A black start method for weakly connected island microgrid with wind and energy storage collaboration

Abstract

The present invention proposes a black start method for a weakly linked island microgrid with "wind-storage" collaboration. The microgrid consists of an energy storage system, wind turbines, transmission lines, and loads. The microgrid is connected to the large power grid outside the island through a single submarine cable. When the submarine cable fails and the island microgrid becomes an isolated network, the island microgrid achieves a black start by collaboratively controlling the energy storage system and wind turbines. The method includes the following stages: in the first stage, the submarine cable fault is first isolated, and the island isolated grid system is checked and operated to meet the black start conditions. Secondly, the energy storage system is remotely controlled to start and boost the voltage of the entire island distribution transformer in an off-grid operation mode to restore power supply to important loads. In the second stage, wind power generation is started, and the energy storage system and wind turbines are precisely controlled by the microgrid controller to coordinate and gradually restore power supply to non-important loads, ultimately achieving long-term stable off-grid operation of the island microgrid. The present invention carries out black starts in an orderly manner in two stages, thereby ensuring the reliability of island power supply during the emergency repair of the submarine cable failure.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy power systems, and in particular to a black start method for a weakly connected island microgrid with "wind and storage" collaboration. Background Art

[0002] Building a new power system with new energy as the main body is the basis for achieving "carbon peak" and "carbon neutrality", and the new power system is an important part of a clean, low-carbon, safe and efficient energy system.

[0003] In order to improve the power supply reliability and power quality of islands, fishing cages and other scenes in the offshore area, improve the utilization efficiency of clean energy, and build a weakly connected microgrid with "wind storage" coordination, it is a typical demonstration application of building a new power system. Taking the Xiyang Island Microgrid in Xiapu, Ningde as an example, the island I circuit is the only incoming power supply for Xiyang Island. The submarine cable is frequently cut due to the anchoring of passing ships, and the average repair time is more than 15 days. The Xiyang Island Microgrid is currently equipped with 3 wind turbines (2MW / unit), 1MW / 2MWh energy storage, and a maximum load of 2.5MW, of which the heavy The load is about 900kW. Due to the low automation level of the island's distribution network, weak basic configuration, and the lack of remote control function of the low-voltage side switch of the distribution transformer, coupled with the strong intermittent fluctuations in wind power output, small energy storage capacity, and the load far exceeding the storage, the Xiyang Island microgrid faces many problems and challenges in achieving a black start after the submarine cable failure. According to the normal power supply mode, after establishing the microgrid switch station voltage with wind turbines and energy storage as the source, by closing the microgrid switch station outgoing switch, the excitation surge current generated by the no-load impact load distribution transformer will cause the energy storage converter to overcurrent trip, resulting in black start failure.

[0004] It can be seen that in order to solve the black start problem of island microgrids similar to the Xiyang Island microgrid, it is very necessary to establish an effective black start method. This method is based on the problems of small energy storage capacity, strong intermittent fluctuation of wind power output, load greater than storage and low level of automation of island distribution network. It carries out microgrid black start in two stages and has been successfully applied in the black start of the Xiyang Island microgrid. This method has a good reference significance for the rational use of clean energy and solving the problem of island power supply reliability during submarine cable failure. Summary of the Invention

[0005] The present invention proposes a black start method for a weakly connected island microgrid with "wind-storage" collaboration, which can effectively solve the problem of black start failure caused by the small energy storage capacity of the island microgrid, the load being greater than the storage, the intermittent fluctuation of wind power, and the insufficient anti-excitation inrush current capability of the energy storage converter. The black start is carried out in an orderly manner in two stages, ensuring the reliability of island power supply during the emergency repair of submarine cable failures.

[0006] The present invention adopts the following technical solutions.

[0007] A black start method for a weakly connected island microgrid with wind and energy storage synergy. The island microgrid consists of an energy storage system, wind turbines, transmission lines, and loads. The microgrid is connected to the main power grid outside the island via a single submarine cable.

[0008] When a submarine cable failure causes the island microgrid to become an isolated network, the island microgrid can achieve a black start by coordinating the energy storage system and wind turbine generators. This includes the following stages:

[0009] In the first phase, the submarine cable fault was isolated, and the island's isolated grid system was checked and operated to meet black start conditions. Next, the energy storage system was remotely controlled to operate in off-grid mode, leading the island's distribution transformers to zero-start and boost voltage, restoring power to critical loads.

[0010] In the second stage, wind power generation is started, and the energy storage system and wind turbines are coordinated and precisely controlled by the microgrid controller to gradually restore power supply to non-critical loads, ultimately achieving long-term stable off-grid operation of the island microgrid.

[0011] The maximum capacity of the energy storage system can meet the short-term power supply needs of important loads in the island microgrid, and the total rated output of the wind turbines is greater than the maximum load on the island.

[0012] The microgrid is a weakly connected microgrid, which is connected to the main power grid outside the island through only one submarine cable. The failure of the submarine cable has caused the island microgrid to become an isolated network, which means that the island is disconnected from the main power grid. The submarine cable maintenance time is at least 15 days, and only diesel generators can be used to guarantee power supply to some users.

[0013] The first stage specifically includes the following steps:

[0014] Step S1: In the dispatching system, operate the island microgrid's entry switch to the open position, disconnect the submarine cable from the island grid, and isolate the fault point;

[0015] Step S2: In the distribution and dispatching system, operate the high-voltage side switch of the distribution transformer in the island microgrid power supply area, the line section / branch switch, the high-voltage side switch of the wind turbine box transformer, and the outgoing line switch of the microgrid switch station to the closed position to ensure that the 10kV system on the island is in a connected state.

[0016] Step S3: locally operate all the low-voltage side switches of the distribution transformer to the open position, and operate the low-voltage side switches of the fan box transformer and the low-voltage side switches of the energy storage transformer to the closed position.

[0017] Step S4: Check that the dispatching system and the microgrid controller are communicating normally, check that the energy storage charge is greater than 30%, check that the energy storage battery fire protection system and water cooling system are operating normally, check that the communication between the microgrid switch station battery management system and the energy storage converter is normal, check that the microgrid controller and the energy storage converter and wind turbine control system are communicating normally, and there are no other abnormal alarms. Verify that the island wind turbine is in a shutdown state.

[0018] After the black start conditions are met in the first stage, the energy storage system is remotely controlled to start the entire island distribution transformer at zero voltage in off-grid operation mode to restore power supply to important loads. The steps are as follows: the distribution system remotely sets the energy storage converter to off-grid operation mode and issues a black start command with one click. The energy storage system completes the zero start voltage of the entire island distribution transformer at a preset rate, and the voltage of the microgrid system is stabilized at 10kV. Then, the low-voltage side switches of the distribution transformer are closed on-site in order of load importance to restore power supply to important loads.

[0019] When the energy storage capacity of the energy storage system is weak, and the energy storage converter is not compatible with the magnetizing inrush current operating condition of the large-capacity load distribution transformer of the island microgrid with no-load closing and an overcurrent tripping phenomenon occurs under this operating condition, the energy storage system completes the zero starting voltage of the distribution transformer of the entire island at a preset rate, and adopts a zero starting voltage boosting method to avoid the magnetizing inrush current generated by the no-load impact distribution transformer, which may cause the energy storage converter to trip due to overcurrent.

[0020] In the second phase, wind power generation is started. The microgrid controller precisely controls the coordination of wind and energy storage, gradually restoring power supply to non-critical loads and achieving long-term stable operation of the island microgrid off-grid. The steps are as follows:

[0021] Step A1: The dispatching master station issues start-up instructions to each wind turbine generator set. The microgrid controller sets the wind turbine start-stop control instructions to the running position one by one and controls the wind turbine generator to operate in a limited power mode.

[0022] Step A2: If the wind turbines in the wind turbine generator station do not meet the starting conditions, the energy storage system will only supply power to the important loads and operate until the wind turbines meet the conditions before automatically starting the wind turbines. If the energy storage system power drops to 30% and the wind turbines still do not meet the starting conditions, all loads will be removed and the next black start will be performed.

[0023] Step A3: The wind turbine is successfully started and connected to the grid, and the energy storage system is in a charging state. When the remaining energy storage capacity reaches 60%, non-critical loads are put into operation in sequence.

[0024] Step A4: Check that the distribution transformers on the entire island are operating normally and the voltage and frequency of the microgrid are stable. Complete the black start of the island microgrid, and then operate the microgrid to enter the off-grid self-balancing mode at the dispatching master station.

[0025] The power limiting mode of the wind turbine is specifically as follows: assuming the load power is PL and the energy storage rated power is PC, the given power value of the wind turbine is (0.8PC+PL) / N, where N is the number of wind turbines, and the energy storage operates in a charging mode of 0.8PC.

[0026] The low-voltage side switches of the island microgrid distribution transformer are devices that do not have remote control functions, and there is no communication link between the island microgrid switch station and the high and low voltage switches on the island.

