Control method and device for parallel energy storage converter switching from grid-connected to off-grid

Abstract

The present application provides a control method and device for the grid-connected to off-grid conversion of parallel energy storage converters, wherein the method includes: when the energy storage converter is in the host mode or the slave mode, when the main grid-connected switch corresponding to the common connection point is disconnected, the energy storage converter is passively switched from the grid-connected working state to the off-grid working state; and, when the energy storage converter is in the host mode, according to the received grid-connected to off-grid conversion instruction, the main grid-connected switch is actively disconnected, so that each energy storage converter can switch from the grid-connected working state to the off-grid working state when it is confirmed that the main grid-connected switch is disconnected. The present application greatly reduces the control complexity of the active and passive grid-connected to off-grid conversion of the parallel energy storage system, and ensures the power quality and reliability of the off-grid operation of the parallel energy storage converter while completing the effective grid-connected operation of the parallel energy storage converter, and can be used as a control architecture for the implementation of such engineering projects.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to a control method and device for switching parallel energy storage converters from grid-connected to off-grid. Background Art

[0002] Energy storage converters based on virtual synchronous generators are widely used in scientific research and engineering practice. The virtual synchronous generator control technology enables the energy storage converter to have the rotational inertia and damping of the synchronous generator. When the energy storage system is connected to the grid through the virtual synchronous generator, it can provide certain power and frequency support. When off-grid, it presents stable power supply characteristics, meets the load power requirements, and can meet seamless switching between on-grid and off-grid.

[0003] The parallel connection of multiple energy storage converters improves the system capacity and fault tolerance, meeting the needs of users. In the prior art, there is little attention paid to the control method of energy storage converters under parallel operation, but this is of vital importance for the implementation of engineering projects. Especially when the energy storage system switches from grid-connected to off-grid, the energy storage converter needs to switch from the grid-connected working state to the off-grid working state. When multiple energy storage converters are connected in parallel to the energy storage system, the operating conditions are complex, and the transient process of switching will affect the stability of the system. It is necessary to combine general control algorithms and effective communication methods to complete information interaction and ensure system stability. Summary of the invention

[0004] In view of the above problems, the present application is proposed to provide a control method and device for the on-grid to off-grid switching of parallel energy storage converters that overcome the above problems or at least partially solve the above problems.

[0005] According to one aspect of the present application, a method for controlling a parallel energy storage converter to switch from grid to off-grid is provided. The method is applied to a parallel energy storage system of multiple energy storage converters. The method comprises:

[0006] When the energy storage converter is in the master mode or the slave mode, when the main grid-connected switch corresponding to the common connection point is disconnected, the energy storage converter is passively switched from the grid-connected working state to the off-grid working state;

[0007] as well as,

[0008] When the energy storage inverter is in the host mode, according to the received grid-connected to off-grid instruction, the main grid-connected switch is actively disconnected, so that each energy storage inverter can switch from the grid-connected working state to the off-grid working state when the main grid-connected switch is confirmed to be disconnected.

[0009] Optionally, in the above method, disconnecting the main grid-connected switch includes:

[0010] Send a disconnect command to the main grid-connected switch;

[0011] The method further includes: after actively sending the disconnection instruction, obtaining the state of the main grid-connected switch, and reporting a fault of the main grid-connected switch if the main grid-connected switch is not disconnected.

[0012] Optionally, the above method further includes:

[0013] During the startup phase of the energy storage converter, the operation mode of the energy storage converter is determined according to the state of the main grid-connected switch.

[0014] Optionally, in the above method, determining the operation mode of the energy storage converter according to the state of the main grid-connected switch includes:

[0015] If the main grid-connected switch is closed, it is determined that the operation mode of the energy storage converter is independent grid-connected operation after completing grid-connected pre-synchronization;

[0016] If the main grid-connected switch is disconnected, the operation mode of the energy storage converter is determined according to the preset mode of the energy storage converter.

[0017] Optionally, in the above method, determining the operation mode of the energy storage converter according to the preset mode of the energy storage converter includes:

[0018] If the preset mode of the energy storage converter is the host mode, then when there is no running energy storage converter in the energy storage system, the operation mode of the energy storage converter is determined to be independent off-grid operation, and when there is a running energy storage converter in the energy storage system, the operation mode of the energy storage converter is determined to be network operation after completing network pre-synchronization;

[0019] If the preset mode of the energy storage converter is the slave mode, then when there is an energy storage converter operating in the master mode in the energy storage system, the operation mode of the energy storage converter is determined to be networking operation after completing the networking pre-synchronization.

[0020] Optionally, the above method further includes:

[0021] When the parallel energy storage inverter system is in an off-grid working state, the power control of the energy storage inverter is performed in response to the dispatching instructions of the energy management system. When the load exceeds the capacity of the online energy storage inverter module and cannot meet the demand, the load can only be put into operation after all energy storage inverters are networked to meet the load demand.

[0022] According to a second aspect of the present application, a control device for a parallel energy storage converter is provided, the device being used in a parallel energy storage system, the device comprising:

[0023] The master mode control unit and the slave mode control unit are used to passively switch the energy storage converter from a grid-connected working state to an off-grid working state when the energy storage converter is in the master mode or the slave mode and the main grid-connected switch corresponding to the common connection point is disconnected;

[0024] as well as,

[0025] The host mode control unit is also used to actively disconnect the main grid-connected switch according to the received grid-connected to off-grid instruction when the energy storage inverter is in the host mode, so that each energy storage inverter can switch from the grid-connected working state to the off-grid working state when it is confirmed that the main grid-connected switch is disconnected.

[0026] In some embodiments of the present application, in the above-mentioned device, disconnecting the main grid-connected switch includes: sending a disconnection instruction to the main grid-connected switch.

[0027] The host mode control unit is further used to obtain the state of the main grid-connected switch after sending the disconnection instruction, and report a main grid-connected switch fault if the main grid-connected switch is not disconnected.

[0028] In some embodiments of the present application, in the above-mentioned device, the host mode control unit or the slave mode control unit is also used to determine the operation mode of the energy storage inverter according to the state of the main grid-connected switch during the startup phase of the energy storage inverter.

[0029] In some embodiments of the present application, in the above-mentioned device, the host mode control unit or the slave mode control unit is used to determine that the operation mode of the energy storage inverter is independent grid-connected operation after completing grid-connected pre-synchronization if the main grid-connected switch is closed; if the main grid-connected switch is disconnected, it is also used to determine the operation mode of the energy storage inverter according to the preset mode of the energy storage inverter.

[0030] In some embodiments of the present application, in the above-mentioned device, the host mode control unit or the slave mode control unit is used to, if the preset mode is the host mode, determine that the operation mode of the energy storage inverter is independent off-grid operation when there is no running energy storage inverter in the energy storage system, and to determine that the operation mode of the energy storage inverter is networked operation after completing network pre-synchronization when there is a running energy storage inverter in the energy storage system; and to, if the preset mode of the energy storage inverter is the slave mode, determine that the operation mode of the energy storage inverter is networked operation after completing network pre-synchronization when there is an energy storage inverter running in the host mode in the energy storage system, and that independent off-grid operation cannot be performed when there is no energy storage inverter running in the host mode.

[0031] In some embodiments of the present application, in the above-mentioned device, the host mode control unit or the slave mode control unit is also used to determine whether the voltage at the parallel point of each energy storage inverter is normal according to the number of energy storage inverters operating in the energy storage system, so that the energy storage inverter can only be started when the voltage is normal, and report a parallel fault when the voltage is abnormal.

[0032] In some embodiments of the present application, in the above-mentioned device, the host mode control unit or the slave mode control unit is also used to respond to the scheduling instructions of the energy management system to perform power control of the energy storage inverter when the parallel energy storage inverter system is in an off-grid working state, and when the load exceeds the capacity of the online energy storage inverter module and cannot meet the demand, the load can only be put into operation after all energy storage inverters are networked and the load demand is met.

[0033] According to a third aspect of the present application, an energy storage converter is provided, and the energy storage converter includes the control device of the parallel energy storage converter described above.

[0034] According to a fourth aspect of the present application, a parallel energy storage system is provided, comprising a plurality of energy storage converters operating in slave mode and a host mode; each energy storage converter comprises a controller; and a memory arranged to store computer executable instructions, which, when executed, causes the controller to execute any of the methods described above.

