Network switching methods, coordination controllers and power systems

Abstract

This application discloses a microgrid switching method, a coordination controller, and a power system, relating to the field of power system control technology. The method is applied to a coordination controller in a microgrid, which includes a master station and multiple substations. The microgrid also includes multiple power plants, which converge at a bus and connect to the grid through a grid connection point. The method includes: acquiring bus-side operating parameters and grid-side operating parameters at the grid connection point in real time through the master station; obtaining the real-time short-circuit ratio of the system using a power flow algorithm; determining the grid strength of the microgrid based on the real-time short-circuit ratio using a hysteresis strategy; determining the target mode based on the system operating conditions and / or grid strength; generating a mode switching command based on the target mode and issuing the mode switching command to each substation, so that each substation issues the mode switching command to the corresponding power plant according to the grid strength, thereby realizing the switching of the microgrid control mode. This application achieves the technical effect of improving the flexibility of coordinated control and realizing better intelligent control.

Description

Technical Field

[0001] This application relates to the field of power system control technology, and in particular to a grid switching method, a coordination controller, and a power system. Background Technology

[0002] In power systems, microgrids, primarily powered by renewable energy, require coordinated controllers to manage and optimize the various energy sources within them. Currently, coordinated controllers mainly employ two methods: centralized control and distributed control. Centralized control is typically used in small-scale systems. However, as the system scales up, the communication demands of centralized control increase significantly, leading to communication bottlenecks and resulting in slow system response and insufficient flexibility. Distributed control, on the other hand, lacks global optimization capabilities, preventing optimal resource allocation and consequently impacting overall system performance. Summary of the Invention

[0003] The main purpose of this application is to provide a network switching method, a coordination controller, and a power system, aiming to solve the technical problem that the coordination control methods in related technologies lack flexibility and cannot achieve better intelligent control.

[0004] To achieve the above objectives, this application proposes a grid-connected switching method applied to a microgrid's coordination controller. The coordination controller includes a master station and multiple substations, each connected to the master station. The microgrid also includes multiple power stations, each connected to a corresponding substation. The power stations converge at a busbar, which is connected to the grid via a grid connection point. The grid-connected switching method includes:

[0005] The bus-side and grid-side operating parameters of the grid connection point are obtained in real time through the main station.

[0006] Using power flow algorithms, the real-time short-circuit ratio of the system is obtained based on the operating parameters of the bus side and the grid side.

[0007] The grid strength of the microgrid is determined based on the real-time short-circuit ratio of the system using a hysteresis strategy.

[0008] The target mode is determined based on the system operating conditions and / or grid strength; the target mode includes grid-connected mode or grid-following mode.

[0009] The mode switching command is generated according to the target mode and sent to each substation so that each substation can send the mode switching command to the corresponding field station according to the grid strength, thereby realizing the switching of microgrid control mode.

[0010] In one embodiment, the bus-side operating parameters include bus-side active power, bus-side reactive power, and bus-side current, while the grid-side operating parameters include grid-side active power and grid-side reactive power.

[0011] Using power flow algorithms, the real-time short-circuit ratio of the system is obtained based on the operating parameters of the bus side and the grid side, including:

[0012] Obtain the rated voltage at the grid connection point, the equivalent resistance of the power grid, the equivalent reactance of the power grid, the equivalent resistance at the grid connection point, and the equivalent reactance at the grid connection point;

[0013] The equivalent short-circuit impedance of the system is obtained by taking the square root of the sum of the first sum (obtained by summing the equivalent resistance of the power grid and the equivalent resistance at the grid connection point) and the second sum (obtained by summing the equivalent reactance of the power grid and the equivalent reactance at the grid connection point).

[0014] The real-time short-circuit ratio of the system is obtained by multiplying the rated voltage at the grid connection point by the product of the system's equivalent short-circuit impedance and the active power on the bus side.

[0015] In one embodiment, determining the target mode based on the system operating conditions includes:

[0016] When the system is operating under a grid fault condition, the target mode is determined to be the grid construction mode;

[0017] When the system is operating under microgrid grid connection conditions, the target mode is determined to be grid-connected mode;

[0018] When the system is operating under the condition of microgrid off-grid, the target mode is determined to be the grid construction mode;

[0019] When the system operates under the microgrid islanding black start condition, the target mode is determined to be the grid construction mode.

[0020] In one embodiment, determining the target mode based on system operating conditions and grid strength includes:

[0021] Determine whether a system scheduling command related to the system's operating condition has been received;

[0022] If so, the target mode is determined directly based on the system operating condition corresponding to the system scheduling instruction; otherwise, it is further determined whether the power grid intensity is a strong power grid.

[0023] If so, the process ends directly; otherwise, the target mode is determined based on the power grid strength.

[0024] In one embodiment, a hysteresis strategy is used to determine the grid strength of the microgrid based on the real-time short-circuit ratio of the system, including:

[0025] The real-time short-circuit ratio of the system is compared with the preset lower boundary and upper boundary of the hysteresis loop, respectively.

[0026] When the real-time short-circuit ratio of the system is less than or equal to the lower boundary of the hysteresis loop, the power grid strength is determined to be a weak power grid.

[0027] When the real-time short-circuit ratio of the system is greater than the lower boundary of the hysteresis loop and less than or equal to the upper boundary of the hysteresis loop, the power grid strength is determined to be a strong power grid.

[0028] When the real-time short-circuit ratio of the system is greater than the upper boundary of the hysteresis loop, the power grid strength is determined to be an extremely strong power grid.

[0029] The target mode is determined based on the power grid strength, including:

[0030] When the power grid strength is weak, the target mode is determined to be the grid construction mode;

[0031] When the power grid strength is a strong grid, the process ends directly.

[0032] When the grid strength is extremely strong, the target mode is determined to be the grid-following mode.

[0033] In one embodiment, each site includes multiple grid-connected inverters / converters and multiple grid-connected inverters / converters;

[0034] Based on the target mode, a mode switching command is generated and issued to each substation. This allows each substation to issue the mode switching command to the corresponding substation according to the grid strength, thereby achieving the switching of the microgrid control mode, including:

[0035] The main station generates a mode switching command based on the target mode and sends the mode switching command to each substation.

[0036] Each substation sends a mode switching command to one batch of the corresponding grid-connected inverters / converters or grid-connected inverters / converters, with the target mode being the first batch of inverters / converters in each site.

[0037] Determine whether the real-time determined power grid strength is a strong power grid;

[0038] If yes, then end directly; otherwise, return to the step of sending the mode switching command to the corresponding batch of multiple grid-connected inverters / converters or multiple grid-connected inverters / converters through each substation, with the target mode being the second batch of inverters / converters in each site, until the real-time determined grid strength is a strong grid.

[0039] In one embodiment, the multiple power stations include a photovoltaic power generation station, a wind turbine power generation station, and an energy storage station. The photovoltaic power generation station and the wind turbine power generation station each include multiple grid-connected inverters and multiple grid-connected inverters, and the energy storage station includes multiple grid-connected converters and multiple grid-connected converters.

[0040] The mode switching command is sent from each substation to a batch of the corresponding multiple grid-connected inverters / converters or multiple grid-connected inverters / converters, including:

[0041] The direction of network switching for mode switching commands is determined by each substation;

[0042] If the switching direction is from grid connection to grid construction, then the energy storage station is the primary switching target, and a batch of multiple grid-connected inverters is controlled to work until all multiple grid-connected inverters have been switched. Then, the photovoltaic power generation station and / or wind turbine power generation station are the secondary switching targets, and a batch of multiple grid-connected inverters is controlled to work.

[0043] If the grid connection switching direction is from grid connection to grid connection, then the photovoltaic power generation station and / or wind turbine power generation station are the primary switching targets, and a batch of multiple grid-connected inverters are controlled to work until all multiple grid-connected inverters have been switched. Then, the energy storage station is the secondary switching target, and a batch of multiple grid-connected converters are controlled to work.

[0044] To achieve the above objectives, this application also proposes a coordination controller for use in a microgrid, which further includes multiple power stations. The coordination controller includes a master station and multiple substations, with each substation connected to the master station and each substation corresponding to a power station. The multiple power stations converge at a busbar, which is connected to the power grid through a grid connection point.

[0045] The master station is used to implement the steps of the network switching method described above, and to control the operation of each substation.

[0046] In one embodiment, multiple substations communicate with the main station via the GOOSE protocol, and multiple substations communicate with multiple field stations via the GOOSE protocol.

[0047] Furthermore, to achieve the above objectives, this application also proposes an electric power system comprising:

[0048] A microgrid includes a coordinating controller and multiple substations as described above; a grid connection point switch; and a power grid. The coordinating controller is connected to multiple substations, which converge at a busbar, which is connected to the power grid via the grid connection point switch.

[0049] In addition, to achieve the above objectives, this application also proposes a storage medium that is a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, it implements the steps of the above-described network switching method.

