Configuration following network switching method, coordination controller and electric power system

Abstract

The invention discloses a network following and constructing switching method, a coordination controller and a power system, and relates to the technical field of power system control, the method is applied to the coordination controller of a micro-grid, the coordination controller comprises a master station and a plurality of substations, the micro-grid further comprises a plurality of stations, and the plurality of stations are gathered on a bus and then are connected with a power grid through a grid-connected point; the method comprises the following steps: acquiring bus side working parameters and power grid side working parameters of a grid-connected point in real time through a master station; a system real-time short-circuit ratio is obtained by using a power flow algorithm; determining the power grid strength of the micro-grid according to the real-time short-circuit ratio of the system by using a hysteresis strategy; determining a target mode according to the system operation condition and / or the power grid strength; and generating a mode switching instruction according to the target mode, and issuing the mode switching instruction to each substation, so that each substation issues the mode switching instruction to the corresponding station according to the power grid strength, and switching of the micro-grid control mode is realized. According to the invention, the technical effects of improving the cooperative control flexibility and realizing better intelligent control are realized.

Description

Technical Field

[0001] The present application relates to the technical field of power system control, and particularly relates to a structure-following network switching method, a coordination controller, and a power system. Background Art

[0002] In a power system, a microgrid mainly composed of renewable energy needs to perform collaborative optimization management on various types of energy therein through a coordination controller. Currently, the coordination controller mainly adopts two methods: centralized control and decentralized control. The centralized control method usually operates in a small-scale system. If the system scale expands, the communication requirements of the centralized control method will increase significantly, causing communication bottlenecks, resulting in slow system response and insufficient flexibility. The decentralized control method lacks the ability of global optimization, resulting in suboptimal resource allocation, which in turn affects the overall performance of the system. Summary of the Invention

[0003] The main purpose of the present application is to provide a structure-following network switching method, a coordination controller, and a power system, aiming to solve the technical problems of insufficient flexibility and inability to achieve better intelligent control in the coordination control method in the related art.

[0004] To achieve the above purpose, the present application proposes a structure-following network switching method, which is applied to a coordination controller of a microgrid. The coordination controller includes a master station and multiple slave stations, and the multiple slave stations are respectively connected to the master station. The microgrid further includes multiple power stations, and the multiple power stations are correspondingly connected to the multiple slave stations. The multiple power stations converge on a bus, and the bus is connected to the power grid through a connection point; the structure-following network switching method includes: Obtaining the working parameters on the bus side and the working parameters on the grid side of the connection point in real time through the master station; Using a power flow algorithm, obtaining the real-time short-circuit ratio of the system according to the working parameters on the bus side and the working parameters on the grid side; Using a hysteresis strategy, determining the grid strength of the microgrid according to the real-time short-circuit ratio of the system; Determining a target mode according to the system operating conditions and / or the grid strength; the target mode includes a structure network mode or a following network mode; Generating a mode switching instruction according to the target mode, and sending the mode switching instruction to each slave station, so that each slave station sends the mode switching instruction to the corresponding power station according to the grid strength, realizing the switching of the microgrid control mode.

[0005] In an embodiment, the working parameters on the bus side include the active power on the bus side, the reactive power on the bus side, and the current on the bus side, and the working parameters on the grid side include the active power on the grid side and the reactive power on the grid side; Using a power flow algorithm, obtaining the real-time short-circuit ratio of the system according to the working parameters on the bus side and the working parameters on the grid side, includes: Obtain the rated voltage of the grid connection point, the equivalent resistance of the power grid, the equivalent reactance of the power grid, the equivalent resistance of the grid connection point, and the equivalent reactance of the grid connection point; Obtain the system equivalent short-circuit impedance according to the square root of the sum of the squares of the first sum value obtained by summing the equivalent resistance of the power grid and the equivalent resistance of the grid connection point and the second sum value obtained by summing the equivalent reactance of the power grid and the equivalent reactance of the grid connection point; Obtain the system real-time short-circuit ratio according to the ratio between the product obtained by multiplying the rated voltage of the grid connection point by the system equivalent short-circuit impedance and the active power on the bus side.

[0006] In one embodiment, determining the target mode according to the system operating conditions includes: When the system operating condition is a power grid fault, determine the target mode as the grid-forming mode; When the system operating condition is a microgrid grid connection, determine the target mode as the grid-following mode; When the system operating condition is a microgrid islanding, determine the target mode as the grid-forming mode; When the system operating condition is a microgrid island black start, determine the target mode as the grid-forming mode.

[0007] In one embodiment, determining the target mode according to the system operating conditions and the power grid strength includes: Judge whether a system dispatch instruction related to the system operating conditions is received; If so, directly determine the target mode according to the system operating conditions corresponding to the system dispatch instruction; otherwise, further judge whether the power grid strength is a strong power grid; If so, directly end; otherwise, determine the target mode according to the power grid strength.

[0008] In one embodiment, using the hysteresis strategy to determine the power grid strength of the microgrid according to the system real-time short-circuit ratio includes: Compare the system real-time short-circuit ratio with the preset hysteresis lower boundary and the hysteresis upper boundary respectively; When the system real-time short-circuit ratio is less than or equal to the hysteresis lower boundary, determine that the power grid strength is a weak power grid; When the system real-time short-circuit ratio is greater than the hysteresis lower boundary and less than or equal to the hysteresis upper boundary, determine that the power grid strength is a strong power grid; When the system real-time short-circuit ratio is greater than the hysteresis upper boundary, determine that the power grid strength is an extremely strong power grid; Determining the target mode according to the power grid strength includes: When the power grid strength is a weak power grid, determine the target mode as the grid-forming mode; When the power grid strength is a strong power grid, directly end; When the power grid strength is an extremely strong power grid, determine the target mode as the grid-following mode.

[0009] In one embodiment, each substation includes a plurality of grid-following inverters / converters and a plurality of grid-forming inverters / converters; Generate a mode switching instruction according to the target mode, and send the mode switching instruction to each substation, so that each substation sends the mode switching instruction to the corresponding substation according to the grid strength, and realize the switching of the microgrid control mode, including: Generate a mode switching instruction by the master station according to the target mode, and send the mode switching instruction to each substation; Send the mode switching instruction to a batch of corresponding multiple grid-following inverters / converters or multiple grid-forming inverters / converters by each substation, so as to switch the control mode of the first batch of inverters / converters in each substation to the target mode; Judge whether the grid strength determined in real time is a strong grid; If so, directly end; otherwise, return to the step of sending the mode switching instruction to a batch of corresponding multiple grid-following inverters / converters or multiple grid-forming inverters / converters by each substation, so as to switch the control mode of the second batch of inverters / converters in each substation to the target mode until the grid strength determined in real time is a strong grid.

[0010] In one embodiment, the multiple substations include a photovoltaic power generation substation, a wind power generation substation and an energy storage substation. The photovoltaic power generation substation and the wind power generation substation both include a plurality of grid-following inverters and a plurality of grid-forming inverters, and the energy storage substation includes a plurality of grid-following converters and a plurality of grid-forming converters; Sending the mode switching instruction to a batch of corresponding multiple grid-following inverters / converters or multiple grid-forming inverters / converters by each substation includes: Determine the grid-forming switching direction of the mode switching instruction by each substation; If the grid-forming switching direction is from grid-following to grid-forming, take the energy storage substation as the main switching object, control a batch of multiple grid-forming converters to work, and when all the multiple grid-forming converters are switched, then take the photovoltaic power generation substation and / or the wind power generation substation as the secondary switching object, and control a batch of multiple grid-forming inverters to work; If the grid-forming switching direction is from grid-forming to grid-following, take the photovoltaic power generation substation and / or the wind power generation substation as the main switching object, control a batch of multiple grid-following inverters to work, and when all the multiple grid-following inverters are switched, then take the energy storage substation as the secondary switching object, and control a batch of multiple grid-following converters to work.

[0011] To achieve the above object, the present application also proposes a coordination controller, which is applied to a microgrid, and the microgrid also includes a plurality of substations; the coordination controller includes a master station and a plurality of sub-stations, the plurality of sub-stations are respectively connected to the master station, the plurality of sub-stations are correspondingly connected to the plurality of substations, the plurality of substations converge on a bus, and the bus is connected to the grid through a connection point; The master station is used to implement the steps of the structure-following network switching method as described above, and to control the operation of each slave station.

[0012] In one embodiment, multiple slave stations are respectively communicatively connected to the master station through the GOOSE protocol, and multiple slave stations are communicatively connected to multiple substations through the GOOSE protocol correspondingly.

[0013] In addition, to achieve the above object, the present application also proposes a power system, including: A microgrid, which includes a coordination controller and multiple substations as described above; a grid connection point switch; and a power grid; wherein, the coordination controller is connected to multiple substations, multiple substations converge on a bus, and the bus is connected to the power grid through the grid connection point switch.

[0014] In addition, to achieve the above object, the present application also proposes a storage medium, which is a computer-readable storage medium, and a computer program is stored on the storage medium. When the computer program is executed by a processor, the steps of the structure-following network switching method as described above are implemented.

