Controllable commutation converter commutation control method and system

Abstract

The invention discloses a commutation control method and system for a controllable commutation converter, and the method comprises the steps: detecting the DC side voltage and current of a DC power transmission line receiving end converter, and respectively controlling a converter valve group to carry out the commutation control operation in different states according to the different powers of the two sides of the converter, the AC side anticipated faults and the different fault types. When the alternating current side operates normally, control operation of each converter valve group is carried out according to a normal time sequence, and when the current of the current-phase converter valve group is controlled to be smaller than a turn-off current reference value # imgabs0 #, the current is transferred from a main branch to an auxiliary branch and then transferred to a next converter valve group needing phase change through the auxiliary branch; and when the alternating current side has a fault, adaptively adjusting the turn-off current reference value to # imgabs1 # according to the fault type, and switching on the lightning arrester branch while the auxiliary branch is turned off until the current of the main branch of the next converter valve group is completely established, and turning off the lightning arrester branch of the current converter valve group. Different commutation operations are realized based on different conditions, and commutation failure of the converter valve group can be effectively avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric power systems, relates to high voltage direct current transmission technology, and specifically relates to a commutation control method and system for a controllable commutation converter. Background Art

[0002] There are various ways to connect the inverter, among which the three-phase bridge inverter is the circuit form commonly used in high-voltage DC transmission inverters. For the inverter to work in the inverter state, the following three conditions must be met: (1) The no-load DC voltage of the rectifier must be greater than the no-load DC voltage of the inverter.

[0003] (2) The inverter must also be provided with commutation current by the AC system to ensure that the inverter bridge arms commutate in the correct order. When the six bridge arms of the inverter are turned on in sequence, the DC current flows through the commutation transformer valve-side winding in sequence. At this time, the grid-side winding will induce the corresponding current, realizing the inverter's function of converting DC to AC.

[0004] (3) A sufficiently large turn-off angle is required to ensure safe operation. The characteristics of thyristors determine that they must withstand negative pressure for a period longer than the reverse turn-off time to be able to shut down reliably. Therefore, a sufficient turn-off angle must be ensured during inverter operation to prevent the bridge arm from turning on again when positive pressure comes, resulting in phase reversal.

[0005] During the commutation process, if the valve that has just exited conduction does not restore its blocking capacity during the reverse pressure period, or the commutation process has not been completed during the reverse pressure period, it will cause the pre-open valve to reverse to the pre-closed valve when the valve voltage changes to the forward direction, resulting in commutation failure. Commutation failure causes the inverter to have a reduced DC reverse voltage and increased DC current for a period of time. The existing technology can only avoid commutation failure under relatively minor and short-duration AC faults; because the joint control logic between the controllable capacitor and the converter is too complicated, it seriously restricts the engineering practicality of the converter.

[0006] Prior art CN202111356001.6 discloses a commutation control method, device, converter and readable storage medium for a converter. The converter includes a plurality of converter valves, each of which includes a main branch and an auxiliary branch. The method includes: obtaining the DC current and the first commutation current on the DC side of the receiving end corresponding to the converter, the first commutation current being used to characterize the conduction state of the first converter valve; based on the DC current and the first commutation current, calculating the second commutation current, the second commutation current being used to characterize the off state of the second converter valve; judging whether the second commutation current is less than a preset value; when the second commutation current is less than the preset value, executing the commutation operation from the main branch of the second converter valve to the auxiliary branch. The patent scheme proposes to ensure the operational stability of the commutation by adding an auxiliary branch. However, the patent does not consider the impact of DC power and AC faults on commutation, and cannot guarantee successful commutation in the event of a fault.

[0007] Prior art CN202111353541.9 discloses a commutation control method, device, electronic device and readable storage medium for a converter. The method includes: obtaining the commutation state of the converter; judging whether the commutation state is normal; when the commutation state is abnormal, controlling the converter to start the energy consumption mode and adjusting the energy consumption parameters of the converter. Although the patented technical solution takes into account that the AC end fault will cause commutation failure, and proposes to reduce the impact of the AC fault on the commutation by adjusting the energy consumption parameters of the converter. However, the scheme does not consider the impact of the DC side power, nor does it implement different control strategies for different faults on the AC side. MOV1 and MOV2 incorporated in the auxiliary branch have always formed a path, which will inevitably affect the current from the main branch to the auxiliary branch, and the transfer of the auxiliary branch to the next valve group for commutation. Summary of the invention

[0008] In order to solve the problem of commutation failure of a converter caused by DC side power and AC side faults, the present invention provides a commutation control method and system for a controllable commutation converter.

