New energy bundled delivery line fault phase selection method based on resistance-inductance parameter homology minimum characteristic

Abstract

The invention discloses a new energy delivery line fault phase selection method based on a resistance-inductance parameter same-frequency minimum characteristic. The method comprises the following steps: establishing an opposite-side equivalent RLC network of a single-ended measurement signal; respectively analyzing the characteristics of the fault phase and the non-fault phase; analyzing resistance-inductance parameter characteristics of a receiving end system; constructing same-frequency minimum phase selection characteristics of resistance-inductance parameters; calculating resistance and inductance parameters of the RLC network through a recursive least square method RLS; and establishing a fault phase selection criterion. According to the method, only the single-end measurement signal is used for constructing the criterion, the calculated amount is small, the phase selection characteristic is remarkable, guidance of split-phase tripping can be provided for distance protection and other single-end in-situ protection, and execution of the reclosing process is assisted.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system fault identification, and in particular relates to a fault phase selection method for a new energy bundled transmission line based on minimum coherent characteristics of resistance and inductance parameters. Background Art

[0002] The concentrated development and long-distance transmission of new energy are the key to promoting the efficient consumption of new energy and resolving the problem of reverse distribution of sources and loads. As a result, a high proportion of new energy and thermal power bundled access to the power system has appeared in Gansu, Inner Mongolia and other regions in my country. The voltage level of the transmission line of this type of system is high, most of which are 500kV and above; the energy structure on the power supply side is complex, including many types of new energy and a high penetration rate of new energy. The fault phase selection configured in today's high-voltage lines is an important basis for realizing phase-by-phase tripping of local quantity protection. The high proportion and multi-type access of new energy on the power supply side has coupled and complex fault characteristics, which seriously interferes with the implementation of conventional fault phase selection methods, and the accuracy of fault phase selection faces great challenges.

[0003] At present, there are some main methods for improving fault phase selection of transmission lines of new energy stations, and they are divided according to the grid-connected type of new energy.

[0004] For example, for inverter power supplies, reference [1]: Liang Yingyu, Lu Zhengjie. Photovoltaic grid-connected inverter sequence impedance angle reconstruction scheme with enhanced adaptability of sequence component phase selection elements [J]. Electric Power Automation Equipment, 2022, 42(1): 133-139. Through the idea of ​​control-protection coordination, by adding certain controls to the inverter controller after a fault, the risks brought by the negative sequence suppression of the inverter power supply are resolved, and the electrical conditions for the traditional phase selection criteria are restored.

[0005] Reference [2]: Zhang Junfeng, Gao Liang, Shen Yifei, et al. Fault voltage sequence component phase selection element for doubly fed wind farm [J]. Power System Protection and Control, 2018, 46(10): 136-143. For doubly fed power sources, a new sequence component phase selection principle is constructed by compensating the phase angle of impedance.

[0006] Obviously, the improved phase selection method for renewable energy access mentioned above has obvious power source dependence characteristics, that is, it has good adaptability to a certain type of renewable energy access. At the same time, the application of the control-protection coordination concept for fault phase selection has a high degree of controllability and flexibility, but it may cover or conflict with the existing control objectives of renewable energy, and also depends on the power source type and injection source.

[0007] In summary, the known improved phase selection methods do not fully consider the scenarios with a high proportion of renewable energy and multi-type cluster access on the power supply side. The existing improved methods may not be suitable for the above scenarios, and there is a gap in the research on fault phase selection methods that are suitable for high-proportion renewable energy bundled transmission lines. Summary of the invention

[0008] In order to solve the problem that conventional fault phase selection criteria are difficult to adapt to high-proportion new energy bundling access, the present invention provides a new energy bundling transmission line fault phase selection method based on the minimum coherent characteristics of resistance and inductance parameters. The method is used as the basis of single-ended on-site quantity protection, and uses single-ended measurement signals to construct an equivalent operation network of its opposite network; through fault network analysis, the resistance and inductance parameter coherent minimization phase selection characteristics existing after the fault are clarified; the single-ended sudden change quantity measurement signal and the recursive least squares (RLS) method are used to calculate the equivalent resistance and inductance parameters on the opposite side, and finally a coherent change criterion that distinguishes between symmetry and asymmetry is constructed, and a fault phase selection criterion is constructed based on the judgment result of the coherent change, so as to realize accurate judgment of the fault phase after high-proportion multi-type new energy access.

[0009] The technical solution adopted by the present invention is:

[0010] The fault phase selection method for renewable energy bundled transmission lines based on the minimum coherent characteristics of resistance and inductance parameters includes the following steps:

[0011] Step 1: Establish an equivalent RLC network on the opposite side of the single-ended measurement signal;

[0012] Step 2: Analyze the characteristics of the fault phase and the non-fault phase respectively;

[0013] Step 3: Analyze the resistance and inductance parameter characteristics of the receiving system;

[0014] Step 4: Construct the phase selection characteristics of the coherent minimization of the resistance and inductance parameters;

[0015] Step 5: Calculate the resistance and inductance parameters of the RLC network by using the recursive least squares method RLS;

[0016] Step 6: Establish fault phase selection criteria.

[0017] In step 1, the single-ended measurement signal of the power supply side line is used as a reference to construct an equivalent RLC network on the opposite side, wherein the line is equivalent to a series-parallel combination of R, L, and C, the receiving end system is equivalent to a passive impedance, and the power supply behavior is described by the numerical change of the resistance and inductance parameters; in steady state, the parameters of the equivalent RLC network have the following relationship:

[0018]

[0019] In formula (1), subscript 0 represents the parameters of steady-state operation before the fault; R', L', C' represent the resistance, inductance, and capacitance parameters of the equivalent RLC network respectively; R, L, C represent the resistance, inductance, and capacitance parameters of the line respectively; R e(0) and L e(0) They respectively represent the equivalent resistance and inductance parameters of the receiving system before the fault.

[0020] In step 2, for the fault phase, the equivalent R, L, and C parameters after the fault can be derived from the fault network:

[0021]

[0022]

[0023] Where R', L', and C' represent the resistance, inductance, and capacitance parameters of the equivalent RLC network, respectively; R1 and R2 represent the line resistance on the left and right sides of the fault point, respectively; R e represents the equivalent resistance of the receiving end system after the fault; A represents the resistance additional coefficient on the right side of the fault point; L1 and L2 represent the line inductance on the left and right sides of the fault point respectively; L e represents the equivalent inductance of the receiving end system after the fault; B represents the additional inductance coefficient on the right side of the fault point; R f is the transition resistance; ω is the rated angular frequency.

[0024] It can be seen that in formula (3), no matter what the fault location and transition resistance are, the numerator is always smaller than the denominator, so the coefficient B is always less than 1; while A will be affected by R f , L e , and the impact of fault location.

[0025] For the non-fault phase, since its topological structure is the same as before the fault, the equivalent parameters of resistance, inductance and capacitance are expressed in the same way as in formula (1).

[0026] Since the capacitive reactance of the capacitor is much larger than the value of the resistor and inductor, it can be seen from equations (1) and (2) that the difference in the parameters of the equivalent RLC network after the fault is reflected between R and L, and C remains unchanged. Therefore, only the characteristic changes of R and L are concerned in the following.

[0027] In step 3, it can be known from the analysis of step 2 that the equivalent resistance-inductance parameters of the fault phase are related to the equivalent impedance parameters of the infinite system at the receiving end; taking the steady-state power flow direction of the line as the reference positive direction, during steady-state operation, the power absorbed by the infinite system at the receiving end can be equivalent to a positive impedance; and after the fault, the infinite system at the receiving end supplies reverse power to the fault point, and there are differences in the resistance-inductance parameters between the phases.

[0028] (1) Fault phase: Since the infinite receiving system supplies reverse power to the fault point, and the fault phase current provided by the infinite receiving system is the largest, R e and L e Compared with the fault, it drops significantly; at the same time, due to reverse power supply, the polarity is reversed, R e and L e Tends to be negative after a fault;

[0029] (2) Non-fault phase: In actual operation, considering the mutual inductance and coupling factors of the line, the current of the non-fault line may fluctuate slightly. Therefore, the R e and L e The change is small compared to before the failure.

[0030] In summary, the behavior of the resistance-inductance parameters of the infinite system at the receiving end can be described from the two aspects of numerical value and numerical polarity. It can be seen that the fault phase tends to a smaller negative value, while the non-fault phase remains basically unchanged compared to before the fault.

[0031] In step 4, the R of the infinite system at the receiving end obtained in step 3 is e and L e By bringing the characteristics into step 2, the variation law of the resistance and inductance parameters between the fault phase and the non-fault phase can be analyzed;

[0032] (1) Non-fault phase: Since the equivalent RLC network structure remains unchanged and the R e and L e Compared with the change before the fault, it is smaller. Finally, it can be seen from the expression of formula (1) that the non-fault equal-value resistance-inductance parameters R′ and L′ represented by the single-ended measurement signal of the power supply side line only have a small change after the fault;

[0033] (2) Fault phase: For the inductance L' parameter, since the coefficient B is always less than 1 and L e It decreases and tends to be negative. Combining equations (2) and (3), it can be seen that the inductance L' parameter of the fault phase is much smaller than the value of the non-fault phase and the steady state after the fault. At the same time, the change law of L' of the fault phase is significantly different from that of the non-fault phase. For the resistance R' parameter, since the R' of the non-fault phase remains unchanged, the change trend of the resistance R' parameter of the fault phase is different from that of the non-fault phase.

[0034] In addition, for the inductance parameter L', since the value of the fault phase L' after the fault is much smaller than the steady-state value before the fault, its change is negative. The change of the resistance and inductance parameters in the equivalent RLC network is characterized by the single-ended measurement of the three-phase voltage and current mutation, that is,

[0035] △L=L′-L ( ' 0) (4); In formula (4): △L is the change of inductance parameter; L' is the inductance parameter after the fault; L( ' 0) is the inductance parameter before fault.

[0036] In step 5, the voltage and current mutations measured at the power supply side line port are used as inputs, and the recursive least squares (RLS) method is applied to calculate the change in the resistance and inductance parameters in real time. The voltage and current equation of the single-port network is:

[0037]

[0038] Among them, u and i represent the voltage and current mutations on the M side respectively; t represents the time variable, R, L, and C are the resistance, capacitance, and inductance parameters of the equivalent network respectively; X1, X2, X3, and X4 are the four parameters to be determined output by the RLS algorithm respectively.

[0039] Rewrite equation (5) into a system linear equation:

[0040] Y(n)=H(n)X(n) (6);

[0041] In formula (5), Y(n) represents the dependent variable matrix of the system equation. Based on formula (5), we can know that Y(n) = [u(1)u(2)…u(n)] T , u(1)u(2)…u(n) represent the values ​​of the 1st, 2nd…nth voltage mutation respectively; H(n) is the input matrix, H(n)=[h(1)h(2)…h(n)] T , h(1)h(2)…h(n) represent the values ​​of the 1st, 2nd…nth sampling points in the input matrix respectively;

[0042] h(n)=[d 2 u / dt 2 du / dtdi / dti]; X(n) is the parameter matrix to be estimated, X(n) = [X1X2X3X4] T .

[0043] The recursion and parameter update formula of the RLS algorithm with forgetting factor is:

[0044]

[0045] Where n represents the current number of sampling points; λ represents the forgetting factor. K(n+1) represents the value of the gain vector corresponding to the n+1th sampling point; P(n+1) represents the value of the estimated error covariance matrix corresponding to the n+1th sampling point; X(n+1) represents the value of the parameter matrix to be estimated corresponding to the n+1th sampling point; h(n+1) represents the value of the n+1th sampling point in the input matrix;

[0046] y(n+1) represents the value of the system equation dependent variable matrix corresponding to the n+1th sampling point, that is, the value of the n+1th voltage mutation; P(n) corresponds to the value of the estimated error covariance matrix of the nth sampling point; h corresponds to the value of the parameter matrix to be estimated at the nth sampling point; T (n+1) Transposed vector of the value at the n+1th sample point in the input matrix.

[0047] The changes in resistance and inductance parameters obtained using RLS are:

[0048]

[0049] Among them, △R represents the change of the resistance parameter, and its value is equal to the fourth value X4 of the parameter matrix to be estimated by the RLS algorithm; △L represents the change of the inductance parameter, and its value is equal to the third value X3 of the parameter matrix to be estimated by the RLS algorithm.

[0050] In step 6, the resistance and inductance parameters of the three-phase equivalent network calculated in step 5 are used to calculate the Euclidean distance between the resistance and inductance of the three phases to characterize the coherent change trend, and a method for identifying the coherent change trend of symmetrical and asymmetrical faults is constructed, and finally a fault phase selection criterion is established. Including:

[0051] (1) Identification of coherent change trends:

[0052] The sliding data window is used to calculate the Euclidean distance of the phase-to-phase resistance and inductance parameters as an indicator of the coherent change trend. The calculation is as follows:

[0053]

[0054] In formula (8), L mn (n) represents the inductance Euclidean distance between phases m and n at the nth sampling point; the values ​​of m and n are A, B or C; D represents the total number of data points in the sliding data window. Considering the requirement of characteristic smoothness, the total number of data points of one cycle is taken; n represents the nth sampling point; N0 is the sampling point number after the judgment is started. △L m (i) represents the change in inductance parameter of phase m at the ith sampling point in the data window; △L n (i) represents the change in inductance parameter of phase n at the ith sampling point in the data window.

[0055] The Euclidean distance of resistors is the same as above, just replace L with R, and the calculation is as follows:

[0056]

[0057] Among them, R mn(n) represents the resistance Euclidean distance between phases m and n at the nth sampling point; the values ​​of m and n are A, B or C; D represents the total number of data points in the sliding data window. Considering the requirement of characteristic smoothness, the total number of data points of one cycle is taken; n represents the nth sampling point; N0 is the sampling point number after the judgment is started. △R m (i) represents the resistance parameter change of phase m at the ith sampling point in the data window; △R n (i) represents the resistance parameter change of the n-phase at the ith sampling point in the data window,

[0058] According to the characteristics of symmetrical and asymmetrical faults, different coherence change criteria are constructed.

[0059] The Euclidean distance of the three-phase parameters of symmetrical faults is small and theoretically approaches 0. The criterion shown in formula (9) is constructed to identify symmetrical faults.

[0060]

[0061] Among them, D Rmn The three-phase Euclidean distance representing the resistance parameter; the subscripts m and n are phase identifiers, which can be A, B or C; N0 is the sampling point number after the criterion is started; R mn (i) is the resistance Euclidean distance of the i-th sampling point; M is the average value calculation window; D set is the symmetric fault discrimination threshold;

[0062] The calculation of inductance parameters is similar, replacing R with L. The calculation is as follows:

[0063]

[0064] Among them, D Lmn The three-phase Euclidean distance representing the inductance parameter; the subscripts m and n are phase identifiers, which can be A, B or C; N0 is the sampling point number after the criterion is started; L mn (i) is the inductance Euclidean distance of the i-th sampling point; M is the average value calculation window; D set is the symmetric fault discrimination threshold;

[0065] There is always a trend of synchronous change between two phases in an asymmetric fault, so the synchronous change criterion of an asymmetric fault is:

[0066]

[0067] In formula (10), R mn Represents the resistance Euclidean distance between phases m and n; R xy represents the resistance Euclidean distance between the x and y phases; L mn Represents the inductance Euclidean distance between phases m and n; L xyIt represents the inductance Euclidean distance between phases x and y. For example, if mn is AB, then xy is BC or CA.

[0068] a and b are the adaptive comparison coefficients of resistance and inductance respectively.

[0069] (2) Fault phase selection criteria:

[0070] Based on the above-identified coherent change phase distinction, the fault phase selection criterion is constructed:

[0071]

[0072] Among them, △L p Indicates the change in the inductance parameter of the p phase; △L m represents the change in the inductance parameter of the m-phase; represents the change in the inductance parameter of the n-phase; && represents the logical "AND" operation.

[0073] The present invention provides a fault phase selection method for new energy bundled transmission lines based on the minimum coherent characteristic of resistance and inductance parameters, and the technical effects are as follows:

[0074] 1) The present invention performs fault phase selection based on the consistency change law of network parameters, is independent of the power source type, and has good adaptability to high-proportion bundled access of new energy on the power source side.

[0075] 2) The present invention only needs to calculate the voltage and current mutations on one side of the line without additional control, which complies with the basic principle of mutual coordination between fault phase selection and local protection such as distance protection.

[0076] 3) The method of the present invention is effective over the entire length of the line, has good tolerance to transition resistance, and can adapt to different fault ride-through behaviors of new energy power sources.

[0077] 4) This method has good adaptability to different types of high-proportion new energy access, is not affected by the fault location, and has a certain ability to tolerate transition resistance.

[0078] 5) This method only uses single-ended measurement signals to construct judgment criteria, with small calculation amount and significant phase selection characteristics. It can provide guidance for phase tripping for single-ended local protection such as distance protection and assist in the execution of the reclosing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] The present invention will be further described below in conjunction with the accompanying drawings and examples;

[0080] Figure 1 This is a schematic diagram of the high-proportion new energy bundled delivery scenario.

[0081] Figure 2 This is the contralateral equivalent operation network diagram for single-ended measurement.

[0082] Figure 3 This is the fault network diagram of the AG fault.

[0083] Figure 4 Schematic diagram of the behavior of resistance and inductance parameters of the infinite receiving end system.

[0084] Figure 5 The figure is a flow chart of the fault phase selection method based on the minimum characteristic of resistance-inductance parameter synchronization.

[0085] Figure 6(a) shows the phase selection result (resistance and inductance parameters) for AG fault;

[0086] Fig. 6(b) shows the phase selection result of AG fault (Euclidean distance of resistance and inductance parameters).

[0087] Figure 7(a) shows the phase selection result (resistance and inductance parameters) for AB fault;

[0088] Fig. 7(b) shows the phase selection result of AB fault (Euclidean distance of resistance and inductance parameters).

[0089] Figure 8(a) shows the phase selection result (resistance and inductance parameters) for ABC fault;

[0090] Fig. 8(b) shows the phase selection result of ABC fault (Euclidean distance of resistance and inductance parameters).

[0091] Figure 9(a) shows the phase selection result (resistance and inductance parameters) for the AG fault transition resistance of 300Ω;

[0092] Figure 9(b) shows the phase selection result (resistance-inductance parameter Euclidean distance) for the AG fault transition resistance of 300Ω.

[0093] Figure 10(a) shows the phase selection result (resistance and inductance parameters) of the AG fault at the head end of the line;

[0094] Figure 10(b) shows the phase selection result (Euclidean distance of resistance and inductance parameters) for the AG fault at the head end of the line. DETAILED DESCRIPTION

[0095] A fault phase selection method for high-proportion renewable energy bundled transmission lines based on the minimum coherence characteristics of resistance-inductance parameters. This method aims to solve the problem that the conventional fault phase selection method fails due to the access of new energy clusters to the power system. The resistance-inductance parameter characteristics of the equivalent system are identified through single-ended measurement signals, thereby realizing the judgment of the fault phase. Starting from the changing law of the consistency of the fault network parameters, this method describes the equivalent RLC network on the opposite side with a single-ended measurement signal. On the basis of analyzing the impedance behavior of the infinite power supply fault at the receiving end, a fault phase selection criterion is constructed based on the coherence minimization characteristics of the resistance-inductance parameters. The method includes the following steps:

[0096] Step 1: Model the equivalent RLC network on the opposite side of the single-ended measurement signal. Fault phase selection serves the single-ended local protection, and the judgment criteria should be constructed only with the electrical quantities measured on the single end. The opposite side of the measurement point on the power supply side, including the line and the infinite system on the receiving end, is equivalent to an equivalent RLC network. The line is a series-parallel relationship of R, L, and C; the infinite system on the receiving end is equivalent to a series model of R and L, and the fault behavior of the infinite system is taken into account in the law of change of its impedance.

[0097] Typical high-proportion new energy bundling delivery systems such as Figure 1 As shown, the voltage level of the transmission line is 500kV, and the power supply side includes typical new energy bundled access such as inverter type and double-fed type. Fault phase selection cooperates with local protection such as distance protection, so the measurement signal of the single end (M side) of the power supply side line is used as the benchmark to build an equivalent RLC passive operation network on the opposite side. The line is equivalent to a series-parallel combination of R, L, and C, and the receiving end system is equivalent to a passive impedance, and the power supply behavior is described by the numerical changes of the resistance and inductance parameters. The basic schematic diagram of the equivalent value is as follows Figure 2 As shown. In steady state, the parameters of the equivalent RLC network have the following relationship:

[0098]

[0099] Where: subscript 0 represents the parameters of steady-state operation before the fault; R', L', C' represent the resistance, inductance, and capacitance parameters of the equivalent RLC network respectively; R, L, C represent the resistance, inductance, and capacitance parameters of the line respectively; R e(0) and L e(0) They respectively represent the equivalent resistance and inductance parameters of the infinite system at the receiving end before the fault.

[0100] Step 2: Fault network analysis. Using the fault phase as a distinction, analyze the characteristics and change rules of equivalent resistance and inductance parameters of different phases after the fault.

[0101] Fault phase, its network is as follows Figure 3 As shown. Figure 3 The fault network shown can be derived, and the equivalent R, L, and C parameters after the fault are:

[0102]

[0103] Where R', L', and C' represent the resistance, inductance, and capacitance parameters of the equivalent RLC network, respectively; R1 and R2 represent the line resistance on the left and right sides of the fault point, respectively; R e represents the equivalent resistance of the infinite system at the receiving end after the fault; A represents the additional resistance coefficient on the right side of the fault point; L1 and L2 represent the line inductance on the left and right sides of the fault point respectively; L e represents the equivalent inductance of the infinite system at the receiving end after the fault; B represents the additional inductance coefficient on the right side of the fault point; Rf is the transition resistance; ω is the rated angular frequency.

[0104] It can be seen that in formula (3), no matter what the fault location and transition resistance are, the numerator is always smaller than the denominator, so the coefficient B is always less than 1; while A will be affected by R f , L e , and the impact of fault location.

[0105] For the non-fault phase, since its topological structure is the same as before the fault, the equivalent parameters of resistance, inductance and capacitance are expressed in the same way as in formula (1).

[0106] Since the capacitive reactance of the capacitor is much larger than the resistance and inductance, it can be seen from equations (1) and (2) that the difference in network parameters after the fault is mainly reflected between R and L, and C remains basically unchanged. Therefore, only the characteristic changes of R and L are concerned in the following.

[0107] Step three: Analysis of the resistance and inductance parameter characteristics of the infinite system at the receiving end. Taking the direction of steady-state power flow as the positive direction, determine the change law of the equivalent resistance and inductance parameters of the infinite system after the line fault, and use the size and positive and negative polarity of the resistance and inductance parameters to characterize the state after the fault. Through the analysis of step two, it can be seen that the equivalent resistance and inductance parameters of the fault phase are also related to the equivalent impedance parameters of the infinite system at the receiving end. Taking the steady-state power flow direction of the line as the reference positive direction, during steady-state operation, the infinite system at the receiving end absorbs power, which can be equivalent to a positive impedance;

[0108] After the fault, the infinite system at the receiving end supplies reverse power to the fault point, and there are large differences in the resistance and inductance parameters between phases.

[0109] (1) Fault phase. Since the infinite receiving system supplies reverse power to the fault point, and the fault phase current provided by the infinite receiving system is the largest, R e and L e Compared with the fault, it drops significantly; at the same time, due to reverse power supply, the polarity is reversed, R e and L e Tends to be negative after a fault.

[0110] (2) Non-fault phase. In actual operation, considering factors such as line mutual inductance and coupling, the current of the non-fault line may fluctuate slightly. Therefore, the R e and L e The change is small compared to before the failure.

[0111] In summary, the behavior of the resistance-inductance parameters of the infinite receiving system is described from the two aspects of numerical value and numerical polarity. It can be seen that the fault phase tends to a smaller negative value, while the non-fault phase remains basically unchanged compared to before the fault.

[0112] Step 4: Construct the coherent minimization phase selection feature. Consider the two parameters of resistance and inductance, bring the infinite impedance law obtained in step 3 into the fault network analysis conclusion of step 2, and construct the coherent minimization phase selection feature of resistance and inductance parameters. e and L e By bringing the characteristics into step 2, we can analyze the variation law of the resistance and inductance parameters between the fault phase and the non-fault phase.

[0113] (1) Non-fault phase: Since the equivalent RLC network structure remains unchanged and the R e and L e Compared with the change before the fault, it is smaller. Finally, it can be seen from the expression of formula (1) that the non-fault equal-value resistance-inductance parameters R′ and L′ represented by the single-ended measurement signal of the power supply side line only have a small change after the fault.

[0114] (2) Fault phase: For the inductance L' parameter, since the coefficient B is always less than 1 and L e It decreases and tends to be negative. Combining equations (2) and (3), it can be seen that the inductance L' parameter of the fault phase tends to be negative after the fault, and is much smaller than the value of the non-fault phase and the steady state. At the same time, the change law of L' of the fault phase is significantly different from that of the non-fault phase. For the resistance R' parameter, although it is coupled by many factors, since the R' of the non-fault phase is basically unchanged, the change trend of the resistance R' parameter of the fault phase is significantly different from that of the non-fault phase.

[0115] In summary, after a fault, the two parameters R' and L' in the equivalent RLC network have a coherent change trend, that is, for an asymmetric fault, there is always a coherent (synchronous) change of the two-phase parameters.

[0116] In addition, for the inductance parameter L', since the value of the fault phase L' after the fault is much smaller than the steady-state value before the fault, its change should be changed to negative. The change of the resistance and inductance parameters in the equivalent RLC network is characterized by the single-ended measurement of the three-phase voltage and current mutation, that is,

[0117] △L=L′-L ( ' 0) (4);

[0118] Where: △L is the change in inductance parameter; L' is the inductance parameter after the fault; L ( ' 0) is the inductance parameter before fault.

[0119] In summary, the method based on the equivalent RLC network has an obvious phase selection feature of coherent minimization in terms of resistance and inductance parameters.

[0120] Step 5: Online driving method of equivalent RLC network. The voltage and current mutation measured at the line port on the power supply side are used as input, and the resistance and inductance parameters of the equivalent network are calculated online through the recursive least squares (RLS) method.

[0121] by Figure 2 The voltage and current equations for the one-port network shown are:

[0122]

[0123] Among them, u and i represent the voltage and current mutations on the M side respectively; t represents the time variable, R, L, and C are the resistance, capacitance, and inductance parameters of the equivalent network respectively; X1, X2, X3, and X4 are the four parameters to be determined output by the RLS algorithm respectively.

[0124] Rewrite equation (5) into a system linear equation:

[0125] Y(n)=H(n)X(n) (6);

[0126] In the formula, Y(n) represents the dependent variable matrix of the system equation. Based on formula (5), we can know that Y(n) = [u(1)u(2)…u(n)] T ; H(n) is the input matrix, H(n) = [h(1)h(2)…h(n)] T , h(n)=[d 2 u / dt 2 du / dtdi / dti], where the first and second order derivatives of discretely sampled voltage and current are calculated by the difference method; X(n) is the parameter matrix to be estimated, X(n) = [X1X2X3X4] T .

[0127] The recursion and parameter update formula of the RLS algorithm with forgetting factor is:

[0128]

[0129] Wherein, K and P are the gain vector matrix and the covariance matrix respectively; n represents the current number of sampling points; h(n) is the independent variable matrix; y(n) is the input variable; λ represents the forgetting factor, which is taken as 0.96 in the present invention.

[0130] The initial values ​​X(n) and P(n) of the RLS algorithm iteration take the first four sets of data for adaptive calculation to increase the adaptability of the algorithm.

[0131] Step 6: Fault phase selection criteria. Aiming at the coherent minimization phase selection characteristics of the resistance and inductance parameters of the equivalent RLC network, the phase selection work is completed according to the process of coherent trend identification and phase selection criteria. Specifically, the resistance and inductance parameters of the three-phase equivalent network calculated in step 5 are used to calculate the Euclidean distance of the resistance and inductance between the three phases to characterize the coherent change trend, construct the coherent change identification method of symmetrical and asymmetrical faults, and finally establish the fault phase selection criteria.

[0132] (1) Identification of coherent change trends:

[0133] The sliding data window is used to calculate the Euclidean distance of the phase-to-phase resistance and inductance parameters as an indicator of the coherent change trend of resistance and inductance. The calculation method of the inductance parameter is as follows:

[0134]

[0135] Where, L mn represents the Euclidean distance of inductance; the subscripts m and n are phase identifiers, which can be A, B or C; D represents the total number of data points in the sliding data window. Considering the requirement of feature smoothness, the total number of data points in one cycle is taken; n represents the nth sampling point; N0 is the sampling point number after the judgment is started. The Euclidean distance of resistance is the same as the above formula, except that L needs to be replaced by R.

[0136] Symmetrical and asymmetric faults have different coherent change characteristics: the Euclidean distance of the three-phase parameters of a symmetrical fault is small and theoretically approaches 0; while for an asymmetric fault, there is always coherent change in the parameters of two phases, and the Euclidean distance between the two phases should be a certain larger value.

[0137] Firstly, the criterion shown in formula (7) is constructed to identify symmetric faults.

[0138]

[0139] Among them, D Rmn The three-phase Euclidean distance representing the resistance parameter; the subscripts m and n are phase identifiers, which can be A, B or C; N0 is the sampling point number after the criterion is started; R mn (i) is the resistance Euclidean distance of the i-th sampling point; M is the average value calculation window, which is 5 in this paper; D set is the symmetry fault judgment threshold, which is 1. The calculation of inductance parameters is similar, except that R is replaced by L.

[0140]

[0141] If equation (8) is satisfied, it is judged as a three-phase symmetrical fault, otherwise, the synchronization trend of an asymmetrical fault is judged.

[0142] There is always a trend of synchronous change between two phases in an asymmetric fault, so the synchronous change criterion of an asymmetric fault is:

[0143]

[0144] In the formula, the subscript xy represents a two-phase combination other than mn. For example, when mn is BC, xy is AB or CA. a and b are the adaptive comparison coefficients of resistance and inductance respectively. The calculation formulas of coefficients a and b are shown in formula (10).

[0145]

[0146] In the formula, K rel is the reliability coefficient. The present invention takes a smaller value to avoid the influence of the sudden increase in the early stage. rel Take 0.2; M represents the calculation length of the adaptive threshold, which is 5 in this paper; i represents the i-th sampling value.

[0147] (2) Fault phase selection criteria.

[0148] Based on the above-identified coherent phase difference, the fault phase selection criterion based on minimization of the fault phase inductance parameter can be constructed:

[0149]

[0150] In the formula, the subscript indicates the phase sign; && indicates the logical "AND" operation; △L indicates the inductance parameter calculated from the voltage and current mutation amount.

[0151] The flow chart of the fault phase selection method based on the minimum characteristic of resistance and inductance parameter synchronization is as follows: Figure 5 shown.

[0152] Verification example:

[0153] In order to verify the effectiveness of the fault phase selection method proposed in this invention, a system is built in PSCAD as follows: Figure 1 The high-proportion renewable energy bundled transmission model shown in the figure. The rated power of various energy sources on the power supply side is: thermal power 500MW, double-fed wind power 500MW, inverter photovoltaic 250MW. The system rated voltage is 500kV, and the line length is 300km; renewable energy is configured with low voltage ride-through strategy, negative sequence suppression, crowbar protection and other strategies according to the general control method. The voltage and current mutation on the M side are used for fault phase selection.

[0154] Scenario 1: Phase selection results for AG fault. An AG metallic grounding fault is set at the midpoint of the line, and the phase selection results are shown in Figures 6(a) and 6(b). As can be seen from Figure 6(a), the resistance and inductance parameters have a significant trend of synchronous change. By calculating the Euclidean distance of the resistance and inductance parameters, it can be seen that the non-fault phase (B and C phases are the smallest) is the smallest. The adaptive thresholds a and b calculated by formula (10) are 1.4 and 6.6, respectively, which meet the synchronous BC phase change criterion shown in formula (11). Further according to the criterion shown in formula (13), it can be seen that only ