CN112787344A

CN112787344A - Control method and device for switching parallel energy storage converters from off-grid to on-grid

Info

Publication number: CN112787344A
Application number: CN202110110050.5A
Authority: CN
Inventors: 高志军; 姜新宇; 孙鹏; 赵明; 邱姣姣; 张乔乔
Original assignee: Guangzhou Zhiguang Energy Storage Technology Co ltd
Current assignee: Guangzhou Zhiguang Energy Storage Technology Co ltd
Priority date: 2021-01-27
Filing date: 2021-01-27
Publication date: 2021-05-11

Abstract

The application provides a control method and a control device for converting an off-grid mode to a grid mode of a parallel energy storage converter, wherein the method comprises the following steps: when the energy storage converter is in a master mode, according to a received off-grid to on-grid command, sending a pre-synchronization enabling signal to each energy storage converter at a first moment when the grid voltage meets a pre-synchronization condition, and ensuring that each slave mode energy storage converter receives the enabling signal, so that each energy storage converter performs pre-synchronization at a second moment when the grid voltage meets the pre-synchronization condition; and under the condition of meeting grid connection requirements, each energy storage converter is switched from off-grid to grid connection. Under the complex working condition, the current impact of an energy storage system containing a plurality of energy storage converters connected in parallel during grid connection can be greatly inhibited, the stability and the smoothness of the grid connection of the plurality of energy storage converters connected in parallel are obviously improved, and the power quality and the reliability are ensured while the scheduling task of 'peak clipping and valley filling' of a power grid is completed.

Description

Control method and device for switching parallel energy storage converters from off-grid to on-grid

Technical Field

The application relates to the technical field of energy storage, in particular to a control method and device for converting an off-grid mode to a grid-connected mode of a parallel energy storage converter.

Background

The energy storage converter based on the virtual synchronous generator is widely applied to scientific research and engineering practice, the virtual synchronous generator control technology enables the energy storage converter to have the rotational inertia and the damping of the synchronous generator, when an energy storage system is connected to the grid through the virtual synchronous generator, a certain power and frequency support can be provided, a stable power characteristic is obtained when the energy storage system is disconnected from the grid, the load power requirement is met, and the seamless switching between connection and disconnection can be met.

The multiple energy storage converters are connected in parallel, so that the system capacity and the fault tolerance are improved, and the use requirements of users are met. In the prior art, attention on a control method of an energy storage converter under parallel operation is less, but the method has a vital significance on implementation of engineering projects. Especially, when the energy storage system is switched from an off-grid state to a grid-connected state, the energy storage converters need to be switched from the off-grid working state to the grid-connected working state, when a plurality of energy storage converters are applied to the energy storage system in parallel, the operation working condition is complex, the switching transient process can affect the stability of the system, information interaction needs to be completed by combining a communication mode, and the stability of the system is ensured.

Disclosure of Invention

In view of the above, the present application is proposed to provide a method and an apparatus for controlling parallel energy storage converters to be switched from grid to grid, which overcome or at least partially solve the above problems.

According to one aspect of the application, an energy storage converter off-grid to grid-connected control method based on a virtual synchronous generator is provided, and the method is applied to an energy storage system with a plurality of energy storage converters connected in parallel, and comprises the following steps:

when the energy storage converter is in a master mode, according to a received off-grid to grid-connected instruction, sending a pre-synchronization enabling signal to each energy storage converter at a first moment when the grid voltage meets a pre-synchronization condition, and ensuring that each slave mode energy storage converter receives the enabling signal, so that each energy storage converter is pre-synchronized at a second moment when the grid voltage meets the pre-synchronization condition, and the energy storage converters are enabled to be pre-synchronized at the same time and are cooperatively connected to the grid in a networking state;

and under the condition of meeting grid connection requirements, each energy storage converter is switched from an off-grid working state to a grid connection working state.

Optionally, in the method, the pre-synchronization condition is that the voltage waveform of the specified phase of the power grid crosses zero via a rising edge of the rising edge.

Optionally, in the method, the step of converting each energy storage converter from an off-grid operating state to a grid-connected operating state includes:

and sending a closing instruction to a main grid-connected switch corresponding to the public connection point so that each energy storage converter can be switched from an off-grid working state to a grid-connected working state under the condition that the main grid-connected switch is closed.

Optionally, in the above method, the method further includes:

when the energy storage converter is in a slave machine mode, pre-synchronization is carried out at a second moment when the power grid voltage meets a pre-synchronization condition according to a received pre-synchronization enabling signal, so that the energy storage converters are enabled to be pre-synchronized at the same time, and are cooperatively connected in a networking state;

after the presynchronization is successfully completed, sending presynchronization completion information to the energy storage converter working in the host mode;

and after the pre-synchronization fails, the grid-connected contactor and/or the alternating current breaker corresponding to the energy storage converter is cut off.

Optionally, in the foregoing method, the pre-synchronization enable signal and the pre-synchronization completion information are transmitted through a CAN bus.

Optionally, the method further includes:

and determining whether the grid-connected requirement is met according to the total capacity of the energy storage converter corresponding to each piece of pre-synchronization completion information received in a preset time period.

According to a second aspect of the present application, there is provided a control apparatus for parallel energy storage converters, the apparatus being used in a single energy storage converter, the apparatus comprising:

the master mode control unit is used for sending pre-synchronization enabling signals to each energy storage converter at the first moment when the grid voltage meets the pre-synchronization condition according to a received off-grid to grid-connected instruction when the energy storage converter is in the master mode, and ensuring that each slave mode energy storage converter receives the enabling signals, so that each energy storage converter is pre-synchronized at the second moment when the grid voltage meets the pre-synchronization condition, the energy storage converters are enabled to be pre-synchronized at the same time, and the energy storage converters are cooperatively connected to the grid in a networking state;

and the host mode control unit is also used for switching each energy storage converter from an off-grid working state to a grid-connected working state under the condition of meeting grid-connected requirements.

Optionally, in the above apparatus, the presynchronization condition is that the voltage waveform of the specified phase of the power grid crosses zero via a rising edge of the rising edge.

Optionally, in the above apparatus, the master mode control unit is further configured to send a closing instruction to a master grid-connected switch corresponding to the common connection point, so that each of the energy storage converters performs switching from an off-grid operating state to a grid-connected operating state in a state that the master grid-connected switch is closed.

Optionally, the above apparatus further comprises:

the slave mode control unit is used for performing presynchronization at a second moment when the grid voltage meets presynchronization conditions according to the received presynchronization enabling signal when the energy storage converter is in a slave mode, so that the energy storage converters are enabled to be presynchronized simultaneously, and are cooperatively connected to the grid in a networking state; after the presynchronization is successfully completed, sending presynchronization completion information to the energy storage converter working in the host mode; and after the pre-synchronization fails, the grid-connected contactor and/or the alternating current breaker corresponding to the energy storage converter is cut off.

