Grid-connected to off-grid seamless switching control method and system and energy storage system

Abstract

The embodiment of the present disclosure discloses a grid-connected to off-grid seamless switching control method, system and energy storage system. The grid-connected to off-grid seamless switching control method is executed by a grid-connected to off-grid seamless switching system, which comprises a switching module, a control module and a power converter. The power converter is connected with the power grid through the switching module. The grid-connected to off-grid seamless switching control method comprises: the control module and the power converter detect the running state of the power grid in parallel; when the control module and the power converter detect that the running state of the power grid is an abnormal state, the control module controls the switching module to be disconnected, and the power converter switches the running mode to a virtual synchronous generator mode. The present disclosure realizes fast and seamless switching from grid-connected to off-grid, so as to ensure the continuous and stable operation of the off-grid microgrid.

Description

Technical Field

[0001] This disclosure relates to the field of power grid technology, and in particular to a seamless switching control method, system and energy storage system for grid-connected to off-grid operation. Background Technology

[0002] In response to increasingly complex distributed generation applications, power converters currently require the cooperation of thyristors or circuit breakers to achieve seamless switching between grid-connected and off-grid operation and reduce voltage and current fluctuations. When a fault occurs in the distribution network, the connection to the distribution network is quickly disconnected, and the converter enters islanded operation mode. Therefore, coordinating the opening and closing of switching devices (thyristors or circuit breakers) and the operating mode of the power converter during distribution network faults has become a crucial aspect of achieving seamless grid-connected to off-grid switching. Summary of the Invention

[0003] This disclosure provides a method, system, and energy storage system for seamless grid-to-off-grid switching control, to achieve rapid and seamless switching from grid to off-grid, thereby ensuring the continuous and stable operation of the off-grid microgrid.

[0004] In a first aspect, embodiments of this disclosure provide a grid-connected to off-grid seamless switching control method, which is executed using a grid-connected to off-grid seamless switching system. The grid-connected to off-grid seamless switching system includes a switching module, a control module, and a power converter; the power converter is connected to the power grid through the switching module.

[0005] The seamless grid-to-off-grid switching control method includes:

[0006] The control module and the power converter detect the operating status of the power grid in parallel;

[0007] When the control module and the power converter detect that the power grid is in an abnormal operating state in parallel, the control module controls the switching module to disconnect, and the power converter switches the operating mode to virtual synchronous generator mode.

[0008] Optionally, after the power converter switches its operating mode to virtual synchronous generator mode, the following method is further included:

[0009] The power converter determines its own operating status and, based on its own operating status, determines whether its operating mode switching was successful.

[0010] Optionally, the seamless switching control method from grid-connected to off-grid also includes:

[0011] If the power converter fails to switch operating modes, the power converter will adjust its operating state to a shutdown state;

[0012] The control module detects the on / off state of the switch module and generates a disconnection indication signal when the on / off state of the switch module is off. The power converter starts by generating waves in virtual synchronous generator mode according to the disconnection indication signal.

[0013] Optionally, the grid-connected to off-grid seamless switching system further includes a transformer; the power grid is connected to the transformer through the switching module, and the transformer is connected to the power converter;

[0014] The control module and the power converter detect the operating status of the power grid in parallel, including:

[0015] The control module collects the power grid operating parameters and determines the operating status of the power grid based on the power grid operating parameters; at the same time, the power converter collects the electrical operating parameters of the connection node between the power converter and the transformer and determines the operating status of the power grid based on the electrical operating parameters.

[0016] Optionally, the power grid operating parameters include at least one of the following: power grid voltage amplitude, power grid voltage frequency, and power grid voltage frequency variation.

[0017] The control module determines the operating status of the power grid based on the power grid operating parameters, including:

[0018] If the grid voltage amplitude is less than a first amplitude threshold or greater than a second amplitude threshold, or the grid voltage frequency is less than a first frequency threshold or greater than a second frequency threshold, or the grid voltage frequency change is less than a first change threshold or greater than a second change threshold, then the grid's operating state is abnormal; otherwise, the grid's operating state is normal; wherein, the first amplitude threshold is less than the second amplitude threshold, the first frequency threshold is less than the second frequency threshold, and the first change threshold is less than the second change threshold.

[0019] Optionally, the electrical operating parameters include at least one of node voltage amplitude, node voltage frequency, and node voltage frequency variation;

[0020] The power converter determines the operating status of the power grid based on the electrical operating parameters, including:

[0021] If the node voltage amplitude is less than the third amplitude threshold or greater than the fourth amplitude threshold, or the node voltage frequency is less than the first frequency threshold or greater than the second frequency threshold, or the node voltage frequency change is less than the first change threshold or greater than the second change threshold, then the power grid is in an abnormal operating state; otherwise, the power grid is in a normal operating state; wherein the third amplitude threshold is less than the fourth amplitude threshold, the first frequency threshold is less than the second frequency threshold, and the first change threshold is less than the second change threshold.

[0022] Optionally, the third amplitude threshold is less than the first amplitude threshold, the first amplitude threshold is less than the fourth amplitude threshold, and the fourth amplitude threshold is less than the second amplitude threshold.

[0023] Optionally, the switching module includes a thyristor, with a first end of the thyristor connected to the power grid and a second end of the thyristor connected to the power converter.

[0024] Optionally, the control module detects the on / off state of the switch module by:

[0025] The control module acquires the thyristor voltage difference or the first current of the thyristor across its terminals; if the thyristor voltage difference equals the thyristor voltage, the thyristor is in a conducting state; otherwise, the thyristor is in a disconnected state; or...

[0026] If the first current is not equal to 0, the thyristor is in the on state; otherwise, the thyristor is in the off state.

[0027] Optionally, the grid-connected to off-grid seamless switching system includes at least two power converters connected in parallel; each power converter is connected to the transformer and the control module.

[0028] After each of the power converters receives the disconnection indication signal, the method further includes:

[0029] The power converters communicate in parallel and start according to the disconnection indication signal in master-slave mode.

[0030] Secondly, this disclosure also provides a grid-connected to off-grid seamless switching system, which includes a switching module, a control module, and a power converter;

[0031] The power converter is connected to the power grid via the switching module;

[0032] The control module and the power converter are used to detect the operating status of the power grid in parallel;

[0033] The control module is used to control the switching module to disconnect when it detects that the operating state of the power grid is abnormal.

[0034] The power converter is used to switch the operating mode to virtual synchronous generator mode when it detects that the operating state of the power grid is abnormal.

[0035] Optionally, the power converter is further configured to determine its own operating status after switching the operating mode to virtual synchronous generator mode, and determine whether the switching of its operating mode was successful based on its own operating status.

[0036] Optionally, the power converter is used to adjust the operating state to a shutdown state when the power converter operation mode switching fails;

[0037] The control module is used to detect the on / off state of the switch module and generate a disconnection indication signal when the on / off state of the switch module is off.

[0038] The power converter is used to start in virtual synchronous generator mode according to the disconnection indication signal.

[0039] Optionally, the power converter is an energy storage converter or an inverter.

[0040] Thirdly, embodiments of this disclosure also provide an energy storage system, which includes the grid-connected to off-grid seamless switching system provided in any embodiment of this disclosure.

[0041] This embodiment detects the grid's operating status in parallel through a control module and a power converter. When both the control module and the power converter detect an abnormal grid operating status, the control module can promptly control the switching module to quickly disconnect from the grid, and the power converter can quickly switch its operating mode to virtual synchronous generator mode, achieving a rapid and seamless switch from grid-connected to off-grid operation, thereby ensuring the continuous and stable operation of the off-grid microgrid. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of this disclosure, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a schematic diagram of the structure of a seamless grid-to-offline switching system provided in an embodiment of the present disclosure;

[0044] Figure 2A flowchart illustrating a seamless grid-to-offline switching control method provided in an embodiment of this disclosure;

[0045] Figure 3 A flowchart illustrating another seamless grid-to-off-grid switching control method provided in this embodiment of the present disclosure;

[0046] Figure 4 This is a schematic diagram of another seamless grid-to-offline switching system provided in an embodiment of the present disclosure. Detailed Implementation

[0047] To enable those skilled in the art to better understand the present disclosure, the technical solutions of the present disclosure will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present disclosure, and not all embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present disclosure.