[0015] One or more technical solutions proposed by the present application have at least the following technical effects: A structure-following network switching method is proposed, which is applied to a hierarchical distributed coordination controller, combines the advantages of centralized control and decentralized control, and can achieve efficient coordination and resource optimization configuration of the microgrid, so that it can be applied to the structure-following network switching control of large-scale microgrids; in this method, after the master station obtains the bus-side working parameters and grid-side working parameters of the grid connection point in real time, the real-time short-circuit ratio of the system is calculated by using the power flow algorithm, and then the hysteresis strategy is used to determine the grid strength of the microgrid according to the real-time short-circuit ratio of the system, and then the target mode is determined as the structure mode or the following network mode according to the system operating conditions and / or grid strength, which can take into account both the system operating conditions and the grid strength, and determine the target mode correspondingly according to different system operating conditions and / or different grid strengths, providing a more intelligent structure-following network mode switching mechanism, and can ensure the safe and stable operation of the microgrid under various system operating conditions; a mode switching instruction is also generated according to the target mode, and the mode switching instruction is sent to each slave station, so that each slave station sends the mode switching instruction to the corresponding substation according to the grid strength, realizing the switching of the microgrid control mode. The hierarchical distributed instruction sending method optimizes the resource utilization efficiency of the coordination controller and can improve the dynamic response ability and operation stability of the system; the present application realizes the technical effects of improving the coordination flexibility and achieving better intelligent control. Description of the Drawings

[0016] The drawings here are incorporated into the specification and constitute a part of this specification, showing the embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0017] To more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the accompanying drawings required for the description of the embodiments. Obviously, for those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0018] Figure 1 It is a schematic flowchart of the first embodiment of the structure network switching method of the present application; Figure 2 It is a connection schematic diagram of a power system provided by an embodiment of the present application; Figure 3 It is another connection schematic diagram of a power system provided by an embodiment of the present application; Figure 4 It is a connection schematic diagram of an example of a power system provided by an embodiment of the present application; Figure 5 It is another connection schematic diagram of an example of a power system provided by an embodiment of the present application; Figure 6 It is a schematic diagram of the hysteresis strategy in the second embodiment of the structure network switching method of the present application; Figure 7 It is a schematic flowchart of an application example of the structure network switching method provided by an embodiment of the present application.

[0019] The realization of the purpose of the present application, functional features and advantages will be further described with reference to the embodiments and the accompanying drawings. Detailed Embodiments

[0020] It should be understood that the specific embodiments described herein are only used to explain the technical solutions of the present application and are not used to limit the present application. To better understand the technical solutions of the present application, the following will be described in detail in combination with the specification drawings and specific embodiments.

[0021] As an emerging form of power system, the microgrid mainly based on renewable energy needs to carry out collaborative optimization management of various types of energy in the microgrid through a coordination controller. At present, the coordination controller mainly adopts two methods: centralized control and decentralized control. The centralized control method relies on the central control unit to issue instructions to each converter and can usually operate effectively in a small-scale system. If the system scale expands, the communication requirements of the centralized control method will increase significantly, causing communication bottlenecks, which may lead to slow system response, insufficient flexibility and the risk of single-point failure. The decentralized control method, although having strong self-adjustment ability and being able to quickly respond to local disturbances, lacks global optimization ability, which may lead to sub-optimal resource allocation and thus affect the overall performance of the system.

[0022] Therefore, in the current power system during the coordinated control process, the coordination between different types of converters is often not fully considered, resulting in poor coordination effects of the system under multiple energy accesses and different operating modes.

[0023] In view of the above problems, embodiments of the present application propose a structure-following network switching method, a coordination controller, and a power system.

[0024] In the embodiments of the present application, for the convenience of description, the following elaborates in detail with the coordination controller of the microgrid in the power system as the execution subject.

[0025] It should be noted that with reference to Figure 2 , Figure 2 which is a connection schematic diagram of a power system, the power system may include a microgrid, a connection point, and a power grid. The microgrid is aggregated through a bus, and the bus is connected to the power grid through the connection point. The microgrid in the power system is an autonomous power system centered on distributed generation devices (such as photovoltaic and wind power) and energy storage devices, and integrates loads, an energy management system, etc.

[0026] Exemplarily, as Figure 2 shown, the microgrid may include a coordination controller, multiple stations, and loads. The coordination controller is respectively connected to the multiple stations, and the multiple stations and loads are aggregated at the bus to be connected to the connection point through the bus. Among them, the coordination controller may adopt a hierarchical distributed architecture, specifically including a master station and multiple slave stations. The multiple slave stations are respectively connected to the master station, and the multiple stations are correspondingly connected to the multiple slave stations. The master station may be a computing service device with data processing, network communication, and program running functions, such as terminal devices like servers, network terminals, embedded computers, industrial control computers, etc.; or it may be a controller, a control module, or a control device including a memory, a processor, and a computer program stored in the memory and running on the processor, and the computer program is configured to implement the steps of the structure-following network switching method of the embodiments of the present application. The slave stations may be of the same type as the master station, which is convenient for communication and control.

[0027] Embodiments of the present application provide a structure-following network switching method.

[0028] With the increasing number of renewable energy units, the grid strength gradually weakens. To improve the stability and inertia support ability of the grid, grid-forming wind-solar-storage units are gradually increasing in substations. Different from grid-following units, grid-forming units can actively support the grid, provide frequency and voltage control, and build a stable power system under weak-grid or off-grid conditions. In this context, the coordination controller needs to have the functions of real-time detecting grid strength and grid-forming / grid-following switching to dynamically adjust the grid-forming capacity of the wind-solar-storage substation. However, most of the current coordination controllers do not consider this important requirement and cannot effectively respond to different grid strength conditions, resulting in non-optimal system resource allocation, thus affecting the system operation efficiency and security. Therefore, the embodiment of this application proposes a grid-forming / grid-following switching method that can dynamically adjust the grid-forming capacity of the microgrid.

[0029] In the first embodiment of the grid-forming / grid-following switching method of this application, the grid-forming / grid-following switching method is applied to the coordination controller of the microgrid, which includes a master station and multiple slave stations. The multiple slave stations are respectively connected to the master station. The microgrid also includes multiple substations, and the multiple substations are correspondingly connected to the multiple slave stations. The multiple substations converge at the bus, and the bus is connected to the grid through the connection point. This grid-forming / grid-following switching method can be specifically applied to the master station, and the master station can control each slave station to perform corresponding operations, including controlling each slave station to perform instruction issuing operations or instruction successive batch issuing operations.

[0030] Refer to Figure 1 , Figure 1 which is the schematic flowchart of the first embodiment of the grid-forming / grid-following switching method of this application. This grid-forming / grid-following switching method can include steps S10 to S50: Step S10, the master station obtains the bus-side working parameters and grid-side working parameters of the connection point in real time.

[0031] As Figure 2 shown, the master station can be connected to the collection points respectively set on the bus side and grid side of the connection point to collect the bus-side working parameters and grid-side working parameters of the connection point. A connection point switch can be set at the connection point to facilitate clearly distinguishing the bus side and the grid side.

[0032] Step S20, using the power flow algorithm, obtain the system real-time short-circuit ratio according to the bus-side working parameters and grid-side working parameters.

[0033] It should be noted that the system real-time short-circuit ratio (RSCR: Real-time Short-Circuit Ratio) can be calculated through the existing power flow algorithm or can be calculated through the specific method combining the power flow algorithm mentioned in the subsequent embodiments of this application.

[0034] Step S30, using the hysteresis strategy, determine the grid strength of the microgrid according to the system real-time short-circuit ratio.

[0035] It should be noted that, according to the specific value of the system real-time short circuit ratio, the grid strength of the microgrid can be divided and classified. The hysteresis strategy is a non-linear control method based on the error range. By setting upper and lower threshold values, the control action is triggered only when the error exceeds the threshold.

[0036] In this embodiment, using the hysteresis strategy, first set the value corresponding to the lower boundary of the hysteresis and the value corresponding to the upper boundary of the hysteresis, and then compare the calculated system real-time short circuit ratio with the lower boundary and the upper boundary of the hysteresis respectively, so as to correspondingly determine the grid strength. Based on the hysteresis strategy, the grid strength can be divided into three different strengths. Below the lower boundary of the hysteresis is the first grid strength, between the lower boundary and the upper boundary of the hysteresis is the second grid strength, and above the upper boundary of the hysteresis is the third grid strength; it can also directly divide the grid strength into weak grid, strong grid and extremely strong grid, which can be specifically set according to actual needs.

[0037] It should also be noted that the aforementioned acquisition of the bus-side working parameters and the grid-side working parameters is real-time acquisition, and the grid strength determined here is also real-time determined. Including when the substation executes the instruction issuing operation later, the master station can also real-time determine the grid strength and then inform the substation, so that the substation can correspondingly decide whether to continue to issue the instruction.

[0038] Step S40, determine the target mode according to the system operation condition and / or the grid strength; the target mode includes the grid-forming mode or the grid-following mode.

