A method for flexible direct current power transmission fault ride through and power supply system

Abstract

The application discloses a method for flexible direct current power transmission fault ride-through and a power supply system, and relates to the technical field of power supply systems, in particular to a method for flexible direct current power transmission fault ride-through and a power supply system. The method comprises the following steps: obtaining a direct current voltage of a flexible direct current power transmission system; when the direct current voltage is greater than a preset voltage threshold, reducing a collecting bus voltage of a new energy station according to the direct current voltage, and controlling the collecting bus of the new energy station to stop outputting reactive power; the new energy station is connected to a power grid through the flexible direct current power transmission system; each station in the new energy station is connected to the collecting bus; and adjusting active power output by each station in the new energy station according to the reduced collecting bus voltage. In order to stabilize the direct current voltage, the collecting bus is controlled to stop outputting reactive power. According to the size of the reduction of the collecting bus voltage, the active power output by the new energy station is adjusted, the active power is reduced, the direct current voltage of the flexible direct current power transmission system is reduced, and the fault ride-through is completed. The method does not depend on communication, has no communication delay, has a fast response speed, and cannot cause the failure of ride-through due to communication faults.

Description

Technical Field

[0001] This application relates to the field of new energy technology, specifically to a method and power system for flexible DC transmission fault ride-through. Background Technology

[0002] Flexible DC transmission is a high-voltage direct current (HVDC) transmission based on voltage source converters (VSCs). It can achieve isolation between the two AC grids and rapid decoupling of power, and there is no commutation failure problem.

[0003] Currently, the generation of new energy sources is increasing. When these new energy sources are transmitted via flexible DC transmission, the voltage fluctuations at the receiving end, especially grid faults, due to the relatively small load at the sending end, will severely affect the stable operation of both the new energy power plants at the sending end and the flexible DC transmission system. When a grid fault occurs at the receiving end, the grid voltage drops, causing a decrease in the output power of the converter at the receiving end of the flexible DC transmission system. However, the new energy power plants cannot directly sense the fault in the AC grid at the receiving end and will continue to send active power to the flexible DC transmission system. Therefore, the converter at the receiving end cannot fully transfer the energy sent by the new energy power plants to the grid, resulting in an imbalance of active power between the converters at the sending and receiving ends. This causes the DC voltage to rise rapidly, and in severe cases, it can lock out the flexible DC transmission system, making fault ride-through difficult. Summary of the Invention

[0004] To address the above technical issues, this application provides a method and power system for fault ride-through of flexible DC transmission, which can control the flexible DC transmission system and new energy power plants to perform fault ride-through.

[0005] This application provides a method for flexible DC transmission fault ride-through, including:

[0006] To obtain the DC voltage of the flexible DC transmission system;

[0007] When the DC voltage exceeds the preset voltage threshold, the voltage of the collecting bus of the new energy power station is reduced according to the DC voltage, and the collecting bus of the new energy power station is controlled to stop outputting reactive power; the new energy power station is connected to the power grid through a flexible DC transmission system; each power station in the new energy power station is connected to the collecting bus.

[0008] Adjust the active power output of each station in the new energy power plant according to the reduced bus voltage.

[0009] Preferably, reducing the bus voltage of the new energy power station based on the DC voltage specifically includes:

[0010] The DC voltage change value is obtained based on the DC voltage of the flexible DC transmission system and a preset voltage threshold.

[0011] The reduced bus voltage of the new energy power station is obtained based on the DC voltage change value.

[0012] Preferably, the DC voltage change value is obtained based on the DC voltage of the flexible DC transmission system and a preset voltage threshold, specifically including:

[0013] The DC voltage change value is obtained based on the difference between the DC voltage of the flexible DC transmission system and the preset voltage threshold.

[0014] The reduced bus voltage Uh of the renewable energy power station is obtained based on the DC voltage change value, specifically including:

[0015] The reduced collection bus voltage of the new energy power station is obtained by using the collection bus voltage and DC voltage change value of the flexible DC transmission system under normal conditions.

[0016] Preferably, adjusting the active power output of each station in the renewable energy power plant according to the reduced bus voltage specifically includes:

[0017] The active power of each station in the new energy power plant is reduced by distributing the current and voltage of the busbars in a proportional manner.

[0018] Preferably, the active power of each station in the renewable energy power plant is reduced by distributing the reduction proportionally based on the bus current and the reduced bus voltage, specifically including:

[0019] The change in the collecting bus voltage is obtained based on the collecting bus voltage under normal conditions and the reduced collecting bus voltage of the flexible DC transmission system.

[0020] The total active power reduction required for the new energy power station is obtained based on the change in the voltage and current of the busbar.

[0021] The reduction in active power for the i-th power station is obtained based on the active power of the i-th power station and the total active power reduction required for the renewable energy power stations. The i-th power station is any one of the renewable energy power stations, where i is 1-N and N is an integer representing the number of renewable energy power stations.

[0022] This application also provides a power supply system, including a flexible DC transmission system, a controller, and at least one new energy power station; the new energy power station is connected to the power grid through the flexible DC transmission system; each power station in the new energy power station is connected to a collecting bus.

[0023] The controller is used to reduce the voltage of the collecting bus of the new energy power station according to the DC voltage when the DC voltage is greater than the preset voltage threshold, and control the collecting bus of the new energy power station to stop outputting reactive power; and adjust the active power output of each station in the new energy power station according to the reduced collecting bus voltage.

[0024] Preferably, the controller is specifically used to obtain the DC voltage change value based on the DC voltage of the flexible DC transmission system and a preset voltage threshold; and to obtain the reduced collection bus voltage of the new energy power station based on the DC voltage change value.

[0025] Preferably, the controller is specifically used to obtain the DC voltage change value based on the DC voltage of the flexible DC transmission system and a preset voltage threshold, specifically including:

[0026] The DC voltage change value is obtained based on the difference between the DC voltage of the flexible DC transmission system and the preset voltage threshold.

[0027] The controller, specifically used to obtain the reduced bus voltage of the renewable energy power station based on the DC voltage change value, includes:

[0028] The reduced collection bus voltage of the new energy power station is obtained by using the collection bus voltage and DC voltage change value of the flexible DC transmission system under normal conditions.

[0029] Preferably, the controller is specifically used to reduce the active power of each station in the new energy power station according to the proportional distribution of the current of the collecting bus and the reduced voltage of the collecting bus.

[0030] Preferably, the controller is specifically used to reduce the active power of each station in the renewable energy power station according to a proportional distribution based on the current of the collecting bus and the reduced voltage of the collecting bus, specifically including:

[0031] The change in the collecting bus voltage is obtained based on the collecting bus voltage under normal conditions and the reduced collecting bus voltage of the flexible DC transmission system.

[0032] The total active power reduction required for the new energy power station is obtained based on the change in the voltage and current of the busbar.

[0033] The reduction in active power for the i-th power station is obtained based on the active power of the i-th power station and the total active power reduction required for the renewable energy power stations. The i-th power station is any one of the renewable energy power stations, where i is 1-N and N is an integer representing the number of renewable energy power stations.

[0034] Therefore, the embodiments of this application have the following beneficial effects:

[0035] The fault ride-through method for flexible DC transmission provided in this application detects the DC voltage of the flexible DC transmission system. When the DC voltage exceeds a preset voltage threshold, a fault is detected, requiring a ride-through. At this point, the voltage of the collecting bus is reduced based on the DC voltage change. To stabilize the DC voltage, the collecting bus needs to stop outputting reactive power. Furthermore, the active power output of the renewable energy power plants needs to be adjusted according to the magnitude of the reduction in the collecting bus voltage. Only by reducing the active power of the renewable energy power plants can the DC voltage of the flexible DC transmission system be fundamentally reduced, thereby completing the fault ride-through. The fault ride-through method for flexible DC transmission provided in this application does not rely on communication, eliminates communication delays, has a fast response speed, and will not fail to ride-through due to communication failures. Attached Figure Description

[0036] Figure 1 A schematic diagram of a flexible DC transmission system provided in an embodiment of this application;

[0037] Figure 2 A flowchart illustrating a method for fault ride-through in flexible DC transmission, as provided in this application embodiment;

[0038] Figure 3 A flowchart for reducing the voltage of the busbar is provided as an embodiment of this application;

[0039] Figure 4 A flowchart illustrating the adjustment of active power at a renewable energy power station, provided as an embodiment of this application;

[0040] Figure 5 This is a schematic diagram of a power supply system provided in an embodiment of this application. Detailed Implementation

[0041] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application scenarios of the technical solutions provided by the embodiments of this application are described below with reference to the accompanying drawings.