Optionally, in the above apparatus, the pre-synchronization enable signal and the pre-synchronization completion message are transmitted through a CAN bus.

Optionally, in the above apparatus, the host mode control unit is further configured to determine whether the grid connection requirement is met according to a total capacity of the energy storage converter corresponding to each piece of pre-synchronization completion information received within a preset time period.

According to a third aspect of the present application, there is provided a storage converter comprising the control device of the parallel storage converter described above.

According to a fourth aspect of the present application, there is provided an energy storage system, comprising a plurality of energy storage converters operating in a slave mode and in a master mode; each energy storage converter comprises a controller; and a memory arranged to store computer executable instructions that, when executed, cause the controller to perform a method as any one of the above.

According to a fifth aspect of the present application, there is provided a computer readable storage medium, wherein the computer readable storage medium stores one or more programs which, when executed by a controller, implement any of the above methods.

In summary, the present application provides a control method for converting an energy storage converter from an off-grid to a grid-connected based on a virtual synchronous generator, which is applied to a plurality of energy storage converters in parallel connection with an energy storage system, and the method includes: when the energy storage converter is in a master mode, according to a received off-grid to grid-connected instruction, sending a pre-synchronization enabling signal to each energy storage converter at a first moment when the grid voltage meets a pre-synchronization condition, and ensuring that each slave mode energy storage converter receives the enabling signal, so that each energy storage converter is pre-synchronized at a second moment when the grid voltage meets the pre-synchronization condition, and the energy storage converters are enabled to be pre-synchronized at the same time and are cooperatively connected to the grid in a networking state; and under the condition of meeting grid connection requirements, each energy storage converter is switched from an off-grid working state to a grid connection working state. The beneficial effect of this application lies in: the method provided by the application can greatly inhibit the current impact when the energy storage system containing a plurality of parallel energy storage converters is connected to the grid under a complex working condition, obviously improves the stability and the smoothness of the parallel connection of the plurality of parallel energy storage converters, ensures the quality and the reliability of electric energy while completing the scheduling task of 'peak clipping and valley filling' of a power grid, effectively solves the problem of the parallel connection and the cooperative grid connection of the plurality of parallel energy storage converters under the complex working condition, and can be used as a control framework implemented by the engineering projects.

The foregoing description is only an overview of the technical solutions of the present application, and the present application can be implemented according to the content of the description in order to make the technical means of the present application more clearly understood, and the following detailed description of the present application is given in order to make the above and other objects, features, and advantages of the present application more clearly understandable.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the application. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:

FIG. 1 illustrates a schematic structural diagram of an energy storage system according to an embodiment of the present application;

fig. 2 shows a schematic diagram of a parallel operation communication architecture of a plurality of energy storage converters according to an embodiment of the present application;

fig. 3 is a schematic flow chart illustrating a control method for converting an off-grid to a on-grid of a parallel energy storage converter according to an embodiment of the present application;

FIG. 4 shows a grid-connection timing diagram of a control method for converting the parallel energy storage converters from grid-connection to grid-connection according to an embodiment of the application;

fig. 5 is a schematic flow chart of a control method for converting an off-grid into a on-grid of a parallel energy storage converter according to another embodiment of the present application;

fig. 6 is a schematic flow chart of a control method for grid-connected to grid-disconnected of parallel energy storage converters according to another embodiment of the present application;

fig. 7 shows a flow chart of a control method for grid-connected to grid-disconnected of parallel energy storage converters according to still another embodiment of the present application;

fig. 8 shows a flow chart of a control method for off-grid and on-grid of an energy storage converter according to an embodiment of the present application;

fig. 9 shows a schematic configuration of a control device of an energy storage converter according to an embodiment of the present application;

fig. 10 shows a schematic structural diagram of an energy storage converter according to an embodiment of the present application;

FIG. 11 illustrates a schematic structural diagram of an energy storage system in an embodiment in accordance with the present application;

fig. 12 shows a schematic structural diagram of an energy storage converter according to another embodiment of the present application;

FIG. 13 shows a schematic structural diagram of a computer-readable storage medium according to an embodiment of the present application.

Detailed Description

Exemplary embodiments of the present application will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

The idea of the application lies in that aiming at the problem that a plurality of energy storage converters are applied to an energy storage system in parallel and the stability of the power grid system is affected in the transient process of grid connection or grid disconnection with the power grid, the energy storage converter control method based on the virtual synchronous generator is provided, the energy storage converters running in a host mode indicate that the energy storage converters are pre-synchronized at the same time, and grid connection is completed under the condition that grid connection conditions are met, the stability and the smoothness of a parallel system formed by the plurality of energy storage converters connected in parallel in the transient state of grid connection with the power grid are obviously improved, and the power quality and the reliability are ensured while the scheduling task of 'peak clipping and valley filling' of the power grid is completed.

Several exemplary control methods are described below, including:

a centralized mode: the method comprises the steps that a central controller collects and processes information of scheduling, loads and energy storage converters, controls the operation mode and the output capacity of the energy storage converters, sends a pre-synchronization enabling instruction by the central controller during on-line/off-line switching, and controls a micro grid connected switch (PCC) after pre-synchronization of each device is received.

In the centralized mode, the information of each device is centralized in the central controller, so that the monitoring is convenient, the system operation efficiency can be improved when the dispatching and load requirements are met, but the central controller and the communication are excessively relied on, and once a fault occurs, the system is broken down, so that great economic loss is brought to a user.

Master-slave mode: the method is another form of a centralized mode, a host is set to collect information and issue commands, and the host sends high-frequency synchronous signals to distribute loads in an off-network mode. When the off-grid conversion is carried out to the grid connection, the host receives a scheduling instruction, issues a pre-synchronization enabling signal, and closes the PCC point switch after the pre-synchronization of each converter is completed. In this mode, there is a master-slave race mechanism, and when the host does not satisfy the operating condition, a new host is automatically generated.

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 master fails and the machine cannot be started, the slave machines compete out a new master in the modes of capacity, running state and the like, but the master-slave mode system has large calculation amount and is difficult to realize the thorough consideration of all working conditions; when the energy storage converters are operated in parallel connection with an off-grid mode, the host receives an off-grid to on-grid command and sends a pre-synchronization enabling signal to the slave, but communication delay often causes the pre-synchronization states of the converters to be inconsistent, and at the moment, circulation current is easily formed.

