Energy storage grid-connected and off-grid switching system and control method thereof

Abstract

The invention discloses an energy storage grid-connected and off-grid switching system and a control method thereof. The invention belongs to an energy storage system control system and method, and provides an energy storage grid-connected and off-grid switching system and a control method thereof for solving the problem that when a power grid in an energy storage system breaks down and is recovered, an existing grid-connected and off-grid switching method is likely to fail in switching. According to the first type, one battery pack, one power conversion system and one static change-over switch are sequentially connected to form an energy storage cabinet, and all the energy storage cabinets are connected in parallel and then connected to a power grid and a local load. According to the other mode, a plurality of static change-over switches are connected in parallel to form a static change-over switch cabinet, a plurality of power conversion systems are connected in parallel to form a power conversion system cabinet, and the static change-over switch cabinet is connected with the power conversion system cabinet and then is connected with a power grid and a load, so that flexible wiring can be realized, and a modularized structure is arranged, so that adjustment and capacity expansion can be conveniently carried out at any time; and the stability of grid-connected and off-grid switching can also be considered.

Description

Technical Field

[0001] This application pertains to a control system and method for an energy storage system, specifically relating to an energy storage and off-grid switching system and its control method. Background Technology

[0002] In energy storage systems, there is an operating mode as a backup power system, or a microgrid system formed by adding photovoltaics, etc. When a grid fault occurs, the STS (Static Transfer Switch) actively switches the PCS (Power Conversion System) from grid-connected operation mode to off-grid operation mode. When the grid is restored, it switches back from off-grid operation mode to grid-connected operation mode. The ability to perform rapid switching while ensuring uninterrupted power supply to the load is called automatic grid-connected / off-grid switching.

[0003] In distributed high-power application scenarios, if a centralized grid-connected switching device and a centralized PCS are used, on the one hand, it is difficult to find such high-power thyristors due to the current level of semiconductor development; on the other hand, expansion is difficult and inflexible. Based on this background, multiple STSs in parallel and multiple PCSs in parallel switching have become a better solution. However, the reliability and stability of this switching solution still face significant challenges: (1) Parallel synchronization between STSs. When STSs cannot achieve synchronization, it is easy for the PCS to be connected in parallel with the grid as a voltage source, or for the PCS to be connected to the local load as a current source, resulting in switching failure; (2) Lack of parallel synchronization between PCSs. When an STS disconnects from or connects to the grid, but the PCSs are not synchronized, the brief moment of switching will cause some PCSs in the system to work as voltage sources and others as current sources, resulting in switching failure. Summary of the Invention

[0004] This application addresses the issue that existing grid-connected / off-grid switching methods in energy storage systems are prone to switching failures during grid faults and recovery. It provides an energy storage grid-connected / off-grid switching system and its control method.

[0005] To achieve the above objectives, this application adopts the following technical solution: In a first aspect, this application proposes an energy storage and off-grid switching system, characterized in that it includes a power grid and a load, as well as an equal number of battery packs, a power conversion system and a static transfer switch; A battery pack, a power conversion system, and a static transfer switch are connected in sequence to form an energy storage cabinet; multiple energy storage cabinets are connected in parallel and respectively connected to the power grid and the load.

[0006] Secondly, this application proposes a control method for the aforementioned energy storage and off-grid switching system, including: The static transfer switch detects the grid voltage status. When a grid voltage fault is detected, the static transfer switch sends an off-grid switching signal to control the thyristors between the grid and the power conversion system to disconnect. When the grid voltage meets the operating requirements, the static transfer switch sends a grid voltage phase synchronization signal, as well as a grid amplitude and grid connection switching signal to control the thyristors between the grid and the power conversion system to close.

[0007] Furthermore, the method for the static transfer switch to issue an off-grid switching signal to control the disconnection of the thyristor between the power grid and the power conversion system includes: One static transfer switch is used as the master unit to detect the mains voltage status; other static transfer switches are used as slave units. When a grid voltage fault is detected, the host sends an off-grid switching signal and disconnects the thyristor between the corresponding power conversion system and the grid after a delay. Upon receiving the off-grid switching signal, the slave device immediately disconnects the thyristor between the corresponding power conversion system and the power grid.