[0035] According to a fifth aspect of the present application, a computer-readable storage medium is provided, wherein the computer-readable storage medium stores one or more programs, and when the one or more programs are executed by a controller, they implement any of the above methods.

[0036] In summary, the present application provides a method for actively and passively controlling a parallel energy storage inverter to switch from a grid-connected state to an off-grid state. The method is applied to a parallel energy storage system of multiple energy storage inverters. The method includes: when the energy storage inverter is in a host mode or a slave mode, when the main grid-connected switch corresponding to the common connection point is disconnected, the energy storage inverter is passively switched from a grid-connected working state to an off-grid working state; and, when the energy storage inverter is in a host mode, according to a received grid-connected to off-grid switching instruction, the main grid-connected switch is actively disconnected, so that each energy storage inverter can switch from a grid-connected working state to an off-grid working state when it is confirmed that the main grid-connected switch is disconnected. The beneficial effects of the present application are: providing a control technology for switching between on-grid and off-grid energy storage converters, mainly a control technology for realizing the active and passive transition from on-grid to off-grid when an energy storage converter based on a virtual synchronous generator is applied to a parallel energy storage system. The method provided by the present application greatly reduces the control complexity of the active and passive off-grid transition to on-grid of the parallel energy storage system, while completing the effective operation of the parallel energy storage converter on-grid, and ensuring the power quality and reliability of the off-grid operation of the parallel energy storage converter, effectively solving the problem of parallel coordinated off-grid operation of multiple energy storage converters under complex working conditions, and can be used as a control architecture for the implementation of such engineering projects.

[0037] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Also, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0039] Figure 1 A structural schematic diagram of a parallel energy storage system according to an embodiment of the present application is shown;

[0040] Figure 2 A schematic diagram of a parallel communication architecture of multiple energy storage converters according to an embodiment of the present application is shown;

[0041] Figure 3 A schematic flow chart of a method for controlling off-grid and grid-connected parallel energy storage converters according to an embodiment of the present application is shown;

[0042] Figure 4 A grid connection timing diagram of a control method for off-grid to grid-connected parallel energy storage converters according to an embodiment of the present application is shown;

[0043] Figure 5 A schematic flow chart of a method for controlling off-grid and grid-connected parallel energy storage converters according to another embodiment of the present application is shown;

[0044] Figure 6 A schematic flow chart of a method for controlling a parallel energy storage converter to switch from grid-connected to off-grid according to another embodiment of the present application is shown;

[0045] Figure 7 A schematic flow chart of a method for controlling a parallel energy storage converter to switch from grid-connected to off-grid according to another embodiment of the present application is shown;

[0046] Figure 8 A schematic flow chart of a method for controlling off-grid and on-grid energy storage converters according to an embodiment of the present application is shown;

[0047] Fig. 9 A schematic structural diagram of a control device for an energy storage converter according to an embodiment of the present application is shown;

[0048] Fig.10 A schematic structural diagram of an energy storage converter according to an embodiment of the present application is shown;

[0049] Fig.11 A schematic diagram of the structure of an energy storage system according to an embodiment of the present application is shown;

[0050] Fig.12 A schematic structural diagram of an energy storage converter according to another embodiment of the present application is shown;

[0051] Fig.13 A schematic diagram of the structure of a computer-readable storage medium according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0052] The exemplary embodiments of the present application will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present application are shown in the accompanying drawings, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present application and to fully convey the scope of the present application to those skilled in the art.

[0053] The idea of ​​the present application is to provide a control method for an energy storage inverter based on a virtual synchronous generator to address the problem that when multiple energy storage inverters are connected in parallel to an energy storage system, the transient process of being connected to or off-grid with the power grid will affect the stability of the power grid system. The energy storage inverter operating in the host mode instructs each energy storage inverter to perform pre-synchronization at the same time, thereby ensuring the power quality and reliability of the parallel energy storage inverters when they are connected to the grid and operating effectively while completing the effective operation of the parallel energy storage inverters.

[0054] Several exemplary control methods are described below, mainly including:

[0055] Centralized mode: There is a central controller to collect and process the information of dispatching, load and each energy storage inverter, control the operation mode and output capacity of each energy storage inverter, and issue a pre-synchronization enable command when switching between on-grid and off-grid. After receiving the pre-synchronization of each device, the central controller controls the microgrid connected switch (PCC point switch).

[0056] In centralized mode, the information of each device is concentrated in the central controller for easy monitoring. When the scheduling and load requirements are met, the system operation efficiency can be improved. However, excessive reliance on the central controller and communication will cause the system to crash once a failure occurs, causing great economic losses to users.

[0057] Master-slave mode: another form of centralized mode, the host is set to collect information and issue instructions. In off-grid mode, the host sends high-frequency synchronization signals to distribute loads. When switching from off-grid to grid-connected, the host receives the dispatch instruction and sends the pre-synchronization enable signal. After the pre-synchronization of each converter is completed, the PCC point switch is closed. In this mode, there is a master-slave competition mechanism. When the host does not meet the operating conditions, a new host will be automatically generated.

[0058] The master-slave mode has the advantages and disadvantages of the centralized mode. The master-slave competition mechanism ensures the reliability of the system. When the host fails and cannot be started, the slave competes for a new host through capacity and operating status, but the master-slave mode system has a large amount of computation and it is difficult to take all operating conditions into consideration. When the energy storage inverter is running in parallel off-grid, the host receives the off-grid to grid command and sends a pre-synchronization enable signal to the slave, but the communication delay often makes the pre-synchronization status of each inverter inconsistent, which is easy to form a loop.

[0059] Peer-to-peer mode: Each converter has information exchange, but there is no master-slave relationship. They all accept dispatching instructions and grid information, and have control over the PCC switch. When off-grid, they detect whether the parallel bus has voltage. If it has voltage, they start the pre-synchronization start-up, otherwise they start the machine directly. When off-grid to grid-connected, each converter receives the dispatching instruction, starts pre-synchronization, and after the pre-synchronization is completed, and the PCC switch closing instruction is issued, the grid connection can be achieved.

[0060] The peer mode is simple in design, and the converters have low interdependence when connected in parallel, which can ensure the operation of the online support system to a certain extent, but the efficiency is low. However, when switching from off-grid to grid-connected, the circulation problem mentioned in the master-slave mode also exists in the parallel case, and the grid connection can only be achieved after all devices are pre-synchronized and the PCC point closing command is issued. When a machine fails, it will affect the grid connection of the entire parallel system.

[0061] Figure 1 A schematic diagram of the structure of a parallel energy storage system according to an embodiment of the present application is shown. Figure 2 A communication connection diagram of multiple energy storage converters according to an embodiment of the present application is shown. Figure 3 A flow chart of a control method for an energy storage converter according to an embodiment of the present application is shown. The control method for an energy storage converter in the present application is applied to a single energy storage converter, and multiple energy storage converters are connected in parallel to form an energy storage system.

[0062] The energy storage inverter is a friendly interface between the energy storage system and the power grid, which can realize the two-way flow of electric energy. While completing the "peak shaving and valley filling" scheduling task of the power grid, it also ensures the quality and reliability of electric energy.

[0063] An energy storage system is provided below, which is only used as an example to help better understand the present application. The method provided in the present application can be implemented by any of the following energy storage systems provided in the present application, but it does not exclude that other energy storage systems can also implement the method of the present application. Figure 1 The schematic diagram of the structure of a parallel energy storage system according to an embodiment of the present application is shown. The energy storage system includes multiple energy storage converters, which are respectively recorded as energy storage converter 1, energy storage converter 2, and energy storage converter n. Multiple energy storage converters are connected in parallel to a common connection point (PCC point). The voltage of the PCC point corresponds to the grid side voltage. A total grid-connected switch is provided corresponding to the PCC point, which is called a PCC point switch. The PCC point switch is also connected to the grid.

[0064] Each energy storage inverter is respectively provided with a grid-connected contactor and an AC side circuit breaker. Compared with a single independently operated energy storage inverter in the prior art, each energy storage inverter in the present application can also be additionally provided with a PCC point voltage collector, a parallel point voltage collector, a PCC point switch feedback circuit, and a PCC point switch control circuit as needed; the PCC point voltage collector of each energy storage inverter is connected in parallel at one point to collect the voltage on the grid side, and the parallel point voltage collector of each energy storage inverter is connected in parallel at one point to collect the voltage on the parallel side of each energy storage inverter, which voltage is the voltage of the parallel points of each energy storage inverter described below; the PCC point switch feedback circuit of each energy storage inverter is connected in parallel at one point to feed back the closed / open state of the PCC point to each energy storage inverter.