Peer-to-peer mode: and each converter has information interaction but no master-slave relation, receives a scheduling instruction and power grid information, controls the PCC (point-to-point control) switch, detects whether the parallel bus has voltage or not when the PCC is off the grid, and starts pre-synchronization startup if the PCC has voltage, or directly starts the startup if the PCC has no voltage. When the off-grid conversion is carried out to the grid connection, each converter receives a scheduling instruction, pre-synchronization is started, and after the pre-synchronization is completed, PCC point switch closing instructions are issued, so that the grid connection can be realized.

The design of the peer-to-peer mode is simple, the mutual dependency of the converters in parallel connection is low, the operation of an online number support system can be guaranteed to a certain extent, and the efficiency is low. However, when the grid connection is switched from the off-grid to the on-grid, the circulation problem mentioned in the master-slave mode also exists under the parallel connection condition, and the grid connection can be realized only when all the equipment pre-synchronization is completed and a PCC point closing command is issued, and when a certain machine has a fault, the grid connection of the whole parallel system is influenced.

Fig. 1 shows a schematic structural diagram of an energy storage system according to an embodiment of the present application, fig. 2 shows a schematic communication connection diagram of a plurality of energy storage converters according to an embodiment of the present application, and fig. 3 shows a schematic flow diagram of a control method of an energy storage converter according to an embodiment of the present application. The control method of the energy storage converter is applied to a single energy storage converter, and a plurality of energy storage converters are connected in parallel to form an energy storage system.

The energy storage converter is friendly as an interface of an energy storage system and a power grid, can realize bidirectional flow of electric energy, and ensures the quality and reliability of the electric energy while finishing the scheduling task of 'peak clipping and valley filling' of the power grid.

The following provides an energy storage system, which is provided as an example only to facilitate better understanding of the present application, and the method provided by the present application can be implemented by any of the following energy storage systems provided by the present application, but does not exclude that other energy storage systems can also implement the method of the present application. Fig. 1 shows a schematic structural diagram of an energy storage system according to an embodiment of the present application, where the energy storage system includes a plurality of energy storage converters, which are respectively denoted as an energy storage converter 1, an energy storage converter 2, and up to an energy storage converter n, the plurality of energy storage converters are connected in parallel to a common connection point (PCC point), a voltage of the PCC point corresponds to a grid-side voltage, and a total grid-connected switch, referred to as a PCC point switch, is arranged corresponding to the PCC point. The PCC point switch is also connected to the power grid.

Each energy storage converter is provided with a grid-connected contactor and an alternating current side breaker respectively, and compared with a single energy storage converter which operates independently in the prior art, each energy storage converter in the application can be additionally provided with a PCC (point of common coupling) voltage collector, a parallel point voltage collector, a PCC switch feedback circuit and a PCC switch control circuit according to needs; the PCC point voltage collectors of each energy storage converter are connected in parallel at one point and used for collecting the voltage of the grid side, and the parallel point voltage collectors of each energy storage converter are connected in parallel at one point and used for collecting the voltage of the parallel side of each energy storage converter, wherein the voltage is the voltage of the parallel point of each energy storage converter; and a PCC point switch feedback circuit of each energy storage converter is connected in parallel to one point and used for feeding back the on/off state of the PCC point to each energy storage converter.

The voltage of the power grid side and the on/off state of the PCC point switch can be fed back to the controller of each energy storage converter through a PCC point switch feedback line, wherein the on/off state of the PCC point switch can be determined according to whether the PCC point switch is consistent with the voltage of the power grid side or not. And each energy storage converter is also provided with a PCC point switch control circuit which is respectively connected with the PCC point switch and used for sending the control information sent by each energy storage converter to the PCC point switch so as to enable the PCC point switch to control the opening/closing state of the PCC point switch according to the control information.

Fig. 2 shows a schematic diagram of a parallel operation communication architecture of an energy storage system according to an embodiment of the present application, where n energy storage converters of the energy storage system are connected in parallel, and a control module of each energy storage converter is in communication connection with an energy management system, and the control modules of the energy storage converters can communicate with each other, and the energy management system can realize centralized monitoring on the control modules of the energy storage converters, so as to ensure real-time performance and reliability of a scheduling instruction.

Fig. 3 is a schematic flowchart illustrating a method for controlling off-grid to on-grid conversion of parallel energy storage converters according to an embodiment of the present application, and as can be seen from fig. 3, the method includes:

step S310, when the energy storage converter is in a host mode, according to a received off-grid to grid-connected instruction, sending a pre-synchronization enabling signal to each energy storage converter at a first moment when the power grid voltage meets a pre-synchronization condition, so that each energy storage converter is pre-synchronized at a second moment when the power grid voltage meets the pre-synchronization condition, and the energy storage converters are enabled to be pre-synchronized simultaneously and cooperatively connected in a networking state.

In the application, each energy storage converter is divided into a master mode and a slave mode in the switching process from an active off-grid working state to a grid-connected working state, and whether each energy storage converter is in the master mode or the slave mode is preset and configured by an energy management system, when the energy storage system is connected with a power grid in a grid mode, one energy storage converter is in the master mode, and other energy storage converters are in the slave mode.

When the energy storage converter is in a master mode, according to a received off-grid to on-grid instruction sent by an energy management system, and at a first moment when the grid voltage meets a pre-synchronization condition, a pre-synchronization enabling signal is sent to the energy storage converters in slave modes, and according to the received pre-synchronization enabling signal, usually an enabling signal, the energy storage converters in slave modes start to detect the arrival of a second moment when the grid voltage meets the pre-synchronization condition, and perform pre-synchronization with the energy storage converter at the same time when the grid voltage meets the second moment of the pre-synchronization condition.

And step S320, under the condition of meeting grid-connected requirements, switching each energy storage converter from an off-grid working state to a grid-connected working state.

After the pre-synchronization is completed, the energy storage converter collects the pre-synchronization completion results of the energy storage converters in the slave mode, and under the condition that the energy storage system formed by the energy storage converters which complete the pre-synchronization meets the grid connection requirement, the energy storage converters are switched from the off-grid working state to the grid connection working state, namely the energy storage system formed by the energy storage converters completes the grid connection work with the power grid.

In some embodiments of the present application, in the above method for controlling the parallel energy storage converters to be switched from the off-grid to the on-grid, the presynchronization condition is that a voltage waveform of a specified phase of the power grid crosses zero via a rising edge. For example, when the waveform is a sine wave, the "zero crossing point of the rising edge" refers to a zero point that is passed when the waveform is inclined upward.

Fig. 4 shows a grid-connection timing diagram of a control method for switching the parallel energy storage converters from grid-disconnection to grid-connection according to an embodiment of the present application, and in order to suppress circulating currents and ensure stability of a grid system, presynchronization is performed at an absolute time of a rising edge zero-crossing point, so that presynchronization consistency of the energy storage converters can be ensured, and the above purpose is achieved. As can be seen from fig. 4, the grid voltage is divided into three phases, for example, phase a, i.e., the PCC-side grid a-phase voltage in fig. 4. The energy storage converter in the master mode receives an active off-grid to on-grid command of an energy management system, responds to the command and starts to prepare presynchronization, then when the energy storage converter detects the first rising edge zero crossing point of a PCC point grid A phase voltage waveform, the energy storage converter in the slave mode issues presynchronization enabling signals, the energy storage converters in the slave mode receive the presynchronization enabling signals, and when the second rising edge zero crossing point of the PCC point grid A phase voltage waveform is detected, the energy storage converters simultaneously start presynchronization, so that the presynchronization consistency is ensured. After the pre-synchronization of the energy storage converters is completed, the pre-synchronization completion information of the energy storage converters in the slave mode is read, and after the pre-synchronization of the energy storage converters in the slave mode is determined, the energy storage converters command the PCC point switch to be closed, so that the switching from the off-grid working state to the grid-connected working state of the energy storage system is completed.

In some embodiments of the present application, in the above control method for converting the parallel energy storage converters from the off-grid to the on-grid, the switching each energy storage converter from the off-grid operating state to the on-grid operating state includes: and sending a closing instruction to a total grid-connected switch corresponding to the public connection point, namely a PCC (point of charge coupled device) switch, so that each energy storage converter can be switched from an off-grid working state to a grid-connected working state under the condition that the total grid-connected switch is closed.

As shown in fig. 1, the energy storage converter 1 in fig. 1 is in the master mode, and the controller of the energy storage converter 1 may send a closing command to the PCC point switch through the PCC point switch control line, so that the PCC point switch may close itself according to the closing command.

And under the condition that the PCC point switch is closed, each energy storage converter completes the switching from the off-grid working state to the grid-connected working state.

In some embodiments of the present application, the control method of the energy storage converter further includes: when the energy storage converter is in a slave machine mode, pre-synchronization is carried out at a second moment when the power grid voltage meets a pre-synchronization condition according to a received pre-synchronization enabling signal, so that the energy storage converters are enabled to be pre-synchronized at the same time, and are cooperatively connected in a networking state; after the presynchronization is successfully completed, sending presynchronization completion information to the energy storage converter working in the host mode; after the presynchronization fails, a grid-connected contactor and/or an alternating current breaker corresponding to the energy storage converter are/is cut off, wherein the grid-connected contactor is respectively used for controlling the off-grid/grid-connected of the corresponding energy storage converter, and as shown in fig. 1, the corresponding energy storage converter is in a grid-connected state when the grid-connected contactor is in a closed state; and when the energy storage converter is in the off state, the corresponding energy storage converter is in the off-grid state. The alternating current circuit breaker is used for avoiding each energy storage converter being damaged due to overlarge current, and in a normal state, the alternating current circuit breaker is in a closed state.

Referring to fig. 4, after receiving the pre-synchronization enable signal sent by the energy storage converter in the master mode, the energy storage converter in the slave mode detects a voltage waveform of the a-phase of the power grid, and starts pre-synchronization when a first rising edge zero-crossing point is detected, where it is noted that the first rising edge zero-crossing point is a second rising edge zero-crossing point detected by the energy storage converter in the master mode.

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 master mode, and the energy storage converter in the master mode commands the PCC point switch to be closed after determining that all the energy storage converters in the slave mode complete the pre-synchronization, so that the switching from the off-grid state to the on-grid state of the energy storage system is completed; if the pre-synchronization fails, it is indicated that the energy storage converter in the slave mode may have a fault, and in order to disconnect the energy storage converter from the grid, the grid-connected contactor and/or the alternating current breaker corresponding to the energy storage converter needs to be cut off. In some embodiments of the present application, the time of the second rising edge zero-crossing point is used as the pre-synchronization trigger time, so as to avoid the problem that the pre-synchronization times of the energy storage converters are inconsistent due to the delay.

In some embodiments of the present application, in the above control method for converting the parallel energy storage converters from the off-network to the on-network, the pre-synchronization enable signal and the pre-synchronization completion information are transmitted through a CAN bus.

The CAN is a controller area network, belongs to the field of industrial field buses, and compared with a general communication bus, the data communication of the CAN bus has outstanding reliability, instantaneity and flexibility. The energy storage converters transmit presynchronization enabling signals and presynchronization finishing information through the CAN bus to ensure the reliability and timeliness of the information.

In some embodiments of the present application, the control method for converting the parallel energy storage converters from an off-grid to a grid-connected mode further includes: and determining whether the grid-connected requirement is met according to the total capacity of the energy storage converter corresponding to each piece of pre-synchronization completion information received in a preset time period.

In order to ensure the effectiveness of active off-grid to on-grid conversion, starting from a second rising edge zero-crossing point of an A-phase voltage waveform of a power grid, starting for a preset time, such as 5s, and after the preset time, if the total capacity of a plurality of energy storage converters which finish pre-synchronization meets the scheduling requirement, namely is greater than the preset capacity, determining that an energy storage system meets the grid-connection requirement; if the total capacity of the energy storage converters which finish the pre-synchronization does not meet the scheduling requirement after the preset time, namely the total capacity is not greater than the preset capacity, the energy storage converter in the host mode reports the pre-synchronization fault, and further, the fault type can be reported.

The following embodiments are helpful to better understand the switching process from active off-grid to grid-connected of the energy storage converter in the master mode and the switching process from off-grid to grid-connected of the energy storage converter in the slave mode, fig. 5 shows a flow diagram of a control method for switching from off-grid to grid-connected of the parallel energy storage converter according to another embodiment of the present application, and as can be seen from fig. 5, after the start, it is first determined whether the energy storage converter is started in the master mode, if so, it is determined whether an active off-grid to grid-connected command sent by an energy management system is received, if so, the energy storage converter enters the off-grid to grid-connected operation, specifically, the pre-synchronization preliminary operation is started, and the first rising edge zero-crossing point detection of the voltage waveform of the a phase of the power grid is started and the failure fault judgment of the first rising edge.

And if the first rising edge zero-crossing point detection of the voltage waveform of the phase A of the power grid fails, reporting a rising edge zero-crossing point fault type.

If the first rising edge zero crossing point of the power grid A-phase voltage waveform is successfully detected, when the first zero crossing point of the power grid A-phase voltage waveform is detected, pre-synchronization enabling signals are sent to the energy storage converters in the slave mode through the CAN bus, the second rising edge zero crossing point detection of the power grid A-phase voltage waveform is started, and the failure fault judgment of the second rising edge zero crossing point detection is started.

