A Method and System for Fault Location on the Valve Side of a Converter Based on an Improved Switching Function

Abstract

A method and system for locating converter valve-side faults based on an improved switching function is proposed. The method includes: when the differential protection of the valve group in the DC control and protection system of the rectifier or inverter station is detected to operate while the transformer protection does not operate, a criterion is constructed to determine whether the fault range is within the Y-bridge or D-bridge; based on the three-phase current of the converter transformer valve side corresponding to the fault bridge, it is determined whether the converter is in the commutation period at the time of the fault, the bridge arm conduction status signal is determined, and an improved switching function model of the rectifier or inverter station is constructed by combining the DC current at the high-voltage end and the DC current at the low-voltage end of the converter; if not in the commutation period, the phase of the fault point is determined based on the distribution of zero elements in the calculation results; if in the commutation period, the phase of the fault point is determined by combining the direction and magnitude of the three-phase current at the converter transformer valve side. This invention enables rapid fault location of single-phase faults on the converter valve side, improves fault analysis efficiency, and avoids the risk of DC false blocking caused by a single abnormal DC measurement.

Description

Technical Field

[0001] This 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 in grid-commutated converters based on improved switching functions. Background Technology

[0002] High-voltage direct current (HVDC) transmission technology boasts advantages such as low transmission loss and high corridor utilization, making it suitable for ultra-large capacity and ultra-long-distance power transmission. It plays a crucial role in national strategic goals such as the national energy grid interconnection and the West-to-East power transmission project. Rapid restoration of power supply after a HVDC transmission system is shut down is essential for ensuring power supply and improving the availability of HVDC energy. The efficiency of fault handling depends on the speed and accuracy of fault diagnosis and location.

[0003] In DC transmission control and protection systems, alarm events and protection action information can only reflect the general range of the fault point, not accurately pinpoint the fault location. Currently, after a defect occurs in DC protection equipment, it is difficult to accurately and quickly determine the cause and location of the defect, heavily relying on human experience and technical service support from equipment manufacturers. This results in lengthy defect analysis and processing times, and the inability to share defect analysis and processing experience hinders the improvement of defect analysis and processing capabilities, while also posing potential risks to the safe and stable operation of the power grid.

[0004] Converter valve-side bushing failure is one of the main causes of converter station lockout. Bushing failure is not easily detected by external equipment observation. Traditional valve-side fault analysis and localization are carried out through post-fault equipment oiling tests and high-pressure tests, which are inefficient, time-consuming, and the accuracy of the results is directly related to the test results. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a fault location method for the valve side of a grid-commutated converter based on an improved switching function. This method avoids the problem of difficulty in quickly and accurately analyzing fault points on the valve side of converters in DC transmission projects, and achieves automatic, accurate, and rapid single-phase fault location on the valve side of the converter, providing a basis for converter station accident analysis and maintenance decisions.

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

[0007] A method for locating valve-side faults in grid-commutated converters based on improved switching functions, the method comprising the following steps:

[0008] Step S1: When the differential protection of the valve group in the DC control and protection system is detected to be activated and the transformer protection is not activated, the fault location algorithm is started.

[0009] Step S2: Determine whether the fault range is in the Y-bridge or D-bridge by constructing criteria based on 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 valve side of the converter transformer.

[0010] Step S3: Construct an improved switching function model based on the trigger pulse code CPRY / CPRD signal in the control and protection system, the three-phase currents Ia / Ib / Ic of the valve side bushing, the high-side DC current IDCP and the low-side DC current IDCN of the converter.

[0011] Step S4: Determine whether the current state is during commutation based on the CPRY / CPRD pulse code and the three-phase current of the valve side bushing.

[0012] Step S5: If the fault occurs outside the commutation period, the phase of the fault is determined based on the calculation results of the improved switching function model; if the fault occurs during the commutation period, the direction and magnitude of the auxiliary converter transformer side bushing current 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 If the value is equal to IDCP, then the Y-bridge is considered to be fault-free; otherwise, the Y-bridge is considered to be faulty.

[0015] (2) Comparison I acD and IDCN size, if I acD If the value is equal to IDCN, then the D-bridge is considered to be fault-free; otherwise, the D-bridge is considered to be faulty.