[0048] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this disclosure are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this disclosure described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0049] Figure 1 This is a schematic diagram of a seamless grid-to-offline handover system provided in an embodiment of this disclosure, as shown below. Figure 1 As shown, the grid-connected to off-grid seamless switching system includes a switch module 11, a control module 12, and a power converter 13; the power converter 13 is connected to the power grid 20 through the switch module 11.

[0050] The switching module 11, the power grid 20, and the power converter 13 are all connected to the control module 12. Both the control module 12 and the power converter 13 can detect faults in the power grid 20 and, when a fault is detected in the power grid 20 within a preset time, cooperate to achieve a fast and seamless switch from grid connection to off-grid operation, ensuring the continuous and stable operation of the off-grid microgrid.

[0051] Specifically, Figure 2This is a flowchart illustrating a seamless grid-to-off-grid switching control method provided in an embodiment of this disclosure. This embodiment is applicable to situations where a grid fault requires a rapid and seamless switching of a microgrid from grid-connected to off-grid. The seamless grid-to-off-grid switching control method provided in this disclosure can be executed by a seamless grid-to-off-grid switching system. Figure 2 As shown, the method specifically includes the following steps:

[0052] S110, the control module, and the power converter detect the operating status of the power grid in parallel.

[0053] The power grid's operating status includes both abnormal states (where faults have occurred) and normal states (where operations are normal). When a power grid fault occurs, its operating parameters change, and the electrical operating parameters transmitted from the grid to the power converter via the switching module also change accordingly. The control module can collect the grid's operating parameters in real time, and the power converter can collect the electrical operating parameters of the nodes connected to the switching module in real time. This allows the control module and the power converter to detect the grid's operating status in parallel; that is, the control module determines the grid's operating status by monitoring its operating parameters, while the power converter simultaneously determines the grid's operating status by monitoring the electrical operating parameters of the nodes connected to the switching module.

[0054] S120. When the control module and the power converter detect that the grid is in an abnormal operating state in parallel, the control module controls the switch module to disconnect, and the power converter switches the operating mode to virtual synchronous generator mode.

[0055] When the power grid is in an abnormal operating state, it indicates that a fault has occurred in the power grid. In order to prevent the power grid fault from affecting the operation of the microgrid, it is necessary to quickly disconnect the connection between the microgrid and the power grid, and control the power converter of the microgrid to independently supply power to the microgrid load.

[0056] Specifically, the control module can disconnect from the power grid by controlling the switch module to perform a disconnection action, enabling the microgrid to be quickly and seamlessly removed from the entire power grid system, thus achieving microgrid off-grid status and avoiding the impact or damage of grid faults on the microgrid. At the same time, the power converter switches its own operating mode to virtual synchronous generator mode, which can provide voltage to the off-grid microgrid like a traditional synchronous generator to maintain the stable operation of the off-grid microgrid.

[0057] This embodiment detects the grid's operating status in parallel through a control module and a power converter. When both the control module and the power converter detect an abnormal grid operating status, the control module can promptly control the switching module to quickly disconnect from the grid, and the power converter can quickly switch its operating mode to virtual synchronous generator mode, achieving a rapid and seamless switch from grid-connected to off-grid operation, thereby ensuring the continuous and stable operation of the off-grid microgrid.

[0058] Based on the above embodiments, optionally, after the power converter switches the operating mode to virtual synchronous generator mode, the method further includes:

[0059] The power converter determines its own operating status and, based on that status, determines whether its operating mode switching was successful.

[0060] The operating status of the power converter includes a shutdown state and a normal state. A failure to switch the power converter's operating mode indicates a fault, and the power converter will activate its self-protection mechanism and stop operating. A successful switching of the power converter's operating mode will allow it to operate in virtual synchronous generator mode, normally providing voltage to the off-grid microgrid. Therefore, the success of the power converter's operating mode switching can be determined by its operating status.

[0061] Specifically, if the power converter stops, its operating status will be "stopped," indicating a failure in the power converter's operating mode switching. If the power converter operates in virtual synchronous generator mode, its operating status will be "normal," indicating a successful operating mode switching.

