Coordination control system and method for sending out new energy through flexible direct current

Abstract

The invention discloses a coordinated control system and method for sending out new energy through flexible direct current, and the method comprises the steps: confirming the operation mode of an alternating current field of a flexible direct current sending end according to the operation power state of the new energy, and carrying out the automatic breaking and closing of a switch and a disconnecting link based on the states of the switch and the disconnecting link of the alternating current field according to a preset switching strategy of the switch and the disconnecting link. Automatic switching of operation modes of an alternating-current field is achieved, transformer overload and large power loss of new energy when a sending-end alternating-current system breaks down are avoided, and based on a stable power limiting instruction, cooperation with a new energy branch is achieved to avoid the situation that execution is not carried out according to the power limiting instruction to affect the stability of a power grid. The technical problems that in the prior art, a double-bus three-section operation mode under a new energy flexible direct current system is low in power flow control intelligence, and disturbance to the system is large when a fault occurs can be solved.

Description

Technical Field

[0001] This invention belongs to the field of DC power transmission grid and equipment technology, specifically relating to a coordinated control system and method for transmitting new energy via flexible DC. Background Technology

[0002] Currently, long-distance power transmission for offshore renewable energy projects and large-scale renewable energy bases generally uses flexible DC systems. Due to the large active power capacity of renewable energy sources, the renewable energy AC system adopts a dual-bus, three-section operation configuration, requiring real-time adjustment of the operation mode based on the operating status of the renewable energy branches. However, there is currently no research on automatically adjusting the operation mode of the dual-bus, three-section AC system based on the operating status of the renewable energy branches, nor on automatically switching the operation mode during faults. This results in low power flow control intelligence in the dual-bus, three-section operation mode of the renewable energy flexible DC system, significant system disturbances during faults, and increased workload for operators. Summary of the Invention

[0003] The purpose of this invention is to provide a coordinated control system and method for transmitting new energy via flexible DC transmission, which solves the technical problems of low power flow control intelligence and large system disturbance during faults in the existing new energy flexible DC system with dual bus and three-segment operation mode.

[0004] To achieve the above objectives, the present invention provides the following technical solutions.

[0005] A coordinated control system for transmitting new energy via flexible DC transmission includes: three new energy branches, a dual-busbar three-section AC subsystem, transformers, a flexible DC transmission system, and a coordinated controller. The new energy branches are connected to the dual-busbar three-section AC subsystem, which is connected to the sending-end converter station of the flexible DC transmission system via three parallel transformers, and then connected to the receiving-end AC grid via the receiving-end converter station of the flexible DC transmission system.

[0006] The coordination controller is used to detect and control the operation of the entire coordination control system.

[0007] The aforementioned new energy transmission coordinated control system via flexible DC transmission includes a dual-busbar three-section AC subsystem comprising: Bus I, Bus II, a transformer, dual-busbar circuit breakers, combined switch one, and combined switch two. Bus I and Bus II are connected to the transformer via dual-busbar circuit breakers, and combined switches one and two are used to divide the dual-busbar system into three sections.

[0008] The aforementioned new energy sources are transmitted via a flexible DC transmission coordination and control system. Each new energy branch includes n new energy sources, and each new energy source is connected to the double busbar through a disconnector circuit breaker.

[0009] A coordinated control method for transmitting new energy via flexible DC transmission includes: evenly starting and connecting new energy branches to a three-section AC subsystem with a dual busbar. Automatic switching of the AC busbar operation mode is achieved by automatically opening and closing disconnectors, combined switches one and two, and the dual busbar circuit breakers according to a preset strategy. When the coordinated controller detects a fault, it only disconnects the equipment in the faulty branch to reduce active power loss; when the new energy fails to respond accurately to stable operation, it automatically switches the faulty branch.

