Grid-connected and off-grid mode switching control method and device and energy storage parallel operation system

Abstract

The invention provides a grid-connected and off-grid mode switching control method and device and an energy storage parallel operation system, and relates to the technical field of energy storage systems.The method comprises the steps that if the energy storage parallel operation system is not connected to mains supply within a preset voltage range, the energy storage parallel operation system is controlled to enter an off-grid mode; based on the first voltage characteristic information of the energy storage converter host, controlling the energy storage converter slave to adjust the first voltage parameter; if the electric supply in the preset voltage range is connected to the energy storage parallel operation system, controlling the energy storage converter host to enter a tracking pre-synchronization mode from an off-grid mode, controlling the energy storage converter host to track the electric supply and sequentially adjust the second voltage parameter, and controlling the energy storage converter host to track the energy storage converter host and sequentially adjust the third voltage parameter; and controlling the energy storage converter host and the energy storage converter slave to enter a grid-connected mode at the same time. According to the technical scheme, it is ensured that the voltage parameters of the host and the slave are consistent, parallel operation circulating current oscillation can be avoided to a great extent, and the possibility of system faults is reduced.

Description

Technical Field

[0001] This invention relates to the field of energy storage system technology, and more specifically, to a grid-connected / off-grid mode switching control method, device, and energy storage parallel operation system. Background Technology

[0002] In energy storage systems, power conversion systems (PCS) are used to convert the direct current (DC) output from battery modules into alternating current (AC) for load use, or to convert AC to DC for battery charging. The power conversion system controls the charging and discharging processes of the battery modules and performs AC / DC conversion.

[0003] As the core component of power control, the power storage system (PCS) can be operated as a standalone unit or expanded in parallel depending on the application scenario. Taking renewable energy power plants as an example: renewable energy power plants (such as photovoltaic power plants and wind farms) need to convert distributed energy into AC power usable by the grid. The capacity of a single PCS is usually insufficient to meet the demands of megawatt-level power generation. Therefore, it is necessary to expand the power capacity of the energy storage system through parallel operation to adapt to the grid connection requirements of large power plants. Furthermore, in home energy storage systems on the user side, multiple PCS units are also connected in parallel to expand capacity to meet different capacity requirements.

[0004] In PCS parallel systems, the smooth switching between parallel and offline modes for PCS masters and slaves has always been a technical challenge in this field. If the output AC characteristics of the PCS master and slave cannot be made consistent, parallel circulating current oscillations will occur, which can easily lead to system failure. Summary of the Invention

[0005] In order to solve or improve the technical problem of how to smoothly switch between parallel and offline modes of PCS master and PCS slave, one object of the present invention is to provide a parallel and offline mode switching control method.

[0006] Another objective of this invention is to provide a control device for switching between on-grid and off-grid modes.

[0007] Another object of the present invention is to provide an energy storage parallel operation system.

[0008] To achieve the above objectives, the first aspect of the present invention provides a grid-connected / off-grid mode switching control method, applied to an energy storage parallel system, the energy storage parallel system including an energy storage converter master and an energy storage converter slave.

[0009] The grid-connected / off-grid mode switching control method includes: when the energy storage parallel system is not connected to mains power within a preset voltage range, controlling the energy storage converter master and slave to enter off-grid mode; based on the first voltage characteristic information of the output AC power of the energy storage converter master, controlling the energy storage converter slave to adjust the first voltage parameter of the off-grid output; wherein, the first voltage characteristic information includes first voltage amplitude information, first voltage frequency information, and first voltage phase information, and the first voltage parameter includes first voltage amplitude, first voltage frequency, and first voltage phase; when the energy storage parallel system is connected to mains power within a preset voltage range, controlling the energy storage converter master to enter tracking pre-synchronization mode from off-grid mode; based on the second voltage amplitude information of the mains power, controlling the energy storage converter master to adjust the second voltage amplitude of the output AC power, and according to... The second voltage amplitude controls the slave unit of the energy storage converter to adjust the third voltage amplitude of the output AC power; based on the second voltage frequency information of the mains power, the master unit of the energy storage converter is controlled to adjust the second voltage frequency of the output AC power, and the slave unit of the energy storage converter is controlled to adjust the third voltage frequency of the output AC power according to the second voltage frequency; based on the second voltage phase information of the mains power, the master unit of the energy storage converter is controlled to adjust the second voltage phase of the output AC power, and the slave unit of the energy storage converter is controlled to adjust the third voltage phase of the output AC power according to the second voltage phase; after the second voltage amplitude, third voltage amplitude, second voltage frequency, third voltage frequency, second voltage phase, and third voltage phase are adjusted, the master unit of the energy storage converter is controlled to enter the grid-connected mode from the tracking pre-synchronization mode, and the slave unit of the energy storage converter is controlled to enter the grid-connected mode from the off-grid mode.

[0010] This invention aims to provide a method for switching between grid-connected and off-grid modes. If the energy storage parallel system is not connected to mains power within a preset voltage range, it enters off-grid mode. The slave energy storage converter tracks the first voltage characteristic information (including first voltage amplitude, first voltage frequency, and first voltage phase information) of the master energy storage converter and adjusts the first voltage parameters (including first voltage amplitude, first voltage frequency, and first voltage phase). If the energy storage parallel system is connected to mains power within a preset voltage range, the master energy storage converter enters a tracking pre-synchronization mode. In the tracking pre-synchronization mode, the master energy storage converter adjusts the second voltage parameters (including second voltage amplitude, second voltage frequency, and second voltage phase) sequentially according to the second voltage characteristic information (including second voltage amplitude, second voltage frequency, and second voltage phase information) of the mains power. The slave energy storage converter tracks the second voltage parameters of the master energy storage converter sequentially and adjusts the third voltage parameters (including third voltage amplitude, third voltage frequency, and third voltage phase) sequentially. After the second and third voltage parameters are adjusted, all devices are controlled to simultaneously enter grid-connected mode.

[0011] Energy storage parallel systems can smoothly switch between grid-connected and off-grid modes according to different application scenarios or operating conditions. The energy storage converter slave tracks the voltage characteristic information sent by the energy storage converter master and adjusts the voltage parameters accordingly. This ensures that the voltage parameters of the AC output power of the energy storage converter master and the energy storage converter slave are consistent, which helps to largely avoid parallel circulating current oscillations and reduce the possibility of system failure.

[0012] Furthermore, by successively adjusting the voltage amplitude, voltage frequency, and voltage phase of the energy storage converter (energy storage converter master or energy storage converter slave), the originally relatively complex adjustment process is decomposed into multiple controllable and minute adjustment processes, which helps to suppress parallel circulating current oscillations and significantly improves the safety of the system and the service life of the equipment.

[0013] In some technical solutions, optionally, based on the second voltage amplitude information of the mains power, the energy storage converter master is controlled to adjust the second voltage amplitude of the output AC power, and the energy storage converter slave is controlled to adjust the third voltage amplitude of the output AC power according to the second voltage amplitude. This includes: based on the second voltage amplitude information of the mains power, controlling the energy storage converter master to adjust the second voltage amplitude of the output AC power, and controlling the energy storage converter master to send information containing the second voltage amplitude to the energy storage converter slave; and based on the second voltage amplitude, controlling the energy storage converter slave to adjust the third voltage amplitude of the output AC power.

[0014] In this technical solution, the energy storage converter master unit can simultaneously adjust the second voltage amplitude based on the second voltage amplitude information and send information containing the second voltage amplitude to the energy storage converter slave unit. This enables the energy storage converter slave unit to track the energy storage converter master unit and adjust the third voltage amplitude accordingly. This design approach can improve the accuracy of tracking results while ensuring tracking efficiency.

[0015] In some technical solutions, optionally, based on the second voltage frequency information of the mains power, the energy storage converter master is controlled to adjust the second voltage frequency of the output AC power, and the energy storage converter slave is controlled to adjust the third voltage frequency of the output AC power according to the second voltage frequency. This includes: based on the second voltage frequency information of the mains power, controlling the energy storage converter master to adjust the second voltage frequency of the output AC power, and controlling the energy storage converter master to send information containing the second voltage frequency to the energy storage converter slave; and based on the second voltage frequency, controlling the energy storage converter slave to adjust the third voltage frequency of the output AC power.

[0016] In this technical solution, the energy storage converter master unit can simultaneously adjust the second voltage frequency based on the second voltage frequency information and send information containing the second voltage frequency to the energy storage converter slave unit. This enables the energy storage converter slave unit to track the energy storage converter master unit and adjust the third voltage frequency accordingly. This design approach can improve the accuracy of tracking results while ensuring tracking efficiency.

[0017] In some technical solutions, optionally, based on the second voltage phase information of the mains power, the energy storage converter master is controlled to adjust the second voltage phase of the output AC power, and the energy storage converter slave is controlled to adjust the third voltage phase of the output AC power according to the second voltage phase. This includes: when the absolute value of the difference between the second voltage amplitude and the mains voltage amplitude is less than a first preset threshold, and the absolute value of the difference between the second voltage frequency and the mains voltage frequency is less than a second preset threshold, based on the second voltage phase information of the mains power, the energy storage converter master is controlled to adjust the second voltage phase of the output AC power, and the energy storage converter master is controlled to send information containing the second voltage phase to the energy storage converter slave; based on the second voltage phase, the energy storage converter slave is controlled to adjust the third voltage phase of the output AC power.

