Diagnostic method and system for LCC valve interphase short circuit fault location

Abstract

The invention provides a diagnosis method and system for LCC valve interphase short circuit fault positioning. The diagnosis method comprises the steps that S1, related data are collected; the data comprises a current value, a voltage value and a waveform characteristic value of a 50Hz component; s2, the fault type is judged based on the monitoring criterion, the phase of the fault is analyzed, and diagnosis positioning is completed; the fault type comprises a single-valve short circuit fault, an interphase short circuit fault and a six-pulse short circuit fault. According to the invention, the method can accurately judge that the type of the valve fault is an interphase short circuit in a plurality of valve fault types, and automatically analyzes the phase of the fault; the fault analysis and positioning time of the operation and maintenance personnel after the fault occurs can be shortened to a great extent, the workload of the operation and maintenance personnel is reduced, troubleshooting and emergency repair of the fault are accelerated, and the reliability and stability of power grid operation are improved.

Description

Technical Field

[0001] The present invention relates to the field of high voltage direct current (HVDC) power transmission, and in particular to a diagnostic method and system for locating an LCC valve interphase short circuit fault. Background Art

[0002] High voltage direct current (HVDC), a high-capacity, long-distance power transmission technology, has been increasingly used in inter-provincial and inter-regional interconnection projects in my country in recent years. With the advancement of science and technology, line commutated converter-based high voltage direct current (LCC-HVDC) transmission technology has become quite mature and widely used in large-capacity, long-distance power transmission and other applications. To prevent overstress caused by faults in the converter, which is the core of the phase-commutated converter, HVDC projects typically configure valve short-circuit protection as the converter's primary protection. Valve short-circuit faults include single-valve short-circuit, valve-phase short-circuit, six-pulse short-circuit, and twelve-pulse short-circuit. However, in current industry standards and actual projects, these valve short-circuit faults all use the same criterion, making distinguishing between different valve short-circuit faults a key challenge.

[0003] In recent years, scholars both domestically and internationally have conducted extensive research on fault analysis and location in LCC-HVDC converters. For ground fault location, the characteristics of typical ground faults inside and outside the rectifier-side area can be analyzed. Ground faults on the inverter side can be located by analyzing the time differences in the presence of fault characteristics at different locations after the fault. However, relevant technologies for locating and analyzing valve faults are still lacking. Due to the structure of the converter, valve short-circuit faults at different locations cannot be mapped one-to-one to valve short-circuit protection. Post-fault analysis relies on experienced operators, which severely restricts rapid fault detection and repair.

[0004] [1] Zheng Tao, Qi Huanhuan, and Fan Ying. "A new method for fault location in HVDC converter area based on valve short-circuit protection." Automation of Electric Power Systems (2013). This document proposes a fault period division to clarify the action of the first type of valve short-circuit protection; however, this document only proposes a method for distinguishing different rectifier faults by analyzing the subsequent actions and fault electrical quantity characteristics, and does not analyze the faults on the inverter side. Compared with the present invention, the fault coverage of this method is smaller and the judgment method is more complicated.

[0005] [1] Chen Deyang et al. "Conventional DC valve area fault and measurement hidden danger location method." 025-81093050, 025-81093053, 10.7500 / AEPS20200519005.2021. This paper divides the conventional DC valve area into partitions and calculates the differential current for each partition. The goal of using the state estimation algorithm to estimate the measurement value is to minimize the sum of squares of the residuals, but this is very easy to cause deviations; at the same time, although this paper uses the converter valve conduction timing to accurately divide the partition corresponding to the differential current to the phase, it greatly increases the complexity of the process.

[0006] Chinese patent publication CN114636897A discloses a method and device for locating valve short-circuit faults in HVDC rectifier stations based on actual control and protection waveform recordings. The method includes: determining the action type of the valve short-circuit protection action information based on acquired DC control and protection system valve short-circuit protection action information; if the valve short-circuit protection action information indicates that both Y-bridge valve short-circuit protection and D-bridge valve short-circuit protection are activated, determining that the fault location is a 12-pulse converter output line short circuit; if the valve short-circuit protection is only Y-bridge valve short-circuit protection or D-bridge valve short-circuit protection, first determining whether the fault is a phase-to-phase short circuit on the converter transformer valve side by determining whether the three-phase currents of the Y / D bridge are all zero at the moment the Y / D bridge trips the AC incoming line switch; if not, further extracting the Y / D bridge three-phase currents corresponding to the different valve conduction stages of the converter after the fault using the converter trigger pulse signal. However, this patent document only locates the fault location and cannot analyze or determine the fault type, thus failing to solve the aforementioned problem. Summary of the Invention

[0007] In view of the defects in the prior art, the object of the present invention is to provide a diagnostic method and system for locating an interphase short circuit fault in an LCC valve.