[0010] The aforementioned coordinated control method, in which the new energy branches are evenly started and connected to the dual-bus, three-section AC subsystem, includes: the coordinated controller continuously detecting the number of new energy branches operating on each bus section in real time. When detected At this time, the coordinating controller further detects the status of each transformer's connection to bus I and bus II. If no fault is found, the transformer branch is determined to be usable, and the coordinating controller issues a closing command for the transformer connected to the double bus circuit breaker. When a transformer is detected connected to the double bus circuit breaker, the new energy branch sharing strategy is initiated. If the double bus circuit breaker fails to close, the sharing control strategy is terminated.

[0011] The aforementioned coordinated control method, wherein the renewable energy branch sharing strategy includes: the coordinated controller detects that the number of renewable energy branches connected to bus I is... .

[0012] If detected At that time, it is necessary to The new energy branch line is switched to bus II. The coordination controller issues the first command. The command to connect the new energy branch to bus II and close the circuit breaker is issued. The command is then sent only after the circuit breaker has been detected as closed. The new energy branch is connected to bus I and the circuit breaker is tripped, so that the new energy branch is evenly connected to both busbars.

[0013] If detected At that time, it is necessary to When switching new energy branch lines to bus I, the coordination controller first issues the command. The new energy branch connects to bus I and the circuit breaker closing command. When the circuit breaker is detected to have completed closing, the command is then issued. The new energy branch is connected to the II busbar and the circuit breaker tripping command is used to realize the even distribution of the new energy branch to the dual busbars.

[0014] The and If the ratio is not in integer form, it is rounded to the nearest integer.

[0015] The aforementioned coordination and control method, wherein the automatic switching process of the AC bus operation mode includes the coordination controller collecting the number k of new energy operation branches connected to each bus segment in real time, and determining the operation mode of the dual-bus three-segment AC subsystem based on the number k of new energy operation branches connected to each bus segment.

[0016] The operating modes include: interconnected operating mode, split-array operating mode, and hybrid operating mode;

[0017] When the operation mode is interconnected, both the first and second joint switches are closed. The active power in the new energy branch flows to the three busbars and is sent to the AC grid through the three parallel transformers and the converter station in the flexible DC transmission system.

[0018] When operating in split mode, both combined switch one and combined switch two are in the open state, and the active power in the new energy branch can only be sent to the AC grid through the transformer of this bus and the converter station in the flexible DC transmission system.

[0019] When the operation mode is a hybrid operation mode, only one of the combined switch one and combined switch two is in the closed state, and the other is in the open state. The active power flow in the new energy branch is naturally distributed to the AC grid through the parallel transformer and the converter station in the flexible DC transmission system.

[0020] The aforementioned coordinated control method, the system controller,

[0021] When the total power of the new energy branch connected to the three busbars is less than the capacity of a single transformer, the coordination controller switches the operation mode of the dual-busbar three-section AC subsystem to interconnected operation mode, and issues a closing command to joint switch one and joint switch two. If either joint switch fails to close, the coordination controller further detects that the other joint switch is closed and determines to switch to hybrid operation mode. If both joint switches fail to close, the automatic switching process stops.

[0022] When the total active power of the renewable energy branches connected to the three busbars is detected to be greater than the capacity of a single transformer but less than the capacity of two transformers, the coordination controller switches the operation mode of the dual-busbar, three-section AC subsystem to a hybrid operation mode. The coordination controller further detects that when the total active power of the renewable energy branches connected to the first and second busbars is less than the capacity of a single transformer, it closes the second joint switch, interconnecting the second and third busbars. When the total active power of the renewable energy branches connected to the first and second busbars, and the total active power of the renewable energy branches connected to the second and third busbars, is greater than the capacity of a single transformer, it opens both the first and second joint switches.

[0023] When the total power of the new energy branch connected to the three busbars is detected to be greater than the capacity of the two transformers, the coordination controller switches the operation mode of the dual-busbar three-section AC subsystem to parallel operation mode. The coordination controller issues a tripping command to joint switch one and joint switch two. When the tripping of either joint switch fails, the coordination controller further detects that the other joint switch is in the tripping state and determines to switch to hybrid operation mode. When both joint switches fail to trip, the automatic switching process stops.