And if the second rising edge zero-crossing point detection of the voltage waveform of the phase A of the power grid fails, reporting a rising edge zero-crossing point fault type.

If the second rising edge zero crossing point of the power grid A-phase voltage waveform is successfully detected, the energy storage converter starts the pre-synchronization function and the pre-synchronization failure fault detection when the second rising edge zero crossing point of the power grid A-phase voltage waveform is detected, and whether each energy storage converter in a slave mode completes presynchronization within the preset time of 5s is judged through the CAN bus, and further judging whether the total capacity of each energy storage converter completing the pre-synchronization within the determined time of 5s is larger than the preset capacity or not, if so, determining that the pre-synchronization is completed and effective, sending a closing instruction to the PCC point switch to close the PCC point switch according to the closing instruction, feeding the closing state of the PCC point switch back to each energy storage converter through a PCC point switch feedback circuit, therefore, 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.

If the pre-synchronization of the energy storage converter fails or the total capacity of each energy storage converter completing the pre-synchronization within 5s is not greater than the preset capacity, the pre-synchronization fault type is reported.

Referring to fig. 5, in the case that the energy storage converter is not started in the master mode, it is determined that it is in the slave mode, after receiving the pre-synchronization enabling signal sent by the energy storage converter in the host mode through the CAN bus, starting the rising edge zero-crossing point detection and the rising edge zero-crossing point detection of the power grid A-phase voltage waveform, when the energy storage converter in the slave mode detects the first rising edge zero crossing point of the voltage waveform of the A phase of the power grid, the pre-synchronization function of the energy storage converter is started, after the presynchronization is finished, a presynchronization finishing signal is sent to the energy storage converter in the host machine mode through the CAN bus, and receives the closed state of the PCC point switch sent by the PCC point switch and fed back by the PCC point switch feedback circuit, and under the condition that the PCC point switch is closed, switching the energy storage system from the off-grid working state to the grid-connected working state is completed. It should be noted here that the first zero-crossing rising edge is the second zero-crossing rising edge detected by the energy storage converter in the master mode.

Fig. 6 is a schematic flow chart of a control method for grid-connected to grid-disconnected of parallel energy storage converters according to another embodiment of the present application, the method is also applied to a parallel energy storage system with multiple energy storage converters, and the method includes:

step S610, when the energy storage converter is in the master mode or the slave mode, the energy storage converter is switched from the grid-connected operating state to the off-grid operating state under the condition that the master grid-connected switch corresponding to the common connection point is turned off.

In the application, each energy storage converter is divided into an active off-grid process and a passive off-grid process in the process of switching from a grid-connected working state to an off-grid working state, and the off-grid operation is performed according to an instruction of an energy management system, namely the active off-grid process; without the instructions of the energy management system, is a passive off-grid process. And each energy storage converter has a host mode and a slave mode, and whether each energy storage converter is in the host mode or the slave mode is preset and configured by the energy management system, when the energy storage system is disconnected from the power grid, one energy storage converter is in the host mode, and other energy storage converters are in the slave mode.

In the passive off-grid process, no matter the energy storage converters are in a master mode or a slave mode, the on/off state of a total grid-connected switch corresponding to the public connection point, namely a PCC (point of charge control) switch is detected, under the condition that the PCC switch is off, the connection between each energy storage converter and the power grid is automatically disconnected, and each energy storage converter is automatically switched from a grid-connected working state to an off-grid working state.

And if the PCC point switch is closed, the energy storage converters are all in a grid-connected working state.

And step S620, when the energy storage converter is in the host mode, disconnecting the main grid-connected switch according to the received grid-connected to grid-disconnected instruction, so that each energy storage converter can be switched from the grid-connected working state to the grid-disconnected working state under the condition that the disconnection of the main grid-connected switch is confirmed.

In the active off-grid process, the energy storage converters in the host mode receive a grid-connected to off-grid instruction of the energy management system and control the PCC point switch to be disconnected, under the condition that the PCC point switch is disconnected, the connection between each energy storage converter and the power grid is automatically disconnected, and each energy storage converter is automatically switched from a grid-connected working state to an off-grid working state.

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

After receiving a grid-connected to grid-disconnected instruction of the energy management system, the energy storage converters in the host mode can send disconnection instructions to the PCC point switch through the PCC point switch control line, so that the PCC point switch disconnects the energy storage converters per se according to the disconnection instructions, under the condition that the PCC point switch is disconnected, the connection between each energy storage converter and a power grid is automatically disconnected, and each energy storage converter is automatically switched from a grid-connected working state to an off-grid working state.

In some embodiments of the present application, the method for controlling grid-connected to off-grid of the parallel energy storage converter further includes: and after the disconnection instruction is sent, the state of the main grid-connected switch is obtained, and if the main grid-connected switch is not disconnected, the fault of the main grid-connected switch is reported.

In the passive off-grid process and the active off-grid process, if the PCC switch cannot be disconnected, the PCC switch failure is described, and the PCC switch failure and the failure type are reported. The following embodiments are helpful to better understand the switching process of grid-connected to grid-disconnected of the energy storage converter, fig. 7 is a flow diagram illustrating a control method of grid-connected to grid-disconnected of the parallel energy storage converter according to still another embodiment of the present application, and as can be seen from fig. 7, the control method can be divided into an active grid-connected to grid-disconnected method and a passive grid-connected to grid-disconnected method according to whether the control method is performed according to the instruction of the energy management system.

The active grid-connected grid-disconnected method comprises the steps of firstly determining whether the energy storage converter is started in a host mode, if so, continuously judging whether a grid-connected grid-disconnected command sent by an energy management system is received, sending a disconnection command to a PCC point switch under the condition that the command is received, enabling the PCC point switch to be automatically disconnected according to the command, feeding back the self on/off state to each energy storage converter through a PCC point switch feedback circuit, after each energy storage converter receives state information of the PCC point switch, under the condition that the PCC point switch is disconnected, each energy storage converter is automatically disconnected with a power grid, and each energy storage converter is switched to an off-grid working state from a grid-connected working state.

If the energy storage converters in the host mode do not receive a grid-connected to grid-disconnected instruction sent by the energy management system, after receiving state information of the PCC point switch, if the PCC point switch is determined to be disconnected, the connection between the energy storage converters in the host mode and the power grid is determined to be disconnected, namely the energy storage converters in the host mode are automatically switched from a grid-connected working state to an off-grid working state, and the process is a process that the energy storage converters in the host mode are passively connected to the grid and are switched to the off-grid.