[0039] It should be noted that the target mode is the grid-forming mode or the grid-following mode; in the grid-forming mode, the inverters of the substations can actively establish the voltage and frequency reference of the grid, imitate the characteristics of synchronous generators, provide inertia and voltage support for the system, and enhance the grid stability. For example, realize voltage regulation and frequency stabilization of new energy units in the microgrid; in the grid-following mode, the inverters of the substations can passively follow the parameters of the main grid by detecting the grid voltage and frequency. For example, realize the power generation of new energy units in the microgrid in the maximum power point tracking (MPPT: Maximum Power Point Tracking) mode and improve the output of new energy units.

[0040] The system operation condition can be obtained from the system scheduling instructions issued externally, or can be directly detected by the master station, and no specific limitation is made here. The system operation condition can include different conditions such as grid faults, microgrid grid connection, microgrid grid disconnection, and microgrid island black start. The master station can determine the target mode according to the system operation condition, which belongs to the grid-forming and grid-following switching strategy for different operation modes; it can determine the target mode according to the grid strength, which belongs to the grid-forming and grid-following switching strategy for different grid strengths; it can also determine the target mode according to the system operation condition and the grid strength, which belongs to the grid-forming and grid-following switching strategy for different operation modes and different grid strengths, and can be specifically selected according to actual needs.

[0041] Step S50: Generate a mode switching instruction according to the target mode, and send the mode switching instruction to each sub-station, so that each sub-station sends the mode switching instruction to the corresponding power station according to the grid strength, realizing the switching of the microgrid control mode.

[0042] It should be noted that after determining the target mode, the master station can generate the corresponding mode switching instruction and send it to each sub-station; in each sub-station, the sub-station can send the mode switching instruction to multiple inverters / converters of the corresponding power station respectively, or can first send the mode switching instruction to a batch of multiple inverters / converters of the corresponding power station, and then judge whether to continue to send the mode switching instruction to the next batch according to the real-time determined grid strength, that is, the sub-station can send the mode switching instruction at one time or send the mode switching instruction in batches successively.

[0043] It can be understood that through the hierarchical distributed control architecture, the functions of the master station and sub-stations of the coordination controller are allocated and coordinated according to specific requirements, realizing the effective coordination of different types of inverters / converters, optimizing resource allocation, improving the system economy and operation stability, and achieving the effect of optimizing resource utilization efficiency; aiming at different strength grid environments and system operation conditions, an intelligent grid connection switching method is proposed, enabling the system to flexibly switch the grid connection mode under different conditions, ensuring the safe and stable operation of the power system.

[0044] This embodiment provides a grid connection switching method, which is applied to a hierarchical distributed coordination controller, combines the advantages of centralized control and decentralized control, can realize the efficient coordination and resource optimization configuration of the microgrid, and thus can be applied to the grid connection switching control of large-scale microgrids; in this method, after the master station obtains the bus-side working parameters and grid-side working parameters of the grid connection point in real time, the system real-time short-circuit ratio is calculated by using the power flow algorithm, and then the hysteresis strategy is used to determine the grid strength of the microgrid according to the system real-time short-circuit ratio, and then the target mode is determined as the grid connection mode or the grid following mode according to the system operation conditions and / or grid strength. It can take into account both the system operation conditions and the grid strength, determine the target mode corresponding to different system operation conditions and / or different grid strengths, provide a more intelligent grid connection mode switching mechanism, and ensure the safe and stable operation of the microgrid under various system operation conditions; it also generates a mode switching instruction according to the target mode, and sends the mode switching instruction to each sub-station, so that each sub-station sends the mode switching instruction to the corresponding power station according to the grid strength, realizing the switching of the microgrid control mode. The hierarchical distributed instruction sending method optimizes the resource utilization efficiency of the coordination controller, and can improve the dynamic response ability and operation stability of the system; this application realizes the technical effects of improving the coordination flexibility and achieving better intelligent control.

[0045] In a feasible implementation manner, in a microgrid, multiple substations may include at least one power generation substation and an energy storage substation, and multiple stations may include at least one power generation station and an energy storage station. The main station is respectively connected to each power generation substation and the energy storage substation. At least one power generation substation is correspondingly connected to at least one power generation station, and each power generation station includes multiple grid-connected inverters and multiple grid-forming inverters. The energy storage substation is connected to the energy storage station, and the energy storage station includes multiple grid-connected converters and multiple grid-forming converters.

[0046] Exemplarily, referring to Figure 3 , Figure 3 FIG. is another connection schematic diagram of the power system provided in this embodiment. The power generation station may include different types of power generation stations such as a photovoltaic power generation station and a wind turbine power generation station. Among them, the photovoltaic power generation station includes multiple photovoltaic grid-connected inverters and multiple photovoltaic grid-forming inverters, and the wind turbine power generation station includes multiple wind turbine grid-connected inverters and multiple wind turbine grid-forming inverters; correspondingly, the power generation substation may include different types of power generation coordination control substations such as a photovoltaic substation and a wind turbine substation. The photovoltaic substation is respectively communicatively connected to multiple photovoltaic grid-connected inverters and multiple photovoltaic grid-forming inverters, and the wind turbine substation is respectively communicatively connected to multiple wind turbine grid-connected inverters and multiple wind turbine grid-forming inverters. The energy storage substation is connected to the energy storage station, and the energy storage station includes multiple energy storage grid-connected converters and multiple energy storage grid-forming converters. The photovoltaic grid-connected inverters, photovoltaic grid-forming inverters, wind turbine grid-connected inverters, wind turbine grid-forming inverters, energy storage grid-connected converters, and energy storage grid-forming converters are all connected to the bus, that is, on the bus side of the point of common coupling, and specifically may be concentrated at one end of the point of common coupling switch. The other end of the point of common coupling switch is connected to the power grid or the simulated power grid through a transmission line, and this transmission line is the grid side of the point of common coupling.

[0047] As Figure 3 shown, the microgrid may further include an energy management system (EMS: Energy Management System). The EMS is connected to the main station of the coordination controller. The main station may receive the system scheduling instructions issued by the EMS, and of course, may also receive the system scheduling instructions sent by an external system.

[0048] In this implementation manner, a new type of coordination controller with grid-connected and grid-forming switching functions is proposed, which adopts a hierarchical distributed architecture. The coordination controller is composed of a main station and multiple substations such as wind, light, and storage, combines the advantages of centralized control and decentralized control, and is suitable for large-scale microgrid systems. This hierarchical distributed architecture can support a control method that combines centralized control and decentralized control, so that the grid-connected and grid-forming switching method executed based on this coordination controller can meet the requirements of flexibility and intelligent control of the power system.

[0049] Exemplarily, referring to Figure 4 ,Figure 4 A connection diagram of an example of the power system provided in this embodiment is specifically shown for the hierarchical distributed architecture of the coordination controller. In Figure 4 , the dashed line represents the control and communication line, and the solid line represents the power line. The coordination controller consists of a coordination control master station and multiple coordination control slave stations, such as coordination control slave stations for wind power, photovoltaics, and energy storage. This architecture can be applied to systems of different scales according to project requirements, which can not only relieve the communication pressure of the centralized control mode but also take into account the rapid self-adjustment of the decentralized control mode.

[0050] Among them, the coordination control master station is located between the EMS and the coordination control slave stations, responsible for global scheduling and coordination control between different slave stations. It can receive the system regulation instructions sent by the EMS, collect the status information of the grid connection point, including the operating parameters on the bus side and the grid side of the grid connection point, and can also quickly synchronously adjust all coordination control slave stations. The coordination control slave station is responsible for the coordination control between the same type of inverters / converters. It can receive the mode switching instructions issued by the coordination control master station, obtain the status information of each inverter / converter, and can also quickly synchronously adjust all the inverters / converters corresponding to it, and can achieve local self-adjustment to improve the dynamic response ability of the system. Among them, the same type of inverters / converters refers to the grid-connected inverters / converters belonging to the same substation or the grid-forming inverters / converters belonging to the same substation. For example, the photovoltaic grid-connected inverters 1-n are the same type of inverters belonging to the photovoltaic substation, and the photovoltaic grid-forming inverters 1-n are another same type of inverters belonging to the photovoltaic substation, both of which are communicatively connected to the photovoltaic coordination control slave station; the wind turbine grid-connected inverters 1-n are the same type of inverters belonging to the wind farm substation, and the wind turbine grid-forming inverters 1-n are another same type of inverters belonging to the wind farm substation, both of which are communicatively connected to the wind turbine coordination control slave station; the energy storage grid-connected converters 1-n are the same type of converters belonging to the energy storage substation, and the energy storage grid-forming converters 1-n are another same type of converters belonging to the energy storage substation, both of which are communicatively connected to the energy storage coordination control slave station.

[0051] It can be understood that by adopting a hierarchical distributed control architecture, the functions of the coordination control master station and the coordination control slave stations can be allocated according to specific requirements, realizing the efficient coordination of each substation and the optimal allocation of resources.

[0052] In addition, the master station is communicatively connected to the EMS through the TCP / IP protocol, multiple slave stations are respectively communicatively connected to the master station through the GOOSE protocol, and multiple slave stations are communicatively connected to multiple substations through the GOOSE protocol correspondingly.

