A triggering method for avoiding commutation failure of an inverter station

Abstract

The application discloses a trigger method for avoiding commutation failure of an inverter station, and the method comprises the following steps: detecting the voltage amplitude of a three-phase line, and determining that a phase is faulty if the voltage amplitude of the phase is less than a preset threshold; wherein, a converter valve is arranged on the three-phase line; determining a fault type according to the determination of the fault of any phase of the three-phase line or the fault of a multi-phase line, wherein the fault type comprises a single-phase fault and a multi-phase fault; and determining a trigger strategy for stable operation of the fault in combination with the corresponding converter valve on the three-phase line and the fault type. According to the different fault types, the trigger sequence of the corresponding converter valve on the three-phase line is changed to realize the stable operation of the circuit and avoid the short circuit of the DC side.

Description

Technical Field

[0001] This invention relates to the field of power grid transmission technology, and in particular to a triggering method to avoid commutation failure at inverter stations. Background Technology

[0002] A short circuit on the DC side caused by commutation failure will result in a short-term interruption of the power transmission of high-voltage direct current (HVDC). Since the DC power transmitted by HVDC is relatively large, a short-term interruption of DC power will bring active and reactive power impacts to the receiving / sending power grid, affecting the safe and stable operation of the system.

[0003] Existing methods for suppressing commutation failure can inhibit subsequent commutation failures by triggering the thyristor earlier and reducing the DC current command value. However, since the process of DC-side short circuits caused by commutation failures occurs within a short period of time, existing methods are insufficient to completely prevent DC-side short circuits. Specifically, the goal of suppressing commutation failures is achieved by increasing the maximum voltage-time area provided by the system through early thyristor triggering. However, early thyristor triggering increases the reactive power absorbed by the inverter station; furthermore, when the grid voltage drops significantly, the space for increasing the maximum voltage-time area provided by the system is limited, making it difficult to be effective and potentially still leading to commutation failures, which in turn cause DC-side short circuits. Summary of the Invention

[0004] The purpose of this invention is to provide a triggering method to avoid commutation failure in inverter stations, thereby solving the problem of DC-side short circuits caused by triggering thyristors.

[0005] To achieve the above objectives, the present invention provides a triggering method for avoiding inverter station commutation failure, comprising:

[0006] The voltage amplitude of the three-phase line is detected. If the voltage amplitude of any phase line is less than a preset threshold, the phase is determined to be faulty. A converter valve is installed on each of the three-phase lines.

[0007] Based on the determination of a fault in any one phase of the three-phase line or a fault in multiple phases of the three-phase line, the fault type is determined, and the fault type includes single-phase fault and multi-phase fault.

[0008] The triggering strategy for steady-state operation of the fault is determined by combining the corresponding converter valves on the three-phase line with the fault type.

[0009] Preferably, the detection of the voltage amplitude of the three-phase line includes:

[0010] The three-phase line includes phase A, phase B, and phase C.

[0011] The A-phase line includes a first converter valve and a fourth converter valve, which are located on the same bridge arm. The B-phase line includes a third converter valve and a sixth converter valve, which are located on the same bridge arm. The C-phase line includes a second converter valve and a fifth converter valve, which are located on the same bridge arm.

[0012] The first converter valve, the second converter valve, the third converter valve, the fourth converter valve, the fifth converter valve, and the sixth converter valve are triggered sequentially to detect the voltage amplitude of the corresponding phase line. Specifically, when the first converter valve is triggered, the fifth converter valve switches phase to the first converter valve; when the second converter valve is triggered, the sixth converter valve switches phase to the second converter valve; when the third converter valve is triggered, the first converter valve switches phase to the third converter valve; when the fourth converter valve is triggered, the second converter valve switches phase to the fourth converter valve; when the fifth converter valve is triggered, the third converter valve switches phase to the fifth converter valve; and when the sixth converter valve is triggered, the fourth converter valve switches phase to the sixth converter valve.

[0013] Preferably, the triggering strategy for determining the steady-state operation of the fault by combining the corresponding converter valve on the three-phase line with the fault type includes:

[0014] Based on the determination of the fault in phase A line, the single-phase fault is identified as the first single-phase fault.

