Flexible direct current transmission project converter valve bridge arm locking method and system

Abstract

The invention provides a flexible direct current transmission project converter valve bridge arm locking method and system. The method comprises the following steps: acquiring a first current value of an upper bridge arm, a second current value of a lower bridge arm, a plurality of first sub-module states and a plurality of second sub-module states in real time; identifying a first current direction of a current upper bridge arm and a second current direction of a current lower bridge arm according to the alternating current connection point; generating a bridge arm locking strategy based on the first current direction, the second current direction, each first sub-module state and each second sub-module state; and locking the first sub-module and the second sub-module through the first current value, the second current value and the converter transformer valve side module based on the bridge arm locking strategy. The problem that the overvoltage after the converter valve breaks down cannot be effectively reduced in the prior art is solved. According to the invention, differential locking of the converter valve bridge arm sub-modules is realized, and the overvoltage after the converter valve breaks down is effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of DC power transmission technology, and in particular to a method and system for locking the bridge arm of a converter valve in a flexible DC power transmission project. Background Technology

[0002] Flexible power transmission technology is currently the main technical means for applications such as large-scale transmission of new energy, flexible interconnection of regional power grids, and power mutual assistance among multiple power grids. Therefore, in the converter valve circuit of DC transmission projects, how to effectively reduce the overvoltage after the converter valve fails has become a problem to be solved.

[0003] Currently, existing technologies mainly employ direct blocking of the bridge arm sub-modules of the converter valve circuit in DC transmission projects to reduce overvoltage after a converter valve failure. However, direct full blocking leads to the superposition of capacitor voltages of all sub-modules in the upper and lower bridge arms, and the overvoltage can reach several times the steady-state value. This approach places high demands on the insulation level of the surge arresters configured in the converter valve circuit of DC transmission projects, resulting in poor overvoltage reduction after a converter valve failure and making it difficult to effectively reduce overvoltage after a converter valve failure. Summary of the Invention

[0004] To address the aforementioned issues, this invention proposes a method and system for locking the converter valve arm in flexible DC transmission projects. This method enables differentiated locking of the converter valve arm sub-modules, effectively reducing overvoltage after a converter valve failure.

[0005] To achieve the above objectives, embodiments of the present invention provide a method for locking the bridge arm of a converter valve in a flexible DC transmission project. This method is applied to a converter valve circuit in a DC transmission project. The converter valve circuit includes several first sub-modules, several second sub-modules, and a converter transformer valve-side module. The first sub-modules are connected to the upper bridge arm of the DC transmission project converter valve circuit; the second sub-modules are connected to the lower bridge arm of the DC transmission project converter valve circuit; the upper and lower bridge arms are connected via an AC connection point. The method includes: real-time acquisition of a first current value of the upper bridge arm, a second current value of the lower bridge arm, the states of the first sub-modules, and the states of the second sub-modules; identification of the first current direction of the current upper bridge arm and the second current direction of the current lower bridge arm based on the AC connection point; generation of a bridge arm locking strategy based on the first current direction, the second current direction, the states of each first sub-module, and the states of each second sub-module; and locking the first and second sub-modules based on the bridge arm locking strategy using the first current value, the second current value, and the converter transformer valve-side module.

[0006] This invention proposes a bridge arm interlocking method for converter valves in flexible DC transmission projects. It obtains the first current value of the upper bridge arm, the second current value of the lower bridge arm, and the states of several first and second sub-modules to reflect the overvoltage mechanism after a converter valve failure. By identifying the current direction of the first current in the upper bridge arm and the current direction of the second current in the lower bridge arm, and combining the states of each first and second sub-module, a bridge arm interlocking strategy is generated. Finally, by combining the bridge arm interlocking strategy with the first current value of the upper bridge arm and the second current value of the lower bridge arm, differentiated interlocking control is applied to the first and second sub-modules after a failure, effectively reducing the overvoltage after a converter valve failure.

[0007] Furthermore, the system acquires in real time the first current value of the upper arm, the second current value of the lower arm, the status of several first submodules, and the status of several second submodules, including: monitoring the current of the upper arm and the lower arm in real time through AC connection points and outputting the first and second current values; monitoring the status of each first submodule in real time and outputting several first submodule statuses, where the first submodule statuses include: engaged and disengaged; and monitoring the status of each second submodule in real time and outputting several second submodule statuses, where the second submodule statuses include: engaged and disengaged.

[0008] In the above scheme, monitoring the upper and lower bridge arm currents, as well as the status of each first and second submodule, can effectively correspond to the overvoltage generation mechanism. The status of the submodules is divided into two states: engaged and disengaged. This provides a more multi-dimensional data foundation for subsequent differentiated blocking of submodules, which helps to differentiate the blocking of the converter valve bridge arm submodules and effectively reduce the overvoltage after the converter valve fails.

[0009] Furthermore, identifying the first current direction of the current upper arm and the second current direction of the current lower arm based on the AC connection point includes: if the first current of the upper arm flows to the AC connection point, then the first current direction of the current upper arm is identified as positive; if the first current of the upper arm flows out of the AC connection point, then the first current direction of the current upper arm is identified as negative; if the second current of the lower arm flows out of the AC connection point, then the second current direction of the current lower arm is identified as positive; if the second current of the lower arm flows to the AC connection point, then the second current direction of the current lower arm is identified as negative.