[0008] Furthermore, the method for controlling the thyristor closure between the power grid and the power conversion system by sending a synchronization signal of the grid voltage phase, as well as the grid amplitude and grid connection switching signal, via the static transfer switch includes: When the host detects that the power grid meets the operating requirements, it sends a power grid recovery signal through the host. All power conversion systems lock in phase according to the power grid recovery signal. After the tracking is completed, the power conversion systems respectively send back a signal that the grid connection is ready to be fully connected to the host. After receiving all grid connection preparation signals, the host sends a grid connection switching signal and simultaneously closes the thyristor between the corresponding power conversion system and the grid after a delay. After receiving the grid connection switching signal from the host, the slave immediately closes the thyristor between the corresponding power conversion system and the grid.

[0009] Furthermore, the off-grid switching signal and the grid-connected switching signal are wired communication signals or hardware control signals.

[0010] Furthermore, the delay time is 2ms.

[0011] Furthermore, the off-grid switching signal is a CAN communication signal; All static transfer switches detect the grid voltage status. When any static transfer switch detects a grid voltage fault, it issues an off-grid switching signal and disconnects the thyristor between the power conversion system corresponding to that static transfer switch and the grid after a delay. After receiving the off-grid switching signal, other static transfer switches stop detecting the grid voltage status, prohibit sending off-grid switching signals or grid-connected switching signals, and disconnect the thyristor between the corresponding power conversion system and the grid.

[0012] Furthermore, the grid connection switching signal is a CAN communication signal; All static transfer switches detect the grid voltage status. When any static transfer switch detects that the grid meets the operating requirements, it sends out a grid recovery signal. After the power conversion system completes grid voltage tracking, it sends back a grid connection preparation complete signal. Once any static transfer switch detects that all power conversion systems have fed back a signal indicating that they are fully prepared for grid connection, it issues a grid connection switching signal and closes the thyristor between the corresponding power conversion system and the grid after a delay. Once the other static transfer switches receive the grid connection switching signal, the thyristors between the other corresponding power conversion systems and the grid immediately close.

[0013] Thirdly, this application also proposes another energy storage and off-grid switching system, including a grid and load, as well as an equal number of battery packs, a power conversion system and a static transfer switch; Multiple power conversion systems together form a power conversion system cabinet, and multiple static transfer switches together form a static transfer switch cabinet; One end of each power conversion system is connected to the corresponding battery pack, and the other ends of all power conversion systems are connected in parallel and then connected to one end of each static transfer switch. One end of all static transfer switches is connected in parallel to the power grid, and the other end of all static transfer switches is connected in parallel to the load.

[0014] Fourthly, this application also proposes another control method for an energy storage and off-grid switching system, including: The static transfer switch detects the grid voltage status. When a grid voltage fault is detected, the static transfer switch sends an off-grid switching signal to control the thyristors between the grid and the power conversion system to disconnect. When the grid voltage meets the operating requirements, the static transfer switch sends a grid voltage phase synchronization signal, as well as a grid amplitude and grid connection switching signal to control the thyristors between the grid and the power conversion system to close.

[0015] Compared with the prior art, this application has the following beneficial effects: This application proposes two energy storage on-grid / off-grid switching systems. The first system consists of a battery pack, a power conversion system, and a static transfer switch connected sequentially to form an energy storage cabinet. These cabinets are then connected in parallel to the power grid and local loads. The second system uses multiple static transfer switches connected in parallel to form a static transfer switch cabinet, and multiple power conversion systems connected in parallel to form a power conversion system cabinet. The static transfer switch cabinet and the power conversion system cabinet are then connected to the power grid and loads. Both energy storage on-grid / off-grid switching systems allow for flexible wiring and modular design, facilitating adjustments and expansions at any time. They can quickly, accurately, and stably connect multiple static transfer switches in parallel, while also ensuring the stability of on-grid / off-grid switching.