[0015] Based on the first single-phase fault and the sequential triggering of the first converter valve, the second converter valve, the third converter valve, the fourth converter valve, the fifth converter valve, and the sixth converter valve within the cycle, the triggering strategy for the steady-state operation of the fault is determined.

[0016] Preferably, the triggering strategy for determining the steady-state operation of the fault by combining the corresponding converter valve on the three-phase line with the fault type includes:

[0017] Based on the determination of the fault in phase B line, the single-phase fault is identified as the second single-phase fault.

[0018] Based on the second single-phase fault and the sequential triggering of the first converter valve, the second converter valve, the third converter valve, the fourth converter valve, the fifth converter valve, and the sixth converter valve within the cycle, the triggering strategy for the steady-state operation of the fault is determined.

[0019] Preferably, the triggering strategy for determining the steady-state operation of the fault by combining the corresponding converter valve on the three-phase line with the fault type includes:

[0020] Based on the determination of the fault in the C-phase line, the single-phase fault is identified as the third single-phase fault.

[0021] Based on the third single-phase fault and the sequential locking of the first converter valve, triggering of the second converter valve, triggering of the third converter valve, locking of the fourth converter valve, triggering of the fifth converter valve, and triggering of the sixth converter valve within the cycle, the triggering strategy for the steady-state operation of the fault is determined.

[0022] Preferably, the triggering strategy for determining the steady-state operation of the fault by combining the corresponding converter valve on the three-phase line with the fault type includes:

[0023] Based on the determination of the fault in phase A line and the fault in phase B line, the multi-phase fault is identified as the first multi-phase fault.

[0024] Based on the first multiphase fault and the corresponding converter valve on the three-phase line, the triggering strategy for the steady-state operation of the fault is determined. The triggering strategy for the steady-state operation of the fault based on the first multiphase fault includes a first triggering strategy and a second triggering strategy.

[0025] The first triggering strategy is determined by triggering the first switching valve, locking the second switching valve, locking the third switching valve, triggering the fourth switching valve, locking the fifth switching valve, and locking the sixth switching valve.

[0026] The second triggering strategy is determined by triggering the first switching valve, locking the second switching valve, triggering the third switching valve, triggering the fourth switching valve, locking the fifth switching valve, and triggering the sixth switching valve.

[0027] Preferably, the triggering strategy for determining the steady-state operation of the fault by combining the corresponding converter valve on the three-phase line with the fault type includes:

[0028] Based on the determination of the fault in phase B and the fault in phase C, the multi-phase fault is identified as the second multi-phase fault.

[0029] Based on the second multiphase fault and the corresponding converter valve on the three-phase line, the triggering strategy for steady-state operation is determined. The triggering strategy for steady-state operation based on the second multiphase fault includes a third triggering strategy and a fourth triggering strategy.

[0030] The third triggering strategy is determined by locking the first switching valve, locking the second switching valve, triggering the third switching valve, locking the fourth switching valve, locking the fifth switching valve, and triggering the sixth switching valve.

[0031] The fourth triggering strategy is determined by locking the first converter valve, triggering the second converter valve, triggering the third converter valve, locking the fourth converter valve, triggering the fifth converter valve, and triggering the sixth converter valve.

[0032] Preferably, the triggering strategy for determining the steady-state operation of the fault by combining the corresponding converter valve on the three-phase line with the fault type includes:

[0033] Based on the determination of the fault in phase A and the fault in phase C, the multi-phase fault is identified as the third multi-phase fault.

[0034] Based on the third multiphase fault and the corresponding converter valve on the three-phase line, the triggering strategy for the steady-state operation of the fault is determined. The triggering strategy for the steady-state operation of the fault based on the third multiphase fault includes a fifth triggering strategy and a sixth triggering strategy.

[0035] The fifth triggering strategy is determined by locking the first converter valve, triggering the second converter valve, locking the third converter valve, locking the fourth converter valve, triggering the fifth converter valve, and locking the sixth converter valve.