[0062] Based on the above embodiments, optionally, Figure 3 This is a flowchart illustrating another seamless grid-to-off-grid handover control method provided in an embodiment of this disclosure. Figure 3 As shown, the method specifically includes the following steps:

[0063] The S210, control module, and power converter detect the operating status of the power grid in parallel.

[0064] S220. When the control module and the power converter detect that the grid is in an abnormal operating state in parallel, the control module controls the switch module to disconnect, and the power converter switches the operating mode to virtual synchronous generator mode.

[0065] S230. If the power converter fails to switch operating modes, the power converter will adjust its operating state to a shutdown state.

[0066] In some cases, if the control module fails to disconnect the control switch module in a timely manner or fails to disconnect, the power converter may be impacted by a grid fault (e.g., excessive voltage difference between the grid and the power converter causing overcurrent in the power converter), leading to a failure in switching the power converter's operating mode. In this situation, when the power converter malfunctions, it will stop operating, switching its operating state to a shutdown state.

[0067] S240: The control module detects the on / off state of the switch module and generates a disconnection indication signal when the switch module is in the off state. The power converter starts by generating waves in virtual synchronous generator mode according to the disconnection indication signal.

[0068] The failure to switch the operating mode of the power converter indicates that the power converter has malfunctioned due to a grid fault. In this case, the control module can quickly troubleshoot the power converter and start it up by controlling the switching module and the power converter in series, thereby achieving a rapid and seamless switch from grid-connected to off-grid operation of the microgrid.

[0069] Specifically, the control module needs to check the on / off state of the switch module to determine the connection status between the power grid and the microgrid. If the switch module is in the on / off state, the control module needs to control the switch module to perform a disconnection action and generate a disconnection indication signal when the switch module is in the off state to inform the power converter that the connection between the power grid and the microgrid has been severed. If the switch module is in the off state, the control module will directly generate a disconnection indication signal to inform the power converter that the connection between the power grid and the microgrid has been severed. After receiving the disconnection indication signal, the power converter will generate a voltage rise in virtual synchronous generator mode to provide voltage to the off-grid microgrid and maintain its stable operation.

[0070] Based on the above embodiments, optionally, Figure 4 A schematic diagram of another grid-to-offline seamless handover system provided in this embodiment of the present disclosure is shown below. Figure 4 As shown, the grid-connected to off-grid seamless switching system also includes a transformer T; the grid 20 is connected to the transformer T through the switch module 11, and the transformer T is connected to the power converter 13.

[0071] The specific process of the control module and power converter detecting the operating status of the power grid in parallel is as follows:

[0072] The control module collects the grid operating parameters and determines the grid operating status based on the grid operating parameters; at the same time, the power converter collects the electrical operating parameters of the connection node between the power converter and the transformer and determines the grid operating status based on the electrical operating parameters.

[0073] Specifically, the power grid operating parameters include at least one of the following: power grid voltage amplitude, power grid voltage frequency, and power grid voltage frequency variation; the electrical operating parameters include at least one of the following: node voltage amplitude, node voltage frequency, and node voltage frequency variation.

[0074] The variation in grid voltage frequency reflects the degree of change in grid frequency. By detecting the variation in grid voltage frequency, it can be determined whether the frequency abrupt change in grid output frequency is within the preset normal range. Similarly, the variation in node voltage frequency reflects the degree of change in voltage frequency between the power converter and the transformer connection node. By detecting the variation in node voltage frequency, it can be determined whether the frequency abrupt change in voltage frequency between the power converter and the transformer connection node is within the preset normal range.

[0075] If the grid voltage amplitude, grid voltage frequency, and grid voltage frequency change are all within the preset range, the control module will determine that the grid is operating normally; if any one or more of the grid voltage amplitude, grid voltage frequency, and grid voltage frequency change exceed the preset range, the control module will determine that the grid is operating abnormally.

[0076] If the node voltage amplitude, node voltage frequency, and node voltage frequency change are all within the preset range, the power converter will determine that the power grid is operating normally; if any one or more of the node voltage amplitude, node voltage frequency, and node voltage frequency change exceed the preset range, the power converter will determine that the power grid is operating abnormally.

[0077] It is important to note that due to the presence of switching modules and transformers between the power grid and the power converter, the voltage output from the power grid will experience a certain voltage drop through these components. To enable parallel monitoring of the power grid by the control module and the power converter, the preset ranges for the power grid voltage amplitude and the node voltage amplitude are set differently. Furthermore, if the power grid voltage amplitude exceeds the preset range, the node voltage amplitude will also exceed the preset range; conversely, if the power grid voltage amplitude does not exceed the preset range, the node voltage amplitude will also remain within the preset range. If the preset ranges for the power grid voltage amplitude and the node voltage amplitude are the same, a power grid fault may occur, causing the power converter to detect the abnormal power grid operation before the control module. Consequently, the power converter may switch operating modes without disconnecting from the power grid, leading to a power converter failure.

[0078] In addition, the time thresholds for the control module and power converter to detect the grid's operating status need to be adjusted in a timely manner according to the grid environment. That is, the time from when the control module receives the grid operating parameters to when it outputs the judgment result, and the time from when the power converter receives the electrical operating parameters to when it outputs the judgment result, need to be adjusted in a timely manner according to the grid environment to avoid the control module and power converter frequently switching between grid connection and off-grid due to grid voltage flicker and other reasons.

[0079] Specifically, the steps by which the control module determines the operating status of the power grid based on the power grid operating parameters are described:

[0080] If the grid voltage amplitude is less than the first amplitude threshold or greater than the second amplitude threshold, or the grid voltage frequency is less than the first frequency threshold or greater than the second frequency threshold, or the grid voltage frequency change is less than the first change threshold or greater than the second change threshold, then the grid is in an abnormal operating state; otherwise, the grid is in a normal operating state; wherein, the first amplitude threshold is less than the second amplitude threshold, the first frequency threshold is less than the second frequency threshold, and the first change threshold is less than the second change threshold.

[0081] Among them, the first amplitude threshold is the minimum value of the grid voltage amplitude set according to the actual situation and the set standard specifications; the second amplitude threshold is the maximum value of the grid voltage amplitude set according to the actual situation and the set standard specifications; the first frequency threshold is the minimum value of the grid voltage frequency set according to the actual situation and the set standard specifications; the second frequency threshold is the maximum value of the grid voltage frequency set according to the actual situation and the set standard specifications; the first variation threshold is the minimum amount of change in the grid voltage frequency set according to the actual situation and the set standard specifications; and the second variation threshold is the maximum amount of change in the grid voltage frequency set according to the actual situation and the set standard specifications.

[0082] Specifically, the steps for the power converter to determine the operating status of the power grid based on electrical operating parameters are explained:

[0083] If the node voltage amplitude is less than the third amplitude threshold or greater than the fourth amplitude threshold, or the node voltage frequency is less than the first frequency threshold or greater than the second frequency threshold, or the node voltage frequency change is less than the first change threshold or greater than the second change threshold, then the power grid is in an abnormal operating state; otherwise, the power grid is in a normal operating state; wherein, the third amplitude threshold is less than the fourth amplitude threshold, the first frequency threshold is less than the second frequency threshold, and the first change threshold is less than the second change threshold.

[0084] Among them, the third amplitude threshold is the minimum value of the node voltage amplitude set according to the actual situation and the set standard specifications; the fourth amplitude threshold is the maximum value of the node voltage amplitude set according to the actual situation and the set standard specifications; the first frequency threshold is the minimum value of the node voltage frequency set according to the actual situation and the set standard specifications; the second frequency threshold is the maximum value of the node voltage frequency set according to the actual situation and the set standard specifications; the first variation threshold is the minimum amount of node voltage frequency variation set according to the actual situation and the set standard specifications; and the second variation threshold is the maximum amount of node voltage frequency variation set according to the actual situation and the set standard specifications.

[0085] In order to achieve parallel detection of the power grid by the control module and the power converter, due to the voltage drop of the switching module and the transformer between the power grid and the power converter, the third amplitude threshold is set to be less than the first amplitude threshold, the first amplitude threshold is less than the fourth amplitude threshold, and the fourth amplitude threshold is less than the second amplitude threshold.

[0086] In addition, there is no frequency difference between the power grid and the power converter. Therefore, the preset range of the grid voltage frequency and the node voltage frequency are the same, and the preset range of the grid voltage frequency change and the node voltage frequency change are also the same.

[0087] Based on the above embodiments, alternatively, refer to the following: Figure 1 The switching module 11 includes a thyristor K, the first end of which is connected to the power grid 20, and the second end of which is connected to the power converter 13.

[0088] Based on the above embodiments, optionally, the control module detects the on / off state of the switch module by including:

[0089] The control module acquires the voltage difference between the two ends of the thyristor or the first current of the thyristor.

[0090] Here, the thyristor voltage difference is the voltage difference across the thyristor, and the first current is the current flowing through the thyristor. When the thyristor is on, the thyristor voltage difference is equal to the thyristor voltage, and the current flowing through the thyristor is not zero. Therefore, the control module can determine the on / off state of the thyristor by detecting the thyristor voltage difference across the thyristor or the first current of the thyristor based on the above characteristics.

[0091] If the thyristor voltage difference equals the thyristor voltage, then the thyristor is in the on / off state; otherwise, the thyristor is in the off state; or...

[0092] If the first current is not equal to 0, the thyristor is in the on state; otherwise, the thyristor is in the off state.

[0093] Based on the above embodiments, optionally, the grid-connected to off-grid seamless switching system includes at least two power converters connected in parallel; each power converter is connected to a transformer and a control module.

[0094] In this system, the power converters communicate in parallel, and the main power converter controls the slave power converters to generate waveforms together to establish voltage, so as to provide voltage for the off-grid microgrid.

[0095] Specifically, after each power converter receives a disconnection indication signal, the process also includes:

[0096] The power converters communicate in parallel and start by sending a wave according to the disconnection indication signal in master-slave mode.

[0097] This disclosure also provides a seamless grid-to-offline switching system, such as... Figure 1 As shown, the grid-connected to off-grid seamless switching system includes a switch module 11, a control module 12, and a power converter 13; the power converter 13 is connected to the power grid 20 through the switch module 11.

[0098] The control module 12 and the power converter 13 are used to detect the operating status of the power grid 20 in parallel;

[0099] The control module 12 is used to control the switch module 11 to disconnect when the operating state of the power grid 20 is detected to be abnormal.

[0100] The power converter 13 is used to switch the operating mode to virtual synchronous generator mode when the operating state of the power grid 20 is detected to be abnormal.

[0101] In this embodiment, the control module 12 and the power converter 13 detect the operating status of the power grid 20 in parallel. When both the control module 12 and the power converter 13 detect that the operating status of the power grid 20 is abnormal, the control module 12 can promptly control the switch module 11 to quickly disconnect from the power grid 20, and the power converter 13 can quickly switch the operating mode to the virtual synchronous generator mode, realizing a fast and seamless switch from grid connection to off-grid, thereby ensuring the continuous and stable operation of the off-grid microgrid.

[0102] Based on the above embodiments, optionally, the power converter is also used to determine its own operating status after switching the operating mode to virtual synchronous generator mode, and determine whether the operating mode switching is successful based on its own operating status.

[0103] Based on the above embodiments, optionally, the power converter is used to adjust the operating state to a shutdown state when the power converter operating mode switching fails;

[0104] The control module is used to detect the on / off state of the switch module and generate a disconnection indication signal when the on / off state of the switch module is off.

[0105] The power converter is used to start in virtual synchronous generator mode based on the disconnection indication signal.

[0106] Based on the above embodiments, optionally, as follows: Figure 4 As shown, the grid-connected to off-grid seamless switching system also includes a transformer T; the grid 20 is connected to the transformer T through the switch module 11, and the transformer T is connected to the power converter 13.

[0107] The control module 12 is used to collect the power grid operating parameters of the power grid 20 and determine the operating status of the power grid 20 based on the power grid operating parameters; at the same time, the power converter 13 is used to collect the electrical operating parameters of the connection node between the power converter 13 and the transformer T and determine the operating status of the power grid 20 based on the electrical operating parameters.

[0108] Based on the above embodiments, optionally, the power grid operating parameters include at least one of the power grid voltage amplitude, power grid voltage frequency, and power grid voltage frequency variation.