[0065] The voltage on the grid side and the closed / open state of the PCC point switch can be fed back to the controller of each energy storage converter through the PCC point switch feedback circuit, wherein the closed / open state of the PCC point switch can be determined based on whether the voltage of the PCC point switch is consistent with that of the grid side. Each energy storage converter also has a PCC point switch control circuit, which is connected to the PCC point switch, respectively, for sending the control information sent by each energy storage converter to the PCC point switch, so that the PCC point switch controls its own open / closed state according to the control information.

[0066] Figure 2 A schematic diagram of the parallel communication architecture of a parallel energy storage system according to an embodiment of the present application is shown, wherein n energy storage inverters of the energy storage system are connected in parallel, and the control module of each energy storage inverter is communicatively connected to the energy management system, and the control modules of each energy storage inverter can communicate with each other, and the energy management system can realize centralized monitoring of the control modules of each energy storage inverter, thereby ensuring the real-time and reliability of the scheduling instructions.

[0067] Figure 3 A schematic diagram of a control method for off-grid to grid-connected parallel energy storage converters according to an embodiment of the present application is shown. Figure 3 It can be seen that the method includes:

[0068] Step S310, when the energy storage inverter is in the host mode, according to the received off-grid to grid-connected instruction, a pre-synchronization enable signal is sent to each of the energy storage inverters at the first moment when the grid voltage meets the pre-synchronization condition, so that each of the energy storage inverters performs pre-synchronization at the second moment when the grid voltage meets the pre-synchronization condition.

[0069] In the present application, each energy storage inverter is divided into a host mode and a slave mode during the switching process from an active off-grid working state to a grid-connected working state, and whether each energy storage inverter is in a host mode or a slave mode is preset by the energy management system. When the energy storage system is connected to the grid, one energy storage inverter is in the host mode and the other energy storage inverters are in the slave mode.

[0070] When the energy storage inverter is in the host mode, according to the off-grid to grid-connected instruction received from the energy management system, and at the first moment when the grid voltage meets the pre-synchronization condition, a pre-synchronization enable signal is sent to each energy storage inverter in the slave mode. Each energy storage inverter in the slave mode starts to detect the arrival of the second moment when the grid voltage meets the pre-synchronization condition according to the received pre-synchronization enable signal, usually an enable signal, and pre-synchronizes with the energy storage inverter at the same time when the grid voltage meets the pre-synchronization condition.

[0071] Step S320, when the grid-connected requirements are met, each energy storage converter is switched from an off-grid working state to a grid-connected working state.

[0072] After the pre-synchronization is completed, the energy storage inverter summarizes the pre-synchronization completion results of each energy storage inverter in the slave mode, and when it is determined that the energy storage system composed of each energy storage inverter that has completed the pre-synchronization meets the grid connection requirements, each energy storage inverter is switched from the off-grid working state to the grid-connected working state, that is, the energy storage system composed of each energy storage inverter completes the grid connection work with the power grid.

[0073] In some embodiments of the present application, in the above-mentioned control method for off-grid switching of parallel energy storage converters, the pre-synchronization condition is that the voltage waveform of the specified phase of the power grid passes through the zero point on the rising edge. For example, when the voltage waveform is a sine wave, the so-called "rising edge zero point" refers to the zero point passed by the waveform when it tilts upward.

[0074] Figure 4 The grid-connected timing diagram of the off-grid to grid-connected control method of parallel energy storage converters according to an embodiment of the present application is shown. In order to suppress the circulating current and ensure the stability of the power grid system, pre-synchronization is performed at the absolute time of the zero crossing point, which can ensure the consistency of the pre-synchronization of each energy storage converter to achieve the above purpose. Figure 4 It can be seen that the grid voltage is divided into three phases, taking phase A as an example, namely Figure 4 The A-phase voltage of the power grid on the PCC point side in the master mode receives the active off-grid to grid-connected command of the energy management system, responds to the command, and starts to prepare for pre-synchronization. Then, when the energy storage converter detects that the first rising edge of the A-phase voltage waveform of the PCC point power grid passes through the zero point, it sends a pre-synchronization enable signal to the energy storage converter in the slave mode. Each energy storage converter in the slave mode receives the pre-synchronization enable signal. When the second rising edge of the A-phase voltage waveform of the PCC point power grid passes through the zero point, each energy storage converter starts pre-synchronization at the same time, thereby ensuring the consistency of pre-synchronization. After completing the pre-synchronization, the energy storage converter reads the pre-synchronization completion information of each energy storage converter in the slave mode. After determining that each energy storage converter in the slave mode has completed pre-synchronization, the energy storage converter commands the PCC point switch to close, thereby completing the switching of the off-grid working state to the grid-connected working state of the energy storage system.

[0075] In some embodiments of the present application, in the above-mentioned control method for off-grid to grid-connected parallel energy storage inverters, switching each energy storage inverter from an off-grid working state to a grid-connected working state includes: issuing a closing instruction to the main grid-connected switch corresponding to the common connection point, i.e., the PCC point switch, so that each energy storage inverter switches from the off-grid working state to the grid-connected working state when the main grid-connected switch is closed.

[0076] like Figure 1 As shown, Figure 1The energy storage converter 1 is in the host mode, and the controller of the energy storage converter 1 can send a closing instruction to the PCC point switch through the PCC point switch control line, so that the PCC point switch can close itself according to the closing instruction.

[0077] When the PCC point switch is closed, each energy storage converter completes the switch from the off-grid working state to the grid-connected working state.

[0078] In some embodiments of the present application, the control method for off-grid to grid-connected parallel energy storage converters further includes: when the energy storage converter is in slave mode, pre-synchronization is performed at the second moment when the grid voltage meets the pre-synchronization condition according to the received pre-synchronization enable signal; after the pre-synchronization is successfully completed, pre-synchronization completion information is sent to the energy storage converter operating in the host mode; after the pre-synchronization fails, the grid-connected contactor and / or AC circuit breaker corresponding to the energy storage converter is cut off, wherein the grid-connected contactor is used to control the off-grid / grid connection of the corresponding energy storage converter, such as Figure 1 As shown, when the grid-connected contactor is closed, the corresponding energy storage converter is in the grid-connected state; when it is disconnected, the corresponding energy storage converter is in the off-grid state. The AC circuit breaker is used to prevent the energy storage converters from being damaged due to excessive current. Under normal conditions, the AC circuit breaker is closed. When the current is too large, the AC circuit breaker will automatically disconnect or fuse to protect the corresponding energy storage converter from short circuit and other faults.

[0079] Please refer to Figure 4 , the energy storage converter in slave mode, after receiving the pre-synchronization enable signal sent by the energy storage converter in master mode, detects the voltage waveform of phase A of the power grid and starts pre-synchronization when the first rising edge crosses the zero point detected. It should be noted here that the first rising edge zero crossing point is the second rising edge zero crossing point detected by the energy storage converter in master mode.

[0080] After the pre-synchronization is successfully completed, the energy storage converter in the slave mode sends pre-synchronization completion information to the energy storage converter working in the host mode. After determining that all energy storage converters in the slave mode have completed pre-synchronization, the energy storage converter in the host mode commands the PCC point switch to close, thereby completing the switching of the energy storage system from the off-grid state to the grid-connected state; if the pre-synchronization fails, it means that the energy storage converter in the slave mode may have a fault. In order to make the energy storage converter offline, it is necessary to cut off the grid-connected contactor and / or AC circuit breaker corresponding to the energy storage converter. In some embodiments of the present application, the second zero-crossing moment is used as the triggering time for pre-synchronization in order to avoid the problem of inconsistent timing of pre-synchronization of each energy storage converter caused by delay.

[0081] In some embodiments of the present application, in the above-mentioned control method for off-grid to grid-connected parallel energy storage converter, the pre-synchronization enable signal and the pre-synchronization completion information are transmitted via the CAN bus.

