Converter valve side fault positioning method and system based on improved switching function

Abstract

The invention discloses a converter valve side fault positioning method and system based on an improved switching function, and the method comprises the steps: building a criterion for judging whether a fault range is in a Y bridge or a D bridge after the differential protection of a valve group in a DC control and protection system of a rectifier station or an inverter station is detected and the protection of a transformer is not detected; judging whether the current converter at the fault moment is in a commutation period or not according to the three-phase current at the converter variable valve side corresponding to the fault bridge, determining a bridge arm conduction state signal, and constructing an improved switch function model of the rectifier station or the inverter station by combining the direct current at the high-voltage end and the direct current at the low-voltage end of the current converter; if not in the commutation period, determining the phase of the fault point based on the zero element distribution condition in the calculation result; and if in the commutation period, judging the phase of the fault point by combining the direction and the size of the three-phase current on the converter transformer valve side. According to the method, the converter valve side single-phase fault can be quickly positioned, the fault analysis efficiency is improved, and the direct current misoperation locking risk caused by single direct current measurement abnormity can be avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of high voltage direct current transmission systems, and more specifically, relates to a method for locating valve-side faults of a power grid commutation converter based on an improved switching function. Background Art

[0002] High-voltage direct current transmission technology has the advantages of low transmission loss and high corridor utilization. It is suitable for ultra-large capacity and ultra-long distance power transmission, and plays an important role in national strategic goals such as national energy networking and west-to-east power transmission. Rapid restoration of power supply after the DC transmission system is locked is crucial to ensuring power supply and improving the availability of DC energy. The efficiency of fault handling depends on the speed and accuracy of fault diagnosis and location.

[0003] The alarm events and protection action information in the DC transmission control and protection system can only reflect the approximate range of the fault point, but cannot accurately locate the fault point. When a defect occurs in the current DC protection equipment, it is difficult to accurately and quickly determine the defect cause, location and other defect information. It is heavily dependent on manual experience and technical service support from equipment manufacturers, resulting in a long defect analysis and processing time, and the defect analysis and processing experience cannot be shared, which is not conducive to improving the defect analysis and processing level, and also brings hidden dangers to the safe and stable operation of the power grid.

[0004] The failure of the bushing on the valve side of the converter is one of the main reasons for the lockout of the converter station. The bushing failure is not easy to be directly discovered through external observation of the equipment. The traditional valve side fault analysis and positioning are carried out through oil test and high-voltage test of the equipment after the failure. The evaluation efficiency is low and time-consuming. The correctness of the result is directly related to the test result. Summary of the invention

[0005] In order to solve the deficiencies in the prior art, the present invention provides a method for locating the valve side fault of a power grid commutating converter based on an improved switching function, thereby avoiding the problem that the fault point on the converter valve side is difficult to analyze quickly and accurately in a DC transmission project, and realizing automatic, accurate and fast single-phase fault location on the converter valve side, thus providing a basis for accident analysis and maintenance decision-making in converter stations.

[0006] The present invention adopts the following technical solution.

[0007] A method for locating valve-side faults of a power grid phase-commutated converter based on an improved switching function, the method comprising the following steps:

[0008] Step S1, when it is detected that the valve group differential protection in the DC control and protection system is actuated and the transformer protection is inactive, the fault point location algorithm is started.

[0009] Step S2, constructing a criterion through the DC current IDCP at the high voltage end of the converter, the DC current IDCN at the low voltage end, and the current on the converter transformer valve side to determine whether the fault range is in the Y bridge or the D bridge.

[0010] Step S3, constructing an improved switch function model according to the trigger pulse code CPRY / CPRD signal in the control and protection system, the valve side bushing three-phase current Ia / Ib / Ic, the converter high-end DC current IDCP and the low-end DC current IDCN.

[0011] Step S4, judging whether the current state is in the phase change period according to the CPRY / CPRD pulse code and the three-phase current of the valve side bushing.

[0012] Step S5, if the fault moment is not during the commutation period, the phase where the fault point is located is determined based on the calculation results of the improved switching function model; if the fault moment is during the commutation period, the auxiliary converter transformer valve side bushing current direction and magnitude are determined based on the calculation results of the improved switching function model.