[0018] In this technical solution, the energy storage converter master unit can simultaneously adjust the second voltage phase based on the second voltage phase information and send information containing the second voltage phase to the energy storage converter slave unit. This enables the energy storage converter slave unit to track the energy storage converter master unit and adjust the third voltage phase. This design approach can improve the accuracy of tracking results while ensuring tracking efficiency.

[0019] When the energy storage parallel system is connected to the mains power within a preset voltage range, the voltage amplitude, voltage frequency, and voltage phase of the grid-connected output of the energy storage converter are adjusted in stages. Employing individual tracking of voltage amplitude, voltage frequency, and voltage phase simplifies the control algorithm, reduces logic switching, effectively suppresses parallel circulating current oscillations, significantly reduces the possibility of system mutations, and results in higher stability.

[0020] In some technical solutions, optionally, after the second voltage amplitude, third voltage amplitude, second voltage frequency, third voltage frequency, second voltage phase, and third voltage phase are adjusted, the energy storage converter master is controlled to enter the grid-connected mode from the tracking pre-synchronization mode, and the energy storage converter slave is controlled to enter the grid-connected mode from the off-grid mode. This includes: after the second voltage amplitude, third voltage amplitude, second voltage frequency, third voltage frequency, second voltage phase, and third voltage phase are adjusted, receiving grid-connection request information from the energy storage converter master; based on the grid-connection request information, controlling the energy storage converter master to enter the grid-connected mode from the tracking pre-synchronization mode, and controlling the energy storage converter slave to enter the grid-connected mode from the off-grid mode.

[0021] In this technical solution, after the voltage parameters are adjusted, both the main unit and the slave unit of the energy storage converter simultaneously enter grid-connected mode. This method ensures that the voltage parameters of the AC output from the main unit and the slave unit are consistent, which helps to largely avoid parallel circulating current oscillations and reduce the possibility of system failure.

[0022] In some technical solutions, optionally, the grid-connected / off-grid mode switching control method further includes: when the energy storage converter master and / or energy storage converter slave detect that the mains voltage is not within a preset voltage range, receiving grid disconnection / off-grid request information from the energy storage converter master and / or energy storage converter slave, and controlling the energy storage converter master and energy storage converter slave to enter off-grid mode based on the grid disconnection / off-grid request information.

[0023] In this technical solution, the control logic for switching the energy storage parallel system from grid-connected mode to off-grid mode adopts a distributed triggering mechanism. Any device can detect whether an anomaly has occurred in the mains power. If an anomaly is detected, any device triggers an off-grid request. With this design, any device in the energy storage parallel system has the ability to make independent judgments, ensuring stable system operation even when the energy storage converter main unit fails, and exhibiting high control independence.

[0024] In some technical solutions, optionally, based on the grid disconnection request information, controlling the energy storage converter master and the energy storage converter slave to enter the off-grid mode includes: based on the grid disconnection request information, controlling the energy storage converter master to enter the off-grid mode according to the second voltage parameters output by the grid, and controlling the energy storage converter slave to enter the off-grid mode according to the third voltage parameters output by the grid; wherein, the second voltage parameters include a second voltage amplitude, a second voltage frequency, and a second voltage phase, and the third voltage parameters include a third voltage amplitude, a third voltage frequency, and a third voltage phase.

[0025] In this technical solution, when the energy storage parallel system is in grid-connected mode, if any device detects a mains power anomaly, it controls all devices to enter off-grid mode. The energy storage converter master and slave devices switch off-grid control algorithms according to the same command, and begin off-grid self-oscillating output according to the current voltage amplitude, voltage frequency, and voltage phase, ensuring continuous output.

[0026] In some technical solutions, optionally, when the energy storage parallel system is not connected to the mains power within a preset voltage range, before controlling the energy storage converter master and the energy storage converter slave to enter the off-grid mode, the on-grid mode switching control method further includes: controlling the energy storage converter master to determine whether the energy storage parallel system is connected to the mains power within a preset voltage range.

[0027] In this technical solution, by controlling the energy storage converter host to determine whether to connect to the mains power and whether the mains voltage is within the preset voltage range, the energy storage parallel system can smoothly switch between grid-connected mode and off-grid mode according to different application scenarios or operating conditions.

[0028] A second aspect of the present invention provides a grid-connected / off-grid mode switching control device, comprising: a first switching control module, configured to control the energy storage converter master and the energy storage converter slave to enter off-grid mode when the energy storage parallel system is not connected to the mains power within a preset voltage range; and to control the energy storage converter slave to adjust the first voltage parameter of the off-grid output based on the first voltage characteristic information of the output AC power of the energy storage converter master; and a second switching control module, configured to control the energy storage converter master to sequentially send the second voltage amplitude information, the second voltage frequency information, and the second voltage phase information of the mains power to the energy storage converter slave when the energy storage parallel system is connected to the mains power within a preset voltage range, and to sequentially adjust the second voltage parameter of the grid-connected output of the energy storage converter slave based on the second voltage amplitude information, the second voltage frequency information, and the second voltage phase information; and to control the energy storage converter master and the energy storage converter slave to simultaneously enter grid-connected mode after the second voltage parameter adjustment is completed.

[0029] This invention aims to provide a grid-connected / off-grid mode switching control device. If the energy storage parallel system is not connected to the mains power within a preset voltage range, it enters the off-grid mode. The energy storage converter slave tracks the first voltage characteristic information of the energy storage converter master and adjusts the first voltage parameter. If the energy storage parallel system is connected to the mains power within a preset voltage range, the energy storage converter slave tracks the second voltage characteristic information about the mains power sent by the energy storage converter master. After the second voltage parameter adjustment is completed, all devices are controlled to simultaneously enter the grid-connected mode.

[0030] Energy storage parallel systems can smoothly switch between grid-connected and off-grid modes according to different application scenarios or operating conditions. The energy storage converter slave tracks the voltage characteristic information sent by the energy storage converter master and adjusts the voltage parameters accordingly. This ensures that the voltage characteristic information of the AC output power of the energy storage converter master and the energy storage converter slave is consistent, which helps to largely avoid parallel circulating current oscillations and reduce the possibility of system failure.

[0031] A third aspect of this invention provides an energy storage parallel operation system, comprising: a memory and a processor, wherein the memory stores a program or instructions executable on the processor, and the processor, when executing the program or instructions, implements the steps of the grid-connected / off-grid mode switching control method in any of the above-described technical solutions. The electronic device possesses the beneficial effects of any of the above-described technical solutions, which will not be elaborated further here.

[0032] Additional aspects and advantages of the technical solutions of the present invention will become apparent in the following description or may be learned by practice of the invention. Attached Figure Description

[0033] Figure 1 A structural block diagram of an energy storage parallel system according to an embodiment of the present invention is shown; Figure 2 A structural block diagram of an energy storage parallel system according to another embodiment of the present invention is shown; Figure 3 A flowchart of a grid-connected / off-grid mode switching control method according to an embodiment of the present invention is shown; Figure 4 A flowchart of a grid-connected / off-grid mode switching control method according to another embodiment of the present invention is shown; Figure 5 A flowchart of a grid-connected / off-grid mode switching control method according to another embodiment of the present invention is shown; Figure 6 A flowchart of a grid-connected / off-grid mode switching control method according to another embodiment of the present invention is shown; Figure 7 A flowchart of a grid-connected / off-grid mode switching control method according to another embodiment of the present invention is shown; Figure 8 A flowchart of a grid-connected / off-grid mode switching control method according to another embodiment of the present invention is shown; Figure 9 A flowchart of a grid-connected / off-grid mode switching control method according to another embodiment of the present invention is shown; Figure 10 A flowchart of a grid-connected / off-grid mode switching control method according to another embodiment of the present invention is shown; Figure 11 A flowchart of a grid-connected / off-grid mode switching control method according to another embodiment of the present invention is shown; Figure 12 A flowchart of a grid-connected / off-grid mode switching control method according to another embodiment of the present invention is shown; Figure 13 A flowchart of a grid-connected / off-grid mode switching control method according to another embodiment of the present invention is shown; Figure 14 A flowchart of a grid-connected / off-grid mode switching control method according to another embodiment of the present invention is shown; Figure 15 A flowchart of a grid-connected / off-grid mode switching control method according to another embodiment of the present invention is shown; Figure 16 A structural block diagram of a grid-connected / off-grid mode switching control device according to an embodiment of the present invention is shown; Figure 17 A structural block diagram of an energy storage parallel system according to another embodiment of the present invention is shown.

[0034] in, Figures 1 to 17 The correspondence between the reference numerals and component names in the attached drawings is as follows: 100: Energy storage parallel system; 110: Energy storage converter master unit; 120: Energy storage converter slave unit; 132: MCAN communication module; 134: EPS interface; 136: Grid connection interface; 140: Memory; 150: Processor; 410: Electrical load; 420: Power grid; 500: On-grid / off-grid mode switching control device; 510: First switching control module; 520: Second switching control module. Detailed Implementation

[0035] To better understand the above-described objectives, features, and advantages of the embodiments of the present invention, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0036] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, embodiments of the invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of this application is not limited to the specific embodiments disclosed below.

[0037] Typically, an energy storage system consists of multiple functional modules, each performing a specific function to ensure the system operates efficiently, stably, and safely. These modules include a power conversion system (PCS), a battery management system (BMS), and an energy management system (EMS).

