A method and control system for unlocking a converter station of a flexible direct current power transmission

Abstract

This invention discloses a method and control system for unlocking a converter station in a flexible DC transmission system. The unlocking method includes: when any control module detects a user-input unlocking command, the control module sends the unlocking command to other control modules; upon receiving the unlocking command, the control module corresponding to the DC power station controls the converter valves in the DC power station to be fully locked; with the converter valves in the DC power station fully locked, the control module corresponding to the DC voltage station controls the converter valves in the DC voltage station to be unlocked; and when the voltage of the DC transmission line reaches a preset range, the control module corresponding to the DC power station controls the converter valves in the DC power station to be unlocked. This solution improves the unlocking security and reliability of the converter station.

Description

Technical Field

[0001] The embodiments of the present invention relate to DC power transmission technology, and more particularly to a converter station unlocking method and control system for flexible DC power transmission. Background Technology

[0002] Flexible DC transmission technology has good economic efficiency, interconnectivity and controllability, and has been widely used and rapidly developed in power systems in recent years.

[0003] In traditional methods for unlocking flexible DC converter stations, the unlocking is typically designed to unlock the DC voltage station first, followed by the unlocking of the DC power station to transmit power. However, in this unlocking method, the DC power station unlocked later is vulnerable to unlocking shocks, resulting in low reliability. Summary of the Invention

[0004] This invention provides a method and control system for unlocking converter stations in flexible DC transmission, so as to improve the unlocking safety and reliability of converter stations.

[0005] In a first aspect, embodiments of the present invention provide a method for unlocking a converter station in a flexible DC transmission system. This method is applied to a flexible DC transmission control system, which includes at least two control modules, each corresponding to a DC converter station and connected to a converter valve in the corresponding DC converter station. The at least two control modules are communicatively connected to each other. The DC converter station includes a DC voltage station or a DC power station.

[0006] The method for unlocking the converter station of the flexible DC transmission includes:

[0007] When any of the control modules detects an unlock command input by the user, the control module sends the unlock command to the other control modules.

[0008] Upon receiving the unlock command, the control module corresponding to the DC power station controls the converter valve in the DC power station to be fully locked.

[0009] When the converter valve in the DC power station is fully locked, the control module corresponding to the DC voltage station controls the converter valve in the DC voltage station to unlock.

[0010] When the voltage of the DC transmission line reaches a preset range, the control module corresponding to the DC power station controls the converter valve in the DC power station to unlock.

[0011] Optionally, the control module includes a polar control unit and a valve control unit; the polar control unit is connected to the valve control unit, and the polar control units of each control module are communicatively connected to each other; the valve control unit is connected to each sub-module in the converter valve, and the polar control unit is used to receive and transmit the unlock command; the valve control unit is connected to the converter valve in the corresponding DC converter station, and is used to control the state of each sub-module in the converter valve according to the control signal of the polar control unit;

[0012] Upon receiving the unlock command, the control module corresponding to the DC power station controls the converter valve in the DC power station to be fully locked, including:

[0013] Upon receiving the unlock command, the pole control unit corresponding to the DC power station immediately issues a full lockout command to the corresponding valve control unit;

[0014] The valve control unit corresponding to the DC power station controls all sub-modules in the converter valve to be locked.

[0015] Optionally, when the converter valve in the DC power station is fully locked, the control module corresponding to the DC voltage station controls the converter valve in the DC voltage station to unlock, including:

[0016] After receiving the unlocking command, at a first preset time, the pole control unit corresponding to the DC voltage station sends an unlocking command to the corresponding valve control unit;

[0017] The valve control unit corresponding to the DC voltage station controls the unlocking of the converter valve.