[0027] The beneficial effects of the present invention are:

[0028] (1) The energy storage system is used to boost the voltage of the distribution transformers on the entire island, thus avoiding the problem of black start failure caused by overcurrent tripping of the energy storage converter due to the excitation surge current of the distribution transformer. Through the coordinated control of "wind, load and storage", the load power supply is restored in an orderly manner, and the black start of the microgrid is successfully achieved, which ensures the reliability of the island power supply, promotes the consumption of clean energy, and replaces the traditional diesel power generation mode, with significant economic benefits.

[0029] (2) This method provides useful experience for the black start of island microgrids equipped with small-capacity energy storage systems.

[0030] The method described in the present invention effectively solves the problem of black start failure caused by small energy storage capacity of the island microgrid, load exceeding storage, intermittent fluctuations in wind power, and insufficient anti-excitation inrush current capability of the energy storage converter. The black start is carried out in an orderly manner in two stages, ensuring the reliability of island power supply during the emergency repair of submarine cable failures.

[0031] The present invention discloses a black start method for a weakly linked island microgrid with "wind storage" coordination, which includes two stages: in the first stage, the submarine cable fault is first isolated, and the island microgrid system is checked and operated to meet the black start conditions. Secondly, the energy storage system is remotely controlled to start the zero-start voltage boost of the distribution transformer of the entire island in an off-grid operation mode to restore the power supply of important loads; in the second stage, wind power generation is started, and the coordination of "wind storage" is precisely controlled by the microgrid controller to gradually restore the power supply of non-important loads, and finally achieve long-term stable operation of the island microgrid off-grid. The black start operation in the above two stages solves the problem of overcurrent tripping of the energy storage converter caused by the excitation surge current of the load distribution transformer. After the microgrid voltage is established, the load power supply is gradually restored through the coordinated control of the wind power generation and energy storage system, and finally the reliability of the island power supply during the isolated island operation is guaranteed. The application of the present invention has promoted the island into a new era of clean energy replacing traditional diesel power generation, has significant economic benefits, and provides a useful reference for assisting the construction of new power systems.

[0032] This invention has been successfully applied in the Xiyang Island Microgrid Demonstration Project in Xiapu, Ningde. It solved the problem of black start of the island power grid after a submarine cable failure, and ushered in a new era of replacing traditional diesel power generation with clean energy. It has significant economic benefits and provides a useful reference for assisting the construction of new power systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0034] Attachment Figure 1 This is a schematic diagram of the "wind storage" weakly connected island microgrid in the present invention.

[0035] Attachment Figure 2Schematic diagram of the black start process of the present invention. DETAILED DESCRIPTION

[0036] As shown in the figure, a black start method for a weakly connected island microgrid with wind and energy storage collaboration is proposed. The island microgrid consists of an energy storage system, wind turbines, transmission lines, and loads. The microgrid is connected to the main power grid outside the island via a single submarine cable.

[0037] When a submarine cable failure causes the island microgrid to become an isolated network, the island microgrid can achieve a black start by coordinating the energy storage system and wind turbine generators. This includes the following stages:

[0038] In the first phase, the submarine cable fault was isolated, and the island's isolated grid system was checked and operated to meet black start conditions. Next, the energy storage system was remotely controlled to operate in off-grid mode, leading the island's distribution transformers to zero-start and boost voltage, restoring power to critical loads.

[0039] In the second stage, wind power generation is started, and the energy storage system and wind turbines are coordinated and precisely controlled by the microgrid controller to gradually restore power supply to non-critical loads, ultimately achieving long-term stable off-grid operation of the island microgrid.

[0040] The maximum capacity of the energy storage system can meet the short-term power supply needs of important loads in the island microgrid, and the total rated output of the wind turbines is greater than the maximum load on the island.

[0041] The microgrid is a weakly connected microgrid, which is connected to the main power grid outside the island through only one submarine cable. The failure of the submarine cable has caused the island microgrid to become an isolated network, which means that the island is disconnected from the main power grid. The submarine cable maintenance time is at least 15 days, and only diesel generators can be used to guarantee power supply to some users.

[0042] The first stage specifically includes the following steps:

[0043] Step S1: In the dispatching system, operate the island microgrid's entry switch to the open position, disconnect the submarine cable from the island grid, and isolate the fault point;

[0044] Step S2: In the distribution and dispatching system, operate the high-voltage side switch of the distribution transformer in the island microgrid power supply area, the line section / branch switch, the high-voltage side switch of the wind turbine box transformer, and the outgoing line switch of the microgrid switch station to the closed position to ensure that the 10kV system on the island is in a connected state.

[0045] Step S3: locally operate all the low-voltage side switches of the distribution transformer to the open position, and operate the low-voltage side switches of the fan box transformer and the low-voltage side switches of the energy storage transformer to the closed position.

[0046] Step S4: Check that the dispatching system and the microgrid controller are communicating normally, check that the energy storage charge is greater than 30%, check that the energy storage battery fire protection system and water cooling system are operating normally, check that the communication between the microgrid switch station battery management system and the energy storage converter is normal, check that the microgrid controller and the energy storage converter and wind turbine control system are communicating normally, and there are no other abnormal alarms. Verify that the island wind turbine is in a shutdown state.

[0047] After the black start conditions are met in the first stage, the energy storage system is remotely controlled to start the entire island distribution transformer at zero voltage in off-grid operation mode to restore power supply to important loads. The steps are as follows: the distribution system remotely sets the energy storage converter to off-grid operation mode and issues a black start command with one click. The energy storage system completes the zero start voltage of the entire island distribution transformer at a preset rate, and the voltage of the microgrid system is stabilized at 10kV. Then, the low-voltage side switches of the distribution transformer are closed on-site in order of load importance to restore power supply to important loads.

[0048] When the energy storage capacity of the energy storage system is weak, and the energy storage converter is not compatible with the magnetizing inrush current operating condition of the large-capacity load distribution transformer of the island microgrid with no-load closing and an overcurrent tripping phenomenon occurs under this operating condition, the energy storage system completes the zero starting voltage of the distribution transformer of the entire island at a preset rate, and adopts a zero starting voltage boosting method to avoid the magnetizing inrush current generated by the no-load impact distribution transformer, which may cause the energy storage converter to trip due to overcurrent.

[0049] In the second phase, wind power generation is started. The microgrid controller precisely controls the coordination of wind and energy storage, gradually restoring power supply to non-critical loads and achieving long-term stable operation of the island microgrid off-grid. The steps are as follows:

[0050] Step A1: The dispatching master station issues start-up instructions to each wind turbine generator set. The microgrid controller sets the wind turbine start-stop control instructions to the running position one by one and controls the wind turbine generator to operate in a limited power mode.

[0051] Step A2: If the wind turbines in the wind turbine generator station do not meet the starting conditions, the energy storage system will only supply power to the important loads and operate until the wind turbines meet the conditions before automatically starting the wind turbines. If the energy storage system power drops to 30% and the wind turbines still do not meet the starting conditions, all loads will be removed and the next black start will be performed.

[0052] Step A3: The wind turbine is successfully started and connected to the grid, and the energy storage system is in a charging state. When the remaining energy storage capacity reaches 60%, non-critical loads are put into operation in sequence.

[0053] Step A4: Check that the distribution transformers on the entire island are operating normally and the voltage and frequency of the microgrid are stable. Complete the black start of the island microgrid, and then operate the microgrid to enter the off-grid self-balancing mode at the dispatching master station.

[0054] The power limiting mode of the wind turbine is specifically as follows: assuming the load power is PL and the energy storage rated power is PC, the given power value of the wind turbine is (0.8PC+PL) / N, where N is the number of wind turbines, and the energy storage operates in a charging mode of 0.8PC.

[0055] The low-voltage side switches of the island microgrid distribution transformer are devices that do not have remote control functions, and there is no communication link between the island microgrid switch station and the high and low voltage switches on the island.

[0056] The dispatching system in this embodiment is a dispatching system of an island microgrid.

[0057] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. A black start method for a weakly linked island microgrid with wind and energy storage synergy, characterized by: The island microgrid consists of an energy storage system, wind turbines, transmission lines, and loads. The microgrid is connected to the main power grid outside the island via a single submarine cable. When a submarine cable failure causes the island microgrid to become an isolated network, the island microgrid can achieve a black start by coordinating the energy storage system and wind turbine generators. This includes the following stages: In the first phase, the submarine cable fault was isolated, and the island's isolated grid system was checked and operated to meet black start conditions. Next, the energy storage system was remotely controlled to operate in off-grid mode, leading the island's distribution transformers to zero-start and boost voltage, restoring power to critical loads. In the second phase, wind power generation is started. The microgrid controller precisely controls the energy storage system and wind turbines to coordinate and gradually restore power to non-critical loads, ultimately achieving long-term stable off-grid operation of the island microgrid. The first stage specifically includes the following steps: Step S1: In the dispatching system, operate the island microgrid's entry switch to the open position, disconnect the submarine cable from the island grid, and isolate the fault point; Step S2: Operate the high-voltage side switch of the distribution transformer in the island microgrid power supply area, the line section / branch switch, the high-voltage side switch of the wind turbine box transformer, and the outgoing line switch of the microgrid switch station to the closed position in the distribution system to ensure that the 10kV system on the island is connected; Step S3: Locally operate all the low-voltage side switches of the distribution transformer to the open position, and operate the low-voltage side switches of the fan box transformer and the low-voltage side switches of the energy storage transformer to the closed position; Step S4: Check that the dispatching system and the microgrid controller are communicating normally, that the energy storage charge is greater than 30%, that the energy storage battery fire protection system and water cooling system are operating normally, that the microgrid switch station battery management system and the energy storage converter are communicating normally, that the microgrid controller is communicating normally with the energy storage converter and the wind turbine control system, and that there are no other abnormal alarms. Verify that the island wind turbine is in a shutdown state. The second phase involves starting wind power generation and using the microgrid controller to precisely control the coordination of wind and storage, gradually restoring power supply to non-critical loads and achieving long-term stable off-grid operation of the island microgrid. The steps are as follows: Step A1: The dispatching master station issues start-up instructions to each wind turbine generator set. The microgrid controller sets the wind turbine start-stop control instructions to the running position one by one and controls the wind turbine generator to operate in a limited power mode. Step A2: If the wind turbines in the wind turbine generator station do not meet the starting conditions, the energy storage system will only supply power to the important loads and operate until the wind turbines meet the conditions before automatically starting the wind turbines. If the energy storage system power drops to 30% and the wind turbines still do not meet the starting conditions, all loads will be removed and the next black start will be performed. Step A3: The wind turbine is successfully started and connected to the grid, and the energy storage system is in a charging state. When the remaining energy storage capacity reaches 60%, non-critical loads are put into operation in sequence. Step A4: Check that the distribution transformers on the entire island are operating normally and the voltage and frequency of the microgrid are stable. Complete the black start of the island microgrid, and then operate the microgrid to enter the off-grid self-balancing mode at the dispatching master station.

2. A black start method for a weakly linked island microgrid with wind and energy storage collaboration according to claim 1, characterized in that: The maximum capacity of the energy storage system can meet the short-term power supply needs of important loads in the island microgrid, and the total rated output of the wind turbines is greater than the maximum load on the island.

3. The black start method of a weakly linked island microgrid with wind and energy storage collaboration according to claim 1 is characterized by: The microgrid is a weakly connected microgrid, which is connected to the main power grid outside the island through only one submarine cable. The failure of the submarine cable has caused the island microgrid to become an isolated network, which means that the island is disconnected from the main power grid. The submarine cable maintenance time is at least 15 days, and only diesel generators can be used to guarantee power supply to some users.

4. The black start method of a weakly linked island microgrid with wind and energy storage coordination according to claim 1 is characterized by: After the black start conditions are met in the first stage, the energy storage system is remotely controlled to start the entire island distribution transformer at zero voltage in off-grid operation mode to restore power supply to important loads. The steps are as follows: the distribution system remotely sets the energy storage converter to off-grid operation mode and issues a black start command with one click. The energy storage system completes the zero start voltage of the entire island distribution transformer at a preset rate, and the voltage of the microgrid system is stabilized at 10kV. Then, the low-voltage side switches of the distribution transformer are closed on-site in order of load importance to restore power supply to important loads.

5. The black start method of a weakly linked island microgrid with wind and energy storage coordination according to claim 4 is characterized by: When the energy storage capacity of the energy storage system is weak, and the energy storage converter is not compatible with the magnetizing inrush current operating condition of the large-capacity load distribution transformer of the island microgrid with no-load closing and an overcurrent tripping phenomenon occurs under this operating condition, the energy storage system completes the zero starting voltage of the distribution transformer of the entire island at a preset rate, and adopts a zero starting voltage boosting method to avoid the magnetizing inrush current generated by the no-load impact distribution transformer, which may cause the energy storage converter to trip due to overcurrent.

6. The black start method of a weakly linked island microgrid with wind and energy storage coordination according to claim 1 is characterized by: The power limiting mode of the wind turbine is specifically as follows: assuming the load power is PL and the energy storage rated power is PC, the given power value of the wind turbine is (0.8PC+PL) / N, where N is the number of wind turbines, and the energy storage operates in a charging mode of 0.8PC.

7. The black start method of a weakly linked island microgrid with wind and energy storage collaboration according to claim 1 is characterized by: The low-voltage side switches of the island microgrid distribution transformer are devices that do not have remote control functions, and there is no communication link between the island microgrid switch station and the high and low voltage switches on the island.

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