[0038] The energy storage converter converts the direct current (DC) output from the battery module into alternating current (AC) for use by electrical loads, or converts AC to DC to charge the battery module. It controls the charging and discharging process of the battery module and performs AC-DC conversion. The battery management system (BMS) monitors parameters such as voltage, current, and temperature of the battery module in real time to ensure its safe and efficient operation. The BMS performs balanced charging and discharging of the battery module to extend its lifespan and largely prevents damage from overcharging, over-discharging, or short circuits. The energy management system (EMS) is the intelligent control system within the energy storage system, responsible for managing and scheduling the entire system. It performs data acquisition, analysis, and energy scheduling to ensure energy balance and normal operation. The EMS also monitors the status of various modules within the energy storage system (such as the PCS, BMS, meters, and air conditioners) in real time. Based on the real-time operating status and external environmental factors, the EMS intelligently allocates energy within the energy storage system to improve its operating efficiency and stability.

[0039] As the core component of power control, the power storage system (PCS) can be operated as a standalone unit or expanded in parallel depending on the application scenario. Taking renewable energy power plants as an example: renewable energy power plants (such as photovoltaic power plants and wind farms) need to convert distributed energy into AC power usable by the grid. The capacity of a single PCS is usually insufficient to meet the demands of megawatt-level power generation. Therefore, it is necessary to expand the power capacity of the energy storage system through parallel operation to adapt to the grid connection requirements of large power plants. Furthermore, in home energy storage systems on the user side, to adapt to different capacity requirements, multiple PCS are connected in parallel to achieve capacity expansion. Compared to using a single large-capacity PCS, this method helps reduce equipment costs.

[0040] In PCS parallel systems, the smooth switching between parallel and offline modes for PCS masters and slaves has always been a technical challenge in this field. If the voltage characteristics of the output AC power of the PCS master and slave cannot be made consistent, parallel circulating current oscillations will occur, which can easily lead to system failure.

[0041] It's important to note that a PCS parallel system refers to a "parallel system" formed by multiple energy storage converters connected in parallel. Ideally, when multiple energy storage converters supply power to an electrical load or the grid, the output current of all converters should flow only to the load or the grid. However, if there are differences in the voltage characteristics (voltage amplitude, frequency, and phase) between the converters, an additional current loop will form between them that does not pass through the load or the grid. This current, flowing only within the parallel-connected converters, is called "parallel circulating current" (essentially, internal current loss between the converters). If the circulating current exceeds the system's allowable safety threshold, it can lead to equipment damage or system malfunction, causing "parallel circulating current oscillation."

[0042] This invention aims to provide a method, device, and energy storage parallel operation system for switching between grid-connected and off-grid modes. When the energy storage parallel operation system is not connected to the mains power within a preset voltage range, the energy storage parallel operation system can achieve capacity expansion operation in off-grid mode. At this time, the slave of the energy storage converter tracks the first voltage characteristic information (including the first voltage amplitude information, the first voltage frequency information, and the first voltage phase information) of the master of the energy storage converter, and adjusts the first voltage parameters (including the first voltage amplitude, the first voltage frequency, and the first voltage phase) of the off-grid output according to the first voltage characteristic information. When the energy storage parallel system is connected to the mains power within a preset voltage range, the energy storage converter master enters the tracking pre-synchronization mode. In the tracking pre-synchronization mode, the energy storage converter master adjusts the second voltage parameters (including the second voltage amplitude, the second voltage frequency, and the second voltage phase) sequentially according to the second voltage characteristic information of the mains power (including the second voltage amplitude, the second voltage frequency, and the second voltage phase). The energy storage converter slave sequentially tracks the second voltage parameters of the energy storage converter master and sequentially adjusts the third voltage parameters (including the third voltage amplitude, the third voltage frequency, and the third voltage phase) of the grid-connected output. After the adjustment of the second and third voltage parameters is completed, all devices (energy storage converter master and energy storage converter slave) are controlled to simultaneously enter the grid-connected mode.

[0043] Energy storage parallel systems can smoothly switch between grid-connected and off-grid modes according to different application scenarios or operating conditions. The energy storage converter slave tracks the voltage characteristic information sent by the energy storage converter master and adjusts the voltage parameters accordingly. This ensures that the voltage parameters of the AC output power of the energy storage converter master and the energy storage converter slave are consistent, which helps to largely avoid parallel circulating current oscillations and reduce the possibility of system failure.

[0044] Furthermore, by successively adjusting the voltage amplitude, voltage frequency, and voltage phase of the energy storage converter (energy storage converter master or energy storage converter slave), the originally relatively complex adjustment process is decomposed into multiple controllable and minute adjustment processes, which helps to suppress parallel circulating current oscillations and significantly improves the safety of the system and the service life of the equipment.

[0045] The following reference Figures 1 to 17 This invention describes a grid-connected / off-grid mode switching control method, apparatus, and energy storage parallel operation system provided according to some embodiments of the present invention.

[0046] In one embodiment of the present invention, such as Figure 1 and Figure 2 As shown, the energy storage parallel system 100 includes an energy storage converter master unit 110 and an energy storage converter slave unit 120 connected in parallel.

[0047] It should be noted that the energy storage parallel system 100 refers to a "parallel system" formed by multiple energy storage converters connected in parallel. The multiple energy storage converters include energy storage converter master units 110 and energy storage converter slave units 120. The number of energy storage converter slave units 120 is at least one; that is, there can be one, two, or more energy storage converter slave units 120. Considering the capacity, space occupied, cost, and other factors of power parallel expansion, the number of energy storage converter slave units 120 can be flexibly configured according to actual needs.

[0048] By connecting the energy storage converter main unit 110 and the energy storage converter slave unit 120 in parallel, it is beneficial to expand the power capacity of the energy storage system in parallel to adapt to the grid connection requirements of large power plants or meet the different capacity requirements of the user-side home energy storage system.

[0049] In some embodiments, the energy storage converter (energy storage converter host 110 or energy storage converter slave 120) optionally uses a TMS320F280039C series (a specific product model) DSP processor (Digital Signal Processor) as the core processing unit.

[0050] The DSP processor includes an MCAN communication module 132. "MCAN" stands for CAN FD Controller, a type of controller area network.

[0051] By configuring the MCAN communication module 132, information exchange between the energy storage converter master unit 110 and the energy storage converter slave unit 120 can be achieved. The MCAN communication module 132 of the energy storage converter master unit 110 is used to send voltage characteristic information (including voltage parameter information) to the MCAN communication module 132 of the energy storage converter slave unit 120. The MCAN communication module 132 of the energy storage converter slave unit 120 is used to receive voltage characteristic information from the MCAN communication module 132 of the energy storage converter master unit 110.

[0052] In some embodiments, the energy storage parallel system 100 may optionally include a main control module. The main control module is communicatively connected to the DSP processor of the energy storage converter (energy storage converter master 110 or energy storage converter slave 120) via a CAN bus.

[0053] It should be noted that CAN (Controller Area Network) refers to the Controller Area Network.

[0054] In some embodiments, optionally, such as Figure 2 As shown, the energy storage converter (energy storage converter host 110 or energy storage converter slave 120) includes an MCAN communication module 132. Multiple energy storage converters exchange information through the MCAN communication module 132.

[0055] The energy storage converter is equipped with an EPS interface 134 (Emergency Power Supply interface) and a grid connection interface 136. The EPS interface 134 is used to connect to the electrical load 410. The grid connection interface 136 is used to connect to the mains power (i.e., the power grid 420).

[0056] In one embodiment of the present invention, the grid-connected / off-grid mode switching control method is applied to the energy storage parallel system 100. Optionally, the grid-connected / off-grid mode switching control method is applied to the main control module of the energy storage parallel system 100.

[0057] like Figure 3 As shown, the on-grid / off-grid mode switching control method includes: S202, when the energy storage parallel system is not connected to the mains power within the preset voltage range, control the energy storage converter master and the energy storage converter slave to enter the off-grid mode; based on the first voltage characteristic information of the output AC power of the energy storage converter master, control the energy storage converter slave to adjust the first voltage parameter of the off-grid output; wherein, the first voltage characteristic information includes the first voltage amplitude information, the first voltage frequency information and the first voltage phase information, and the first voltage parameter includes the first voltage amplitude, the first voltage frequency and the first voltage phase.

[0058] Optionally, the energy storage converter host determines whether the energy storage parallel system is connected to the mains power and generates a first determination result. If the first determination result is yes (the energy storage converter host determines that the energy storage parallel system is connected to the mains power), then it further determines whether the voltage of the mains power is within a preset voltage range and generates a second determination result; if the first determination result is no (the energy storage converter host determines that the energy storage parallel system is not connected to the mains power), then the energy storage converter host and the energy storage converter slave are controlled to enter off-grid mode; based on the first voltage characteristic information of the output AC power of the energy storage converter host, the energy storage converter slave is controlled to adjust the first voltage parameter of the off-grid output (execute S202).

[0059] If the second judgment result is yes (the mains voltage is within the preset voltage range), then execute S204; if the second judgment result is no (the mains voltage is not within the preset voltage range), then control the energy storage converter master and the energy storage converter slave to enter the off-grid mode; based on the first voltage characteristic information of the output AC power of the energy storage converter master, control the energy storage converter slave to adjust the first voltage parameter of the off-grid output (execute S202).

