Fault identification processing method and device for low-frequency side of low-frequency power transmission system

Abstract

The invention provides a fault identification processing method and device for a low-frequency side of a low-frequency power transmission system, and relates to the technical field of control. The method comprises the following steps: acquiring a three-phase voltage characteristic quantity and a three-phase current characteristic quantity of a low-frequency side of the low-frequency power transmission system; comparing the three-phase voltage characteristic quantity with a preset voltage characteristic quantity threshold value to obtain a first comparison result; comparing the three-phase current characteristic quantity with a preset current characteristic quantity threshold value to obtain three second comparison results; and determining a fault identification result of the low-frequency side of the low-frequency power transmission system according to the first comparison result and the three second comparison results. The device executes the method. According to the fault identification processing method and device for the low-frequency side of the low-frequency power transmission system provided by the embodiment of the invention, rapid fault identification of the low-frequency side of the low-frequency power transmission system can be realized.

Description

Technical Field

[0001] The present invention relates to the field of control technology, and in particular to a method and device for fault identification and processing on the low-frequency side of a low-frequency power transmission system. Background Art

[0002] Low-Frequency Transmission System (LFTS) is a new transmission technology that converts industrial frequency power into low frequency (such as 20Hz or 50 / 3Hz) for transmission. It combines the advantages of AC transmission and DC transmission, and has the advantages of high transmission efficiency, low loss, and no need to build offshore converter stations. It is particularly suitable for the transmission of long-distance offshore wind power. However, low-frequency transmission systems are significantly different from traditional power systems in terms of fault characteristics and protection methods. In particular, when an asymmetric fault occurs on the low-frequency side, fault identification and phasing face many challenges.

[0003] Offshore wind power low frequency transmission system Figure 1 As shown in the figure, power electronic devices such as modular multilevel matrix converter (M3C) and permanent magnet direct-drive wind turbine (PMSG) are highly controllable, but they exhibit complex electrical characteristics when faults occur, such as amplitude limitation and phase angle shift, making traditional protection methods difficult to apply. When an asymmetric fault occurs in a low-frequency transmission system, the characteristics of the fault current and voltage are significantly different from those of a traditional synchronous generator system. M3C will adopt complex control strategies during the fault, such as negative sequence current suppression and positive sequence current amplitude limitation, which increases the difficulty of fault identification. Power electronic devices respond quickly to faults, requiring protection devices to make accurate judgments in a short time. Traditional protection methods based on fundamental frequency phasors have a slow action speed in low-frequency systems and are difficult to meet the needs of rapid response. Summary of the invention

[0004] In view of the problems in the prior art, an embodiment of the present invention provides a method and device for fault identification and processing on the low-frequency side of a low-frequency power transmission system, which can at least partially solve the problems in the prior art.

[0005] On the one hand, the present invention provides a method for identifying and processing a fault on the low-frequency side of a low-frequency power transmission system, comprising:

[0006] Obtaining three-phase voltage characteristic quantities and three-phase current characteristic quantities on the low-frequency side of the low-frequency power transmission system;

[0007] Compare the three-phase voltage characteristic quantity with a preset voltage characteristic quantity threshold value to obtain a first comparison result; and compare the three-phase current characteristic quantity with a preset current characteristic quantity threshold value respectively to obtain three second comparison results;

[0008] A fault identification result of the low-frequency side of the low-frequency power transmission system is determined according to the first comparison result and the three second comparison results.

[0009] Wherein, determining the fault identification result of the low-frequency side of the low-frequency power transmission system according to the first comparison result and the three second comparison results includes:

[0010] If it is determined that the first comparison result is that the three-phase voltage characteristic quantity is less than the preset voltage characteristic quantity threshold, and at least one second comparison result is that the single-phase current characteristic quantity is greater than the preset current characteristic quantity threshold, then the fault identification result is determined to be abnormal.

[0011] Wherein, determining the fault identification result of the low-frequency side of the low-frequency power transmission system according to the first comparison result and the three second comparison results further includes:

[0012] If it is determined that the fault identification result is abnormal, the single phase causing the fault is determined based on the single-phase current characteristic quantity greater than the preset current characteristic quantity threshold.

[0013] Wherein, determining the preset voltage characteristic value threshold comprises:

[0014] The preset voltage characteristic value threshold is determined according to a first quantitative constraint relationship between the three-phase voltage and the voltage amplitude when the low-frequency power transmission system operates normally.

[0015] The step of determining the preset voltage characteristic value threshold according to the first quantitative constraint relationship between the three-phase voltage and the voltage amplitude when the low-frequency power transmission system is operating normally includes:

[0016] The first quantitative constraint relationship is as follows:

[0017]

[0018] Among them, u a (t),u b (t) and u c (t) is the three-phase voltage that changes with time t, U m is the voltage amplitude;

[0019] The first constant is used as the upper limit of the preset voltage feature value threshold, and the lower limit of the preset voltage feature value threshold is determined according to the lower limit of the fluctuation value interval of the first constant.

[0020] Wherein, determining the preset current characteristic value threshold comprises:

[0021] When the low-frequency power transmission system is operating normally, determining whether a fault occurs according to a second quantitative constraint relationship of low-frequency side phase currents corresponding to three consecutive sampling points;

[0022] Determine the upper limit of the low-frequency side phase current fluctuation when no fault occurs and determine the numerical range of the mutation multiple of the low-frequency side phase current when a fault occurs;

[0023] The preset current characteristic value threshold is determined according to the low-frequency side phase current fluctuation upper limit value and the mutation multiple value interval.