[0009] To achieve the above-mentioned object of the invention, the present invention adopts the following technical solution.

[0010] On one hand, the present invention discloses a controllable commutation converter commutation control method, the converter includes VT1-VT6 converter valve groups, each converter valve group includes a main branch, an auxiliary branch and a controllable lightning arrester branch connected in parallel, the main branch includes a main branch thyristor valve V11, a main branch IGBT valve V12 and a second thyristor valve V122 connected in parallel, and the auxiliary branch includes an auxiliary branch IGBT valve V13 and an auxiliary branch thyristor valve V14; the method comprises the following steps: Step 1: Real-time detection of the voltage and current on the DC side of the DC transmission line receiving-end converter, the three-phase voltage and current on the AC side, and calculation of the DC side power and AC side power ,when > , go to step 2, otherwise go to step 6; Step 2: Put the main branch and auxiliary branch of each converter valve group into operation and disconnect the controllable lightning arrester branch; Step 3: According to the three-phase voltage and current of the AC side, determine the operating status of the AC side. When there is no fault on the AC side, proceed to step 4 for phase change operation; otherwise, proceed to step 5 for phase change operation; Step 4: After receiving the valve control command, control the current phase commutation valve group to turn off the current when the current is less than the reference value of the shutdown current. When the current is switched, the current is transferred from the main branch to the auxiliary branch, and then transferred to the next converter valve group that needs to be switched through the auxiliary branch; Step 5: After receiving the valve control command, the shut-off current reference value is adaptively adjusted to , and the arrester branch is put into operation while the auxiliary branch is turned off, until the main branch current of the next converter valve group is fully established, and the arrester branch of the current valve group is disconnected; Step 6: Lock the main branch IGBT valve V12, close the second thyristor valve connected in parallel with the main branch IGBT valve, lock the auxiliary branch IGBT valve V13, disconnect the arrester branch, and perform control operations on each converter valve group according to the normal operating sequence.

[0011] The present invention further includes the following preferred embodiments: In step 2, the main branch thyristor valve V11 is turned on, the main branch IGBT valve V12 is turned on, and the second thyristor valve V122 connected in parallel with the main branch IGBT valve V12 is locked; the auxiliary branch thyristor V14 is turned on, the auxiliary branch IGBT valve V13 is turned on, and the lightning arrester branch is disconnected.

[0012] More preferably, In step 3, the AC side operation state includes a normal operation state and a fault operation state, wherein the fault operation state includes a single-phase short circuit fault and an inter-phase short circuit fault.

[0013] More preferably, In step 4, the current reference is turned off I d_off Set to 0.15-0.25 times the rated DC pole current.

[0014] More preferably, In step 6, the control operation of each converter valve group is performed according to the normal operation sequence, specifically including: Receive valve control instructions, and trigger the main branch thyristor valve V11 and main branch IGBT valve V12 of the current phase commutation valve group to turn on. When the valve group commutation current is less than the shutdown current reference value, I d_off When the main branch IGBT valve V12 is turned off, the auxiliary branch IGBT valve V13 and the auxiliary branch thyristor valve V14 are closed, so that the valve current is transferred from the main branch to the auxiliary branch. After a set fixed delay, the auxiliary branch IGBT valve V13 is turned off, and the current is transferred to the next converter valve group.

[0015] More preferably, In step 5, when a single-phase short circuit fault occurs on the AC side, the shutdown current reference value is adaptively adjusted to ;

[0016] in, is the shutdown current reference value after adaptive adjustment, is the zero-sequence voltage amplitude on the AC side, is the rated voltage amplitude on the AC side.

[0017] More preferably, In step 5, when a phase-to-phase short circuit fault occurs on the AC side, the shutdown current reference value is adaptively adjusted to ;

[0018] in, is the short-circuit current value, is the rated current value, is the minimum amplitude of the three-phase voltage during a short-circuit fault. is the DC pole current rating, is the current weight, is the voltage weight, .

[0019] More preferably, When the AC fault is a two-phase short circuit, , ; When the AC fault is a three-phase short circuit, , .

