and the A-phase terminal 11 on the AC power grid side, the B-phase terminal 12 on the AC power grid side, the C-phase terminal 13 on the AC power grid side, and the N-phase terminal 14 on the AC power grid side are respectively connected to the A-phase, B-phase, and C-phase of the AC power grid; the A-phase AC power grid terminal 21 on the photovoltaic inverter side, the B-phase AC power grid terminal 22 on the photovoltaic inverter side, and the C-phase AC power grid terminal 23 on the photovoltaic inverter side are respectively connected to the A-phase output terminal, the B-phase output terminal, and the C-phase output terminal of the photovoltaic inverter;

[0034] Preferably, the photovoltaic power grid safety improvement circuit includes a first DC bus support capacitor 5, a second DC bus support capacitor 6, a second group of normally open contacts 8A-3 of the first contactor, a second group of normally open contacts 8B-3 of the second contactor, a second group of normally open contacts 8C-3 of the third contactor, and a DC bus neutral point terminal 4;

[0035] The negative input terminal of the DC bus of the photovoltaic inverter 3 is connected to one end of the first DC bus support capacitor 5, and the positive input terminal of the DC bus of the photovoltaic inverter 3 is connected to the second DC bus support capacitor 6. The other end of the first DC bus support capacitor 5 and the other end of the second DC bus support capacitor 6 are both connected through the DC bus neutral point terminal 4 inside the photovoltaic inverter;

[0036] One end of the second group of normally open contacts 8A-3 of the first contactor, one end of the second group of normally open contacts 8B-3 of the second contactor, and one end of the second group of normally open contacts 8C-3 of the third contactor are all connected to the neutral point terminal 4 of the DC bus inside the photovoltaic inverter, and the other end of the second group of normally open contacts 8A-3 of the first contactor, the other end of the second group of normally open contacts 8B-3 of the second contactor, and the other end of the second group of normally open contacts 8C-3 of the third contactor are all connected to the N phase on the AC grid side.

[0037] Preferably, the first zinc oxide varistor 71 , the second zinc oxide varistor 72 , and the third zinc oxide varistor 73 are identical zinc oxide varistors, and their breakdown voltages are all 25% of the grid power supply voltage.

[0038] Preferably, the first compensation capacitor 91, the second compensation capacitor 92, and the third compensation capacitor 93 are capacitors of the same specification, and the capacitance value is 50 microfarads.

[0039] Preferably, the first DC bus supporting capacitor 5 and the second DC bus supporting capacitor 6 are capacitors of the same specification.

[0040] Preferably, when the voltage of the coil 8C of the first contactor, the coil 8C of the second contactor or the coil 8C of the third contactor drops to a set threshold, the corresponding normally closed contacts open and the corresponding normally open contacts close; the set threshold is specifically 0.7-0.8 times the grid power supply voltage.

[0041] Embodiment 2 of the present invention provides a method for improving the safety of a photovoltaic power grid using the circuit described in Embodiment 1 of the present invention, comprising:

[0042] When a phase of the power grid fails, the voltage of the power grid decreases, and the coil voltage of the contactor of the corresponding phase decreases to the set threshold value, so that all normally open contacts corresponding to the contactor are closed and all normally closed contacts are opened;

[0043] The normally closed contact 8A-1 of the first contactor, the normally closed contact 8B-1 of the second contactor and the normally closed contact 8C-1 of the third contactor are opened, so that the corresponding first zinc oxide varistor 71, the second zinc oxide varistor 71 and the third zinc oxide varistor 71 are connected in series to the power grid loop, and the AC voltage and current waveforms are made to be zero for 1-3 milliseconds by utilizing the elimination characteristics of the varistor, so that the arc at the fault point of the power grid is extinguished;

[0044] The first group of normally open contacts 8A-2 of the first contactor, the first group of normally open contacts 8B-2 of the second contactor and the first group of normally open contacts 8C-2 of the third contactor are closed, and the corresponding first compensation capacitor 91, second compensation capacitor 92 and third compensation capacitor 93 are connected to the power grid loop to increase the reactive power output of the power grid;

[0045] The second group of normally open contacts 8A-3 of the first contactor, the second group of normally open contacts 8B-3 of the second contactor and the second group of normally open contacts 8C-3 of the third contactor are closed; the first DC bus support capacitor 5 and the second DC bus support capacitor 6 are connected to the AC power grid N to form a compressed rectifier circuit to provide power output.

[0046] Embodiment 3 of the present invention provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program, when loaded into the processor, implements the method for improving the safety of a photovoltaic power grid according to Embodiment 2 of the present invention.

[0047] Embodiment 4 of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method for improving the safety of a photovoltaic power grid according to Embodiment 2 of the present invention is implemented.

[0048] The beneficial effect of the present invention is that, compared with the prior art, the technical solution of the present invention can achieve both ensuring that the power grid can remove faults and not interrupt power transmission, greatly reducing the potential hidden dangers of new energy converters to the safety of the power grid. The present invention cleverly uses simple passive devices. When the power grid fails at the moment when the power grid voltage is reduced, the zinc oxide varistor is connected in series to the power grid loop through the switching of the contactor. In this way, the voltage-cutting characteristics of the varistor are used to achieve the continuous zero-point effect of the AC voltage and current waveforms, and the complete voltage and current of about 1-3 milliseconds can be achieved. Zero, which creates conditions for the extinguishing of the arc at the fault point of the power grid, so that the fault arc can be de-ionized and extinguished using a few milliseconds of complete power-off time, thereby eliminating the fault point; the switching of the other two groups of contacts of the contactor, one group is used for instantaneous The capacitor is put into use at the same time to increase the reactive output of the power grid and improve the instantaneous stability of the power grid failure, while offsetting the voltage drop caused by the series connection of the zinc oxide varistor. The other group realizes any one-phase power grid failure through the combination of the neutral point of the DC bus of the photovoltaic inverter and the two supporting capacitors. The DC side of the photovoltaic inverter can form a compressed rectifier circuit, thereby increasing the DC bus voltage inside the inverter by about 10%, so that the photovoltaic inverter maintains sufficient power output when the power grid fails and the low voltage is low, and the stability of the active output of the low voltage ride through is achieved. The present invention changes the output waveform of the photovoltaic inverter fault state through the cooperation of the above circuit, so that it maintains power output while having a long zero-crossing time period, providing conditions for the fault arc to be extinguished, and achieving both ensuring that the power grid can remove the fault and not interrupting power transmission.

[0049] The present disclosure may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0050] A computer-readable storage medium may be a tangible device that can hold and store instructions used by an instruction execution device. A computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the above. More specific examples (a non-exhaustive list) of computer-readable storage media include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a raised structure in a groove on which instructions are stored, and any suitable combination of the above. The computer-readable storage medium used herein is not to be interpreted as a transient signal itself, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through a fiber optic cable), or an electrical signal transmitted through a wire.

[0051] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, optical fiber transmissions, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in the computer-readable storage medium in each computing / processing device.

[0052] The computer program instructions for performing the operations of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages, such as Smalltalk, C++, etc., and conventional procedural programming languages, such as "C" language or similar programming languages. The computer-readable program instructions may be executed entirely on the user's computer, partially on the user's computer, as a separate software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., using an Internet service provider to connect through the Internet). In some embodiments, by using the state information of the computer-readable program instructions to personalize an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), the electronic circuit may execute the computer-readable program instructions, thereby implementing various aspects of the present disclosure.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A photovoltaic power grid safety improvement circuit, comprising: A photovoltaic inverter (3), a first zinc oxide varistor (71), a second zinc oxide varistor (72), a third zinc oxide varistor (73), a coil (8A) of a first contactor, a coil (8B) of a second contactor, a coil (8C) of a third contactor, a normally closed contact (8A-1) of the first contactor, a normally closed contact (8B-1) of the second contactor, and a normally closed contact (8C-1) of the third contactor, a first compensation capacitor (91), a second compensation capacitor (92), a third compensation capacitor (93), a first group of normally open contacts (8A-2) of the first contactor, a first group of normally open contacts (8B-2) of the second contactor, and a first group of normally open contacts (8C-2) of the third contactor, characterized in that: The A, B and C phase output ends of the photovoltaic inverter (3) are respectively connected to one end of the first, second and third zinc oxide varistors; and the A, B and C phase output ends of the photovoltaic inverter (3) are also connected to one end of the normally closed contacts of the first, second and third contactors; The other end of the first zinc oxide varistor (71), the other end of the normally closed contact (8A-1) of the first contactor, and one end of the coil (8A) of the first contactor are connected to the AC power grid phase A; the other end of the second zinc oxide varistor (72), the other end of the normally closed contact (8B-1) of the second contactor, and one end of the coil (8B) of the second contactor are connected to the AC power grid phase B; the other end of the third zinc oxide varistor (73), the other end of the normally closed contact (8C-1) of the third contactor, and one end of the coil (8C) of the third contactor are connected to the AC power grid phase C; The other end of the coil (8A) of the first contactor, the other end of the coil (8B) of the second contactor, and the other end of the coil (8C) of the third contactor are connected to the N phase on the AC power grid side; One end of the first group of normally open contacts of the first, second and third contactors is respectively connected to one end of the first, second and third zinc oxide varistors, and the other end of the first group of normally open contacts of the first, second and third contactors is respectively connected to the N phase on the AC power grid side through the first, second and third compensation capacitors in series.

2. A photovoltaic power grid safety improvement circuit according to claim 1, characterized in that: The photovoltaic power grid safety improvement circuit comprises a first DC bus support capacitor (5), a second DC bus support capacitor (6), a second group of normally open contacts (8A-3) of a first contactor, a second group of normally open contacts (8B-3) of a second contactor, a second group of normally open contacts (8C-3) of a third contactor, and a DC bus neutral point terminal (4); The negative input terminal of the DC bus of the photovoltaic inverter (3) is connected to one end of the first DC bus support capacitor (5), the positive input terminal of the DC bus of the photovoltaic inverter (3) is connected to the second DC bus support capacitor (6), and the other end of the first DC bus support capacitor (5) and the other end of the second DC bus support capacitor (6) are both connected through the DC bus neutral point terminal (4) inside the photovoltaic inverter; One end of the second group of normally open contacts (8A-3) of the first contactor, one end of the second group of normally open contacts (8B-3) of the second contactor, and one end of the second group of normally open contacts (8C-3) of the third contactor are all connected to the neutral point terminal (4) of the DC bus inside the photovoltaic inverter, and the other end of the second group of normally open contacts (8A-3) of the first contactor, the other end of the second group of normally open contacts (8B-3) of the second contactor, and the other end of the second group of normally open contacts (8C-3) of the third contactor are all connected to the N phase on the AC grid side.

3. A photovoltaic power grid safety improvement circuit according to claim 1, characterized in that: The first zinc oxide varistor (71), the second zinc oxide varistor (72), and the third zinc oxide varistor (73) are identical zinc oxide varistors, and their breakdown voltages are all 25% of the grid power supply voltage.

4. A photovoltaic power grid safety improvement circuit according to claim 1, characterized in that: The first compensation capacitor (91), the second compensation capacitor (92), and the third compensation capacitor (93) are capacitors of the same specification, and the capacitance value is 50 microfarads.

5. A photovoltaic power grid safety improvement circuit according to claim 2, characterized in that: The first DC bus supporting capacitor (5) and the second DC bus supporting capacitor (6) are capacitors of the same specification.

6. A photovoltaic power grid safety improvement circuit according to claim 2, characterized in that: When the voltage of the coil (8C) of the first contactor, the coil (8C) of the second contactor or the coil (8C) of the third contactor drops to a set threshold value, the corresponding normally closed contact opens and the corresponding normally open contact closes; the set threshold value is specifically 0.7-0.8 times the grid power supply voltage.

7. A method for improving the safety of a photovoltaic power grid using the circuit of claim 2, characterized in that: When a phase of the power grid fails, the voltage of the power grid decreases, and the coil voltage of the contactor of the corresponding phase decreases to the set threshold value, so that all normally open contacts corresponding to the contactor are closed and all normally closed contacts are opened; The normally closed contact (8A-1) of the first contactor, the normally closed contact (8B-1) of the second contactor and the normally closed contact (8C-1) of the third contactor are opened, so that the corresponding first zinc oxide varistor (71), the second zinc oxide varistor (71) and the third zinc oxide varistor (71) are connected in series to the power grid loop, and the AC voltage and current waveforms are made to be zero for 1-3 milliseconds by utilizing the clipping characteristics of the varistor, thereby extinguishing the arc at the power grid fault point; The first group of normally open contacts (8A-2) of the first contactor, the first group of normally open contacts (8B-2) of the second contactor, and the first group of normally open contacts (8C-2) of the third contactor are closed, and the corresponding first compensation capacitor (91), second compensation capacitor (92), and third compensation capacitor (93) are connected to the power grid loop to increase the reactive power output of the power grid; The second group of normally open contacts (8A-3) of the first contactor, the second group of normally open contacts (8B-3) of the second contactor, and the second group of normally open contacts (8C-3) of the third contactor are closed; the first DC busbar support capacitor (5) and the second DC busbar support capacitor (6) are connected to the AC power grid N to form a voltage rectifier circuit and provide power output.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the computer program is loaded into a processor, the method for improving the safety of a photovoltaic power grid according to claim 7 is implemented.

9. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method for improving the safety of a photovoltaic power grid according to claim 7 is implemented.

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