[0010] In the above scheme, the positive and negative directions of current flow in the upper and lower bridge arms are calibrated according to the direction of current flow at the AC connection point, providing a more multi-dimensional data basis for the subsequent differentiated interlocking submodule, which helps to differentiate the interlocking of the converter valve bridge arm submodule and effectively reduce the overvoltage after the converter valve fails.

[0011] Furthermore, based on the first current direction, the second current direction, the state of each first submodule, and the state of each second submodule, a bridge arm locking strategy is generated, including: if both the first current direction and the second current direction are positive, then a first bridge arm locking strategy is generated according to the state of each first submodule and the state of each second submodule; if the first current direction and the second current direction are opposite, then a second bridge arm locking strategy is generated; if the first current direction and / or the second current direction are negative, then a second bridge arm locking strategy is generated.

[0012] In the above scheme, a corresponding bridge arm blocking strategy is generated according to the current direction. Multiple discrimination logics are used to fully consider all possible current flow situations during a fault, providing more dimensions of judgment criteria for various differentiated blocking sub-modules. This helps to differentiate the blocking of the converter valve bridge arm sub-modules and effectively reduce the overvoltage after the converter valve fails.

[0013] Furthermore, based on the bridge arm blocking strategy, the first and second sub-modules are blocked using a first current value, a second current value, and the converter transformer valve-side module. This includes: if the bridge arm blocking strategy is the first bridge arm blocking strategy, then the valve-controlled overcurrent protection setting is obtained based on the converter transformer valve-side module; if both the first and second current values ​​are less than the valve-controlled overcurrent protection setting, then the number of first sub-modules in the activated state and the number of second sub-modules in the activated state are obtained; if the number of first sub-modules in the activated state is greater than the number of second sub-modules in the activated state, then the first sub-module is blocked, and the second sub-module is blocked when the second current direction is negative; if the number of first sub-modules in the activated state is less than the number of second sub-modules in the activated state, then the second sub-module is blocked, and the first sub-module is blocked when the first current direction is negative. If the bridge arm blocking strategy is the second bridge arm blocking strategy, then the valve-controlled overcurrent protection action signal is obtained based on the converter transformer valve-side module; and all first and second sub-modules are blocked based on the valve-controlled overcurrent protection action signal.

[0014] In the above scheme, after generating the bridge arm locking strategy, the bridge arms are further locked in a differentiated manner according to different strategies. When executing the first bridge arm locking strategy, the difference in the number of sub-module states is also considered. The sub-modules with more engaged states are locked first to reduce the base number of capacitors. The other bridge arm waits for the current direction to be negative before shutting down the sub-module to avoid capacitor charging caused by locking when the current is positive. Thus, the converter valve bridge arm sub-modules are locked in a differentiated manner, which effectively reduces the overvoltage after the converter valve fails.

[0015] Furthermore, the converter valve circuit of the DC transmission project also includes: an upper arm reactor of the converter valve, a first surge arrester, a lower arm reactor of the converter valve, and a second surge arrester; the first end of the upper arm reactor of the converter valve is connected to the DC circuit, the second end of the upper arm reactor of the converter valve is electrically connected to the first end of the first surge arrester, and the second end of the first surge arrester is electrically connected to the first submodule; the first end of the lower arm reactor of the converter valve is connected to the DC circuit, the second end of the lower arm reactor of the converter valve is electrically connected to the first end of the second surge arrester; the second end of the second surge arrester is electrically connected to the second submodule. Before performing the step of identifying the first current direction of the current upper arm and the second current direction of the current lower arm based on the AC connection point, the method includes: if fault phase selection is not required, setting a first current measuring point at the second end of the first surge arrester and a second current measuring point at the second end of the second surge arrester; if fault phase selection is required, setting a first current measuring point at the second end of the first surge arrester and a third current measuring point at the second end of the reactor of the upper arm of the converter valve, and setting a second current measuring point at the second end of the second surge arrester and a fourth current measuring point at the second end of the reactor of the lower arm of the converter valve.

[0016] In the above scheme, two different circuit designs are set according to the fault phase selection requirements. When fault phase selection is not required, only the surge arrester valve side current measuring device is configured, which simplifies the circuit design cost. When fault phase selection is required, a bridge arm reactor valve side measuring device is added to achieve fault phase selection through differential protection. This helps to differentiate the interlocking of the converter valve bridge arm sub-module and effectively reduces the overvoltage after the converter valve fails.

[0017] This invention also provides a converter valve arm interlocking system for flexible DC transmission projects, comprising: a data acquisition module, a current direction identification module, an arm interlocking strategy generation module, and an arm interlocking module; the data acquisition module is used to acquire in real time the first current value of the upper arm, the second current value of the lower arm, the status of several first sub-modules, and the status of several second sub-modules; the current direction identification module is used to identify the first current direction of the current upper arm and the second current direction of the current lower arm based on the AC connection point; the arm interlocking strategy generation module is used to generate an arm interlocking strategy based on the first current direction, the second current direction, the status of each first sub-module, and the status of each second sub-module; the arm interlocking module is used to interlock the first and second sub-modules based on the arm interlocking strategy, using the first current value, the second current value, and the converter transformer valve side module.