[0050] One or more technical solutions proposed in this application have at least the following technical effects:

[0051] A grid-connection switching method is proposed and applied to a hierarchical distributed coordination controller. Combining the advantages of centralized and decentralized control, it enables efficient coordination and optimal resource allocation for microgrids, making it applicable to grid-connection switching control in large-scale microgrids. In this method, after real-time acquisition of bus-side and grid-side operating parameters at the grid connection point by the master station, the real-time short-circuit ratio of the system is calculated using a power flow algorithm. Then, a hysteresis strategy is employed to determine the grid strength of the microgrid based on the real-time short-circuit ratio. Finally, the target mode (grid-connection mode or grid-connection mode) is determined based on the system operating conditions and / or grid strength, simultaneously considering both system operating conditions and grid strength. This invention provides a more intelligent grid-based mode switching mechanism to determine target modes corresponding to different system operating conditions and / or different grid strengths, ensuring the safe and stable operation of the microgrid under various system operating conditions. It also generates mode switching commands based on the target mode and distributes these commands to each substation, enabling each substation to distribute the commands to the corresponding power stations based on grid strength, thus achieving microgrid control mode switching. The hierarchical distributed command distribution method optimizes the resource utilization efficiency of the coordinating controller, improving the system's dynamic response capability and operational stability. This application achieves the technical effect of improving collaborative control flexibility and realizing superior intelligent control. Attached Figure Description

[0052] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0053] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0054] Figure 1 This is a flowchart illustrating the first embodiment of the network switching method of this application;

[0055] Figure 2 A connection diagram of a power system provided in an embodiment of this application;

[0056] Figure 3 Another connection diagram of the power system provided in this application embodiment;

[0057] Figure 4 A connection diagram of an example power system provided in an embodiment of this application;

[0058] Figure 5 A connection diagram illustrating another example of a power system provided in this application embodiment;

[0059] Figure 6 This is a schematic diagram of the hysteresis strategy in the second embodiment of the network switching method of this application;

[0060] Figure 7 This is a flowchart illustrating an application example of the network switching method provided in this application embodiment.

[0061] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0062] It should be understood that the specific embodiments described herein are merely illustrative of the technical solutions of this application and are not intended to limit this application. To better understand the technical solutions of this application, a detailed description will be provided below in conjunction with the accompanying drawings and specific implementation methods.

[0063] Microgrids, primarily powered by renewable energy, are an emerging form of power system that requires coordinated controllers to manage and optimize various energy sources within the microgrid. Currently, coordinated controllers mainly employ two methods: centralized control and distributed control. Centralized control relies on a central control unit to issue commands to each converter. While effective in small-scale systems, the communication demands of centralized control increase significantly as the system scales up, leading to communication bottlenecks and potentially causing slow system response, insufficient flexibility, and single-point failure risks. Distributed control, while possessing strong self-adjustment capabilities and the ability to quickly respond to local disturbances, lacks global optimization capabilities, potentially resulting in suboptimal resource allocation and impacting overall system performance.

[0064] Therefore, current power systems often fail to fully consider the coordination between different types of converters during the collaborative control process, resulting in poor collaborative performance of the system under multiple energy access and different operating modes.

[0065] To address the aforementioned issues, this application proposes a network switching method, a coordination controller, and a power system.

[0066] In the embodiments of this application, for ease of description, the following detailed description will focus on the coordination controller of a microgrid in a power system.

[0067] It should be noted that, referring to Figure 2 , Figure 2 This is a schematic diagram of a power system, which can include microgrids, grid connection points, and the power grid. Microgrids are aggregated through busbars, which are connected to the power grid through grid connection points. A microgrid within a power system is an autonomous power system centered around distributed generation devices (such as photovoltaics and wind power) and energy storage devices, integrating load and energy management systems.

[0068] For example, such as Figure 2 As shown, a microgrid may include a coordination controller, multiple power stations, and loads. The coordination controller is connected to multiple power stations, and the power stations and loads converge at a busbar to connect to the grid connection point. The coordination controller may adopt a hierarchical distributed architecture, specifically including a master station and multiple substations. Each substation is connected to the master station, and each power station is correspondingly connected to a substation. The master station can be a computing service device with data processing, network communication, and program execution functions, such as a server, network terminal, embedded computer, industrial control computer, or other terminal device; it can also be a controller, control module, or control device including a memory, a processor, and a computer program stored in the memory and running on the processor, wherein the computer program is configured to implement the steps of the microgrid switching method described in this application embodiment. Substations can be of the same type as the master station for ease of communication and control.

[0069] This application provides a method for switching network structures.

[0070] With the increasing number of renewable energy units, grid strength is gradually weakening. To improve grid stability and inertia support capabilities, grid-connected wind, solar, and energy storage units are increasingly used in power plants. Unlike grid-connected units, grid-connected units can actively support the grid, providing frequency and voltage control, and building a stable power system under weak or no grid conditions. In this context, the coordination controller needs to have real-time grid strength detection and grid-connected switching capabilities to dynamically adjust the grid capacity of wind, solar, and energy storage power plants. However, most current coordination controllers do not consider this important requirement and cannot effectively cope with different grid strength conditions, leading to suboptimal system resource allocation and affecting system operating efficiency and security. Therefore, this application proposes a grid-connected switching method that can dynamically adjust the grid capacity of a microgrid.

[0071] In the first embodiment of the grid-connected switching method of this application, the method is applied to the coordination controller of a microgrid, including a master station and multiple substations. Each substation is connected to the master station. The microgrid also includes multiple power stations, each connected to a corresponding substation. These power stations converge at a busbar, which is connected to the power grid through a grid connection point. This grid-connected switching method can be specifically applied to the master station, and the master station can control each substation to perform corresponding operations, including controlling each substation to issue commands or issuing commands sequentially in batches.

[0072] Reference Figure 1 , Figure 1 This is a flowchart illustrating the first embodiment of the network switching method of this application. The network switching method may include steps S10 to S50:

[0073] Step S10: Obtain the bus-side operating parameters and grid-side operating parameters of the grid connection point in real time through the master station.

[0074] like Figure 2 As shown, the master station can connect to data acquisition points set up on both the bus side and the grid side of the grid connection point to collect operating parameters from both sides. A grid connection point switch can be installed at the grid connection point to clearly distinguish between the bus side and the grid side.

[0075] Step S20: Using a power flow algorithm, the real-time short-circuit ratio of the system is obtained based on the operating parameters of the bus side and the operating parameters of the grid side.

[0076] It should be noted that the system real-time short-circuit ratio (RSCR) can be calculated using existing power flow algorithms, or it can be calculated using the specific method of combining power flow algorithms mentioned later in the embodiments of this application.

[0077] Step S30: Using a hysteresis strategy, determine the grid strength of the microgrid based on the real-time short-circuit ratio of the system.

[0078] It should be noted that the grid strength of a microgrid can be divided and classified based on the specific value of the system's real-time short-circuit ratio. Hysteresis strategy is a nonlinear control method based on error range; by setting upper and lower thresholds, control action is triggered only when the error exceeds the threshold.

[0079] In this embodiment, a hysteresis strategy is used. First, the values ​​corresponding to the lower and upper boundaries of the hysteresis loop are set. Then, the calculated real-time short-circuit ratio of the system is compared with the lower and upper boundaries of the hysteresis loop, respectively, to determine the grid strength. Based on the hysteresis strategy, the grid strength can be divided into three different strengths: below the lower boundary is the first grid strength, between the lower and upper boundaries is the second grid strength, and above the upper boundary is the third grid strength. Alternatively, the grid strength can be directly divided into weak, strong, and extremely strong grids, which can be set according to actual needs.

[0080] It should also be noted that the aforementioned acquisition of bus-side and grid-side operating parameters is done in real time, and the grid strength determined here is also determined in real time. This includes the fact that when the substation executes the command issuance operation, the master station can also determine the grid strength in real time and then inform the substation, so that the substation can decide whether to continue issuing commands.

[0081] Step S40: Determine the target mode based on the system operating conditions and / or grid strength; the target mode includes grid-connected mode or grid-following mode.

[0082] It should be noted that the target mode is either grid-connected mode or grid-following mode. In grid-connected mode, the inverters at the power station can actively establish voltage and frequency references for the power grid, mimicking the characteristics of synchronous generators, providing inertia and voltage support for the system, and enhancing grid stability. For example, this can be used to achieve voltage regulation and frequency stabilization of new energy units in microgrids. In grid-following mode, the inverters at the power station can passively follow the parameters of the main grid by detecting the grid voltage and frequency. For example, this can be used to enable new energy units in microgrids to generate electricity in maximum power point tracking (MPPT) mode, thereby increasing the output of new energy units.

[0083] System operating conditions can be obtained from externally issued system dispatch commands or directly detected by the master station; no specific limitations are specified here. System operating conditions can include different scenarios such as grid faults, microgrid grid connection, microgrid off-grid operation, and microgrid islanding black start. The master station can determine the target mode based on the system operating conditions, which is a grid-connected switching strategy for different operating modes; it can also determine the target mode based on grid strength, which is a grid-connected switching strategy for different grid strengths; or it can determine the target mode based on both system operating conditions and grid strength, which is a grid-connected switching strategy for different operating modes and different grid strengths. The specific choice depends on actual needs.

[0084] Step S50: Generate a mode switching command based on the target mode and send the mode switching command to each substation so that each substation sends the mode switching command to the corresponding field station according to the grid strength, thereby realizing the switching of the microgrid control mode.

[0085] It should be noted that after the target mode is determined, the master station can generate a mode switching command and send it to each substation. In each substation, the substation can send the mode switching command to multiple inverters / converters in the corresponding field station, or it can send the mode switching command to a batch of multiple inverters / converters in the corresponding field station first, and then determine whether to continue to send the mode switching command to the next batch based on the real-time determined grid strength. That is, the substation can send the mode switching command at once, or send the mode switching command in batches.

[0086] Understandably, by using a hierarchical distributed control architecture, the master station and substation functions of the coordination controller are allocated according to specific needs, enabling effective coordination of different types of inverters / converters, optimizing resource allocation, improving system economy and operational stability, and achieving the effect of optimizing resource utilization efficiency. For different grid environments and system operating conditions, an intelligent grid switching method is proposed, enabling the system to flexibly switch grid modes under different operating conditions, ensuring the safe and stable operation of the power system.

[0087] This embodiment provides a grid-connected switching method applied to a hierarchical distributed coordination controller. Combining the advantages of centralized and decentralized control, it enables efficient coordination and optimized resource allocation for microgrids, making it suitable for grid-connected switching control in large-scale microgrids. In this method, after real-time acquisition of bus-side and grid-side operating parameters at the grid connection point by the master station, the real-time short-circuit ratio of the system is calculated using a power flow algorithm. Then, a hysteresis strategy is used to determine the grid strength of the microgrid based on the real-time short-circuit ratio. Finally, the target mode (grid-connected mode or grid-connected mode) is determined based on the system operating conditions and / or grid strength, simultaneously considering both system operating conditions and grid strength. This invention provides a more intelligent grid-based mode switching mechanism that determines the target mode for different system operating conditions and / or different grid strengths, ensuring the safe and stable operation of the microgrid under various system operating conditions. It also generates mode switching commands based on the target mode and distributes these commands to each substation, enabling each substation to distribute the commands to the corresponding substations based on grid strength, thus achieving microgrid control mode switching. The hierarchical distributed command distribution method optimizes the resource utilization efficiency of the coordinating controller, improving the system's dynamic response capability and operational stability. This application achieves the technical effect of improving collaborative control flexibility and realizing superior intelligent control.

[0088] In one feasible implementation, the microgrid may include at least one power generation substation and at least one energy storage substation, and multiple power stations may include at least one power generation power station and at least one energy storage power station. A master station is connected to each power generation substation and energy storage substation. At least one power generation substation is connected to at least one power generation power station, and each power station includes multiple grid-connected inverters and multiple grid-connected inverters. The energy storage substation is connected to the energy storage power station, and the energy storage power station includes multiple grid-connected converters and multiple grid-connected converters.

[0089] For example, refer to Figure 3 , Figure 3This embodiment provides another connection diagram of the power system. The power generation station can include different types of power generation stations such as photovoltaic power generation stations and wind turbine power generation stations. The photovoltaic power generation station includes multiple photovoltaic grid-connected inverters and multiple photovoltaic grid-connected inverters, while the wind turbine power generation station includes multiple wind turbine grid-connected inverters and multiple wind turbine grid-connected inverters. Correspondingly, the power generation substation can include different types of power generation coordination and control substations such as photovoltaic substations and wind turbine substations. The photovoltaic substation is communicatively connected to multiple photovoltaic grid-connected inverters and multiple photovoltaic grid-connected inverters, and the wind turbine substation is communicatively connected to multiple wind turbine grid-connected inverters and multiple wind turbine grid-connected inverters. The energy storage substation is connected to the energy storage station, which includes multiple energy storage grid-connected converters and multiple energy storage grid-connected converters. The energy storage substation is communicatively connected to both the grid-connected and grid-connected energy storage converters. Photovoltaic grid-connected inverters, photovoltaic grid-connected inverters, wind turbine grid-connected inverters, wind turbine grid-connected inverters, energy storage grid-connected converters, and energy storage grid-connected converters are all connected to the bus, that is, they are gathered on the bus side of the grid connection point. Specifically, they can be gathered at one end of the grid connection point switch, and the other end of the grid connection point switch is connected to the power grid or simulated power grid through the transmission line. This transmission line is the power grid side of the grid connection point.

[0090] like Figure 3 As shown, a microgrid may also include an Energy Management System (EMS). The EMS is connected to the master station of the coordinating controller. The master station can receive system dispatch instructions issued by the EMS, and of course, it can also receive system dispatch instructions sent by external systems.

[0091] This embodiment proposes a novel coordination controller with grid-connected switching capabilities. Employing a hierarchical distributed architecture, the controller comprises a master station and multiple wind, solar, and energy storage substations, combining the advantages of centralized and decentralized control. This architecture is suitable for large-scale microgrid systems. The hierarchical distributed architecture supports a control method that combines centralized and decentralized control, enabling the grid-connected switching method executed by this coordination controller to meet the requirements of power system flexibility and intelligent control.

[0092] For example, refer to Figure 4 , Figure 4 This is a connection diagram of an example power system provided in this embodiment, specifically illustrating the hierarchical distributed architecture of the coordination controller. Figure 4 In the diagram, dashed lines represent control and communication lines, while solid lines represent power lines. The coordination controller consists of a master coordination control station and multiple substations, such as those for wind, solar, and energy storage systems. This architecture can be applied to systems of different scales as needed, alleviating the communication pressure of centralized control modes while also accommodating the rapid self-adjustment of distributed control modes.

[0093] The coordination control master station, located between the EMS and the coordination control substations, is responsible for global scheduling and coordination control between different substations. It can receive system control commands from the EMS, collect status information from the grid connection point (including operating parameters on the bus side and grid side), and quickly synchronize and adjust all coordination control substations. The coordination control substations are responsible for coordination control between inverters / converters of the same type. They can receive mode switching commands from the coordination control master station, acquire status information from each inverter / converter, and quickly synchronize and adjust all corresponding inverters / converters, enabling local self-adjustment and improving the system's dynamic response capability. Among them, "inverters of the same type" refers to grid-connected inverters / converters belonging to the same power station or grid-connected inverters / converters belonging to the same power station. For example, photovoltaic grid-connected inverters 1-n are inverters of the same type belonging to photovoltaic power stations, and photovoltaic grid-connected inverters 1-n are another inverter of the same type belonging to photovoltaic power stations, both of which are connected to the photovoltaic coordination control substation; wind turbine grid-connected inverters 1-n are inverters of the same type belonging to wind farm stations, and wind turbine grid-connected inverters 1-n are another inverter of the same type belonging to wind farm stations, both of which are connected to the wind turbine coordination control substation; energy storage grid-connected inverters 1-n are inverters of the same type belonging to energy storage power stations, and energy storage grid-connected inverters 1-n are another inverter of the same type belonging to energy storage power stations, both of which are connected to the energy storage coordination control substation.

[0094] Understandably, adopting a hierarchical distributed control architecture allows for the allocation of functions between the coordination control master station and coordination control substations according to specific needs, thereby achieving efficient coordination and optimized resource allocation for each site.

[0095] In addition, the main station communicates with EMS via TCP / IP protocol, multiple substations communicate with the main station via GOOSE protocol, and multiple substations communicate with multiple field stations via corresponding GOOSE protocol.

[0096] For example, such as Figure 4 The EMS and the coordination control master station can interact via the TCP / IP protocol, which features high reliability, flexibility, and strong compatibility, ensuring accurate transmission of commands issued by the EMS and real-time feedback of data signals from the master station. Communication between the coordination control master station and the coordination control substation, and between the coordination control substation and the wind-solar-storage inverter, uses the GOOSE protocol. This protocol is characterized by strong real-time performance, high efficiency, and high reliability, enabling the transmission of control commands and data within milliseconds, making it particularly suitable for scenarios requiring rapid dynamic response.

[0097] like Figure 4As shown, a microgrid can also include multiple loads, which are aggregated on the bus together with the inverters / converters of wind, solar and energy storage power plants. The microgrid can also include a load monitoring and control unit, which is connected to the loads and to the coordination control master station. The load monitoring and control unit and the coordination control master station can also communicate using the GOOSE protocol to meet the needs of more power systems or microgrids.