[0013] Furthermore, the criterion in step S2 is:

[0014] (1) Comparison I acY and IDCP size, if I acY =IDCP, the Y bridge is judged to be fault-free, otherwise it is judged to be faulty.

[0015] (2) Comparison I acD and IDCN size, if I acD =IDCN, then the D bridge is judged to be fault-free, otherwise it is judged to be faulty.

[0016] Among them, I acY is the absolute maximum value of the three-phase current on the valve side of the star-connected converter transformer, I acD It is the absolute maximum value of the three-phase current on the valve side of the delta-connected converter transformer. To ensure the accuracy and reliability of the judgment, the judgment time window should be greater than 6.6ms, that is, the trigger interval between the upper bridge arms or the lower bridge arms.

[0017] Due to the existence of measurement errors, the current magnitude in the same branch cannot be exactly the same. acY and IDCP, I acD When the size of IDCN is smaller than 3%, they are considered equal.

[0018] Furthermore, the improved switch function model constructed in step S3 is different according to the topology of the rectifier station and the inverter station. The improved switch function model of the inverter station is shown in the following formula:

[0019]

[0020] Wherein, V1~V6 are bridge arm conduction state signals, which are obtained according to the trigger pulse code CPRY / CPRD in binary format in the control and protection system and the three-phase current Ia / Ib / Ic signal of the valve side bushing.

[0021] Due to different wiring methods of the rectifier station, the improved switch function model is shown as follows:

[0022]

[0023] Where Δ=I DCP -I DCN .

[0024] Furthermore, the current state of the conductive valve group and the values ​​of V1~V6 are obtained according to the CPRY / CPRD pulse coding, and the corresponding conductive state of the conductive valve group is set to 1, and the non-conductive valve group is set to 0; if the three-phase current Ia / Ib / Ic of the valve side bushing is detected to have current at the same time, indicating that it is in the phase change process, then the conductive state of the valve group that is about to be turned on is set to 1.

[0025] Furthermore, in step S5, the principle for determining the fault point when the fault moment is not during the commutation period is as follows:

[0026] (1) The first two elements in the calculation result I correspond to phase a. When the first two elements are both equal to zero, the third and fourth elements are not both equal to 0, and the fifth and sixth elements are not both equal to 0, it is determined that the a phase of the bushing on the valve side of the converter is faulty;

[0027] (2) The third and fourth elements in the calculation result I correspond to phase b. When the third and fourth elements are both zero, the first and second elements are not both 0, and the fifth and sixth elements are not both 0, it is determined that the a-phase of the bushing on the valve side of the converter is faulty.

[0028] (3) The 5th and 6th elements in the calculation result I correspond to phase c. When the 5th and 6th elements are equal to zero, and the 1st and 2nd elements are not 0 at the same time, and the 3rd and 4th elements are not 0 at the same time, it is determined that the c-phase of the bushing on the valve side of the converter is faulty.

[0029] Furthermore, in step S5, the principle of fault point determination during commutation is the same as the method described in claim 7. If the calculation result determines that two phases are faulty at the same time, further determination is made based on the direction and magnitude of the bushing current on the converter transformer valve side. If the direction of the bushing current on the valve side of one of the two phases shows a reverse increasing trend relative to before the fault, the phase is determined to be the faulty phase.

[0030] Compared with the prior art, the beneficial effects of the present invention include at least:

[0031] (1) The present invention constructs a grid-commutated converter valve-side fault location method based on an improved switching function model, which can achieve rapid fault location after a single-phase fault on the converter valve side, can timely discover and handle equipment defects, and improve defect handling efficiency.

[0032] (2) The present invention can greatly improve the efficiency of fault analysis and shorten the power outage time of DC transmission projects by extracting and identifying fault characteristics under different fault scenarios and converting them into diagnostic algorithms.

