Photovoltaic station island stability control and grid re-connection method based on energy storage cooperative regulation and control

Abstract

The invention discloses a photovoltaic station island stability control and re-grid-connection method based on energy storage cooperative regulation and control, and the method comprises the steps: carrying out the island detection in real time in a normal grid-connection state, and switching a photovoltaic system from a first working mode to a second working mode if tie line protection trips, so as to reduce the output power of the photovoltaic system; detecting the state of a grid-connected point circuit breaker, if the connection line circuit breaker is changed from closing to opening, executing connection line current detection, and when the connection line current is judged to be smaller than a current threshold value, switching the energy storage system from the first working mode to a second working mode to provide voltage and frequency support for the photovoltaic system; grid-connected detection: judging whether the island voltage, frequency and phase meet grid-connected conditions or not, if not, continuing grid-connected detection, and if yes, reclosing grid connection; and then, firstly switching the energy storage system from the second working mode to the first working mode, then switching the photovoltaic system from the second working mode to the first working mode, and recovering normal operation of the station.

Description

Technical Field

[0001] The present invention belongs to the technical field of photovoltaic power generation, and particularly relates to a method for stable control and reconnection of a photovoltaic power station island based on energy storage collaborative regulation. Background Art

[0002] With the development of the new power system, the number of terminal power stations accessing photovoltaic, energy storage, and load in the power grid is increasing day by day. According to the current operation requirements, when the main supply line fails, it is necessary to cut off the photovoltaic and energy storage before performing backup power supply automatic input (backup power supply automatic input device) and reclosing (automatically reclosing the circuit breaker that has tripped due to a fault as needed). However, the current control strategy is difficult to stabilize the grid voltage and frequency of the island when the tie line fails and the photovoltaic power station becomes an island because it does not utilize the energy storage of the photovoltaic power station for collaborative regulation, resulting in the anti-island protection action. The photovoltaic power station connected to the terminal load power station cannot achieve islanding crossing, the photovoltaic inverter is disconnected from the photovoltaic power station, and the photovoltaic power station cannot be quickly reconnected to the grid, resulting in the photovoltaic power station being disconnected from the grid and the phenomenon of light abandonment, causing a large amount of wind and light power generation losses and affecting the safe and stable operation of the power grid. Summary of the Invention

[0003] In order to solve the deficiencies of the prior art, achieve stable control of island voltage and frequency, quickly reconnect the photovoltaic power station to the grid, and ensure that the photovoltaic power station does not disconnect from the grid, the present invention adopts the following technical solutions: A method for stable control and reconnection of a photovoltaic system island based on energy storage collaborative regulation, comprising the following steps: Step 1: In the normal grid-connected state, perform island detection in real time to determine whether the tie line protection trips. If it does not trip, continue with island detection. If it trips, switch the photovoltaic system from the first working mode to the second working mode to reduce the output power of the photovoltaic system; Step 2: Detect the state of the grid connection point circuit breaker to determine whether the position of the tie line circuit breaker changes from closed to open. If it does not change to open, continue with the detection of the grid connection point circuit breaker state. If it changes to open, execute Step 3; By detecting the circuit breaker state, the true state of the line can be determined, thereby improving the accuracy of island determination; Step 3: Detect the tie line current to determine whether the tie line current is less than the current threshold of 0.05 A. If it is greater than or equal to the current threshold, continue with the tie line current detection; If it is less than the current threshold, switch the energy storage system from the first working mode to the second working mode to provide voltage and frequency support for the photovoltaic system, and execute Step 4; By detecting the tie line current, on the basis of the circuit breaker state detection, the true state of the line is further confirmed, which can avoid the risk brought by incorrect circuit breaker operation and further improve the accuracy of island determination; Step 4: Grid connection detection. Determine whether the island voltage, frequency, and phase meet the grid connection conditions. If not, continue with the grid connection detection. If they meet, perform reclosing grid connection. Step 5: After successful grid connection, first switch the energy storage system from the second working mode to the first working mode, and then switch the photovoltaic system from the second working mode to the first working mode, so that the photovoltaic power station returns to the normal grid-connected operation state.