[0042] See Figure 1 The figure is a schematic diagram of a flexible DC transmission system provided in an embodiment of this application.

[0043] This embodiment uses the combination of flexible DC power transmission and new energy sources as an example for introduction.

[0044] A renewable energy power station typically includes multiple renewable energy plants. This application does not specifically limit the number of renewable energy plants in its embodiments; the figure uses N as an example, where N is greater than or equal to 2. Of course, a power system can also include only one renewable energy plant, i.e., N = 1.

[0045] This application uses multiple new energy fields as examples for illustration, such as... Figure 1As shown, new energy field 1, new energy field 2, and so on up to new energy field N are all connected to the busbar BUS, where the voltage of the busbar is AC voltage.

[0046] A transformer is also included between the busbar BUS and the flexible DC transmission system 1000. A transformer is also included between the power grid 300 and the flexible DC transmission system 1000.

[0047] The flexible DC transmission system 1000 includes a sending-end converter 100 and a receiving-end converter 200. The sending-end converter 100 is used to convert AC power into DC power and transmit it to the receiving-end converter 200. The receiving-end converter 200 is used to convert DC power into AC power and connect it to the grid through a transformer. Figure 1 Udc in this context refers to the DC voltage of the flexible DC transmission system 1000.

[0048] In actual operation, when the power output of the sending-end converter 100 is relatively large, while the receiving-end converter 200 cannot consume too much power, the DC voltage Udc will rise. When Udc rises to a certain value, such as exceeding the preset voltage threshold Udcmax, an overvoltage fault is considered to have occurred, and voltage ride-through is required.

[0049] At this point, it is necessary to reduce the output of the renewable energy power plant, specifically the output power of the step-down converter 100. Traditionally, this is achieved by relying on communication methods to adjust the output of the renewable energy power plant and balance the power at both ends of the flexible DC transmission system. However, this method suffers from issues of communication reliability and latency.

[0050] The technical solution provided in this application does not rely on communication, but directly reduces the voltage of the collecting bus based on the DC voltage Udc, thereby reducing the active power of the collecting bus. Furthermore, to achieve controllable voltage on the collecting bus, the reactive power output of the collecting bus is stopped, effectively controlling the renewable energy power station to not output reactive power. This control method allows the renewable energy power station to respond to voltage and power control as quickly as possible, thereby reducing the DC voltage Udc and achieving fault ride-through.

[0051] To facilitate understanding of the technical solutions of the embodiments of this application, the technical solutions provided by the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0052] See Figure 2 The figure is a flowchart of a method for flexible DC transmission fault ride-through provided in an embodiment of this application.

[0053] The method for flexible DC transmission fault ride-through provided in this application includes:

[0054] S201: Obtain the DC voltage of the flexible DC transmission system;

[0055] This scheme uses changes in the DC voltage of the flexible DC transmission system as a marker to trigger fault ride-through, and monitors the magnitude of the DC voltage in real time.

[0056] S202: When the DC voltage is greater than the preset voltage threshold, reduce the voltage of the collecting bus of the new energy power station according to the DC voltage, and control the collecting bus of the new energy power station to stop outputting reactive power.

[0057] During normal operation, the renewable energy power station operates at maximum power output. However, during fault ride-through, the operating mode of the renewable energy power station needs to be switched to variable active power output. That is, when the voltage of the collecting bus of the renewable energy power station is reduced, the active power of the collecting bus will change as the voltage of the collecting bus decreases. In addition, in order to keep the collecting bus voltage controllable and prevent the renewable energy power station from supplying AC power and causing fluctuations in the collecting bus voltage, it is necessary to stop the reactive power output of the renewable energy power station, thereby improving the system's fault ride-through capability.