[0008] According to the present invention, a diagnostic method for locating an interphase short circuit fault in an LCC valve is provided, comprising:

[0009] Step S1: collecting relevant data;

[0010] The data includes current value, voltage value and waveform characteristic value of 50Hz component;

[0011] Step S2: Determine the fault type based on the monitoring criteria and analyze the phase where the fault occurs to complete the diagnosis and positioning;

[0012] The fault types include single valve short circuit fault, phase short circuit fault and six-pulse short circuit fault.

[0013] Preferably, the monitoring criteria include the first type of criteria, the second type of criteria, the third type of criteria and the fourth type of criteria; assuming that the Y bridge AB phases are short-circuited in the preset circuit, define I VYis the valve side current value of the AC side star connection, I VD is the valve side current value of the AC side delta connection, I D is the DC side current value, I DCP is the DC voltage at the non-grounded end of the converter, I DNC is the DC voltage at the ground terminal of the converter, I D_NOM is the rated current value of the DC side, I set is the preset current value, U ABC is the AC side voltage, U set is the preset voltage value.

[0014] Preferably, the first type of criterion includes the criterion of meeting the VSCP protection constant value, the AC side current and the DC side current meet I VY >I D or I VD >I D When the AC current value is greater than the DC current value, the protection action is performed; where I VY , I VD are the valve side current values ​​of the AC side star connection and the AC side delta connection, I D Indicates the DC side current value.

[0015] Preferably, the second type of criterion includes bypass, lockout, and when the fault valve still has current after the VSCP is started, the bypass is defined as BPPO, which is 1 if the bypass is put into operation and 0 if it is not put into operation; the lockout is defined as BLOCK, which is 1 when the lockout occurs and 0 if the lockout does not occur; the protection VSCP action is defined as 1 and 0 if it is not acted;

[0016] IF(BPPO==1&BLOCK==1&VSCP==1),I VY , I VD >(I set );

[0017] Among them, I set is the preset current value.

[0018] Preferably, the third type of criterion includes that when the AC voltage and the valve side voltage exist or disappear at the same time, after the protection signal is issued for a preset time, the AC circuit breaker is disconnected, and the AC voltage and the current on the valve side disappear;

[0019] IF(U ABC >U set );I VY , I VD >(I set )&IF(U ABC set );I VY , I VD <(I​set );

[0020] Among them, I VY , I VD are the valve side current values ​​of the AC side star connection and the AC side delta connection, U ABC is the AC side voltage, I set is the preset current value, U set is the preset voltage value.

[0021] Preferably, the fourth type of criterion includes that in the two phases where the fault occurs, the AC side current amplitudes are the same and the directions are opposite, the two phase currents of the valve side fault are 50Hz, the 50Hz component is extracted, and the two phases with a sudden increase in the 50Hz component are determined to be the fault phases.

[0022] According to the present invention, a diagnostic system for locating an interphase short circuit fault in an LCC valve is provided, comprising:

[0023] Module M1: Collect relevant data;

[0024] The data includes current value, voltage value and waveform characteristic value of 50Hz component;

[0025] Module M2: Determine the fault type based on monitoring criteria and analyze the fault phase to complete diagnosis and positioning;

[0026] The fault types include single valve short circuit fault, phase short circuit fault and six-pulse short circuit fault.

[0027] Preferably, the monitoring criteria include the first type of criteria, the second type of criteria, the third type of criteria and the fourth type of criteria; assuming that the Y bridge AB phases are short-circuited in the preset circuit, define I VY is the valve side current value of the AC side star connection, I VD is the valve side current value of the AC side delta connection, I D is the DC side current value, I DCP is the DC voltage at the non-grounded end of the converter, I DNC is the DC voltage at the ground terminal of the converter, I D_NOM is the rated current value of the DC side, I set is the preset current value, U ABC is the AC side voltage, U set is the preset voltage value.