[0020] On the other hand, the present invention discloses a controllable commutation converter commutation control system using the above commutation control method, comprising an electrical quantity measurement module on both sides of the converter, an AC / DC power calculation module, an AC side fault detection module, a shutdown current reference value calculation module, and a valve group commutation operation module; characterized in that: The electrical quantity measurement module on both sides of the converter detects the voltage and current on the DC side of the converter at the receiving end of the DC transmission line and the three-phase voltage and current on the AC side in real time; The AC / DC power calculation module calculates the DC side power and the AC side power. When the DC side power is not greater than the AC side power, the valve group commutation operation module performs the following operations: lock the main branch IGBT valve V12, close the second thyristor valve connected in parallel with the main branch IGBT valve, lock the auxiliary branch IGBT valve V13, disconnect the arrester branch, and perform control operations on each commutation valve group according to the normal operating sequence; When the DC side power is greater than the AC side power, and the AC side fault detection module determines that the AC side is operating normally, the valve group phase change operation module performs the following operations: control operations of each commutation valve group according to the normal operating sequence, and after receiving the valve control command, control the current phase commutation valve to switch on when the current is less than the shutdown current reference value. When the current is transferred from the main branch to the auxiliary branch, it is then transferred to the next converter valve group through the auxiliary branch; When the DC side power is greater than the AC side power, and the AC side fault detection module determines that the AC side is short-circuited, the valve group phase change operation module performs the following operations: Adaptively adjust the shutdown current reference value to , and then the valve group phase change operation is controlled according to the same timing as normal operation.

[0021] The present invention also discloses a computer-readable storage medium storing one or more programs, characterized in that the one or more programs include instructions, which, when executed by a computing device, enable the computing device to execute any one of the aforementioned commutation control methods.

[0022] A computing device, comprising: One or more processors, one or more memories, and one or more programs, wherein the one or more programs are stored in the one or more memories and are configured to be executed by the one or more processors, and the one or more programs include instructions for executing any of the aforementioned commutation control methods.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects.

[0024] (1) The present invention can timely control the activation and deactivation of the lightning arrester by setting an independently controllable lightning arrester branch, without affecting the orderly commutation operation under normal operating conditions. Moreover, when a fault occurs on the AC side, the lightning arrester can be relied upon to establish a forced commutation voltage, successfully complete the commutation, and avoid commutation failure.

[0025] (2) The present invention associates a second thyristor at both ends of the main branch IGBT. When the DC side power is not greater than the AC side power, the main branch IGBT can be effectively locked and the auxiliary branch can be exited. The natural commutation method is adopted to improve the commutation reliability when the DC side power is not greater than the AC side power.

[0026] (3) For different AC side faults, an adaptive adjustment of the shutdown current reference value is proposed The algorithm enables the converter to reliably complete active commutation operation under different fault types. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the topological structure of a controllable commutation converter; Figure 2 The present invention Figure 1 A schematic diagram of the structure of each converter valve group; Figure 3 It is a schematic flow chart of the commutation control method of the controllable commutation converter of the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only embodiments of a part of the present invention, rather than all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0029] like Figure 1 As shown in FIG. 1 , the topological structure of the controllable commutation converter is shown. The converters in the converter station are all composed of 6-pulse or 12-pulse converters. In a DC power transmission project, in order to increase the output DC voltage level, the DC ends of two converter valves can be connected in series to form a 12-pulse converter. However, the two series-connected 6-pulse converter valves are decoupled. The embodiment of the present application is introduced based on the 6-pulse inverter. The basic structure of the 6-pulse inverter is shown in FIG. Figure 1 As shown, its DC side is connected to the output end of the rectifier. L d Indicates smoothing reactor, connected on the AC side e a , e b , e c They represent the equivalent phase voltages of the AC system, L μis the inductance of each phase of the AC system. The converter includes VT1-VT6 converter valve group, VT1, VT3, VT5 form a cathode half bridge, VT4, VT6, VT2 form an anode half bridge, VT1, VT3, VT5 are connected to VT4, VT6, VT2 respectively.

[0030] In order to achieve the purpose of the invention, the following Figure 2 Demonstration of the invention Figure 1 In the present invention, each converter valve group VT1-VT6 includes a main branch, an auxiliary branch and a lightning arrester branch, wherein the main branch includes a main branch thyristor valve V11, a main branch IGBT valve V12, and a second thyristor valve V122 connected in parallel with the main branch IGBT valve V12; the auxiliary branch includes an auxiliary branch IGBT valve V13 and an auxiliary branch thyristor valve V14; in the embodiment of the present invention, an independently controllable lightning arrester branch is also provided including a switch K and a lightning arrester Arr.