[0082] CAN, or controller area network, belongs to the category of industrial fieldbus. Compared with general communication buses, CAN bus data communication has outstanding reliability, real-time and flexibility. The transmission of pre-synchronization enable signal and pre-synchronization completion information between energy storage converters through CAN bus ensures the reliability and timeliness of information.

[0083] In some embodiments of the present application, the above-mentioned control method for off-grid to grid-connected parallel energy storage converters further includes: determining whether the grid-connected requirements are met based on the total capacity of the energy storage converters corresponding to each pre-synchronization completion information received within a preset time period.

[0084] To ensure the effectiveness of active off-grid to grid connection, the energy storage converter in the host mode can be turned on for a preset time, such as 5s, starting from the second rising edge of the A-phase voltage waveform of the power grid crossing the zero point. After the preset time, if the total capacity of multiple energy storage converters that have completed pre-synchronization meets the scheduling requirements, that is, it is greater than the preset capacity, then it is determined that the energy storage system meets the grid connection requirements; if after the preset time, if the total capacity of multiple energy storage converters that have completed pre-synchronization does not meet the scheduling requirements, that is, it is not greater than the preset capacity, the energy storage converter in the host mode reports a pre-synchronization fault, and further, the fault type can be reported.

[0085] The following embodiments help to better understand the active off-grid to grid switching process of the energy storage converter in the master mode and the off-grid to grid switching process of the energy storage converter in the slave mode. Figure 5 A schematic diagram of a control method for switching a parallel energy storage converter from off-grid to on-grid according to another embodiment of the present application is shown. Figure 5 It can be seen that after the start, it is first determined whether the energy storage converter is started in the host mode. If so, it is determined whether the active off-grid to grid-connected command issued by the energy management system is received. If received, the energy storage converter enters the off-grid to grid-connected operation. Specifically, the preparatory work of pre-synchronization is started, and the first rising edge zero crossing of the grid A phase voltage waveform and the failure of the first rising edge zero crossing are started. Fault judgment.

[0086] If the first rising edge of the grid A phase voltage waveform fails to cross the zero point, a zero crossing fault type is reported.

[0087] If the first rising edge of the grid A phase voltage waveform passes through zero successfully, then when the grid A phase voltage waveform passes through zero for the first time, a pre-synchronization enable signal is sent to each energy storage converter in slave mode through the CAN bus, and the second rising edge of the grid A phase voltage waveform passes through zero, and the second rising edge passes through zero failure fault judgment is started.

[0088] If the second rising edge of the grid A phase voltage waveform fails to cross the zero point, a zero crossing fault type is reported.

[0089] If the second rising edge of the grid A phase voltage waveform passes through the zero point successfully, then when the grid A phase voltage waveform is detected to pass through the zero point for the second time, the energy storage inverter starts the pre-synchronization function and the pre-synchronization failure fault detection, and determines through the CAN bus whether the energy storage inverters in the slave mode have completed the pre-synchronization within the preset 5s, and further determines whether the total capacity of the energy storage inverters that have completed the pre-synchronization within the determined 5s is greater than the preset capacity. If greater, it is determined that the pre-synchronization is completed and valid, and a closing instruction is sent to the PCC point switch, so that the PCC point switch closes itself according to the closing instruction, and its closing state is fed back to each energy storage inverter through the PCC point switch feedback line, so that each energy storage inverter completes the switching of the energy storage system from the off-grid working state to the grid-connected working state according to the feedback information.

[0090] If the pre-synchronization of the energy storage converter fails or the total capacity of the energy storage converters that complete pre-synchronization within 5 seconds is not greater than the preset capacity, the pre-synchronization fault type is reported.

[0091] Please also refer to Figure 5 , when the energy storage converter is not started in the host mode, it is determined that it is in the slave mode. After it receives the pre-synchronization enable signal sent by the energy storage converter in the host mode through the CAN bus, it starts the fault judgment of the rising edge zero crossing point and the rising edge zero crossing failure of the grid A phase voltage waveform. When the energy storage converter in the slave mode detects the first zero crossing point of the grid A phase voltage waveform, the pre-synchronization function of the energy storage converter is turned on. After the pre-synchronization is completed, the pre-synchronization completion signal is sent to the energy storage converter in the host mode through the CAN bus, and the closed state of the PCC point switch fed back through the PCC point switch feedback line is received from the PCC point switch. When the PCC point switch is closed, the energy storage system is switched from the off-grid working state to the grid-connected working state. It should be noted here that the first rising edge zero crossing point is the second rising edge zero crossing point detected by the energy storage converter in the host mode.

[0092] Figure 6A flow chart of a control method for switching parallel energy storage converters from grid-connected to off-grid according to another embodiment of the present application is shown. The method is also applied to a single energy storage converter. Multiple energy storage converters can be applied in parallel in an energy storage system. The method includes:

[0093] Step S610, when the energy storage converter is in the master mode or the slave mode, when the main grid-connected switch corresponding to the common connection point is disconnected, the energy storage converter is switched from the grid-connected working state to the off-grid working state.

[0094] In this application, each energy storage converter is divided into active off-grid and passive off-grid in the process of switching from the grid-connected working state to the off-grid working state. The off-grid operation is performed according to the instructions of the energy management system, which is an active off-grid process; in the absence of instructions from the energy management system, it is a passive off-grid process. And each energy storage converter is divided into a host mode and a slave mode. Whether each energy storage converter is in the host mode or the slave mode is preset by the energy management system. When the energy storage system is off-grid from the power grid, one energy storage converter is in the host mode, and the other energy storage converters are in the slave mode.

[0095] During the passive off-grid process, whether the energy storage inverter is in the host mode or the slave mode, the closed / open state of the main grid-connected switch corresponding to the common connection point, i.e., the PCC point switch, is detected. When the PCC point switch is disconnected, the connection between each energy storage inverter and the grid is automatically disconnected, and each energy storage inverter automatically switches from the grid-connected working state to the off-grid working state.

[0096] If the PCC point switch is closed, it means that all energy storage converters are in grid-connected working state.

[0097] And, step S620, when the energy storage inverter is in the host mode, according to the received grid-connected to off-grid instruction, the main grid-connected switch is disconnected, so that each energy storage inverter can switch from the grid-connected working state to the off-grid working state when the main grid-connected switch is confirmed to be disconnected.

[0098] During the active off-grid process, the energy storage inverter in the host mode receives the grid-connected to off-grid command from the energy management system and controls the PCC point switch to disconnect. When the PCC point switch is disconnected, the connection between each energy storage inverter and the grid is automatically disconnected, and each energy storage inverter automatically switches from the grid-connected working state to the off-grid working state.

[0099] In some embodiments of the present application, in the above-mentioned control method for the parallel energy storage converter to switch from grid-connected to off-grid, disconnecting the main grid-connected switch includes: sending a disconnection instruction to the main grid-connected switch.

[0100] After receiving the grid-connected to off-grid instruction from the energy management system, the energy storage inverter in the host mode can send a disconnection instruction to the PCC point switch through the PCC point switch control line, so that the PCC point switch will disconnect itself according to the disconnection instruction. When the PCC point switch is disconnected, the connection between each energy storage inverter and the power grid is automatically disconnected, and each energy storage inverter automatically switches from the grid-connected working state to the off-grid working state.

[0101] In some embodiments of the present application, the above-mentioned control method for the parallel energy storage converter to switch from grid-connected to off-grid further includes: after sending a disconnection instruction, obtaining the state of the main grid-connected switch, and if the main grid-connected switch is not disconnected, reporting a main grid-connected switch fault.

[0102] In the above-mentioned passive off-grid process and active off-grid process, if the PCC point switch cannot be disconnected, it means that the PCC point switch is faulty, and the PCC point switch fault and fault type are reported. The following embodiments help to better understand the switching process of the energy storage converter from grid-connected to off-grid. Figure 7 A flow chart of a control method for switching a parallel energy storage converter from grid-connected to off-grid according to another embodiment of the present application is shown. Figure 7 It can be seen from the figure that the control method can be divided into an active grid-connected to off-grid method and a passive grid-connected to off-grid method according to whether it is performed according to the instruction of the energy management system.