[0016] This application also proposes a control method for the aforementioned energy storage and off-grid switching system. Based on the aforementioned system structure, it can be controlled flexibly and easily, and possesses all the advantages of the aforementioned energy storage and off-grid switching system. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the energy storage and off-grid switching system in the embodiments of this application; Figure 2 This is a block diagram of the STS parallel operation signal in the embodiments of this application; Figure 3 This is a schematic diagram of the process of STS host switching from network connection to offline in an embodiment of this application; Figure 4 This is a schematic diagram of the STS slave device switching from on-grid to off-grid operation in an embodiment of this application; Figure 5 This is a schematic diagram of the PCS grid-connection to offline process in an embodiment of this application; Figure 6 This is a schematic diagram of the process of STS host switching from network connection to offline in an embodiment of this application; Figure 7 This is a schematic diagram of the STS slave device switching from on-grid to off-grid operation in an embodiment of this application; Figure 8 This is a schematic diagram of the PCS grid-connection to offline process in an embodiment of this application; Figure 9 This is another schematic diagram of the energy storage and off-grid switching system in the embodiments of this application; Figure 10This is a block diagram of the parallel signal connection between the STS cabinet and the PCS cabinet in an embodiment of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0021] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0022] In the description of the embodiments of this application, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0023] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0024] In the description of the embodiments of this application, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0025] To address the issues of poor switching flexibility, difficulty in controlling synchronization, and difficulty in expanding capacity when the power grid fails in energy storage systems, STS and PCS are used. Existing technologies have proposed several improvements: Chinese invention patent CN118889543B discloses a parallel and off-grid system and its control method. It proposes fitting the historical transmission timestamps of the STS modules in each electrical cabinet when they send opening and closing commands in the same time sequence to a Lagrange curve. The Lagrange curve can express the smoothness of the instantaneous time difference between the opening and closing commands of each STS module. Then, by further transforming the Lagrange curve into a system of difference equations for solution, if the solution to the instantaneous time difference equation is within the range of allowable instantaneous time difference, it indicates that the instantaneous time difference between the STS modules of N electrical cabinets is within the allowable instantaneous time difference range, and therefore, it is not necessary to activate the synchronization controller for coordinated control. Conversely, if the instantaneous time difference between the STS modules deviates from the allowable instantaneous time difference range, it indicates that some STS modules may not be able to send opening and closing commands synchronously, thus requiring the activation of the synchronization controller for synchronous coordinated control to correct the instantaneous time difference. Chinese invention patent application CN119813300A discloses a method for switching between grid connection and off-grid operation in a multi-unit parallel energy storage system, a controller, and the energy storage system itself. It proposes that when the energy storage system is operating in off-grid mode, if the grid is detected to have returned to normal, each energy storage converter is controlled to track the grid voltage, ensuring that the off-grid voltage of each energy storage converter is synchronized with the grid voltage. Once the off-grid voltage of each energy storage converter is synchronized with the grid voltage, the grid connection switch is closed, thus achieving a smooth switching. Finally, the operating loop of each energy storage converter is switched from an off-grid loop to a grid-connected loop.

[0026] The first scheme proposed above requires an additional synchronization controller for the on-grid / off-grid system. It also needs to record transmission timestamps and use complex algorithms to calculate whether the time difference between the switching commands of each STS (Stationary Switching System) is within an acceptable range. If it is, switching occurs; otherwise, the synchronization controller needs to synchronize and update the switching commands. This algorithm is complex, computationally intensive, and always results in a switching time difference. Furthermore, it only considers STS synchronization, not the synchronization between PCS (Power Control Systems). The second scheme detects grid recovery, tracks grid voltage, and maintains synchronization between the grid voltage and the PCS off-grid voltage. However, it does not consider parallel connection between STSs or synchronization between controllers, thus failing to achieve true synchronous switching. It also does not consider the operating conditions during grid-connected to off-grid switching.

[0027] Based on the existing technology, this application proposes an energy storage and off-grid switching system and its control method. The following is a detailed description of this application in conjunction with embodiments and accompanying drawings.