[0036] The sixth triggering strategy is determined by triggering the first converter valve, triggering the second converter valve, locking the third converter valve, triggering the fourth converter valve, triggering the fifth converter valve, and locking the sixth converter valve.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] The voltage amplitude of a three-phase line is detected. If the voltage amplitude of any phase is less than a preset threshold, that phase is determined to be faulty. Each of the three phase lines is equipped with a converter valve. Based on whether any one phase or multiple phases of the three-phase line is faulty, the fault type is determined. The fault type includes single-phase and multi-phase faults. The triggering strategy for steady-state operation is determined by combining the corresponding converter valve on the three-phase line with the fault type. This invention fully considers fault types and avoids DC-side short circuits caused by commutation failure by changing the converter valve triggering method, thereby preventing power transmission interruption. Attached Figure Description

[0039] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1This is a flowchart illustrating a triggering method for avoiding inverter station commutation failure according to a certain embodiment of the present invention.

[0041] Figure 2 This is a six-pulse inverter circuit structure provided in a certain embodiment of the present invention;

[0042] Figure 3 This is a graph showing a fault in phase A of the line.

[0043] Figure 4 This is a flowchart illustrating a fault in phase A of the line.

[0044] Figure 5 This is a graph showing a fault in phase B of the line.

[0045] Figure 6 This is a flowchart illustrating a fault in phase B of the line.

[0046] Figure 7 This is a graph showing a fault in phase C of the line.

[0047] Figure 8 This is a flowchart illustrating a C-phase line fault.

[0048] Figure 9 This is a graph showing a fault in phase A / B of the line.

[0049] Figure 10 This is a flowchart illustrating a fault in phase A / B of the line.

[0050] Figure 11 This is a graph showing a fault in phase B / C of the line.

[0051] Figure 12 This is a flowchart illustrating a fault in phase B / C of the circuit.

[0052] Figure 13 This is a graph showing a fault in phase A / C of the line.

[0053] Figure 14 This is a flowchart illustrating a fault in phase A / C of the circuit. Detailed Implementation

[0054] 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.

[0055] It should be understood that the step numbers used in the text are for ease of description only and are not intended to limit the order in which the steps are performed.

[0056] It should be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0057] The terms “comprising” and “including” indicate the presence of the described feature, whole, step, operation, element and / or component, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0058] The term “and / or” refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes these combinations.

[0059] Please see Figure 1 One embodiment of the present invention provides a triggering method to avoid commutation failure in an inverter station. For example... Figure 1 As shown, the triggering method for avoiding inverter station commutation failure includes steps S10 to S30. The specific steps are as follows:

[0060] S10: Detect the voltage amplitude of the three-phase line. If the voltage amplitude of a certain phase line is less than a preset threshold, the phase is determined to be faulty. A converter valve is installed on each of the three-phase lines.

[0061] Please see Figure 2 , specifically Figure 2 The circuit structure of the six-pulse inverter includes three phase lines: phase A, phase B, and phase C. Each phase line has two thyristors and corresponding converter valves: V1, V2, V3, V4, V5, and V6, for a total of six converter valves. Phase A includes the first and fourth converter valves, which are located on the same bridge arm. Phase B includes the third and sixth converter valves, which are also located on the same bridge arm. Phase C includes the second and fifth converter valves, which are also located on the same bridge arm.

[0062] Under normal steady-state operation, six commutation processes occur within one cycle, triggered sequentially in the order of the first converter valve V1, the second converter valve V2, the third converter valve V3, the fourth converter valve V4, the fifth converter valve V5, and the sixth converter valve V6. The voltage amplitude of the corresponding phase line is detected. Specifically, when the first converter valve is triggered, the fifth converter valve commutates to the first converter valve; when the second converter valve is triggered, the sixth converter valve commutates to the second converter valve; when the third converter valve is triggered, the first converter valve commutates to the third converter valve; when the fourth converter valve is triggered, the second converter valve commutates to the fourth converter valve; when the fifth converter valve is triggered, the third converter valve commutates to the fifth converter valve; and when the sixth converter valve is triggered, the fourth converter valve commutates to the sixth converter valve.