[0018] Optionally, the flexible DC transmission control system further includes: a voltage sensing module, which is disposed on the bus of the DC transmission line and is communicatively connected to the control module, for collecting the voltage value of the DC transmission line and transmitting it to the control module;

[0019] When the voltage of the DC transmission line reaches a preset range, the control module corresponding to the DC power station controls the unlocking of the converter valve in the DC power station, including:

[0020] The voltage sensing module collects the voltage value of the DC transmission line and transmits it to the control module corresponding to the DC power station;

[0021] After receiving the unlocking command for a second preset time, if the voltage value of the DC transmission line is within the preset range, the pole control unit corresponding to the DC power station issues an unlocking command to the corresponding valve control unit, wherein the second preset time is greater than the first preset time;

[0022] The valve control unit corresponding to the DC power station controls the unlocking of the converter valve.

[0023] Optionally, the preset range is 95% higher than the rated voltage value.

[0024] Optionally, the number of control modules is 2, and the number of DC voltage stations and DC power stations is 1 each.

[0025] Secondly, embodiments of the present invention also provide a flexible DC transmission control system, which includes at least two control modules;

[0026] The control module is used to send the unlock command to other control modules when it detects an unlock command input by the user.

[0027] The control module corresponding to the DC power station is used to control the converter valve in the DC power station to be fully locked after receiving the unlocking command, and to control the converter valve in the DC power station to be unlocked when the voltage of the DC transmission line reaches a preset range.

[0028] The control module corresponding to the DC voltage station is used to control the unlocking of the converter valve in the DC voltage station when the converter valve in the DC power station is fully locked.

[0029] Optionally, the control module includes a pole control unit and a valve control unit;

[0030] The pole control unit corresponding to the DC power station is used to immediately issue a full lockout command to the corresponding valve control unit when it receives the unlock command;

[0031] The valve control unit corresponding to the DC power station is used to control all sub-modules in the converter valve to be locked according to the full lockout command;

[0032] The pole control unit corresponding to the DC voltage station is used to send an unlock command to the corresponding valve control unit at a first preset time after receiving the unlock command;

[0033] The valve control unit corresponding to the DC voltage station is used to control the unlocking of the converter valve according to the unlocking command.

[0034] Optionally, the flexible DC transmission control system further includes: a voltage sensing module, which is disposed on the bus of the DC transmission line and is communicatively connected to the control module, for collecting the voltage value of the DC transmission line and transmitting it to the control module corresponding to the DC power station.

[0035] Thirdly, embodiments of the present invention also provide a flexible DC transmission system, which includes a flexible DC transmission control system as described in any of the second aspects, at least one DC power station, at least one DC voltage station, and a DC transmission line.

[0036] The converter station unlocking method and control system provided in this embodiment for flexible DC transmission involves a control module that, upon detecting an unlocking command, sends it to other control modules. The control module corresponding to the DC power station, upon detecting or receiving the unlocking command, immediately locks the DC power station to prevent the DC transmission line from affecting it. After the DC power station is fully locked, the control module unlocks the DC voltage station. Once the voltage level of the DC transmission line rises to a preset range, the control module unlocks the DC power station, thus achieving the unlocking of the converter station for flexible DC transmission. This prevents the DC transmission line from impacting the DC power station during the unlocking process and improves the unlocking safety and reliability of the converter station. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of a flexible DC power transmission control system and a DC converter station provided in an embodiment of the present invention;

[0038] Figure 2 A flowchart of a converter station unlocking method for flexible DC transmission provided in an embodiment of the present invention;

[0039] Figure 3 A flowchart of another method for unlocking a converter station in flexible DC transmission provided by an embodiment of the present invention;

[0040] Figure 4 A schematic diagram of another flexible DC power transmission control system and DC converter station provided in an embodiment of the present invention;

[0041] Figure 5 This is a schematic diagram of a flexible DC transmission system provided in an embodiment of the present invention. Detailed Implementation