[0109] The control module is used to determine that the grid's operating state is abnormal when the grid voltage amplitude is less than a first amplitude threshold or greater than a second amplitude threshold, or the grid voltage frequency is less than a first frequency threshold or greater than a second frequency threshold, or the grid voltage frequency change is less than a first change threshold or greater than a second change threshold; otherwise, it determines that the grid's operating state is normal. Wherein, the first amplitude threshold is less than the second amplitude threshold, the first frequency threshold is less than the second frequency threshold, and the first change threshold is less than the second change threshold.

[0110] Based on the above embodiments, optionally, the electrical operating parameters include at least one of node voltage amplitude, node voltage frequency, and node voltage frequency variation.

[0111] The power converter is used to determine that the grid is in an abnormal state when the node voltage amplitude is less than a third amplitude threshold or greater than a fourth amplitude threshold, or the node voltage frequency is less than a first frequency threshold or greater than a second frequency threshold, or the node voltage frequency change is less than a first change threshold or greater than a second change threshold; otherwise, it determines that the grid is in a normal state. Wherein, the third amplitude threshold is less than the fourth amplitude threshold, the first frequency threshold is less than the second frequency threshold, and the first change threshold is less than the second change threshold.

[0112] Based on the above embodiments, optionally, as follows: Figure 1 As shown, the switching module 11 includes a thyristor K, the first end of which is connected to the power grid 20, and the second end of which is connected to the power converter 13.

[0113] The control module 12 is used to collect the thyristor voltage difference across the thyristor K or the first current of the thyristor K, and to determine the on / off state of the thyristor K as the on state when the thyristor voltage difference is equal to the thyristor voltage of the thyristor K; otherwise, the on / off state of the thyristor K is the off state; or, to determine the on / off state of the thyristor K as the on state when the first current is not equal to 0; otherwise, the on / off state of the thyristor K is the off state.

[0114] Based on the above embodiments, optionally, the grid-connected to off-grid seamless switching system includes two power converters connected in parallel; each power converter is connected to a transformer and a control module;

[0115] Each power converter is used to communicate in parallel after receiving a disconnection indication signal, and to start the operation by sending a wave according to the disconnection indication signal in master-slave mode.

[0116] Based on the above embodiments, the power converter may optionally be an energy storage converter or an inverter.

[0117] This disclosure also provides an energy storage system, which includes the grid-connected to off-grid seamless switching system provided in any embodiment of this disclosure.

[0118] It should be understood that the various forms of processes shown above can be used to rearrange, add, or delete steps. For example, the steps described in this disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this disclosure can be achieved, and this is not limited herein.

[0119] The specific embodiments described above do not constitute a limitation on the scope of protection of this disclosure. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A grid-connected to off-grid seamless switching control method, characterized in that, The process is performed using a seamless grid-connected to off-grid switching system, which includes a switching module, a control module, and a power converter; the power converter is connected to the power grid through the switching module. The seamless grid-to-off-grid switching control method includes: The control module and the power converter detect the operating status of the power grid in parallel; When the control module and the power converter detect that the power grid is in an abnormal operating state in parallel, the control module controls the switching module to disconnect, and the power converter switches the operating mode to virtual synchronous generator mode.

2. The grid-connected to off-grid seamless switching control method according to claim 1, characterized in that, After the power converter switches its operating mode to virtual synchronous generator mode, the following is also included: The power converter determines its own operating status and, based on its own operating status, determines whether its operating mode switching was successful.

3. The grid-connected off-grid seamless switching control method according to claim 1 or 2, characterized in that, Also includes: If the power converter fails to switch operating modes, the power converter will adjust its operating state to a shutdown state; The control module detects the on / off state of the switch module and generates a disconnection indication signal when the on / off state of the switch module is off. The power converter starts by generating waves in virtual synchronous generator mode according to the disconnection indication signal.

4. The grid-connected off-grid seamless switching control method according to claim 3, characterized in that, The grid-connected to off-grid seamless switching system also includes a transformer; the power grid is connected to the transformer through the switching module, and the transformer is connected to the power converter; The control module and the power converter detect the operating status of the power grid in parallel, including: The control module collects the power grid operating parameters and determines the operating status of the power grid based on the power grid operating parameters; Meanwhile, the power converter collects the electrical operating parameters of the connection node between the power converter and the transformer, and determines the operating status of the power grid based on the electrical operating parameters.

5. The grid-connected off-grid seamless switchover control method according to claim 4, characterized in that, The power grid operating parameters include at least one of the following: power grid voltage amplitude, power grid voltage frequency, and power grid voltage frequency variation. The control module determines the operating status of the power grid based on the power grid operating parameters, including: If the grid voltage amplitude is less than a first amplitude threshold or greater than a second amplitude threshold, or the grid voltage frequency is less than a first frequency threshold or greater than a second frequency threshold, or the grid voltage frequency change is less than a first change threshold or greater than a second change threshold, then the grid's operating state is abnormal; otherwise, the grid's operating state is normal; wherein, the first amplitude threshold is less than the second amplitude threshold, the first frequency threshold is less than the second frequency threshold, and the first change threshold is less than the second change threshold.

6. The grid-connected off-grid seamless switchover control method according to claim 5, characterized by, The electrical operating parameters include at least one of node voltage amplitude, node voltage frequency, and node voltage frequency variation. The power converter determines the operating status of the power grid based on the electrical operating parameters, including: If the node voltage amplitude is less than the third amplitude threshold or greater than the fourth amplitude threshold, or the node voltage frequency is less than the first frequency threshold or greater than the second frequency threshold, or the node voltage frequency change is less than the first change threshold or greater than the second change threshold, then the power grid is in an abnormal operating state; otherwise, the power grid is in a normal operating state; wherein the third amplitude threshold is less than the fourth amplitude threshold, the first frequency threshold is less than the second frequency threshold, and the first change threshold is less than the second change threshold.

7. The grid-connected off-grid seamless switchover control method according to claim 6, characterized by, The third amplitude threshold is less than the first amplitude threshold, the first amplitude threshold is less than the fourth amplitude threshold, and the fourth amplitude threshold is less than the second amplitude threshold.

8. The grid-connected to off-grid seamless switchover control method according to claim 3, characterized by, The switching module includes a thyristor, with a first end of the thyristor connected to the power grid and a second end of the thyristor connected to the power converter.

9. The grid-connected off-grid seamless switchover control method according to claim 8, characterized by, The control module detects the on / off state of the switch module by including: The control module acquires the voltage difference between the two ends of the thyristor or the first current of the thyristor; If the voltage difference between the thyristors is equal to the thyristor voltage, then the thyristor is in a conducting state; otherwise, the thyristor is in a disconnected state; or... If the first current is not equal to 0, the thyristor is in the on state; otherwise, the thyristor is in the off state.

10. The grid-connected off-grid seamless switchover control method according to claim 4, characterized by, The grid-connected to off-grid seamless switching system includes at least two power converters connected in parallel; each power converter is connected to the transformer and the control module. After each of the power converters receives the disconnection indication signal, the method further includes: The power converters communicate in parallel and start according to the disconnection indication signal in master-slave mode.

11. A grid-connected to off-grid seamless switching system, characterized in that, Includes a switching module, a control module, and a power converter; The power converter is connected to the power grid via the switching module; The control module and the power converter are used to detect the operating status of the power grid in parallel; The control module is used to control the switching module to disconnect when it detects that the operating state of the power grid is abnormal. The power converter is used to switch the operating mode to virtual synchronous generator mode when it detects that the operating state of the power grid is abnormal.

12. The grid-tie to off-grid seamless switchover system of claim 11, wherein, The power converter is also used to determine its own operating status after switching the operating mode to virtual synchronous generator mode, and to determine whether the switching of its operating mode was successful based on its own operating status.

13. The grid-tie to off-grid seamless switchover system of claim 11, wherein, The power converter is used to adjust the operating state to a shutdown state when the power converter operation mode switching fails; The control module is used to detect the on / off state of the switch module and generate a disconnection indication signal when the on / off state of the switch module is off. The power converter is used to start in virtual synchronous generator mode according to the disconnection indication signal.

14. The grid-connected off-grid seamless handover system according to any of claims 11-13, characterized in that, The power converter is an energy storage converter or an inverter.

15. An energy storage system characterized by, Includes the grid-connected to off-grid seamless switching system as described in any one of claims 11-14.

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