And if the energy storage converters in the host mode do not receive the grid-connected to grid-disconnected instruction sent by the energy management system and receive the state information of the PCC point switch and determine that the PCC point switch is closed, the energy storage converters are in a grid-connected working state.

After receiving the state information of the PCC point switch, each energy storage converter in the slave mode determines that the connection with the power grid is in a disconnection state if the PCC point switch is determined to be in a disconnection state, namely, the energy storage converter automatically switches from a grid-connected working state to an off-grid working state; and if each energy storage converter in the slave mode receives the state information of the PCC point switch and determines that the PCC point switch is closed, each energy storage converter is in a grid-connected working state. In some embodiments of the present application, the control method of the energy storage converter further includes: and at the starting stage of the energy storage converter, determining the operation mode of the energy storage converter according to the state of the main grid-connected switch.

In the starting stage of the energy storage converter, the working states of the energy storage system are different due to different states of a main grid-connected switch, namely a PCC (point of common charge control) switch, and the running modes of the energy storage converters are also different according to the different working states of the energy storage system. Therefore, when the energy storage converter is started, the corresponding operation mode of the energy storage converter is determined according to different states of the main grid-connected switch.

In some embodiments of the present application, in the method for controlling grid-connected to off-grid of a parallel energy storage converter, determining an operation mode of the energy storage converter according to a state of a master grid-connected switch includes: and if the main grid-connected switch is closed, determining that the operation mode of the energy storage converter is independent grid-connected operation after the grid-connected pre-synchronization is completed. Under the condition that a main grid-connected switch, namely a PCC point switch, is closed, an energy storage system is in a grid-connected working state, all energy storage converters forming the energy storage system are in the grid-connected working state, the specific stage is the grid-connected working state after pre-synchronization is finished, and all the energy storage converters run independently.

In some embodiments of the present application, if the main grid-connected switch is turned off, the operation mode of the energy storage converter is determined according to the preset mode of the energy storage converter.

Under the condition that a main grid-connected switch, namely a PCC point switch is disconnected, the energy storage system is in an off-grid working state, and each energy storage converter of the energy storage system or a plurality of the energy storage converters of the energy storage system can be mutually networked to supply load electric energy. In the off-grid networking process, the preset modes of the energy storage converters are divided into a master mode and a slave mode, and the energy storage converter in the master mode is taken as the leading factor to complete the networking process of the energy storage system in the off-grid working state. Furthermore, the operation mode of the energy storage converter needs to be determined according to the preset mode of the energy storage converter.

In some embodiments of the present application, in the method for controlling grid-connected to off-grid of a parallel energy storage converter, determining an operation mode of the energy storage converter according to a preset mode of the energy storage converter includes: and if the preset mode of the energy storage converter is the host mode and under the condition that the energy storage converter which is already operated does not exist 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 in operation, and other energy storage converters in the energy storage system are not in operation, so that the energy storage converter can independently provide electric energy for external load equipment.

And under the condition that the preset mode of the energy storage converter is a host mode and the energy storage converter which is already operated exists in the energy storage system, determining the operation mode of the energy storage converter to be networking operation after networking presynchronization is completed. At this time, it is indicated that networking of other energy storage converters is completed, and it is determined that the operation mode of the energy storage converter is networking operation after networking pre-synchronization is completed, and the energy storage converter and other energy storage converters provide electric energy for external load equipment together.

And determining the operation mode of the energy storage converter as networking operation after networking presynchronization is finished under the condition that the preset mode of the energy storage converter is a slave mode and the energy storage converter operating in a master mode exists in an energy storage system. At this time, it is stated that the existing energy storage converter in the host mode completes networking independently or together with other energy storage converters, and it is determined that the operation mode of the energy storage converter is networking operation after networking pre-synchronization is completed, and the energy storage converter and other energy storage converters provide electric energy for external load equipment together.

In some embodiments of the present application, the method for controlling grid-connected to off-grid of the parallel energy storage converter further includes: and determining whether the voltage and/or the current at the parallel points of the energy storage converters are normal or not according to the number of the energy storage converters operating in the energy storage system, so that the energy storage converters can be started only when the voltage and/or the current are normal, and reporting a parallel fault when the voltage and/or the current are abnormal.

The energy storage converters are connected in parallel, the output voltages of the energy storage converters are the same, and the voltage at the parallel point of each energy storage converter is consistent with the voltage of any one of the energy storage converters connected in parallel; and 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 a plurality of energy storage converters. According to the rule, whether the voltage and/or the current at the parallel connection point of each energy storage converter is normal or not can be determined according to the number of the energy storage converters operating in the energy storage system.

The energy storage converter can be started only when the voltage and/or the current are normal; and when the voltage and/or the current are abnormal, the fault of the energy storage converters connected in parallel is indicated, and the parallel fault and the fault type are reported.

In some embodiments of the present application, the method for controlling grid-connected to off-grid of the parallel energy storage converter further includes: under the condition that the energy storage converter is in a grid-connected working state, responding to a scheduling instruction of an energy management system, performing power control on the energy storage converter, and under the condition that the running condition cannot be met, disconnecting a grid-connected contactor and/or an alternating current breaker of the energy storage converter.

And under the condition that the main grid-connected switch, namely the PCC point switch, is closed and the energy storage system is in a grid-connected working state, all the energy storage converters in the energy storage system are in the grid-connected working state. The energy storage converters do not have master-slave relation and can run independently, namely, a master mode and a slave mode do not need to be distinguished. Each energy storage converter can respond to a scheduling instruction of the energy management system and determine whether the energy storage converter operates or not by combining the condition of the energy storage converter so as to realize the equal division of power among the energy storage converters.

And if the operating condition cannot be met, disconnecting the grid-connected contactor and/or the alternating current breaker of the energy storage converter, and if the rated power of the energy storage converter is less than the preset power required in the scheduling command of the energy management system, determining that the energy storage converter cannot meet the operating condition.

Fig. 8 is a flowchart illustrating a control method for grid disconnection and connection of parallel energy storage converters according to an embodiment of the present application, which is helpful for understanding the grid disconnection operating state and the grid connection operating state of the energy storage system.

The off-grid working state can be described as follows, under the condition that a PCC point switch is disconnected, an energy storage system is in the off-grid working state, whether the energy storage converter is started in a host mode is judged, if yes, the voltage of a parallel point is obtained, whether the voltage of the parallel point is normal is judged, if yes, pre-synchronization is carried out, and after the pre-synchronization is completed, a grid-connected contactor and/or an alternating current breaker is closed, so that networking is completed; and if the current is abnormal, directly closing the grid-connected contactor and/or the alternating current circuit breaker to supply the load with electric energy.