[0018] This invention proposes a converter valve arm interlocking system for flexible DC transmission projects. It obtains the first current value of the upper arm, the second current value of the lower arm, and the states of several first and second sub-modules to reflect the overvoltage mechanism after a converter valve failure. By identifying the current first current direction of the upper arm and the current second current direction of the lower arm, and combining the states of each first and second sub-module, an arm interlocking strategy is generated. Finally, the arm interlocking strategy, combined with the first current value of the upper arm and the second current value of the lower arm, enables differentiated interlocking control of the first and second sub-modules after a failure, effectively reducing the overvoltage after a converter valve failure.

[0019] Furthermore, the data acquisition module is used to acquire in real time the first current value of the upper bridge arm, the second current value of the lower bridge arm, the status of several first sub-modules, and the status of several second sub-modules. It includes: a current value monitoring unit, a first module status acquisition unit, and a second module status acquisition unit. The current value monitoring unit is used to monitor the current of the upper bridge arm and the lower bridge arm in real time through AC connection points and output the first and second current values. The first module status acquisition unit is used to monitor the status of each first sub-module in real time and output several first sub-module statuses, including: engaged and disengaged. The second module status acquisition unit is used to monitor the status of each second sub-module in real time and output several second sub-module statuses, including: engaged and disengaged.

[0020] Furthermore, the current direction recognition module is used to identify the first current direction of the current upper arm and the second current direction of the current lower arm based on the AC connection point, including: a first direction judgment unit, a second direction judgment unit, a third direction judgment unit, and a fourth direction judgment unit; the first direction judgment unit is used to identify the first current direction of the current upper arm as positive if the first current of the upper arm flows to the AC connection point; the second direction judgment unit is used to identify the first current direction of the current upper arm as negative if the first current of the upper arm flows out of the AC connection point; the third direction judgment unit is used to identify the second current direction of the current lower arm as positive if the second current of the lower arm flows out of the AC connection point; the fourth direction judgment unit is used to identify the second current direction of the current lower arm as negative if the second current of the lower arm flows to the AC connection point. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the steps of a method for locking up a converter valve bridge arm in a flexible DC transmission project, according to a certain embodiment of the present invention. Figure 2 A schematic diagram of the converter valve circuit connection for a flexible DC transmission project converter valve bridge arm interlocking method provided in a certain embodiment of the present invention; Figure 3A schematic diagram comparing the interlocking of a converter valve bridge arm in a flexible DC transmission project under different current directions and submodule states, as provided in a certain embodiment of the present invention. Figure 1 ; Figure 4 A schematic diagram comparing the interlocking of a converter valve bridge arm in a flexible DC transmission project under different current directions and submodule states, as provided in a certain embodiment of the present invention. Figure 2 ; Figure 5 A schematic diagram comparing the interlocking of a converter valve bridge arm in a flexible DC transmission project under different current directions and submodule states, as provided in a certain embodiment of the present invention. Figure 3 ; Figure 6 A schematic diagram comparing the interlocking of a converter valve bridge arm in a flexible DC transmission project under different current directions and submodule states, as provided in a certain embodiment of the present invention. Figure 4 ; Figure 7 A schematic diagram showing the comparison of overvoltage suppression effects before and after a converter valve bridge arm interlocking method for a flexible DC transmission project according to a certain embodiment of the present invention; Figure 8 This is a schematic diagram of the module structure of a converter valve bridge arm interlocking system for a flexible DC transmission project, provided in one embodiment of the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1 See Figure 1 , Figure 1 This is a flowchart illustrating the steps of a method for locking up a converter valve arm in a flexible DC transmission project, provided by a certain embodiment of the present invention. Figure 1 As shown in the figure, this invention proposes a method for locking up the converter valve arm in a flexible DC transmission project, including steps 101 to 104, each step of which is as follows: Step 101: Real-time acquisition of the first current value of the upper bridge arm, the second current value of the lower bridge arm, the status of several first sub-modules 1, and the status of several second sub-modules 2; Step 102: Identify the first current direction of the current upper bridge arm and the second current direction of the current lower bridge arm based on the AC connection point; Step 103 generates a bridge arm locking strategy based on the first current direction, the second current direction, the state of each first submodule 1, and the state of each second submodule 2. Step 104: Based on the bridge arm blocking strategy, the first submodule 1 and the second submodule 2 are blocked by the first current value, the second current value and the converter transformer side module 3.

[0024] One specific implementation method is described in [reference]. Figure 2 , Figure 2 This is a schematic diagram of the converter valve circuit connection for a flexible DC transmission project, illustrating a converter valve arm interlocking method for a converter valve in a specific embodiment of the present invention; as shown. Figure 2 As shown, the flexible DC transmission engineering converter valve arm interlocking method proposed in this embodiment is applied to the converter valve circuit of a DC transmission engineering project. The DC transmission engineering converter valve circuit includes: several first sub-modules 1, several second sub-modules 2, and a converter transformer valve side module 3. The several first sub-modules 1 are connected to the upper bridge arm of the DC transmission engineering converter valve circuit; the several second sub-modules 2 are connected to the lower bridge arm of the DC transmission engineering converter valve circuit; the upper bridge arm and the lower bridge arm are connected through an AC connection point; in addition, the DC transmission engineering converter valve circuit also includes: a converter valve upper bridge arm reactor 4, a first surge arrester 5, a converter valve lower bridge arm reactor 6, and a second surge arrester 7; the first end of the converter valve upper bridge arm reactor 4 is connected to the DC circuit, the second end of the converter valve upper bridge arm reactor 4 is electrically connected to the first end of the first surge arrester 5, and the second end of the first surge arrester 5 is electrically connected to the first sub-module 1. Module 1 is electrically connected; the first end of the lower bridge arm reactor 6 of the converter valve is connected to the DC circuit, and the second end of the lower bridge arm reactor 6 of the converter valve is electrically connected to the first end of the second surge arrester 7; the second end of the second surge arrester 7 is electrically connected to the second sub-module 2; based on the basic design of the converter valve circuit of the DC transmission project, the mechanism of overvoltage generation is analyzed as follows: when a single-phase ground fault occurs on the valve side of the converter valve bridge arm reactor, a single-phase ground fault occurs at the position of the surge arrester on the upper bridge arm of the converter valve. At this time, the bridge arm current will rise rapidly and lock the sub-module on the bridge arm after reaching the valve-controlled bridge arm overcurrent protection setting. For example, if a fault occurs on the valve side of the upper bridge arm reactor, a single-phase ground fault occurs at the position of the surge arrester on the upper bridge arm of the converter valve, and the voltage is 0. At this time, the voltage on the valve side of the lower bridge arm reactor will be the sum of the capacitor voltages of all sub-modules of the upper and lower bridge arms. At this time, an overvoltage much greater than that in steady-state operation will be generated. Based on the overvoltage generation mechanism analyzed above, the system monitors whether the arm current changes in real time and obtains the status of each arm submodule. Then, by identifying the direction of the arm current and combining it with the obtained status of each arm submodule, an arm blocking strategy is generated. The converter valve side module 3 uses the arm blocking strategy and the arm current value to determine how to perform differentiated blocking on each arm submodule. In this embodiment, the arm current includes: the first current of the upper arm and the second current of the lower arm. The arm submodule includes: the first submodule 1 of the upper arm and the second submodule 2 of the lower arm.

[0025] This invention proposes a bridge arm interlocking method for converter valves in flexible DC transmission projects. It obtains the first current value of the upper bridge arm, the second current value of the lower bridge arm, and the states of several first sub-modules 1 and several second sub-modules 2, which can reflect the overvoltage mechanism after a converter valve failure. By identifying the current first current direction of the upper bridge arm and the current second current direction of the lower bridge arm, and combining the states of each first sub-module 1 and each second sub-module 2, a bridge arm interlocking strategy is generated. Finally, by combining the bridge arm interlocking strategy with the first current value of the upper bridge arm and the second current value of the lower bridge arm, differentiated interlocking control is applied to the first sub-modules 1 and the second sub-modules 2 after a failure, effectively reducing the overvoltage after a converter valve failure.

[0026] A preferred embodiment involves real-time acquisition of a first current value of the upper bridge arm, a second current value of the lower bridge arm, a plurality of first submodule 1 states, and a plurality of second submodule 2 states, including: real-time monitoring of the upper bridge arm current and the lower bridge arm current and outputting the first current value and the second current value through AC connection points; real-time monitoring of the states of each first submodule 1 and outputting a plurality of first submodule 1 states, wherein the states of the first submodule 1 include: engaged and disengaged; and real-time monitoring of the states of each second submodule 2 and outputting a plurality of second submodule 2 states, wherein the states of the second submodule 2 include: engaged and disengaged.

[0027] In one preferred implementation, a first current value is obtained by monitoring the current between the current measuring point and the AC connection point of the upper bridge arm, and a second current value is obtained by monitoring the current between the current measuring point and the AC connection point of the lower bridge arm. Before locking, the first submodule 1 and the second submodule 2 have two states: engaged and disengaged. In the above scheme, monitoring the upper and lower bridge arm currents, as well as the status of each first and second submodule, can effectively correspond to the overvoltage generation mechanism. The status of the submodules is divided into two states: engaged and disengaged. This provides a more multi-dimensional data foundation for subsequent differentiated blocking of submodules, which helps to differentiate the blocking of the converter valve bridge arm submodules and effectively reduce the overvoltage after the converter valve fails.

[0028] A preferred embodiment identifies the first current direction of the current upper arm and the second current direction of the current lower arm based on the AC connection point, including: if the first current of the upper arm flows to the AC connection point, then the first current direction of the current upper arm is identified as positive; if the first current of the upper arm flows out of the AC connection point, then the first current direction of the current upper arm is identified as negative; if the second current of the lower arm flows out of the AC connection point, then the second current direction of the current lower arm is identified as positive; if the second current of the lower arm flows to the AC connection point, then the second current direction of the current lower arm is identified as negative.

[0029] In one preferred implementation, the bridge arm current flowing through the submodule before locking has two directions: a positive direction and a negative direction. For the upper bridge arm, the direction in which the first current flows into the AC connection point is defined as the positive direction, and the direction in which the first current flows out of the AC connection point is defined as the negative direction. For the lower bridge arm, the direction in which the second current flows out of the AC connection point is defined as the positive direction, and the direction in which the first current flows into the AC connection point is defined as the negative direction.

[0030] In the above scheme, the positive and negative directions of current flow in the upper and lower bridge arms are calibrated according to the direction of current flow at the AC connection point, providing a more multi-dimensional data basis for the subsequent differentiated interlocking submodule, which helps to differentiate the interlocking of the converter valve bridge arm submodule and effectively reduce the overvoltage after the converter valve fails.

[0031] A preferred embodiment generates a bridge arm locking strategy based on a first current direction, a second current direction, the states of each first submodule 1 and each second submodule 2, including: if both the first current direction and the second current direction are positive, then a first bridge arm locking strategy is generated according to the states of each first submodule 1 and each second submodule 2; if the first current direction and the second current direction are opposite, then a second bridge arm locking strategy is generated; if the first current direction and / or the second current direction are negative, then a second bridge arm locking strategy is generated. Then, based on the bridge arm blocking strategy, the first submodule 1 and the second submodule 2 are blocked using the first current value, the second current value, and the converter transformer valve side module 3. This includes: if the bridge arm blocking strategy is the first bridge arm blocking strategy, then the valve-controlled overcurrent protection setting is obtained based on the converter transformer valve side module 3; if both the first current value and the second current value are less than the valve-controlled overcurrent protection setting, then the number of each first submodule 1 in the active state and the number of each second submodule 2 in the active state are obtained; if the number of each first submodule 1 in the active state is greater than the number of each second submodule 2 in the active state, then the first submodule 1 is blocked and the second submodule 2 is blocked when the second current direction is negative; if the number of each first submodule 1 in the active state is less than the number of each second submodule 2 in the active state, then the second submodule 2 is blocked and the first submodule 1 is blocked when the first current direction is negative. If the bridge arm blocking strategy is the second bridge arm blocking strategy, then the valve-controlled overcurrent protection action signal is obtained based on the converter transformer valve side module 3; based on the valve-controlled overcurrent protection action signal, all first sub-modules 1 and second sub-modules 2 are blocked.

[0032] One preferred implementation method first involves analyzing the relationship between the current direction and the state of each submodule before and after latch-up. (See [link to relevant documentation]). Figure 3 , Figure 3 A schematic diagram comparing the interlocking of a converter valve bridge arm in a flexible DC transmission project under different current directions and submodule states, as provided in a certain embodiment of the present invention. Figure 1 ;like Figure 3As shown, the bridge arm current is in the positive direction, the submodule is in the engaged state, and the voltage will not rise sharply after the submodule is locked out; see also Figure 4 , Figure 4 A schematic diagram comparing the interlocking of a converter valve bridge arm in a flexible DC transmission project under different current directions and submodule states, as provided in a certain embodiment of the present invention. Figure 2 ;like Figure 4 As shown, the bridge arm current is in the positive direction, the submodule is in the disconnected state, and after the submodule is locked, the capacitor will be connected to the fault circuit, the submodule capacitor will be charged, causing a voltage surge; see also Figure 5 , Figure 5 A schematic diagram comparing the interlocking of a converter valve bridge arm in a flexible DC transmission project under different current directions and submodule states, as provided in a certain embodiment of the present invention. Figure 3 ;like Figure 5 As shown, the bridge arm current is in the negative direction, the submodule is in the engaged state, and the submodule blocking will not cause overvoltage; see also Figure 6 , Figure 6 A schematic diagram comparing the interlocking of a converter valve bridge arm in a flexible DC transmission project under different current directions and submodule states, as provided in a certain embodiment of the present invention. Figure 4 ;like Figure 6 As shown, the bridge arm current is in the negative direction, the submodule is in the disconnected state, and the submodule lockout will not cause overvoltage. According to the above analysis results, the current direction of the bridge arm current and the submodule state will affect the voltage change after the submodule is lockedout. Therefore, a corresponding submodule lockout strategy can be generated by the bridge arm current direction and the submodule state. Specifically, after a fault occurs, when the currents of both the upper and lower bridge arms are in the positive direction, a first bridge arm lockout strategy is generated; when the currents of the upper and lower bridge arms are in opposite directions, a second bridge arm lockout strategy is generated; when the currents of both the upper and lower bridge arms are in the negative direction, a second bridge arm lockout strategy is generated. Among them, the first bridge arm lockout strategy is to first obtain the valve-controlled overcurrent protection setting based on the converter transformer valve side module 3. Before the bridge arm current exceeds the valve-controlled overcurrent protection setting, the bridge arm with more submodules in operation is locked out first, and the other bridge arm is locked out when the current direction is negative. The second bridge arm lockout strategy is to obtain the valve-controlled overcurrent protection action signal from the converter transformer valve side module 3, and then directly lock out all submodules on the upper and lower bridge arms according to the valve-controlled overcurrent protection action signal. See Figure 7 , Figure 7 This is a schematic diagram comparing the overvoltage suppression effects before and after implementation of a converter valve arm interlocking method for a flexible DC transmission project, according to a certain embodiment of the present invention; as shown. Figure 7As shown, in an application scenario, assuming a single-phase ground fault in the upper bridge arm, after applying the flexible DC transmission engineering converter valve bridge arm blocking method proposed in this embodiment, the voltage to ground of the surge arrester of the lower bridge arm of the converter valve is measured. Then, the voltage to ground of the surge arrester of the lower bridge arm of the converter valve is measured without applying the flexible DC transmission engineering converter valve bridge arm blocking method proposed in this embodiment. The comparison results show that the overvoltage reduction effect of the method proposed in this embodiment is significantly better than that of the method not proposed in this embodiment.

[0033] In the above scheme, a corresponding bridge arm blocking strategy is generated based on the current direction. Multiple discrimination logics are used to fully consider all possible current flow situations during a fault, providing more dimensions of judgment benchmarks for various differentiated blocking sub-modules. After generating the bridge arm blocking strategy, the bridge arms are further blocked in a differentiated manner according to different strategies. When executing the first bridge arm blocking strategy, the difference in the number of sub-module states is also considered. The sub-modules with more engaged states are blocked first to reduce the base of capacitor superposition. The other bridge arm waits for the current direction to be negative before closing the sub-module to avoid capacitor charging caused by blocking when the current is positive. Thus, the converter valve bridge arm sub-modules are blocked in a differentiated manner, effectively reducing the overvoltage after the converter valve fails.

[0034] In a preferred embodiment, before performing the step of identifying the first current direction of the current upper arm and the second current direction of the current lower arm based on the AC connection point, the method includes: if fault phase selection is not required, setting a first current measuring point 8 at the second end of the first surge arrester 5 and a second current measuring point 9 at the second end of the second surge arrester 7; if fault phase selection is required, setting a first current measuring point 8 at the second end of the first surge arrester 5 and a third current measuring point 10 at the second end of the upper arm reactor 4 of the converter valve, and setting a second current measuring point 9 at the second end of the second surge arrester 7 and a fourth current measuring point 11 at the second end of the lower arm reactor 6 of the converter valve.

[0035] One preferred implementation scheme provides a bridge arm blocking current measuring device configuration scheme, wherein if fault phase selection is not required, the current measuring device is only configured on the side of the surge arrester near the valve; if fault phase selection is required, the current measuring device is configured on both the side of the surge arrester near the valve and the side of the converter valve bridge arm reactor valve, and the fault phase selection is achieved using the differential protection principle.

[0036] In the above scheme, two different circuit designs are set according to the fault phase selection requirements. When fault phase selection is not required, only the surge arrester valve side current measuring device is configured, which simplifies the circuit design cost. When fault phase selection is required, a bridge arm reactor valve side measuring device is added to achieve fault phase selection through differential protection. This helps to differentiate the interlocking of the converter valve bridge arm sub-module and effectively reduces the overvoltage after the converter valve fails.

[0037] Example 2 See Figure 8 , Figure 8 This is a schematic diagram of the modular structure of a converter valve bridge arm interlocking system for a flexible DC transmission project, provided in one embodiment of the present invention. Figure 8 As shown in the figure, this embodiment of the invention also provides a converter valve arm interlocking system for flexible DC transmission projects, including: a data acquisition module 201, a current direction identification module 202, an arm interlocking strategy generation module 203, and an arm interlocking module 204; the data acquisition module 201 is used to acquire in real time the first current value of the upper arm, the second current value of the lower arm, the status of several first sub-modules, and the status of several second sub-modules; the current direction identification module 202 is used to identify the first current direction of the current upper arm and the second current direction of the current lower arm according to the AC connection point; the arm interlocking strategy generation module 203 is used to generate an arm interlocking strategy based on the first current direction, the second current direction, the status of each first sub-module, and the status of each second sub-module; the arm interlocking module 204 is used to interlock the first and second sub-modules based on the arm interlocking strategy, using the first current value, the second current value, and the converter valve side module.

[0038] This invention proposes a converter valve arm interlocking system for flexible DC transmission projects. It obtains the first current value of the upper arm, the second current value of the lower arm, and the states of several first and second sub-modules to reflect the overvoltage mechanism after a converter valve failure. By identifying the current first current direction of the upper arm and the current second current direction of the lower arm, and combining the states of each first and second sub-module, an arm interlocking strategy is generated. Finally, the arm interlocking strategy, combined with the first current value of the upper arm and the second current value of the lower arm, enables differentiated interlocking control of the first and second sub-modules after a failure, effectively reducing the overvoltage after a converter valve failure.