[0103] Among them, the active grid-connected to off-grid method includes first determining whether the energy storage inverter is started in host mode. If so, continue to determine whether a grid-connected to off-grid instruction issued by the energy management system is received. When it is determined that the above instruction has been received, a disconnect instruction is issued to the PCC point switch, so that the PCC point switch automatically disconnects according to the instruction, and feeds back its own closed / disconnected state to each energy storage inverter through the PCC point switch feedback line. After each energy storage inverter receives the status information of the PCC point switch, when it is determined that the PCC point switch is disconnected, each energy storage inverter is automatically disconnected from the power grid, and each energy storage inverter completes the switch from the grid-connected working state to the off-grid working state.

[0104] If each energy storage inverter in the host mode has not received the grid-connected to off-grid instruction issued by the energy management system, after receiving the status information of the PCC point switch, if it is determined that the PCC point switch is disconnected, it is determined that the connection with the power grid is disconnected, that is, it automatically switches from the grid-connected working state to the off-grid working state. This process is the process of passive grid-connected to off-grid switching of each energy storage inverter in the host mode.

[0105] If each energy storage inverter in the host mode does not receive the grid-connected to off-grid command issued by the energy management system, and after receiving the status information of the PCC point switch and determining that the PCC point switch is closed, each energy storage inverter is in the grid-connected working state.

[0106] After receiving the status information of the PCC point switch, if each energy storage converter in the slave mode determines that the PCC point switch is disconnected, it determines that the connection with the power grid is disconnected, that is, it automatically switches from the grid-connected working state to the off-grid working state; if each energy storage converter in the slave mode receives the status information of the PCC point switch and determines that the PCC point switch is closed, then each energy storage converter is in the grid-connected working state. In some embodiments of the present application, the control method of the energy storage converter further includes: during the startup phase of the energy storage converter, determining the operation mode of the energy storage converter according to the state of the total grid-connected switch.

[0107] During the startup phase of the energy storage inverter, due to the different states of the total grid-connected switch, i.e., the PCC point switch, the working state of the energy storage system is different, and the operation mode of each energy storage inverter is also different according to the different working states of the energy storage system. Therefore, when the energy storage inverter is started, it is necessary to first determine the corresponding operation mode of the energy storage inverter according to the different states of the total grid-connected switch.

[0108] In some embodiments of the present application, in the control method for the parallel energy storage inverter to switch from grid to off-grid, determining the operation mode of the energy storage inverter according to the state of the total grid-connected switch includes: if the total grid-connected switch is closed, then determining the operation mode of the energy storage inverter is independent grid-connected operation after completing grid-connected pre-synchronization. When the total grid-connected switch, that is, the PCC point switch is closed, the energy storage system is in a grid-connected working state, and each energy storage inverter constituting the energy storage system is in a grid-connected working state. The specific stage is the grid-connected working state after completing pre-synchronization, and each energy storage inverter operates independently of each other.

[0109] In some embodiments of the present application, if the main grid-connected switch is disconnected, the operation mode of the energy storage inverter is determined according to a preset mode of the energy storage inverter.

[0110] When the main grid-connected switch, that is, the PCC point switch, is disconnected, the energy storage system is in an off-grid working state, and each energy storage inverter of the energy storage system can be networked individually or several of them can be networked to supply load power. In the process of off-grid networking, the preset modes of each energy storage inverter are divided into host mode and slave mode, and the energy storage inverter in the host mode is dominant to complete the networking process of the energy storage system in the off-grid working state. Furthermore, it is necessary to determine the operating mode of this energy storage inverter according to the preset mode of this energy storage inverter.

[0111] In some embodiments of the present application, in the above-mentioned control method for parallel energy storage converters to switch from grid-connected to off-grid, determining the operation mode of the energy storage converter according to the preset mode of the energy storage converter includes: if the preset mode of the energy storage converter is the host mode, and there is no running energy storage converter in the energy storage system, determining that the operation mode of the energy storage converter is independent off-grid operation. In this case, only the energy storage converter is running, and the other energy storage converters in the energy storage system are not running. At this time, the energy storage converter can independently provide power to the external load device.

[0112] When the preset mode of the energy storage converter is the host mode, and there is an already running energy storage converter in the energy storage system, it is determined that the operation mode of the energy storage converter is to be networked and operated after completing the network pre-synchronization. At this time, it means that other energy storage converters have completed the network, and it can be determined that the operation mode of the energy storage converter is to be networked and operated after completing the network pre-synchronization. The energy storage converter and other energy storage converters provide power to the external load equipment together.

[0113] When the preset mode of the energy storage converter is the slave mode, and there is an energy storage converter operating in the master mode in the energy storage system, it is determined that the operation mode of the energy storage converter is to operate in the network after completing the network pre-synchronization. At this time, it means that the energy storage converter in the master mode has completed the network independently or with other energy storage converters, and it can be determined that the operation mode of the energy storage converter is to operate in the network after completing the network pre-synchronization, and the energy storage converter and other energy storage converters provide power to the external load equipment.

[0114] In some embodiments of the present application, the control method for the above-mentioned parallel energy storage inverter on-grid to off-grid conversion also includes: determining whether the voltage and / or current at the parallel point of each energy storage inverter is normal according to the number of energy storage inverters operating in the energy storage system, so that the energy storage inverter can only be started when the above-mentioned voltage and / or current is normal, and reporting a parallel fault when the voltage and / or current is abnormal.

[0115] Multiple energy storage converters are connected in parallel, and the output voltages of each energy storage converter are the same. The voltage at the parallel connection point of each energy storage converter is consistent with the voltage of any one of the multiple energy storage converters in parallel. The value of the current at the parallel connection point of each energy storage converter is between the rated current of a single energy storage converter and the sum of the rated currents of multiple energy storage converters. According to the above rules, whether the voltage and / or current at the parallel connection point of each energy storage converter is normal can be determined based on the number of energy storage converters running in the energy storage system.

[0116] The energy storage converter can only be started when the voltage and / or current are normal. When the voltage and / or current are abnormal, it indicates that a fault exists in the multiple energy storage converters connected in parallel. In this case, the parallel fault and the fault type are reported.

[0117] In some embodiments of the present application, the control method for the on-grid to off-grid switching of the above-mentioned parallel energy storage inverter also includes: when the energy storage inverter is in a grid-connected working state, responding to the dispatching instructions of the energy management system, performing power control of the energy storage inverter, and disconnecting the grid-connected contactor and / or AC circuit breaker of the energy storage inverter when the operating conditions cannot be met.

[0118] When the main grid-connected switch, i.e., the PCC point switch, is closed and the energy storage system is in a grid-connected working state, each energy storage converter in the energy storage system is in a grid-connected working state. There is no master-slave relationship between the energy storage converters, and they can operate independently of each other, i.e., there is no need to distinguish between the master mode and the slave mode. Each energy storage converter can respond to the dispatching instructions of the energy management system and decide whether to operate the energy storage converter in combination with its own situation, so as to achieve equal power distribution among the energy storage converters.

[0119] If the operating conditions cannot be met, the grid-connected contactor and / or AC circuit breaker of the energy storage inverter are disconnected. If the rated power of the energy storage inverter is less than the predetermined power required in the dispatching instruction of the energy management system, it is determined that the energy storage inverter cannot meet the operating conditions.

[0120] Figure 8 A flow chart of a method for controlling off-grid and on-grid operation of parallel energy storage converters according to an embodiment of the present application is shown, which is helpful for understanding the off-grid and on-grid operating states of the energy storage system.

[0121] The off-grid working state can be described as follows: when the PCC point switch is disconnected, the energy storage system is in an off-grid working state, and it is determined whether the energy storage inverter is started in the host mode. If so, the parallel point voltage is obtained, and it is determined whether the parallel point voltage is normal. If normal, pre-synchronization is performed. After the pre-synchronization is completed, the grid-connected contactor and / or AC circuit breaker are closed to complete the networking; if abnormal, the grid-connected contactor and / or AC circuit breaker are directly closed to supply load power.

[0122] If the energy storage converter is not started in the host mode, the energy storage converter is in the slave mode, then the parallel point voltage is obtained, and it is determined whether the parallel point voltage is normal, and whether the energy storage converter in the host mode is in operation. If so, pre-synchronization is performed, and after the pre-synchronization is completed, the grid contactor and / or AC circuit breaker are closed to complete the networking. If the parallel point voltage is abnormal, and the energy storage converter in the host mode is not in operation, the energy storage converter cannot be started, and the energy storage system fault is reported, and further, the fault type can be reported.

[0123] The grid-connected working state can be described as follows: when the PCC point switch is closed, the energy storage system is in the grid-connected working state, then the parallel point voltage is obtained, and it is determined whether the parallel point voltage is normal. If so, pre-synchronization is performed. After the pre-synchronization is completed, the grid-connected contactor and / or AC circuit breaker are closed to complete the networking; if there is no abnormality, the energy storage inverter cannot be started, and the energy storage system fault is reported. Furthermore, the fault type can be reported.

[0124] Fig. 9 A schematic structural diagram of a control device for parallel energy storage converters according to an embodiment of the present application is shown. The device 900 is used in a single energy storage converter. The device 900 includes:

[0125] The host mode control unit 910 is used to send a pre-synchronization enable signal to each energy storage inverter when the energy storage inverter is in the host mode, according to the received off-grid to grid-connected instruction, at the first moment when the grid voltage meets the pre-synchronization condition, so that each energy storage inverter performs pre-synchronization at the second moment when the grid voltage meets the pre-synchronization condition.

[0126] In the present application, each energy storage inverter is divided into a host mode and a slave mode during the switching process from an active off-grid working state to a grid-connected working state, and whether each energy storage inverter is in a host mode or a slave mode is preset by the energy management system. When the energy storage system is connected to the grid, one energy storage inverter is in the host mode and the other energy storage inverters are in the slave mode.

[0127] When the energy storage inverter is in the host mode, according to the off-grid to grid-connected instruction received from the energy management system, and at the first moment when the grid voltage meets the pre-synchronization condition, a pre-synchronization enable signal is sent to each energy storage inverter in the slave mode. Each energy storage inverter in the slave mode starts to detect the arrival of the second moment when the grid voltage meets the pre-synchronization condition according to the received pre-synchronization enable signal, usually an enable signal, and pre-synchronizes with the energy storage inverter at the same time when the grid voltage meets the pre-synchronization condition.

[0128] The host mode control unit 910 is also used to switch each energy storage converter from an off-grid working state to a grid-connected working state when the grid-connected requirements are met.

[0129] After the pre-synchronization is completed, the energy storage inverter summarizes the pre-synchronization completion results of each energy storage inverter in the slave mode, and when it is determined that the energy storage system composed of each energy storage inverter that has completed the pre-synchronization meets the grid connection requirements, each energy storage inverter is switched from the off-grid working state to the grid-connected working state, that is, the energy storage system composed of each energy storage inverter completes the grid connection work with the power grid.

[0130] In some embodiments of the present application, in the control device 900 of the parallel energy storage converter described above, the pre-synchronization condition is that the voltage waveform of a specified phase of the power grid passes through a zero point.

[0131] In some embodiments of the present application, in the control device 900 of the above-mentioned parallel energy storage inverter, the host mode control unit 910 is also used to issue a closing instruction to the main grid-connected switch corresponding to the common connection point, so that each of the energy storage inverters can switch from an off-grid working state to a grid-connected working state when the main grid-connected switch is closed.

[0132] In some embodiments of the present application, the control device 900 of the above-mentioned parallel energy storage inverter also includes: a slave mode control unit 920, which is used to perform pre-synchronization at the second moment when the grid voltage meets the pre-synchronization condition according to the received pre-synchronization enable signal when the energy storage inverter is in slave mode; after the pre-synchronization is successfully completed, send pre-synchronization completion information to the energy storage inverter working in the host mode; after the pre-synchronization fails, cut off the grid-connected contactor and / or AC circuit breaker corresponding to the energy storage inverter.

[0133] In some embodiments of the present application, in the control device 900 of the parallel energy storage converter described above, the pre-synchronization enable signal and the pre-synchronization completion information are transmitted via a CAN bus.

[0134] In some embodiments of the present application, in the above-mentioned parallel energy storage inverter control device 900, the host mode control unit 910 is also used to determine whether the grid connection requirements are met based on the total capacity of the energy storage inverter corresponding to each pre-synchronization completion information received within a preset time period.

[0135] Fig. 9 The host mode control unit 910 and the slave mode control unit 920 of the control device 900 of the parallel energy storage inverter shown are also used to switch the energy storage inverter from the grid-connected working state to the off-grid working state when the energy storage inverter is in the host mode or the slave mode and the main grid-connected switch corresponding to the common connection point is disconnected.

[0136] In this application, each energy storage converter is divided into active off-grid and passive off-grid in the process of switching from the grid-connected working state to the off-grid working state. The off-grid operation is performed according to the instructions of the energy management system, which is an active off-grid process; in the absence of instructions from the energy management system, it is a passive off-grid process. And each energy storage converter is divided into a host mode and a slave mode. Whether each energy storage converter is in the host mode or the slave mode is preset by the energy management system. When the energy storage system is off-grid from the power grid, one energy storage converter is in the host mode, and the other energy storage converters are in the slave mode.

[0137] During the passive off-grid process, whether the energy storage inverter is in the host mode or the slave mode, the closed / open state of the main grid-connected switch corresponding to the common connection point, i.e., the PCC point switch, is detected. When the PCC point switch is disconnected, the connection between each energy storage inverter and the grid is automatically disconnected, and each energy storage inverter automatically switches from the grid-connected working state to the off-grid working state.

[0138] If the PCC point switch is closed, it means that all energy storage converters are in grid-connected working state.

[0139] In addition, the host mode control unit 910 is also used to disconnect the main grid-connected switch according to the received grid-connected to off-grid instruction when the energy storage inverter is in the host mode, so that each energy storage inverter can switch from the grid-connected working state to the off-grid working state after confirming that the main grid-connected switch is disconnected.

[0140] During the active off-grid process, the energy storage inverter in the host mode receives the grid-connected to off-grid command from the energy management system and controls the PCC point switch to disconnect. When the PCC point switch is disconnected, the connection between each energy storage inverter and the grid is automatically disconnected, and each energy storage inverter automatically switches from the grid-connected working state to the off-grid working state.

[0141] In some embodiments of the present application, in the control device 900 of the parallel energy storage converter, disconnecting the main grid-connected switch includes: sending a disconnection instruction to the main grid-connected switch.

[0142] The host mode control unit 910 is further used to obtain the state of the main grid-connected switch after sending the disconnection instruction, and report a main grid-connected switch fault if the main grid-connected switch is not disconnected.

[0143] In some embodiments of the present application, in the control device 900 of the above-mentioned parallel energy storage inverter, the host mode control unit 910 or the slave mode control unit 920 is also used to determine the operation mode of the energy storage inverter according to the state of the main grid-connected switch during the startup phase of the energy storage inverter.

[0144] In some embodiments of the present application, in the control device 900 of the above-mentioned parallel energy storage inverter, the host mode control unit 910 or the slave mode control unit 920, if the main grid-connected switch is closed, is used to determine that the operation mode of the energy storage inverter is independent grid-connected operation after completing grid-connected pre-synchronization; if the main grid-connected switch is disconnected, it is also used to determine the operation mode of the energy storage inverter according to the preset mode of the energy storage inverter.

[0145] In some embodiments of the present application, in the control device 900 of the above-mentioned parallel energy storage inverter, the host mode control unit 910 or the slave mode control unit 920 is used to determine that the operation mode of the energy storage inverter is independent off-grid operation if the preset mode of the energy storage inverter is the host mode, and to determine that the operation mode of the energy storage inverter is networked operation after completing network pre-synchronization if there is an already running energy storage inverter in the energy storage system; and to determine that the operation mode of the energy storage inverter is networked operation after completing network pre-synchronization if there is an already running energy storage inverter in the energy storage system if the preset mode of the energy storage inverter is the slave mode.

[0146] In some embodiments of the present application, in the control device 900 of the above-mentioned parallel energy storage inverter, the host mode control unit 910 or the slave mode control unit 920 is also used to determine whether the voltage at the parallel point of each energy storage inverter is normal according to the number of energy storage inverters operating in the energy storage system, so that the energy storage inverter can only start when the voltage is normal, and report a parallel fault when the voltage is abnormal.

[0147] In some embodiments of the present application, in the control device 900 of the above-mentioned parallel energy storage inverter, the host mode control unit 910 or the slave mode control unit 920 is also used to respond to the scheduling instructions of the energy management system when the energy storage inverter is in a grid-connected working state, perform power control of the energy storage inverter, and disconnect the grid-connected contactor and / or AC circuit breaker of the energy storage inverter when the operating conditions cannot be met.

[0148] It should be noted that the specific implementation of the above-mentioned device embodiments can be carried out with reference to the specific implementation of the above-mentioned corresponding method embodiments, which will not be repeated here.

[0149] Fig.10 A schematic structural diagram of an energy storage converter according to an embodiment of the present application is shown. The energy storage converter 1000 includes any of the above-mentioned control devices 900 for energy storage converters.

[0150] Fig.11 A schematic diagram of the structure of an energy storage system 1100 according to an embodiment of the present application is shown, the energy storage system 1100 includes a plurality of energy storage converters 1002 working in slave mode, an energy storage converter 1001 working in master mode, and a plurality of energy storage converters 1001 and 1002 are connected in parallel and applied in the energy storage system 1100. The energy storage system 1100 also includes an energy management system 1101.

[0151] The beneficial effects of the present application are: providing a control technology for switching between on-grid and off-grid energy storage converters, mainly a control technology for realizing the active and passive transition from on-grid to off-grid when an energy storage converter based on a virtual synchronous generator is applied to a parallel energy storage system. The method provided by the present application greatly reduces the control complexity of the active and passive off-grid transition to on-grid of the parallel energy storage system, while completing the effective operation of the parallel energy storage converter on-grid, and ensuring the power quality and reliability of the off-grid operation of the parallel energy storage converter, effectively solving the problem of parallel coordinated off-grid operation of multiple energy storage converters under complex working conditions, and can be used as a control architecture for the implementation of such engineering projects.

[0152] It should be noted that:

[0153] The algorithm and display provided herein are not inherently related to any particular computer, virtual device or other equipment. Various general purpose devices can also be used together with the teachings based on this. According to the above description, it is obvious to construct the structure required for this type of device. In addition, the application is not directed to any specific programming language either. It should be understood that various programming languages ​​can be utilized to realize the content of the application described herein, and the description of the specific language above is for the purpose of disclosing the best mode of the application.

[0154] In the description provided herein, a large number of specific details are described. However, it is understood that the embodiments of the present application can be practiced without these specific details. In some instances, well-known methods, structures and techniques are not shown in detail so as not to obscure the understanding of this description.

[0155] Similarly, it should be understood that in order to streamline the present application and help understand one or more of the various application aspects, in the above description of the exemplary embodiments of the present application, the various features of the present application are sometimes grouped together into a single embodiment, figure, or description thereof. However, the disclosed method should not be interpreted as reflecting the following intention: the claimed application requires more features than the features clearly stated in each claim. More specifically, as reflected in the claims below, the application aspects are less than all the features of the single embodiment disclosed above. Therefore, the claims following the specific embodiment are hereby expressly incorporated into the specific embodiment, wherein each claim itself serves as a separate embodiment of the present application.

[0156] Those skilled in the art will appreciate that the modules in the devices in the embodiments may be adaptively changed and arranged in one or more devices different from the embodiments. The modules or units or components in the embodiments may be combined into one module or unit or component, and in addition they may be divided into a plurality of submodules or subunits or subcomponents. Except that at least some of such features and / or processes or units are mutually exclusive, all features disclosed in this specification (including the accompanying claims, abstracts and drawings) and all processes or units of any method or device disclosed in this manner may be combined in any combination. Unless otherwise expressly stated, each feature disclosed in this specification (including the accompanying claims, abstracts and drawings) may be replaced by an alternative feature providing the same, equivalent or similar purpose.

[0157] In addition, those skilled in the art will appreciate that, although some embodiments described herein include certain features included in other embodiments but not other features, the combination of features of different embodiments is meant to be within the scope of the present application and form different embodiments. For example, in the claims below, any one of the claimed embodiments may be used in any combination.

[0158] The various component embodiments of the present application may be implemented in hardware, or in software modules running on one or more processors, or in a combination thereof. It should be understood by those skilled in the art that a microprocessor or a digital signal processor (DSP) may be used in practice to implement some or all of the functions of some or all of the components in the control device of the energy storage converter according to the embodiment of the present application. The present application may also be implemented as a device or apparatus program (e.g., a computer program and a computer program product) for executing part or all of the methods described herein. Such a program implementing the present application may be stored on a computer-readable medium, or may be in the form of one or more signals. Such a signal may be downloaded from an Internet website, or provided on a carrier signal, or provided in any other form.

[0159] For example, Fig.12A schematic diagram of the structure of an energy storage converter according to another embodiment of the present application is shown. The energy storage converter 1000 also includes a controller 1010 and a memory 1020 arranged to store computer executable instructions (computer readable program code). The memory 1020 may be an electronic memory such as a flash memory, an EEPROM (electrically erasable programmable read-only memory), an EPROM, a hard disk or a ROM. The memory 1020 has a storage space 1030 for storing a computer readable program code 1031 for executing any method step in the above method. For example, the storage space 1030 for storing computer readable program code may include individual computer readable program codes 1031 for implementing various steps in the above method, respectively. The computer readable program code 1031 can be read from or written to one or more computer program products. These computer program products include program code carriers such as hard disks, compact disks (CDs), memory cards or floppy disks. Such computer program products are typically, for example Fig.13 The computer-readable storage medium. Fig.13 A schematic diagram of the structure of a computer-readable storage medium according to an embodiment of the present application is shown. The computer-readable storage medium 1300 stores a computer-readable program code 1031 for executing the method steps according to the present application, which can be read by the controller 1010 of the energy storage converter 1000. When the computer-readable program code 1031 is run by the energy storage converter 1000, the energy storage converter 1000 is caused to execute the various steps in the method described above. Specifically, the computer-readable program code 1031 stored in the computer-readable storage medium can execute the method shown in any of the above embodiments. The computer-readable program code 1031 can be compressed in an appropriate form.

[0160] It should be noted that the above embodiments illustrate the present application rather than limit the present application, and that those skilled in the art may design alternative embodiments without departing from the scope of the appended claims. In the claims, any reference symbol between brackets should not be constructed as a limitation to the claims. The word "comprising" does not exclude the presence of elements or steps not listed in the claims. The word "one" or "an" preceding an element does not exclude the presence of multiple such elements. The present application can be implemented by means of hardware including several different elements and by means of appropriately programmed computers. In a unit claim that lists several devices, several of these devices may be embodied by the same hardware item. The use of the words first, second, and third, etc. does not indicate any order.