[0004] Further, in Step 1, if a trip occurs, switch the photovoltaic inverter in the photovoltaic system from the MPPT working mode to the P / Q working mode, and set both the output power P and Q to 0. The MPPT working mode of the photovoltaic inverter is for the photovoltaic inverter to dynamically output the maximum power, and the P / Q working mode of the photovoltaic inverter is for the photovoltaic inverter to output the given active power P and reactive power Q. Reducing the output power of the photovoltaic inverter to 0 is because only by reducing the output power of the photovoltaic can the stable control of the island based on energy storage support be achieved. In Step 5, the photovoltaic system switches from the P / Q working mode to the MPPT working mode.

[0005] Further, in Step 3, if it is less than the current threshold, switch the energy storage system from the P / Q working mode to the V / F working mode. The P / Q working mode of the energy storage system is for the energy storage system to output the given active power P and reactive power Q, and the V / F working mode of the energy storage system is for the energy storage system to provide a voltage source with a given frequency to support the voltage and frequency in the case of an island in the photovoltaic power station. In Step 5, the energy storage system switches from the V / F working mode to the P / Q working mode, and the set values of P and Q are the same as before the fault.

[0006] Further, in Step 3, the current load is mainly the station service load of the photovoltaic power station. Therefore, the power of at least one energy storage inverter is greater than the maximum power of the station service load of the photovoltaic power station. The electricity quantity of the energy storage is at least: 10% of the rated capacity + P×t, where P represents the maximum power of the photovoltaic power station for electricity consumption, and t represents the action time to avoid the anti-islanding protection.

[0007] Before entering the islanding crossing control, it is first necessary to determine whether the strategic new energy power station meets the stable operation limit index. If not, do not start the islanding crossing control strategy. The stable operation index is that the power of at least one energy storage inverter is greater than the maximum power of the station service load of the photovoltaic power station, and the electricity quantity of the energy storage is at least: 10% of the rated capacity + P×t. By supporting the island system through the energy storage system to maintain stable operation, it can ensure that the photovoltaic inverter does not trip off the grid, providing hardware support for the next island reconnection to the grid.

[0008] Further, the current threshold is 0.05 A.

[0009] Further, the operation time for avoiding the anti-islanding protection is 2 seconds.

[0010] Further, in the fifth step, if a permanent fault is reclosed onto, after the circuit breaker trips, the backup power supply automatic switching device is started. If the photovoltaic power station is not equipped with a backup power supply automatic switching device, the islanding crossing control is terminated.

[0011] The method for stable control and reconnection of an island in a photovoltaic power station based on energy storage collaborative regulation is applied to an islanding crossing controller. The islanding crossing controller is respectively set in cooperation with the automatic generation control system and the local communication network of the photovoltaic power station, obtains the line operation information from the protection and measurement device of the photovoltaic power station, and uses the above-mentioned method for stable control and reconnection of an island in a photovoltaic system based on energy storage collaborative regulation to perform island reconnection.

[0012] Further, the signals connected to the islanding crossing controller include but are not limited to the tie line protection tripping signal, the tie line local side switch state signal, the one-phase, three-phase current, voltage, and power signals of the tie line, the reclosing device signal, the state of charge SOC (State of Charge) and power signal of the energy storage system, and the output power signal of the photovoltaic system.

[0013] The method for stable control and reconnection of an island in a photovoltaic power station based on energy storage collaborative regulation is applied to the automatic generation control system of the photovoltaic power station. The automatic generation control system controls the power distribution of each inverter on the station side according to the total power instruction issued by the superior dispatching master station system. When a tie line fault is detected and the protection device operates, the automatic generation control system transfers the control right to the islanding crossing controller connected thereto, so that the islanding crossing controller can perform island reconnection according to the above-mentioned method for stable control and reconnection of an island in a photovoltaic power station based on energy storage collaborative regulation applied to islanding crossing control. After grid connection, it retrieves the control right from the islanding crossing controller and continues the power distribution.