[0024] The aforementioned coordinated control method involves the coordinated controller detecting a fault and minimizing active power loss, or automatically switching the faulty branch when the renewable energy source fails to respond accurately to stable operation. When the voltage of the dual-bus, three-section AC subsystem is detected to be below a set threshold, and further, if it is detected that the current from a particular renewable energy branch is flowing to the transformer branch, the coordinated controller determines that the fault point in the system is on the transformer branch side. The threshold determination is divided into two categories: less than 0.8 pu (indicating fault ride-through) and less than 0.5 pu (indicating severe fault ride-through).

[0025] When the total power of the new energy branch connected to the three busbars is less than the capacity of the two transformers, the coordinating controller further checks the status of the joint switch. If both are in the open state, the AC protection device will disconnect the fault point and the joint switch will return to the closed state to prevent the active power of the new energy branch from being unable to be sent out after the transformer is removed, thus establishing an active power flow channel.

[0026] When the number of new energy branch lines connected to the three busbars is detected When the number of new energy branches exceeds the capacity allowed by two transformers, the coordination controller calculates the maximum number of new energy branches that can be connected. The capacity will be greater than that of the transformer. When a new energy branch is disconnected, priority is given to disconnecting new energy branches without transformers. The coordinating controller further detects the path between the new energy branch and the transformer. If there is no path, the coordinating controller sends a closing command to the joint switch after the fault point is disconnected, and an active power flow path is established.

[0027] The aforementioned coordination control method, wherein the coordination controller;

[0028] When a fault is detected at busbar I, the coordinating controller disconnects the combined switch on busbar I and trips the circuit breakers connecting the renewable energy source and the transformer to busbar I. It then further checks whether the capacity of the renewable energy branch is greater than the capacity of the operating transformer. If the capacity of the renewable energy branch is greater than the transformer capacity, the coordinating controller disconnects the excess renewable energy branch. If a renewable energy branch is detected not being isolated from busbar I, it further checks whether the renewable energy branch is connected to busbar II. If connected, the renewable energy branch is disconnected from busbar II.

[0029] When a fault is detected at bus II, the coordination controller disconnects the combined switch on bus II and trips the circuit breakers connecting the renewable energy source and the transformer to bus II. Simultaneously, the renewable energy branch is connected to bus I. If the coordination controller detects that the transformer is not isolated from bus II, it trips the circuit breaker connected to the transformer and further checks whether the capacity of the renewable energy branch is greater than the capacity of the operating transformer. If the capacity of the renewable energy branch is greater than the transformer capacity, the coordination controller disconnects the excess renewable energy branch. If a renewable energy branch is detected not being isolated from bus II, it further checks whether the renewable energy branch is connected to bus I; if so, it disconnects the renewable energy branch from bus I.

[0030] The aforementioned coordinated control method involves receiving stability-based power limiting commands in real time. When a stability-based power limiting command is received and activated, the real-time active power value of the renewable energy branch is monitored. If the real-time active power of the renewable energy branch fails to decrease according to the stability-based power limiting command within a time threshold, a fault is determined in this renewable energy branch. The coordinated controller then initiates a faulty branch switching strategy, issues a trip command to the circuit breaker of the faulty renewable energy branch, and cuts off the renewable energy command that did not respond to the stability-based power limiting command.

[0031] The time threshold constraint is related to the AC power grid strength. When the AC power grid strength is high, the time requirement is more lenient, and when the AC power grid strength is low, the time requirement is shorter, with the time threshold being in the order of seconds.

[0032] If the circuit breaker of the faulty new energy branch fails to trip, the coordinating controller further determines the real-time value of the active power that needs to be cut off, selects a new energy branch with a power value equivalent to this from all new energy branches to cut off, and issues a circuit breaker trip command to the newly selected new energy branch to complete the power limiting action.

[0033] The beneficial effects of this invention are:

[0034] The beneficial effects of the present invention are as follows: The present invention provides a coordinated control method for transmitting new energy via flexible DC, which can ensure automatic power flow control in the dual-bus three-segment operation mode under the flexible DC system and reduce the large disturbance to the system during faults.