[0031] Figure 3 The present invention is a flow chart of a controllable phase-commutation converter commutation control method. The controllable phase-commutation converter commutation control method disclosed in the present invention comprises the following steps: Step 1: Real-time detection of the voltage and current on the DC side of the DC transmission line receiving-end converter, the three-phase voltage and current on the AC side, and calculation of the DC side power and AC side power , during normal operation, > , go to step 2 to perform the phase change control operation, otherwise go to step 6 to perform the phase change control operation; In the present application, when the DC side power is reduced to be lower than the AC side power, the commutation operation is performed in accordance with step 6, otherwise, the process goes to step 2.

[0032] Step 2: Put the main branch and auxiliary branch of each converter valve group into operation and disconnect the arrester branch; The main branch thyristor valve V11 is put into operation, the main branch IGBT valve V12 is put into operation, and at the same time, the second thyristor valve V122 connected in parallel with the main branch IGBT valve V12 is locked; the auxiliary branch thyristor valve V14 is put into operation, the auxiliary branch IGBT valve V13 is put into operation, and the lightning arrester branch is disconnected.

[0033] Step 3: According to the three-phase voltage and current of the AC side, determine the operating status of the AC side. When there is no fault on the AC side, proceed to step 4 for phase change operation; otherwise, proceed to step 5 for phase change operation; The AC side operation state includes a normal operation state and a fault operation state, wherein the fault operation state includes a single-phase short circuit fault and an inter-phase short circuit fault.

[0034] Step 4: Perform control operations on each converter valve group according to the normal operating sequence. After receiving the valve control command, control the current phase converter valve to turn on when the current is less than the shutdown current reference value. When the current is transferred from the main branch to the auxiliary branch, it is then transferred to the next converter valve group through the auxiliary branch; Shutdown current reference value I d_off Set to 0.15-0.25 times the rated DC pole current.

[0035] The control operation of each converter valve group is performed according to the normal operating sequence, including: Receive valve control instructions, and trigger the main branch thyristor valve V11 and main branch IGBT valve V12 of the current phase commutation valve group to turn on. When the valve group commutation current is less than the shutdown current reference value, I d_off When the main branch IGBT valve V12 is turned off, the auxiliary branch IGBT valve V13 and the auxiliary branch thyristor valve V14 are closed, so that the valve current is transferred from the main branch to the auxiliary branch. After a set fixed delay, the auxiliary branch IGBT valve V13 is turned off, and the current is transferred to the next converter valve group.

[0036] Step 5: The commutation sequence is the same as the normal operation sequence. After receiving the valve control command, the shutdown current reference value is adaptively adjusted to , and the arrester branch is put into operation while the auxiliary branch is turned off, until the main branch current of the next converter valve group is fully established, and the arrester branch of the current valve group is disconnected; In step 5, 5.1 When a single-phase short circuit fault occurs on the AC side, the shutdown current reference value is adaptively adjusted to ;

[0037] in, is the shutdown current reference value after adaptive adjustment, is the zero-sequence voltage amplitude on the AC side, is the rated voltage amplitude on the AC side.

[0038] 5.2 When a phase-to-phase short circuit fault occurs on the AC side, the shutdown current reference value is adaptively adjusted to ;

[0039] in, is the short-circuit current value, is the rated current value, is the minimum amplitude of the three-phase voltage during a short-circuit fault. is the DC pole current rating, is the current weight, is the voltage weight, .

[0040] In a preferred embodiment of the present invention, When the AC fault is a two-phase short circuit, , ; When the AC fault is a three-phase short circuit, , .