[0014] The advantages and beneficial effects of the present invention are as follows: The present invention makes full use of the existing energy storage configuration in the photovoltaic power station, without the need to increase the investment in additional energy storage systems. Through cooperation with the tie line reclosing and backup power supply automatic switching device, rapid reconnection can be achieved within 2 s after a fault occurs, avoiding the long-term disconnection of the photovoltaic power station from the grid. The present invention can realize rapid reconnection of the photovoltaic power station after it becomes an island, reducing the loss of wind and solar power generation. Most line faults are transient faults, and the existing treatment methods cause the new energy power station to be disconnected from the grid for a long time, which is not conducive to the economic operation of the power system. By using the energy storage system equipped in the new energy power station to achieve stable operation of the island and using reclosing to quickly connect to the grid after fault crossing, the power loss of photovoltaic and wind energy can be greatly reduced. The present invention can reduce the impact on the power grid caused by the large-area disconnection of the photovoltaic power station from the grid and enhance the stability of the power grid. Description of the Drawings

[0015] Figure 1 It is a schematic diagram of the failure of the interconnection line of a photovoltaic power station in the prior art.

[0016] Figure 2 It is a flowchart of the method in the embodiment of the present invention for implementing the fault ride-through strategy of the interconnection line of a photovoltaic power station.

[0017] Figure 3 It is a diagram showing the changes in voltage and current at the 110 kV grid connection point in the embodiment of the present invention.

[0018] Figure 4 It is a diagram showing the change in frequency at the 110 kV grid connection point in the embodiment of the present invention.

[0019] Figure 5 It is a diagram showing the change in the total power of the energy storage system in the embodiment of the present invention.

[0020] Figure 6 It is a diagram showing the change in the total power of the photovoltaic system in the embodiment of the present invention.

[0021] Figure 7 It is a schematic diagram of the application of the control strategy to a photovoltaic power station in the embodiment of the present invention. Detailed Embodiment

[0022] The following will describe in detail the specific embodiments of the present invention with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0023] As Figure 1 shown, in the prior art, when a fault occurs in the interconnection line, the line circuit breakers BRK1 and BRK2 will open, and the photovoltaic power station and the auxiliary power load will operate in an island mode. Due to the serious imbalance of power in the island power grid, the frequency and voltage will quickly deviate from the rated values, and the frequency / voltage protection of the photovoltaic inverter may quickly act, causing the photovoltaic inverter to disconnect from the photovoltaic power station, resulting in the inability of the new energy power station to achieve fault ride-through.

[0024] When a fault occurs in the tie line and the PV power station becomes an island, the current control strategy is difficult to stabilize the voltage and frequency of the island and cannot achieve the rapid reconnection of the PV power station to the grid because it does not utilize the energy storage of the PV power station for coordinated regulation. As a result, new energy is disconnected from the grid, leading to curtailment of wind and light, which affects the safe and stable operation of the power grid. According to the relevant technical regulations for distributed power sources connected to the grid, after the system is disturbed and disconnected from the grid, distributed power sources are not allowed to be reconnected to the grid until the grid voltage and frequency return to the normal operating range, and reconnection also requires permission from the dispatching department. However, since the anti-islanding protection time is only 2 s, once a fault occurs in the tie line of the PV power station, all control steps must be completed within 2 s to stabilize the frequency and voltage in the island, and then through reclosing, the tie line of the new energy power station can be reconnected to the grid. To achieve rapid reconnection to avoid the problem of new energy power stations being disconnected from the grid, it is necessary to first quickly stabilize the frequency and voltage of the system and then perform reclosing for reconnection.

[0025] Aiming at the problem that the PV new energy power station cannot achieve islanding through-fault when a fault occurs in the tie line, the present invention proposes a method for stable control and reconnection of a PV power station island based on energy storage coordinated regulation, enabling the stable control of the system voltage and frequency in the island by utilizing the existing energy storage configuration of the PV power station after a fault occurs in the tie line of the PV power station, and achieving the rapid reconnection of the PV power station within 2 s through the backup power supply automatic switching device and the reclosing device, thereby ensuring that the PV power station is not disconnected from the grid.

[0026] The PV inverters in the PV power station have two working modes respectively: one is the MPPT working mode (the PV inverter dynamically outputs the maximum power), and the other is the P / Q working mode (the PV inverter outputs the given active power P and reactive power Q).