[0063] It should be noted that when V1 is triggered, V5 commutates to V1. If the commutation is successful, the current on V5 is transferred to V1. If the commutation fails, the current on V5 cannot be transferred to V1.

[0064] Please see Figure 3 During steady-state operation, the three-phase voltage at the receiving-end converter bus is as follows: Figure 3 As shown by the solid lines, the voltage amplitudes of all phases are equal. After a ground fault in phase A, the voltage amplitude of phase A decreases, as shown... Figure 3 As shown by the dashed line in (a). If consistent with steady-state operation, and triggering continues in the order of V1, V2, V3, V4, V5, V6, the commutation process during the six steady-state operations within one cycle is as follows:

[0065] When V1 is triggered, V5 commutates to V1, from Figure 3 (a) It can be seen that after the voltage amplitude of phase A decreases, the maximum voltage-time area that the system can provide increases, and the commutation from V5 to V1 is successful. When V2 is triggered, V6 commutates to V2, and the maximum voltage-time area that the system can provide remains unchanged, so the commutation from V6 to V2 is successful. When V3 is triggered, V1 commutates to V3. When V4 is triggered, V2 commutates to V4. When V5 is triggered, V3 commutates to V5. When V6 is triggered, V4 commutates to V6.

[0066] S20: Determine the fault type based on whether any one phase of the three-phase line or a multi-phase line is faulty. The fault type includes single-phase faults and multi-phase faults.

[0067] Specifically, during the sequential triggering process within the cycle, single-phase line faults or multi-phase line faults may occur. When a fault is detected in phase A, phase B, or phase C, the corresponding single-phase fault triggering strategy is executed. When a multi-phase line fault is detected, the corresponding multi-phase fault triggering strategy is executed.

[0068] It is worth noting that when V3 is triggered, V1 commutates to V3, reducing the maximum voltage-time area that the system can provide. When the voltage amplitude of phase A decreases to a certain extent, making the maximum voltage-time area that the system can provide less than the voltage-time area required for successful commutation, the commutation fails, and V1 continues to conduct. When V4 is triggered, V1 and V4 are on the same bridge arm, causing a short circuit on the DC side, resulting in a short-term interruption of DC power and a single-phase fault.

[0069] S30: Determine the triggering strategy for steady-state operation of the fault by combining the corresponding converter valve on the three-phase line with the fault type.

[0070] Specifically, single-phase faults include A-phase line faults, B-phase line faults, and C-phase line faults. When an A-phase line fault occurs, the triggering sequence within one cycle is V1, V2, V3 blocking, V4, V5, V6 blocking. When a B-phase line fault occurs, the triggering sequence within one cycle is V1, V2 blocking, V3, V4, V5 blocking, V6 blocking. When a C-phase line fault occurs, the triggering sequence within one cycle is V1 blocking, V2, V3, V4 blocking, V5, V6 blocking.

[0071] Multiphase faults include A / B phase line faults, B / C phase line faults, and A / C phase line faults. When a fault occurs in phases A and B, the triggering strategies are as follows: First triggering strategy: the triggering sequence within one cycle is V1, V2, V3, V4, V5, and V6 blocking; Second triggering strategy: the triggering sequence within one cycle is V1, V2, V3, V4, V5, and V6 blocking. When a fault occurs in phases B and C, the triggering strategies are as follows: Third triggering strategy: the triggering sequence within one cycle is V1, V2, V3, V4, V5, and V6 blocking; Fourth triggering strategy: the triggering sequence within one cycle is V1, V2, V3, V4, V5, and V6 blocking; Fifth triggering strategy: the triggering sequence within one cycle is V1, V2, V3, V4, V5, and V6 blocking; Sixth triggering strategy: the triggering sequence within one cycle is V1, V2, V3, V4, V5, and V6 blocking.

[0072] Please see Figure 3 and Figure 4 In one specific embodiment, step S30 further includes the following sub-steps:

[0073] S31: Based on the determination of the fault in phase A line, the single-phase fault is identified as the first single-phase fault.