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

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

[0018] Furthermore, the improved switching function model constructed in step S3 varies depending on the topology of the rectifier station and the inverter station. The improved switching function model for the inverter station is shown in the following equation:

[0019]

[0020] In the formula, V1 to V6 are the bridge arm conduction status signals, which are obtained based on the binary format trigger pulse codes CPRY / CPRD and the three-phase current signals Ia / Ib / Ic of the valve side bushing in the control and protection system.

[0021] Due to the different wiring methods, the improved switching function model of the rectifier station is shown in the following equation:

[0022]

[0023] Where Δ=I DCP -I DCN .

[0024] Furthermore, the current state of the conducting valve group and the values ​​of V1 to V6 are obtained according to the CPRY / CPRD pulse encoding, and the conducting state of the corresponding conducting valve group is set to 1, while the non-conducting valve group is set to 0; if the three-phase currents Ia / Ib / Ic of the valve side bushing are detected simultaneously, it indicates that the commutation process is underway, and the conducting 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 fault points where the fault occurs outside 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 equal to zero at the same time, 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 converter valve side bushing phase a fault is present.

[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 zero, and the fifth and sixth elements are not both zero, it is determined that there is a phase a fault in the converter valve side bushing.

[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 both 0 at the same time, and the 3rd and 4th elements are not both 0 at the same time, it is determined that there is a phase c fault in the converter valve side bushing.

[0029] Furthermore, in step S5, the fault point determination principle during commutation is the same as that described in claim 7. If the calculation result indicates that two phases are simultaneously faulty, the determination is further 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, then that phase is determined to be the faulty phase.

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

[0031] (1) This invention constructs a fault location method for the valve side of a power grid phase-switching converter based on an improved switching function model. This method enables rapid fault location after a single-phase fault on the valve side of the converter, allowing for timely detection and handling of equipment defects and improving the efficiency of defect handling.

[0032] (2) This invention extracts and identifies fault features under different fault scenarios and transforms them into diagnostic algorithms, which can greatly improve the efficiency of fault analysis and shorten the power outage time of DC transmission projects.

[0033] (3) The fault location method proposed in this invention is based on the identification of alarm events and fault recording electrical quantities of DC control and protection system, which can directly avoid the risk of DC false blocking caused by a single DC measurement abnormality. Attached Figure Description

[0034] Figure 1 This is a flowchart of the converter valve-side fault location method based on the improved switching function in this invention;

[0035] Figure 2 This is the primary topology diagram of the 12-pulse converter in the rectifier station;

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

[0037] Figure 4 This is a schematic diagram of a phase a short circuit fault during the conduction of inverter station valves 4 and 5, according to a specific embodiment of the present invention.

[0038] Figure 5 This is a schematic diagram of a phase b short circuit fault during the conduction of inverter station valves 4 and 5, provided according to a specific embodiment of the present invention.

[0039] Figure 6 This is a schematic diagram of a phase C short-circuit fault during the conduction of inverter station valves 4 and 5, provided according to a specific embodiment of the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, other embodiments obtained by those skilled in the art without creative effort are all within the protection scope of this invention.

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

[0042] Step S1: When the differential protection of the valve group in the DC control and protection system of the rectifier station or inverter station is detected to be activated and the transformer protection is not activated, the fault location algorithm is started.

[0043] Understandably, locating fault points based on alarm events and fault recording electrical quantities in the DC control and protection system increases the redundancy of fault identification start conditions and reduces the risk of DC false blocking caused by a single DC measurement anomaly.

[0044] Step S2: Based on 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, construct the criteria to determine whether the fault range is in the Y-bridge or the D-bridge, and determine the fault bridge.

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

[0046] (1) Comparison I acY and IDCP size, if I acY If the value is equal to IDCP, then the Y-bridge is considered to be fault-free; otherwise, the Y-bridge is considered to be faulty.

[0047] (2) Comparison I acD and IDCN size, if I acD If the value is equal to IDCN, then the D-bridge is considered to be fault-free; otherwise, the D-bridge is considered to be faulty.

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

[0049] More preferably, 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 arm or the lower bridge arm should be greater than 6.6ms.