[0027] Similarly, the energy storage system also has two working modes. One is the P / Q mode (the energy storage system outputs the given active power P and reactive power Q); the other is the V / F working mode (the energy storage system provides a voltage source with a given frequency to support the voltage and frequency in the case of the PV power station island). After the PV power station becomes an island, by changing the control modes of the PV and the energy storage and cooperating with the inherent backup power supply automatic switching / reclosing device of the line, rapid reconnection of the island within 2 s is achieved on the premise of ensuring that the PV power station is not disconnected from the grid.

[0028] Specifically, as Figure 2 shown, the following control strategy is executed through the method of the present invention: Step 1: During the normal grid connection state, island detection is performed in real time; Normal grid connection state: The PV inverter operates in the maximum power tracking mode (MPPT); the energy storage system operates in the P / Q mode and absorbs or emits power according to the set target value; The system performs islanding detection in real time to determine whether a tie-line protection trip command is detected. If the determination is negative, continue with islanding detection; if the determination is positive, i.e., a tie-line protection trip command is detected, immediately act to switch the PV inverter from the MPPT mode to the P / Q operating mode, set both the output power P and Q to 0, and execute Step 2.

[0029] Once a tie-line protection trip command is detected, first reduce the output power of the PV inverter to 0. This is a very crucial step. Only by reducing the output power of the PV can stable islanding control based on energy storage support be achieved.

[0030] Step 2: Detection of the grid connection point breaker status. Determine whether the position of the tie-line breaker has changed from closed to open. If the determination is negative, continue with the detection of the grid connection point breaker status; if the determination is positive, i.e., the position of the tie-line breaker has changed from closed to open, then perform the tie-line current detection in Step 3. By detecting the breaker status, the true status of the line can be determined, thereby improving the accuracy of islanding determination.

[0031] Step 3: Tie-line current detection. Determine whether the tie-line current is less than the current threshold of 0.05 A. If the determination is negative, continue with the tie-line current detection; if the determination is positive, immediately switch the energy storage from the P / Q operating mode to the V / F operating mode to provide voltage and frequency support for the PV power station, and execute Step 4.

[0032] By detecting the tie-line current, on the basis of the breaker status detection, the true status of the line is further confirmed, which can avoid the risk brought by incorrect breaker operation and further improve the accuracy of islanding determination. Once it is determined that the PV power station has entered the islanding state, the energy storage system needs to be immediately switched from the P / Q operating state to the V / F control mode to provide voltage and frequency support for the PV power station and ensure the stable operation of the PV power station islanding system. At this time, the load is mainly the station service load of the PV power station. It is set according to the operating time of 2 s to avoid the anti-islanding protection. At least one energy storage inverter's power > the maximum power of the PV power station's station service load; the electricity of this energy storage is at least: 10% of the rated capacity + P × 2 s, where P is the maximum power of the station service. By the support of the energy storage system, the islanding system can maintain stable operation, which can ensure that the PV inverter does not trip off the grid and provide hardware support for the next islanding reconnection.

[0033] Step 4: Grid connection detection. Determine whether the island voltage, frequency, and phase meet the grid connection conditions. If the determination is negative, continue with the grid connection detection; if the determination is positive, immediately perform reclosing grid connection; Step 5: After successful grid connection, immediately switch the energy storage from V / F operating mode to P / Q operating mode, and keep the P and Q set values the same as before the fault; switch the PV from P / Q operating mode to MPPT mode; the PV power station returns to the normal grid-connected operation state.

[0034] Once the synchronization detection for grid connection is successful, it is necessary to first switch the control mode of the energy storage system from V / F control mode to P / Q control mode, and then switch the PV system to MPPT mode. The entire control process can be completed within 2 s to successfully avoid the anti-islanding protection action of the inverter, thereby realizing the islanding crossing of the tie line fault of the PV power station.

[0035] To prove the effectiveness of the present invention, a topology diagram of the PV power station was constructed to build a corresponding simulation model: Simulation settings: At the initial state, the PV is fully loaded (MPPT, output power 100 MW), the energy storage is fully loaded (PQ, output power 10 MW), and the load is 1 MW; three-phase short-circuit fault (phase-to-phase fault resistance Ron = 2 Ω), islanding f = 49.5 Hz. The fault occurs at t = 0.5 s; at t = 0.53 s, the protection action occurs; at t = 0.63 s, the switches on both sides of the 110 kV tie line trip, and the fault is removed; at t = 1.5 s, the switch on the opposite side of the 110 kV recloses. Protection action time: 30 ms, delay of the control command to the PV inverter: 20 ms; breaker action time: 100 ms, delay of the control command to the energy storage inverter: 20 ms.