[0053] Exemplarily, such as Figure 4Data interaction can be achieved between the EMS shown and the coordinated control master station through the TCP / IP protocol. This protocol features high reliability, good flexibility, and strong compatibility, and can ensure the accurate transmission of commands issued by the EMS and the real-time feedback of data signals from the master station. The coordinated control master station communicates with the coordinated control sub-stations, and the coordinated control sub-stations communicate with the wind-solar-storage inverters using the GOOSE protocol. This protocol has the characteristics of strong real-time performance, high efficiency, and high reliability, and can complete the transmission of control commands and data within milliseconds, especially suitable for scenarios with high requirements for fast dynamic response.

[0054] As Figure 4 shown, the microgrid can also include multiple loads, which are aggregated with the inverters / converters of stations such as wind-solar-storage at the busbar; the microgrid can also include a load measurement and control unit, which is connected to the load and the coordinated control master station. The load measurement and control unit can also communicate with the coordinated control master station using the GOOSE protocol to meet the needs of more power systems or microgrid operations.

[0055] In this example, the TCP / IP protocol supports wide-area communication and is suitable for efficient interaction between the EMS and the master station; the GOOSE protocol focuses on local communication to ensure rapid coordination between the devices of the master station, sub-stations, and stations. By combining the advantages of the TCP / IP protocol and the GOOSE protocol, hierarchical optimization control is achieved, ensuring rapid coordination between the master station, sub-stations, and stations, which can enhance the response speed and regulation ability of the microgrid under external disturbance conditions, ensure that the system can remain stable in a rapidly changing power environment, and achieve the effect of improving the system's dynamic response ability.

[0056] In this embodiment, this hierarchical distributed architecture of the coordinated controller can not only relieve the communication pressure of centralized control but also make full use of the fast response characteristics of decentralized control, integrate various energy resources such as wind-solar-storage, optimize the resource utilization efficiency, and provide a solid technical support for the efficient operation of the power system; different communication methods are also adopted to improve the dynamic response ability of the coordinated controller, ensuring that the microgrid can quickly adjust and remain stable in a rapidly changing power environment; moreover, as a system-level structure network switching strategy proposed for the coordinated controller, which is the upper-layer device for the inverters / converters of each station, control optimization is carried out from the source-network-load-storage system level, which can ensure the stable operation of the power system.

[0057] In a feasible implementation manner, this structure network switching method may further include steps S60 to S70: Step S60, when the target mode is the grid-following mode, detect the operating states of each station.

[0058] When it is necessary to switch to the grid-connected mode, the coordination controller detects the operating states of the PV power station and the wind power station, which can be specifically detected by their respective coordination control substations and fed back to the master station. For example, the PV coordination control substation detects the operating state of the PV power station and feeds it back to the master station; the wind turbine coordination control substation detects the operating state of the wind power station and feeds it back to the master station. When the target mode is the grid-forming mode, it is not necessary to detect the operating states of each power station.

[0059] Step S70: The substation issues a mode switching command to the power station whose operating state meets the preset operating conditions, so as to switch the microgrid control mode to the grid-connected mode.

[0060] The substation can detect the operating state of the corresponding power station and feed it back to the master station. After receiving the feedback, the master station can identify whether the operating states of each power station meet the preset operating conditions. If they meet, it controls the substation to act, specifically controlling the substation to issue a mode switching command to the power station whose operating state meets the preset operating conditions, so as to switch the microgrid control mode to the grid-connected mode. If they do not meet, it directly ends.

[0061] For example, for a PV power station, the operating state meeting the preset operating conditions means that the light intensity and temperature meet the preset light and temperature conditions. If the current light intensity and temperature of the PV power station meet, the PV power station continues to operate. At this time, the PV coordination control substation can control the PV grid-connected inverter to perform the grid-connected mode switching corresponding to the received mode switching command, that is, the grid-connected switching command. For a wind power station, the operating state meeting the preset operating conditions means that the wind speed meets the preset wind speed conditions. If the current wind speed of the wind power station meets, the wind power station continues to operate. At this time, the wind turbine coordination control substation can control the wind turbine grid-connected inverter to perform the grid-connected mode switching corresponding to the received mode switching command, that is, the grid-connected switching command.

[0062] Based on the first embodiment of the grid-forming and grid-connected switching method of the present application, in the second embodiment of the grid-forming and grid-connected switching method of the present application, the same or similar content as the above embodiment can be referred to the above introduction and will not be repeated hereinafter. On this basis, the bus-side working parameters can include the bus-side active power P pcc , the bus-side reactive power Q pcc and the bus-side current I pcc , and the grid-side working parameters can include the grid-side active power P grid and the grid-side reactive power Q grid .

[0063] Refer to Figure 5 , Figure 5Schematic connection diagram of another example of a power system, which may include a data acquisition device, connected to a master station and respectively connected to a collection point A on the bus side of the grid connection point and a collection point B on the grid side, for real-time acquisition of the operating parameters on the bus side and the grid side and sending them to the master station, so that the master station receives and obtains the operating parameters on the bus side and the grid side of the grid connection point.

[0064] In an actual power grid, the power grid is not an ideal source and has a certain short-circuit capacity of its own, which cannot be ignored especially in a poor power grid environment. Therefore, the calculation of the system real-time short-circuit ratio (RSCR) needs to consider both the equivalent short-circuit impedance of the grid connection point and the equivalent short-circuit impedance of the power grid. Correspondingly, Figure 5 also shows an equivalent schematic diagram between the grid connection point and the power grid, including the equivalent impedance of the grid connection point Z pcc and the equivalent impedance of the power grid Z grid .

[0065] In a feasible implementation, step S20 may include steps S21 to S23: Step S21, obtain the rated voltage of the grid connection point, the equivalent resistance of the power grid, the equivalent reactance of the power grid, the equivalent resistance of the grid connection point, and the equivalent reactance of the grid connection point; Step S22, obtain the system equivalent short-circuit impedance according to the square root of the sum of the squares of the first sum value obtained by summing the equivalent resistance of the power grid and the equivalent resistance of the grid connection point and the second sum value obtained by summing the equivalent reactance of the power grid and the equivalent reactance of the grid connection point; Step S23, obtain the system real-time short-circuit ratio according to the ratio between the product of the rated voltage of the grid connection point and the system equivalent short-circuit impedance and the active power on the bus side.

[0066] It should be noted that for the equivalent impedance of the power grid Z grid , , the corresponding equivalent resistance of the power grid R grid and the equivalent reactance of the power grid X grid can be obtained. For the equivalent impedance of the grid connection point Z pcc , , the corresponding equivalent resistance of the grid connection point R pcc and the equivalent reactance of the grid connection point X pcc .

[0067] Then, the real-time system equivalent short-circuit impedance Z sc can be obtained using the system equivalent short-circuit impedance calculation formula. The involved calculation formula is: .

[0068] After that, using the system 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 among the bus side operating parameters P pcc the system real-time short-circuit ratio RSCR can obtain the specific value, and the involved calculation formula is: .

[0069] In a specific embodiment, "obtaining the grid equivalent resistance, grid equivalent reactance, grid connection point equivalent resistance, and grid connection point equivalent reactance" in step S21 may include steps S21.1 to S21.4: Step S21.1, obtaining the grid short-circuit capacity and grid quality factor; Step S21.2, obtaining the grid equivalent short-circuit impedance according to the ratio of the grid connection point rated voltage to the grid short-circuit capacity; Step S21.3, obtaining the grid equivalent resistance and grid equivalent reactance according to the grid equivalent short-circuit impedance and grid quality factor; among them, the involved calculation formula is: , wherein, Q represents the grid quality factor, R grid represents the grid equivalent resistance, X grid represents the grid equivalent reactance, Z grid represents the grid equivalent short-circuit impedance; Step S21.4, obtaining the grid connection point equivalent resistance and grid connection point equivalent reactance according to the bus side operating parameters and grid side operating parameters; among them, the involved calculation formula is: , wherein, R pcc represents the grid connection point equivalent resistance, X pcc represents the grid connection point equivalent reactance, P pcc represents the active power on the bus side, P grid represents the active power on the grid side, I pcc represents the bus side current, Q pcc represents the reactive power on the bus side, Q gridRepresents the reactive power on the grid side.

[0070] In the specific implementation process, steps S21.1 - S21.3 can be carried out simultaneously with step S21.4 to obtain the grid equivalent resistance synchronously R grid , the grid equivalent reactance X grid , the equivalent resistance at the grid connection point R pcc and the equivalent reactance at the grid connection point X pcc .