[0028] In one embodiment of the energy storage-to-grid switching system of this application, it may include a power grid and a load, as well as multiple battery packs, power conversion systems, and static transfer switches of equal number. A battery pack, a power conversion system, and a static transfer switch are sequentially connected to form an energy storage cabinet, and multiple energy storage cabinets are connected in parallel and respectively connected to the power grid and the load. Figure 1 The diagram shown is a schematic of the energy storage and off-grid switching system in this embodiment.

[0029] It should be noted that the power grid, as the grid-connected AC power source, is the main power supply in grid-connected mode and also the energy source for charging the battery packs. The load is the energy consumption terminal of the system and the core basis for system power expansion. The battery pack is the core energy storage unit of the system, providing the energy source for the entire system in off-grid mode. In grid-connected mode, it can achieve peak-valley charging and discharging, and energy storage. The PCS connects to the DC battery pack on one end and to the AC STS on the other, its core function being to complete the bidirectional conversion between DC and AC power. The STS connects to the PCS on one end and to the power grid on the other, and is also connected to the load side. It is used to detect the power grid operating status, switch the grid-side thyristors on and off, and send grid-connected and off-grid switching commands. All energy storage cabinets share the same grid bus for their grid-side interfaces, enabling coordinated grid-connected charging and discharging of multiple cabinets.

[0030] Under grid-connected operation, when the grid is functioning normally, the system is primarily powered by the grid, and the loads are directly supplied with power from the grid. Simultaneously, the PCS (Power Control System) in each energy storage unit can rectify the grid power into DC to charge the corresponding battery packs, or invert the DC power from the battery packs into AC for grid connection. Under off-grid operation, when the grid is abnormal, the STS (Power Supply System) in each energy storage unit disconnects the grid-side path. The battery packs output AC power through the PCS, directly supplying power to the local loads, ensuring uninterrupted power supply. When the power demand of the local loads increases, only adding an energy storage unit of the same specifications and connecting it in parallel to the grid bus and load bus is required to expand the system capacity; no modifications to the existing energy storage units or wiring are necessary.

[0031] In this application, each energy storage cabinet is an independent functional module, capable of independently performing energy storage, power conversion, grid monitoring, and grid-connected / off-grid switching. When connected to the grid, it is powered by the grid; when off-grid, the battery pack supplies power to the load via a power conversion system. Adopting a modular parallel architecture, capacity expansion can be achieved simply by adding new energy storage cabinets when the load power increases. This design features convenient expansion, strong compatibility, and no cascading effects from a single cabinet failure, significantly improving system stability and fault tolerance while balancing power supply continuity and economic efficiency.

[0032] The specific methods for grid connection or disconnection in this application are as follows: STS (Automatic Switching System) is an automatic grid-connected / off-grid switching device that detects the grid voltage status. When a grid voltage fault is detected, it sends an off-grid switching signal, disconnecting the thyristor between the grid and the PCS (Power Control System). When the grid returns to normal, it provides a synchronization signal for the grid voltage phase, the grid amplitude, and a grid-connected switching signal, closing the thyristor between the grid and the PCS. Upon receiving the off-grid switching signal from the STS, the PCS switches from the grid-connected algorithm to the off-grid algorithm. Upon receiving the grid-connected switching signal from the STS, the PCS phase-locks according to the synchronization signal and outputs a voltage according to the grid amplitude issued by the STS, switching from the off-grid algorithm to the grid-connected algorithm. The above describes the switching process for a single unit.

[0033] When operating in parallel, several STSs and several PCSs form a single system, with synchronization signals and switching signals connected in parallel across these devices. For example... Figure 2 The diagram shows the STS parallel operation signal block diagram. One STS acts as the master, detecting the grid status, while the others act as slaves. When a grid voltage fault is detected, the master sends an off-grid switching signal, delaying the disconnection of the thyristors between the grid and the PCS. Upon receiving the switching signal, the other slave STSs immediately disconnect the thyristors between the grid and the PCS. Upon receiving this signal, the PCS switches from the grid-connected algorithm to the off-grid algorithm. For example... Figure 3 The diagram shown illustrates the process of switching an STS host from network connection to offline operation. Figure 4 The diagram shown illustrates the process of switching an STS slave device from grid connection to offline operation. Figure 5 The diagram illustrates the process of PCS switching from grid connection to off-grid operation. When the master STS detects grid restoration, it sends a grid restoration signal. Upon receiving this signal, the PCS locks onto the grid according to the synchronization signal sent by the STS. After achieving full tracking, the PCS sends a grid connection preparation signal to the STS. When the master STS detects all PCS preparation signals, it sends a grid connection switching signal and simultaneously closes its thyristor after a delay. Other STS slaves receive this signal and immediately close their thyristors. Upon receiving this signal, the PCS switches from off-grid algorithm to grid connection algorithm, completing the switching process. Figure 6 The diagram shown illustrates the process of switching an STS host from network connection to offline operation. Figure 7 The diagram shown illustrates the process of switching an STS slave device from grid connection to offline operation. Figure 8 The diagram shown illustrates the process of switching PCS from grid connection to off-grid operation.