[0036] As Figures 3 to 6 shown, at t = 0 s, the system is in a normal grid-connected state: the PV inverter operates in the maximum power tracking mode (MPPT); the energy storage system operates in the P / Q mode and absorbs or emits power according to the set target value; at t = 0.5 s, a three-phase short-circuit fault occurs at 5 km from the outlet of the 110 kV tie line; after the fault, the field control system of the power station automatically executes the control strategy of the present invention: According to the simulation settings: at t = 0.5 s, a three-phase short-circuit fault occurs at the midpoint of the tie line; at t = 1.5 s, the switch on the opposite side of the 110 kV recloses. The target frequency of the islanding system of the PV power station is set to 49.5 Hz.

[0037] The set grid connection conditions are that the voltage amplitude difference between both sides of the tie line switch ≤ ±10%, the phase angle difference ≤ ±30°, and the frequency difference ≤ ±1 Hz. The system automatically detects, and when the three conditions are simultaneously met, the switch automatically closes, and the PV power station operates in grid connection.

[0038] From the simulation results, when the proposed islanding operation control strategy of the PV power station is adopted and a three-phase short-circuit fault occurs at the midpoint of the tie line at t = 0.5 s under the working conditions set above, the PV power station can achieve stable control of the station voltage and frequency through the support of the energy storage system after the fault, and can achieve automatic grid connection at about t = 2.175 s (1.675 s after the fault).

[0039] Considering the initial states of the PV and energy storage systems and different fault types, the proposed control strategy of the present invention is further verified by simulation. The simulation results are shown in Table 1: Table 1: Simulation verification results of the control strategy

[0040] The islanding operation control strategy of the present invention is applied on site as follows: (1) Before entering the islanding operation control, it is necessary to first determine whether the new energy power station meets the stable operation limit index. If not, the islanding operation control strategy is not started; (the stable operation index is: to maintain the stable operation of the new energy power station in islanding, at least the power of one energy storage inverter > the maximum power of the station service load of the PV power station; the power of this energy storage is at least: 10% of the rated capacity + P × 2 s, where P is the maximum power of the station service). (2) If the stable operation limit index is met, the islanding operation control strategy is started, and the stable control of the island voltage and frequency is first achieved. (3) After the protection of the 110 kV tie line operates, the reclosing is started. In the way of checking synchronization, it is judged whether the island voltage, frequency and phase meet the grid connection conditions. If so, the reclosing is immediately carried out for grid connection. (4) If it is an instantaneous fault, the grid connection is successful, and then the PV is switched from the P / Q operation mode to the MPPT mode; the energy storage is switched from the V / F control mode to the P / Q operation mode, and the set values of P and Q are the same as those before the fault. The PV power station returns to the normal grid-connected operation state.

[0041] (5) If the reclosing is to a permanent fault and the circuit breaker trips, the backup power supply automatic switching device is started. If the power station is not equipped with a backup power supply automatic switching device, the islanding operation control is terminated.

[0042] When the proposed control strategy of the present invention is applied on site, it is necessary to develop a prototype of the islanding operation controller according to the control strategy. Then the prototype cooperates with the existing AGC (Automatic Generation Control) system and the local communication network of the PV power station to achieve the goal. As Figure 7As shown in the figure, the flexible island controller prototype obtains the line operation information from the substation protection and measurement device, and analyzes and detects the substation operation status in real time. The signals that need to be connected to the islanding crossing controller prototype mainly include: (1) the tripping signal of the tie line protection; (2) the switch status signal of the local side of the tie line; (3) the current, voltage, and power signals of one circuit of the connecting line, three-phase; (4) the reclosing device signal; (5) the SOC and power signals of the energy storage system; (6) the output power signal of the photovoltaic system. The input of these signals provides a judgment basis for the prototype to execute the control strategy.