[0041] The present application also discloses a controllable commutation converter commutation control system of the above commutation control method, including an electrical quantity measurement module on both sides of the converter, an AC / DC power calculation module, an AC side fault detection module, a shutdown current reference value calculation module, and a valve group commutation operation module; The electrical quantity measurement module on both sides of the converter detects the voltage and current on the DC side of the converter at the receiving end of the DC transmission line and the three-phase voltage and current on the AC side in real time; The AC / DC power calculation module calculates the DC side power and the AC side power. When the DC side power is not greater than the AC side power, the valve group commutation operation module performs the following operations: lock the main branch IGBT valve V12, close the second thyristor valve connected in parallel with the main branch IGBT valve, lock the auxiliary branch IGBT valve V13, disconnect the arrester branch, and perform control operations on each commutation valve group according to the normal operating sequence; When the DC side power is greater than the AC side power, and the AC side fault detection module determines that the AC side is operating normally, the valve group phase change operation module performs the following operations: control operations of each commutation valve group according to the normal operating sequence, and after receiving the valve control command, control the current phase commutation valve to switch on when the current is less than the shutdown current reference value. When the current is transferred from the main branch to the auxiliary branch, it is then transferred to the next converter valve group through the auxiliary branch; When the DC side power is greater than the AC side power, and the AC side fault detection module determines that the AC side is short-circuited, the valve group commutation operation module performs the following operations: Adaptively adjust the shutdown current reference value according to the fault type , and then the valve group phase change operation is controlled according to the same timing as normal operation.

[0042] The present invention also discloses a computer-readable storage medium storing one or more programs, characterized in that the one or more programs include instructions, which, when executed by a computing device, enable the computing device to execute any one of the aforementioned commutation control methods.

[0043] A computing device, comprising: One or more processors, one or more memories, and one or more programs, wherein the one or more programs are stored in the one or more memories and are configured to be executed by the one or more processors, and the one or more programs include instructions for executing any of the aforementioned commutation control methods.

[0044] The present disclosure may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0045] A computer-readable storage medium may be a tangible device that can hold and store instructions used by an instruction execution device. A computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the above. More specific examples (a non-exhaustive list) of computer-readable storage media include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a raised structure in a groove on which instructions are stored, and any suitable combination of the above. The computer-readable storage medium used herein is not to be interpreted as a transient signal itself, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through a fiber optic cable), or an electrical signal transmitted through a wire.

[0046] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, optical fiber transmissions, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in the computer-readable storage medium in each computing / processing device.

[0047] The computer program instructions for performing the operations of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages, such as Smalltalk, C++, etc., and conventional procedural programming languages, such as "C" language or similar programming languages. The computer-readable program instructions may be executed entirely on the user's computer, partially on the user's computer, as a separate software package, partially on the user's computer, partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., using an Internet service provider to connect through the Internet). In some embodiments, by using the state information of the computer-readable program instructions to personalize an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), the electronic circuit may execute the computer-readable program instructions, thereby implementing various aspects of the present disclosure.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A controllable commutation converter commutation control method, the converter includes VT1-VT6 commutation valve groups, each commutation valve group includes a main branch, an auxiliary branch and a controllable lightning arrester branch in parallel, the main branch includes a main branch thyristor valve V11, a main branch IGBT valve V12 and a second thyristor valve V122 in parallel, and the auxiliary branch includes an auxiliary branch IGBT valve V13 and an auxiliary branch thyristor valve V14; characterized in that: The method comprises the following steps: Step 1: Real-time detection of the voltage and current on the DC side of the DC transmission line receiving-end converter, the three-phase voltage and current on the AC side, and calculation of the DC side power and AC side power ,when > , go to step 2, otherwise go to step 6; Step 2: Put the main branch and auxiliary branch of each converter valve group into operation and disconnect the controllable lightning arrester branch; Step 3: According to the three-phase voltage and current of the AC side, determine the operating status of the AC side. When there is no fault on the AC side, proceed to step 4 for phase change operation; otherwise, proceed to step 5 for phase change operation; Step 4: After receiving the valve control command, control the current phase commutation valve group to turn off the current when the current is less than the reference value of the shutdown current. When the current is switched, the current is transferred from the main branch to the auxiliary branch, and then transferred to the next converter valve group that needs to be switched through the auxiliary branch; Step 5: After receiving the valve control command, the shut-off current reference value is adaptively adjusted to , and the arrester branch is put into operation while the auxiliary branch is turned off, until the main branch current of the next converter valve group is fully established, and the arrester branch of the current valve group is disconnected; Step 6: Lock the main branch IGBT valve V12, close the second thyristor valve connected in parallel with the main branch IGBT valve, lock the auxiliary branch IGBT valve V13, disconnect the arrester branch, and perform control operations on each converter valve group according to the normal operating sequence.