[0035] This invention solves the problem of operators manually switching AC system switches and disconnectors based on the active power output of renewable energy by designing an automatic switching strategy for the operation of a large-scale renewable energy AC system. It achieves automatic switching based on the renewable energy system and the status of the transmitting transformer branches according to a preset strategy. By designing a strategy in conjunction with stability and power limiting, it addresses the risk of grid voltage and frequency instability when renewable energy fails to meet performance requirements, and automatically disconnects renewable energy branches that fail to effectively respond to stability requirements. Through coordinated AC system operation, this invention enables fault ride-through and continuously provides power support to the AC grid system, stabilizing the grid voltage and ensuring reliable large-scale renewable energy transmission via flexible DC and the safe and stable operation of the system. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a coordinated control system for transmitting new energy via flexible DC transmission according to the present invention.

[0037] Figure 2 This is a schematic diagram of the steps of a coordinated control method for transmitting new energy via flexible DC transmission according to the present invention.

[0038] Figure 3 This is a schematic diagram of the new energy branch distribution process in the system of the present invention;

[0039] Figure 4 This is a schematic diagram of the automatic switching process of the operating mode in the system of the present invention;

[0040] Figure 5 This is a schematic diagram of the automatic switching process for AC fault operation mode in the system of the present invention. Detailed Implementation

[0041] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0042] Example 1: As Figure 1 and Figure 2 As shown, this embodiment provides a coordinated control system and method for transmitting new energy via flexible DC transmission.

[0043] The system includes: three new energy branch lines, a dual-busbar three-section AC subsystem, transformers, a flexible DC transmission system, and a coordination controller. The new energy branch lines are connected to the dual-busbar three-section AC subsystem, which is connected to the sending-end converter station of the flexible DC transmission system via three parallel transformers, and then connected to the receiving-end AC grid via the receiving-end converter station of the flexible DC transmission system.

[0044] The coordination controller is used to detect and control the operation of the entire coordination control system.

[0045] The aforementioned new energy transmission coordinated control system via flexible DC transmission includes a dual-busbar three-section AC subsystem comprising: Bus I, Bus II, a transformer, dual-busbar circuit breakers, combined switch one, and combined switch two. Bus I and Bus II are connected to the transformer via dual-busbar circuit breakers, and combined switches one and two are used to divide the dual-busbar system into three sections.

[0046] The aforementioned new energy sources are transmitted via a flexible DC transmission coordination and control system. Each new energy branch includes n new energy sources, and each new energy source is connected to the double busbar through a disconnector circuit breaker.

[0047] A coordinated control method for transmitting new energy via flexible DC transmission includes: evenly starting and connecting new energy branches to a three-section AC subsystem with a dual busbar. Automatic switching of the AC busbar operation mode is achieved by automatically opening and closing disconnectors, combined switches one and two, and the dual busbar circuit breakers according to a preset strategy. When the coordinated controller detects a fault, it automatically switches the faulty branch to minimize active power loss or when the new energy fails to respond accurately to stability measures.

[0048] Example 2: As Figure 3 As shown, based on Example 1, this example provides a process for evenly distributing new energy branches, including: evenly starting and connecting new energy branches to the dual-bus three-section AC subsystem, including: the coordination controller real-time detecting the number of new energy branches operating on each bus section. When detected At this time, the coordinating controller further detects the status of each transformer's connection to bus I and bus II. If no fault is found, the transformer branch is determined to be usable, and the coordinating controller issues a closing command for the transformer connected to the double bus circuit breaker. When a transformer is detected connected to the double bus circuit breaker, the new energy branch sharing strategy is initiated. If the double bus circuit breaker fails to close, the sharing control strategy is terminated.

[0049] The shared distribution strategy for new energy branches includes: the coordination controller detects that the number of new energy branches connected to bus I is... .

[0050] If detected At that time, it is necessary to The new energy branch line is switched to bus II. The coordination controller issues the first command. The command to connect the new energy branch to bus II and close the circuit breaker is issued. The command is then sent only after the circuit breaker has been detected as closed. The new energy branch is connected to bus I and the circuit breaker is tripped, so that the new energy branch is evenly connected to both busbars.