[0024] Wherein, when the low-frequency power transmission system is operating normally, determining whether a fault occurs according to the second quantitative constraint relationship of the low-frequency side phase currents corresponding to three consecutive sampling points respectively includes:

[0025] The second quantitative constraint relationship is as follows:

[0026] i 2 (t k-1 )-i(t k-2 )i(t k ) = Second constant

[0027] Among them, i(t k-2 )、i(t k-1 ) and i(t k ) are the low-frequency side phase currents corresponding to three consecutive sampling points;

[0028] If it is determined according to the second quantitative constraint relationship that the calculation result between the low-frequency side phase currents sampled three times in succession is equal to the second constant, it is determined that no fault has occurred;

[0029] If it is determined according to the second quantitative constraint relationship that the calculation result between the low-frequency side phase currents sampled three times in succession is not equal to the second constant, it is determined that a fault has occurred.

[0030] On the one hand, the present invention provides a fault identification and processing device for a low-frequency side of a low-frequency power transmission system, comprising:

[0031] An acquisition unit, used for acquiring three-phase voltage characteristic quantities and three-phase current characteristic quantities at the low-frequency side of the low-frequency power transmission system;

[0032] A comparison unit, configured to compare the three-phase voltage characteristic quantity with a preset voltage characteristic quantity threshold value to obtain a first comparison result; and to compare the three-phase current characteristic quantity with a preset current characteristic quantity threshold value respectively to obtain three second comparison results;

[0033] An identification unit is used to determine a fault identification result of the low-frequency side of the low-frequency power transmission system according to the first comparison result and the three second comparison results.

[0034] In another aspect, an embodiment of the present invention provides an electronic device, including: a processor, a memory, and a bus, wherein:

[0035] The processor and the memory communicate with each other via the bus;

[0036] The memory stores program instructions that can be executed by the processor, and the processor calls the program instructions to execute the following method:

[0037] Obtaining three-phase voltage characteristic quantities and three-phase current characteristic quantities on the low-frequency side of the low-frequency power transmission system;

[0038] Compare the three-phase voltage characteristic quantity with a preset voltage characteristic quantity threshold value to obtain a first comparison result; and compare the three-phase current characteristic quantity with a preset current characteristic quantity threshold value respectively to obtain three second comparison results;

[0039] A fault identification result of the low-frequency side of the low-frequency power transmission system is determined according to the first comparison result and the three second comparison results.

[0040] An embodiment of the present invention provides a non-transitory computer-readable storage medium, including:

[0041] The non-transitory computer-readable storage medium stores computer instructions, which cause the computer to execute the following method:

[0042] Obtaining three-phase voltage characteristic quantities and three-phase current characteristic quantities on the low-frequency side of the low-frequency power transmission system;

[0043] Compare the three-phase voltage characteristic quantity with a preset voltage characteristic quantity threshold value to obtain a first comparison result; and compare the three-phase current characteristic quantity with a preset current characteristic quantity threshold value respectively to obtain three second comparison results;

[0044] A fault identification result of the low-frequency side of the low-frequency power transmission system is determined according to the first comparison result and the three second comparison results.

[0045] The fault identification and processing method and device for the low-frequency side of a low-frequency power transmission system provided in an embodiment of the present invention obtain three-phase voltage characteristic quantities and three-phase current characteristic quantities on the low-frequency side of the low-frequency power transmission system; compare the three-phase voltage characteristic quantities with a preset voltage characteristic quantity threshold to obtain a first comparison result; and compare the three-phase current characteristic quantities with a preset current characteristic quantity threshold respectively to obtain three second comparison results; determine the fault identification result on the low-frequency side of the low-frequency power transmission system based on the first comparison result and the three second comparison results, thereby realizing rapid fault identification on the low-frequency side of the low-frequency power transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0047] Figure 1 It is a structural schematic diagram of an offshore wind power low-frequency transmission system provided by the prior art.

[0048] Figure 2 It is a flowchart of a fault identification and processing method on the low-frequency side of a low-frequency power transmission system provided by an embodiment of the present invention.

[0049] Figure 3 It is a flowchart of a fault identification and processing method on the low-frequency side of a low-frequency power transmission system provided by another embodiment of the present invention.

[0050] FIG4( a ) is a diagram of extracted characteristic quantities of three-phase voltage under criterion I of experimental verification 1 provided in an embodiment of the present invention.

[0051] FIG. 4( b ) is a diagram showing the extracted characteristic quantities of the a-phase current under criterion II of experimental verification 1 provided in an embodiment of the present invention.

[0052] FIG. 4( c ) is a diagram showing the extracted characteristic quantities of the b-phase current under criterion II of experimental verification 1 provided in an embodiment of the present invention.

[0053] FIG4( d ) is a diagram showing the extracted characteristic quantities of the c-phase current under criterion II of experimental verification 1 provided in an embodiment of the present invention.

[0054] FIG5( a ) is a diagram of extracted characteristic quantities of three-phase voltage under criterion I of experimental verification 2 provided in an embodiment of the present invention.

[0055] FIG5( b ) is a diagram showing the extracted characteristic quantities of the a-phase current under criterion II of experimental verification 2 provided in an embodiment of the present invention.