2. The controllable commutation converter commutation control method according to claim 1, characterized in that: In step 2, the main branch thyristor valve V11 is turned on, the main branch IGBT valve V12 is turned on, and the second thyristor valve V122 connected in parallel with the main branch IGBT valve V12 is locked; the auxiliary branch thyristor valve V14 is turned on, the auxiliary branch IGBT valve V13 is turned on, and the lightning arrester branch is disconnected.

3. The controllable commutation converter commutation control method according to claim 2, characterized in that: In step 3, the AC side operation state includes a normal operation state and a fault operation state, wherein the fault operation state includes a single-phase short circuit fault and an inter-phase short circuit fault.

4. The commutation control method of a controllable commutation converter according to claim 1 or 3, characterized in that: In step 4, the current reference is turned off I d_off Set to 0.15-0.25 times the rated DC pole current.

5. The commutation control method of a controllable commutation converter according to claim 4, characterized in that: In step 6, the control operation of each converter valve group is performed according to the normal operation sequence, specifically including: Receive valve control instructions, and trigger the main branch thyristor valve V11 and main branch IGBT valve V12 of the current phase commutation valve group to turn on. When the commutation current of the commutation valve group is less than the reference value of the commutation current, I d_off When the main branch IGBT valve V12 is turned off, the auxiliary branch IGBT valve V13 and the auxiliary branch thyristor valve V14 are closed, so that the valve current is transferred from the main branch to the auxiliary branch. After a set fixed delay, the auxiliary branch IGBT valve V13 is turned off, and the current is transferred to the next converter valve group.

6. The commutation control method of a controllable commutation converter according to claim 1 or 3, characterized in that: In step 5, when a single-phase short circuit fault occurs on the AC side, the shutdown current reference value is adaptively adjusted to ; in, is the shutdown current reference value after adaptive adjustment, is the zero-sequence voltage amplitude on the AC side, is the rated voltage amplitude on the AC side.

7. The commutation control method of a controllable commutation converter according to claim 6, characterized in that: In step 5, when a phase-to-phase short circuit fault occurs on the AC side, the shutdown current reference value is adaptively adjusted to ; in, is the short-circuit current value, is the rated current value, is the minimum amplitude of the three-phase voltage during a short-circuit fault. is the DC pole current rating, is the current weight, is the voltage weight, .

8. The commutation control method of a controllable commutation converter according to claim 7, characterized in that: When the AC fault is a two-phase short circuit, , ; When the AC fault is a three-phase short circuit, , .

9. A control system for a controllable commutation converter using the method according to any one of claims 1 to 8, comprising a converter electrical quantity measurement module, an AC / DC power calculation module, an AC side fault detection module, a shutdown current reference value calculation module, and a valve group commutation operation module; characterized in that: The electrical quantity measurement module on both sides of the converter detects the voltage and current on the DC side of the converter at the receiving end of the DC transmission line and the three-phase voltage and current on the AC side in real time; The AC / DC power calculation module calculates the DC side power and the AC side power. When the DC side power is not greater than the AC side power, the valve group commutation operation module performs the following operations: lock the main branch IGBT valve V12, close the second thyristor valve connected in parallel with the main branch IGBT valve, lock the auxiliary branch IGBT valve V13, disconnect the arrester branch, and perform control operations on each commutation valve group according to the normal operating sequence; When the DC side power is greater than the AC side power, and the AC side fault detection module determines that the AC side is operating normally, the valve group phase change operation module performs the following operations: control operations of each commutation valve group according to the normal operating sequence, and after receiving the valve control command, control the current phase commutation valve to switch on when the current is less than the shutdown current reference value. When the current is transferred from the main branch to the auxiliary branch, it is then transferred to the next converter valve group through the auxiliary branch; When the DC side power is greater than the AC side power, and the AC side fault detection module determines that the AC side is short-circuited, the valve group commutation operation module performs the following operations: Adaptively adjust the shutdown current reference value to , and then the valve group phase change operation is controlled according to the same timing as normal operation.

10. A computer-readable storage medium storing one or more programs, characterized in that: The one or more programs include instructions which, when executed by a computing device, cause the computing device to perform any one of the methods according to claims 1-8.

11. A computing device, characterized in that: include: One or more processors, one or more memories, and one or more programs, wherein the one or more programs are stored in the one or more memories and are configured to be executed by the one or more processors, and the one or more programs include instructions for executing any of the methods according to claims 1-8.

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