[0051] If detected At that time, it is necessary to When switching new energy branch lines to bus I, the coordination controller first issues the command. The new energy branch connects to bus I and the circuit breaker closing command. When the circuit breaker is detected to have completed closing, the command is then issued. The new energy branch is connected to the II busbar and the circuit breaker tripping command is used to realize the even distribution of the new energy branch to the dual busbars.

[0052] Example 3: As Figure 4 As shown, this embodiment provides the automatic switching process for the system operation mode of the present invention.

[0053] The automatic switching process of the AC bus operation mode includes the coordinating controller collecting the number k of new energy operation branches connected to each bus segment in real time, and determining the operation mode of the dual-bus three-segment AC subsystem based on the number k of new energy operation branches connected to each bus segment.

[0054] The operating modes include: interconnected operating mode, split-array operating mode, and hybrid operating mode;

[0055] When the operation mode is interconnected, both the first and second joint switches are closed. The active power in the new energy branch naturally flows to the three busbars and is sent to the AC grid through the three parallel transformers and the converter station in the flexible DC transmission system.

[0056] When operating in split mode, both combined switch one and combined switch two are in the open state, and the active power in the new energy branch can only be sent to the AC grid through the transformer of this bus and the converter station in the flexible DC transmission system.

[0057] When the operation mode is a hybrid operation mode, only one of the combined switch one and combined switch two is in the closed state, and the other is in the open state. The active power flow in the new energy branch is naturally distributed to the AC grid through the parallel transformer and the converter station in the flexible DC transmission system.

[0058] In the aforementioned coordinated control method, when the system controller detects that the total power of the new energy branch connected to the three busbars is less than the capacity of a single transformer, the coordinated controller switches the operation mode of the dual-busbar three-section AC subsystem to an interconnected operation mode, and issues a closing command to joint switch one and joint switch two. When either joint switch fails to close, the coordinated controller further detects that the other joint switch is closed and determines to switch to a hybrid operation mode. When both joint switches fail to close, the automatic switching process stops.

[0059] When the total active power of the renewable energy branches connected to the three busbars is detected to be greater than the capacity of a single transformer but less than the capacity of two transformers, the coordination controller switches the operation mode of the dual-busbar, three-section AC subsystem to a hybrid operation mode. The coordination controller further detects that when the total active power of the renewable energy branches connected to the first and second busbars is less than the capacity of a single transformer, it closes the second joint switch, interconnecting the second and third busbars. When the total active power of the renewable energy branches connected to the first and second busbars, and the total active power of the renewable energy branches connected to the second and third busbars, is greater than the capacity of a single transformer, it opens both the first and second joint switches.

[0060] When the total power of the new energy branch connected to the three busbars is detected to be greater than the capacity of the two transformers, the coordination controller switches the operation mode of the dual-busbar three-section AC subsystem to parallel operation mode. The coordination controller issues a tripping command to joint switch one and joint switch two. When the tripping of either joint switch fails, the coordination controller further detects that the other joint switch is in the tripping state and determines to switch to hybrid operation mode. When both joint switches fail to trip, the automatic switching process stops.

[0061] Example 4: Figure 5 As shown, this embodiment provides an automatic switching process for AC fault operation mode in the system of the present invention, including:

[0062] The coordination controller detects a fault and minimizes active power loss to the greatest extent possible. When renewable energy sources fail to respond accurately to stability measures, it automatically switches the faulty branch. If the voltage of the dual-bus, three-section AC subsystem is detected to be below a set threshold, and further if it is detected that current from a particular renewable energy branch is flowing to the transformer branch, the coordination controller determines that the fault point is on the transformer branch side. The threshold determination is divided into two categories: less than 0.8 pu (indicating fault ride-through) and less than 0.5 pu (indicating severe fault ride-through).

[0063] When the total power of the new energy branch connected to the three busbars is less than the capacity of the two transformers, the coordinating controller further checks the status of the joint switch. If both are in the open state, the AC protection device will disconnect the fault point and the joint switch will return to the closed state to prevent the active power of the new energy branch from being unable to be sent out after the transformer is removed, thus establishing an active power flow channel.