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

[0051] Step S3: Based on the three-phase currents 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. Combined with the bridge arm conduction status signals V1 to V6, the DC current IDCP at the high voltage end of the converter, and the DC current IDCN at the low voltage end, 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: Determine whether the converter is currently in the commutation period based on the three-phase current of the valve-side bushing. Specifically, if the three-phase currents Ia / Ib / Ic of the valve-side bushing are detected simultaneously, it indicates that the commutation process is underway.

[0054] Step S302: Determine the values ​​of the bridge arm conduction status signals V1 to V6 based on the CPRY / CPRD pulse code and the current state of the converter. The trigger pulse code CPRY / CPRD is a binary digital code that contains time-domain information of the conduction status of each bridge arm.

[0055] More preferably, when not in the commutation process, the conduction state of the conducting 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 that is about to be turned on is set to 1.

[0056] In step S303, due to different wiring methods and different topologies of the rectifier station and inverter station, the constructed improved switching function models are somewhat different. The improved switching function model for the inverter station is expressed by the following formula.

[0057]

[0058] In the formula:

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

[0060] V1 to V6 are bridge arm conduction status signals;

[0061] I a I b I c This represents the three-phase current in the valve-side bushing.

[0062] I DCP This refers to the DC current at the high-voltage end of the converter.

[0063] I DCN This refers to the DC current at the low-voltage side of the converter.

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

[0065] Step S304: Construct an improved switching function model for the rectifier station, expressed by the following formula:

[0066]

[0067] In the formula:

[0068] I e The results are from the calculation of the improved switching function model of the rectifier station.

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

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

[0071] Preferably, the principle for determining fault points where the fault does not occur during commutation is as follows:

[0072] (1) The first two elements in the calculation result I correspond to phase a. 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 converter valve side bushing phase a fault is present.

[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 zero, and the fifth and sixth elements are not both zero, it is determined that there is a phase b fault in the converter valve side bushing.

[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 both 0, and the 3rd and 4th elements are not both 0, it is determined that there is a phase c fault in the converter valve side bushing.

[0075] Preferably, the calculation principle of the improved switching function model during commutation and the basic principle for determining fault points are the same as the fault point determination principle described above for faults occurring outside the commutation period. That is, in the calculation result I, the first two elements correspond to phase a, the third and fourth elements correspond to phase b, and the fifth and sixth elements correspond to phase c. If two elements are both 0, then that phase is determined to be faulty. Additional auxiliary criteria include: if the calculation result I determines that two phases are simultaneously faulty, then further determination 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 increasing trend relative to before the fault, then that phase is determined to be the faulty phase.

[0076] Embodiment 2 of the present invention provides a fault location system for the valve side of a grid commutator based on an improved switching function, which operates the fault location method for the valve side of a grid commutator based on an improved switching function as described in Embodiment 1, including:

[0077] The location start-up module is used to detect the operation signals of valve group differential protection and transformer protection non-operation signals in the DC control and protection system, and to start fault point location;

[0078] The YD bridge positioning module is used to determine whether the fault is located in the Y bridge or the 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] To verify the effectiveness of this invention in practical applications, the following is a specific simulation verification example:

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

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

[0084] Define the current flow from the converter valve side towards the converter valve as the positive direction, from... Figure 4 The current relationship at each measuring point is as follows: -Ia = Ic = IDCN.

[0085] Applying the improved switching function model of the inverter station in step S3, the calculation result is as follows:

[0086]

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

[0088] (2) During the conduction of valves 4 and 5, a short circuit fault occurs in phase b.

[0089] Define the current flow from the converter valve side towards the converter valve as the positive direction, from... Figure 5 The current relationships at each measuring point are as follows: IDCP = -Ia, Ic = IDCN.

[0090] Applying the improved switching function model of the inverter station in step S3, the calculation result is as follows:

[0091]

[0092] Therefore, phase b faults 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 of valves 4 and 5, a short circuit fault occurs in phase C.

[0094] Define the current flow from the converter valve side towards the converter valve as the positive direction, from... Figure 6 The current relationship at each measuring point in the figure is as follows: IDCP = -Ia = Ic.

[0095] Applying the improved switching function model of the inverter station in step S3, the calculation result is as follows:

[0096]

[0097] Therefore, a phase c 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 the following:

[0099] (1) This invention constructs a fault location method for the valve side of a power grid phase-switching converter based on an improved switching function model. This method enables rapid fault location after a single-phase fault on the valve side of the converter, allowing for timely detection and handling of equipment defects and improving the efficiency of defect handling.

[0100] (2) This invention extracts and identifies fault features under different fault scenarios and transforms them into diagnostic algorithms, which can greatly improve the efficiency of fault analysis and shorten the power outage time of DC transmission projects.

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

[0102] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A converter valve-side fault location method based on improved switching functions, characterized in that, Includes the following steps: Step S1: When the differential protection of the valve group in the DC control and protection system of the rectifier station or inverter station is detected to be activated and the transformer protection is not activated, the fault location algorithm is started. Step S2: Based on the DC current at the high-voltage end of the converter, the DC current at the low-voltage end, and the current on the valve side of the converter transformer, construct a criterion to determine whether the fault range is in the Y-bridge or the D-bridge, so as to determine the fault bridge. Step S3: Determine whether the converter is in the commutation period at the time of the fault based on the three-phase current on the converter transformer valve side corresponding to the faulty bridge, determine the bridge arm conduction status signals V1 to V6 during or outside the commutation period, and construct and solve an improved switching function model for the rectifier station or inverter station by combining the DC current at the high voltage end and the DC current at the low voltage end of the converter, and obtain the calculation result of the improved switching function model. The calculation result is a matrix with at least six elements, where each element corresponds to a phase, and each phase includes at least two corresponding elements. The improved switching function model for the inverter station is expressed by the following formula: In the formula: I n The matrix of calculation results for the improved switching function model of the inverter station; V1 to V6 are bridge arm conduction status signals; I a I b I c This refers to the three-phase current on the valve side; I DCP This refers to the DC current at the high-voltage end of the converter. I DCN This refers to the DC current at the low-voltage side of the converter. Δ is the difference between the high and low DC currents of the converter, Δ = I DCP -I DCN ; The improved switching function model of the rectifier station is expressed by the following formula. In the formula: I e The matrix of calculation results for the improved switching function model of the rectifier station; Step S4: If the converter is not in the commutation period at the time of the fault, the phase of the fault point 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 of the fault point is determined based on the direction and magnitude of the three-phase current on the converter transformer valve side in conjunction with the calculation results.

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 is in the Y-bridge or the D-bridge is: Comparison I acY and the DC current I at the high voltage end DCP Size, if I acY =I DCP If the condition is met, the Y-bridge is determined to be fault-free; otherwise, the Y-bridge is determined to be faulty. Comparison I acD and low-voltage side DC current I DCN Size, if I acD =I DCN If the condition is met, then bridge D is determined to be fault-free; otherwise, bridge D is determined to be faulty. Among them, I acY I represents the maximum absolute value of the three-phase current on the valve side of the Y-bridge converter transformer. acD This represents 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 D-bridge, the trigger interval between the upper arm or the lower arm 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 comparison I acY and I DCP When the size is less than 3%, the two are considered equal. In comparison 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: The values ​​of the bridge arm conduction status signals V1 to V6 in step S3 are determined based on the trigger pulse code CPRY / CPRD and whether the converter is in the commutation period. The trigger pulse code CPRY / CPRD is a binary digital code that contains the conduction status information of each valve group. When not in the commutation period, the bridge arm conduction status signal of the conducting valve group is set to 1, and the bridge arm conduction status signal of the non-conducting valve group is set to 0; when in the commutation period, the bridge arm conduction status signal of the valve group that will be turned on at the next trigger pulse is set to 1.

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

7. The converter valve-side fault location method based on improved switching function according to claim 1, characterized in that: In step S4, if the converter is in the commutation period at the time of the fault, and it is determined from the calculation results that two phases are simultaneously faulted, 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 faulted phase.

8. A converter valve-side fault location system based on an improved switching function, operating the converter valve-side fault location method based on an improved switching function as described in any one of claims 1-7, characterized in that, include: The location start-up module is used to detect the operation signals of valve group differential protection and transformer protection non-operation signals in the DC control and protection system, and to start fault point location; The YD bridge positioning module is used to determine whether the fault is located in the Y bridge or the 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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