[0074] Specifically, when V3 is triggered, V1 commutates to V3, reducing the maximum voltage-time area that the system can provide. When the voltage amplitude of phase a decreases to a certain extent, making the maximum voltage-time area that the system can provide less than the voltage-time area required for successful commutation, the commutation fails, and V1 continues to conduct. When V4 is triggered, V1 and V4 are on the same bridge arm, causing a short circuit on the DC side and a brief interruption of DC power.

[0075] S32: Determine the triggering strategy for steady-state operation based on the first single-phase fault and the sequential triggering of the first converter valve, the second converter valve, the third converter valve, the fourth converter valve, the fifth converter valve, and the sixth converter valve within the cycle.

[0076] Specifically, to avoid short-term DC power interruption caused by DC-side short circuits, valves V3 and V6 are locked out corresponding to the reduction in voltage-time area. V3 triggers V1, and V6 triggers V4. In this case, the triggering sequence within one cycle is V1, V2, V3 locked out, V4, V5, V6 locked out. The inverter can continue to output A and C phase AC power to the AC system, allowing it to continue supplying power to two-phase loads.

[0077] Please see Figure 5 and Figure 6 In one specific embodiment, step S30 further includes the following sub-steps:

[0078] S33: Based on the determination of the B-phase line fault, the single-phase fault is identified as the second single-phase fault.

[0079] S34: Determine the triggering strategy for steady-state operation based on the second single-phase fault and the sequential triggering of the first converter valve, the second converter valve, the third converter valve, the fourth converter valve, the fifth converter valve, and the sixth converter valve within the cycle.

[0080] Similarly, in the case of a phase A fault, after a phase B ground fault, to avoid a DC side short circuit caused by commutation failure, valves V2 and V5 corresponding to the reduction in voltage-time area are blocked. Specifically, V2 triggers V6, and V5 triggers V3. At this time, the triggering sequence within one cycle is V1, V2 blocking, V3, V4, V5 blocking, V6, as follows... Figure 5 As shown, the inverter can continue to output A and B phase AC power to the AC system, thus continuing to supply power to two-phase loads.

[0081] Please see Figure 7 and Figure 8 In one specific embodiment, step S30 further includes the following sub-steps:

[0082] S35: Based on the determination of the C-phase line fault, the single-phase fault is identified as the third single-phase fault.

[0083] S36: Based on the third single-phase fault and the sequential locking of the first converter valve, triggering of the second converter valve, triggering of the third converter valve, locking of the fourth converter valve, triggering of the fifth converter valve, and triggering of the sixth converter valve within the cycle, determine the triggering strategy for the steady-state operation of the fault.

[0084] After a C-phase ground fault, to prevent a DC-side short circuit caused by commutation failure, valves V1 and V4 are blocked when the voltage-time area decreases. Specifically, triggering V1 corresponds to triggering V5, and triggering V4 corresponds to triggering V2. At this time, the triggering sequence within one cycle is V1 blocking, V2, V3, V4 blocking, V5, V6, as follows: Figure 7 As shown, the inverter can continue to output phase B and phase C AC power to the AC system, thus continuing to supply power to two-phase loads.

[0085] Please see Figure 9 and Figure 10 In one specific embodiment, step S30 further includes the following sub-steps:

[0086] S37: Based on the determination of the fault in phase A line and the fault in phase B line, the multi-phase fault is determined as the first multi-phase fault.

[0087] Please see Figure 9 After determining a two-phase ground fault based on the decrease in voltage amplitude of two phases, if the voltage amplitudes of phases A and B decrease, such as... Figure 9 As shown by the dashed line in (a), if it is consistent with steady-state operation, and the triggering continues in the order of V1, V2, V3, V4, V5, V6, the six commutation processes within one cycle are as follows:

[0088] When V1 is triggered, V5 commutates to V1, from Figure 9 (a) As can be seen, after the voltage amplitude of phase A decreases, the maximum voltage-time area that the system can provide increases, and V5 successfully commutates to V1. When V2 is triggered, V6 commutates to V2, and the maximum voltage-time area that the system can provide decreases. When the voltage amplitude of phase b decreases to a certain extent, making the maximum voltage-time area that the system can provide less than the voltage-time area required for successful commutation, the commutation fails, and V6 continues to conduct. When V3 is triggered, V3 and V6 are on the same bridge arm, causing a short circuit on the DC side and a short-term interruption of DC power.