[0064] When the number of new energy branch lines connected to the three busbars is detected When the number of new energy branches exceeds the capacity allowed by two transformers, the coordination controller calculates the maximum number of new energy branches that can be connected. The capacity will be greater than that of the transformer. When a new energy branch is disconnected, priority is given to disconnecting new energy branches without transformers. The coordinating controller further detects the path between the new energy branch and the transformer. If there is no path, the coordinating controller sends a closing command to the joint switch after the fault point is disconnected, and an active power flow path is established.

[0065] When a fault is detected at busbar I, the coordinating controller disconnects the combined switch on busbar I and trips the circuit breakers connecting the renewable energy source and the transformer to busbar I. It then further checks whether the capacity of the renewable energy branch is greater than the capacity of the operating transformer. If the capacity of the renewable energy branch is greater than the transformer capacity, the coordinating controller disconnects the excess renewable energy branch. If a renewable energy branch is detected not being isolated from busbar I, it further checks whether the renewable energy branch is connected to busbar II. If connected, the renewable energy branch is disconnected from busbar II.

[0066] When a fault is detected at bus II, the coordination controller disconnects the combined switch on bus II and trips the circuit breakers connecting the renewable energy source and the transformer to bus II. Simultaneously, the renewable energy branch is connected to bus I. If the coordination controller detects that the transformer is not isolated from bus II, it trips the circuit breaker connected to the transformer and further checks whether the capacity of the renewable energy branch is greater than the capacity of the operating transformer. If the capacity of the renewable energy branch is greater than the transformer capacity, the coordination controller disconnects the excess renewable energy branch. If a renewable energy branch is detected not being isolated from bus II, it further checks whether the renewable energy branch is connected to bus I; if so, it disconnects the renewable energy branch from bus I.

[0067] The aforementioned coordinated control method involves receiving stability-based power limiting commands in real time. When a stability-based power limiting command is received and activated, the real-time active power value of the renewable energy branch is monitored. If the real-time active power of the renewable energy branch fails to decrease according to the stability-based power limiting command within a time threshold, a fault is determined in this renewable energy branch. The coordinated controller then initiates a faulty branch switching strategy, issues a trip command to the circuit breaker of the faulty renewable energy branch, and cuts off the renewable energy command that did not respond to the stability-based power limiting command.

[0068] The time threshold constraint is related to the AC power grid strength. When the AC power grid strength is high, the time requirement is more lenient, and when the AC power grid strength is low, the time requirement is shorter, with the time threshold being in the order of seconds.

[0069] If the circuit breaker of the faulty new energy branch fails to trip, the coordinating controller further determines the real-time value of the active power that needs to be cut off, selects a new energy branch with a power value equivalent to this from all new energy branches to cut off, and issues a circuit breaker trip command to the newly selected new energy branch to complete the power limiting action.

Claims

1. A coordinated control system for transmitting new energy via flexible DC transmission, characterized in that, include: The system consists of three new energy branch lines, a dual-busbar three-section AC subsystem, transformers, a flexible DC transmission system, and a coordination controller. The new energy branch lines are connected to the dual-busbar three-section AC subsystem, which is connected to the sending-end converter station of the flexible DC transmission system through three parallel transformers, and then connected to the receiving-end AC grid through the receiving-end converter station of the flexible DC transmission system. The coordination controller is used to detect and control the operation of the entire coordination control system.

2. The coordinated control system for new energy transmission via flexible DC transmission according to claim 1, characterized in that, The dual-busbar three-section AC subsystem includes: Bus I, Bus II, transformer, dual-busbar circuit breaker, combined switch one, and combined switch two; Bus I and Bus II are respectively connected to the transformer through the dual-busbar circuit breaker, and combined switch one and combined switch two are used to divide the dual-busbar into three sections.

3. The coordinated control system for new energy transmission via flexible DC transmission according to claim 1, characterized in that, Each new energy branch includes n new energy sources, and each new energy source is connected to the double busbar through a disconnector circuit breaker.