[0042] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0043] As mentioned in the background section, in traditional flexible DC transmission converter station unlocking methods, the unlocking sequence is generally as follows: the control DC voltage station is unlocked first, and after the DC voltage station establishes a DC voltage, the DC power station is unlocked to achieve power transmission. Before the converter station is unlocked, the converter valves of both the DC voltage station and the DC power station are in a controllable charging state. In this state, the number of sub-modules engaged by the converter valves is small, and the sub-module capacitor voltage has risen to near its rated value. After the control DC voltage station is unlocked first, the DC voltage on the DC line will rise from its current voltage to its rated value at a relatively fast rate. The converter valves of the DC power station will be charged from the DC side by the increased DC voltage, and the sub-module capacitor voltage will rise, triggering switching operations. If the sub-module capacitor voltage is not fully stable when the DC power station is unlocked, the unlocking impact will be significant. Therefore, in this unlocking method, the DC power station unlocked later is susceptible to unlocking impacts, resulting in low reliability.

[0044] This invention provides a flexible DC power transmission control system. Figure 1 This is a schematic diagram of a flexible DC transmission control system and a DC converter station provided in an embodiment of the present invention, with reference to... Figure 1 The flexible DC transmission control system 100 includes at least two control modules 101 and a voltage sensing module 106. Each control module 101 corresponds to a DC converter station 105 and is connected to the corresponding converter valve in the DC converter station 105. The at least two control modules 101 are communicatively connected to each other. The DC converter station 105 includes a DC voltage station or a DC power station. The voltage sensing module 106 is located on the bus of the DC transmission line and is communicatively connected to the control module 101. It is used to collect the voltage value of the DC transmission line and transmit it to the control module 101.

[0045] Specifically, the control module 101 is a communication and control device installed in each DC converter station 105. The control module 101 includes a polar control unit 103 and a valve control unit 104. The polar control unit 103 is connected to the valve control unit 104, and the polar control units 103 of each control module 101 are communicatively connected. When any polar control unit 103 receives an unlock command, it will transmit the unlock command to the other polar control units 103, realizing command sharing. The valve control unit 104 is connected to each sub-module in the converter valve. The valve control unit 104 is a valve control and protection device that can directly control the switching state of each sub-unit in the converter valve of the DC converter station 105. The polar control unit 103 is used to receive and transmit unlock commands, and can also send unlock commands to the valve control unit 104. The valve control unit 104 is connected to the corresponding converter valve in the DC converter station 105 and is used to control the state of each sub-module in the converter valve according to the control signal of the polar control unit 103. The converter valve can be a modular multilevel converter, comprising multiple sub-modules. The voltage sensing module 106 can be a DC voltage sensor, capable of detecting the DC voltage value on the DC transmission line and feeding it back to the control module 101.

[0046] Continue to refer to Figure 1 Optionally, control module 101 is used to send an unlock command to other control modules 101 when a user-input unlock command is detected; control module 101 corresponding to the DC power station is used to control the converter valve in the DC power station to be fully locked after receiving the unlock command, and to control the converter valve in the DC power station to be unlocked when the voltage of the DC transmission line reaches a preset range; control module 101 corresponding to the DC voltage station is used to control the converter valve in the DC voltage station to be unlocked when the converter valve in the DC power station is fully locked.

[0047] Continue to refer to Figure 1 Optionally, the pole control unit 103 corresponding to the DC power station is used to immediately issue a full lockout command to the corresponding valve control unit 104 upon receiving an unlock command; the valve control unit 104 corresponding to the DC power station is used to control all sub-modules of the converter valve to lock out according to the full lockout command; the pole control unit 103 corresponding to the DC voltage station is used to issue an unlock command to the corresponding valve control unit 104 after receiving an unlock command for a first preset time; the valve control unit 104 corresponding to the DC voltage station is used to control the converter valve to unlock according to the unlock command. The voltage sensing module 106 is disposed on the bus of the DC transmission line (the relative relationship between the voltage sensing module 106 and the bus of the DC transmission line is not shown in the figure), and is communicatively connected to the control module 101, for collecting the voltage value of the DC transmission line and transmitting it to the control module 101 corresponding to the DC power station.