[0056] FIG5(c) is a diagram showing the extracted characteristic quantities of the b-phase current under criterion II of experimental verification 2 provided in an embodiment of the present invention.

[0057] FIG5(d) is a diagram showing the extracted characteristic quantities of the c-phase current under criterion II of experimental verification 2 provided in an embodiment of the present invention.

[0058] FIG6( a ) is a diagram of extracted characteristic quantities of three-phase voltage under criterion I of experimental verification 3 provided in an embodiment of the present invention.

[0059] FIG6( b ) is a diagram showing the extracted characteristic quantities of the a-phase current under criterion II of experimental verification 3 provided in an embodiment of the present invention.

[0060] FIG6( c ) is a diagram showing the extracted characteristic quantities of the b-phase current under criterion II of experimental verification 3 provided in an embodiment of the present invention.

[0061] FIG6( d ) is a diagram showing the extracted characteristic quantities of the c-phase current under criterion II of experimental verification 3 provided in an embodiment of the present invention.

[0062] FIG. 7( a ) is a schematic diagram illustrating the startup actions of Criterion I and Criterion II of Experimental Verification 1 provided in an embodiment of the present invention.

[0063] FIG. 7( b ) is a schematic diagram illustrating a fault phase of experimental verification 1 provided in an embodiment of the present invention.

[0064] FIG. 7( c ) is a schematic diagram illustrating the startup actions of Criterion I and Criterion II of Experimental Verification 2 provided in an embodiment of the present invention.

[0065] FIG. 7( d ) is a schematic diagram illustrating a fault phase of Experimental Verification 2 provided in an embodiment of the present invention.

[0066] FIG. 7( e ) is a schematic diagram illustrating the startup actions of Criterion I and Criterion II of Experimental Verification 3 provided in an embodiment of the present invention.

[0067] FIG. 7( f ) is a schematic diagram illustrating a fault phase of experimental verification 3 provided in an embodiment of the present invention.

[0068] Figure 8 It is a structural schematic diagram of a fault identification and processing device on the low-frequency side of a low-frequency power transmission system provided by an embodiment of the present invention.

[0069] Fig. 9 A schematic diagram of the physical structure of an electronic device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0070] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention more clear, the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention. It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other arbitrarily.

[0071] In response to the challenges faced by low-frequency transmission system protection, some new protection principles and technologies have emerged in recent years. For example, the method based on time domain model identification judges the fault by comparing the relationship between the line model and the actual measured voltage and current, avoiding the phase extraction process and being unaffected by system frequency changes, thereby improving the protection action speed. In addition, a method based on the singular spectrum distribution of current before and after the fault has also been proposed. This method performs singular value decomposition on the Hankel matrix composed of the current sampling values ​​before and after the fault, and constructs the protection criterion using the singular spectrum difference, effectively solving the problem of decreased sensitivity of traditional current differential protection in low-frequency transmission systems.

[0072] Despite these research advances, how to further improve the speed and accuracy of fault identification and fault phasing in low-frequency transmission systems, especially when asymmetric faults occur on the low-frequency side, remains an urgent problem to be solved.

[0073] Figure 2 FIG. 1 is a flow chart of a method for identifying and processing a fault on the low-frequency side of a low-frequency power transmission system provided by an embodiment of the present invention. Figure 2 As shown, the fault identification and processing method of the low-frequency side of the low-frequency power transmission system provided by the embodiment of the present invention includes:

[0074] Step S1: Obtain three-phase voltage characteristic quantities and three-phase current characteristic quantities on the low-frequency side of the low-frequency power transmission system.

[0075] Step S2: Compare the three-phase voltage characteristic quantity with the preset voltage characteristic quantity threshold value to obtain a first comparison result; and compare the three-phase current characteristic quantity with the preset current characteristic quantity threshold value respectively to obtain three second comparison results.

[0076] Step S3: Determine a fault identification result of the low-frequency side of the low-frequency power transmission system according to the first comparison result and the three second comparison results.

[0077] In the above step S1, the device obtains the three-phase voltage characteristic quantity and the three-phase current characteristic quantity of the low-frequency side of the low-frequency power transmission system. The device can be a computer device that executes the method, for example, a server. It should be noted that the acquisition and analysis of data involved in the embodiment of the present invention is authorized by the user. Figure 3 As shown, the current sensor and voltage sensor can be used to collect the instantaneous value of the three-phase current on the low-frequency side. x And the instantaneous value of three-phase voltage u x (x=a, b, c represents the corresponding phase voltage or phase current).

[0078] According to the instantaneous value of three-phase current i x And the instantaneous value of three-phase voltage u x , the three-phase voltage characteristic quantities and three-phase current characteristic quantities on the low-frequency side are calculated and extracted in real time.

[0079] In the above step S2, the device compares the three-phase voltage characteristic quantity with the preset voltage characteristic quantity threshold value to obtain a first comparison result; and compares the three-phase current characteristic quantity with the preset current characteristic quantity threshold value respectively to obtain three second comparison results. The first comparison result corresponds to the start criterion I, and the second comparison result corresponds to the start criterion II.

[0080] In the above step S3, the device determines the fault identification result of the low-frequency side of the low-frequency power transmission system according to the first comparison result and the three second comparison results. The method of determining the fault identification result of the low-frequency side of the low-frequency power transmission system according to the first comparison result and the three second comparison results includes:

[0081] If it is determined that the first comparison result is that the three-phase voltage characteristic quantity is less than the preset voltage characteristic quantity threshold, and at least one second comparison result is that the single-phase current characteristic quantity is greater than the preset current characteristic quantity threshold, then the fault identification result is determined to be abnormal.