[0028] Preferably, the first type of criterion includes the criterion of meeting the VSCP protection constant value, the AC side current and the DC side current meet I VY >I D or I VD >I D When the AC current value is greater than the DC current value, the protection action is performed; where I VY , IVD are the valve side current values ​​of the AC side star connection and the AC side delta connection, I D Indicates the DC side current value.

[0029] Preferably, the second type of criterion includes bypass, lockout, and when the fault valve still has current after the VSCP is started, the bypass is defined as BPPO, which is 1 if the bypass is put into operation and 0 if it is not put into operation; the lockout is defined as BLOCK, which is 1 when the lockout occurs and 0 if the lockout does not occur; the protection VSCP action is defined as 1 and 0 if it is not acted;

[0030] IF(BPPO==1&BLOCK==1&VSCP==1),I VY , I VD >(I set );

[0031] Among them, I set is the preset current value.

[0032] Preferably, the third type of criterion includes that when the AC voltage and the valve side voltage exist or disappear at the same time, after the protection signal is issued for a preset time, the AC circuit breaker is disconnected, and the AC voltage and the current on the valve side disappear;

[0033] IF(U ABC >U set );I VY , I VD >(I set )&IF(U ABC set );I VY , I VD <(I set );

[0034] Among them, I VY , I VD are the valve side current values ​​of the AC side star connection and the AC side delta connection, U ABC is the AC side voltage, I set is the preset current value, U set is the preset voltage value.

[0035] Preferably, the fourth type of criterion includes that in the two phases where the fault occurs, the AC side current amplitudes are the same and the directions are opposite, the two phase currents of the valve side fault are 50Hz, the 50Hz component is extracted, and the two phases with a sudden increase in the 50Hz component are determined to be the fault phases.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] ​1. The present invention can accurately determine that the type of valve fault is a phase short circuit among multiple valve fault types, and automatically analyze the phase where the fault occurs; the proposed judgment criteria can directly determine the type and location of the fault, greatly shortening the fault locating time.

[0038] 2. The present invention can greatly shorten the time it takes for operation and maintenance personnel to analyze and locate the fault after the fault occurs, reduce the workload of operation and maintenance personnel, speed up the investigation and repair of the fault, and improve the reliability and stability of the power grid operation.

[0039] Other beneficial effects of the present invention will be explained through the introduction of specific technical features and technical solutions in the specific implementation methods. Those skilled in the art should be able to understand the beneficial technical effects brought about by the introduction of these technical features and technical solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0041] Figure 1 Flow chart of the method of the present invention.

[0042] Figure 2 Schematic diagram of converter regional fault types in the present invention.

[0043] Figure 3 This is a schematic diagram of the LCC in the present invention operating in a normal operating mode.

[0044] Figure 4 This is a schematic diagram of a single-valve short-circuit fault occurring in the LCC of the present invention.

[0045] Figure 5 This is a schematic diagram of the LCC after the pulse stops due to a single valve short circuit fault in the present invention.

[0046] Figure 6 This is a schematic diagram of an LCC in the present invention when a phase-to-phase short circuit fault occurs.

[0047] Figure 7 This is a schematic diagram of the LCC after the phase-to-phase short circuit fault protection is activated in the present invention.

[0048] Figure 8 This is a schematic diagram of a six-pulse short-circuit fault occurring in the LCC of the present invention.

[0049] Figure 9 Schematic diagram of the VSCP protection setting criterion in the present invention.

[0050] Figure 10 This is the first part of the phase-to-phase short-circuit protection criterion diagram in the present invention.

[0051] Figure 11 This is the second part of the phase-to-phase short-circuit protection criterion diagram in the present invention.

[0052] Figure 12 This is the logic diagram for extracting the 50Hz component in the present invention.

[0053] Figure 13 Schematic diagram of a phase-to-phase short circuit occurring in the BC phase of a Y bridge in an embodiment of the present invention.

[0054] Figure 14 Schematic diagram of a single-valve short-circuit fault occurring in the Y-bridge V1 valve in an embodiment of the present invention.