[0098] In this example, the TCP / IP protocol supports wide-area communication, suitable for efficient interaction between the EMS and the master station; the GOOSE protocol focuses on local-area communication, ensuring rapid coordination between equipment at the master station, substations, and field stations. By combining the advantages of TCP / IP and GOOSE protocols, hierarchical optimized control is achieved, ensuring rapid coordination between the master station, substations, and field stations. This enhances the microgrid's response speed and regulation capability under external disturbances, ensuring the system remains stable in rapidly changing power environments, thus improving the system's dynamic response capability.

[0099] In this embodiment, the hierarchical distributed architecture of the coordinating controller can alleviate the communication pressure of centralized control, fully utilize the rapid response characteristics of distributed control, integrate multiple energy resources such as wind, solar, and energy storage, optimize resource utilization efficiency, and provide solid technical support for the efficient operation of the power system. Furthermore, the use of different communication methods can improve the dynamic response capability of the coordinating controller, ensuring that the microgrid can quickly adjust and remain stable in a rapidly changing power environment. Moreover, this method, as a system-level grid-connected switching strategy proposed by the coordinating controller for the inverters / converters of each power station, optimizes control from the source-grid-load-storage system level, ensuring the stable operation of the power system.

[0100] In one feasible implementation, the network switching method may further include steps S60-S70:

[0101] Step S60: When the target mode is network-following mode, detect the operating status of each station.

[0102] When switching to grid-connected mode, the coordinating controller monitors the operational status of both photovoltaic (PV) and wind turbine power stations. This monitoring can be done through their respective coordinating control substations, which then relay the data back to the master station. For example, the PV coordinating control substation monitors the operational status of the PV PV system and sends the data back to the master station; the wind turbine coordinating control substation monitors the operational status of the wind turbine power station and sends the data back to the master station. When the target mode is grid-connected mode, it is not necessary to monitor the operational status of each power station.

[0103] Step S70: The substation issues a mode switching command to the substation whose operating status meets the preset operating conditions, so as to switch the microgrid control mode to grid-following mode.

[0104] The substation can detect the operating status of the corresponding substation and feed it back to the master station. After receiving the feedback, the master station can identify whether the operating status of each substation meets the preset operating conditions. If it does, the master station controls the substation to take action. Specifically, the master station sends a mode switching command to the substation whose operating status meets the preset operating conditions so that the microgrid control mode is switched to grid-following mode. If the conditions are not met, the operation ends directly.

[0105] For example, for photovoltaic (PV) power plants, meeting preset operating conditions means that the light intensity and temperature meet preset light and temperature conditions. If the current light intensity and temperature of the PV power plant meet these conditions, the PV power plant continues to operate. At this time, the PV coordination control substation can control the PV grid-connected inverters to perform the corresponding grid-connected mode switch in response to the received mode switching command, i.e., the grid-connected switching command. For wind turbine power plants, meeting preset operating conditions means that the wind speed meets preset wind speed conditions. If the current wind speed of the wind turbine power plant meets these conditions, the wind turbine power plant continues to operate. At this time, the wind turbine coordination control substation can control the wind turbine grid-connected inverters to perform the corresponding grid-connected mode switch in response to the received mode switching command, i.e., the grid-connected switching command.

[0106] Based on the first embodiment of the network switching method of this application, in the second embodiment of the network switching method of this application, the same or similar content as the above embodiment can be referred to the above description, and will not be repeated hereafter. On this basis, the bus-side operating parameters may include the bus-side active power. P pcc Busbar side reactive power Q pcc and bus side current I pcc Grid-side operating parameters can include grid-side active power. P grid and grid-side reactive power Q grid .

[0107] Reference Figure 5 , Figure 5 The diagram illustrates another example of a power system connection. This power system may include a data acquisition device connected to a master station and to acquisition point A on the bus side and acquisition point B on the grid side of the grid connection point, respectively. This device is used to acquire bus-side operating parameters and grid-side operating parameters in real time and send them to the master station, so that the master station can receive and acquire the bus-side operating parameters and grid-side operating parameters of the grid connection point.

[0108] Because the power grid in a real-world scenario is not an ideal source and inherently possesses a certain short-circuit capacity, which is even more significant in harsh grid environments, the calculation of the system's real-time short-circuit ratio (RSCR) requires considering both the equivalent short-circuit impedance at the grid connection point and the equivalent short-circuit impedance of the power grid. Correspondingly, in Figure 5The diagram also shows an equivalent schematic between the grid connection point and the power grid, including the equivalent impedance of the grid connection point. Z pcc Equivalent impedance of the power grid Z grid .

[0109] In one possible implementation, step S20 may include steps S21 to S23:

[0110] Step S21: Obtain the rated voltage at the grid connection point, the equivalent resistance of the power grid, the equivalent reactance of the power grid, the equivalent resistance at the grid connection point, and the equivalent reactance at the grid connection point;

[0111] Step S22: Obtain the system equivalent short-circuit impedance by taking the square root of the sum of the squares of the first sum obtained by summing the equivalent resistance of the power grid and the equivalent resistance at the grid connection point and the second sum obtained by summing the equivalent reactance of the power grid and the equivalent reactance at the grid connection point.

[0112] Step S23: The real-time short-circuit ratio of the system is obtained by multiplying the rated voltage at the grid connection point by the product of the equivalent short-circuit impedance of the system and the active power on the bus side.

[0113] It should be noted that for the equivalent impedance of the power grid Z grid , The corresponding equivalent resistance of the power grid can be obtained. R grid Equivalent reactance of the power grid X grid For the equivalent impedance of the grid connection point Z pcc , The corresponding grid connection point equivalent resistance can be obtained. R pcc Equivalent reactance at grid connection point X pcc .

[0114] Then, the real-time equivalent short-circuit impedance of the system can be obtained using the formula for calculating the equivalent short-circuit impedance of the system. Z sc The calculation formula involved is:

[0115] .

[0116] Then, using the system's real-time short-circuit ratio calculation formula, based on the obtained grid connection point rated voltage... U n 2 and the active power on the bus side in the bus side operating parameters P pcc The real-time short-circuit ratio of the system can be obtained. RSCR The specific value involves the following calculation formula:

[0117] .

[0118] In one specific implementation, step S21, "obtaining the equivalent resistance of the power grid, the equivalent reactance of the power grid, the equivalent resistance at the grid connection point, and the equivalent reactance at the grid connection point," may include steps S21.1 to S21.4:

[0119] Step S21.1: Obtain the grid short-circuit capacity and grid quality factor;

[0120] Step S21.2: Obtain the equivalent short-circuit impedance of the power grid based on the ratio of the rated voltage at the grid connection point to the short-circuit capacity of the power grid;

[0121] Step S21.3: Obtain the equivalent resistance and equivalent reactance of the power grid based on the equivalent short-circuit impedance and the power grid quality factor; the calculation formulas involved are as follows:

[0122] ,

[0123] in, Q Indicates the power grid quality factor. R grid Represents the equivalent resistance of the power grid. X grid Represents the equivalent reactance of the power grid. Z grid Indicates the equivalent short-circuit impedance of the power grid;

[0124] Step S21.4: Obtain the equivalent resistance and equivalent reactance at the grid connection point based on the operating parameters on the bus side and the grid side; the calculation formulas involved are:

[0125] ,

[0126] in, R pcc Indicates the equivalent resistance at the grid connection point. X pcc Indicates the equivalent reactance at the grid connection point. P pcc Indicates the active power on the bus side. P grid Indicates the active power on the grid side. I pcc Indicates the current on the bus side. Q pcc Indicates the reactive power on the bus side. Q grid This indicates the reactive power on the grid side.

[0127] In practice, steps S21.1-S21.3 can be performed simultaneously with step S21.4 to obtain the equivalent resistance of the power grid at the same time.R grid Equivalent reactance of power grid X grid Equivalent resistance at grid connection point R pcc Equivalent reactance at grid connection point X pcc .

[0128] For example, the process of calculating the system real-time short-circuit ratio (RSCR) in step S20 will be described in detail:

[0129] First, based on the preset or known grid connection point rated voltage. U n 2 and grid short-circuit capacity S grid Obtain the equivalent short-circuit impedance of the power grid Z grid :

[0130] ;

[0131] Reuse of calculation formula:

[0132] ,

[0133] Based on the equivalent short-circuit impedance of the power grid Z grid and power grid quality factor Q Obtain the equivalent resistance of the power grid R grid Equivalent reactance of the power grid X grid Specifically, this process can be:

[0134] ,

[0135] ,

[0136] ,

[0137] ,

[0138] Therefore, the specific equivalent resistance of the power grid can be calculated. R grid Equivalent reactance of the power grid X grid ;

[0139] At the same time, using the calculation formula:

[0140] ,

[0141] Based on the active power on the bus side Ppcc Busbar side reactive power Q pcc Busbar side current I pcc Active power on the grid side P grid and grid-side reactive power Q grid Obtain the equivalent resistance at the grid connection point R pcc Equivalent reactance at grid connection point X pcc ;

[0142] Then, using the calculation formula:

[0143] ,

[0144] Based on the equivalent resistance of the power grid R grid Equivalent resistance at grid connection point R pcc Equivalent reactance of power grid X grid Equivalent reactance at grid connection point X pcc Obtain the system's equivalent short-circuit impedance Z sc ;

[0145] Finally, using the calculation formula:

[0146] ,

[0147] in, S sc This indicates the system's real-time short-circuit capacity, based on the rated voltage at the grid connection point. U n 2 System equivalent short-circuit impedance Z sc Active power on the bus side P pcc The real-time short-circuit ratio of the system was calculated. RSCR .