[0089] S38: Based on the first multiphase fault and the corresponding converter valves on the three-phase line, determine the triggering strategy for the steady-state operation of the fault. The triggering strategy for the steady-state operation of the fault based on the first multiphase fault includes a first triggering strategy and a second triggering strategy. The first triggering strategy is determined by triggering the first converter valve, locking the second converter valve, locking the third converter valve, triggering the fourth converter valve, locking the fifth converter valve, and locking the sixth converter valve. The second triggering strategy is determined by triggering the first converter valve, locking the second converter valve, triggering the third converter valve, triggering the fourth converter valve, locking the fifth converter valve, and triggering the sixth converter valve.

[0090] To avoid a short-term interruption of DC power caused by a DC-side short circuit, valves V2 and V5, corresponding to the reduction in voltage-time area, are blocked. The maximum voltage-time area that the system can provide, corresponding to valves V3 and V6, decreases on the one hand as the voltage of phase A decreases, and increases on the other hand as the voltage of phase B decreases. It should be noted that this increase, decrease, or no change is possible. Considering the case of decrease, V3 and V6 need to be blocked.

[0091] In summary, the system employs both a first triggering strategy and a second triggering strategy. The first triggering strategy works as follows: Since phases A and B are faulty, phase C is the normal phase. Phase C has V2 and V5 valves. Based on the commutation from V5 to V1 when V1 is triggered and from V2 to V4 when V4 is triggered, the triggering sequence within one cycle is V1, V2 (locked out), V3 (locked out), V4, V5 (locked out), and V6 (locked out). According to these converter valve settings, the inverter can continue to output phase A AC power to the AC system, providing power to single-phase loads. The second triggering strategy works as follows: Since the voltage amplitude of phases A and B decreases after the fault, the voltage amplitude of phases A and B can be increased by locking the converter valve of phase C, allowing continued power supply. Specifically, with the triggering sequence within one cycle being V1, V2 (locked out), V3, V4, V5 (locked out), and V6 (locked out), the inverter can continue to output both phases A and B AC power to the AC system, providing power to two-phase loads.

[0092] Please see Figure 11 and Figure 12 In one specific embodiment, step S30 further includes the following sub-steps:

[0093] S39: Based on the determination of the B-phase line fault and the C-phase line fault, the multi-phase fault is determined as the second multi-phase fault.

[0094] S40: Based on the second multiphase fault and the corresponding converter valve on the three-phase line, determine the triggering strategy for the steady-state operation of the fault. The triggering strategy for the steady-state operation of the fault based on the second multiphase fault includes a third triggering strategy and a fourth triggering strategy. The third triggering strategy is determined by locking the first converter valve, locking the second converter valve, triggering the third converter valve, locking the fourth converter valve, locking the fifth converter valve, and triggering the sixth converter valve. The fourth triggering strategy is determined by locking the first converter valve, triggering the second converter valve, triggering the third converter valve, locking the fourth converter valve, triggering the fifth converter valve, and triggering the sixth converter valve.

[0095] Please see Figure 11 The pulse triggering scheme after a two-phase (B / C) ground fault includes two scenarios: a third triggering strategy and a fourth triggering strategy. Third triggering strategy: The triggering sequence within one cycle is V1 lockout, V2 lockout, V3, V4 lockout, V5 lockout, V6. The inverter can continue to output B-phase AC power to the AC system, allowing it to continue supplying power to single-phase loads. Fourth triggering strategy: The triggering sequence within one cycle is V1 lockout, V2, V3, V4 lockout, V5, V6. The inverter can continue to output B / C-phase AC power to the AC system, allowing it to continue supplying power to two-phase loads.

[0096] Please see Figure 13 and Figure 14 In one specific embodiment, step S30 further includes the following sub-steps:

[0097] S41: Based on the determination of the fault in the A-phase line and the fault in the C-phase line, the multi-phase fault is determined as the third multi-phase fault.

[0098] S42: Based on the third multiphase fault and the corresponding converter valve on the three-phase line, determine the triggering strategy for the steady-state operation of the fault. The triggering strategy for the steady-state operation of the fault based on the third multiphase fault includes a fifth triggering strategy and a sixth triggering strategy. The fifth triggering strategy is determined by locking the first converter valve, triggering the second converter valve, locking the third converter valve, locking the fourth converter valve, triggering the fifth converter valve, and locking the sixth converter valve. The sixth triggering strategy is determined by triggering the first converter valve, triggering the second converter valve, locking the third converter valve, triggering the fourth converter valve, triggering the fifth converter valve, and locking the sixth converter valve.

[0099] Please see Figure 13This includes the fifth and sixth triggering strategies, and a pulse triggering scheme after an A / C two-phase ground fault. Fifth triggering strategy: The triggering sequence within one cycle is V1 lockout, V2, V3 lockout, V4 lockout, V5, V6 lockout. The inverter can continue to output c-phase AC power to the AC system, allowing it to continue supplying power to single-phase loads. Sixth triggering strategy: The triggering sequence within one cycle is V1, V2, V3 lockout, V4, V5, V6 lockout. The inverter can continue to output ac-phase AC power to the AC system, allowing it to continue supplying power to two-phase loads.

[0100] It should be noted that during a three-phase ground fault, if the voltage amplitude drops to a level that causes commutation failure at the inverter station, all thyristors must be locked, and the DC transmission will be shut down. If the voltage amplitude drops only slightly and commutation is successful, the thyristors do not need to be locked, and the DC transmission can continue to operate.

[0101] This invention fully considers various commutation failure scenarios in three-phase circuits, including single-phase and multi-phase faults, and provides a new pulse triggering method to avoid DC-side short circuits caused by commutation failures.

[0102] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A triggering method to avoid commutation failure in an inverter station, characterized in that, include: The voltage amplitude of a three-phase line is detected. If the voltage amplitude of any phase line is less than a preset threshold, that phase is determined to be faulty. Each of the three-phase lines is equipped with a converter valve. The three-phase line includes an A-phase line, a B-phase line, and a C-phase line. The A-phase line includes a first converter valve and a fourth converter valve, both located on the same bridge arm. The B-phase line includes a third converter valve and a sixth converter valve, both located on the same bridge arm. The C-phase line includes a second converter valve and a fifth converter valve, both located on the same bridge arm. Based on the determination of line faults in the three-phase lines, the fault type is determined, and the fault type includes single-phase faults; The triggering strategy for steady-state operation of the fault is determined by combining the corresponding converter valves on the three-phase line with the fault type; the triggering strategy is the triggering sequence of the corresponding converter valves on the three-phase line within one cycle; The step of determining the steady-state operation triggering strategy by combining the corresponding converter valves on the three-phase line with the fault type includes: Based on the determination of the fault in phase A line, the single-phase fault is identified as the first single-phase fault. Based on the first single-phase fault and the sequential triggering of the first converter valve, the second converter valve, the third converter valve, the fourth converter valve, the fifth converter valve, and the sixth converter valve within the cycle, the triggering strategy for the steady-state operation of the fault is determined.

2. The triggering method for avoiding inverter station commutation failure according to claim 1, characterized in that, The detection of the voltage amplitude of the three-phase line includes: The first converter valve, the second converter valve, the third converter valve, the fourth converter valve, the fifth converter valve, and the sixth converter valve are triggered sequentially to detect the voltage amplitude of the corresponding phase line. Specifically, when the first converter valve is triggered, the fifth converter valve switches phase to the first converter valve; when the second converter valve is triggered, the sixth converter valve switches phase to the second converter valve; when the third converter valve is triggered, the first converter valve switches phase to the third converter valve; when the fourth converter valve is triggered, the second converter valve switches phase to the fourth converter valve; when the fifth converter valve is triggered, the third converter valve switches phase to the fifth converter valve; and when the sixth converter valve is triggered, the fourth converter valve switches phase to the sixth converter valve.