If the energy storage converter is not started in the master mode, the energy storage converter is in the slave mode, the voltage of the parallel point is obtained, whether the voltage of the parallel point is normal or not is judged, whether the energy storage converter in the master mode is in the running state or not is judged, if yes, pre-synchronization is carried out, and after the pre-synchronization is completed, a grid-connected contactor and/or an alternating current breaker is/are closed, so that networking is completed. If the voltage of the parallel point is abnormal and the energy storage converter in the host mode is not in the running state, the energy storage converter cannot be started, the fault of the energy storage system is reported, and further, the fault type can be reported.

The grid-connected working state can be explained as follows, under the condition that a PCC point switch is closed, the energy storage system is in the grid-connected working state, the voltage of a parallel point is obtained, whether the voltage of the parallel point is normal or not is judged, if yes, pre-synchronization is carried out, and after the pre-synchronization is finished, a grid-connected contactor and/or an alternating current circuit breaker are/is closed, so that networking is finished; if not, the energy storage converter cannot be started, and the fault of the energy storage system can be reported, and further, the fault type can be reported.

Fig. 9 shows a schematic structural diagram of a control device of parallel energy storage converters according to an embodiment of the present application, the device 900 is used in a single energy storage converter, the device 900 includes:

the master mode control unit 910 is configured to send a pre-synchronization enable signal to each energy storage converter at a first time when the grid voltage meets a pre-synchronization condition according to a received off-grid to grid connection instruction when the energy storage converter is in the master mode, and ensure that each slave mode energy storage converter has received the enable signal, so that each energy storage converter performs pre-synchronization at a second time when the grid voltage meets the pre-synchronization condition, and ensures that each energy storage converter simultaneously starts pre-synchronization and is cooperatively connected to a grid in a networking state.

The host mode control unit 910 is further configured to switch each energy storage converter from the off-grid operating state to the grid-connected operating state when the grid-connected requirement is met.

In some embodiments of the present application, in the control apparatus 900 for parallel energy storage converters described above, the presynchronization condition is that the voltage waveform of the grid specified phase crosses zero via a rising edge.

In some embodiments of the present application, in the control apparatus 900 for parallel energy storage converters, the master mode control unit 910 is further configured to send a closing command to a main grid-connected switch corresponding to the point of common connection, so that each energy storage converter performs switching from an off-grid operating state to a grid-connected operating state when the main grid-connected switch is closed.

In some embodiments of the present application, the control apparatus 900 of the parallel energy storage converter further includes: the slave mode control unit 920 is configured to perform presynchronization at a second time when the grid voltage meets presynchronization conditions according to the received presynchronization enabling signal when the energy storage converter is in the slave mode, so as to ensure that the energy storage converters are simultaneously started to perform presynchronization and cooperatively grid-connected in a networking state; after the presynchronization is successfully completed, sending presynchronization completion information to the energy storage converter working in the host mode; and after the pre-synchronization fails, the grid-connected contactor and/or the alternating current breaker corresponding to the energy storage converter is cut off.

In some embodiments of the present application, in the control apparatus 900 for a parallel energy storage converter, the pre-synchronization enable signal and the pre-synchronization completion message are transmitted through a CAN bus.

In some embodiments of the present application, in the control apparatus 900 for parallel energy storage converters, the master mode control unit 910 is further configured to determine whether the grid connection requirement is met according to a total capacity of the energy storage converter corresponding to each piece of pre-synchronization completion information received within a preset time period.

The master mode control unit 910 and the slave mode control unit 920 of the control apparatus 900 for parallel energy storage converters shown in fig. 9 are further configured to switch the energy storage converter from the grid-connected operating state to the off-grid operating state when the master grid-connected switch corresponding to the common connection point is turned off when the energy storage converter is in the master mode or the slave mode.

And the master mode control unit 910 is further configured to disconnect the master grid-connected switch according to a received grid-connected to grid-disconnected instruction when the energy storage converter is in the master mode, so that each energy storage converter can be switched from the grid-connected working state to the grid-disconnected working state when the master grid-connected switch is determined to be disconnected.

In some embodiments of the present application, in the above control apparatus 900 for a parallel energy storage converter, the disconnecting the main grid-connected switch includes: and sending a disconnection instruction to the main grid-connected switch.

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

In some embodiments of the present application, in the control apparatus 900 for a parallel energy storage converter, the master mode control unit 910 or the slave mode control unit 920 is further configured to determine an operation mode of the energy storage converter according to a state of the master grid-connected switch during a start-up phase of the energy storage converter.

In some embodiments of the present application, in the control apparatus 900 for parallel energy storage converters, if the master mode control unit 910 or the slave mode control unit 920 is turned on, it is determined that the energy storage converter operates in an independent grid-connected mode after the grid-connected pre-synchronization is completed; and if the main grid-connected switch is disconnected, the method is also used for determining the operation mode of the energy storage converter according to the preset mode of the energy storage converter.

In some embodiments of the present application, in the control apparatus 900 for parallel energy storage converters, the master mode control unit 910 or the slave mode control unit 920 is configured to determine that the operation mode of the energy storage converter is independent off-grid operation when the energy storage converter already operating does not exist in the energy storage system if the preset mode of the energy storage converter is the master mode, and determine that the operation mode of the energy storage converter is networking operation after networking pre-synchronization is completed when the energy storage converter already operating exists in the energy storage system; and if the preset mode of the energy storage converter is a slave mode, determining that the operation mode of the energy storage converter is networking operation after networking pre-synchronization is completed under the condition that the energy storage converter operating in a master mode exists in the energy storage system.

In some embodiments of the present application, in the control apparatus 900 for parallel energy storage converters described above, the master mode control unit 910 or the slave mode control unit 920 is further configured to determine whether the voltage at the parallel point of each energy storage converter is normal according to the number of energy storage converters operating in the energy storage system, so that the energy storage converter can only be started when the voltage is normal, and report a parallel fault when the voltage is abnormal.

In some embodiments of the present application, in the control apparatus 900 for parallel energy storage converters, the master mode control unit 910 or the slave mode control unit 920 is further configured to perform power control on the energy storage converter in response to a scheduling instruction of an energy management system when the energy storage converter is in a grid-connected operating state, and disconnect a grid-connected contactor and/or an ac current breaker of the energy storage converter when an operating condition cannot be met.

It should be noted that, for the specific implementation of each apparatus embodiment, reference may be made to the specific implementation of the corresponding method embodiment, which is not described herein again.

Fig. 10 shows a schematic structural diagram of a power converter according to an embodiment of the present application, and the power converter 1000 includes a control device 900 of any of the parallel power converters described above.