Claims

1. A control method for parallel energy storage converters to switch from grid-connected to off-grid, characterized in that: The method is applied to a parallel energy storage system of multiple energy storage converters to distinguish between master and slave modes for active and passive grid-connected to off-grid switching, and the method includes: When the energy storage converter is in the master mode or the slave mode, when the main grid-connected switch corresponding to the common connection point is disconnected, the energy storage converter is passively switched from the grid-connected working state to the off-grid working state; and, when the energy storage converter is in the master mode, according to the received grid-connected to off-grid instruction, the main grid-connected switch is actively disconnected, so that each energy storage converter can switch from the grid-connected working state to the off-grid working state when the main grid-connected switch is confirmed to be disconnected; The method further comprises: Determine whether the energy storage converter is started in the host mode. If so, determine whether it has received an active off-grid to grid-connected command issued by the energy management system. If received, the energy storage converter enters the off-grid to grid-connected operation, performs pre-synchronization preparations, and starts the first rising edge zero crossing of the grid A phase voltage waveform and the first rising edge zero crossing failure fault judgment; If the first rising edge zero crossing of the grid A phase voltage waveform is successful, then when the first zero crossing of the grid A phase voltage waveform is detected, a pre-synchronization enable signal is sent to each energy storage converter in slave mode through the CAN bus, and the second rising edge zero crossing of the grid A phase voltage waveform is started, and the second rising edge zero crossing failure fault judgment is started; If the second rising edge of the grid A phase voltage waveform passes through the zero point successfully, then when the grid A phase voltage waveform passes through the zero point for the second time, the energy storage converter starts the pre-synchronization function and determines through the CAN bus whether each energy storage converter in the slave mode has completed the pre-synchronization within the preset time, and further determines whether the total capacity of each energy storage converter that has completed the pre-synchronization within the preset time is greater than the preset capacity. If it is greater, it is determined that the pre-synchronization is completed and valid, and a closing instruction is sent to the PCC point switch, so that the PCC point switch closes itself according to the closing instruction, and its closing state is fed back to each energy storage converter through the PCC point switch feedback line, so that each energy storage converter completes the switching of the energy storage system from the off-grid working state to the grid-connected working state according to the feedback information; In the case where the energy storage converter is not started in the host mode, it is determined that it is in the slave mode. After it receives the pre-synchronization enable signal sent by the energy storage converter in the host mode through the CAN bus, it starts the fault judgment of the rising edge zero crossing point and the rising edge zero crossing failure of the A-phase voltage waveform of the power grid. When the energy storage converter in the slave mode detects the first zero crossing point of the A-phase voltage waveform of the power grid, the pre-synchronization function of the energy storage converter is turned on. After the pre-synchronization is completed, a pre-synchronization completion signal is sent to the energy storage converter in the host mode through the CAN bus, and the closed state of the PCC point switch fed back through the PCC point switch feedback line sent by the PCC point switch is received. When the PCC point switch is closed, the energy storage system is switched from the off-grid working state to the grid-connected working state, wherein the first rising edge zero crossing point is the second rising edge zero crossing point detected by the energy storage converter in the host mode. Disconnecting the main grid-connected switch comprises: actively sending a disconnection instruction to the main grid-connected switch; The method further comprises: after actively sending the disconnection instruction, obtaining the state of the main grid-connected switch, and if the main grid-connected switch is not disconnected, reporting a fault of the main grid-connected switch; In the startup phase of the energy storage inverter, the operation mode of the energy storage inverter is determined according to the state of the total grid-connected switch; the operation mode of the energy storage inverter is determined according to the state of the total grid-connected switch, including: if the total grid-connected switch is closed, the operation mode of the energy storage inverter is determined to be independent grid-connected operation after completing grid-connected pre-synchronization; if the total grid-connected switch is disconnected, the operation mode of the energy storage inverter is determined according to the preset mode of the energy storage inverter; Determining the operation mode of the energy storage converter according to the preset mode of the energy storage converter includes: The main grid-connected switch is disconnected. If the preset mode of the energy storage inverter is the host mode, then when there is no running energy storage inverter in the parallel energy storage system, the operation mode of the energy storage inverter is determined to be independent off-grid operation, and when there is a running energy storage inverter in the energy storage system, the operation mode of the energy storage inverter is determined to be networked operation after completing network pre-synchronization; the main grid-connected switch is disconnected. If the preset mode of the energy storage inverter is the slave mode, then when there is an energy storage inverter running in the host mode in the parallel energy storage system, the operation mode of the energy storage inverter is determined to be networked operation after completing network pre-synchronization, and off-grid operation is not performed when there is no voltage reference at the parallel point.

2. The method according to claim 1, characterized in that The method further comprises: Whether the voltage at the parallel connection point of each energy storage converter is normal is determined according to the number of energy storage converters running in the energy storage system, so that the energy storage converter can only start when the voltage is normal, and report a parallel fault when the voltage is abnormal.

3. The method according to claim 1, characterized in that The method further comprises: When the parallel energy storage inverter system is in an off-grid working state, the power control of the energy storage inverter is performed in response to the dispatching instructions of the energy management system. When the load exceeds the capacity of the online energy storage inverter module and cannot meet the demand, the load can only be put into operation after all energy storage inverters are successfully networked and meet the demand.

4. A control device for parallel energy storage converters, characterized in that: The device is used in a parallel energy storage converter system, and the device comprises: The host mode control unit and the slave mode control unit are used to enable the energy storage converter to passively switch from a grid-connected working state to an off-grid working state when the energy storage converter is in the host mode or the slave mode and the main grid-connected switch corresponding to the common connection point is disconnected; and the host mode control unit is also used to actively disconnect the main grid-connected switch according to the received grid-connected to off-grid instruction when the energy storage converter is in the host mode, so that each energy storage converter can switch from the grid-connected working state to the off-grid working state when it is confirmed that the main grid-connected switch is disconnected; Determine whether the energy storage converter is started in the host mode. If so, determine whether it has received an active off-grid to grid-connected command issued by the energy management system. If received, the energy storage converter enters the off-grid to grid-connected operation, performs pre-synchronization preparations, and starts the first rising edge zero crossing of the grid A phase voltage waveform and the first rising edge zero crossing failure fault judgment; If the first rising edge zero crossing of the grid A phase voltage waveform is successful, then when the first zero crossing of the grid A phase voltage waveform is detected, a pre-synchronization enable signal is sent to each energy storage converter in slave mode through the CAN bus, and the second rising edge zero crossing of the grid A phase voltage waveform is started, and the second rising edge zero crossing failure fault judgment is started; If the second rising edge of the grid A phase voltage waveform passes through the zero point successfully, then when the grid A phase voltage waveform passes through the zero point for the second time, the energy storage converter starts the pre-synchronization function and determines through the CAN bus whether each energy storage converter in the slave mode has completed the pre-synchronization within the preset time, and further determines whether the total capacity of each energy storage converter that has completed the pre-synchronization within the preset time is greater than the preset capacity. If it is greater, it is determined that the pre-synchronization is completed and valid, and a closing instruction is sent to the PCC point switch, so that the PCC point switch closes itself according to the closing instruction, and its closing state is fed back to each energy storage converter through the PCC point switch feedback line, so that each energy storage converter completes the switching of the energy storage system from the off-grid working state to the grid-connected working state according to the feedback information; In the case where the energy storage converter is not started in the host mode, it is determined that it is in the slave mode. After it receives the pre-synchronization enable signal sent by the energy storage converter in the host mode through the CAN bus, it starts the fault judgment of the rising edge zero crossing point and the rising edge zero crossing failure of the A-phase voltage waveform of the power grid. When the energy storage converter in the slave mode detects the first zero crossing point of the A-phase voltage waveform of the power grid, the pre-synchronization function of the energy storage converter is turned on. After the pre-synchronization is completed, a pre-synchronization completion signal is sent to the energy storage converter in the host mode through the CAN bus, and the closed state of the PCC point switch fed back through the PCC point switch feedback line sent by the PCC point switch is received. When the PCC point switch is closed, the energy storage system is switched from the off-grid working state to the grid-connected working state, wherein the first rising edge zero crossing point is the second rising edge zero crossing point detected by the energy storage converter in the host mode. Disconnecting the main grid-connected switch comprises: actively sending a disconnection instruction to the main grid-connected switch; After actively sending the disconnection instruction, obtaining the state of the main grid-connected switch, and if the main grid-connected switch is not disconnected, reporting the fault of the main grid-connected switch; In the startup phase of the energy storage inverter, the operation mode of the energy storage inverter is determined according to the state of the total grid-connected switch; the operation mode of the energy storage inverter is determined according to the state of the total grid-connected switch, including: if the total grid-connected switch is closed, the operation mode of the energy storage inverter is determined to be independent grid-connected operation after completing grid-connected pre-synchronization; if the total grid-connected switch is disconnected, the operation mode of the energy storage inverter is determined according to the preset mode of the energy storage inverter; Determining the operation mode of the energy storage converter according to the preset mode of the energy storage converter includes: The main grid-connected switch is disconnected. If the preset mode of the energy storage inverter is the host mode, then when there is no running energy storage inverter in the parallel energy storage system, the operation mode of the energy storage inverter is determined to be independent off-grid operation, and when there is a running energy storage inverter in the energy storage system, the operation mode of the energy storage inverter is determined to be networked operation after completing network pre-synchronization; the main grid-connected switch is disconnected. If the preset mode of the energy storage inverter is the slave mode, then when there is an energy storage inverter running in the host mode in the parallel energy storage system, the operation mode of the energy storage inverter is determined to be networked operation after completing network pre-synchronization, and off-grid operation is not performed when there is no voltage reference at the parallel point.

5. An energy storage converter, characterized in that: The energy storage converter comprises the control device of the parallel energy storage converter as claimed in claim 4.

6. A parallel energy storage system, characterized in that: It comprises several energy storage converters operating in slave mode and one master mode; each energy storage converter comprises a controller; and a memory arranged to store computer executable instructions, wherein when the executable instructions are executed, the controller executes the method as described in any one of claims 1-3.

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