[0060] It should be noted that there are two situations regarding "the energy storage parallel system is not connected to the mains power within the preset voltage range": the first situation is "the energy storage parallel system is not connected to the mains power"; the second situation is "although the energy storage parallel system is connected to the mains power, the voltage of the mains power is not within the preset voltage range".

[0061] When the energy storage parallel system enters off-grid mode, the energy storage converter slave tracks the first voltage characteristic information of the energy storage converter master and adjusts the first voltage parameter of the off-grid output according to the first voltage characteristic information.

[0062] It should be noted that the first voltage characteristic information is the voltage characteristic information of the AC power output by the energy storage converter itself.

[0063] By controlling the slave unit of the energy storage converter to adjust the first voltage parameter of the off-grid output based on the first voltage characteristic information of the output AC power of the main unit of the energy storage converter, it is possible to ensure that the voltage parameters of the output AC power of the main unit and the slave unit of the energy storage converter are consistent. This helps to avoid parallel circulating current oscillation to a large extent and reduce the possibility of system failure.

[0064] S204: When the energy storage parallel system is connected to mains power within a preset voltage range, the main unit of the energy storage converter is controlled to enter the tracking pre-synchronization mode from the off-grid mode; based on the second voltage amplitude information of the mains power, the main unit of the energy storage converter is controlled to adjust the second voltage amplitude of the output AC power, and the slave unit of the energy storage converter is controlled to adjust the third voltage amplitude of the output AC power according to the second voltage amplitude; based on the second voltage frequency information of the mains power, the main unit of the energy storage converter is controlled to adjust the second voltage frequency of the output AC power, and the slave unit of the energy storage converter is controlled to adjust the third voltage frequency of the output AC power according to the second voltage frequency; based on the second voltage phase information of the mains power, the main unit of the energy storage converter is controlled to adjust the second voltage phase of the output AC power, and the slave unit of the energy storage converter is controlled to adjust the third voltage phase of the output AC power according to the second voltage phase; after the second voltage amplitude, third voltage amplitude, second voltage frequency, third voltage frequency, second voltage phase, and third voltage phase are adjusted, the main unit of the energy storage converter is controlled to enter the grid-connected mode from the tracking pre-synchronization mode, and the slave unit of the energy storage converter is controlled to enter the grid-connected mode from the off-grid mode.

[0065] "The energy storage parallel system is connected to the mains power within the preset voltage range" means that the energy storage parallel system is connected to the mains power, and the voltage of the mains power is within the preset voltage range.

[0066] The system controls the energy storage converter master to acquire the second voltage characteristic information of the mains power. Based on this second voltage characteristic information (including second voltage amplitude, second voltage frequency, and second voltage phase information), the system controls the energy storage converter master to adjust the second voltage parameters (including second voltage amplitude, second voltage frequency, and second voltage phase) of the grid-connected output. Simultaneously, while adjusting its own voltage parameters, the system controls the energy storage converter master to send information containing the second voltage parameters to the energy storage converter slave. Based on the second voltage parameters of the energy storage converter master, the system controls the energy storage converter slave to adjust the third voltage parameters (including third voltage amplitude, third voltage frequency, and third voltage phase) of the grid-connected output.

[0067] In other words, during the process of adjusting the voltage parameters of the energy storage converter master and the energy storage converter slave, the energy storage converter master “tracks” the mains power; the energy storage converter slave does not directly “track” the mains power, but indirectly “tracks” the mains power through the energy storage converter master.

[0068] It should be noted that while the main unit of the energy storage converter adjusts the second voltage parameter of the grid-connected output, it sends information containing the second voltage parameter to the slave unit of the energy storage converter so that the slave unit of the energy storage converter can adjust the third voltage parameter of the grid-connected output.

[0069] The main unit of the energy storage converter sequentially adjusts the second voltage amplitude, the second voltage frequency, and the second voltage phase in the second voltage parameters, while the slave unit of the energy storage converter sequentially adjusts the third voltage amplitude, the third voltage frequency, and the third voltage phase in the third voltage parameters.

[0070] Optionally, first adjust the third voltage amplitude of the slave device of the energy storage converter to make the third voltage amplitude of the slave device consistent with the second voltage amplitude of the master device of the energy storage converter; then adjust the third voltage frequency of the slave device to make the third voltage frequency of the slave device consistent with the second voltage frequency of the master device of the energy storage converter; then adjust the third voltage phase of the slave device to make the third voltage phase of the slave device consistent with the second voltage phase of the master device of the energy storage converter.

[0071] By adjusting the voltage amplitude, voltage frequency, and voltage phase sequentially, the complex three-dimensional synchronization problem can be decomposed into three independent one-dimensional adjustment problems, which helps to simplify the control algorithm and thus improve the response speed.

[0072] This invention aims to provide a control method for switching between grid-connected and off-grid modes. When the energy storage parallel system is not connected to the mains power within a preset voltage range, the energy storage parallel system can achieve capacity expansion operation in off-grid mode. At this time, the slave of the energy storage converter tracks the first voltage characteristic information (including the first voltage amplitude information, the first voltage frequency information, and the first voltage phase information) of the master of the energy storage converter, and adjusts the first voltage parameters (including the first voltage amplitude, the first voltage frequency, and the first voltage phase) of the off-grid output according to the first voltage characteristic information. When the energy storage parallel system is connected to the mains power within a preset voltage range, the energy storage converter master enters the tracking pre-synchronization mode. In the tracking pre-synchronization mode, the energy storage converter master adjusts the second voltage parameters (including the second voltage amplitude, the second voltage frequency, and the second voltage phase) sequentially according to the second voltage characteristic information of the mains power (including the second voltage amplitude, the second voltage frequency, and the second voltage phase). The energy storage converter slave sequentially tracks the second voltage parameters of the energy storage converter master and sequentially adjusts the third voltage parameters (including the third voltage amplitude, the third voltage frequency, and the third voltage phase) of the grid-connected output. After the adjustment of the second and third voltage parameters is completed, all devices (energy storage converter master and energy storage converter slave) are controlled to simultaneously enter the grid-connected mode.

[0073] Energy storage parallel systems can smoothly switch between grid-connected and off-grid modes according to different application scenarios or operating conditions. The energy storage converter slave tracks the voltage characteristic information sent by the energy storage converter master and adjusts the voltage parameters accordingly. This ensures that the voltage parameters of the AC output power of the energy storage converter master and the energy storage converter slave are consistent, which helps to largely avoid parallel circulating current oscillations and reduce the possibility of system failure.

[0074] Furthermore, when the energy storage parallel system is connected to mains power within a preset voltage range, the voltage amplitude, voltage frequency, and voltage phase of the grid-connected output of the energy storage converter (main unit and slave unit) are adjusted in stages. Employing individual tracking of voltage amplitude, voltage frequency, and voltage phase simplifies the control algorithm, reduces logic switching, effectively suppresses parallel circulating current oscillations, significantly reduces the possibility of system mutations, and results in higher stability.

[0075] It should be noted that parallel energy storage systems do not require additional hardware, are low in cost, highly scalable, and have a wider range of applications.

[0076] In some embodiments, optionally, such as Figure 4 As shown, based on the second voltage amplitude information of the mains power, the main unit of the energy storage converter is controlled to adjust the second voltage amplitude of the output AC power, and the slave unit of the energy storage converter is controlled to adjust the third voltage amplitude of the output AC power according to the second voltage amplitude, including: S2042, based on the second voltage amplitude information of the mains power, controls the main unit of the energy storage converter to adjust the second voltage amplitude of the output AC power, and controls the main unit of the energy storage converter to send information containing the second voltage amplitude to the slave unit of the energy storage converter; based on the second voltage amplitude, controls the slave unit of the energy storage converter to adjust the third voltage amplitude of the output AC power.

[0077] The system controls the energy storage converter master to acquire the second voltage amplitude information of the mains power; based on the second voltage amplitude information of the mains power, the system controls the energy storage converter master to adjust the second voltage amplitude of the output AC power. While the energy storage converter master adjusts its own voltage parameters (second voltage parameters), the system controls the energy storage converter master to send information containing the second voltage amplitude to the energy storage converter slave; based on the second voltage amplitude of the energy storage converter master, the system controls the energy storage converter slave to adjust the third voltage amplitude of the output AC power.

[0078] It should be noted that voltage amplitude differences are the primary cause of circulating current. If the voltage amplitude difference is too large, a significant and continuous circulating current will immediately form between the energy storage converter main unit and the energy storage converter slave unit, easily burning out power devices. Adjusting the voltage amplitude of all energy storage converters (including the main unit and slave unit) to match the mains voltage amplitude can eliminate the greatest potential for circulating current at its source.

[0079] In some embodiments, optionally, such as Figure 5 As shown, based on the second voltage frequency information of the mains power, the main unit of the energy storage converter is controlled to adjust the second voltage frequency of the output AC power, and the slave unit of the energy storage converter is controlled to adjust the third voltage frequency of the output AC power according to the second voltage frequency, including: S2044, based on the second voltage frequency information of the mains power, controls the main unit of the energy storage converter to adjust the second voltage frequency of the output AC power, and controls the main unit of the energy storage converter to send information containing the second voltage frequency to the slave unit of the energy storage converter; based on the second voltage frequency, controls the slave unit of the energy storage converter to adjust the third voltage frequency of the output AC power.