[0082] The determining, according to the first comparison result and the three second comparison results, a fault identification result of the low-frequency side of the low-frequency power transmission system further includes:

[0083] If the fault identification result is determined to be abnormal, the single phase causing the fault is determined based on the single-phase current characteristic quantity greater than the preset current characteristic quantity threshold. If the single-phase current characteristic quantity greater than the preset current characteristic quantity threshold is one, for example, phase a, the single phase causing the fault is determined to be phase a.

[0084] If there are two single-phase current characteristic quantities greater than the preset current characteristic quantity threshold, for example, phase a and phase b, it is determined that the single phases causing the fault are phase a and phase b.

[0085] If there are three single-phase current characteristic quantities greater than the preset current characteristic quantity threshold, it is determined that the single phases causing the fault are phase a, phase b, and phase c.

[0086] The method of the present invention determines that a fault occurs on the low-frequency side of the low-frequency power transmission system only when both the start criterion I and the start criterion II are satisfied. If only the start criterion I is activated and the start criterion II is not activated, or the start criterion I is not activated and the start criterion II is activated, it is not determined that a fault occurs in the system. This is to avoid misjudgment caused by system power changes.

[0087] Determining the preset voltage characteristic value threshold includes:

[0088] The preset voltage characteristic value threshold is determined according to a first quantitative constraint relationship between the three-phase voltage and the voltage amplitude when the low-frequency power transmission system operates normally.

[0089] The step of determining the preset voltage characteristic value threshold value according to the first quantitative constraint relationship between the three-phase voltage and the voltage amplitude when the low-frequency power transmission system is operating normally includes:

[0090] The first quantitative constraint relationship is as follows:

[0091]

[0092] Among them, u a (t),u b (t) and u c (t) is the three-phase voltage that changes with time t, U m is the voltage amplitude;

[0093] The first constant is used as the upper limit of the preset voltage feature value threshold, and the lower limit of the preset voltage feature value threshold is determined according to the lower limit of the fluctuation value interval of the first constant.

[0094] When the system is operating normally, the three-phase voltage characteristic quantity on the low-frequency side, the sum of the squares of the three-phase voltage differences and the square of the voltage amplitude at any time, satisfies the first quantitative constraint relationship;

[0095] When the system is operating normally, the three-phase voltage on the low-frequency side is:

[0096]

[0097] Among them, U m is the voltage amplitude; ω is the angular frequency on the low-frequency side.

[0098] The first quantitative constraint relationship is:

[0099]

[0100] The first constant is 4.5. When the system is in normal operation, the three-phase voltage characteristic quantity on the low-frequency side fluctuates in the range of 4.42 to 4.58; however, at the moment of the fault, these characteristic quantities will drop significantly. Based on this, 4.5 can be used as the upper limit value of the preset voltage characteristic quantity threshold, and the preset amplitude value can be adjusted down on the basis of 4.42. For example, 4.1 can be used as the lower limit value of the preset voltage characteristic quantity threshold, and 4.2 can be selected as the preset voltage characteristic quantity threshold between the upper limit value of the preset voltage characteristic quantity threshold and the lower limit value of the preset voltage characteristic quantity threshold.

[0101] When the three-phase voltage characteristic quantity is less than a preset voltage characteristic quantity threshold, a fault signal f1=1 may be output; when the three-phase voltage characteristic quantity is greater than or equal to the preset voltage characteristic quantity threshold, a fault signal f1=0 may be output.

[0102] Determining the preset current characteristic value threshold includes:

[0103] When the low-frequency power transmission system is operating normally, determining whether a fault occurs according to a second quantitative constraint relationship of low-frequency side phase currents corresponding to three consecutive sampling points;

[0104] Determine the upper limit of the low-frequency side phase current fluctuation when no fault occurs and determine the numerical range of the mutation multiple of the low-frequency side phase current when a fault occurs;

[0105] The preset current characteristic value threshold is determined according to the low-frequency side phase current fluctuation upper limit value and the mutation multiple value interval.

[0106] The determining whether a fault occurs according to the second quantitative constraint relationship of the low-frequency side phase currents corresponding to three consecutive sampling points when the low-frequency power transmission system is operating normally includes:

[0107] The second quantitative constraint relationship is as follows:

[0108] i 2 (t k-1 )-i(t k-2 )i(t k ) = Second constant

[0109] Among them, i(t k-2 )、i(t k-1 ) and i(t k ) are the low-frequency side phase currents corresponding to three consecutive sampling points;

[0110] If it is determined according to the second quantitative constraint relationship that the calculation result between the low-frequency side phase currents sampled three times in succession is equal to the second constant, it is determined that no fault has occurred;

[0111] If it is determined according to the second quantitative constraint relationship that the calculation result between the low-frequency side phase currents sampled three times in succession is not equal to the second constant, it is determined that a fault has occurred.

[0112] When the system is operating normally, the low-frequency side phase current can be expressed as:

[0113] i(t)=I m sin(ωt+θ)

[0114] Among them, I m is the current amplitude, and θ is the initial phase angle.