[0148] In this embodiment, considering that the system short-circuit capacity is often unknown, in order to solve the problem that the traditional SCR (Short-Circuit Ratio) cannot be calculated when the system short-circuit capacity is unknown, a specific calculation method is proposed that uses a power flow algorithm to calculate the system equivalent short-circuit impedance in real time, and then calculates the system real-time short-circuit ratio in real time, so that the grid strength can be determined in real time based on the real-time calculated system real-time short-circuit ratio; system equivalent short-circuit impedance Z scThe calculation takes into account both the equivalent impedance at the grid connection point and the equivalent impedance of the power grid, and adjusts for the short-circuit capacity of the actual power grid itself, enabling accurate measurement of grid strength in weak grid environments. Furthermore, traditional SCRs only reflect the grid strength of the generating unit at its rated output power; this embodiment uses the active power on the bus side. P pcc Instead of the rated power of the grid connection point, it can dynamically and accurately measure the changes in grid strength corresponding to different actual output power of the power generation station of the microgrid, which significantly improves the accuracy and applicability of grid strength assessment.

[0149] In one feasible implementation, step S30 may include steps S31 to S34:

[0150] Step S31: Compare the real-time short-circuit ratio of the system with the preset lower boundary and upper boundary of the hysteresis loop, respectively.

[0151] Step S32: When the real-time short-circuit ratio of the system is less than or equal to the lower boundary of the hysteresis loop, the power grid strength is determined to be a weak power grid.

[0152] Step S33: When the real-time short-circuit ratio of the system is greater than the lower boundary of the hysteresis loop and less than or equal to the upper boundary of the hysteresis loop, the power grid strength is determined to be a strong power grid.

[0153] Step S34: When the real-time short-circuit ratio of the system is greater than the upper boundary of the hysteresis loop, the power grid strength is determined to be an extremely strong power grid.

[0154] To ensure that the system does not repeatedly switch grid connection functions within a short period of time due to power plant output fluctuations, a hysteresis strategy is adopted to assess grid strength. The lower boundary r1 of the hysteresis can be determined according to the grid strength evaluation criteria shown in Table 1, or it can be determined by user definition.

[0155] Table 1

[0156]

[0157] As shown in Table 1, when the real-time short-circuit ratio of the system is less than 2, it belongs to an extremely weak power grid; when the real-time short-circuit ratio of the system is between 2 and 3, it belongs to a weak power grid; and when the real-time short-circuit ratio of the system is greater than 3, it belongs to a strong power grid.

[0158] Based on the requirement of grid switching, the system must always maintain a strong grid state. If it is not in a strong grid state, grid switching is required. Therefore, the value of the lower boundary r1 of the hysteresis loop can be set to 3. Of course, in practical applications, it can be flexibly adjusted according to the actual project. The upper boundary r2 of the hysteresis loop is related to the lower boundary r1 by r2 > r1. Based on this, the upper boundary r2 of the hysteresis loop can be determined in combination with the specific operating characteristics of the power plant. For example, for the example where r1=3, the value of the upper boundary r2 of the hysteresis loop can be set to 4 or 5.

[0159] Reference Figure 6 , Figure 6 This diagram illustrates the hysteresis strategy in this embodiment. The horizontal axis represents the specific value of the real-time short-circuit ratio of the system obtained in step S20, and the vertical axis represents the system grid capacity of the microgrid. For example, when the value of the real-time short-circuit ratio of the system is lower than the lower boundary r1 of the hysteresis strategy... RSCR When r1 ≤ r1, the current grid strength is determined to be a weak grid. In this case, the system needs to switch to grid-building mode to increase the capacity of the grid-building units. Therefore, when determining the target mode based on the grid strength, the target mode is grid-building mode. When the real-time short-circuit ratio of the system is between the lower boundary r1 and the upper boundary r2 of the hysteresis loop (i.e., r1 < r1), the system is considered to have a weak grid. RSCR When the current grid strength is ≤ r2, it is determined to be a strong grid. At this time, according to the hysteresis strategy, the unit's control module does not need to be changed, and the grid switching method can be directly terminated; when the real-time short-circuit ratio of the system is higher than the upper boundary r2 of the hysteresis, i.e. RSCR When the current grid strength is greater than r2, it is determined that the current grid strength is extremely strong. At this time, the system needs to switch to grid-following mode to improve the output of the generator set. Therefore, when determining the target mode based on the grid strength, the target mode is grid-following mode.

[0160] Understandably, using a hysteresis strategy to assess grid strength and defining the upper and lower boundaries of the hysteresis can ensure that the microgrid will not repeatedly switch its grid switching function in a short period of time due to fluctuations in the output of power generation stations.

[0161] In a first feasible implementation, step S40, "determine the target mode based on the system operating conditions," may include steps A1 to A4:

[0162] Step A1: When the system operating condition is a grid fault, determine the target mode as the grid construction mode;

[0163] Step A2: When the system is operating under microgrid grid connection conditions, the target mode is determined to be grid-connected mode;

[0164] Step A3: When the system is operating under the condition of microgrid off-grid, the target mode is determined to be the grid construction mode;

[0165] Step A4: When the system is operating under the microgrid islanding black start condition, the target mode is determined to be the grid construction mode.

[0166] It should be noted that during microgrid operation, grid fault conditions may occur, or grid-connected / off-grid switching functions may be required, or black start of power plants may be necessary. Therefore, target modes can be determined for different system operating conditions to adjust the power plant grid capacity according to different scenarios such as grid faults, microgrid grid connection, off-grid operation, and black start, thereby achieving system grid capacity adjustment for the microgrid. Specifically, microgrid islanding black start refers to the process of gradually restoring power supply when the microgrid is completely de-energized due to a fault or external grid outage (i.e., a "completely dark" state), without relying on the external grid or other power sources, solely through internal power sources with self-starting capabilities (such as energy storage stations, power generation stations, etc.).

[0167] In practical implementation, when a grid fault occurs, the grid strength generally weakens. At this time, generator sets are needed for voltage regulation and frequency stabilization, and the microgrid needs to switch to grid-connected control mode. Therefore, when the system operating condition is a grid fault, the target mode is grid-connected mode. When the microgrid is to be connected to the grid, the grid strength generally strengthens. At this time, generator sets are not needed for voltage regulation and frequency stabilization, but generator sets need to operate in maximum power point tracking (MPPT) mode as much as possible. The microgrid needs to switch to grid-following control mode. Therefore, when the system operating condition is a microgrid connected to the grid, the target mode is grid-following mode. When the microgrid is to be disconnected from the grid, the grid strength generally weakens. At this time, generator sets are needed for voltage regulation and frequency stabilization, and the microgrid needs to switch to grid-connected control mode. Therefore, when the system operating condition is a microgrid disconnected from the grid, the target mode is grid-connected mode. When the microgrid needs to undergo islanded black start, generator sets are needed as supporting power sources for voltage regulation and frequency stabilization, and the microgrid needs to switch to grid-connected control mode. Therefore, when the system operating condition is a microgrid islanded black start, the target mode is grid-connected mode. Optionally, when the target mode is grid-connected mode, the irradiance and temperature of power generation stations such as photovoltaic power stations and the wind speed of wind farm stations are also detected to ensure that their respective preset operating conditions are met before proceeding with subsequent steps.

[0168] In this embodiment, the target mode is specifically determined for different system operating conditions, so that the coordinated control of different power stations can be carried out stably under different operating conditions such as external disturbances, such as load changes, renewable energy fluctuations or faults, thereby ensuring that the power system can operate safely and stably under various operating conditions.

[0169] In a second feasible implementation, step S40, "determining the target mode based on grid strength," may include steps B1 to B3:

[0170] Step B1: When the grid strength is weak, the target mode is determined to be the grid construction mode;

[0171] Step B2: When the power grid strength is strong, the process ends directly.

[0172] Step B3: When the grid strength is extremely strong, the target mode is determined to be the grid-following mode.

[0173] It should be noted that after determining the grid strength through the aforementioned steps S31-S34, the target mode can be further determined based on the determined grid strength. This is related to the real-time short-circuit ratio of the system. RSCR When the value is less than or equal to the hysteresis lower boundary r1, the grid strength is considered weak, requiring a switch from microgrid control mode to grid-building mode. Therefore, the target mode is determined to be grid-building mode. The system's real-time short-circuit ratio... RSCR When the value exceeds the upper boundary r2 of the hysteresis loop, the grid strength is considered extremely strong, requiring a switch from microgrid control mode to grid-following mode. Therefore, the target mode is determined to be grid-connected mode. Optionally, when the target mode is grid-following mode, the irradiance and temperature of power generation stations such as photovoltaic power stations, and the wind speed of wind farms are also monitored to ensure they meet their respective preset operating conditions before proceeding with subsequent steps.

[0174] In this embodiment, the target mode is specifically determined for different grid strengths, which has a faster dynamic response speed and can improve the dynamic response capability of the system. Moreover, after calculating the real-time short-circuit ratio of the system and evaluating the grid strength using a hysteresis strategy, the target mode is determined in real time based on the evaluation results, which facilitates the subsequent issuance of corresponding mode switching commands and realizes intelligent grid-based mode switching.

[0175] In a third feasible implementation, step S40, "determining the target mode based on system operating conditions and grid strength," may include steps C1 to C3:

[0176] Step C1: Determine whether a system scheduling instruction related to the system's operating condition has been received;

[0177] Step C2: If a system scheduling instruction is received, the target mode is determined directly based on the system operating condition corresponding to the system scheduling instruction.

[0178] Step C3: If no system dispatch instruction is received, further determine whether the power grid strength is a strong grid.

[0179] Step C4: If the current power grid strength is a strong grid, then the process ends directly.

[0180] Step C5: If the current power grid strength is not a strong power grid, then determine the target mode based on the power grid strength.

[0181] It should be noted that the system dispatch command can be a command sent to the master station by an external system or the EMS in the microgrid. The command can contain a specific target mode or the current system operating condition. In other words, the command can be a command generated by an external system or the EMS based on the actual system operating condition of the power system, including but not limited to commands generated by manually operating relevant buttons or generated after detecting different system states.

[0182] In the specific implementation process, when determining the target mode based on the system operating conditions and grid strength, it is first determined whether there is a corresponding grid switching requirement for a higher priority system dispatch instruction. If so, the target mode is directly determined based on the system operating conditions corresponding to the system dispatch instruction, and subsequent mode switching instruction generation and issuance are executed. If not, it is determined based on the real-time obtained grid strength to determine whether there is a grid switching requirement. Specifically, it can be determined whether the current grid strength is a strong grid. If so, it means there is no grid switching requirement, and the process can be terminated directly. If not, it means the current grid strength does not meet the actual operating requirements, and a grid switching mode is required, and the target mode is determined accordingly based on the grid strength. The specific implementation method for determining the target mode based on the system operating conditions corresponding to the system dispatch instruction is described in steps A1-A4 above, and will not be repeated here. The specific implementation method for determining the target mode based on grid strength is described in steps B1-B3 above, and will not be repeated here.

[0183] In this implementation, the target mode is specifically determined by combining different system operating conditions and different grid strengths. This enables the power system to have an intelligent grid-connection switching mechanism when facing different grid strengths (e.g., strong grid, weak grid) and different system operating modes (e.g., off-grid, grid-connected, fault, black start), achieving flexible grid-connection mode switching. Furthermore, the early-stage dispatch planning can pre-convert the grid-connection switching mode according to system dispatch instructions, adaptively adjusting the grid capacity of power plants; the real-time grid strength detection switching mode can also fully consider the characteristics of real-time changes in system operation, using the system RSCR and the status of wind and solar power plants as the basis for decision-making, maintaining stable grid operation.

[0184] It should be noted that the above are only three feasible implementation methods of step S40 provided in this embodiment. This embodiment does not specifically limit the specific implementation method of step S40.

[0185] In one optional implementation, each site may include multiple grid-connected inverters / converters and multiple grid-connected inverters / converters; step S50 may include steps S51~S55:

[0186] Step S51: The main station generates a mode switching instruction based on the target mode and sends the mode switching instruction to each substation.

[0187] Step S52: Each substation sends a mode switching command to a batch of the corresponding grid-connected inverters / converters or grid-connected inverters / converters, with the target mode being the first batch of inverters / converters in each site.

[0188] Step S53: Determine whether the real-time determined power grid strength is a strong power grid;

[0189] Step S54: If the power grid strength is a strong grid, then the process ends directly.

[0190] Step S55: If the grid strength is not a strong grid, return to step S52, which sends the mode switching command to one batch of the corresponding multiple grid-connected inverters / converters or multiple grid-connected inverters / converters through each substation, with the control mode of the second batch of inverters / converters in each substation as the target mode, until the grid strength is determined to be a strong grid in real time.

[0191] It should be noted that the master station of the coordinating controller sends site-level mode switching commands to each substation. After receiving the commands, the substations gradually send them in batches to the inverters / converters of each wind, solar, and energy storage site. Assuming the number of inverters / converters in a site is n (which could be tens, hundreds, or even thousands), the switching quantity per batch can be set to 10%*n, thus allowing for gradual adjustment of the site's grid capacity. Furthermore, the switching can be stopped promptly when the real-time grid strength meets the requirements. The site's grid capacity refers to the total rated capacity of all grid-connected generator units in the entire microgrid, and is a key indicator for measuring the microgrid's scale and power supply capacity.

[0192] In practical applications, when switching subsequent batches, the process can stop either when the real-time determined grid strength is a strong grid, or when all inverters / converters have been switched. Specifically, in step S55, if the grid strength is not a strong grid, the process returns to step S52, using the control mode of the next batch of inverters / converters in each site as the target mode, until the real-time determined grid strength is a strong grid or until the control mode of all inverters / converters in all sites has been switched to the target mode.

[0193] Understandably, by first issuing instructions from the master station to each substation, and then using different substations to specifically execute the coordinated control of different site inverters / converters, the resource utilization efficiency of the coordination controller is improved and the power distribution is optimized.

[0194] In one alternative implementation, such as Figure 3As shown, multiple substations include photovoltaic substations, wind turbine substations, and energy storage substations, and multiple power stations include photovoltaic power generation power stations, wind turbine power generation power stations, and energy storage power stations. In step S51, when the master station issues mode switching commands to each substation, the issuance order can be determined based on the target mode. That is, when the master station issues power station-level mode switching commands to each substation, the issuance order and timing of the mode switching commands can be determined based on the specific network switching direction.

[0195] When the target mode is grid-connected mode, the master station can first send a command to the energy storage substation, instructing it to switch multiple grid-connected inverters or a batch of grid-connected inverters in the energy storage site to grid-connected mode. If multiple grid-connected inverters in the entire energy storage site have switched to grid-connected mode, and the real-time detected grid strength is still not a strong grid, then the command is sent to the photovoltaic substation and the wind turbine substation. The execution logic of these two substations is not sequential; each substation controls multiple grid-connected inverters or a batch of grid-connected inverters in its respective site to switch to grid-connected mode, until the grid strength becomes a strong grid or all inverters have been switched.

[0196] When the target mode is grid-connected mode, the master station can first send the command to the photovoltaic substation and the wind turbine substation. The execution logic of these two substations is not sequential. Each substation controls multiple grid-connected inverters or a batch of multiple grid-connected inverters in its respective field to switch to grid-connected mode. If the real-time grid strength is still not a strong grid after all inverters have been switched, the command is then sent to the energy storage substation, which switches multiple grid-connected converters or a batch of multiple grid-connected converters in the energy storage field to grid-connected mode until the grid strength becomes a strong grid or all converters have been switched.

[0197] Another alternative implementation, such as Figure 3 As shown, the multiple power stations include photovoltaic power generation stations, wind turbine power generation stations, and energy storage stations. Both photovoltaic and wind turbine power generation stations include multiple grid-connected inverters and multiple grid-connected inverters, while the energy storage stations include multiple grid-connected converters and multiple grid-connected converters. Step S52, "issuing mode switching commands to a batch of the corresponding multiple grid-connected inverters / converters or multiple grid-connected inverters / converters through each substation," can include steps S52.1 to S52.3:

[0198] Step S52.1: Determine the network switching direction of the mode switching command through each substation;

[0199] Step S52.2: If the grid switching direction is from grid-connected to grid-connected, then the energy storage station is the primary switching target, and a batch of multiple grid-connected inverters is controlled to work until all multiple grid-connected inverters have been switched. Then, the photovoltaic power generation station and / or wind turbine power generation station are the secondary switching targets, and a batch of multiple grid-connected inverters is controlled to work.

[0200] Step S52.3: If the grid connection switching direction is from grid connection to grid connection, then the photovoltaic power generation station and / or wind turbine power generation station are the main switching targets, and a batch of multiple grid-connected inverters are controlled to work until all multiple grid-connected inverters have been switched. Then, the energy storage station is the secondary switching target, and a batch of multiple grid-connected converters are controlled to work.

[0201] When the determined grid switching direction is from grid connection to grid construction, the energy storage substation is the primary switching target. The energy storage substation can control a batch of multiple grid-connected inverters in the energy storage substation to operate and switch the grid construction mode until all multiple grid-connected inverters have been switched. If the real-time detected grid strength is still not a strong grid, then the photovoltaic power generation substation and / or wind turbine power generation substation are the secondary switching targets. The photovoltaic substation and wind turbine substation each control a batch of multiple grid-connected inverters in their respective substations to switch to grid construction mode until the grid strength becomes a strong grid or all inverters have been switched.

[0202] When the determined grid connection switching direction is from grid connection to grid connection, the photovoltaic power generation station and / or wind turbine power generation station are the primary switching targets. The photovoltaic substation and wind turbine substation each control a batch of multiple grid-connected inverters in their respective stations to switch to grid connection mode. This continues until all multiple grid-connected inverters have been switched. If the real-time detected grid strength is still not a strong grid, then the energy storage station is the secondary switching target. The energy storage substation can control a batch of multiple grid-connected converters in the energy storage station to switch to grid connection mode. This continues until the grid strength becomes a strong grid or all converters have been switched.

[0203] In this implementation, mode switching commands are sent to multiple inverters or converters in batches to achieve phased mode switching. The coordination controller, based on a hierarchical distributed structure, issues the network mode switching commands. The master station of the coordination controller performs preliminary scheduling planning response, RSCR calculation, site condition analysis, and issues mode switching commands for different sites. The substations of the coordination controller gradually issue mode switching commands to the inverters / converters of the wind, solar, and energy storage sites in batches, switching 10% * the rated capacity of the site in each batch. This achieves the purpose of adjusting the network capacity of the sites, thereby realizing intelligent adjustment of the system network capacity of the entire microgrid.

[0204] For example, to help understand the implementation flow of the network switching method in the embodiments of this application, refer to Figure 7 , Figure 7 A flowchart illustrating an application example of a network switching method is provided, specifically:

[0205] First, the active power at the bus side of the grid connection point is collected synchronously. P pcc reactive powerQ pcc Current I pcc and the active power on the grid side. P grid reactive power Q grid The real-time short-circuit ratio of the system is calculated using power flow algorithms. RSCR The specific calculation method is described above and will not be repeated here. Then, the hysteresis strategy is used to evaluate the grid strength. The above process can be performed in real time to obtain the grid strength in real time.

[0206] Then, the coordination and control master station can determine the direction of the grid connection switching command, i.e., determine the target mode, based on the system operating conditions and / or grid strength; and detect the status of photovoltaic power plants and wind farms. The command direction includes switching to grid connection mode, switching to grid connection mode, and not switching; the detection operation is only performed when the command direction is to switch to grid connection mode. Specific determination methods include determining based solely on system operating conditions, determining based solely on grid strength, and determining based on both system operating conditions and grid strength, which can be selected according to actual needs. When the system is operating normally, the coordination and control master station directly determines the direction of the grid connection switching command based on grid strength; under certain specific system operating conditions, it determines the corresponding direction of the grid connection switching command for different system operating conditions. The system operating conditions can be detected by the coordination and control master station itself or fed back externally. When fed back externally, the external system can send corresponding system scheduling commands, causing the coordination and control master station to prioritize the grid connection switching based on the system scheduling commands.

[0207] Next, it is determined whether there is an external grid connection switching requirement. Since the system operating status can be obtained from externally sent system dispatch commands, if a system dispatch command is received and the target mode is determined based on the system operating status, it is considered that there is an external grid connection switching requirement. When an external grid connection switching requirement is determined, the coordination control master station directly executes the step of issuing a mode switching command based on the command direction and the status of the wind and solar power plants. If no system dispatch command is received, regardless of whether the target mode is determined based on the system operating status detected by the system itself or based on the grid strength, it is considered that there is no external grid connection switching requirement. When it is determined that there is no external grid connection switching requirement, the process jumps to the next judgment step.

[0208] Further determine whether the grid strength requirement is met. Specifically, compare the real-time obtained grid strength with the set grid strength requirement, such as a strong grid. If the grid strength requirement is met, i.e., the current grid strength is a strong grid, then there is no need to switch the microgrid control mode, and the process can be terminated directly; otherwise, execute the steps of the coordinated control master station issuing a mode switching command based on the command direction and the status of the wind and solar power plants.

[0209] The coordination and control master station issues mode switching commands based on the command direction and the status of the wind and solar power plants. The order of issuing mode switching commands is determined according to the direction of grid connection switching. When a power plant needs to switch from grid connection to grid connection, the energy storage power plant is the primary target for switching, followed by the solar and wind power plants; when a power plant needs to switch from grid connection to grid connection, the solar and wind power plants are the primary target for switching, followed by the energy storage power plant.

[0210] The wind-solar-storage coordination control substation receives mode switching commands and gradually distributes them in batches to the inverters / converters of each wind-solar-storage site to adjust the system grid capacity. The batch distribution method is described above and will not be repeated here.

[0211] Finally, determine whether the handover meets the criteria. Specifically, determine whether the grid strength is a strong grid and whether the system dispatch command's grid handover requirements have been completed. If the criteria are met, end the entire process; if not, return to the data collection step and repeat the entire process.

[0212] It should be noted that the above examples are only for understanding this application and do not constitute a limitation on this application and the network switching method. Any simple modifications based on this technical concept are within the protection scope of this application.

[0213] This application also provides a coordination controller, referring to... Figure 2 , Figure 3 and Figure 4 The coordination controller is applied to a microgrid, which also includes multiple power stations. The coordination controller may include a master station and multiple substations. The substations are connected to the master station and to the corresponding power stations. The power stations converge at a busbar, which is connected to the power grid through a grid connection point.

[0214] The master station is used to implement the steps of the grid switching method as described in any of the above embodiments, and to control the operation of each substation. Each substation is used to receive instructions from the master station and to control the inverters / converters of the corresponding field station. It should be noted that more functions and examples of the coordination controller can be found in the description of the specific implementation methods in the foregoing embodiments of the grid switching method, and will not be repeated here.

[0215] The coordination controller provided in this application, employing the network switching method described in the above embodiments, can solve the technical problem that the coordination control methods in related technologies lack flexibility and cannot achieve better intelligent control. Compared with related technologies, the beneficial effects of the coordination controller provided in this application are the same as those of the network switching method provided in the above embodiments, and other technical features of the coordination controller are the same as those disclosed in the network switching method of the above embodiments, and will not be repeated here.

[0216] This application also provides an electric system, referring to... Figure 2 , Figure 3 and Figure 4 The power system may include a microgrid, which includes a coordination controller and multiple power substations as described in the above embodiments; a grid connection point switch; and a power grid. The coordination controller is connected to multiple power substations, which converge at a busbar, which is connected to the power grid via the grid connection point switch. It should be noted that more functions and examples of the power system can be found in the descriptions of the specific implementation methods in the foregoing embodiments of the grid switching method, and will not be repeated here.

[0217] The power system provided in this application, employing the grid-connected switching method described in the above embodiments, can solve the technical problem that the coordinated control methods in related technologies lack flexibility and cannot achieve better intelligent control. Compared with related technologies, the beneficial effects of the power system provided in this application are the same as those of the grid-connected switching method provided in the above embodiments, and other technical features of this power system are the same as those disclosed in the grid-connected switching method of the above embodiments, and will not be repeated here.

[0218] It should be understood that the various parts disclosed in this application can be implemented using hardware, software, firmware, or a combination thereof. In the description of the above embodiments, specific features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples.

[0219] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0220] This application also provides a computer-readable storage medium having computer-readable program instructions (i.e., a computer program) stored thereon, the computer-readable program instructions being used to execute the network switching method in the above embodiments.

[0221] The computer-readable storage medium provided in this application may be, for example, a USB flash drive, but is not limited to, electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems or devices, or any combination thereof. More specific examples of computer-readable storage media may include, but are not limited to, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory) with one or more wires electrically connected, optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, etc., or any suitable combination thereof. In this embodiment, the computer-readable storage medium may be any tangible medium containing or storing a program that can be used by an instruction execution system or device, or a combination thereof. The program code contained on the computer-readable storage medium may be transmitted using any suitable medium, including but not limited to: wires, optical cables, RF (Radio Frequency), etc., or any suitable combination thereof.

[0222] The aforementioned computer-readable storage medium may be included in the coordination controller; or it may exist independently and not assembled into the coordination controller. The aforementioned computer-readable storage medium carries one or more programs, which, when executed by the coordination controller, enable the coordination controller to perform the functions defined in the network handover method disclosed in the embodiments of this application.