[0034] In practical applications, both grid-connected and off-grid switching signals can use various communication signals, such as CAN, 485, Ethernet, hard-wired I / O signals, or fiber optic signals.

[0035] As a specific example of this application, both the grid-connected switching signal and the off-grid switching signal are hardwired I / O signals, and the delay time during delayed switching is 2ms. In another specific example of this application: Both the grid-connected switching signal and the off-grid switching signal are CAN communication signals. The specific control method at this time is as follows: (1) Grid-connected to off-grid switching: When the system is operating in grid-connected mode, each STS detects the grid status. When any STS detects an abnormal grid voltage, it sends a grid-connected to off-grid command via CAN communication signal. At the same time, the STS starts a 2ms delay, after which the STS disconnects the thyristor on the grid side. After receiving the grid-connected to off-grid command on the bus, other STSs stop detecting the grid, prohibit sending switching commands to the bus, and disconnect the thyristor on the grid side of the STS. When the PCS detects that it has received the grid-connected to off-grid command, it switches the algorithm from a current source to a voltage source.

[0036] (2) Off-grid to grid-connected switching: When the system operates in off-grid mode, each STS detects the grid status. When any STS detects that the grid voltage is normal, it sends the normal grid status to the PCS and other STSs via CAN communication, and simultaneously sends a grid voltage synchronization signal. Upon receiving the normal grid status, the PCS begins to follow the grid voltage signal. After following the grid voltage signal, it sends the "following grid voltage OK" signal to the CAN communication bus via CAN communication. Any STS checks whether it has received the "following grid voltage OK" signal from all PCS in the system. When one STS detects that all PCS are following the main grid voltage, it sends an off-grid to grid-connected command via CAN communication. At the same time, the STS master delays for 2ms, and after 2ms, the STS closes the thyristor on the grid side. Other STSs, upon receiving the off-grid to grid-connected command, close the thyristor on the grid side of their respective STSs. Upon receiving the off-grid to grid-connected command, the PCS switches its algorithm from a voltage source to a current source.

[0037] The aforementioned energy storage on-grid / off-grid switching system adopts a distributed structure. A battery pack, an STS (Solving Technology System), and a PCS (Power Control System) form an energy storage cabinet, with multiple cabinets interconnected for control. This control method can also be applied to multiple STSs connected in parallel to form an STS cabinet, and multiple PCSs connected in parallel to form a PCS cabinet. The STS cabinets and PCS cabinets are then connected to the grid and load. For example... Figure 9The diagram shown is another schematic of the energy storage and off-grid switching system in this embodiment. Multiple power conversion systems together form a power conversion system cabinet, and multiple static transfer switches together form a static transfer switch cabinet. One end of each power conversion system is connected to its corresponding battery pack, and the other ends of all power conversion systems are connected in parallel and then connected to one end of each static transfer switch. One end of all static transfer switches is connected in parallel to the power grid, and the other end of all static transfer switches is connected in parallel to the load. This method can reduce wiring in actual engineering and reduce wiring complexity.