[0048] The flexible DC transmission control system provided in this embodiment sends an unlocking command to other control modules when the control module detects it. The control module corresponding to the DC power station immediately locks the DC power station upon detecting or receiving the unlocking command to prevent the DC transmission line from affecting the DC power station. After the DC power station is fully locked, the control module unlocks the DC voltage station. The control module also unlocks the DC power station after the voltage level of the DC transmission line rises to a preset range. This system enables the unlocking of the converter station in flexible DC transmission, prevents the DC transmission line from impacting the DC power station during the unlocking process, and improves the unlocking safety and reliability of the converter station.

[0049] This invention also provides a converter station unlocking method for flexible DC transmission, which is applied to the flexible DC transmission control system. Figure 2 A flowchart illustrating a converter station unlocking method for flexible DC transmission provided in this embodiment of the invention is shown below. Figure 2 The unlocking methods for converter stations in flexible DC transmission include:

[0050] S201. When any control module detects an unlock command input by the user, the control module will send the unlock command to other control modules.

[0051] Specifically, the control module can also be equipped with an unlock command input device or an unlock command receiving device. The unlock command input device can be a keyboard, touchscreen, or button, allowing maintenance personnel to input unlock commands. The unlock command receiving device can be a Bluetooth receiver, cellular network signal receiver, or mobile network signal receiver, and can communicate wirelessly or wiredly with the signal input device. Maintenance personnel can input unlock commands using the unlock command input device or transmit the unlock command to the control module when the DC converter station needs to be unlocked. When any control module in the flexible DC transmission control system detects an unlock command, the control module sends the unlock command to other control modules within the flexible DC transmission system, sharing the unlock command.

[0052] S202. Upon receiving the unlock command, the control module corresponding to the DC power station controls the converter valve in the DC power station to be fully locked.

[0053] Specifically, the control module is connected to the corresponding DC converter station. If the corresponding DC converter station is a DC power station, the control module will immediately control the converter valve in the DC converter station to be fully locked after detecting the unlock command. Full locking means that all sub-modules in the converter valve are closed and isolated from the DC line to prevent the DC line voltage rise from affecting the DC power station.

[0054] S203. When the converter valve in the DC power station is fully locked, the control module corresponding to the DC voltage station controls the converter valve in the DC voltage station to unlock.

[0055] Specifically, when the DC power station is determined to be fully locked, the control module corresponding to the DC voltage station can control the unlocking of the converter valves of the DC voltage station according to the unlocking command. The unlocking command can include the number of unlocking converter valve sub-modules and the sub-module labels. The method for determining the full lockout of the DC power station can be either that the control module corresponding to the DC voltage station determines that the DC power station has completed full lockout based on the full lockout completion signal issued by the control module corresponding to the DC power station, or that the DC voltage station directly controls the unlocking of the converter valves in the DC voltage station after receiving the unlocking command for a preset time period. This preset time period is the longest time between receiving the unlocking command and the DC power station completing full lockout, as measured through multiple experiments. After receiving the unlocking command for the preset time period, it can be guaranteed that the converter valves in the DC power station have completed full lockout.

[0056] S204. When the voltage of the DC transmission line reaches the preset range, the control module corresponding to the DC power station controls the converter valve in the DC power station to unlock.

[0057] Specifically, after the DC voltage station is unlocked, the voltage of the DC transmission line will begin to rise. When the voltage of the DC transmission line reaches a preset range, the control module corresponding to the DC power station can control the converter valve in the DC power station to unlock. For example, the preset range can be higher than 3 / 4 times the rated voltage value. The voltage of the DC transmission line can be collected by the voltage sensing module and transmitted to the control module.

[0058] The converter station unlocking method for flexible DC transmission provided in this embodiment involves the control module issuing an unlocking command to other control modules upon detection. The control module corresponding to the DC power station immediately locks the DC power station upon detection or receipt of the unlocking command to prevent the DC transmission line from affecting the DC power station. After the DC power station is fully locked, the control module unlocks the DC voltage station. The control module also unlocks the DC power station after the voltage level of the DC transmission line rises to a preset range. This method achieves the unlocking of the converter station for flexible DC transmission, prevents the DC transmission line from impacting the DC power station during the unlocking process, and improves the unlocking safety of the converter station.