[0039] Furthermore, the data acquisition module 201 is used to acquire in real time the first current value of the upper bridge arm, the second current value of the lower bridge arm, the status of several first sub-modules, and the status of several second sub-modules, including: a current value monitoring unit 301, a first module status acquisition unit 302, and a second module status acquisition unit 303; the current value monitoring unit 301 is used to monitor the current of the upper bridge arm and the current of the lower bridge arm in real time through the AC connection point and output the first current value and the second current value; the first module status acquisition unit 302 is used to monitor the status of each first sub-module in real time and output several first sub-module statuses, wherein the first sub-module statuses include: engaged and disengaged; the second module status acquisition unit 303 is used to monitor the status of each second sub-module in real time and output several second sub-module statuses, wherein the second sub-module statuses include: engaged and disengaged.

[0040] Furthermore, the current direction identification module 202 is used to identify the first current direction of the current upper arm and the second current direction of the current lower arm based on the AC connection point, including: a first direction judgment unit 401, a second direction judgment unit 402, a third direction judgment unit 403, and a fourth direction judgment unit 404; the first direction judgment unit 401 is used to identify the first current direction of the current upper arm as positive if the first current of the upper arm flows to the AC connection point; the second direction judgment unit 402 is used to identify the first current direction of the current upper arm as negative if the first current of the upper arm flows out of the AC connection point; the third direction judgment unit 403 is used to identify the second current direction of the current lower arm as positive if the second current of the lower arm flows out of the AC connection point; the fourth direction judgment unit 404 is used to identify the second current direction of the current lower arm as negative if the second current of the lower arm flows to the AC connection point.

[0041] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

[0042] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. Furthermore, the described specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples.

[0043] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

Claims

1. A method for blocking a bridge arm of a converter valve in a flexible HVDC power transmission project, characterized in that, The application is applied to a DC power transmission project converter valve circuit, and the DC power transmission project converter valve circuit comprises: a plurality of first sub-modules, a plurality of second sub-modules and a converter transformer valve side module, the plurality of first sub-modules are connected to an upper bridge arm of the DC power transmission project converter valve circuit; the plurality of second sub-modules are connected to a lower bridge arm of the DC power transmission project converter valve circuit; and the upper bridge arm and the lower bridge arm are connected through an AC connection point; The flexible DC power transmission project converter valve bridge arm blocking method comprises: Real-time acquisition of a first current value of the upper bridge arm, a second current value of the lower bridge arm, a plurality of first sub-module states and a plurality of second sub-module states; According to the AC connection point, the first current direction of the current upper bridge arm and the second current direction of the current lower bridge arm are identified; Based on the first current direction, the second current direction, each first sub-module state and each second sub-module state, a bridge arm blocking strategy is generated; Based on the bridge arm blocking strategy, the first sub-modules and the second sub-modules are blocked through the first current value, the second current value and the converter transformer valve side module.

2. The method of claim 1, wherein the method further comprises: The real-time acquisition of the first current value of the upper bridge arm, the second current value of the lower bridge arm, the plurality of first sub-module states and the plurality of second sub-module states comprises: Through the AC connection point, the upper bridge arm current and the lower bridge arm current are monitored in real time, and the first current value and the second current value are outputted; Each first sub-module state is monitored in real time, and the plurality of first sub-module states are outputted, wherein the first sub-module state comprises: input and removal; Each second sub-module state is monitored in real time, and the plurality of second sub-module states are outputted, wherein the second sub-module state comprises: input and removal.

3. A method of blocking a bridge arm of a converter valve of a flexible HVDC power transmission project as claimed in claim 2, characterized in that, According to the AC connection point, the first current direction of the current upper bridge arm and the second current direction of the current lower bridge arm are identified, which comprises: If the first current of the upper bridge arm flows to the AC connection point, the first current direction of the current upper bridge arm is identified as a positive direction; If the first current of the upper bridge arm flows out of the AC connection point, the first current direction of the current upper bridge arm is identified as a negative direction; If the second current of the lower bridge arm flows out of the AC connection point, the second current direction of the current lower bridge arm is identified as a positive direction; If the second current of the lower bridge arm flows to the AC connection point, the second current direction of the current lower bridge arm is identified as a negative direction.

4. The method of claim 3, wherein the method further comprises: Based on the first current direction, the second current direction, each first sub-module state and each second sub-module state, a bridge arm blocking strategy is generated, which comprises: If the first current direction and the second current direction are both positive directions, a first bridge arm blocking strategy is generated according to each first sub-module state and each second sub-module state; If the first current direction and the second current direction are opposite, a second bridge arm blocking strategy is generated; If the first current direction and / or the second current direction is a negative direction, the second bridge arm blocking strategy is generated.