4. A coordinated control method for transmitting new energy via flexible DC transmission, characterized in that, include: The new energy branch circuits are started up and evenly connected to the dual-busbar three-section AC subsystem; Based on the automatic opening and closing of disconnectors, combined switches 1 and 2 and double busbar circuit breakers according to preset strategies, the automatic switching of AC busbar operation mode is realized; when the coordination controller detects a fault, only the equipment of the faulty branch is disconnected to reduce active power loss; when the new energy fails to respond accurately to the stable action, the faulty branch is automatically switched.

5. The coordinated control method according to claim 4, characterized in that, The evenly distributed startup and uniform connection of the new energy branches to the dual-bus, three-section AC subsystem includes: a coordination controller that monitors in real time the number of new energy branches operating on each bus section. When detected At this time, the coordinating controller further detects the status of each transformer's connection to bus I and bus II. If there is no fault, it is determined that the transformer branch is available. At this time, the coordinating controller issues a command to close the transformer connected to the double bus circuit breaker. When the double bus circuit breaker is detected, the new energy branch equalization control strategy is started. When the double bus circuit breaker fails to close, the equalization control strategy ends.

6. The coordinated control method according to claim 5, characterized in that, The shared control strategy for new energy branch lines includes: the coordination controller detects that the number of new energy branch lines connected to bus I is... ; If detected At that time, it is necessary to Each new energy branch is switched to connect to bus II; the coordination controller first issues the command. A new energy branch is connected to the II busbar and a circuit breaker closing command is issued. The command is then sent only after the circuit breaker has been detected as closed. Each new energy branch is connected to bus I and the circuit breaker trips, so that the new energy branch is evenly connected to both busbars; If detected At that time, it is necessary to In the process of switching and connecting each new energy branch to the I bus, the coordination controller first issues a command. Each new energy branch is connected to the I busbar and the circuit breaker closing command. When the circuit breaker is detected to have completed closing, a new energy branch is then issued. Each new energy branch is connected to the II busbar and the circuit breaker tripping command is executed to achieve equal access of the new energy branch to the dual busbar.

7. The coordinated control method according to claim 4, characterized in that, The automatic switching process of the AC bus operation mode includes the coordination controller collecting the number k of new energy operation branches connected to each bus segment in real time, and determining the operation mode of the dual-bus three-section AC subsystem based on the number k of new energy operation branches connected to each bus segment; the operation modes include: interconnected operation mode, split operation mode and hybrid operation mode; When the operation mode is interconnected, both the first and second joint switches are closed. The active power in the new energy branch naturally flows to the three busbars and is sent to the AC grid through the three parallel transformers and the converter station in the flexible DC transmission system. When the operation mode is split, both the first and second joint switches are in the open state, and the active power in the new energy branch is sent to the AC grid through the transformer of this bus and the converter station in the flexible DC transmission system. When the operation mode is a hybrid operation mode, only one of the combined switch one and combined switch two is in the closed state, and the other is in the open state. The active power flow in the new energy branch is sent to the AC grid through the parallel transformer and the converter station in the flexible DC transmission system.

8. The coordinated control method according to claim 7, characterized in that, The system controller control process includes: When the total power of the new energy branch connected to the three busbars is less than the capacity of a single transformer, the coordination controller switches the operation mode of the dual-busbar three-section AC subsystem to the interconnected operation mode. The coordination controller issues a closing command to joint switch one and joint switch two. When either joint switch fails to close, the coordination controller further detects that the other joint switch is in the closed state and determines to switch to the hybrid operation mode. When both joint switches fail to close, the automatic switching process stops. When the total power of the new energy branches connected to the three busbars is detected to be greater than the capacity of a single transformer but less than the capacity of two transformers, the coordination controller switches the operation mode of the dual-busbar three-section AC subsystem to a mixed operation mode. The coordination controller further detects that when the total active power of the new energy branches connected to the first and second busbars is less than the capacity of a single transformer, it closes the second joint switch and interconnects the second and third busbars. When the total active power of the new energy branches connected to the first and second busbars and the total active power of the new energy branches connected to the second and third busbars are both greater than the capacity of a single transformer, it opens the first and second joint switches. When the total power of the new energy branch connected to the three busbars is detected to be greater than the capacity of the two transformers, the coordination controller switches the operation mode of the dual-busbar three-section AC subsystem to parallel operation mode. The coordination controller issues a tripping command to joint switch one and joint switch two. When the tripping of either joint switch fails, the coordination controller further detects that the other joint switch is in the tripping state and determines to switch to hybrid operation mode. When both joint switches fail to trip, the automatic switching process stops.