[0058] Among them, the new energy power stations are connected to the power grid through a flexible DC transmission system; each power station in the new energy power station is connected to a collection bus.

[0059] It should be understood that, under normal circumstances, DC voltage has an operating range. Voltage within this range is considered normal, while voltage exceeding the maximum value of the operating range is considered an overvoltage fault. For example, the minimum value of the operating range is Udcmin, and the maximum value is Udcmax. The maximum value can be used as a preset voltage threshold. Alternatively, the preset voltage threshold can be slightly larger than the maximum value. For example, if the per-unit value of the DC voltage is 1, the preset voltage threshold can be any value within a range, such as 1.03-1.05. Specifically, 1.03, 1.04, or 1.05 can be selected. This application does not impose specific limitations on these values.

[0060] The embodiments of this application do not specifically limit the specific value of the working range, which can be determined according to the parameters and performance of the flexible DC transmission system.

[0061] During fault ride-through, the operating modes of the sending-end and receiving-end converters need to be changed. The sending-end converter switches to constant DC voltage control, adjusting the AC voltage amplitude to maintain power balance when the DC voltage changes. The receiving-end converter switches to constant AC bus voltage control, providing reactive power support to the receiving-end grid, thereby reducing the impact on system voltage during fault ride-through and improving system stability. Under normal operation, the sending-end converter generally uses constant AC bus voltage, and the receiving-end converter uses constant DC bus voltage.

[0062] S203: Adjust the active power output of each station in the new energy power station according to the reduced collection bus voltage.

[0063] Specifically, the active power output of each station in the renewable energy power plant can be adjusted based on the change in the bus voltage. This application does not specifically limit the amount of active power reduction for each station. To balance the active power of each renewable energy power plant, reduce fluctuations, improve the working efficiency of each renewable energy power plant, and maximize the output of renewable energy power plants with higher output capacity, a proportional allocation principle can be adopted to reduce the active power of each station.

[0064] The fault ride-through method for flexible DC transmission provided in this application detects the DC voltage of the flexible DC transmission system. When the DC voltage exceeds a preset voltage threshold, a fault is determined to have occurred, requiring a ride-through. At this point, the voltage of the collecting bus is reduced based on the DC voltage change. To stabilize the DC voltage, the collecting bus needs to stop outputting reactive power. Furthermore, the active power output of the renewable energy power plants needs to be adjusted according to the magnitude of the reduction in the collecting bus voltage. Only by reducing the active power of the renewable energy power plants can the DC voltage of the flexible DC transmission system be fundamentally reduced, thereby completing the fault ride-through. The method provided in this application does not rely on communication, eliminates communication delays, has a fast response speed, and will not fail to ride-through due to communication failures.

[0065] The method provided in this application embodiment can be implemented in the controller of the new energy power station. Only the DC voltage feedback from the flexible DC transmission system is required. All other controls are implemented by the controller of the new energy power station, including the collector bus voltage, the reactive power of the collector bus, and the active power of the new energy power station.

[0066] The specific implementation of each step in the method provided in the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0067] See Figure 3 This figure is a flowchart of a method for reducing the voltage of the busbar provided in an embodiment of this application.

[0068] The reduction of the bus voltage at renewable energy power plants based on DC voltage specifically includes:

[0069] S301: Obtain the DC voltage change value based on the DC voltage of the flexible DC transmission system and a preset voltage threshold;

[0070] The DC voltage change value ΔUdc is obtained based on the DC voltage Udc of the flexible DC transmission system and the preset voltage threshold Udcmax, specifically including:

[0071] ΔUdc = Udc - Udcmax;

[0072] S302: Obtain the reduced bus voltage of the new energy power station based on the DC voltage change value.