[0115] The low-frequency side phase current is sampled at a sampling period of Ts to obtain the following formula:

[0116] i(t k )=I m sin(ωt k +θ)=I m sin(ωt k-1+θ+ωT s )

[0117] Using trigonometric transformation, the relationship between adjacent sampling values ​​of low-frequency side phase current can be obtained as follows:

[0118]

[0119] Then we can get the following formula by recursion method:

[0120]

[0121] Finally, the relationship between the three sampling points on the low-frequency side phase current and the phase current amplitude is as follows:

[0122]

[0123] The feature extraction calculation of the low-frequency side phase current is based on the relationship between the three sampling points on the low-frequency side phase current and the phase current amplitude. However, due to improper or too small selection of the sampling time interval Ts, the denominator of the relationship may be 2 (ωT s ) is zero or close to zero, so further optimization is needed to ensure the stability and accuracy of the calculation.

[0124] Considering that the characteristic quantity of the low-frequency side phase current is mainly used for fault phase determination, the optimization process only needs to extract the fault characteristics of this phase. Since the sampling frequency Ts is given in advance and the angular frequency ω of the system is also fixed, ωT s is a constant value. By omitting this constant term, the characteristic expression extracted from the three sampling points of the low-frequency side phase current is obtained, that is, the binary constraint relationship:

[0125] i 2 (t k-1 )-i(t k-2 )i(t k ) = Second constant

[0126] It is a constant when the system is operating normally, but changes suddenly when a system failure occurs.

[0127] The sampling time interval Ts is 10 microseconds.

[0128] Since the sampling time interval Ts is in microseconds, sin 2 (ωT s) is close to 0, so the characteristic quantity of the low-frequency side phase current fluctuates around 0.001 under normal system operation, and does not exceed 0.01 (the upper limit of the low-frequency side phase current fluctuation); however, at the moment of the fault, these characteristic quantities will show a significant mutation: the characteristic quantity of the non-fault phase will mutate to less than 10 times of the normal operation at most, and the characteristic quantity of the fault phase will mutate to more than 80-200 times (the mutation multiple numerical range) of the normal operation. In summary, the product of the upper limit of the low-frequency side phase current fluctuation and the lower limit of the mutation multiple numerical range can be used as the preset current characteristic quantity threshold, that is, 0.01×80=0.8.

[0129] When the low-frequency side phase current characteristic quantity is greater than the preset current characteristic quantity threshold value 0.8, the fault phase will be recorded and a fault signal fx(x=a, b, c)=1 will be output.

[0130] When the low-frequency side phase current characteristic value is less than or equal to the preset current characteristic value threshold value 0.8, the fault phase will be recorded and a fault signal fx(x=a, b, c)=0 will be output.

[0131] If the phase number of the recorded characteristic quantity is 1, it is determined that a single-phase fault has occurred in this phase; if the phase number of the recorded characteristic quantity is 2, it is determined that two phases of the record have failed; if the phase number of the recorded characteristic quantity is 3, it is determined that all three phases of the record have failed.

[0132] In order to verify the correctness of the method proposed in this invention, an offshore wind power low-frequency transmission system connected to the grid via M3C is built in PSCAD / EMTDC. The wind farm is connected to the M3C frequency conversion station on the shore via a low-frequency line and then connected to the industrial frequency grid.

[0133] Among them, the low-frequency line frequency is 20Hz, the voltage level is 330kV, the low-frequency line length is 120km, the line parameters are resistance 0.012Ω / km, inductance 0.207mH / km, capacitance 0.344μF / km; the wind farm has 200 wind turbines, each with a rated power of 5MW; the M3C rated voltage is 160kV, and the total rated power of the wind turbines is 1GW.

[0134] Based on experimental verification 1, the implementation effect of the method of the present invention is described as follows:

[0135] The fault point is set on the M3C low-frequency valve side. At t=2s, a single-phase ground short circuit occurs on phase A of the low-frequency valve side, which lasts for 0.5s.

[0136] As shown in Figure 4(a), it can be seen that after the fault occurs, the extracted feature quantity of the three-phase voltage on the low-frequency side drops below the threshold within 3ms after the fault occurs, and the judgment criterion I action is initiated.

[0137] As shown in Figure 4(b), it can be concluded that within 1ms of the fault, the maximum extracted characteristic value of the fault phase A current on the low-frequency side is about 0.95, which is 950 times that of normal operation (0.001 in normal operation). Criterion II is activated and phase A is recorded. As shown in Figures 4(c) and 4(d), the currents of the non-fault phases B and C on the low-frequency side are still fluctuating around the normal operating range and the current extraction characteristic value threshold is not triggered.

[0138] As shown in FIG7(a), the starting criterion II is activated within 1 ms, and the starting criterion I is activated within 3 ms. As shown in FIG7(b), it is finally determined to be a phase A fault.

[0139] Based on experimental verification 2, the implementation effect of the method of the present invention is described as follows:

[0140] The fault point is set at the M3C low-frequency valve side. At t=2s, a two-phase ground short circuit occurs on the BC phase of the low-frequency valve side, which lasts for 0.5s.

[0141] As shown in Figure 5(a), it can be seen that after the fault occurs, the extracted feature quantity of the three-phase voltage on the low-frequency side drops below the threshold within 1ms of the fault occurrence, and the judgment criterion I action is initiated.

[0142] As shown in Figure 5(b), it can be concluded that the extracted characteristic quantity of the non-fault phase A current on the low-frequency side fluctuates within the normal range and does not trigger the current extraction characteristic quantity threshold; while as shown in Figures 5(c) and 5(d), the maximum extracted characteristic quantities of the fault phases B and C on the low-frequency side exceed 2 and 1.5 respectively, which are greater than the current extraction characteristic quantity threshold, and the judgment criterion II action is initiated, and phases B and C are recorded.