3. The triggering method for avoiding inverter station commutation failure according to claim 1, characterized in that, The triggering strategy for determining steady-state operation by combining the corresponding converter valves on the three-phase lines with the fault type includes: Based on the determination of the fault in phase B line, the single-phase fault is identified as the second single-phase fault. The triggering strategy for steady-state operation is determined based on the second single-phase fault and the sequential triggering of the first converter valve, the locking of the second converter valve, the triggering of the third converter valve, the triggering of the fourth converter valve, the locking of the fifth converter valve, and the triggering of the sixth converter valve within the cycle.

4. The triggering method for avoiding inverter station commutation failure according to claim 1, characterized in that, The triggering strategy for determining steady-state operation by combining the corresponding converter valves on the three-phase lines with the fault type includes: Based on the determination of the fault in the C-phase line, the single-phase fault is identified as the third single-phase fault. The triggering strategy for steady-state operation is determined based on the third single-phase fault and the sequential locking of the first converter valve, triggering of the second converter valve, triggering of the third converter valve, locking of the fourth converter valve, triggering of the fifth converter valve, and triggering of the sixth converter valve within the cycle.

5. The triggering method for avoiding inverter station commutation failure according to claim 1, characterized in that, The fault types also include multiphase faults; the triggering strategy for determining steady-state operation by combining the corresponding converter valves on the three-phase lines with the fault types includes: Based on the determination of the fault in phase A line and the fault in phase B line, the multi-phase fault is identified as the first multi-phase fault. Based on the first multiphase fault and the corresponding converter valve on the three-phase line, the triggering strategy for steady-state operation is determined. The triggering strategy for steady-state operation based on the first multiphase fault includes a first triggering strategy and a second triggering strategy. The first triggering strategy is determined by triggering the first switching valve, locking the second switching valve, locking the third switching valve, triggering the fourth switching valve, locking the fifth switching valve, and locking the sixth switching valve. The second triggering strategy is determined by triggering the first switching valve, locking the second switching valve, triggering the third switching valve, triggering the fourth switching valve, locking the fifth switching valve, and triggering the sixth switching valve.

6. The triggering method for avoiding inverter station commutation failure according to claim 1, characterized in that, The fault types also include multiphase faults; the triggering strategy for determining steady-state operation by combining the corresponding converter valves on the three-phase lines with the fault types includes: Based on the determination of the fault in phase B and the fault in phase C, the multi-phase fault is identified as the second multi-phase fault. Based on the second multiphase fault and the corresponding converter valve on the three-phase line, the triggering strategy for the steady-state operation of the fault is determined. The triggering strategy for the steady-state operation of the fault based on the second multiphase fault includes a third triggering strategy and a fourth triggering strategy. The third triggering strategy is determined by locking the first switching valve, locking the second switching valve, triggering the third switching valve, locking the fourth switching valve, locking the fifth switching valve, and triggering the sixth switching valve. The fourth triggering strategy is determined by locking the first converter valve, triggering the second converter valve, triggering the third converter valve, locking the fourth converter valve, triggering the fifth converter valve, and triggering the sixth converter valve.

7. The triggering method for avoiding inverter station commutation failure according to claim 1, characterized in that, The fault types also include multiphase faults; the triggering strategy for determining steady-state operation by combining the corresponding converter valves on the three-phase lines with the fault types includes: Based on the determination of the faults in phase A and phase C, the multi-phase fault is identified as the third multi-phase fault. Based on the third multiphase fault and the corresponding converter valve on the three-phase line, the triggering strategy for the steady-state operation of the fault is determined. The triggering strategy for the steady-state operation of the fault based on the third multiphase fault includes a fifth triggering strategy and a sixth triggering strategy. The fifth triggering strategy is determined by locking the first converter valve, triggering the second converter valve, locking the third converter valve, locking the fourth converter valve, triggering the fifth converter valve, and locking the sixth converter valve. The sixth triggering strategy is determined by triggering the first converter valve, triggering the second converter valve, locking the third converter valve, triggering the fourth converter valve, triggering the fifth converter valve, and locking the sixth converter valve.

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