[0033] (3) The fault location method proposed in the present invention is based on the identification of DC control and protection system alarm events and fault recording electrical quantities, which can directly avoid the risk of DC false locking caused by a single DC measurement abnormality. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a flow chart of a converter valve side fault location method based on an improved switching function in the present invention;

[0035] Figure 2 It is the primary topology diagram of the 12-pulsation converter of the rectifier station;

[0036] Figure 3 This is the primary topology diagram of the 12-pulsation converter of the inverter station;

[0037] Figure 4 It is a schematic diagram of a phase short circuit fault during the conduction period of the inverter station valve 4 and valve 5 provided according to a specific example of the present invention;

[0038] Figure 5 It is a schematic diagram of a short circuit fault of phase b during the conduction period of valves 4 and 5 of an inverter station provided according to a specific example of the present invention;

[0039] Figure 6 It is a schematic diagram of a phase C short circuit fault during the conduction period of the inverter station valve 4 and the valve 5 provided according to a specific example of the present invention. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0041] like Figure 1 As shown, embodiment 1 of the present invention provides a method for locating a valve-side fault of a power grid commutated converter based on an improved switching function, comprising the following steps:

[0042] Step S1, when it is detected that the valve group differential protection in the DC control and protection system of the rectifier station or the inverter station is actuated and the transformer protection is inactive, the fault point location algorithm is started.

[0043] It can be understood that locating the fault point based on the DC control and protection system alarm events and fault recording electrical quantities increases the redundancy of the fault identification start conditions and reduces the risk of DC false locking caused by a single DC measurement abnormality.

[0044] Step S2, constructing a criterion for determining whether the fault range is in the Y bridge or the D bridge according to the DC current IDCP at the high voltage end of the converter, the DC current IDCN at the low voltage end, and the current on the converter transformer valve side, and determining the faulty bridge.

[0045] In a preferred but non-limiting embodiment of the present invention, the criteria for determining whether the fault range is in the Y bridge or the D bridge are as follows:

[0046] (1) Comparison I acY and IDCP size, if I acY =IDCP, the Y bridge is judged to be fault-free, otherwise it is judged to be faulty.

[0047] (2) Comparison I acD and IDCN size, if I acD =IDCN, then the D bridge is judged to be fault-free, otherwise it is judged to be faulty.

[0048] Among them, I acY is the absolute maximum value of the three-phase current on the valve side of the star-connected converter transformer, I acD It is the absolute maximum value of the three-phase current on the valve side of the delta-connected converter transformer.

[0049] Further preferably, in order to ensure the accuracy and reliability of the determination, the determination time window should be greater than 6.6 ms, that is, the trigger interval between the upper bridge arms or between the lower bridge arms should be greater than 6.6 ms.

[0050] Further preferably, due to the existence of measurement errors, the current magnitudes in the same branch cannot be exactly the same. acY and IDCP, I acD When the size of IDCN is smaller than 3%, they are considered equal.

[0051] Step S3, based on the three-phase current Ia / Ib / Ic of the valve-side bushing in the fault bridge in step S2, determine whether the converter is in the commutation period at the time of the fault, and combine the bridge arm conduction state signals V1~V6, the high-voltage end DC current IDCP and the low-voltage end DC current IDCN of the converter to construct and solve the improved switching function model of the rectifier station or inverter station.

[0052] In a preferred but non-limiting embodiment of the present invention, step S3 specifically includes:

[0053] Step S301, judging whether the current state of the converter is in the phase change period according to the three-phase current of the valve side bushing. Specifically, if the three-phase current Ia / Ib / Ic of the valve side bushing is detected to have current at the same time, it means that the converter is in the phase change process.

[0054] Step S302, determining the values ​​of the bridge arm conduction state signals V1-V6 according to the CPRY / CPRD pulse code and the current state of the converter, wherein the trigger pulse code CPRY / CPRD is a digital code in binary format, including the time domain information of the conduction state of each bridge arm.

[0055] Further preferably, when not in the commutation process, the conduction state of the conduction valve group corresponding to the CPRY / CPRD pulse code is set to 1, and the non-conducting valve group is set to 0; when in the commutation process, the conduction state of the valve group to be turned on is set to 1.