[0223] Computer program code for performing the operations of this application can be written in one or more programming languages ​​or a combination thereof. These programming languages ​​include object-oriented programming languages—such as Java, Smalltalk, and C++—and conventional procedural programming languages—such as the "C" language or similar programming languages. The program code can be executed entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving remote computers, the remote computer can be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or connected to an external computer, such as using an internet connection provided by an internet service provider.

[0224] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of methods, apparatuses, systems, and computer program products according to various embodiments of this application. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0225] The modules described in the embodiments of this application can be implemented in software or hardware. The names of the modules do not necessarily limit the functionality of the unit itself.

[0226] The storage medium provided in this application is a computer-readable storage medium, which stores computer-readable program instructions (i.e., a computer program) for executing the above-described network switching method. This addresses the technical problem that the coordination control methods in related technologies lack flexibility and cannot achieve better intelligent control. Compared with related technologies, the beneficial effects of the computer-readable storage medium provided in this application are the same as those of the network switching method provided in the above embodiments, and will not be elaborated upon here.

[0227] The above are only some embodiments of this application and do not limit the patent scope of this application. All equivalent structural transformations made under the technical concept of this application and using the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included in the patent protection scope of this application.

Claims

1. A method for switching network structures, characterized in that, A coordination controller for a microgrid includes a master station and multiple substations, each of which is connected to the master station. The microgrid also includes multiple power stations, which are connected to the substations. The power stations converge at a busbar, which is connected to the power grid through a grid connection point. The plurality of substations includes at least one generator substation and an energy storage substation, and the plurality of substations are respectively connected to the main station, specifically: the main station is respectively connected to each generator substation and energy storage substation; The plurality of power stations include at least one power generation power station and one energy storage power station. The plurality of power stations are connected to the plurality of substations in a corresponding manner, specifically: the at least one power generation power station is connected to the at least one power generation power station, and the energy storage substation is connected to the energy storage power station. Each of the power generation stations includes multiple grid-connected inverters and multiple grid-connected inverters. The at least one power generation substation is connected to the at least one power generation station. Specifically, each power generation substation is communicatively connected to the multiple grid-connected inverters and multiple grid-connected inverters within the corresponding power generation station. The energy storage station includes multiple grid-connected converters and multiple grid-connected converters. The energy storage substation is connected to the energy storage station, specifically: the energy storage substation is communicatively connected to the multiple grid-connected converters and the multiple grid-connected converters respectively. The network handover method includes: The main station obtains the bus-side operating parameters and grid-side operating parameters of the grid connection point in real time. Using a power flow algorithm, the real-time short-circuit ratio of the system is obtained based on the operating parameters of the bus side and the operating parameters of the power grid side; The grid strength of the microgrid is determined based on the real-time short-circuit ratio of the system using a hysteresis strategy. The target mode is determined based on the system operating conditions and / or the power grid strength; the target mode includes a grid-building mode or a grid-following mode. A mode switching instruction is generated according to the target mode, and the mode switching instruction is sent to each substation so that each substation sends the mode switching instruction to the corresponding field station according to the grid strength, thereby realizing the switching of microgrid control mode.

2. The network switching method as described in claim 1, characterized in that, The bus-side operating parameters include bus-side active power, bus-side reactive power, and bus-side current; the grid-side operating parameters include grid-side active power and grid-side reactive power. The method of using a power flow algorithm to obtain the real-time short-circuit ratio of the system based on the bus-side operating parameters and the grid-side operating parameters includes: Obtain the rated voltage at the grid connection point, the equivalent resistance of the power grid, the equivalent reactance of the power grid, the equivalent resistance at the grid connection point, and the equivalent reactance at the grid connection point; The equivalent short-circuit impedance of the system is obtained by taking the square root of the sum of the squares of the first sum obtained by summing the equivalent resistance of the power grid and the equivalent resistance of the grid connection point and the second sum obtained by summing the equivalent reactance of the power grid and the equivalent reactance of the grid connection point. The real-time short-circuit ratio of the system is obtained by multiplying the rated voltage at the grid connection point by the product of the equivalent short-circuit impedance of the system and the active power on the bus side.

3. The network switching method as described in claim 1, characterized in that, Determining the target mode based on the system's operating conditions includes: When the system is operating under a grid fault condition, the target mode is determined to be the grid construction mode; When the system is operating under microgrid grid connection conditions, the target mode is determined to be grid-connected mode; When the system is operating under the condition of microgrid off-grid, the target mode is determined to be grid construction mode; When the system operates under the condition of microgrid islanding black start, the target mode is determined to be the grid construction mode.

4. The network switching method as described in claim 1, characterized in that, The determination of the target mode based on the system operating conditions and the power grid strength includes: Determine whether a system scheduling command related to the system's operating condition has been received; If so, the target mode is determined directly based on the system operating condition corresponding to the system scheduling instruction; otherwise, it is further determined whether the power grid strength is a strong power grid. If so, the process ends directly; otherwise, the target mode is determined based on the power grid strength.

5. The network switching method as described in claim 1 or 4, characterized in that, The method of determining the grid strength of the microgrid based on the real-time short-circuit ratio of the system using a hysteresis strategy includes: The real-time short-circuit ratio of the system is compared with the preset lower boundary and upper boundary of the hysteresis loop, respectively. When the real-time short-circuit ratio of the system is less than or equal to the lower boundary of the hysteresis loop, the power grid strength is determined to be a weak power grid. When the real-time short-circuit ratio of the system is greater than the lower boundary of the hysteresis loop and less than or equal to the upper boundary of the hysteresis loop, the power grid strength is determined to be a strong power grid. When the real-time short-circuit ratio of the system is greater than the upper boundary of the hysteresis loop, the power grid strength is determined to be an extremely strong power grid. The step of determining the target mode based on the power grid strength includes: When the power grid strength is a weak grid, the target mode is determined to be the grid construction mode; When the power grid strength is a strong grid, the process ends directly. When the power grid strength is extremely strong, the target mode is determined to be the grid-following mode.

6. The network switching method as described in claim 5, characterized in that, Each of the aforementioned stations includes multiple grid-connected inverters / converters and multiple grid-connected inverters / converters; The step of generating a mode switching command based on the target mode and issuing the mode switching command to each substation, so that each substation issues the mode switching command to the corresponding field station according to the grid strength, thereby realizing the switching of the microgrid control mode, includes: The main station generates a mode switching instruction based on the target mode and sends the mode switching instruction to each substation. The mode switching command is sent from each of the substations to the corresponding plurality of grid-connected inverters / converters or a batch of the plurality of grid-connected inverters / converters, so as to switch the control mode of the first batch of inverters / converters in each site to the target mode. Determine whether the power grid strength determined in real time is a strong power grid; If yes, then end directly; otherwise, return to the step of issuing the mode switching command to the corresponding batch of multiple grid-connected inverters / converters or multiple grid-connected inverters / converters through each of the substations, so as to switch the control mode of the second batch of inverters / converters in each site to the target mode, until the real-time determined grid strength is a strong grid.

7. The network switching method as described in claim 6, characterized in that, The multiple power stations include photovoltaic power generation stations, wind turbine power generation stations, and energy storage stations. Both the photovoltaic power generation stations and the wind turbine power generation stations include multiple grid-connected inverters and multiple grid-connected inverters. The step of sending the mode switching command through each of the substations to the corresponding plurality of grid-connected inverters / converters or a batch of the plurality of grid-connected inverters / converters includes: The network switching direction of the mode switching instruction is determined by each of the substations; If the grid switching direction is from grid connection to grid connection, then the energy storage station is the primary switching target, and a batch of the multiple grid-connected inverters is controlled to work until all the multiple grid-connected inverters have been switched. Then, the photovoltaic power generation station and / or the wind turbine power generation station are the secondary switching targets, and a batch of the multiple grid-connected inverters is controlled to work. If the grid connection switching direction is from grid connection to grid connection, then the photovoltaic power generation station and / or the wind turbine power generation station are the primary switching targets, and a batch of the multiple grid-connected inverters are controlled to work until all the multiple grid-connected inverters have been switched. Then, the energy storage station is the secondary switching target, and a batch of the multiple grid-connected converters are controlled to work.

8. A coordination controller, characterized in that, The system is applied to a microgrid, which also includes multiple power stations; the coordination controller includes a master station and multiple substations, each of which is connected to the master station and correspondingly connected to the multiple power stations, which converge at a busbar, and the busbar is connected to the power grid through a grid connection point; The master station is used to implement the steps of the network switching method as described in any one of claims 1 to 7, and to control the operation of each of the substations.

9. The coordination controller as claimed in claim 8, characterized in that, The multiple substations are connected to the master station via the GOOSE protocol, and the multiple substations are connected to the multiple field stations via the GOOSE protocol.

10. An electric power system, characterized in that, include: A microgrid, comprising a coordination controller as described in claim 8 or 9 and multiple field stations; Grid connection point switch; Power grid; The coordination controller is connected to the plurality of power stations, which converge at a busbar, and the busbar is connected to the power grid via the grid connection point switch.

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