[0073] The reduced bus voltage Uh of the renewable energy power station is obtained based on the DC voltage change value, specifically including:

[0074] Uh = UN - kΔUdc;

[0075] k = UN / ΔUdcmax;

[0076] UN represents the collection bus voltage of the flexible DC transmission system under normal conditions, such as the rated voltage. ΔUdcmax represents the preset maximum voltage change. ΔUdcmax can generally be the maximum DC voltage change value when there is an AC fault at the receiving end and no measures are taken.

[0077] See Figure 4 The figure is a flowchart of adjusting the active power of a new energy power station according to an embodiment of this application.

[0078] Adjusting the active power output of each station in the renewable energy power plant based on the reduced bus voltage specifically includes:

[0079] The active power of each station in the new energy power plant is reduced by distributing the current and voltage of the busbars in a proportional manner.

[0080] S401: Obtain the change value of the collecting bus voltage based on the reduced collecting bus voltage;

[0081] S402: Based on the changes in the bus current and bus voltage, the active power of each station in the renewable energy power plant is reduced proportionally, specifically including:

[0082] ΔUh=UN-Uh;

[0083] ΔP=ΔUh*IN;

[0084]

[0085] ΔUh is the change in the collector bus voltage, Uh is the reduced collector bus voltage, UN is the collector bus voltage under normal conditions of the flexible DC transmission system, IN is the collector bus current, which is the sum of the currents collected by each new energy power station to the collector bus; N represents the number of power stations in the new energy power station network; ΔP is the total active power that the new energy power station needs to reduce; Pi is the active power of the i-th power station, and ΔPi represents the reduction of active power of the i-th power station. It represents the sum of the active power of all new energy power plants.

[0086] Pi needs to monitor the active power of the i-th power station in real time, i.e., the actual output.

[0087] For the active power allocation of renewable energy power stations during a fault, a proportional allocation principle is adopted. This means that after the voltage of the collecting bus at a renewable energy power station drops, the unbalanced active power of the system is calculated based on the magnitude of the voltage drop. The active power of the renewable energy power station is then reduced according to the proportional allocation principle, thereby achieving power balance between the sending and receiving ends and enabling fault ride-through of the flexible DC transmission system. Specifically, the active power reduction required for the i-th power station is determined by its proportion of the active power of all power stations. This embodiment of the application adopts the proportional allocation principle to adjust the active power of each renewable energy power station, which can balance the active power of the renewable energy power stations and improve system stability.

[0088] Based on the above embodiments, which provide a method for flexible DC transmission fault ride-through, this application also provides a power supply system, which will be described in detail below with reference to the accompanying drawings.

[0089] See Figure 5 This figure is a schematic diagram of the power supply system provided in an embodiment of this application.

[0090] The power system provided in this application embodiment is described using the combination of new energy and flexible DC transmission system as an example. That is, the power system includes a flexible DC transmission system 1000, a controller 501 and at least one new energy power station 502; the new energy power station 502 is connected to the power grid through the flexible DC transmission system 1000; each power station in the new energy power station 502 is connected to a collecting bus.

[0091] This application does not specifically limit the number of new energy power stations 502; there can be one or more, generally two or more. The following description uses N new energy power stations as an example, where N is greater than or equal to 2.

[0092] The controller 501 is used to reduce the voltage of the collecting bus of the new energy power station according to the DC voltage when the DC voltage is greater than the preset voltage threshold, and control the collecting bus of the new energy power station to stop outputting reactive power; and adjust the active power output of each station in the new energy power station according to the reduced collecting bus voltage.

[0093] Changes in the DC voltage of the flexible DC transmission system are used as a marker to trigger fault ride-through, and the magnitude of the DC voltage is monitored in real time.

[0094] During normal operation, the renewable energy power station operates at maximum power output. However, during fault ride-through, the operating mode of the renewable energy power station needs to be switched to variable active power output. That is, when the voltage of the collecting bus of the renewable energy power station is reduced, the active power of the collecting bus will change as the voltage of the collecting bus decreases. In addition, in order to keep the collecting bus voltage controllable and prevent the renewable energy power station from supplying AC power and causing fluctuations in the collecting bus voltage, it is necessary to stop the reactive power output of the renewable energy power station, thereby improving the system's fault ride-through capability.

[0095] Specifically, the active power output of each station in the renewable energy power plant can be adjusted based on the change in the bus voltage. This application does not specifically limit the amount of active power reduction for each station. To balance the active power of each renewable energy power plant, reduce fluctuations, improve the working efficiency of each renewable energy power plant, and maximize the output of renewable energy power plants with higher output capacity, a proportional allocation principle can be adopted to reduce the active power of each station.

[0096] The power system provided in this application embodiment detects the DC voltage of the flexible DC transmission system. When the DC voltage exceeds a preset voltage threshold, a fault is detected, requiring a fault ride-through. At this point, the voltage of the collecting bus is reduced based on the DC voltage change. To stabilize the DC voltage, the collecting bus needs to stop outputting reactive power. Furthermore, the active power output of the renewable energy power station needs to be adjusted according to the magnitude of the reduction in the collecting bus voltage. Only by reducing the active power of the renewable energy power station can the DC voltage of the flexible DC transmission system be fundamentally reduced, thereby completing the fault ride-through. The method provided in this application embodiment does not rely on communication, has no communication delay, has a fast response speed, and will not fail to ride-through due to communication failures.

[0097] The controller is specifically used to obtain the DC voltage change value based on the DC voltage of the flexible DC transmission system and a preset voltage threshold; and to obtain the reduced collection bus voltage of the new energy power station based on the DC voltage change value.

[0098] The controller, specifically used to obtain the DC voltage change value ΔUdc based on the DC voltage Udc of the flexible DC transmission system and a preset voltage threshold Udcmax, includes:

[0099] ΔUdc=Udc-Udcmax;

[0100] The controller, specifically used to obtain the reduced collection bus voltage Uh of the new energy power station based on the DC voltage change value, includes:

[0101] Uh = UN - kΔUdc;

[0102] k = UN / ΔUdcmax;

[0103] UN represents the collecting bus voltage of the flexible DC transmission system under normal conditions, and ΔUdcmax represents the preset maximum voltage change. ΔUdcmax can generally be the maximum DC voltage change value when there is an AC fault at the receiving end and no measures are taken.

[0104] The controller is specifically used to reduce the active power of each station in the new energy power plant by proportionally distributing the power according to the current of the bus and the reduced voltage of the bus.

[0105] The controller, specifically, is used to proportionally reduce the active power of each station in the renewable energy power plant based on the combined bus current and the reduced combined bus voltage. Specifically, it includes:

[0106] ΔUh=UN-Uh;

[0107] ΔP=ΔUh*IN;

[0108]

[0109] ΔUh is the change in the collector bus voltage, Uh is the reduced collector bus voltage, UN is the collector bus voltage under normal conditions of the flexible DC transmission system, IN is the collector bus current; N represents the number of power stations in the new energy power plant; Pi is the active power of the i-th power station, ΔP is the total active power that the new energy power plant needs to reduce; ΔPi represents the active power reduction of the i-th power station.

[0110] Pi needs to monitor the active power of the i-th power station in real time, i.e., the actual output.

[0111] By reducing the active power of renewable energy power plants according to the principle of proportional allocation, power balance between the sending and receiving ends is achieved, thereby enabling fault ride-through of the flexible DC transmission system. Specifically, the reduction in active power required for the i-th power plant is determined by its proportion of the total active power of all power plants. This embodiment of the application adopts the principle of proportional allocation to adjust the active power of each renewable energy power plant, which can balance the active power of the renewable energy power plants and improve system stability.

[0112] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems or apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and relevant parts can be referred to the method section.

Claims

1. A method for fault ride-through in flexible DC transmission, characterized in that, include: To obtain the DC voltage of the flexible DC transmission system; When the DC voltage exceeds a preset voltage threshold, the voltage of the collecting bus of the new energy power station is reduced according to the DC voltage, and the collecting bus of the new energy power station is controlled to stop outputting reactive power; the new energy power station is connected to the power grid through the flexible DC transmission system; each power station in the new energy power station is connected to the collecting bus. The active power output of each station in the new energy power station is adjusted according to the reduced bus voltage.