Fig. 11 shows a schematic structural diagram of an energy storage system 1100 according to an embodiment of the present application, where the energy storage system 1100 includes a plurality of energy storage converters 1002 operating in a slave mode, one energy storage converter 1001 operating in a master mode, and a plurality of

energy storage converters

1001 and 1002 are applied to the energy storage system 1100 in parallel. The energy storage system 1100 also includes an energy management system 1101.

The beneficial effect of this application lies in: the method provided by the application can greatly inhibit the current impact when the energy storage system containing a plurality of parallel energy storage converters is connected to the grid under a complex working condition, obviously improves the stability and the smoothness of the parallel connection of the plurality of parallel energy storage converters, completes the scheduling task of 'peak clipping and valley filling' of a power grid, ensures the quality and the reliability of electric energy, effectively solves the problem of the parallel connection and the cooperative grid connection of the plurality of parallel energy storage converters under the complex working condition, and can be used as a control framework implemented by the engineering projects.

It should be noted that:

the algorithms and displays presented herein are not inherently related to any particular computer, virtual machine, or other apparatus. Various general purpose devices may be used with the teachings herein. The required structure for constructing such a device will be apparent from the description above. In addition, this application is not directed to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the present application as described herein, and any descriptions of specific languages are provided above to disclose the best modes of the present application.

In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the application may be practiced without these specific details. In some instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the application, various features of the application are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the application and aiding in the understanding of one or more of the various application aspects. However, the disclosed method should not be interpreted as reflecting an intention that: this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains. Rather, as the following claims reflect, application is directed to less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this application.

Those skilled in the art will appreciate that the modules in the device in an embodiment may be adaptively changed and disposed in one or more devices different from the embodiment. The modules or units or components of the embodiments may be combined into one module or unit or component, and furthermore they may be divided into a plurality of sub-modules or sub-units or sub-components. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and all of the processes or elements of any method or apparatus so disclosed, may be combined in any combination, except combinations where at least some of such features and/or processes or elements are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise.

Furthermore, those skilled in the art will appreciate that while some embodiments described herein include some features included in other embodiments, rather than other features, combinations of features of different embodiments are meant to be within the scope of the application and form different embodiments. For example, in the following claims, any of the claimed embodiments may be used in any combination.

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 will be appreciated by those skilled in the art that a microprocessor or 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 arrangement of the energy storage converter according to embodiments of the present application. The present application may also be embodied as apparatus or device programs (e.g., computer programs and computer program products) for performing a portion or all of the methods described herein. Such programs 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 in any other form.

For example, fig. 12 shows a schematic structural diagram of an energy storage converter according to another embodiment of the present application. The energy storage converter 1000 further comprises 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 memory space 1030 storing computer readable program code 1031 for performing any of the method steps described above. For example, the storage space 1030 for storing computer readable program code may comprise respective computer readable program code 1031 for implementing various steps in the above method, respectively. The computer readable program code 1031 may be read from or written to one or more computer program products. These computer program products comprise a program code carrier such as a hard disk, a Compact Disc (CD), a memory card or a floppy disk. Such a computer program product is typically a computer readable storage medium such as described in fig. 13. FIG. 13 shows a schematic diagram of a computer-readable storage medium according to an embodiment of the present application. The computer readable storage medium 1300 stores computer readable program code 1031 for performing the method steps according to the present application, which is readable by the controller 1010 of the energy storage converter 1000 and causes the energy storage converter 1000 to perform the steps of the method described above when the computer readable program code 1031 is executed by the energy storage converter 1000, and in particular, the computer readable program code 1031 stored by the computer readable storage medium may perform the method shown in any of the embodiments described above. The computer readable program code 1031 may be compressed in a suitable form.

It should be noted that the above-mentioned embodiments illustrate rather than limit the application, and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps not listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The application may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the unit claims enumerating several means, several of these means may be embodied by one and the same item of hardware. The usage of the words first, second and third, etcetera do not indicate any ordering. These words may be interpreted as names.

Claims

1. A control method for switching an off-grid mode to a on-grid mode of a parallel energy storage converter is characterized in that the method is applied to a plurality of energy storage converter parallel energy storage systems, and comprises the following steps:

when the energy storage converter is in a host mode, according to a received off-grid to grid-connected instruction, sending a pre-synchronization enabling signal to each energy storage converter at a first moment when the power grid voltage meets a pre-synchronization condition, so that each energy storage converter is pre-synchronized at a second moment when the power grid voltage meets the pre-synchronization condition, and the energy storage converters are enabled to be pre-synchronized simultaneously and cooperatively connected to the grid under a networking state;

2. A method according to claim 1, characterized in that the presynchronization condition is a zero crossing of a rising edge of a voltage waveform of a specified phase of the grid.

3. The method of claim 1, wherein said transitioning each energy storage converter from an off-grid operating state to a grid-connected operating state comprises:

and sending a closing instruction to a main grid-connected switch corresponding to the public connection point so as to switch each energy storage converter from an off-grid working state to a grid-connected working state under the condition that the main grid-connected switch is closed.

4. The method of claim 1, further comprising:

when the energy storage converter is in a slave machine mode, pre-synchronization is carried out at a second moment when the power grid voltage meets a pre-synchronization condition according to the received pre-synchronization enabling signal, so that the energy storage converters are enabled to be pre-synchronized at the same time, and are cooperatively connected to the grid in a networking state;

5. The method of claim 4, wherein the pre-synchronization enable signal and the pre-synchronization complete message are transmitted over a CAN bus.

6. The method of claim 1, further comprising:

7. A control apparatus for parallel energy storage converters, wherein the apparatus is used in a single energy storage converter, the apparatus comprising:

the host mode control unit is used for sending pre-synchronization enabling signals to the energy storage converters at a first moment when the power grid voltage meets a pre-synchronization condition according to a received off-grid to on-grid instruction when the energy storage converters are in a host mode, so that the energy storage converters are pre-synchronized at a second moment when the power grid voltage meets the pre-synchronization condition, the energy storage converters are enabled to be pre-synchronized simultaneously, and the energy storage converters are cooperatively connected to the grid in a networking state;

8. A power converter, characterized in that it comprises a control device of a parallel power converter as claimed in claim 7.

9. An energy storage system is characterized by comprising a plurality of energy storage converters working in a slave mode and a master mode; each energy storage converter comprises a controller; and a memory arranged to store computer-executable instructions that, when executed, cause the controller to perform the method of any one of claims 1-6.

10. A computer readable storage medium, wherein the computer readable storage medium stores one or more programs which, when executed by a controller, implement the method of any of claims 1-6.