[0038] This embodiment can also use the aforementioned control method, with one grid-connected switching signal and one off-grid switching signal, one synchronization signal, and one CAN communication channel connected to the PCS cabinet via the STS cabinet. These signals in the STS cabinet are connected in parallel, and these signals in the PCS cabinet are connected in parallel, such as... Figure 10 The diagram shown is a block diagram of the parallel signal connection between the STS cabinet and the PCS cabinet in an embodiment of this application. Two specific control methods are corresponding to this: (1) Take STS1 (the first one) in the STS cabinet as the master. STS1 detects the grid status. When it detects an abnormal grid status, the grid connection switching signal is low and the thyristor on the grid side is disconnected after a 2ms delay. When other STS detect the grid connection switching signal is low, the other STS disconnects the thyristor on the grid side. When the PCS detects the grid connection switching signal is low, it switches the algorithm from current source to voltage source. When working in off-grid mode, STS1 detects the grid status. When it detects that the grid voltage is normal, it sends the normal grid status to the PCS through CAN communication and sends out the grid voltage synchronization signal. When the PCS receives the normal grid status, it starts to follow the grid voltage signal. When it follows the grid voltage signal, it sends the grid voltage ready signal to STS1. When STS1 receives the grid voltage ready signal, it raises the grid connection switching signal. At the same time, the STS1 master starts to delay for 2ms. After 2ms, STS1 closes the thyristor on the grid side. If other STSs detect that the grid-connected switching signal is high, they immediately close the thyristors on the grid side of other STSs; if the PCS detects that the grid-connected switching signal is high, it switches the algorithm from a voltage source to a current source.

[0039] (2) Both the grid-connected switching signal and the off-grid switching signal are CAN communication signals.

[0040] Grid-connected to off-grid switching: When the system is operating in grid-connected mode, each STS in the STS cabinet detects the grid status. When any STS detects an abnormal grid voltage, it sends a grid-connected to off-grid command via CAN communication signal. At the same time, the STS starts a 2ms delay, after which the STS disconnects the thyristor on the grid side. After receiving the grid-connected to off-grid command on the bus, other STSs stop detecting the grid, prohibit sending switching commands to the bus, and disconnect the thyristor on the grid side of the STS. When the PCS in the PCS cabinet detects that it has received the grid-connected to off-grid command, it immediately switches the algorithm from current source to voltage source.

[0041] Off-grid to grid-connected switching: When operating in off-grid mode, each STS in the STS cabinet detects the grid status. When any STS detects that the grid voltage is normal, it sends the normal grid status to the PCS and other STS via CAN communication, and simultaneously sends a grid voltage synchronization signal. Upon receiving the normal grid status, the PCS in the PCS cabinet begins to follow the grid voltage signal. Once it follows the grid voltage signal, it sends a grid voltage-ready signal to the CAN communication bus via CAN communication. Any STS in the STS cabinet checks whether it has received the grid voltage-ready signal from all PCS in the PCS cabinet. When one STS first detects that all PCS in the PCS cabinet are following the main grid voltage, that STS sends an off-grid to grid-connected command via CAN communication. Simultaneously, the STS master delays for 2ms, after which the STS closes the thyristor on the grid side. Other STSs receiving the off-grid to grid-connected command close their grid-side thyristors. Upon receiving the off-grid to grid-connected command, the PCS switches its algorithm from a voltage source to a current source.

[0042] This application proposes two methods for transmitting switching signals: one method involves fixing one STS as the master, with all other STSs and PCS acting as slaves, enabling unified control and off-grid switching. This method allows for a wider range of synchronization signal types. When the synchronization signal is a CAN signal, the STS does not need to be fixed. All STSs transmit grid signals, with the STS that first detects a change in grid status transmitting first. Once other STSs receive this signal, they no longer transmit switching signals.

[0043] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An energy storage and off-grid switching system, characterized in that, This includes the power grid and loads, as well as an equal number of battery packs, power conversion systems, and static transfer switches; A battery pack, a power conversion system, and a static transfer switch are connected in sequence to form an energy storage cabinet; multiple energy storage cabinets are connected in parallel and respectively connected to the power grid and the load.

2. A control method for the energy storage and off-grid switching system as described in claim 1, characterized in that, include: The static transfer switch detects the grid voltage status. When a grid voltage fault is detected, the static transfer switch sends an off-grid switching signal to control the thyristors between the grid and the power conversion system to disconnect. When the grid voltage meets the operating requirements, the static transfer switch sends a grid voltage phase synchronization signal, as well as a grid amplitude and grid connection switching signal to control the thyristors between the grid and the power conversion system to close.