[0080] The system controls the energy storage converter master to acquire the second voltage frequency information of the mains power; based on the second voltage frequency information of the mains power, the system controls the energy storage converter master to adjust the second voltage frequency of the output AC power. While the energy storage converter master adjusts its own voltage parameters (second voltage parameters), the system controls the energy storage converter master to send information containing the second voltage frequency to the energy storage converter slave; based on the second voltage frequency of the energy storage converter master, the system controls the energy storage converter slave to adjust the third voltage frequency of the output AC power.

[0081] It should be noted that changes in voltage frequency cause continuous changes in voltage phase, resulting in periodically fluctuating circulating current. By adjusting the voltage frequency while maintaining a consistent voltage amplitude, the circulating current can be controlled within a relatively small fluctuation range determined by the voltage frequency, effectively suppressing parallel circulating current oscillations.

[0082] In some embodiments, optionally, such as Figure 6 As shown, based on the second voltage phase information of the mains power, the main unit of the energy storage converter is controlled to adjust the second voltage phase of the output AC power, and the slave unit of the energy storage converter is controlled to adjust the third voltage phase of the output AC power according to the second voltage phase, including: S2045, when the absolute value of the difference between the second voltage amplitude and the mains voltage amplitude is less than the first preset threshold, and the absolute value of the difference between the second voltage frequency and the mains voltage frequency is less than the second preset threshold, based on the second voltage phase information of the mains, the energy storage converter host is controlled to adjust the second voltage phase of the output AC power, and the energy storage converter host is controlled to send information containing the second voltage phase to the energy storage converter slave.

[0083] S2046, based on the second voltage phase, controls the slave of the energy storage converter to adjust the third voltage phase of the output AC power.

[0084] The system controls the energy storage converter master to acquire the second voltage phase information of the mains power; based on the second voltage phase information of the mains power, the system controls the energy storage converter master to adjust the second voltage phase of the output AC power. While the energy storage converter master adjusts its own voltage parameters (second voltage parameters), the system also controls the energy storage converter master to send information containing the second voltage parameters to the energy storage converter slave; based on the second voltage parameters of the energy storage converter master, the system controls the energy storage converter slave to adjust the third voltage phase of the output AC power.

[0085] It should be noted that when the voltage amplitude and voltage frequency are already consistent, adjusting the voltage phase will minimize the instantaneous current generated at the moment the voltage phase is aligned, which is beneficial to further suppress the parallel circulating current oscillation.

[0086] By successively adjusting the second voltage amplitude, the second voltage frequency, and the second voltage phase, the complex three-dimensional synchronization problem can be decomposed into three independent one-dimensional adjustment problems, which helps to simplify the control algorithm and thus improve the response speed.

[0087] By eliminating different types of voltage differences in stages (adjusting voltage amplitude, voltage frequency, and voltage phase sequentially), the originally relatively complex adjustment process is broken down into multiple controllable and minute adjustment processes, which helps to suppress parallel circulating current oscillations and significantly improves system safety and equipment lifespan.

[0088] The system determines whether the absolute value of the difference between the second voltage amplitude and the mains voltage amplitude is less than a first preset threshold, and generates a third determination result. If the third determination result is yes (the absolute value of the difference between the second voltage amplitude and the mains voltage amplitude is less than the first preset threshold), it further determines whether the absolute value of the difference between the second voltage frequency and the mains voltage frequency is less than the second preset threshold, and generates a fourth determination result; if the third determination result is no (the absolute value of the difference between the second voltage amplitude and the mains voltage amplitude is greater than or equal to the first preset threshold), it continues to adjust the grid-connected output voltage amplitude of the energy storage converter.

[0089] If the fourth judgment result is yes (the absolute value of the difference between the second voltage frequency and the mains voltage frequency is less than the second preset threshold), it means that the voltage amplitude and voltage frequency between the energy storage converter master and the energy storage converter slave are consistent, and the voltage phase needs to be further adjusted; if the fourth judgment result is no (the absolute value of the difference between the second voltage frequency and the mains voltage frequency is greater than or equal to the second preset threshold), then the voltage frequency needs to be adjusted.

[0090] When the energy storage parallel system is connected to the mains power within a preset voltage range, the voltage amplitude, voltage frequency, and voltage phase of the grid-connected output of the energy storage converter (main energy storage converter and slave energy storage converter) are adjusted in stages. Employing individual tracking of voltage amplitude, voltage frequency, and voltage phase simplifies the control algorithm, reduces logic switching, effectively suppresses parallel circulating current oscillations, significantly reduces the possibility of system mutations, and results in higher stability.

[0091] In some embodiments, optionally, such as Figure 7As shown, after the second voltage amplitude, third voltage amplitude, second voltage frequency, third voltage frequency, second voltage phase, and third voltage phase are adjusted, the main unit of the energy storage converter is controlled to enter the grid-connected mode from the tracking pre-synchronization mode, and the slave unit of the energy storage converter is controlled to enter the grid-connected mode from the off-grid mode, including: S2047 After the second voltage amplitude, third voltage amplitude, second voltage frequency, third voltage frequency, second voltage phase, and third voltage phase are adjusted, the grid connection request information is received from the energy storage converter host.

[0092] S2048, based on the grid connection request information, controls the energy storage converter master to enter the grid connection mode from the tracking pre-synchronization mode, and controls the energy storage converter slave to enter the grid connection mode from the off-grid mode.

[0093] After the voltage parameters are adjusted, both the main unit and the slave unit of the energy storage converter simultaneously enter grid-connected mode. This method ensures that the voltage parameters of the AC output from the main unit and the slave unit are consistent, which helps to largely avoid parallel circulating current oscillations and reduce the possibility of system failure.

[0094] In some embodiments, optionally, such as Figure 8 As shown, the on-grid / off-grid mode switching control method also includes: S206: When the energy storage converter master and / or energy storage converter slave detect that the mains voltage is not within the preset voltage range, the master receives grid disconnection request information from the energy storage converter master and / or energy storage converter slave, and controls the energy storage converter master and energy storage converter slave to enter the off-grid mode based on the grid disconnection request information.

[0095] When the energy storage parallel system is in grid-connected mode, if any device (energy storage converter master or energy storage converter slave) detects an abnormality in the mains power (the mains voltage is not within the preset voltage range), it will control all devices (energy storage converter master and energy storage converter slave) to enter off-grid mode.

[0096] The control logic for switching from grid-connected mode to off-grid mode in an energy storage parallel system adopts a distributed triggering mechanism. This means that any device in the energy storage parallel system (either the energy storage converter master or slave) can detect whether there is an anomaly in the mains power. If the energy storage converter master and / or the energy storage converter slave detect that the mains voltage is not within a preset voltage range, they receive a grid disconnection request from the energy storage converter master and / or the energy storage converter slave, and based on this request, control the energy storage converter master and the energy storage converter slave to enter off-grid mode.

[0097] The control system switches the off-grid control algorithm for both the main unit and slave unit of the energy storage converter according to the same instruction. It starts off-grid self-oscillation output according to the current voltage amplitude, voltage frequency and voltage phase to ensure output continuity.

[0098] It is important to emphasize that, because the control logic for switching from grid-connected to off-grid mode in the energy storage parallel system adopts a distributed triggering mechanism, any device can detect whether an anomaly has occurred in the mains power (grid). Upon detecting an anomaly, any device triggers a grid disconnection / off-grid request (grid-connected / off-grid command). This design ensures that any device in the energy storage parallel system has the ability to independently determine its operation, guaranteeing stable system operation even in the event of a fault in the energy storage converter, demonstrating high control independence.

[0099] In some embodiments, the second voltage amplitude information of the mains power can be obtained based on a second-order generalized integrator.

[0100] Based on the second-order generalized integrator and the three-phase AC signal of the mains power, the main unit of the energy storage converter is controlled to obtain the second voltage amplitude information of the mains power (to determine the voltage amplitude of the mains power).

[0101] Optionally, based on the second-order generalized integrator and the three-phase AC signal of the mains power, the energy storage converter host calculates Alpha and Beta, and then performs Park transformation to obtain the second voltage amplitude information of the mains power.

[0102] It should be noted that Alpha refers to the voltage component on the α-axis, and Beta refers to the voltage component on the β-axis. The α-axis is usually aligned with the phase direction of the mains voltage in phase A, and its voltage component is used to reflect the trend of phase A voltage variation. The β-axis is an auxiliary axis perpendicular to the α-axis, and its voltage component is used to supplement phase information that the α-axis cannot cover.

[0103] A second-order generalized integrator (SOGI) is a signal processing module whose core function is to filter out noise interference in the three-phase AC mains signal and extract the voltage components on the α-axis and β-axis.

[0104] Park transformation is a technique that converts a two-phase stationary coordinate system (a coordinate system composed of the α-axis and β-axis) into a two-phase rotating coordinate system. Its core purpose is to convert AC signals into DC signals so that the voltage amplitude can be read directly.

[0105] In some embodiments, the second preset threshold is optionally between 0.08 Hz and 0.15 Hz.

[0106] In one specific embodiment, the second preset threshold is 0.08Hz.

[0107] In one specific embodiment, the second preset threshold is 0.1Hz.

[0108] In one specific embodiment, the second preset threshold is 0.12Hz.

[0109] In one specific embodiment, the second preset threshold is 0.15Hz.

