A grid-connected and off-grid switching device for a multi-machine parallel energy storage system, a station system and a grid-connected and off-grid switching method thereof

Abstract

The present invention discloses an on-grid and off-grid switching device for a multi-machine parallel energy storage system, a station system and an on-grid and off-grid switching method thereof, comprising a station control server; the station control server is connected to an I / O module, the I / O module is connected to a frame circuit breaker, a first live-operated molded case circuit breaker, a second live-operated molded case circuit breaker and a plurality of energy storage cabinet molded case circuit breakers, and reads their opening and closing states; the frame circuit breaker and the first live-operated molded case circuit breaker inlet side are used to connect to the mains; the frame circuit breaker outlet side is connected to a second live-operated molded case circuit breaker, the first live-operated molded case circuit breaker and the second live-operated molded case circuit breaker outlet side are both used to connect important loads, and a plurality of energy storage cabinet molded case circuit breakers and the second live-operated molded case circuit breakers are both connected to the frame circuit breaker outlet side. The energy storage system is realized to achieve rapid response and continuous power supply capability when the power grid is out of power.

Description

Technical Field

[0001] The present invention belongs to the field of on-grid and off-grid switching, and relates to an on-grid and off-grid switching device for a multi-machine parallel energy storage system, a station system and an on-grid and off-grid switching method thereof. Background Art

[0002] In modern society, the power system has become an indispensable part of people's lives and industrial production. With the development of renewable energy technology, energy storage technology is also constantly improving. Energy storage technology mainly stores electrical energy through batteries so that it can be released when needed. Energy storage integrated machine is a common energy storage device, which can be operated independently or in parallel. In the power system, the on-grid and off-grid switching device is an important electrical device that can realize the switching of energy storage equipment on and off the grid.

[0003] The existing on-grid and off-grid control devices usually use dual power transfer switches (ATS) to achieve on-grid and off-grid switching. A mechanical switch is a switching device that can automatically switch to another power source when one side of the dual power transfer switch fails for some reason.

[0004] In addition, there is also automatic switching between grid-connected and off-grid through a static transfer switch (STS). STS is a fast-response electronic switch that ensures that the energy storage system can immediately take over the load power supply when a grid failure occurs.

[0005] However, most of the existing off-grid energy storage system solutions have the following shortcomings: 1. High switching failure rate: The off-grid mode starts abnormally, and automatic off-grid operation cannot be achieved at the moment of grid failure. The control system is decentralized and has a high failure rate.

[0006] 2. Low system security: When multiple energy storage devices are connected to the same grid and switched off, the system is prone to abnormal power supply.

[0007] 3. Poor system stability: When switching between on-grid and off-grid, especially when multiple energy storage devices are running in parallel, the system voltage and frequency fluctuate significantly, making it difficult to achieve stable off-grid power supply. When using ATS to control power supply switching, the energy storage system will supply power to the load when the off-grid power supply is not stable, which may cause some loads to fail to start or malfunction.

[0008] 4. High system cost: Using STS to control the on and off of the circuit will increase the complexity and cost of the system. Summary of the invention

[0009] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide an on-grid and off-grid switching device, a station system and an on-grid and off-grid switching method for a multi-machine parallel energy storage system, so as to achieve rapid response and continuous power supply capability of the energy storage system when the power grid is out of power.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions: A grid-connected and off-grid switching device for a multi-machine parallel energy storage system, comprising a station control server; The station control server is connected to an I / O module, which connects the frame circuit breaker, the first energized molded case circuit breaker, the second energized molded case circuit breaker and multiple energy storage cabinet molded case circuit breakers, and reads their opening and closing states; the incoming line side of the frame circuit breaker and the first energized molded case circuit breaker is used to connect to the AC power; the outgoing line side of the frame circuit breaker is connected to the second energized molded case circuit breaker, and the outgoing line sides of the first energized molded case circuit breaker and the second energized molded case circuit breaker are both used to connect important loads, and multiple energy storage cabinet molded case circuit breakers and the second energized molded case circuit breaker are both connected to the outgoing line side of the frame circuit breaker.

[0011] Preferably, the incoming line sides of the frame circuit breaker and the first energized molded case circuit breaker are both connected to a 400V busbar.

[0012] Preferably, it further comprises a photovoltaic circuit breaker, one end of which is connected to a busbar, and the other end of which is connected to an inverter and a photovoltaic system in sequence.

[0013] Preferably, it also includes an uninterruptible power supply, which uses a first miniature circuit breaker to input a 220V power supply.

[0014] A station system, comprising an on-grid and off-grid switching device and an upper-level circuit breaker for a multi-machine parallel energy storage system; An upper-level circuit breaker is arranged on the incoming line side of the on-grid and off-grid switching device, and an anti-reverse current meter is arranged on the incoming line side of the upper-level circuit breaker. The first energized molded case circuit breaker and the second energized molded case circuit breaker are connected to important loads, and each energy storage cabinet molded case circuit breaker is connected to an energy storage cabinet.

[0015] Preferably, each energy storage cabinet is provided with an EMS and a PCS system.

[0016] A method for switching between grid connection and off-grid connection of a station system, comprising the following processes: S1: If the upper circuit breaker can trip due to undervoltage, and the upper circuit breaker status dry contact signal and the anti-reverse current meter voltage are both 0V, the mains power is abnormally cut off and the energy storage cabinet is shut down for protection; S2, after the mains power fails abnormally, the station control server opens the frame circuit breaker and the first energized molded case circuit breaker in turn, and the second energized molded case circuit breaker is in the open state; the station control server sends an executable off-grid command to each energy storage cabinet, and each energy storage cabinet controls the corresponding cabinet to start the off-grid VF mode after determining that there is no fault in the cabinet, and the station control server controls the second energized molded case circuit breaker to close; S3, judging whether the mains power is restored according to whether the voltage value of the anti-backflow meter returns to normal; S4, after the mains power is restored, each energy storage cabinet is shut down, and the control server controls the second energized molded case circuit breaker to open, the first energized molded case circuit breaker to close, and the frame circuit breaker to close in sequence; the energy storage cabinet starts the grid-connected mode and executes the peak shaving and valley filling strategy according to the settings.

[0017] Preferably, after an abnormal power outage of the mains, the station control server controls the photovoltaic circuit breaker to open.

[0018] Preferably, after the EMS collects the PCS output voltage in each cabinet and it is stable, the station control server controls the second energized molded case circuit breaker to close.

[0019] Preferably, the energy storage cabinet collects the current output voltage and frequency value of each energy storage cabinet in real time during the process of supplying power to important loads. If the value exceeds the set protection threshold, a protection shutdown operation is immediately performed.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The present invention integrates various on-grid and off-grid devices into a whole, and the device can be directly applied to most industrial and commercial energy storage off-grid demand scenarios. It solves the problems of long switching delay, low efficiency, poor system stability, etc. in the off-grid operation of the existing energy storage system, and centralizes the components of the on-grid and off-grid devices to facilitate unified management and data volume detection, reducing the transformation of the station system. It has a wide range of applications, and multiple energy storage integrated cabinets are added to the device for grid connection. For most stations, industrial and commercial energy storage integrated cabinets can be directly designed and used as backup power supplies. The on-grid and off-grid solution can realize parallel connection of multiple energy storage cabinets, and the capacity increase of the energy storage system does not affect the system control method. It has low cost and high safety factor, and adds protection measures to each link of the control system. The on-grid and off-grid switching is realized through automatic control, which reduces manual intervention, improves the timeliness of power supply, and realizes the rapid response and continuous power supply capability of the energy storage system when the power grid is out of power. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of the main components of the grid-connected and off-grid device provided in an embodiment of the present invention; Figure 2 A schematic diagram of a station system provided in an embodiment of the present invention; Figure 3 A flow chart of switching between grid and off-grid provided by an embodiment of the present invention; Figure 4 A communication topology diagram provided for a multi-machine parallel system according to an embodiment of the present invention.

[0022] In the figure: 1. Station control server, 2. I / O module, 3. Energy storage meter, 4. First miniature circuit breaker, 5. 24V switching power supply, 6. Second miniature circuit breaker, 7. Frame circuit breaker, 8. First live-operated molded case circuit breaker, 9. Second live-operated molded case circuit breaker, 10. Uninterruptible power supply, 11. Photovoltaic circuit breaker, 12. First energy storage cabinet molded case circuit breaker, 13. Second energy storage cabinet molded case circuit breaker, 14. Third energy storage cabinet molded case circuit breaker, 15. Fourth energy storage cabinet molded case circuit breaker, 16. Anti-reverse current meter, 17. Upper circuit breaker, 18. Other load circuit breakers. DETAILED DESCRIPTION

[0023] The embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0024] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which the present invention belongs. The terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or can communicate with each other; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. The term "and / or" used in this article includes any and all combinations of one or more related listed items. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0026] The disclosure below provides many different embodiments or examples to realize different structures of the present invention. In order to simplify the disclosure of the present invention, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present invention. In addition, the present invention can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplicity and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides various specific examples of processes and materials, but those of ordinary skill in the art can be aware of the application of other processes and / or the use of other materials.

[0027] like Figure 1 As shown, the grid-connected and off-grid switching device of the present invention comprises three parts, namely, an upper part, a middle part and a lower part. The upper part of the grid-connected and off-grid switching device is provided with a station control server 1, an I / O module 2, an energy storage meter 3, a first miniature circuit breaker 4, a 24V switching power supply 5 and a second miniature circuit breaker 6; the middle part of the grid-connected and off-grid switching device is provided with a frame circuit breaker 7; the lower part of the grid-connected and off-grid switching device is provided with a first live-operated molded case circuit breaker 8, a second live-operated molded case circuit breaker 9, an uninterruptible power supply 10, a photovoltaic circuit breaker 11 and a plurality of energy storage cabinet molded case circuit breakers, each energy storage cabinet molded case circuit breaker is connected to an energy storage cabinet. In this embodiment, four energy storage cabinet molded case circuit breakers are used, namely, a first energy storage cabinet molded case circuit breaker 12, a second energy storage cabinet molded case circuit breaker 13, a third energy storage cabinet molded case circuit breaker 14 and a fourth energy storage cabinet molded case circuit breaker 15.

[0028] The station control server 1 is connected to the I / O module 2, and the I / O module 2 is connected to the frame circuit breaker 7, the first live-operated molded case circuit breaker 8, the second live-operated molded case circuit breaker 9, the photovoltaic circuit breaker 11, the first energy storage cabinet molded case circuit breaker 12, the second energy storage cabinet molded case circuit breaker 13, the third energy storage cabinet molded case circuit breaker 14 and the fourth energy storage cabinet molded case circuit breaker 15, and reads the opening and closing status of each of the above circuit breakers. The frame circuit breaker 7 and the first live-operated molded case circuit breaker 8 are connected to the mains on the incoming line side. Specifically, the frame circuit breaker 7 and the first live-operated molded case circuit breaker 8 are connected to the incoming line 4. 00V busbar; the first live-operated molded case circuit breaker 8 and the second live-operated molded case circuit breaker 9 are used to connect important external loads, the outgoing side of the frame circuit breaker 7 is connected to the second live-operated molded case circuit breaker 9, the first energy storage cabinet molded case circuit breaker 12, the second energy storage cabinet molded case circuit breaker 13, the third energy storage cabinet molded case circuit breaker 14 and the fourth energy storage cabinet molded case circuit breaker 15 and the second live-operated molded case circuit breaker 9 are all connected to the outgoing side of the frame circuit breaker 7, and the outgoing side of the frame circuit breaker 7 is provided with an energy storage meter 3; the uninterruptible power supply 10 inputs 220V power supply through the first miniature circuit breaker 4.