[0055] Figure 15 Schematic diagram of a 6-pulse short-circuit fault occurring in a Y bridge according to an embodiment of the present invention.

[0056] Figure 16 This is a flow chart of the phase-to-phase short circuit fault judgment criteria of the present invention. DETAILED DESCRIPTION

[0057] The present invention is described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, without departing from the scope of the present invention, a number of variations and improvements may be made by those skilled in the art. These all fall within the scope of protection of the present invention.

[0058] First, the fault characteristics of the LCC converter valve are analyzed.

[0059] Under normal operating conditions, when the converter is in operation, only two valves are turned on at the same time: one in the upper arm of one phase and the other in the lower arm of a different phase. The two turned-on valves connect two phases of the three-phase AC power in series and connect to the DC port. Figure 3 As shown, under normal operation, the DC output voltage at any time is a combination of the series superposition of two-phase AC.

[0060] Under the conditions of phase control and load current, taking into account the resistive voltage drop in the commutation circuit and the valve conduction voltage drop:

[0061] ——The DC voltage on the rectifier side is:

[0062]

[0063] ——The DC voltage on the inverter side is:

[0064]

[0065] Where U dioR 、U dioIis the ideal no-load DC voltage of the converter without phase control (abbreviated as ideal no-load DC voltage); U T is the pressure drop when the converter valve is turned on.

[0066] α——the actual trigger angle of the valve;

[0067] γ——the actual shut-off angle of the valve;

[0068] I d ——actual value of DC current;

[0069] I dN - rated value of DC current;

[0070] d x ——Relative inductive DC voltage drop;

[0071] d r ——Relative resistive DC voltage drop.

[0072] The subscript R represents the rectifier side, the subscript I represents the inverter side, N represents the nominal value of the rated operating condition of the project, and n represents the number of 6 pulsations.

[0073] In case of single valve short circuit fault:

[0074] The single valve short circuit fault on the rectifier side is the most serious fault that harms the converter. Its fault current peak value is large and the rising rate is fast. Figure 4 As shown in Figure (a), when valves 2 and 3 begin conducting normally, if valve 1 shorts, a two-phase short circuit between valves 1 and 3 occurs due to the reverse voltage applied to valve 1. The current in the converter valve originates from the B-phase power supply, passes through valves 3 and 1, and then returns to the A-phase power supply. At this point, the current in the D-bridge valves of the rectifier converter is zero, and the DC current in the DC link is zero, causing the DC voltage to drop during the fault.

[0075] On the inverter side, when a single valve short circuit fault occurs, intermittent commutation failure will occur. Figure 4 As shown in (b), when valves 5 and 6 are turned on, valve 2 is short-circuited, forming a bypass pair, which causes the DC current to increase and the DC voltage to drop.

[0076] When a single valve fault occurs on the rectifier side, the fault current is:

[0077] or

[0078] When a single valve fault occurs on the inverter side, the fault current is:

[0079] or

[0080] Where R thRepresents the resistance of a converter bridge arm when it is conducting, R dN represents the DC line resistance, ω represents the angular velocity (angular frequency), ωt is the electrical angle, E is the effective value of the AC line voltage, L c is the inductance of each phase on the AC side of the valve.

[0081] In the case of a phase-to-phase short circuit fault:

[0082] Reference Figure 6 As shown in (a), when a phase-to-phase fault occurs on the converter valve side, the fault current only flows through the converter transformer winding connected to the faulty phase of the bridge and the valve-side connection part. At this time, the current of all converter valves on the rectifier and inverter sides and the DC line current quickly drop to zero. Its transient current value is the two-phase short-circuit current on the converter transformer valve side ( Where, E is the effective value of the AC line voltage, L c is the inductance of each phase on the AC side of the valve). The phase-to-phase short circuit fault phenomenon continues until the AC circuit breaker is disconnected.

[0083] Reference Figure 6 As shown in (b), when a phase short circuit occurs on the valve side of the inverter-side converter transformer, the current in the two-phase short-circuited converter transformer winding increases. The inverter-side converter valve current and DC current increase, while the DC voltage decreases.

[0084] When a non-metallic two-phase short circuit occurs, the two-phase short-circuit current is as follows:

[0085] ——When an interphase fault occurs on the rectifier side:

[0086]

[0087] ——When an interphase fault occurs on the inverter side:

[0088]

[0089] Where Z f Indicates the resistance of the transition resistor.