[0110] In some embodiments, optionally, when the energy storage parallel system is connected to mains power within a preset voltage range, the energy storage converter master is controlled to switch from off-grid state (off-grid mode) to tracking pre-synchronization state (tracking pre-synchronization mode). Based on the second-order generalized integrator and the three-phase AC signal of the mains power, the energy storage converter master is controlled to acquire the second voltage characteristic information of the mains power (including second voltage amplitude information, second voltage frequency information, and second voltage phase information), and synchronously send the second voltage characteristic information of the mains power to the energy storage converter slave, so that the energy storage converter slave adjusts the grid-connected output voltage parameters together with the energy storage converter master.

[0111] In an energy storage parallel system, all devices (including the energy storage converter master and slave devices) independently determine whether they have completed voltage amplitude, voltage frequency, and voltage phase synchronization. Devices that have completed synchronization send a flag indicating they can switch to grid-connected mode to the CAN bus; those that have not completed synchronization continue to wait for tracking commands. Once all devices have completed synchronization, the control unit sends a grid-connection request to the energy storage converter master, and the slave devices respond to this request. Both the energy storage converter master and slave devices simultaneously enter grid-connected mode.

[0112] In some embodiments, optionally, such as Figure 9 As shown, based on the grid disconnection request information, the energy storage converter master and energy storage converter slave are controlled to enter the off-grid mode, including: S2049, based on the grid disconnection request information, controls the main unit of the energy storage converter to enter the off-grid mode according to the second voltage parameters output by the grid, and controls the slave unit of the energy storage converter to enter the off-grid mode according to the third voltage parameters output by the grid; wherein, the second voltage parameters include the second voltage amplitude, the second voltage frequency and the second voltage phase, and the third voltage parameters include the third voltage amplitude, the third voltage frequency and the third voltage phase.

[0113] When the energy storage parallel system is in grid-connected mode, if any device (energy storage converter master or energy storage converter slave) detects an abnormality in the mains power (the mains voltage is not within the preset voltage range), it will control all devices (energy storage converter master and energy storage converter slave) to enter off-grid mode.

[0114] The control system switches the off-grid control algorithm for both the main unit and slave unit of the energy storage converter according to the same instruction. It starts off-grid self-oscillation output according to the current voltage amplitude, voltage frequency and voltage phase to ensure output continuity.

[0115] In some embodiments, optionally, such as Figure 10 As shown, when the energy storage parallel system is not connected to the mains power within a preset voltage range, the on-grid mode switching control method before controlling the energy storage converter master and the energy storage converter slave to enter off-grid mode also includes: S201 controls the main unit of the energy storage converter to determine whether the energy storage parallel system is connected to the mains power within the preset voltage range.

[0116] Optionally, the energy storage converter host determines whether the energy storage parallel system is connected to the mains power and generates a first determination result. If the first determination result is yes (the energy storage converter host determines that the energy storage parallel system is connected to the mains power), then it further determines whether the voltage of the mains power is within a preset voltage range and generates a second determination result; if the first determination result is no (the energy storage converter host determines that the energy storage parallel system is not connected to the mains power), then the energy storage converter host and the energy storage converter slave are controlled to enter off-grid mode; based on the first voltage characteristic information of the output AC power of the energy storage converter host, the energy storage converter slave is controlled to adjust the first voltage parameter of the off-grid output (execute S202).

[0117] If the second judgment result is yes (the mains voltage is within the preset voltage range), then execute S204; if the second judgment result is no (the mains voltage is not within the preset voltage range), then control the energy storage converter master and the energy storage converter slave to enter the off-grid mode; based on the first voltage characteristic information of the output AC power of the energy storage converter master, control the energy storage converter slave to adjust the first voltage parameter of the off-grid output (execute S202).

[0118] It should be noted that there are two situations regarding "the energy storage parallel system is not connected to the mains power within the preset voltage range": the first situation is "the energy storage parallel system is not connected to the mains power"; the second situation is "although the energy storage parallel system is connected to the mains power, the voltage of the mains power is not within the preset voltage range".

[0119] By controlling the main unit of the energy storage converter to determine whether to connect to the mains power and whether the voltage of the mains power is within the preset voltage range, the energy storage parallel system can smoothly switch between grid-connected mode and off-grid mode according to different application scenarios or operating conditions.

[0120] In some embodiments, optionally, such as Figure 11 As shown, the on-grid / off-grid mode switching control method includes the following when the energy storage parallel system is not connected to the mains power within a preset voltage range: S301, the host controller calculates its own output parameters; among which, the own output parameters include voltage phase, voltage frequency and voltage amplitude.

[0121] It should be noted that "main unit" refers to the main unit of the energy storage converter. "Main unit controller" refers to the control module of the main unit of the energy storage converter. "Self-output parameters" refers to the first voltage characteristic information of the output AC power of the main unit of the energy storage converter.

[0122] S302 sends the master's own output parameters to the slave controller via the MCAN communication module.

[0123] It should be noted that "slave" refers to the slave unit of the energy storage converter. "Slave controller" refers to the control module of the slave unit of the energy storage converter.

[0124] S303, the slave controller receives the output parameters of the master.

[0125] S304 sets the output parameters of the slave device based on the output parameters of the host device.

[0126] S305, the slave device obtains the output current information through the MCAN communication module.

[0127] S306 obtains the output current of all slave devices via the CAN bus.

[0128] S307 calculates the average current based on the output current of all slave devices.

[0129] S308, calculates compensation based on the average current to determine the current sharing loop.

[0130] S309 adjusts the first voltage parameter of the off-grid output based on the slave device's output parameters and the compensation calculated by the current sharing loop using a droop control method.

[0131] When the energy storage parallel system is not connected to the mains power within the preset voltage range, the energy storage parallel system realizes off-grid output capacity expansion based on the output parameters of the slave unit and the control logic of current sharing loop calculation compensation.

[0132] In some embodiments, optionally, such as Figure 12 As shown, when the energy storage parallel system is connected to mains power within a preset voltage range, the on-grid / off-grid mode switching control method includes: S311, the host switches from the off-network output state to the pre-synchronization state.

[0133] It should be noted that "off-network output state" refers to off-network mode, and "pre-synchronization state" refers to tracking pre-synchronization mode.

[0134] S312, the host calculates the mains power parameters through a second-order generalized integrator.

[0135] It should be noted that the mains parameters refer to the voltage amplitude, voltage frequency, and voltage phase of the mains power.

[0136] S313: The host sends mains power parameters to all slave devices in real time.

[0137] S314, the slave device receives the mains power parameters sent by the master device.

[0138] S315 is the slave device that adjusts the third voltage parameter of the grid-connected output.

[0139] In some embodiments, optionally, such as Figure 13 As shown, when the energy storage parallel system is connected to mains power within a preset voltage range, the on-grid / off-grid mode switching control method includes: The S321 main unit calculates the mains power parameters based on a second-order generalized integrator.

[0140] S322, calculate the Alpha and Beta values.

[0141] S323 performs a Park transformation to obtain the voltage amplitude of the mains power.

[0142] The S324 approximates the voltage amplitude of the mains power supply in a step-by-step manner.

[0143] S325 begins tracking the voltage and frequency of the mains power.

[0144] S326, adjust the voltage frequency in the voltage parameters to approximate the voltage frequency of the mains power.

[0145] S327, determine whether the absolute value of the difference between the voltage frequency in the voltage parameters and the mains voltage frequency is less than 0.1Hz.

[0146] If yes, then execute S328; otherwise, return to S326.

[0147] S328, initiate phase synchronization.

[0148] Start tracking the voltage phase of the mains power.

[0149] S329, the slave device follows the master device's changes.

[0150] In some embodiments, optionally, such as Figure 14 As shown, when the energy storage parallel system is connected to mains power within a preset voltage range, the on-grid / off-grid mode switching control method includes: S331, all devices determine their own synchronization status.

[0151] It should be noted that "all devices" refers to both the main unit and slave unit of the energy storage converter.

[0152] S332 determines whether the voltage amplitude, voltage frequency, and voltage phase are synchronized.

[0153] If yes, then execute S333; otherwise, execute S334.

[0154] S333, synchronous completion, sending grid-connection mode identification information.

[0155] S334, synchronization not completed, continue to wait for tracking.

[0156] S335, the host determines whether the parallel system has completed tracking.

[0157] It should be noted that "parallel system" refers to energy storage parallel system.

[0158] If yes, then execute S336; otherwise, return to S334.

[0159] S336, send the command to switch to grid connection mode.

[0160] S337: When the slave device responds to the command to switch to grid-connected mode, both the master and slave devices simultaneously enter grid-connected mode.

[0161] In some embodiments, optionally, such as Figure 15 As shown, the on-grid / off-grid mode switching control method includes: S341, any device detects an abnormal mains power supply.

[0162] It should be noted that "equipment" refers to either the main unit or slave unit of the energy storage converter. "Main power abnormality" means that the mains voltage is outside the preset voltage range.

[0163] S342 sends a disconnection request message to the CAN bus.

[0164] It should be noted that "disconnection request information" refers to disconnection request information.

[0165] S343, All devices receive the request.

[0166] It should be noted that "all devices" refers to both the main unit and slave unit of the energy storage converter.

[0167] S344 switches the off-grid control algorithm according to the same instruction.

[0168] S345 starts off-grid self-oscillation output based on the current voltage amplitude, voltage frequency, and voltage phase.

[0169] In one embodiment of the present invention, such as Figure 16 As shown, the on-grid / off-grid mode switching control device 500 includes a first switching control module 510 and a second switching control module 520.

[0170] The first switching control module 510 is used to control the energy storage converter master 110 and the energy storage converter slave 120 to enter the off-grid mode when the energy storage parallel system 100 is not connected to the mains power within the preset voltage range; based on the first voltage characteristic information of the output AC power of the energy storage converter master 110, it controls the energy storage converter slave 120 to adjust the first voltage parameter of the off-grid output; wherein, the first voltage characteristic information includes first voltage amplitude information, first voltage frequency information and first voltage phase information, and the first voltage parameter includes first voltage amplitude, first voltage frequency and first voltage phase.

[0171] Optionally, the energy storage converter host 110 determines whether the energy storage parallel system 100 is connected to the mains power and generates a first determination result. If the first determination result is yes (the energy storage converter host 110 determines that the energy storage parallel system 100 is connected to the mains power), then it further determines whether the voltage of the mains power is within a preset voltage range and generates a second determination result; if the first determination result is no (the energy storage converter host 110 determines that the energy storage parallel system 100 is not connected to the mains power), then the energy storage converter host 110 and the energy storage converter slave 120 are controlled to enter off-grid mode; based on the first voltage characteristic information of the output AC power of the energy storage converter host 110, the energy storage converter slave 120 is controlled to adjust the first voltage parameter of the off-grid output.

[0172] If the second judgment result is yes (the mains voltage is within the preset voltage range), then the second voltage parameter of the energy storage converter host 110 is adjusted sequentially, and the third voltage parameter of the energy storage converter slave 120 is adjusted sequentially; after the second and third voltage parameters are adjusted, the energy storage converter host 110 and the energy storage converter slave 120 are controlled to simultaneously enter the grid-connected mode; if the second judgment result is no (the mains voltage is not within the preset voltage range), then the energy storage converter host 110 and the energy storage converter slave 120 are controlled to enter the off-grid mode; based on the first voltage characteristic information of the output AC power of the energy storage converter host 110, the energy storage converter slave 120 is controlled to adjust the first voltage parameter of the off-grid output.

[0173] It should be noted that there are two situations regarding "the energy storage parallel system 100 is not connected to the mains power within the preset voltage range": the first situation is that "the energy storage parallel system 100 is not connected to the mains power"; the second situation is that "although the energy storage parallel system 100 is connected to the mains power, the voltage of the mains power is not within the preset voltage range".

[0174] When the energy storage parallel system 100 enters the off-grid mode, the energy storage converter slave 120 tracks the first voltage characteristic information of the energy storage converter master 110 and adjusts the first voltage parameter of the off-grid output according to the first voltage characteristic information.

[0175] It should be noted that the first voltage characteristic information is the voltage characteristic information of the AC power output by the energy storage converter host 110 itself.

[0176] By controlling the slave unit 120 of the energy storage converter to adjust the first voltage parameter of the off-grid output based on the first voltage characteristic information of the AC output of the energy storage converter host 110, it can be ensured that the voltage parameters of the AC output of the energy storage converter host 110 and the energy storage converter slave unit 120 are consistent. This helps to avoid parallel circulating current oscillation to a large extent and reduce the possibility of system failure.

[0177] The second switching control module 520 is used to control the energy storage converter host 110 to enter the tracking pre-synchronization mode from the off-grid mode when the energy storage parallel system 100 is connected to the mains power within a preset voltage range; based on the second voltage amplitude information of the mains power, it controls the energy storage converter host 110 to adjust the second voltage amplitude of the output AC power, and controls the energy storage converter slave 120 to adjust the third voltage amplitude of the output AC power according to the second voltage amplitude; based on the second voltage frequency information of the mains power, it controls the energy storage converter host 110 to adjust the second voltage frequency of the output AC power, and controls the energy storage converter according to the second voltage frequency. The slave device 120 adjusts the third voltage frequency of the output AC power; based on the second voltage phase information of the mains power, the main device 110 of the energy storage converter is controlled to adjust the second voltage phase of the output AC power, and the slave device 120 of the energy storage converter is controlled to adjust the third voltage phase of the output AC power according to the second voltage phase; after the second voltage amplitude, third voltage amplitude, second voltage frequency, third voltage frequency, second voltage phase and third voltage phase are adjusted, the main device 110 of the energy storage converter is controlled to enter the grid-connected mode from the tracking pre-synchronization mode, and the slave device 120 of the energy storage converter is controlled to enter the grid-connected mode from the off-grid mode.

[0178] "The energy storage parallel system 100 is connected to the mains power within the preset voltage range" means that the energy storage parallel system 100 is connected to the mains power, and the voltage of the mains power is within the preset voltage range.

[0179] The control unit 110 of the energy storage converter acquires the second voltage characteristic information of the mains power. Based on the second voltage characteristic information of the mains power (including second voltage amplitude information, second voltage frequency information, and second voltage phase information), the control unit 110 adjusts the second voltage parameters (including second voltage amplitude, second voltage frequency, and second voltage phase) of the grid-connected output. While the energy storage converter 110 adjusts its own voltage parameters, the control unit 110 sends information containing the second voltage parameters to the energy storage converter slave unit 120. Based on the second voltage parameters of the energy storage converter 110, the control unit 120 adjusts the third voltage parameters (including third voltage amplitude, third voltage frequency, and third voltage phase) of the grid-connected output.

[0180] In other words, during the process of adjusting the voltage parameters of the energy storage converter master 110 and the energy storage converter slave 120, the energy storage converter master 110 "tracks" the mains power; the energy storage converter slave 120 does not directly "track" the mains power, but indirectly "tracks" the mains power through the energy storage converter master 110.

[0181] It should be noted that while adjusting the grid-connected output voltage parameters, the energy storage converter master 110 sends information containing the second voltage parameters to the energy storage converter slave 120, so that the energy storage converter slave 120 can adjust the grid-connected output third voltage parameters.

[0182] The main unit 110 of the energy storage converter sequentially adjusts the second voltage amplitude, the second voltage frequency and the second voltage phase in the second voltage parameters, while the slave unit 120 of the energy storage converter sequentially adjusts the third voltage amplitude, the third voltage frequency and the third voltage phase in the third voltage parameters.

[0183] Optionally, first adjust the third voltage amplitude of the energy storage converter slave 120 so that the third voltage amplitude of the energy storage converter slave 120 is consistent with the second voltage amplitude of the energy storage converter master 110; then adjust the third voltage frequency of the energy storage converter slave 120 so that the third voltage frequency of the energy storage converter slave 120 is consistent with the second voltage frequency of the energy storage converter master 110; then adjust the third voltage phase of the energy storage converter slave 120 so that the third voltage phase of the energy storage converter slave 120 is consistent with the second voltage phase of the energy storage converter master 110.

[0184] By adjusting the voltage amplitude, voltage frequency, and voltage phase sequentially, the complex three-dimensional synchronization problem can be decomposed into three independent one-dimensional adjustment problems, which helps to simplify the control algorithm and thus improve the response speed.

[0185] This invention aims to provide a grid-connected / off-grid mode switching control device 500. When the energy storage parallel system is not connected to the mains power within a preset voltage range, the energy storage parallel system can achieve capacity expansion operation in off-grid mode. At this time, the energy storage converter slave 120 tracks the first voltage characteristic information (including the first voltage amplitude information, the first voltage frequency information, and the first voltage phase information) of the energy storage converter master 110, and adjusts the first voltage parameters (including the first voltage amplitude, the first voltage frequency, and the first voltage phase) of the off-grid output according to the first voltage characteristic information. When the energy storage parallel system is connected to the mains power within a preset voltage range, the energy storage converter host 110 enters the tracking pre-synchronization mode. In the tracking pre-synchronization mode, the energy storage converter host 110 adjusts the second voltage parameters (including the second voltage amplitude, the second voltage frequency, and the second voltage phase) sequentially according to the second voltage characteristic information of the mains power (including the second voltage amplitude, the second voltage frequency, and the second voltage phase). The energy storage converter slave 120 sequentially tracks the second voltage parameters of the energy storage converter host 110 and sequentially adjusts the third voltage parameters (including the third voltage amplitude, the third voltage frequency, and the third voltage phase) of the grid-connected output. After the adjustment of the second and third voltage parameters is completed, all devices (energy storage converter host 110 and energy storage converter slave 120) are controlled to simultaneously enter the grid-connected mode.

[0186] The energy storage parallel system 100 can smoothly switch between grid-connected and off-grid modes according to different application scenarios or operating conditions. The energy storage converter slave 120 tracks the voltage characteristic information transmitted by the energy storage converter master 110 and adjusts the voltage parameters, which can ensure that the voltage characteristic information of the AC output of the energy storage converter master 110 and the energy storage converter slave 120 is consistent. This helps to avoid parallel circulating current oscillation to a large extent and reduce the possibility of system failure.

[0187] Furthermore, when the energy storage parallel system 100 is connected to mains power within a preset voltage range, the voltage amplitude, voltage frequency, and voltage phase of the grid-connected output of the energy storage converters (energy storage converter master 110 and energy storage converter slave 120) are adjusted in stages. Employing individual tracking of voltage amplitude, voltage frequency, and voltage phase simplifies the control algorithm, reduces logic switching, effectively suppresses parallel circulating current oscillations, significantly reduces the possibility of system mutations, and results in higher stability.

[0188] It should be noted that the energy storage parallel system 100 does not require additional hardware, has low cost, strong scalability, and a wider range of applications.

[0189] In one embodiment of the present invention, such as Figure 17As shown, the energy storage parallel system 100 includes a memory 140 and a processor 150. The memory 140 stores programs or instructions that can run on the processor 150. When the processor 150 executes the programs or instructions, it implements the steps of the grid-connected / off-grid mode switching control method in any of the above embodiments. The energy storage parallel system 100 has the beneficial effects of any of the above embodiments, which will not be elaborated further here.

[0190] In this invention, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance; the term "multiple" refers to two or more unless otherwise explicitly defined. The terms "install," "connect," "link," and "fix" should be interpreted broadly. For example, "connect" can be a fixed connection, a detachable connection, or an integral connection; "link" can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0191] In the description of this invention, it should be understood that the terms "upper," "lower," "left," "right," "front," "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or unit referred to must have a specific orientation or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0192] In the description of this specification, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0193] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for switching between grid-connected and off-grid modes, characterized in that, Applied to energy storage parallel operation systems, the energy storage parallel operation system includes an energy storage converter master and an energy storage converter slave; The on-grid / off-grid mode switching control method includes: When the energy storage parallel system is not connected to mains power within a preset voltage range, the main energy storage converter and the slave energy storage converter are controlled to enter off-grid mode; based on the first voltage characteristic information of the output AC power of the main energy storage converter, the slave energy storage converter is controlled to adjust the first voltage parameter of the off-grid output; wherein, the first voltage characteristic information includes first voltage amplitude information, first voltage frequency information and first voltage phase information, and the first voltage parameter includes first voltage amplitude, first voltage frequency and first voltage phase; When the energy storage parallel system is connected to mains power within the preset voltage range, the main unit of the energy storage converter is controlled to switch from the off-grid mode to the tracking pre-synchronization mode. Based on the second voltage amplitude information of the mains power, the main unit of the energy storage converter is controlled to adjust the second voltage amplitude of the output AC power, and the slave unit of the energy storage converter is controlled to adjust the third voltage amplitude of the output AC power according to the second voltage amplitude. Based on the second voltage frequency information of the mains power, the main unit of the energy storage converter is controlled to adjust the second voltage frequency of the output AC power, and the slave unit of the energy storage converter is controlled to adjust the second voltage frequency of the output AC power according to the second voltage frequency. The third voltage frequency; based on the second voltage phase information of the mains power, the main unit of the energy storage converter is controlled to adjust the second voltage phase of the output AC power, and the slave unit of the energy storage converter is controlled to adjust the third voltage phase of the output AC power according to the second voltage phase; after the second voltage amplitude, the third voltage amplitude, the second voltage frequency, the third voltage frequency, the second voltage phase and the third voltage phase are adjusted, the main unit of the energy storage converter is controlled to enter the grid-connected mode from the tracking pre-synchronization mode, and the slave unit of the energy storage converter is controlled to enter the grid-connected mode from the off-grid mode.

2. The grid-connected / off-grid mode switching control method according to claim 1, characterized in that, The method of controlling the main unit of the energy storage converter to adjust the second voltage amplitude of the output AC power based on the second voltage amplitude information of the mains power, and controlling the slave unit of the energy storage converter to adjust the third voltage amplitude of the output AC power according to the second voltage amplitude, includes: Based on the second voltage amplitude information of the mains power, the main unit of the energy storage converter is controlled to adjust the second voltage amplitude of the output AC power, and the main unit of the energy storage converter is controlled to send information containing the second voltage amplitude to the slave unit of the energy storage converter. Based on the second voltage amplitude, the slave of the energy storage converter is controlled to adjust the third voltage amplitude of the output AC power.

3. The grid-connected / off-grid mode switching control method according to claim 1, characterized in that, The method of controlling the main unit of the energy storage converter to adjust the second voltage frequency of the output AC power based on the second voltage frequency information of the mains power, and controlling the slave unit of the energy storage converter to adjust the third voltage frequency of the output AC power according to the second voltage frequency, includes: Based on the second voltage frequency information of the mains power, the main unit of the energy storage converter is controlled to adjust the second voltage frequency of the output AC power, and the main unit of the energy storage converter is controlled to send information containing the second voltage frequency to the slave unit of the energy storage converter. Based on the second voltage frequency, the slave of the energy storage converter is controlled to adjust the third voltage frequency of the output AC power.

4. The grid-connected / off-grid mode switching control method according to claim 1, characterized in that, The second voltage phase information based on the mains power is used to control the main unit of the energy storage converter to adjust the second voltage phase of the output AC power, and the second voltage phase is used to control the slave unit of the energy storage converter to adjust the third voltage phase of the output AC power, including: When the absolute value of the difference between the second voltage amplitude and the mains voltage amplitude is less than a first preset threshold, and the absolute value of the difference between the second voltage frequency and the mains voltage frequency is less than a second preset threshold, based on the second voltage phase information of the mains, the energy storage converter host is controlled to adjust the second voltage phase of the output AC power, and the energy storage converter host is controlled to send information containing the second voltage phase to the energy storage converter slave. Based on the second voltage phase, the slave of the energy storage converter is controlled to adjust the third voltage phase of the output AC power.

5. The grid connection / off-grid mode switching control method according to any one of claims 1 to 4, characterized in that, After the second voltage amplitude, the third voltage amplitude, the second voltage frequency, the third voltage frequency, the second voltage phase, and the third voltage phase are adjusted, the energy storage converter master is controlled to enter the grid-connected mode from the tracking pre-synchronization mode, and the energy storage converter slave is controlled to enter the grid-connected mode from the off-grid mode, including: After the second voltage amplitude, the third voltage amplitude, the second voltage frequency, the third voltage frequency, the second voltage phase, and the third voltage phase are adjusted, a grid connection request information is received from the energy storage converter host. Based on the grid connection request information, the main unit of the energy storage converter is controlled to enter the grid connection mode from the tracking pre-synchronization mode, and the slave unit of the energy storage converter is controlled to enter the grid connection mode from the off-grid mode.

6. The grid connection / off-grid mode switching control method according to any one of claims 1 to 4, characterized in that, Also includes: When the energy storage converter master and / or the energy storage converter slave detect that the mains voltage is not within the preset voltage range, they receive grid disconnection request information from the energy storage converter master and / or the energy storage converter slave, and based on the grid disconnection request information, control the energy storage converter master and the energy storage converter slave to enter the off-grid mode.

7. The grid-connected / off-grid mode switching control method according to claim 6, characterized in that, The step of controlling the energy storage converter master and the energy storage converter slave to enter the off-grid mode based on the grid disconnection request information includes: Based on the grid disconnection request information, the main unit of the energy storage converter is controlled to enter the off-grid mode according to the second voltage parameters output by the grid, and the slave unit of the energy storage converter is controlled to enter the off-grid mode according to the third voltage parameters output by the grid; wherein, the second voltage parameters include the second voltage amplitude, the second voltage frequency and the second voltage phase, and the third voltage parameters include the third voltage amplitude, the third voltage frequency and the third voltage phase.

8. The grid connection / off-grid mode switching control method according to any one of claims 1 to 4, characterized in that, When the energy storage parallel system is not connected to mains power within a preset voltage range, before controlling the energy storage converter master and the energy storage converter slave to enter off-grid mode, the grid connection / off-grid mode switching control method further includes: The controller of the energy storage converter determines whether the energy storage parallel system is connected to the mains power within the preset voltage range.

9. A grid-connected / off-grid mode switching control device, characterized in that, include: The first switching control module is used to control the main unit and slave unit of the energy storage converter to enter the off-grid mode when the energy storage parallel system is not connected to the mains power within the preset voltage range. Based on the first voltage characteristic information of the output AC power of the energy storage converter host, the slave of the energy storage converter is controlled to adjust the first voltage parameter of the off-grid output; wherein, the first voltage characteristic information includes first voltage amplitude information, first voltage frequency information and first voltage phase information, and the first voltage parameter includes first voltage amplitude, first voltage frequency and first voltage phase; The second switching control module is used to control the energy storage converter master to switch from the off-grid mode to the tracking pre-synchronization mode when the energy storage parallel system is connected to the mains power within the preset voltage range; based on the second voltage amplitude information of the mains power, control the energy storage converter master to adjust the second voltage amplitude of the output AC power, and control the energy storage converter slave to adjust the third voltage amplitude of the output AC power according to the second voltage amplitude; based on the second voltage frequency information of the mains power, control the energy storage converter master to adjust the second voltage frequency of the output AC power, and control the energy storage converter slave to adjust according to the second voltage frequency. The third voltage frequency of the output AC power; based on the second voltage phase information of the mains power, the main unit of the energy storage converter is controlled to adjust the second voltage phase of the output AC power, and the slave unit of the energy storage converter is controlled to adjust the third voltage phase of the output AC power according to the second voltage phase; after the second voltage amplitude, the third voltage amplitude, the second voltage frequency, the third voltage frequency, the second voltage phase, and the third voltage phase are adjusted, the main unit of the energy storage converter is controlled to enter the grid-connected mode from the tracking pre-synchronization mode, and the slave unit of the energy storage converter is controlled to enter the grid-connected mode from the off-grid mode.

10. An energy storage parallel operation system, characterized in that, include: A memory and a processor, wherein the memory stores a program or instructions executable on the processor, and the processor, when executing the program or instructions, implements the steps of the on-grid / off-grid mode switching control method as described in any one of claims 1 to 8.

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