[0059] Figure 3 A flowchart illustrating another method for unlocking a converter station in flexible DC transmission provided by an embodiment of the present invention. Figure 4 This is a schematic diagram of another flexible DC transmission control system and DC converter station provided in an embodiment of the present invention, with reference to... Figure 3 The unlocking methods for converter stations in flexible DC transmission include:

[0060] S301. When any control module detects an unlock command input by the user, the control module will send the unlock command to other control modules.

[0061] Step 301 is the same as step 201, and will not be repeated here.

[0062] S302. Upon receiving the unlocking command, the pole control unit corresponding to the DC power station immediately sends a full lockout command to the corresponding valve control unit.

[0063] Specifically, whether it is the first control module to detect the unlock command or the control module that receives the unlock command from other control modules, as long as the pole control unit in the control module corresponding to the DC power station receives the unlock command, it will immediately issue a full lockout command to the generator control unit corresponding to the pole control unit.

[0064] S303, the valve control unit corresponding to the DC power station controls all sub-modules in the converter valve to be locked.

[0065] Specifically, when the valve control unit corresponding to the DC power station receives a full lockout command, it controls all sub-modules in the converter valve of the corresponding DC power station to lock out. Lockout includes closing the sub-modules in the converter valve and isolating the sub-modules from the DC transmission line.

[0066] S304. After receiving the unlock command, at the first preset time, the pole control unit corresponding to the DC voltage station sends an unlock command to the corresponding valve control unit.

[0067] Specifically, after the control module corresponding to the DC voltage station receives the unlocking command, the pole control unit corresponding to the DC voltage station issues an unlocking command to the corresponding valve control unit within a first preset time. For example, the first preset time can be 20 minutes to ensure that all DC power stations in the DC transmission system have completed full interlocking.

[0068] S305, the valve control unit corresponding to the DC voltage station controls the unlocking of the converter valve.

[0069] Specifically, upon receiving the unlocking command, the valve control unit corresponding to the DC voltage station controls the converter valve in the DC voltage station to unlock. After the DC voltage station is unlocked, the voltage of the DC transmission line begins to rise, tending towards the rated voltage.

[0070] S306, The voltage sensing module collects the voltage value of the DC transmission line and transmits it to the control module corresponding to the DC power station.

[0071] Specifically, after the DC voltage station is unlocked, the control module corresponding to the DC power station constantly determines whether the unlocking requirements of the DC power station are met based on the voltage value of the DC transmission line detected by the voltage sensor. The voltage sensing module can be a digital voltage meter installed on the DC transmission line, which has a signal output function and can transmit the voltage value of the DC transmission line to the control module corresponding to the DC power station at all times.

[0072] S307. After receiving the unlocking command for a second preset time, if the voltage value of the DC transmission line is within the preset range, the pole control unit corresponding to the DC power station issues an unlocking command to the corresponding valve control unit.

[0073] Specifically, the second preset time is longer than the first preset time. Within the second preset time after the polar control unit corresponding to the DC power station receives the unlock command, the polar control unit determines whether the voltage value of the DC transmission line received from the voltage sensing module is within a preset range. If so, it indicates that the voltage of the DC transmission line has stabilized and will not cause excessive voltage fluctuations that could impact the various sub-modules in the DC power station. At this time, the polar control unit issues an unlock command to the valve control unit. Otherwise, the polar control unit continues to determine whether the voltage value of the DC transmission line received from the voltage sensing module is within the preset range until the voltage value of the DC transmission line is within the preset range, at which point the polar control unit issues an unlock command to the valve control unit.

[0074] S308, the valve control unit corresponding to the DC power station controls the unlocking of the converter valve.

[0075] Specifically, when the valve control unit receives the unlocking command from the corresponding pole control unit, it controls the converter valve of the DC power station to unlock. The unlocking command may also include the number and sequence number of the sub-modules that the DC power module needs to unlock.

[0076] For example, refer to Figure 4The number of DC converter stations is two, with one DC voltage station 401 and one DC power station 402. Correspondingly, the number of control modules 101 in the flexible DC transmission control system 100 is two. The DC power station 402 is the main control station, and maintenance personnel can input or transmit unlocking commands only to the control module 101 corresponding to the main control station. First, when the pole control unit 103 corresponding to the DC power station 402 issues an unlocking command, it immediately transmits the unlocking command to the pole control unit 103 of the DC voltage station 401. Simultaneously, after receiving the unlocking command, the pole control unit 103 corresponding to the DC power station 402 immediately issues a command to stop the active charging of the converter valve to the valve control unit 104 corresponding to the DC power station 402, controlling the valve control unit 104 to perform full valve locking. Then, after receiving the unlock command, the pole control unit 103 corresponding to the DC voltage station 401 delays for 20 minutes before issuing an unlock command to the corresponding valve control unit 104. After the valve unlocks, the DC voltage is raised to the rated value. Finally, after receiving the unlock command, the pole control unit 103 of the DC power station 402 delays for 25 minutes and, after detecting that the DC voltage is higher than 95% of the rated voltage, issues an unlock command to the valve control unit 104. After the valve unlocks, the DC power is controlled to the set value. It should be noted that the above 20-minute delay is designed based on the longest time for the DC power station 402 to be fully locked, and the 25-minute delay is designed based on the longest time for the DC voltage of the DC voltage station 401 to have risen to the rated value.

[0077] The converter station unlocking method for flexible DC transmission provided in this embodiment involves the control module issuing an unlocking command to other control modules upon detection. The control module corresponding to the DC power station immediately locks the DC power station upon detection or receipt of the unlocking command to prevent the DC transmission line from affecting the DC power station. After the DC power station is fully locked, the control module unlocks the DC voltage station. The control module also unlocks the DC power station after the voltage level of the DC transmission line rises to a preset range. This method achieves the unlocking of the converter station for flexible DC transmission, prevents the DC transmission line from impacting the DC power station during the unlocking process, and improves the unlocking safety of the converter station.

[0078] This invention also provides a flexible DC transmission system. Figure 5 This is a schematic diagram of a flexible DC transmission system provided in an embodiment of the present invention, with reference to... Figure 5 The flexible DC transmission system 500 includes any of the aforementioned flexible DC transmission control systems 100, at least one DC power station 402, at least one DC voltage station 401, and DC transmission lines 501.

[0079] The above-described products can perform the methods provided in any embodiment of the present invention, and have the corresponding functional modules and beneficial effects for performing the methods.

[0080] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, combinations, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A method for unlocking a converter station in a flexible DC transmission system, characterized in that, An application is made in a flexible DC transmission control system, the flexible DC transmission control system comprising: at least two control modules, each control module corresponding to a DC converter station and connected to a converter valve in the corresponding DC converter station, the at least two control modules being communicatively connected to each other, wherein the DC converter station includes a DC voltage station or a DC power station; The method for unlocking the converter station of the flexible DC transmission includes: When any of the control modules detects an unlock command input by the user, the control module sends the unlock command to the other control modules. Upon receiving the unlock command, the control module corresponding to the DC power station controls the converter valve in the DC power station to be fully locked. When the converter valve in the DC power station is fully locked, the control module corresponding to the DC voltage station controls the converter valve in the DC voltage station to unlock. When the voltage of the DC transmission line reaches a preset range, the control module corresponding to the DC power station controls the converter valve in the DC power station to unlock.

2. The converter station unlocking method for flexible DC transmission according to claim 1, characterized in that, The control module includes a polar control unit and a valve control unit; the polar control unit is connected to the valve control unit, and the polar control units of each control module are communicatively connected to each other; the valve control unit is connected to each sub-module in the converter valve, and the polar control unit is used to receive and transmit the unlock command; the valve control unit is connected to the converter valve in the corresponding DC converter station, and is used to control the state of each sub-module in the converter valve according to the control signal of the polar control unit; Upon receiving the unlock command, the control module corresponding to the DC power station controls the converter valve in the DC power station to be fully locked, including: Upon receiving the unlocking command, the pole control unit corresponding to the DC power station immediately issues a full lockout command to the corresponding valve control unit. The valve control unit corresponding to the DC power station controls all sub-modules in the converter valve to be locked.

3. The converter station unlocking method for flexible DC transmission according to claim 2, characterized in that, When the converter valve in the DC power station is fully locked, the control module corresponding to the DC voltage station controls the converter valve in the DC voltage station to unlock, including: After receiving the unlocking command, at a first preset time, the pole control unit corresponding to the DC voltage station sends an unlocking command to the corresponding valve control unit; The valve control unit corresponding to the DC voltage station controls the unlocking of the converter valve.

4. The converter station unlocking method for flexible DC transmission according to claim 3, characterized in that, The flexible DC transmission control system also includes: a voltage sensing module, which is installed on the bus of the DC transmission line and is communicatively connected to the control module, for collecting the voltage value of the DC transmission line and transmitting it to the control module; When the voltage of the DC transmission line reaches a preset range, the control module corresponding to the DC power station controls the unlocking of the converter valve in the DC power station, including: The voltage sensing module collects the voltage value of the DC transmission line and transmits it to the control module corresponding to the DC power station; After receiving the unlocking command for a second preset time, if the voltage value of the DC transmission line is within the preset range, the pole control unit corresponding to the DC power station issues an unlocking command to the corresponding valve control unit, wherein the second preset time is greater than the first preset time; The valve control unit corresponding to the DC power station controls the unlocking of the converter valve.

5. The converter station unlocking method for flexible DC transmission according to claim 4, characterized in that, The preset range is 95% higher than the rated voltage value.

6. The converter station unlocking method for flexible DC transmission according to claim 1, characterized in that, The number of control modules is 2, and the number of DC voltage stations and DC power stations is 1 each.

7. A flexible DC transmission control system, characterized in that, include: At least two control modules are connected via communication. The control module is used to send the unlock command to other control modules when it detects an unlock command input by the user. The control module corresponding to the DC power station is connected to the converter valve in the DC power station. After receiving the unlocking command, it controls the converter valve in the DC power station to be fully locked, and controls the converter valve in the DC power station to be unlocked when the voltage of the DC transmission line reaches a preset range. The control module corresponding to the DC voltage station is connected to the converter valve in the corresponding DC voltage station and is used to control the converter valve of the DC voltage station to unlock when the converter valve in the DC power station is fully locked.

8. The flexible DC transmission control system according to claim 7, characterized in that, The control module includes a polar control unit and a valve control unit; The pole control unit corresponding to the DC power station is used to immediately issue a full lockout command to the corresponding valve control unit when it receives the unlock command; The valve control unit corresponding to the DC power station is used to control all sub-modules in the converter valve to be locked according to the full lockout command; The pole control unit corresponding to the DC voltage station is used to send an unlock command to the corresponding valve control unit at a first preset time after receiving the unlock command; The valve control unit corresponding to the DC voltage station is used to control the unlocking of the converter valve according to the unlocking command.

9. The flexible DC transmission control system according to claim 7, characterized in that, Also includes: A voltage sensing module is installed on the bus of the DC transmission line and is communicatively connected to the control module. It is used to collect the voltage value of the DC transmission line and transmit it to the control module corresponding to the DC power station.

10. A flexible DC transmission system, characterized in that, It includes the flexible DC transmission control system as described in any one of claims 7-9, at least one DC power station, at least one DC voltage station, and DC transmission line.

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