9. The coordinated control method according to claim 4, characterized in that, The coordination controller detects a fault and only disconnects the equipment in the faulty branch to reduce active power loss. It automatically switches the faulty branch when the renewable energy fails to respond accurately to the stable action. When the voltage of the dual-bus three-section AC system is detected to be less than the set threshold, if it is further detected that the current of a certain renewable energy branch is flowing to the transformer branch, the coordination controller determines that the fault point of the system is on the transformer branch side. The threshold determination includes: less than 0.8 pu is considered to be entering fault ride-through and less than 0.5 pu is considered to be severe fault ride-through. When the total power of the new energy branch connected to the three busbars is less than the capacity of the two transformers, the coordinating controller further detects the status of the joint switch. If both are in the open state, the AC protection device will cut off the fault point and the joint switch will return to the closed state to avoid the new energy branch from being unable to send out active power after the transformer is removed, thus establishing an active power flow channel. When the number of new energy branch lines connected to the three busbars is detected When the number of new energy branches exceeds the capacity allowed by two transformers, the coordination controller calculates the maximum number of new energy branches that can be connected. The capacity will be greater than that of the transformer. When a new energy branch is disconnected, priority is given to disconnecting new energy branches without transformers. The coordinating controller further detects the path between the new energy branch and the transformer. If there is no path, the coordinating controller sends a closing command to the joint switch after the fault point is disconnected, and an active power flow path is established.

10. The coordinated control method according to claim 9, characterized in that, The coordination controller control process includes: When a fault is detected at busbar I, the coordinating controller disconnects the combined switch on busbar I and trips the circuit breakers connecting the new energy source and the transformer to busbar I. It then further checks whether the capacity of the new energy branch is greater than the capacity of the operating transformer. If the capacity of the new energy branch is greater than the transformer capacity, the coordinating controller disconnects the excess new energy branch. If a new energy branch is detected not being isolated from busbar I, it further checks whether the new energy branch is connected to busbar II. If connected, the new energy branch is disconnected from busbar II. When a fault is detected at bus II, the coordinating controller disconnects the combined switch on bus II and trips the circuit breakers connecting the new energy source and the transformer to bus II. Simultaneously, the new energy branch is connected to bus I. When the coordinating controller detects that the transformer is not isolated from bus II, it trips the circuit breaker connected to the transformer and further checks whether the capacity of the new energy branch is greater than the capacity of the operating transformer. If the capacity of the new energy branch is greater than the transformer capacity, the coordinating controller disconnects the excess new energy branch. If the new energy branch is detected as not isolated from bus II, it further checks whether the new energy branch is connected to bus I. If it is connected, the new energy branch is disconnected from bus I.

11. The coordinated control method according to claim 4, characterized in that, The coordinated control receives the stability power limiting command in real time. When the stability power limiting command is received and the action is taken, the real-time active power value of the renewable energy branch will be detected in real time. When the real-time active power of the renewable energy is not detected to decrease in accordance with the stability power limiting command within the time threshold, the renewable energy branch is judged to be faulty. The coordinated controller starts the faulty branch switching strategy, issues the circuit breaker trip command of the faulty renewable energy branch, and cuts off the renewable energy command that does not respond to the stability power limiting command. If the circuit breaker of the faulty new energy branch fails to trip, the coordinating controller further determines the real-time value of the active power that needs to be cut off, selects a new energy branch with a power value equivalent to this from all new energy branches to cut off, and issues a circuit breaker trip command to the newly selected new energy branch to complete the power limiting action.

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