[0071] Exemplarily, the process of specifically calculating the real - time short - circuit ratio (RSCR) of the system in step S20 is described in detail: First, based on the preset or known rated voltage at the grid connection point U n 2 and the grid short - circuit capacity S grid the grid equivalent short - circuit impedance is obtained Z grid : ; Then, using the calculation formula: , Based on the grid equivalent short - circuit impedance Z grid and the grid quality factor Q the grid equivalent resistance R grid and the grid equivalent reactance X grid are obtained. This process can specifically be , , , , Thus, the specific grid equivalent resistance R grid and the grid equivalent reactance X grid can be calculated; Meanwhile, using the calculation formula: , Based on the active power on the bus side P pcc , the reactive power on the bus side Q pcc , the bus - side current I pcc, the active power on the grid side P grid and the reactive power on the grid side Q grid to obtain the equivalent resistance at the grid connection point R pcc and the equivalent reactance at the grid connection point X pcc ; Then, using the calculation formula: , According to the equivalent resistance of the power grid R grid , the equivalent resistance at the grid connection point R pcc , the equivalent reactance of the power grid X grid and the equivalent reactance at the grid connection point X pcc to obtain the equivalent short-circuit impedance of the system Z sc ; Finally, using the calculation formula: , where S sc represents the real-time short-circuit capacity of the system. According to the rated voltage at the grid connection point U n 2 , the equivalent short-circuit impedance of the system Z sc and the active power on the bus side P pcc calculate the real-time short-circuit ratio of the system RSCR .

[0072] In this embodiment, considering that the short-circuit capacity of the system is often unknown, in order to solve the problem that the traditional SCR (Short-Circuit Ratio) cannot be measured when the short-circuit capacity of the system is unknown, a specific calculation method is proposed to calculate the equivalent short-circuit impedance of the system in real time using the power flow algorithm, and then calculate the real-time short-circuit ratio of the system in real time, so as to determine the grid strength in real time according to the real-time short-circuit ratio of the system obtained by real-time calculation; the calculation of the equivalent short-circuit impedance of the system Z sc takes into account both the equivalent impedance at the grid connection point and the equivalent impedance of the power grid, and converts the existing short-circuit capacity of the actual power grid, which can realize accurate measurement of the grid strength in a weak grid environment; in addition, the traditional SCR can only reflect the grid strength of the power generation unit at the rated output power. In this embodiment, the active power on the bus side P pccInstead of the rated power of the grid connection point, it can dynamically and accurately measure the change in grid strength corresponding to the actual output power of the power generation station in the microgrid, significantly improving the accuracy and applicability of grid strength assessment.

[0073] In a feasible implementation manner, step S30 may include steps S31 to S34: Step S31, comparing the real-time short-circuit ratio of the system with the preset lower hysteresis boundary and upper hysteresis boundary respectively; Step S32, when the real-time short-circuit ratio of the system is less than or equal to the lower hysteresis boundary, determining that the grid strength is a weak grid; Step S33, when the real-time short-circuit ratio of the system is greater than the lower hysteresis boundary and less than or equal to the upper hysteresis boundary, determining that the grid strength is a strong grid; Step S34, when the real-time short-circuit ratio of the system is greater than the upper hysteresis boundary, determining that the grid strength is an extremely strong grid.

[0074] To ensure that the system will not repeatedly switch the grid-forming function due to the output fluctuation of the power generation station in a short time, a hysteresis strategy is adopted to evaluate the grid strength. The lower hysteresis boundary r1 can be determined according to the grid strength evaluation criteria shown in Table 1, or can be determined according to user-defined settings.

[0075] Table 1

[0076] As can be seen from Table 1, when the real-time short-circuit ratio of the system is less than 2, it belongs to an extremely weak grid; when the real-time short-circuit ratio of the system is between 2 and 3, it belongs to a weak grid; when the real-time short-circuit ratio of the system is greater than 3, it belongs to a strong grid.

[0077] Based on the grid-forming switching requirements, it is required that the system always maintains a strong grid state. If it is not in the strong grid state, grid-forming switching is required. Therefore, the value of the lower hysteresis boundary r1 can be set to 3. Of course, in actual applications, it can also be flexibly adjusted according to the actual project; there is a relationship r2 > r1 between the upper hysteresis boundary r2 and the lower hysteresis boundary r1. On this basis, the upper hysteresis boundary r2 can be determined in combination with the working characteristics of the specific power generation station. For example, for the example where r1 = 3 here, the value of the upper hysteresis boundary r2 can be set to 4 or 5.

[0078] Refer to Figure 6 , Figure 6 is a schematic diagram of 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 grid-forming capacity of the microgrid. Exemplarily, when the value of the real-time short-circuit ratio of the system is lower than the lower hysteresis boundary r1, that is RSCRWhen ≤ r1, it is determined that the current grid strength is a weak grid. At this time, the system needs to switch to the grid-forming mode to increase the grid-forming unit capacity. Therefore, when determining the target mode according to the grid strength subsequently, the target mode is the grid-forming mode; when the value of the system's real-time short-circuit ratio is between the lower boundary r1 and the upper boundary r2 of the hysteresis loop, i.e., r1 < RSCR ≤ r2, it is determined that the current grid strength is a strong grid. At this time, according to the hysteresis strategy, the control module of the unit can remain unchanged, and this grid-forming and switching method can end directly; when the value of the system's real-time short-circuit ratio is higher than the upper boundary r2 of the hysteresis loop, i.e., RSCR > r2, it is determined that the current grid strength is an extremely strong grid. At this time, the system needs to switch to the grid-following mode to increase the output of the generating units. Therefore, when determining the target mode according to the grid strength subsequently, the target mode is the grid-following mode.

[0079] It can be understood that using the hysteresis strategy to evaluate the grid strength and customizing the determination of the upper and lower boundaries of the hysteresis loop can ensure that the microgrid will not cause the grid-forming and switching function to switch repeatedly in a short time due to the output fluctuation of the power generation station.

[0080] In the first feasible implementation manner, step S40 "determine the target mode according to the system operating conditions" may include steps A1 to A4: Step A1, when the system operating condition is a grid fault, determine the target mode as the grid-forming mode; Step A2, when the system operating condition is the microgrid grid connection, determine the target mode as the grid-following mode; Step A3, when the system operating condition is the microgrid islanding, determine the target mode as the grid-forming mode; Step A4, when the system operating condition is the microgrid island black start, determine the target mode as the grid-forming mode.

[0081] It should be noted that during the operation of the microgrid, grid fault conditions may occur, or the grid connection-disconnection switching function may be required, or the station black start may be needed. Therefore, the target mode can be determined according to different system operating conditions to adjust the grid-forming capacity of the station according to different scenarios such as grid faults, microgrid grid connection, islanding, and black start, so as to realize the adjustment of the system grid-forming capacity of the microgrid. Among them, the microgrid island black start refers to the process of gradually restoring power supply only through the internal power sources with self-starting capabilities (such as energy storage stations, power generation stations, etc.) without relying on the external grid or other power sources when the microgrid is completely de-energized (i.e., "fully black" state) due to faults or external grid power outages.

[0082] During the specific implementation process, when a power grid fault occurs, the strength of the power grid generally weakens. At this time, the generator set needs to regulate voltage and frequency, and the microgrid needs to switch to the grid-forming control mode. Therefore, when the system operating condition is a power grid fault, the determined target mode is the grid-forming mode; when the microgrid is to be connected to the grid, the strength of the power grid generally increases. At this time, the generator set does not need to regulate voltage and frequency, but the generator set needs to work in the maximum power point tracking (MPPT) mode as much as possible to generate electricity, and the microgrid needs to switch to the grid-following control mode. Therefore, when the system operating condition is the microgrid connected to the grid, the determined target mode is the grid-following mode; when the microgrid is to be disconnected from the grid, the strength of the power grid generally weakens. At this time, the generator set needs to regulate voltage and frequency, and the microgrid needs to switch to the grid-forming control mode. Therefore, when the system operating condition is the microgrid disconnected from the grid, the determined target mode is the grid-forming mode; when the microgrid is to perform island black start, the generator set needs to be used as a support power source to regulate voltage and frequency, and the microgrid needs to switch to the grid-forming control mode. Therefore, when the system operating condition is the microgrid island black start, the determined target mode is the grid-forming mode. Optionally, when the target mode is the grid-following mode, the light intensity and temperature of power generation stations such as photovoltaic power stations and the wind speed of wind power stations are also detected to meet their respective preset operating conditions, and then the subsequent steps are executed.

[0083] In this embodiment, the target mode is specifically determined according to different system operating conditions, so that the coordinated control of different stations can be stably carried out under different conditions of external disturbances such as load mutations, renewable energy fluctuations or faults, thereby ensuring the safe and stable operation of the power system under various conditions.

[0084] In the second feasible embodiment, step S40 "determine the target mode according to the grid strength" may include steps B1 to B3: Step B1, when the grid strength is a weak grid, determine the target mode as the grid-forming mode; Step B2, when the grid strength is a strong grid, directly end; Step B3, when the grid strength is an extremely strong grid, determine the target mode as the grid-following mode.

[0085] It should be noted that after determining the grid strength through the foregoing steps S31-S34, the target mode can be correspondingly determined according to the determined grid strength. When the real-time short-circuit ratio of the system RSCR is less than or equal to the lower boundary r1 of the hysteresis loop, the grid strength at this time is a weak grid, and the microgrid control mode needs to be switched to the grid-forming mode. Therefore, the target mode is determined as the grid-forming mode; when the real-time short-circuit ratio of the system RSCRWhen it is greater than the upper boundary r2 of the hysteresis loop, the grid strength at this time is an extremely strong grid, and it is necessary to switch the microgrid control mode to the grid-following mode. Therefore, the target mode is determined to be the grid-forming mode. Optionally, when the target mode is the grid-following mode, the light intensity and temperature of power generation stations such as photovoltaic power stations and the wind speed of wind farms are also detected to meet their respective preset operating conditions before performing the subsequent steps.

[0086] In this embodiment, the target mode is specifically determined according to different grid strengths, which has a fast dynamic response speed and can improve the dynamic response ability of the system. Moreover, after calculating the real-time short-circuit ratio of the system and evaluating the grid strength with the hysteresis loop strategy, the target mode is determined in real time according to the evaluation result, which is convenient for subsequent corresponding issuance of mode switching instructions to achieve intelligent grid-following and grid-forming mode switching.

[0087] In the third feasible embodiment, step S40 "determine the target mode according to the system operating conditions and grid strength" may include steps C1 to C3: Step C1, determine whether a system scheduling instruction related to the system operating conditions is received; Step C2, if a system scheduling instruction is received, directly determine the target mode according to the system operating conditions corresponding to the system scheduling instruction; Step C3, if a system scheduling instruction is not received, further determine whether the grid strength is a strong grid; Step C4, if the current grid strength is a strong grid, directly end; Step C5, if the current grid strength is not a strong grid, determine the target mode according to the grid strength.

[0088] It should be noted that the system scheduling instruction can be an instruction sent by an external system or the EMS in the microgrid to the master station. This instruction can include a specific target mode or the current system operating conditions. That is to say, this instruction can be an instruction generated by an external system or the EMS according to the actual system operating conditions of the power system, including but not limited to corresponding generation by manually operating relevant buttons and corresponding generation after detecting different system states.

[0089] In the specific implementation process, when determining the target mode according to the system operating conditions and grid strength, first judge whether there is a grid connection and disconnection switching requirement corresponding to a system scheduling instruction with a higher priority; if so, directly determine the target mode according to the system operating conditions corresponding to the system scheduling instruction, and execute the subsequent mode switching instruction generation and distribution; if not, judge whether there is a grid connection and disconnection switching requirement according to the grid strength obtained in real time; specifically, it can be judged whether the current grid strength is a strong grid; if so, it means that there is no grid connection and disconnection switching requirement, and the process can be directly ended; if not, it means that the current grid strength does not meet the actual operation requirements, and grid connection and disconnection mode switching is required, and the target mode is correspondingly determined according to the grid strength. Among them, the specific implementation method for determining the target mode according to the system operating conditions corresponding to the system scheduling instruction can be referred to the foregoing steps A1-A4, which will not be elaborated here; the specific implementation method for correspondingly determining the target mode according to the grid strength can be referred to the foregoing steps B1-B3, which will not be elaborated here.

[0090] In this embodiment, different system operating conditions and different grid strengths are combined to specifically determine the target mode, so that the power system has an intelligent grid connection and disconnection switching mechanism when facing different grid strengths such as strong grids and weak grids, and different system operating modes such as off-grid, grid-connected, fault, and black start, realizing flexible grid connection and disconnection mode switching. Moreover, the preliminary scheduling plan can pre-convert the grid connection and disconnection switching mode according to the system scheduling instruction, and adaptively adjust the grid connection capacity of the substation; the switching mode that real-time detects the grid strength can fully consider the characteristics of the real-time change of the system operation, and use the system RSCR and the status of the wind and light power stations as the decision-making basis to maintain the stable operation of the grid.

[0091] It should be noted that the above are only three feasible implementation methods of step S40 provided in this embodiment, and the specific implementation method of step S40 in this embodiment is not specifically limited.

[0092] In an alternative embodiment, each substation may include a plurality of grid-connected inverters / converters and a plurality of grid-forming inverters / converters; step S50 may include steps S51-S55: Step S51, generate a mode switching instruction by the master station according to the target mode, and send the mode switching instruction to each substation; Step S52, each substation sends the mode switching instruction to a batch of the corresponding plurality of grid-connected inverters / converters or a plurality of grid-forming inverters / converters to switch the control mode of the first batch of inverters / converters in each substation to the target mode; Step S53, judge whether the grid strength determined in real time is a strong grid; Step S54, if the grid strength is a strong grid, directly end; Step S55: If the grid strength is not strong, return to step S52 of sending the mode switching instruction to a batch of corresponding grid-connected inverters / converters or a batch of grid-forming inverters / converters through each substation, so as to switch the control mode of the second batch of inverters / converters in each substation to the target mode until the grid strength determined in real time is strong.

[0093] It should be noted that the master station of the coordination controller sends the substation-level mode switching instruction to each substation. After receiving the instruction, the substation gradually sends it to the inverters / converters of each wind-solar-storage substation in batches. Assuming the number of inverters / converters in the substation is n, and n may be dozens, hundreds or even thousands, it can be set that the switching quantity per batch is 10%*n, so as to gradually adjust the grid-forming capacity of the substation; and it can be stopped in time when the grid strength determined in real time meets the requirements. Among them, the grid-forming capacity of the substation refers to the sum of the rated capacities of all grid-connected generating units in the entire microgrid, which is a key indicator to measure the scale and power supply capacity of the microgrid.

[0094] In practical applications, when performing subsequent batch switching, it can be stopped when the grid strength determined in real time is strong, or it can be stopped when all inverters / converters are switched. That is, in step S55, if the grid strength is not strong, return to step S52 to switch the control mode of the next batch of inverters / converters in each substation to the target mode until the grid strength determined in real time is strong or until the control modes of all inverters / converters in all substations are switched to the target mode.

[0095] It can be understood that the instruction is first sent from the master station to each substation, and then the coordination control of the inverters / converters of different substations is specifically executed by different substations, which improves the resource utilization efficiency of the coordination controller and optimizes the power distribution.

[0096] In an optional implementation manner, as Figure 3 shown, the multiple substations include a photovoltaic substation, a wind turbine substation and an energy storage substation, and the multiple substations include a photovoltaic power generation substation, a wind turbine power generation substation and an energy storage substation. When the master station sends the mode switching instruction to each substation in step S51, the sending order can be determined according to the target mode. That is, when the master station sends the substation-level mode switching instruction to each substation, the sending order and timing of the mode switching instruction can be determined according to the specific grid-forming switching direction.

[0097] When the target mode is the grid-forming mode, the master station can first send it to the energy storage substation, so that it first switches the grid-forming mode of multiple grid-forming converters in the energy storage station or a batch of multiple grid-forming converters. If the grid strength detected in real time is still not a strong grid after all the multiple grid-forming converters in the entire energy storage station have been switched to the grid-forming mode, then it is sent to the PV substation and the wind turbine substation. The execution logics of these two substations have no priority, and each controls a batch of multiple grid-forming inverters or multiple grid-forming inverters in its respective station to switch to the grid-forming mode until the grid strength becomes a strong grid or all the inverters have been switched.

[0098] When the target mode is the grid-following mode, the master station can first send it to the PV substation and the wind turbine substation. The execution logics of these two substations have no priority, and each controls a batch of multiple grid-following inverters or multiple grid-following inverters in its respective station to switch to the grid-following mode. If the grid strength detected in real time is still not a strong grid after all the inverters have been switched, then it is sent to the energy storage substation to switch the grid-following mode of multiple grid-following converters in the energy storage station or a batch of multiple grid-following converters until the grid strength becomes a strong grid or all the converters have been switched.

[0099] In another alternative implementation, as Figure 3 shown, multiple stations include a PV power generation station, a wind turbine power generation station, and an energy storage station. The PV power generation station and the wind turbine power generation station both include multiple grid-following inverters and multiple grid-forming inverters, and the energy storage station includes multiple grid-following converters and multiple grid-forming converters. "Issuing the mode switching instruction to a batch of corresponding multiple grid-following inverters / converters or multiple grid-forming inverters / converters through each substation" in step S52 may include steps S52.1 to S52.3: Step S52.1, determining the grid-following / grid-forming switching direction of the mode switching instruction through each substation; Step S52.2, if the grid-following / grid-forming switching direction is from grid-following to grid-forming, taking the energy storage station as the main switching object, controlling a batch of multiple grid-forming converters to work, and when all the multiple grid-forming converters have been switched, then taking the PV power generation station and / or the wind turbine power generation station as the secondary switching object, controlling a batch of multiple grid-forming inverters to work; Step S52.3, if the grid-following / grid-forming switching direction is from grid-forming to grid-following, taking the PV power generation station and / or the wind turbine power generation station as the main switching object, controlling a batch of multiple grid-following inverters to work, and when all the multiple grid-following inverters have been switched, then taking the energy storage station as the secondary switching object, controlling a batch of multiple grid-following converters to work.

[0100] When the determined follow - to - grid - forming switching direction is from following the grid to forming the grid, the energy storage station is taken as the main switching object. The energy storage sub - station can control a batch of the grid - forming converters in the energy storage station to work, and perform the grid - forming mode switching. Until all the grid - forming converters are switched, if the grid strength detected in real - time is still not a strong grid, then the photovoltaic power generation station and / or the wind power generation station is taken as the secondary switching object. The photovoltaic sub - station and the wind power generation sub - station respectively control a batch of the grid - forming inverters in their respective stations to work and switch to the grid - forming mode until the grid strength becomes a strong grid or all the inverters have been switched.

[0101] When the determined follow - to - grid - forming switching direction is from forming the grid to following the grid, the photovoltaic power generation station and / or the wind power generation station is taken as the main switching object. The photovoltaic sub - station and the wind power generation sub - station respectively control a batch of the grid - following inverters in their respective stations to work and perform the grid - following mode switching. Until all the grid - following inverters are switched, if the grid strength detected in real - time is still not a strong grid, then the energy storage station is taken as the secondary switching object. The energy storage sub - station can control a batch of the grid - following converters in the energy storage station to work and switch to the grid - following mode until the grid strength becomes a strong grid or all the converters have been switched.

[0102] In this embodiment, a method of sending mode - switching instructions to multiple inverters or converters in batches is adopted, so as to perform mode - switching in batches. Based on the hierarchical distributed structure, the coordination controller issues the follow - to - grid - forming mode - switching instructions. The master station of the coordination controller performs the early - stage scheduling planning response, RSCR calculation, analysis of the station operating conditions, and issuance of mode - switching instructions for different stations, etc.; the sub - station of the coordination controller gradually issues mode - switching instructions to the inverters / converters of the wind - solar - storage stations in batches, with each batch switching 10% of the rated capacity of the station, achieving the purpose of adjusting the grid - forming capacity of the station, and thus realizing the intelligent adjustment of the system grid - forming capacity of the entire micro - grid.

[0103] Exemplarily, to help understand the implementation process of the follow - to - grid - forming switching method of the embodiments of the present application, refer to Figure 7 , Figure 7 A flowchart of an application example of the follow - to - grid - forming switching method is provided. Specifically: First, synchronously collect the active power P pcc ,reactive power Q pcc ,and current I pcc on the bus side of the grid connection point, as well as the active power P grid ,reactive power Q grid on the grid side, and use the power flow algorithm to calculate the real - time short - circuit ratio of the system RSCR, the specific calculation method is as described above and will not be elaborated here. Then, the hysteresis strategy is adopted to evaluate the grid strength. The above process can be carried out in real time to obtain the grid strength in real time.

[0104] Then, the coordinated control master station can determine the direction of the grid connection and grid formation switching command, that is, determine the target mode, according to the system operation conditions and / or grid strength; and detect the states of the photovoltaic power station and the wind power station. Among them, the command direction includes switching to the grid-following mode, switching to the grid-forming mode, and not switching. The detection operation is only executed when the command direction is to switch to the grid-following mode. The specific determination method includes determining only according to the system operation conditions, determining only according to the grid strength, and determining according to the system operation conditions and grid strength, which can be selected according to actual needs. When the system is operating normally, the coordinated control master station directly determines the direction of the grid connection and grid formation switching command according to the grid strength; under specific system operation conditions, the corresponding grid connection and grid formation switching command direction is determined for different system operation conditions. The system operation conditions can be detected by the coordinated control master station itself or externally feedback. When it is externally feedback, the external can send the corresponding system dispatching instruction to make the coordinated control master station give priority to executing the grid connection and grid formation switching according to the system dispatching instruction.

[0105] Next, it is judged whether there is an external grid connection and grid formation switching demand. Since the system operation conditions can be obtained from the system dispatching instruction sent externally, if the system dispatching instruction is received and the target mode is determined according to the system operation conditions, it is considered that there is an external grid connection and grid formation switching demand. When it is determined that there is an external grid connection and grid formation switching demand, directly execute the step of the coordinated control master station issuing the mode switching instruction according to the command direction and the states of the wind-solar power stations. If the system dispatching instruction is not received, whether the target mode is determined according to the system operation conditions detected by itself or according to the grid strength, it is considered that there is no external grid connection and grid formation switching demand. When it is determined that there is no external grid connection and grid formation switching demand, jump to the next judgment step.

[0106] Furthermore, it is judged whether the grid strength requirement is met. Specifically, the real-time obtained grid strength can be compared with the set grid strength requirement such as a strong grid. If the grid strength requirement is met, that is, the current grid strength is a strong grid, it means that there is no need to switch the microgrid control mode and it can be directly ended; otherwise, execute the step of the coordinated control master station issuing the mode switching instruction according to the command direction and the states of the wind-solar power stations.

[0107] The coordinated control master station issues a mode switching instruction according to the command direction and the states of the wind-solar power stations. The order of issuing the mode switching instruction is determined according to the grid connection and grid formation switching direction. When the power station needs to switch from grid-following to grid-forming, the energy storage power station is the main switching object, followed by the photovoltaic and wind power stations; when the power station needs to switch from grid-forming to grid-following, the photovoltaic and wind power stations are the main switching objects, followed by the energy storage power station.

[0108] The wind-solar-storage coordinated control substation receives the mode switching instruction and gradually distributes it in batches to the inverters / converters of each wind-solar-storage power station to adjust the system grid-forming capacity. The batch distribution method is as described above and will not be elaborated here.

[0109] Finally, determine whether the switching is up to standard. Specifically, it can be determined whether the grid strength is a strong grid and whether the grid-forming switching requirement of the system dispatching instruction is completed. If it meets the standard, the entire process ends. If it does not meet the standard, it can return to the acquisition step and repeat the entire process.

[0110] It should be noted that the above examples are only for understanding the present application and do not constitute a limitation on the grid-forming switching method of the present application. Based on this technical concept, more forms of simple transformations are within the protection scope of the present application.

[0111] The present application also provides a coordination controller, referring to Figure 2 、 Figure 3 and Figure 4 . This coordination controller is applied to a microgrid, and the microgrid also includes multiple power stations; the coordination controller can include a master station and multiple sub-stations. The multiple sub-stations are respectively connected to the master station, the multiple sub-stations are correspondingly connected to the multiple power stations, the multiple power stations converge on the bus, and the bus is connected to the power grid through the grid connection point.

[0112] Among them, the master station is used to implement the steps of the grid-forming switching method in any of the above embodiments and is used to control the operation of each sub-station. Each sub-station is used to receive the instructions issued by the master station and is used to control the inverters / converters of the corresponding power stations. It should be noted that more functions and more examples of the coordination controller can refer to the descriptions of the specific implementation methods in the above grid-forming switching method embodiments and will not be elaborated here.

[0113] The coordination controller provided by the present application adopts the grid-forming switching method in the above embodiments and can solve the technical problems that the coordination control method in the related technology has insufficient flexibility and cannot achieve better intelligent control. Compared with the related technology, the beneficial effects of the coordination controller provided by the present application are the same as those of the grid-forming switching method provided by the above embodiments, and other technical features in this coordination controller are the same as those disclosed in the above embodiments of the grid-forming switching method and will not be elaborated here.

[0114] The present application also provides a power system, referring to Figure 2 、 Figure 3 and Figure 4, the power system may include a microgrid, which includes a coordination controller and multiple stations as described in the above embodiments; a grid connection point switch; and a power grid. Among them, the coordination controller is connected to multiple stations, the multiple stations converge on a bus, and the bus is connected to the power grid through the grid connection point switch. It should be noted that more functions and more examples of the power system can be referred to the description of the specific implementation in the foregoing embodiment of the structure-following network switching method, which will not be elaborated here.

[0115] The power system provided by this application adopts the structure-following network switching method in the above embodiments, which can solve the technical problem that the coordination control method in the related art lacks flexibility and cannot achieve better intelligent control. Compared with the related art, the beneficial effects of the power system provided by this application are the same as those of the structure-following network switching method provided in the above embodiments, and other technical features in this power system are the same as those disclosed in the structure-following network switching method of the above embodiments, which will not be elaborated here.

[0116] It should be understood that each part disclosed in this application can be implemented by hardware, software, firmware or a combination of them. In the description of the above embodiments, specific features, structures, materials or characteristics can be combined in a suitable manner in any one or more embodiments or examples.

[0117] The above is only the specific implementation manner of this application, but the protection scope of this application is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in this application should be covered by the protection scope of this application. Therefore, the protection scope of this application should be subject to the protection scope of the claims.

[0118] This application also provides a computer-readable storage medium, on which there are computer-readable program instructions (i.e., computer programs) for executing the structure-following network switching method in the above embodiments.

[0119] The computer-readable storage medium provided by this application can 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 of the above. More specific examples of computer-readable storage media may include, but are not limited to: portable computer disks with electrical connections having one or more wires, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM) or flash memory, optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, and so on, or any suitable combination of the above. In this embodiment, the computer-readable storage medium can be any tangible medium that contains or stores a program that can be used by an instruction execution system or device, or both in combination. The program code contained on the computer-readable storage medium can be transmitted using any appropriate medium, including but not limited to: wires, optical cables, RF (Radio Frequency), and so on, or any suitable combination of the above.

[0120] The above computer-readable storage medium can be included in the coordination controller; it can also exist separately and not be assembled into the coordination controller. The above computer-readable storage medium carries one or more programs, and when the above one or more programs are executed by the coordination controller, the coordination controller can implement the above functions defined in the structure network switching method disclosed in the embodiments of this application.

[0121] Computer program code for performing the operations of this application can be written in one or more programming languages or combinations thereof. The above programming languages include object-oriented programming languages - such as Java, Smalltalk, C++; it also includes 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, executed as an independent software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer can be connected to the user's computer through any type of network - including a local area network (LAN) or a wide area network (WAN) - or connected to an external computer, for example, using the Internet connection provided by an Internet service provider.

[0122] The flowcharts and block diagrams in the accompanying drawings illustrate the possible architectures, functions, and operations of methods, apparatuses, systems, and computer program products according to various embodiments of the present application. In this regard, each block in the flowchart or block diagram may represent a module, a segment of a program, or a part of code that contains one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than that marked in the accompanying drawings. For example, two consecutive blocks shown may actually be executed substantially in parallel, and they may sometimes be executed in the reverse order, depending on the functions involved. It should also be noted that each block in the block diagram and / or flowchart, as well as combinations of blocks in the block diagram and / or flowchart, may be implemented by a dedicated hardware-based system that performs the specified functions or operations, or may be implemented by a combination of dedicated hardware and computer instructions.

[0123] The modules described in the embodiments of the present application can be implemented in software or in hardware. Among them, the name of the module does not constitute a limitation on the unit itself in some cases.

[0124] The storage medium provided by the present application is a computer-readable storage medium, on which computer-readable program instructions (i.e., computer programs) for executing the above-mentioned network structure switching method are stored, which can solve the technical problem that the coordination control method in the related art lacks flexibility and cannot achieve better intelligent control. Compared with the related art, the beneficial effects of the computer-readable storage medium provided by the present application are the same as those of the network structure switching method provided by the above embodiments, and will not be elaborated here.

[0125] The above are only some embodiments of the present application, and do not limit the patent scope of the present application. Any equivalent structural transformation made using the specification and drawings of the present application under the technical concept of the present application, or direct / indirect application in other related technical fields, is included in the patent protection scope of the present application.

Claims

1. A handover method for a follow-up network, characterized in that, A coordination controller applied to a microgrid, the coordination controller includes a master station and multiple slave stations, the multiple slave stations are respectively connected to the master station, the microgrid further includes multiple substations, the multiple substations are correspondingly connected to the multiple slave stations, the multiple substations converge on a bus, and the bus is connected to the power grid through a connection point; The grid-connected switching method includes: Obtain the bus-side working parameters and grid-side working parameters of the connection point in real time through the master station; Using a power flow algorithm, obtain the real-time short-circuit ratio of the system according to the bus-side working parameters and the grid-side working parameters; Using a hysteresis strategy, determine the grid strength of the microgrid according to the real-time short-circuit ratio of the system; Determine the target mode according to the system operating conditions and / or the grid strength; the target mode includes a grid-forming mode or a grid-following mode; Generate a mode switching instruction according to the target mode, and send the mode switching instruction to each slave station, so that each slave station sends the mode switching instruction to the corresponding substation according to the grid strength, realizing the switching of the microgrid control mode.

2. The handover method of the root structure network according to claim 1, characterized in that, The bus-side working parameters include bus-side active power, bus-side reactive power, and bus-side current, and the grid-side working parameters include grid-side active power and grid-side reactive power; The step of using a power flow algorithm to obtain the real-time short-circuit ratio of the system according to the bus-side working parameters and the grid-side working parameters includes: Obtain the rated voltage of the connection point, the equivalent resistance of the power grid, the equivalent reactance of the power grid, the equivalent resistance of the connection point, and the equivalent reactance of the connection point; Obtain the system equivalent short-circuit impedance according to the square root of the sum of the squares of the first sum value obtained by summing the equivalent resistance of the power grid and the equivalent resistance of the connection point and the second sum value obtained by summing the equivalent reactance of the power grid and the equivalent reactance of the connection point; Obtain the real-time short-circuit ratio of the system according to the ratio between the rated voltage of the connection point and the product of the system equivalent short-circuit impedance and the bus-side active power.

3. The handover method of the root structure network according to claim 1, wherein The step of determining the target mode according to the system operating conditions includes: When the system operating condition is a power grid fault, determine the target mode as the grid-forming mode; When the system operating condition is the grid connection of the microgrid, determine the target mode as the grid-following mode; When the system operating condition is the islanding of the microgrid, determine the target mode as the grid-forming mode; When the system operating condition is the black start of the microgrid island, determine the target mode as the grid-forming mode.

4. The handover method of the root structure network according to claim 1, wherein, The step of determining the target mode according to the system operating conditions and the grid strength includes: Judge whether a system dispatching instruction related to the system operating conditions is received; If so, directly determine the target mode according to the system operating conditions corresponding to the system dispatching instruction; otherwise, further judge whether the grid strength is a strong power grid; If so, directly end; otherwise, determine the target mode according to the grid strength.

5. The handover method of the follow-up network according to claim 1 or 4, characterized in that The step of using a hysteresis strategy to determine the grid strength of the microgrid according to the real-time short-circuit ratio of the system includes: Compare the real-time short-circuit ratio of the system with a preset hysteresis lower boundary and a hysteresis upper boundary respectively; When the real-time short-circuit ratio of the system is less than or equal to the hysteresis lower boundary, determine that the grid strength is 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, it is determined that the grid strength is a strong grid; When the real-time short-circuit ratio of the system is greater than the upper boundary of the hysteresis loop, it is determined that the grid strength is an extremely strong grid; The determining of the target mode according to the grid strength includes: When the grid strength is a weak grid, it is determined that the target mode is the grid-forming mode; When the grid strength is a strong grid, directly end; When the grid strength is an extremely strong grid, it is determined that the target mode is the grid-following mode.

6. The handover method for a follow-up network as claimed in claim 5, wherein Each of the stations includes a plurality of grid-following inverters / converters and a plurality of grid-forming inverters / converters; The generating of the mode switching instruction according to the target mode and sending the mode switching instruction to each substation, so that each substation sends the mode switching instruction to the corresponding station according to the grid strength to realize the switching of the microgrid control mode includes: The master station generates a mode switching instruction according to the target mode and sends the mode switching instruction to each substation; Each substation sends the mode switching instruction to a batch of the corresponding plurality of grid-following inverters / converters or the plurality of grid-forming inverters / converters to switch the control mode of the first batch of inverters / converters in each station to the target mode; Judge whether the grid strength determined in real time is a strong grid; If so, directly end; otherwise, return to the step of each substation sending the mode switching instruction to a batch of the corresponding plurality of grid-following inverters / converters or the plurality of grid-forming inverters / converters to switch the control mode of the second batch of inverters / converters in each station to the target mode until the grid strength determined in real time is a strong grid.

7. The handover method of the follow-up network according to claim 6, characterized in that, The plurality of stations include a photovoltaic power generation station, a wind power generation station and an energy storage station. The photovoltaic power generation station and the wind power generation station both include a plurality of grid-following inverters and a plurality of grid-forming inverters, and the energy storage station includes a plurality of grid-following converters and a plurality of grid-forming converters; The sending of the mode switching instruction by each substation to a batch of the corresponding plurality of grid-following inverters / converters or the plurality of grid-forming inverters / converters includes: Each substation determines the grid-forming switching direction of the mode switching instruction; If the grid-forming switching direction is from grid-following to grid-forming, the energy storage station is used as the main switching object to control a batch of the plurality of grid-forming converters to work. When all the plurality of grid-forming converters are switched, then the photovoltaic power generation station and / or the wind power generation station is used as the secondary switching object to control a batch of the plurality of grid-forming inverters to work; If the grid-forming switching direction is from grid-forming to grid-following, the photovoltaic power generation station and / or the wind power generation station is used as the main switching object to control a batch of the plurality of grid-following inverters to work. When all the plurality of grid-following inverters are switched, then the energy storage station is used as the secondary switching object to control a batch of the plurality of grid-following converters to work.

8. A coordination controller, characterized in that Applied to a microgrid, the microgrid further includes a plurality of stations; the coordination controller includes a master station and a plurality of slave stations, the plurality of slave stations are respectively connected to the master station, the plurality of slave stations are correspondingly connected to the plurality of stations, the plurality of stations converge on a bus, and the bus is connected to the power grid through a connection point. The master station is used to implement the steps of the grid connection switching method according to any one of claims 1 to 7, and is used to control the operation of each of the slave stations.

9. The coordination controller according to claim 8, characterized in that, The plurality of slave stations are respectively communicatively connected to the master station through the GOOSE protocol, and the plurality of slave stations are correspondingly communicatively connected to the plurality of stations through the GOOSE protocol.

10. A power system, characterized in that, Comprising: A microgrid, the microgrid includes a coordination controller and a plurality of stations according to claim 8 or 9; A connection point switch; A power grid; Wherein, the coordination controller is connected to the plurality of stations, the plurality of stations converge on a bus, and the bus is connected to the power grid through the connection point switch.

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