[0143] As shown in Figure 7(c), both the start criterion I and the start criterion II are activated within 1ms, and as shown in Figure 7(d), it is finally determined to be a BC phase fault.

[0144] Based on experimental verification 3, the implementation effect of the method of the present invention is described as follows:

[0145] The fault point is set on the M3C low-frequency valve side. At t=2s, a ground short circuit occurs on the three phases of the low-frequency valve side, which lasts for 0.5s.

[0146] As shown in Figure 6(a), it can be seen that after the fault occurs, the extracted feature quantity of the three-phase voltage on the low-frequency side drops below the threshold within 1ms of the fault occurrence, and the judgment criterion I action is initiated.

[0147] As shown in Figure 6(b), Figure 6(c) and Figure 6(d), the maximum extracted characteristic quantities of the currents of the fault phases A, B and C on the low-frequency side exceed 0.9, 2 and 1.5 respectively, which are greater than the current extraction characteristic quantity threshold. The judgment criterion II action is initiated and the A, B and C phases are recorded.

[0148] As shown in Figure 7(e), both the start criterion I and the start criterion II are activated within 1ms, and as shown in Figure 7(f), it is finally determined to be a three-phase fault.

[0149] The fault identification and processing method for the low-frequency side of the low-frequency power transmission system provided by the embodiment of the present invention can complete the actions of the rapid identification start-up criterion I and the fault phasing start-up criterion II of the low-frequency side fault within 3ms, providing an effective solution for the rapid protection of the low-frequency side of the low-frequency power transmission system. In addition, the rapid fault identification method can also effectively prevent IGBT damage caused by overcurrent in the short period of time from the occurrence of the fault to the action of the circuit breaker to cut off the fault, thereby significantly improving the safety and stability of the low-frequency power transmission system. The simulation experiment results further confirmed the reliability and effectiveness of the protection mechanism.

[0150] The method provided in the embodiment of the present invention collects and analyzes real-time data of the three-phase voltage and its corresponding current of the low-frequency transmission line, extracts key characteristic parameters therefrom, and can then quickly determine whether there is a fault condition on the low-frequency side of the system, and accurately identify which specific phase has a problem.

[0151] The fault identification and processing method for the low-frequency side of a low-frequency power transmission system provided in an embodiment of the present invention obtains three-phase voltage characteristic quantities and three-phase current characteristic quantities on the low-frequency side of the low-frequency power transmission system; compares the three-phase voltage characteristic quantities with a preset voltage characteristic quantity threshold to obtain a first comparison result; and compares the three-phase current characteristic quantities with a preset current characteristic quantity threshold respectively to obtain three second comparison results; determines the fault identification result on the low-frequency side of the low-frequency power transmission system based on the first comparison result and the three second comparison results, thereby realizing rapid fault identification on the low-frequency side of the low-frequency power transmission system.

[0152] Further, determining the fault identification result of the low-frequency side of the low-frequency power transmission system according to the first comparison result and the three second comparison results includes:

[0153] If it is determined that the first comparison result is that the three-phase voltage characteristic quantity is less than the preset voltage characteristic quantity threshold, and at least one second comparison result is that the single-phase current characteristic quantity is greater than the preset current characteristic quantity threshold, then the fault identification result is determined to be abnormal. The above embodiments can be referred to for explanation and will not be repeated here.

[0154] Further, the determining of the fault identification result of the low-frequency side of the low-frequency power transmission system according to the first comparison result and the three second comparison results further includes:

[0155] If the fault identification result is determined to be abnormal, the single phase causing the fault is determined according to the single-phase current characteristic quantity greater than the preset current characteristic quantity threshold.

[0156] Further, determining the preset voltage characteristic value threshold includes:

[0157] The preset voltage characteristic value threshold is determined according to the first quantitative constraint relationship between the three-phase voltage and the voltage amplitude when the low-frequency power transmission system is operating normally.

[0158] Furthermore, the step of determining the preset voltage characteristic value threshold value according to the first quantitative constraint relationship between the three-phase voltage and the voltage amplitude when the low-frequency power transmission system is operating normally includes:

[0159] The first quantitative constraint relationship is as follows:

[0160]

[0161] Among them, u a (t),u b (t) and u c (t) is the three-phase voltage that changes with time t, U m is the voltage amplitude; please refer to the above embodiment for description and will not be repeated here.

[0162] The first constant is used as the upper limit of the preset voltage characteristic value threshold, and the lower limit of the preset voltage characteristic value threshold is determined according to the lower limit of the fluctuation value interval of the first constant.

[0163] Further, determining the preset current characteristic value threshold includes:

[0164] When the low-frequency power transmission system is operating normally, it is determined whether a fault occurs according to the second quantitative constraint relationship of the low-frequency side phase currents corresponding to three consecutive sampling points. The above description can be referred to and will not be repeated here.

[0165] Determine the upper limit of the low-frequency side phase current fluctuation when no fault occurs and determine the numerical range of the mutation multiple of the low-frequency side phase current when a fault occurs; refer to the above embodiment for description and no further details will be given.

[0166] The preset current characteristic value threshold is determined according to the low-frequency side phase current fluctuation upper limit value and the mutation multiple value interval. The above-mentioned embodiment can be referred to for explanation and will not be described in detail.