[0043] The islanding crossing controller prototype is connected to the substation AGC system. After detecting the islanding operation status of the substation, it timely issues a predetermined inverter mode switching control command to the corresponding photovoltaic and energy storage inverters, and realizes the stable control of the system through the switching of the inverter operation mode; after the prototype receives the reclosing command and detects the island reconnection to the grid, the prototype can timely issue a predetermined inverter mode switching control command to realize the island reconnection to the grid.

[0044] When the photovoltaic substation is operating normally, the AGC control system controls the power distribution of each inverter on the substation side according to the total power instruction issued by the superior dispatching master station system. The flexible island controller mainly performs the island detection task and does not interfere with the substation power adjustment; when detecting a tie line fault and the protection device operates, the AGC control system is transferred to be controlled by the flexible island controller, and the predetermined power adjustment instruction of the prototype is sent to each inverter for inverter control mode conversion and power adjustment. Until the reclosing is completed and the substation system resumes normal operation, the AGC system continues to control the power distribution of each inverter on the substation side according to the total power instruction issued by the superior dispatching master station system, and the flexible island controller continues to perform the island detection task and does not participate in the power adjustment.

[0045] The present invention utilizes the existing energy storage configuration of the photovoltaic substation, without the need to increase the investment in an additional energy storage system. Through the cooperation with the tie line reclosing and the backup power supply automatic switching device, it can achieve rapid reconnection to the grid within 2 s after a fault occurs, and avoid the long-term disconnection of the photovoltaic substation from the grid.

[0046] The present invention can realize the rapid reconnection to the grid after the photovoltaic substation becomes an island, and reduce the loss of wind and solar power generation. Most of the line faults are instantaneous faults, and the existing processing methods cause the new energy substation to be disconnected from the grid for a long time, which is not conducive to the economic operation of the power system. By using the energy storage system configured in the new energy substation to realize the stable operation of the island, and using the reclosing to quickly connect to the grid after the fault crossing, the power loss of photovoltaic and wind energy can be greatly reduced.

[0047] The method proposed by the present invention can reduce the impact on the power grid caused by the large-area disconnection of the photovoltaic substation from the grid, and enhance the stability of the power grid.

[0048] This invention fully exploits the multifunctional application scenarios of energy storage. In new power systems, energy storage not only needs to provide basic functions such as smooth transition, peak shaving, and frequency and voltage regulation, but also plays a more important role in fault protection for new energy stations. Energy storage can be used to achieve stable operation of isolated new energy stations, improve their fault ride-through capabilities, and further expand the application scenarios of energy storage.

[0049] The present invention utilizes energy storage to achieve stable operation of the photovoltaic station island, which is beneficial to the setting of the reclosing constant and improves the success rate of the photovoltaic station reclosing action. The reclosing constant of the photovoltaic station interconnection line has always been difficult to adjust. If the synchronization check method is adopted, when all new energy inverters are off-grid, line reclosing is difficult to succeed; if the no-voltage check method is adopted, when the photovoltaic inverter and the commonly used electrical load form an island operation, line reclosing is also difficult to succeed. Therefore, if energy storage can be used to control the stable operation of the photovoltaic station island, the island of the new photovoltaic station can be connected to the grid again through the synchronization check reclosing, which is of great benefit to the setting of the reclosing.

[0050] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for islanding stability control and reconnection of a photovoltaic system based on coordinated energy storage regulation, characterized in that It includes the following steps: Step 1: During normal grid connection, perform islanding detection in real time to determine whether the tie-line protection trips. If it does not trip, continue with islanding detection. If it trips, switch the photovoltaic system from the first working mode to the second working mode to reduce the output power of the photovoltaic system; Step 2: Detect the state of the grid connection point breaker to determine whether the tie-line breaker changes from closed to open. If it does not change to open, continue with the detection of the grid connection point breaker state. If it changes to open, execute Step 3; Step 3: Detect the tie-line current to determine whether the tie-line current is less than the current threshold. If it is greater than or equal to the current threshold, continue with the tie-line current detection; If it is less than the current threshold, switch the energy storage system from the first working mode to the second working mode to provide voltage and frequency support for the photovoltaic system, and execute Step 4; Step 4: Perform grid connection detection to determine whether the island voltage, frequency, and phase meet the grid connection conditions. If they do not meet, continue with the grid connection detection. If they meet, perform reclosing grid connection; Step 5: After successful grid connection, first switch the energy storage system from the second working mode to the first working mode, and then switch the photovoltaic system from the second working mode to the first working mode.

2. The method for islanding stability control and reconnection of a photovoltaic system based on energy storage collaborative regulation according to claim 1, wherein: In Step 1, if it trips, switch the photovoltaic inverter in the photovoltaic system from the MPPT working mode to the P / Q working mode, and set both the output power P and Q to 0. The MPPT working mode of the photovoltaic inverter is that the photovoltaic inverter dynamically outputs the maximum power, and the P / Q working mode of the photovoltaic inverter is that the photovoltaic inverter outputs the given active power P and reactive power Q; In Step 5, the photovoltaic system switches from the P / Q working mode to the MPPT working mode.

3. The method for islanding stability control and reconnection of a photovoltaic system based on energy storage collaborative regulation according to claim 1, wherein: In Step 3, if it is less than the current threshold, switch the energy storage system from the P / Q working mode to the V / F working mode. The P / Q working mode of the energy storage system is that the energy storage system outputs the given active power P and reactive power Q, and the V / F working mode of the energy storage system is that the energy storage system provides a voltage source with a given frequency to support the voltage and frequency in the case of an island in the photovoltaic power station; In Step 5, the energy storage system switches from the V / F working mode to the P / Q working mode, and the set values of P and Q are the same as those before the fault.

4. The method for islanding stability control and reconnection of a photovoltaic system based on energy storage collaborative regulation according to claim 3, wherein: In Step 3, the power of at least one energy storage inverter is greater than the maximum power of the on-site power load of the photovoltaic power station, and the electricity quantity of the energy storage is at least: 10% of the rated capacity + P × t, where P represents the maximum power of the photovoltaic power station for electricity consumption, and t represents the action time to avoid the anti-islanding protection.

5. The method for islanding stability control and reconnection of a photovoltaic system based on energy storage collaborative regulation according to claim 3, wherein: The current threshold is 0.05 A.

6. The method for islanding stability control and reconnection of a photovoltaic system based on energy storage collaborative regulation according to claim 3, wherein: The action time to avoid the anti-islanding protection is 2 seconds.

7. The method for islanding stability control and reconnection of a photovoltaic system based on energy storage collaborative regulation according to claim 1, characterized in that: In Step 5, if reclosing onto a permanent fault and the breaker trips, then start the backup power supply automatic switching device. If the photovoltaic power station is not equipped with a backup power supply automatic switching device, terminate the islanding crossing control.

8. A photovoltaic power station island stability control and reconnection method based on energy storage collaborative regulation, applied to an islanding crossing controller, characterized in that: The islanding crossing controller is respectively set in cooperation with the automatic generation control system and the local communication network of the photovoltaic power station, obtains the line operation information from the protection and measurement device of the photovoltaic power station, and performs islanding reconnection using the method for stable control and reconnection of the photovoltaic system islanding based on energy storage collaborative regulation described in any one of claims 1 to 7.

9. The method for stable control and reconnection of an islanded photovoltaic power station based on energy storage collaborative regulation according to claim 8, wherein: The signals connected to the islanding crossing controller include but are not limited to the tie line protection tripping signal, the tie line local side switch status signal, the one-phase and three-phase current, voltage, and power signals of the tie line, the reclosing device signal, the charge state and power signal of the energy storage system, and the output power signal of the photovoltaic system.

10. A method for stable control and reconnection of an islanded photovoltaic power station based on coordinated energy storage regulation, which is applied to the automatic generation control system of a photovoltaic power station, characterized in that: The automatic generation control system controls the power distribution of each inverter on the station side according to the total power instruction issued by the superior dispatching master station system. When a tie line fault is detected and the protection device operates, the automatic generation control system transfers the control right to the connected islanding crossing controller, so that the islanding crossing controller can perform islanding reconnection according to the method for stable control and reconnection of a photovoltaic power station island based on energy storage collaborative regulation described in claim 8. After grid connection, it retrieves the control right from the islanding crossing controller and continues the said power distribution.

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