[0090] In a six-pulse short-circuit fault:

[0091] Reference Figure 8 As shown in Figure (a), assume a short-circuit fault occurs on the rectifier-side Y-bridge. In this case, only the rectifier-side Y-bridge and the short-circuit wire form a six-pulse circuit. The fault current flows only through the conduction valve, while the remaining rectifier-side D-bridge and the inverter-side converter are isolated. Consequently, the current in the rectifier-side Y-bridge conducting valve increases rapidly, while the remaining currents—the DC pole line current, the rectifier-side neutral bus current, and the inverter-side Y-bridge and D-bridge currents—rapidly drop to zero, causing the DC voltage to decrease.

[0092] Reference Figure 8As shown in Figure (b), assume a short circuit occurs on the inverter-side Y-bridge. In this case, only the rectifier, inverter-side D-bridge, and fault point form the circuit, and the inverter-side Y-bridge is isolated. Therefore, the current in the remaining circuit increases, while the inverter-side Y-bridge current and the neutral bus current quickly drop to zero, causing the DC voltage to drop.

[0093] ——When a short circuit occurs on the rectifier side, the fault current is:

[0094] or

[0095] ——When a short circuit occurs on the inverter side, the fault current is:

[0096]

[0097] Traditional converter valve short-circuit protection is required to protect all converter valves, primarily to protect the thyristor valves from overstress caused by a short circuit on the DC side of the converter transformer. This protection measures the difference between the currents in the Y and D windings on the valve side of the converter transformer and the high- and low-voltage terminals of the associated 12-pulse converter. Furthermore, the protection must detect faults quickly before the second healthy valve in the same half-bridge conducts, and must not include a bypass for locking valves.

[0098] During normal operation, the valve-side current and the DC current of the converter transformer are balanced. The higher amplitude of the valve-side current of the converter transformer than the DC current is a criterion for valve short circuit or other phase-to-phase short circuit. The protection criterion is derived as follows:

[0099] Δ=max(I VY ,I VD )-maxI D (I DP ,I DCN );

[0100] I VY =max(I VY1 ,I VY2 ,I VY3 );

[0101] I VD =max(I VD1 ,I VD2 ,I VD3 );

[0102] Among them, I VY is the valve side current value of the AC side star connection, I VD is the valve side current value of the AC side delta connection, I D is the DC side current value, I DCP is the DC voltage at the non-grounded end of the converter, I DNC is the DC voltage at the ground terminal of the converter, ID_NOM is the rated current value of the DC side, I set is the preset current value, U ABC is the AC side voltage, U set is the preset voltage value.

[0103] Requirement Δ>(0.5I D_NOM +0.2maxI D If the current satisfies all of the above equations, the protection system immediately shifts all converters and trips the faulty valve. When the bypass switch of the faulty valve closes, the healthy valve releases the phase shift and resumes normal operation. The faulty valve executes X_BLOCK; the healthy valve first shifts phase and then resumes normal operation.

[0104] Because the protection criteria use the valve-side and DC-side currents of the converter transformer, it is impossible to determine and distinguish the specific fault type occurring within the converter. After a fault occurs, fault analysis still relies on experienced operators.

[0105] The following takes the Y bridge AB phase short circuit as an example to illustrate the criterion of the present invention:

[0106] 1. Criteria for meeting VSCP protection setting values:

[0107] Reference Figure 9 As shown, if after a fault occurs, the AC side current and the DC side current meet I VY >I D (I DCP ,I DNC ) or I VD >I D (I DCP ,I DNC ) relationship, I VY , I VD is the current value of the star connection and delta connection on the AC side, I D Indicates the DC side current value. That is, when the AC current is greater than the DC current, the protection will be activated.

[0108] 2. After bypass, lockout, and VSCP activation, the faulty valve still has current:

[0109] Reference Figure 10 As shown in the figure, bypass is defined as BPPO, which is 1 if bypass is enabled and 0 if it is not enabled; blocking is defined as BLOCK, which is 1 when blocking occurs and 0 if blocking does not occur; protection VSCP action is defined as 1 and 0 if it is not enabled.

[0110] IF(BPPO==1&BLOCK==1&VSCP==1),I VY , I VD >(I set ).

[0111] Among them I set is the set current value.

[0112] 3. When AC voltage exists, there is current on the valve side; when AC voltage disappears, there is current on the valve side.

[0113] Reference Figure 11 As shown, after the protection signal is sent for a period of time (50ms to 100ms), the AC circuit breaker is disconnected. At this time, the AC voltage disappears and the current on the valve side also disappears.

[0114] IF(U ABC >U set );I VY , I VD >(I set )&IF(U ABC set );I VY , I VD <(I set ).

[0115] Among them, U ABC Refers to the AC side voltage, U set is the set voltage value.

[0116] 4. For the two phases with fault, the AC side current amplitude is the same but the direction is opposite. For the two phases with fault on the valve side, the current is 50Hz.

[0117] Reference Figure 12 As shown in FIG, by extracting the 50 Hz component, the two phases where the 50 Hz component suddenly increases can be determined as the fault phases.

[0118] The present invention can accurately determine that the type of valve fault is a phase short circuit among multiple valve fault types, and automatically analyze the phase where the fault occurs; the proposed judgment criterion can directly determine the type and location of the fault, greatly shortening the fault locating time.

[0119] The above is a basic embodiment of the present invention. The technical solution of the present invention is further described below through a preferred embodiment.

[0120] Example 1

[0121] This embodiment establishes a DC transmission system model based on the PSCAD simulation environment for verification. The system parameters are shown in Table 1, and the fault parameters are shown in Table 2.

[0122] Table 1 Related parameters of DC transmission system

[0123]

[0124] Table 2 Fault setting parameters ​

[0125]

[0126] Simulation result 1: Y bridge BC phase short circuit:

[0127] In order to verify the accuracy of the newly proposed monitoring criterion when a valve short circuit occurs, a DC transmission system model is designed for simulation, and the fault parameter settings are shown in Table 2.

[0128] Reference Figure 13 As shown in Figure (a), if a phase-to-phase short circuit occurs in the AB phase of the inverter-side Y bridge at a certain moment, V1 and V4 are bypassed when the harp pulse is 9. It can be seen that after the bypass is applied, current still flows through the faulty valve, but the current on the valve side disappears immediately after the AC full-scale voltage disappears.

[0129] Reference Figure 13 As shown in (b), the harp pulses and currents in the section near the fault are amplified. At time T1, the harp pulse is 6, V2V3 is conducting, and the current commutation is normal. At time T2, V2 and V4 commutate normally, the harp pulse is 12, and V3V4 is conducting. At this time, the current in phase A should have increased to approximately 3kA, but due to the fault occurring at 0.8s, the current in phase A reverses. At time T3, the currents in phases A and B form a loop, and the current in phase C drops to zero. The two phase currents in the valve-side fault have the same amplitude but opposite directions, which allows harmonic analysis of the valve-side current.

[0130] Reference Figure 13 As shown in (c), the 50Hz component is approximately at the DC current level during normal operation. When a fault occurs, the 50Hz components of the fault phases A and B suddenly increase with equal amplitudes, while the 50Hz component of phase C drops to zero. This verifies the monitoring criteria.

[0131] Simulation result 2: Single valve short circuit occurs in the Y-bridge V1 valve:

[0132] Reference Figure 14 As shown in the figure, in order to verify the accuracy of the newly proposed monitoring criterion when valve short circuit occurs, a DC transmission system model is designed for simulation.

[0133] If a single valve short-circuit occurs in valve V1 of the inverter-side Y-bridge, the bypass pair is activated, and the current in the faulty valve disappears immediately. This means that the current disappears approximately 100ms before the AC voltage disappears. However, the fault current still meets the requirement of equal amplitude and opposite direction for both phases. This verifies the monitoring criteria.

[0134] Simulation result 3: 6-pulse short circuit fault occurs in the Y bridge:

[0135] Reference Figure 15 As shown in the figure, in order to verify the accuracy of the newly proposed monitoring criterion when valve short circuit occurs, a DC transmission system model is designed for simulation.

[0136] When a 6-pulse short circuit occurs on the inverter-side Y-bridge, the entire Y-bridge is isolated, the AC-side current is zero, the DC-side current is greater than the AC-side current, and the lockout is not triggered. Thus, the monitoring criteria are verified.

[0137] The present invention also provides a diagnostic system for locating an LCC valve interphase short-circuit fault. The diagnostic system for locating an LCC valve interphase short-circuit fault can be implemented by executing the process steps of the diagnostic method for locating an LCC valve interphase short-circuit fault. That is, those skilled in the art can understand the diagnostic method for locating an LCC valve interphase short-circuit fault as a preferred implementation of the diagnostic system for locating an LCC valve interphase short-circuit fault.

[0138] Specifically, a diagnostic system for locating an LCC valve interphase short circuit fault includes:

[0139] Module M1: Collect relevant data;

[0140] The data includes current value, voltage value and waveform characteristic value of 50Hz component;

[0141] Module M2: Determine the fault type based on monitoring criteria and analyze the fault phase to complete diagnosis and positioning;

[0142] The fault types include single valve short circuit fault, phase short circuit fault and six-pulse short circuit fault.

[0143] The monitoring criteria include the first, second, third and fourth categories of criteria; assuming that the Y bridge AB phases are short-circuited in the preset circuit, define I VY is the valve side current value of the AC side star connection, I VD is the valve side current value of the AC side delta connection, I D is the DC side current value, I DCP is the DC voltage at the non-grounded end of the converter, I DNC is the DC voltage at the ground terminal of the converter, I D_NOM is the rated current value of the DC side, I set is the preset current value, U ABC is the AC side voltage, U set is the preset voltage value.

[0144] The first type of criterion includes the criterion of meeting the VSCP protection setting value, the AC side current and the DC side current meeting I VY >I D or I VD >I D When the AC current value is greater than the DC current value, the protection action is performed; where I VY , I VD are the valve side current values ​​of the AC side star connection and the AC side delta connection, ID Indicates the DC side current value.

[0145] The second type of judgment criteria includes bypass, lockout, and when the fault valve still has current after VSCP is activated, the bypass is defined as BPPO, which is 1 if the bypass is activated and 0 if it is not activated; the lockout is defined as BLOCK, which is 1 when the lockout occurs and 0 if it does not occur; the protection VSCP action is defined as 1 and 0 if it is not activated;

[0146] IF(BPPO==1&BLOCK==1&VSCP==1),I VY , I VD >(I set );

[0147] Among them, I set is the preset current value.

[0148] The third type of criterion includes: when the AC voltage and the valve side voltage exist or disappear at the same time, after the protection signal is issued for a preset time, the AC circuit breaker is disconnected, and the AC voltage and the valve side current disappear;

[0149] IF(U ABC >U set );I VY , I VD >(I set )&IF(U ABC set );I VY , I VD <(I set );

[0150] Among them, I VY , I VD are the valve side current values ​​of the AC side star connection and the AC side delta connection, U ABC is the AC side voltage, I set is the preset current value, U set is the preset voltage value.

[0151] The fourth type of criterion includes that, in the two phases where the fault occurs, the AC side current amplitudes are the same and the directions are opposite, the two phase currents of the valve side fault are 50Hz, the 50Hz component is extracted, and the two phases where the 50Hz component suddenly increases are determined to be the fault phases.

[0152] ​Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, and units provided by the present invention in purely computer-readable program code, it is entirely possible to implement the same functions of the system and its various devices, modules, and units provided by the present invention in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; the devices, modules, and units for implementing various functions can also be considered as both software modules implementing the method and structures within the hardware component.

[0153] In the description of this application, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0154] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A diagnostic method for locating an LCC valve interphase short circuit fault, characterized in that: include: Step S1: collecting relevant data; The data includes current value, voltage value and waveform characteristic value of 50Hz component; Step S2: Determine the fault type based on the monitoring criteria and analyze the phase where the fault occurs to complete the diagnosis and positioning; The fault types include single valve short circuit fault, phase short circuit fault and six-pulse short circuit fault.

2. A diagnostic method for locating an LCC valve interphase short circuit fault according to claim 1, characterized in that: The monitoring criteria include the first, second, third and fourth categories of criteria; assuming that the Y bridge AB phases are short-circuited in the preset circuit, define I VY is the valve side current value of the AC side star connection, I VD is the valve side current value of the AC side delta connection, I D is the DC side current value, I DCP is the DC voltage at the non-grounded end of the converter, I DNC is the DC voltage at the ground terminal of the converter, I D_NOM is the rated current value of the DC side, I set is the preset current value, U ABC is the AC side voltage, U set is the preset voltage value.

3. The diagnostic method for locating an LCC valve interphase short circuit fault according to claim 2, characterized in that: The first type of criterion includes the criterion of meeting the VSCP protection setting value, the AC side current and the DC side current meeting I VY >I D or I VD >I D When the AC current value is greater than the DC current value, the protection action is performed; where I VY , I VD are the valve side current values ​​of the AC side star connection and the AC side delta connection, I D Indicates the DC side current value.

4. The diagnostic method for locating an LCC valve interphase short circuit fault according to claim 2, characterized in that: The second type of judgment criteria includes bypass, lockout, and when the fault valve still has current after VSCP is activated, the bypass is defined as BPPO, which is 1 if the bypass is activated and 0 if it is not activated; the lockout is defined as BLOCK, which is 1 when the lockout occurs and 0 if it does not occur; the protection VSCP action is defined as 1 and 0 if it is not activated; IF(BPPO==1&BLOCK==1&VSCP==1),I VY 、I VD >(I set ); Among them, I set is the preset current value.

5. The diagnostic method for locating an LCC valve interphase short circuit fault according to claim 2, characterized in that: The third type of criterion includes: when the AC voltage and the valve side voltage exist or disappear at the same time, after the protection signal is issued for a preset time, the AC circuit breaker is disconnected, and the AC voltage and the valve side current disappear; IF(U ABC >U set );I VY 、I VD >(I set )&IF(U ABC <U set );I VY 、I VD <(I set ); Among them, I VY , I VD are the valve side current values ​​of the AC side star connection and the AC side delta connection, U ABC is the AC side voltage, I set is the preset current value, U set is the preset voltage value.

6. The diagnostic method for locating an LCC valve interphase short circuit fault according to claim 2, characterized in that: The fourth type of criterion includes that, in the two phases where the fault occurs, the AC side current amplitudes are the same and the directions are opposite, the two phase currents of the valve side fault are 50Hz, the 50Hz component is extracted, and the two phases where the 50Hz component suddenly increases are determined to be the fault phases.

7. A diagnostic system for locating interphase short circuit faults in LCC valves, characterized in that: include: Module M1: Collect relevant data; The data includes current value, voltage value and waveform characteristic value of 50Hz component; Module M2: Determine the fault type based on monitoring criteria and analyze the fault phase to complete diagnosis and positioning; The fault types include single valve short circuit fault, phase short circuit fault and six-pulse short circuit fault.

8. The diagnostic system for locating interphase short circuit faults of LCC valves according to claim 7, characterized in that: The monitoring criteria include the first, second, third and fourth categories of criteria; assuming that the Y bridge AB phases are short-circuited in the preset circuit, define I VY is the valve side current value of the AC side star connection, I VD is the valve side current value of the AC side delta connection, I D is the DC side current value, I DCP is the DC voltage at the non-grounded end of the converter, I DNC is the DC voltage at the ground terminal of the converter, I D_NOM is the rated current value of the DC side, I set is the preset current value, U ABC is the AC side voltage, U set is the preset voltage value.

9. The diagnostic system for locating an LCC valve interphase short circuit fault according to claim 8, characterized in that: The first type of criterion includes the criterion of meeting the VSCP protection setting value, the AC side current and the DC side current meeting I VY >I D or I VD >I D When the AC current value is greater than the DC current value, the protection action is performed; where I VY , I VD are the valve side current values ​​of the AC side star connection and the AC side delta connection, I D Indicates the DC side current value.

10. The diagnostic system for locating an LCC valve interphase short circuit fault according to claim 8, characterized in that: The second type of judgment criteria includes bypass, lockout, and when the fault valve still has current after VSCP is activated, the bypass is defined as BPPO, which is 1 if the bypass is activated and 0 if it is not activated; the lockout is defined as BLOCK, which is 1 when the lockout occurs and 0 if it does not occur; the protection VSCP action is defined as 1 and 0 if it is not activated; IF(BPPO==1&BLOCK==1&VSCP==1),I VY 、I VD >(I set ); Among them, I set is the preset current value.

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