[0029] The station control server 1 can detect the state quantities of the frame circuit breaker 7, the first energized molded case circuit breaker 8, the second energized molded case circuit breaker 9, the photovoltaic circuit breaker 11, the first energy storage cabinet molded case circuit breaker 12, the second energy storage cabinet molded case circuit breaker 13, the third energy storage cabinet molded case circuit breaker 14 and the fourth energy storage cabinet molded case circuit breaker 15 in the device through the I / O module 2, and can control the first energized molded case circuit breaker 8 and the second energized molded case circuit breaker 9, wherein the first miniature circuit breaker 4 in the upper part of the device serves as the power supply switch of the uninterruptible power supply 10 in the lower part of the device, and the second miniature circuit breaker 6 serves as the secondary power switch. The 24V switching power supply 5 is connected to the station control server 1, the I / O module 2 and the energy storage meter 3 through the second miniature circuit breaker 6. The 24V switching power supply 5 provides 24V power for the control circuit. When the power grid loses power abnormally, the uninterruptible power supply 10 provides power for the control system. In addition, the energy storage meter 3 can measure the charging and discharging data, and the energy management system can collect power information to calculate the efficiency of the energy storage system. If the energy storage system needs to be increased in capacity, an energy storage cabinet power supply circuit can be added to the on-grid and off-grid switching device.

[0030] like Figure 2As shown, this is the station system of the on-grid and off-grid switching device. In addition to the on-grid and off-grid device, the entire station is also mainly equipped with an upper circuit breaker 17, an anti-reverse current meter 16 and other load circuit breakers 18 at this grid-connected point. Among them: the upper circuit breaker 17 is arranged on the incoming line side of the on-grid and off-grid switching device, and the anti-reverse current meter 16 is arranged on the incoming line side of the upper circuit breaker 17. The photovoltaic circuit breaker 11 is connected to the external photovoltaic system through the inverter. The 400V bus is connected to the first miniature circuit breaker 4, the first live plastic case circuit breaker 8 and other load circuit breakers 18. The entire energy storage system adjusts the operating power of all energy storage integrated cabinets of the energy storage system in real time according to the data of the anti-reverse current meter 16 when they are connected to the grid and discharged, to prevent the surplus electricity from being connected to the grid. In this embodiment, the energy storage system is composed of multiple industrial and commercial energy storage integrated cabinets in parallel, and each energy storage integrated cabinet contains a set of EMS and PCS systems, which can realize the independent operation of the energy storage cabinet.

[0031] like Figure 3 As shown, the on-grid and off-grid switching method of the above-mentioned station system includes the following processes: Step S301, determine whether the mains power is off. If the mains power is off abnormally, the PCS in the energy storage cabinet will immediately shut down for protection; at the same time, the station control server 1 starts to determine whether this step is executed. To prevent misjudgment, if the upper circuit breaker 17 can trip due to undervoltage, it is necessary to read the status dry contact signal of the upper circuit breaker 17 and the voltage of the anti-backflow meter 16 to be 0V at the same time. Only then can it be determined that the mains power is off abnormally; if the upper circuit breaker 17 cannot trip due to undervoltage, a relay can be installed on the incoming line side, and the presence or absence of the mains signal can be fed back by the relay output dry contact, or only the voltage value of the anti-backflow meter 16 can be used to determine whether the mains power is off abnormally.

[0032] Step S302: After the abnormal power failure of the mains is determined in step S301, the station control server 1 controls the photovoltaic circuit breaker 11 to open, and the station control server 1 sequentially opens the frame circuit breaker 7 in the device and the first live molded case circuit breaker 8 used to directly supply power to important loads; wherein the second live molded case circuit breaker 9 used to connect the energy storage system with important loads is initially in the open state. The station control server 1 reads the above circuit breaker state quantity through the I / O module 2 to ensure that the action is executed. Next, the station control server 1 sends an executable off-grid command to the EMS in each energy storage cabinet. After each energy storage cabinet EMS determines that there is no fault in the cabinet, it controls the PCS off-grid VF mode in the corresponding cabinet to start. After the EMS collects the stable output voltage of the PCS in each cabinet, the station control server 1 controls the second live molded case circuit breaker 9 used to connect the energy storage system with important loads to close. To ensure safety, the first live molded case circuit breaker 6 and the second live molded case circuit breaker 7 are designed with electrical interlocking, and they cannot be closed at the same time. When the energy storage system is supplying power to important loads, the current output voltage and frequency value of each energy storage cabinet is collected in real time. If the value exceeds the set protection threshold, a protective shutdown operation is immediately performed.

[0033] Step S303, determining whether the mains power is restored. When the mains power is restored, firstly detecting that the voltage value of the anti-backflow meter 16 has returned to normal.

[0034] Step S304: After the mains power is restored in step S303, the EMS controls each energy storage cabinet to shut down. The station control server 1 controls the second live molded case circuit breaker 9 used to connect the energy storage system to important loads to open, the first live molded case circuit breaker 8 used to directly power important loads with the mains power to close, and the frame circuit breaker 7 in the device to close. At this time, if the system upper circuit breaker 17 contains an undervoltage tripping function, it needs to be manually closed. If there is no undervoltage tripping function or the relay signal is used to determine whether the mains power is supplied, manual closing is required. After the action is completed, if the EMS determines that each energy storage cabinet has no faults and starts the grid-connected mode, it will execute the peak shaving and valley filling strategy according to the settings. To ensure the safety of power supply, the photovoltaic circuit breaker 8 needs to be closed and connected after the site operation and maintenance personnel determine that the photovoltaic system is fault-free. If the site does not have a photovoltaic system, photovoltaic circuit breakers may not be installed.

[0035] like Figure 4 As shown, the energy storage system formed by the energy storage integrated cabinet of the present invention is directly connected to the station control server. Each energy storage cabinet PCS synchronizes the industrial frequency signal and the carrier signal through the parallel line to prevent inconsistent output of the PCS in each energy storage cabinet when off-grid. Each energy storage cabinet and the energy storage cabinet and the station control server are connected through a switch. The anti-backflow meter and the energy storage meter can be connected to energy storage cabinet No. 1, which is used for anti-backflow control and charge and discharge electricity statistics of the entire energy storage system. If the energy storage system in the embodiment of the present invention needs to be increased in capacity, the access point of the energy storage integrated cabinet can be reserved for the off-grid device, and the control scheme does not need to be redesigned.

[0036] Definitions of the above abbreviations and professional terms Energy Management System (EMS): Responsible for real-time monitoring and optimization of the entire energy storage system, including monitoring of voltage, frequency, load and other status parameters to ensure efficient operation of the system.

[0037] Power Storage Converter (PCS): Core equipment used to achieve energy conversion in energy storage systems, converting DC power into stable AC output, or converting AC power in the grid into DC power for storage in batteries.

[0038] Station control server: responsible for the intelligent control of the system, managing the signal collection and command issuance during the on-grid and off-grid switching process, realizing the automated control of the entire energy storage station, and the intelligent management of the on-grid and off-grid switching of the entire station.

[0039] The serial numbers of the above-mentioned embodiments of the present application are for description only and do not represent the advantages or disadvantages of the embodiments.

[0040] In the above embodiments of the present application, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, please refer to the relevant description of other embodiments.

[0041] In the several embodiments provided in this application, it should be understood that the disclosed technical content can be implemented in other ways. Among them, the device embodiments described above are only schematic. For example, the division of the units can be a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of units or modules, which can be electrical or other forms.

[0042] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple units. Some or all of the units may be selected according to actual needs to achieve the purpose of the present embodiment.

[0043] The above is only a preferred implementation of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

[0044] It should be understood that the above description is for illustration and not for limitation. Many embodiments and many applications beyond the examples provided will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of this patent should not be determined with reference to the above description, but rather with reference to the preceding claims and the full scope of equivalents to which such claims are entitled. For the purpose of comprehensiveness, all articles and references, including disclosures of patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the preceding claims is not intended to be a waiver of such subject matter, nor should it be considered that the applicant has not considered such subject matter to be part of the disclosed inventive subject matter.

Claims

1. A grid-connected and off-grid switching device for a multi-machine parallel energy storage system, characterized in that: including a station control server (1); The station control server (1) is connected to an I / O module (2), and the I / O module (2) is connected to a frame circuit breaker (7), a first live molded case circuit breaker (8), a second live molded case circuit breaker (9), and a plurality of energy storage cabinet molded case circuit breakers, and reads their opening and closing states; the incoming line side of the frame circuit breaker (7) and the first live molded case circuit breaker (8) is used to connect to the mains; the outgoing line side of the frame circuit breaker (7) is connected to the second live molded case circuit breaker (9); the outgoing line sides of the first live molded case circuit breaker (8) and the second live molded case circuit breaker (9) are both used to connect to important loads, and the plurality of energy storage cabinet molded case circuit breakers and the second live molded case circuit breaker (9) are both connected to the outgoing line side of the frame circuit breaker (7).

2. The on-grid and off-grid switching device for a multi-machine parallel energy storage system according to claim 1, characterized in that: The incoming line sides of the frame circuit breaker (7) and the first live-operated molded case circuit breaker (8) are both connected to a 400V busbar.

3. The on-grid and off-grid switching device for a multi-machine parallel energy storage system according to claim 1, characterized in that: It also includes a photovoltaic circuit breaker (11), one end of the photovoltaic circuit breaker (11) is connected to the busbar, and the other end is connected to the inverter and the photovoltaic system in sequence.

4. The on-grid and off-grid switching device for a multi-machine parallel energy storage system according to claim 1, characterized in that: It also includes an uninterruptible power supply (10), which uses a first miniature circuit breaker (4) to input a 220V power supply.

5. A station system, characterized in that: A device for switching between an on-grid and an off-grid for a multi-machine parallel energy storage system and an upper circuit breaker (17) as claimed in any one of claims 1 to 4; An upper circuit breaker (17) is provided on the incoming line side of the on-grid switching device, an anti-reverse current meter (16) is provided on the incoming line side of the upper circuit breaker (17), a first energized molded case circuit breaker (8) and a second energized molded case circuit breaker (9) are connected to important loads, and each energy storage cabinet molded case circuit breaker is connected to an energy storage cabinet.

6. The station system according to claim 5, characterized in that: Each energy storage cabinet is equipped with EMS and PCS systems.

7. A method for switching between grid and off-grid based on the station system according to any one of claims 5 to 6, characterized in that: The process includes: S1, if the upper circuit breaker (17) can trip due to undervoltage, and at the same time the upper circuit breaker (17) status dry contact signal and the voltage of the anti-reverse current meter (16) are read as 0V, the mains power is abnormally cut off and the energy storage cabinet is shut down for protection; S2, after the mains power fails abnormally, the station control server (1) opens the frame circuit breaker (7) and the first energized molded case circuit breaker (8) in sequence, and the second energized molded case circuit breaker (9) is in an open state; the station control server (1) sends an executable off-grid command to each energy storage cabinet, and each energy storage cabinet controls the corresponding cabinet to start the off-grid VF mode after determining that there is no fault in the cabinet, and the station control server (1) controls the second energized molded case circuit breaker (9) to close; S3, judging whether the city power is restored according to whether the voltage value of the anti-backflow meter (16) has returned to normal; S4, after the mains power is restored, each energy storage cabinet is shut down, and the control server (1) sequentially controls the second energized molded case circuit breaker (9) to open, the first energized molded case circuit breaker (8) to close, and the frame circuit breaker (7) to close; the energy storage cabinet starts the grid-connected mode and executes the peak shaving and valley filling strategy according to the setting.

8. The on-grid and off-grid switching method according to claim 7, characterized in that: After the mains power fails abnormally, the station control server (1) controls the photovoltaic circuit breaker (11) to open.

9. The on-grid and off-grid switching method according to claim 7, characterized in that: After the EMS collects the PCS output voltage in each cabinet and it becomes stable, the station control server (1) controls the second energized molded case circuit breaker (9) to close.

10. The on-grid and off-grid switching method according to claim 7, characterized in that: When the energy storage cabinet supplies power to important loads, the output voltage and frequency values ​​of each energy storage cabinet are collected in real time. If the value exceeds the set protection threshold, a protection shutdown operation is immediately performed.

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