3. The control method for the energy storage and off-grid switching system according to claim 2, characterized in that, The method for the static transfer switch to send an off-grid switching signal to control the disconnection of the thyristors between the power grid and the power conversion system includes: One static transfer switch is used as the master unit to detect the mains voltage status; other static transfer switches are used as slave units. When a grid voltage fault is detected, the host sends an off-grid switching signal and disconnects the thyristor between the corresponding power conversion system and the grid after a delay. Upon receiving the off-grid switching signal, the slave device immediately disconnects the thyristor between the corresponding power conversion system and the power grid.

4. The control method for the energy storage and off-grid switching system according to claim 2, characterized in that, The method for controlling the thyristor closure between the power grid and the power conversion system by sending a synchronization signal of the grid voltage phase, as well as the grid amplitude and grid connection switching signal, through the static transfer switch includes: When the host detects that the power grid meets the operating requirements, it sends a power grid recovery signal through the host. All power conversion systems lock in phase according to the power grid recovery signal. After the tracking is completed, the power conversion systems respectively send back a signal that the grid connection is ready to be fully connected to the host. After receiving all grid connection preparation signals, the host sends a grid connection switching signal and simultaneously closes the thyristor between the corresponding power conversion system and the grid after a delay. After receiving the grid connection switching signal from the host, the slave immediately closes the thyristor between the corresponding power conversion system and the grid.

5. The control method for the energy storage and off-grid switching system according to claim 2, characterized in that, The off-grid switching signal and the grid-connected switching signal are wired communication signals or hardware control signals.

6. The control method for the energy storage and off-grid switching system according to claim 2, characterized in that, The delay time is 2ms.

7. The control method for the energy storage and off-grid switching system according to claim 2, characterized in that, The off-grid switching signal is a CAN communication signal; All static transfer switches detect the grid voltage status. When any static transfer switch detects a grid voltage fault, it issues an off-grid switching signal and disconnects the thyristor between the power conversion system corresponding to that static transfer switch and the grid after a delay. After receiving the off-grid switching signal, other static transfer switches stop detecting the grid voltage status, prohibit sending off-grid switching signals or grid-connected switching signals, and disconnect the thyristor between the corresponding power conversion system and the grid.

8. The control method for the energy storage and off-grid switching system according to claim 2, characterized in that, The grid connection switching signal is a CAN communication signal; All static transfer switches detect the grid voltage status. When any static transfer switch detects that the grid meets the operating requirements, it sends out a grid recovery signal. After the power conversion system completes grid voltage tracking, it sends back a grid connection preparation complete signal. Once any static transfer switch detects that all power conversion systems have fed back a signal indicating that they are fully prepared for grid connection, it issues a grid connection switching signal and closes the thyristor between the corresponding power conversion system and the grid after a delay. Once the other static transfer switches receive the grid connection switching signal, the thyristors between the other corresponding power conversion systems and the grid immediately close.

9. An energy storage and off-grid switching system, characterized in that, This includes the power grid and loads, as well as an equal number of battery packs, power conversion systems, and static transfer switches; Multiple power conversion systems together form a power conversion system cabinet, and multiple static transfer switches together form a static transfer switch cabinet; One end of each power conversion system is connected to the corresponding battery pack, and the other ends of all power conversion systems are connected in parallel and then connected to one end of each static transfer switch. One end of all static transfer switches is connected in parallel to the power grid, and the other end of all static transfer switches is connected in parallel to the load.

10. A control method for the energy storage and off-grid switching system as described in claim 9, characterized in that, include: The static transfer switch detects the grid voltage status. When a grid voltage fault is detected, the static transfer switch sends an off-grid switching signal to control the thyristors between the grid and the power conversion system to disconnect. When the grid voltage meets the operating requirements, the static transfer switch sends a grid voltage phase synchronization signal, as well as a grid amplitude and grid connection switching signal to control the thyristors between the grid and the power conversion system to close.

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