2. The method according to claim 1, characterized in that, The step of reducing the bus voltage of the renewable energy power station based on the DC voltage specifically includes: The DC voltage change value is obtained based on the DC voltage of the flexible DC transmission system and the preset voltage threshold. The reduced bus voltage of the new energy power station is obtained based on the DC voltage change value.

3. The method according to claim 2, characterized in that, The step of obtaining the DC voltage change value based on the DC voltage of the flexible DC transmission system and the preset voltage threshold specifically includes: The DC voltage change value is obtained based on the difference between the DC voltage of the flexible DC transmission system and the preset voltage threshold. The step of obtaining the reduced bus voltage Uh of the new energy power station based on the DC voltage change value specifically includes: The reduced collection bus voltage of the new energy power station is obtained based on the normal collection bus voltage of the flexible DC transmission system and the DC voltage change value.

4. The method according to claim 1, characterized in that, The adjustment of the active power output of each station in the renewable energy power station based on the reduced collection bus voltage specifically includes: The active power of each station in the new energy power station is reduced by distributing the current of the busbar and the reduced voltage of the busbar in a proportional manner.

5. The method according to claim 4, characterized in that, The reduction of active power in each station of the renewable energy power plant is achieved by proportionally distributing the reduction based on the bus current and the reduced bus voltage. Specifically, this includes: The change value of the collecting bus voltage is obtained based on the collecting bus voltage under normal conditions of the flexible DC transmission system and the reduced collecting bus voltage. The total active power that the new energy power station needs to reduce is obtained based on the change in the voltage of the collecting bus and the current of the collecting bus. The reduction in active power for the i-th power station is obtained based on the active power of the i-th power station and the total active power reduction required for the new energy power station. The i-th power station is any one of the new energy power stations, i is 1-N, and N is an integer representing the number of new energy power stations.

6. A power supply system, characterized in that, It includes a flexible DC transmission system, a controller, and at least one renewable energy power station; the renewable energy power station is connected to the power grid through the flexible DC transmission system; each power station in the renewable energy power station is connected to a collecting bus. The controller is configured to, when the DC voltage is greater than a preset voltage threshold, reduce the voltage of the collecting bus of the new energy power station according to the DC voltage, and control the collecting bus of the new energy power station to stop outputting reactive power; and adjust the active power output of each power station in the new energy power station according to the reduced collecting bus voltage.

7. The power supply system according to claim 6, characterized in that, The controller is specifically used to obtain the DC voltage change value based on the DC voltage of the flexible DC transmission system and the preset voltage threshold; and to obtain the reduced collection bus voltage of the new energy power station based on the DC voltage change value.

8. The power supply system according to claim 6, characterized in that, The controller is specifically used to obtain the DC voltage change value based on the DC voltage of the flexible DC transmission system and the preset voltage threshold, specifically including: The DC voltage change value is obtained based on the difference between the DC voltage of the flexible DC transmission system and the preset voltage threshold. The controller is specifically used to obtain the reduced collection bus voltage of the new energy power station based on the DC voltage change value, specifically including: The reduced collection bus voltage of the new energy power station is obtained based on the normal collection bus voltage of the flexible DC transmission system and the DC voltage change value.

9. The power supply system according to claim 6, characterized in that, The controller is specifically used to reduce the active power of each station in the new energy power station by distributing the power according to the combined bus current and the reduced combined bus voltage in a proportional manner.

10. The power supply system according to claim 6, characterized in that, The controller is specifically used to reduce the active power of each station in the renewable energy power station according to a proportional distribution based on the bus current and the reduced bus voltage, specifically including: The change value of the collecting bus voltage is obtained based on the collecting bus voltage under normal conditions of the flexible DC transmission system and the reduced collecting bus voltage. The total active power reduction required for the new energy power station is obtained based on the change in the bus voltage and the bus current. The reduction in active power for the i-th power station is obtained based on the active power of the i-th power station and the total active power reduction required for the new energy power station. The i-th power station is any one of the new energy power stations, i is 1-N, and N is an integer representing the number of new energy power stations.

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