[0056] Step S303: Due to different wiring modes and different topologies of the rectifier station and the inverter station, the constructed improved switch function models are different. The improved switch function model of the inverter station is constructed and expressed by the following formula:

[0057]

[0058] Where:

[0059] I n The calculation results of the improved switching function model for the inverter station;

[0060] V1~V6 are bridge arm conduction state signals;

[0061] I a , I b , I c is the three-phase current of the bushing on the valve side;

[0062] I DCP is the DC current at the high voltage end of the converter;

[0063] I DCN is the DC current at the low voltage end of the converter;

[0064] Δ is the DC current difference between the high and low ends of the converter, Δ=I DCP -I DCN .

[0065] Step S304, constructing an improved switch function model of the rectifier station, which is expressed by the following formula:

[0066]

[0067] Where:

[0068] I e Calculation results of the improved switching function model for the rectifier station.

[0069] It can be understood that by selecting fault feature quantities for fault diagnosis in the improved switching function model, calculation results containing fault phase information can be obtained through simple matrix calculations, which can greatly improve the efficiency of fault analysis, reduce manual test costs and analysis and processing time, thereby realizing rapid determination of defect location information.

[0070] Step S4: If the converter is not in the commutation period at the moment of the fault, the phase where the fault point is located is directly determined based on the calculation results of the improved switching function model; if the converter is in the commutation period at the moment of the fault, the current direction and magnitude of the bushing on the converter transformer valve side are auxiliary determined based on the calculation results of the improved switching function model.

[0071] Preferably, the fault point determination principle when the fault moment is not during the commutation period is as follows:

[0072] (1) The first two elements in the calculation result I correspond to phase a. When the first two elements are both zero, and the third and fourth elements are not both zero, and the fifth and sixth elements are not both zero, it is determined that the a phase of the bushing on the valve side of the converter is faulty;

[0073] (2) The third and fourth elements in the calculation result I correspond to phase b. When the third and fourth elements are both zero, and the first and second elements are not both 0, and the fifth and sixth elements are not both 0, it is determined that the b-phase of the converter valve-side bushing is faulty.

[0074] (3) The 5th and 6th elements in the calculation result I correspond to phase c. When the 5th and 6th elements are equal to zero, and the 1st and 2nd elements are not 0 at the same time, and the 3rd and 4th elements are not 0 at the same time, it is determined that the c-phase of the bushing on the valve side of the converter is faulty.

[0075] Preferably, the improved switching function model calculation and fault point basic judgment principle during the commutation period are the same as the fault point judgment principle described above when the fault moment is not during the commutation period, that is, the first two elements in the calculation result I correspond to phase a, the third and fourth elements correspond to phase b, and the fifth and sixth elements correspond to phase c. If both elements are 0 at the same time, it is determined that the phase is faulty. The auxiliary judgment criteria added on this basis include: if the calculation result I determines that two phases are faulty at the same time, further judgment is made based on the direction and magnitude of the bushing current on the converter transformer valve side. If the bushing current on the valve side of one of the two phases shows a reverse increase trend relative to before the fault, the phase is determined to be the faulty phase.

[0076] Embodiment 2 of the present invention provides a grid-commutated converter valve-side fault location system based on an improved switching function, and runs the grid-commutated converter valve-side fault location method based on an improved switching function as described in Embodiment 1, including:

[0077] Positioning start module, used to detect the valve group differential protection action and transformer protection non-action signal in the DC control and protection system, and start fault point positioning;

[0078] YD bridge positioning module, used to determine whether the fault range is in the Y bridge or D bridge;

[0079] The switching function module is used to determine whether the converter is in the commutation period at the time of the fault, and to construct and solve the improved switching function model of the rectifier station or inverter station;

[0080] The phase location module is used to determine the phase where the fault point is located.

[0081] In order to verify the effect of the present invention in practical applications, the following is a specific simulation verification example of the present invention:

[0082] The grid-commutated converter valve-side fault location method based on the improved switching function as described in Example 1 is used to identify alarm events and fault recordings in the DC control and protection system. Figure 2 and Figure 3 The primary topology diagrams of the 12-pulse converters of the rectifier station and the inverter station are shown respectively. The correctness of the proposed method is verified by taking different types of valve-side short-circuit faults occurring during the conduction period of valves 4 and 5 of the inverter station as an example.

[0083] (1) During the conduction period between valves 4 and 5, phase a short circuit fault

[0084] Define the current flowing toward the converter valve side as the positive direction, Figure 4 It can be seen that the current relationship between each measuring point is as follows: -Ia=Ic=IDCN.

[0085] Apply the improved switching function model of the inverter station in step S3, and the calculation result is:

[0086]

[0087] Therefore, the a-phase fault can be identified based on the fact that the first two elements in the calculation result are simultaneously zero.

[0088] (2) During the conduction period between valves 4 and 5, phase b is short-circuited.

[0089] Define the current flowing toward the converter valve side as the positive direction, Figure 5 It can be seen that the current relationship between each measuring point is as follows: IDCP = -Ia, Ic = IDCN.

[0090] Apply the improved switching function model of the inverter station in step S3, and the calculation result is:

[0091]

[0092] Therefore, the b-phase fault can be identified based on the fact that the third and fourth elements in the calculation results are both zero.

[0093] (3) During the conduction period between valves 4 and 5, phase c is short-circuited

[0094] Define the current flowing toward the converter valve side as the positive direction, Figure 6 It can be seen that the current relationship between the measuring points in the figure is as follows: IDCP = -Ia = Ic.

[0095] Apply the improved switching function model of the inverter station in step S3, and the calculation result is:

[0096]

[0097] Therefore, the C phase fault can be identified based on the fact that the last two elements in the calculation result are both zero.

[0098] Compared with the prior art, the beneficial effects of the present invention include at least:

[0099] (1) The present invention constructs a grid-commutated converter valve-side fault location method based on an improved switching function model, which can achieve rapid fault location after a single-phase fault on the converter valve side, can timely discover and handle equipment defects, and improve defect handling efficiency.

[0100] (2) The present invention can greatly improve the efficiency of fault analysis and shorten the power outage time of DC transmission projects by extracting and identifying fault characteristics under different fault scenarios and converting them into diagnostic algorithms.

[0101] (3) The fault location method proposed in the present invention is based on the identification of DC control and protection system alarm events and fault recording electrical quantities, which can directly avoid the risk of DC false locking caused by a single DC measurement abnormality.

[0102] The present disclosure may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A converter valve side fault location method based on an improved switching function, characterized in that: The following steps are involved: Step S1, when it is detected that the valve group differential protection in the DC control and protection system of the rectifier station or the inverter station is actuated and the transformer protection is inactive, the fault point location algorithm is started; Step S2, constructing a criterion for determining whether the fault range is in the Y bridge or the D bridge according to the DC current at the high voltage end of the converter, the DC current at the low voltage end, and the current at the converter transformer valve side, so as to determine the fault bridge; Step S3, judging whether the converter at the time of the fault is in the commutation period according to the three-phase current on the converter transformer valve side corresponding to the fault bridge, determining the bridge arm conduction state signals V1-V6 during the commutation period or the non-commutation period, and combining the DC current at the high-voltage end and the DC current at the low-voltage end of the converter, constructing and solving the improved switch function model of the rectifier station or the inverter station, and obtaining the calculation result of the improved switch function model, wherein the calculation result is a matrix including at least six elements, wherein each element corresponds to a phase, and each phase includes at least two corresponding elements; Step S4, if the converter is not in the commutation period at the time of the fault, the phase where the fault point is located is determined based on the distribution of zero elements in the calculation results; if the converter is in the commutation period at the time of the fault, the phase where the fault point is located is determined based on the calculation results combined with the direction and size of the three-phase current on the converter transformer side.

2. The converter valve side fault location method based on improved switching function according to claim 1, characterized in that: In step S2, the criterion for determining whether the fault range is in the Y bridge or the D bridge is: Comparison I acY and the high voltage DC current I DCP Size, if I acY =I DCP , then it is determined that the Y bridge has no fault, otherwise it is determined that the Y bridge has fault; Comparison I acD and low voltage DC current I DCN Size, if I acD =I DCN , then the D bridge is judged to be fault-free, otherwise the D bridge is judged to be faulty; Among them, I acY is the maximum absolute value of the three-phase current on the valve side of the Y-bridge converter transformer, I acD It is the maximum absolute value of the three-phase current on the valve side of the D-bridge converter transformer.

3. The converter valve side fault location method based on improved switching function according to claim 2, characterized in that: When the criterion is applied to a Y bridge or a D bridge, the trigger interval between the upper bridge arms or the lower bridge arms of the bridge is greater than 6.6 ms.

4. The converter valve side fault location method based on improved switching function according to claim 2, characterized in that: In contrast I acY and I DCP If the difference between the two is less than 3%, they are considered equal. In contrast I acD and I DCN If the difference between the two is less than 3%, they are considered equal.

5. The converter valve side fault location method based on improved switching function according to claim 1, characterized in that: In step S3, an improved switching function model of the inverter station is constructed, which is expressed by the following formula: Where: I n Calculate the result matrix for the improved switching function model of the inverter station; V1~V6 are bridge arm conduction state signals; I a , I b , I c is the three-phase current on the valve side; I DCP is the DC current at the high voltage end of the converter; I DCN is the DC current at the low voltage end of the converter; Δ is the DC current difference between the high and low ends of the converter, Δ=I DCP -I DCN .

6. The converter valve side fault location method based on improved switching function according to claim 1, characterized in that: In step S3, an improved switching function model of the rectifier station is constructed, which is expressed by the following formula: Where: I e Calculate the result matrix for the improved switching function model of the rectifier station; V1~V6 are bridge arm conduction state signals; I a , I b , I c is the three-phase current on the valve side; I DCP is the DC current at the high voltage end of the converter; I DCN is the DC current at the low voltage end of the converter; Δ is the DC current difference between the high and low ends of the converter, Δ=I DCP -I DCN .

7. The converter valve side fault location method based on improved switching function according to claim 1, characterized in that: Determine the value of the bridge arm conduction state signal V1-V6 in step S3 according to the trigger pulse code CPRY / CPRD and whether the converter is in the commutation period, wherein the trigger pulse code CPRY / CPRD is a digital code in binary format, including the conduction state information of each valve group; When not in the commutation period, the bridge arm conduction state signal of the conducting valve group is set to 1, and the bridge arm conduction state signal of the non-conducting valve group is set to 0; when in the commutation period, the bridge arm conduction state signal of the valve group that is turned on at the next trigger pulse is set to 1.

8. The converter valve side fault location method based on improved switching function according to claim 5 or 6, characterized in that: In step S4, the criterion for determining the phase where the fault point is located when the converter at the time of the fault is not in the commutation period is as follows: Calculation result matrix I n or I e In the equation, when the first two elements are equal to zero at the same time, and the third and fourth elements are not equal to 0 at the same time, and the fifth and sixth elements are not equal to 0 at the same time, it is determined that the a phase of the bushing on the valve side of the converter is faulty; When the 3rd and 4th elements are both zero, and the 1st and 2nd elements are not both 0, and the 5th and 6th elements are not both 0, it is determined that the b-phase of the bushing on the valve side of the converter is faulty; When the 5th and 6th elements are equal to zero, and the 1st and 2nd elements are not 0 at the same time, and the 3rd and 4th elements are not 0 at the same time, it is determined that the c-phase of the bushing on the valve side of the converter is faulty.

9. The converter valve side fault location method based on improved switching function according to claim 1, characterized in that: In step S4, when the converter is in the phase change period at the time of the fault, if it is determined according to the calculation result that two phases have simultaneous faults, then the phase in which the valve side bushing current shows a reverse increasing trend relative to before the fault is determined to be the faulty phase.

10. A converter valve side fault location system based on an improved switching function, running a converter valve side fault location method based on an improved switching function as claimed in any one of claims 1 to 9, characterized in that: include: Positioning start module, used to detect the valve group differential protection action and transformer protection non-action signal in the DC control and protection system, and start fault point positioning; YD bridge positioning module, used to determine whether the fault range is in the Y bridge or D bridge; The switching function module is used to determine whether the converter is in the commutation period at the time of the fault, and to construct and solve the improved switching function model of the rectifier station or inverter station; The phase location module is used to determine the phase where the fault point is located.

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