5. A method of blocking a bridge arm of a converter valve of a flexible HVDC power transmission project as claimed in claim 4, characterized in that, Based on the bridge arm blocking strategy, the first sub-modules and the second sub-modules are blocked through the first current value, the second current value and the converter transformer valve side module, which comprises: If the bridge arm blocking strategy is a first bridge arm blocking strategy, a valve control overcurrent protection setting value is obtained based on the converter transformer valve side module; If the first current value and the second current value are both less than the valve control overcurrent protection setting value, the number of the first sub-modules in the on state and the number of the second sub-modules in the on state are obtained; If the number of the first sub-modules in the on state is greater than the number of the second sub-modules in the on state, the first sub-modules are blocked and the second sub-modules are blocked when the second current direction is negative; If the number of the first sub-modules in the on state is less than the number of the second sub-modules in the on state, the second sub-modules are blocked and the first sub-modules are blocked when the first current direction is negative.

6. A method of blocking a bridge arm of a converter valve of a flexible HVDC power transmission project as claimed in claim 4, characterized in that, Based on the bridge arm blocking strategy, the first sub-modules and the second sub-modules are blocked by the first current value, the second current value and the converter transformer valve side module, including: If the bridge arm blocking strategy is a second bridge arm blocking strategy, a valve control overcurrent protection action signal is obtained based on the converter transformer valve side module; All the first sub-modules and the second sub-modules are blocked based on the valve control overcurrent protection action signal.

7. A method for blocking a bridge arm of a converter valve of a flexible HVDC power transmission project as claimed in claim 1, characterized in that, The DC power transmission project converter valve circuit further comprises a converter valve upper bridge arm reactor, a first arrester, a converter valve lower bridge arm reactor and a second arrester; a first end of the converter valve upper bridge arm reactor is connected with a DC circuit, a second end of the converter valve upper bridge arm reactor is electrically connected with a first end of the first arrester, a second end of the first arrester is electrically connected with the first sub-module; a first end of the converter valve lower bridge arm reactor is connected with the DC circuit, a second end of the converter valve lower bridge arm reactor is electrically connected with a first end of the second arrester; a second end of the second arrester is electrically connected with the second sub-module; Before the step of identifying a first current direction of a current upper bridge arm and a second current direction of a current lower bridge arm according to the AC connection point, comprising: If fault selection is not needed, a first current measuring point is arranged at the second end of the first arrester and a second current measuring point is arranged at the second end of the second arrester; If fault selection is needed, a first current measuring point is arranged at the second end of the first arrester and a third current measuring point is arranged at the second end of the converter valve upper bridge arm reactor, and a second current measuring point is arranged at the second end of the second arrester and a fourth current measuring point is arranged at the second end of the converter valve lower bridge arm reactor.

8. A flexible HVDC transmission engineering converter valve bridge arm blocking system, characterized in that, A flexible DC power transmission project converter valve bridge arm blocking method is executed, comprising: A data acquisition module, a current direction identification module, a bridge arm blocking strategy generation module and a bridge arm blocking module; The data acquisition module is used to acquire a first current value of an upper bridge arm, a second current value of a lower bridge arm, a number of first sub-module states and a number of second sub-module states in real time; The current direction identification module is used to identify a first current direction of a current upper bridge arm and a second current direction of a current lower bridge arm according to the AC connection point; The bridge arm blocking strategy generation module is configured to generate a bridge arm blocking strategy based on the first current direction, the second current direction, the first sub-module states, and the second sub-module states; The bridge arm blocking module is configured to block the first sub-module and the second sub-module by the first current value, the second current value, and the converter transformer valve side module based on the bridge arm blocking strategy.

9. A flexible HVDC power transmission project converter valve leg blocking system as claimed in claim 8, characterised in that, The data acquisition module is configured to acquire a first current value of an upper bridge arm, a second current value of a lower bridge arm, a plurality of first sub-module states, and a plurality of second sub-module states in real time, including: a current value monitoring unit, a first module state acquisition unit, and a second module state acquisition unit; The current value monitoring unit is configured to monitor the upper bridge arm current and the lower bridge arm current in real time through the AC connection point and output the first current value and the second current value; The first module state acquisition unit is configured to monitor the first sub-module states in real time and output the plurality of first sub-module states, wherein the first sub-module states include: being put into operation and being cut off; The second module state acquisition unit is configured to monitor the second sub-module states in real time and output the plurality of second sub-module states, wherein the second sub-module states include: being put into operation and being cut off.

10. A flexible HVDC power transmission project converter valve leg blocking system as claimed in claim 9, characterised in that, The current direction identification module is configured to identify a first current direction of a current upper bridge arm and a second current direction of a current lower bridge arm according to the AC connection point, including: a first direction judgment unit, a second direction judgment unit, a third direction judgment unit, and a fourth direction judgment unit; The first direction judgment unit is configured to identify the first current direction of the current upper bridge arm as a positive direction if the upper bridge arm first current flows to the AC connection point; The second direction judgment unit is configured to identify the first current direction of the current upper bridge arm as a negative direction if the upper bridge arm first current flows out of the AC connection point; The third direction judgment unit is configured to identify the second current direction of the current lower bridge arm as a positive direction if the lower bridge arm second current flows out of the AC connection point; The fourth direction judgment unit is configured to identify the second current direction of the current lower bridge arm as a negative direction if the lower bridge arm second current flows to the AC connection point.

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