[0167] Furthermore, when the low-frequency power transmission system is operating normally, determining whether a fault occurs according to the second quantitative constraint relationship of the low-frequency side phase currents corresponding to three consecutive sampling points respectively includes:

[0168] The second quantitative constraint relationship is as follows:

[0169] i 2 (tk-1 )-i(t k-2 )i(t k ) = Second constant

[0170] Among them, i(t k-2 )、i(t k-1 ) and i(t k ) are low-frequency side phase currents corresponding to three consecutive sampling points respectively; the above description may be referred to and will not be repeated herein.

[0171] If it is determined according to the second quantitative constraint relationship that the calculation result between the low-frequency side phase currents sampled three times in succession is equal to the second constant, it is determined that no fault has occurred; the above-mentioned embodiment can be referred to for description and will not be repeated here.

[0172] If it is determined according to the second quantitative constraint relationship that the calculation result between the low-frequency side phase currents sampled three times in succession is not equal to the second constant, it is determined that a fault has occurred. The above-mentioned embodiments can be referred to for explanation and will not be described in detail.

[0173] Figure 8 FIG. 1 is a schematic diagram of a structure of a fault identification and processing device on the low-frequency side of a low-frequency power transmission system provided by an embodiment of the present invention. Figure 8 As shown, the fault identification and processing device for the low-frequency side of the low-frequency power transmission system provided by the embodiment of the present invention includes an acquisition unit 801, a comparison unit 802 and an identification unit 803, wherein:

[0174] The acquisition unit 801 is used to acquire the three-phase voltage characteristic quantities and the three-phase current characteristic quantities on the low-frequency side of the low-frequency power transmission system; the comparison unit 802 is used to compare the three-phase voltage characteristic quantities with the preset voltage characteristic quantity thresholds to obtain a first comparison result; and to compare the three-phase current characteristic quantities with the preset current characteristic quantity thresholds respectively to obtain three second comparison results; the identification unit 803 is used to determine the fault identification result on the low-frequency side of the low-frequency power transmission system based on the first comparison result and the three second comparison results.

[0175] Specifically, the acquisition unit 801 in the device is used to acquire the three-phase voltage characteristic quantity and the three-phase current characteristic quantity on the low-frequency side of the low-frequency power transmission system; the comparison unit 802 is used to compare the three-phase voltage characteristic quantity with the preset voltage characteristic quantity threshold to obtain a first comparison result; and to compare the three-phase current characteristic quantity with the preset current characteristic quantity threshold respectively to obtain three second comparison results; the identification unit 803 is used to determine the fault identification result on the low-frequency side of the low-frequency power transmission system according to the first comparison result and the three second comparison results.

[0176] The fault identification and processing device for the low-frequency side of a low-frequency power transmission system provided in an embodiment of the present invention obtains three-phase voltage characteristic quantities and three-phase current characteristic quantities on the low-frequency side of the low-frequency power transmission system; compares the three-phase voltage characteristic quantities with a preset voltage characteristic quantity threshold to obtain a first comparison result; and compares the three-phase current characteristic quantities with a preset current characteristic quantity threshold respectively to obtain three second comparison results; determines the fault identification result on the low-frequency side of the low-frequency power transmission system based on the first comparison result and the three second comparison results, thereby realizing rapid fault identification on the low-frequency side of the low-frequency power transmission system.

[0177] The embodiment of the present invention provides an embodiment of a fault identification and processing device on the low-frequency side of a low-frequency power transmission system, which can be specifically used to execute the processing flow of the above-mentioned method embodiments. Its functions are not repeated here, and reference can be made to the detailed description of the above-mentioned method embodiments.

[0178] Fig. 9 A schematic diagram of the physical structure of an electronic device provided by an embodiment of the present invention, such as Fig. 9 As shown, the electronic device includes: a processor (processor) 901, a memory (memory) 902 and a bus 903;

[0179] The processor 901 and the memory 902 communicate with each other via a bus 903;

[0180] The processor 901 is used to call the program instructions in the memory 902 to execute the methods provided by the above method embodiments, for example, including:

[0181] Obtaining three-phase voltage characteristic quantities and three-phase current characteristic quantities on the low-frequency side of the low-frequency power transmission system;

[0182] Compare the three-phase voltage characteristic quantity with a preset voltage characteristic quantity threshold value to obtain a first comparison result; and compare the three-phase current characteristic quantity with a preset current characteristic quantity threshold value respectively to obtain three second comparison results;

[0183] A fault identification result of the low-frequency side of the low-frequency power transmission system is determined according to the first comparison result and the three second comparison results.

[0184] This embodiment discloses a computer program product, which includes a computer program stored on a non-transitory computer-readable storage medium. The computer program includes program instructions. When the program instructions are executed by a computer, the computer can perform the methods provided by the above method embodiments, for example, including:

[0185] Obtaining three-phase voltage characteristic quantities and three-phase current characteristic quantities on the low-frequency side of the low-frequency power transmission system;

[0186] Compare the three-phase voltage characteristic quantity with a preset voltage characteristic quantity threshold value to obtain a first comparison result; and compare the three-phase current characteristic quantity with a preset current characteristic quantity threshold value respectively to obtain three second comparison results;

[0187] A fault identification result of the low-frequency side of the low-frequency power transmission system is determined according to the first comparison result and the three second comparison results.

[0188] This embodiment provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, wherein the computer program enables the computer to execute the methods provided by the above method embodiments, for example, including:

[0189] Obtaining three-phase voltage characteristic quantities and three-phase current characteristic quantities on the low-frequency side of the low-frequency power transmission system;

[0190] Compare the three-phase voltage characteristic quantity with a preset voltage characteristic quantity threshold value to obtain a first comparison result; and compare the three-phase current characteristic quantity with a preset current characteristic quantity threshold value respectively to obtain three second comparison results;

[0191] A fault identification result of the low-frequency side of the low-frequency power transmission system is determined according to the first comparison result and the three second comparison results.

[0192] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0193] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0194] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0195] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0196] In the description of this specification, the description with reference to the terms "one embodiment", "a specific embodiment", "some embodiments", "for example", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0197] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for identifying and processing faults on the low-frequency side of a low-frequency power transmission system, characterized in that: include: Obtaining three-phase voltage characteristic quantities and three-phase current characteristic quantities on the low-frequency side of the low-frequency power transmission system; Compare the three-phase voltage characteristic quantity with a preset voltage characteristic quantity threshold value to obtain a first comparison result; and compare the three-phase current characteristic quantity with a preset current characteristic quantity threshold value respectively to obtain three second comparison results; A fault identification result of the low-frequency side of the low-frequency power transmission system is determined according to the first comparison result and the three second comparison results.

2. The fault identification and processing method for the low-frequency side of the low-frequency power transmission system according to claim 1, characterized in that: Determining the fault identification result of the low-frequency side of the low-frequency power transmission system according to the first comparison result and the three second comparison results includes: If it is determined that the first comparison result is that the three-phase voltage characteristic quantity is less than the preset voltage characteristic quantity threshold, and at least one second comparison result is that the single-phase current characteristic quantity is greater than the preset current characteristic quantity threshold, then the fault identification result is determined to be abnormal.

3. The fault identification and processing method for the low-frequency side of the low-frequency power transmission system according to claim 2, characterized in that: The determining, according to the first comparison result and the three second comparison results, a fault identification result of the low-frequency side of the low-frequency power transmission system further includes: If it is determined that the fault identification result is abnormal, the single phase causing the fault is determined based on the single-phase current characteristic quantity greater than the preset current characteristic quantity threshold.

4. The fault identification and processing method for the low-frequency side of a low-frequency power transmission system according to claim 1, characterized in that: Determining the preset voltage characteristic value threshold includes: The preset voltage characteristic value threshold is determined according to a first quantitative constraint relationship between the three-phase voltage and the voltage amplitude when the low-frequency power transmission system operates normally.

5. The fault identification and processing method for the low-frequency side of the low-frequency power transmission system according to claim 4, characterized in that: The step of determining the preset voltage characteristic value threshold value according to the first quantitative constraint relationship between the three-phase voltage and the voltage amplitude when the low-frequency power transmission system is operating normally includes: The first quantitative constraint relationship is as follows: Among them, u a (t),u b (t) and u c (t) is the three-phase voltage that changes with time t, U m is the voltage amplitude; The first constant is used as the upper limit of the preset voltage feature value threshold, and the lower limit of the preset voltage feature value threshold is determined according to the lower limit of the fluctuation value interval of the first constant.

6. The fault identification and processing method for the low-frequency side of a low-frequency power transmission system according to claim 1, characterized in that: Determining the preset current characteristic value threshold includes: When the low-frequency power transmission system is operating normally, determining whether a fault occurs according to a second quantitative constraint relationship of low-frequency side phase currents corresponding to three consecutive sampling points; Determine the upper limit of the low-frequency side phase current fluctuation when no fault occurs and determine the numerical range of the mutation multiple of the low-frequency side phase current when a fault occurs; The preset current characteristic value threshold is determined according to the low-frequency side phase current fluctuation upper limit value and the mutation multiple value interval.

7. The fault identification and processing method for the low-frequency side of the low-frequency power transmission system according to claim 6, characterized in that: The determining whether a fault occurs according to the second quantitative constraint relationship of the low-frequency side phase currents corresponding to three consecutive sampling points when the low-frequency power transmission system is operating normally includes: The second quantitative constraint relationship is as follows: i 2 (t k-1 )-i(t k-2 )i(t k ) = second constant Among them, i(t k-2 )、i(t k-1 ) and i(t k ) are the low-frequency side phase currents corresponding to three consecutive sampling points; If it is determined according to the second quantitative constraint relationship that the calculation result between the low-frequency side phase currents sampled three times in succession is equal to the second constant, it is determined that no fault has occurred; If it is determined according to the second quantitative constraint relationship that the calculation result between the low-frequency side phase currents sampled three times in succession is not equal to the second constant, it is determined that a fault has occurred.

8. A fault identification and processing device for a low-frequency power transmission system at the low-frequency side, characterized in that: include: An acquisition unit, used for acquiring three-phase voltage characteristic quantities and three-phase current characteristic quantities at the low-frequency side of the low-frequency power transmission system; A comparison unit, configured to compare the three-phase voltage characteristic quantity with a preset voltage characteristic quantity threshold value to obtain a first comparison result; and to compare the three-phase current characteristic quantity with a preset current characteristic quantity threshold value respectively to obtain three second comparison results; An identification unit is used to determine a fault identification result of the low-frequency side of the low-frequency power transmission system according to the first comparison result and the three second comparison results.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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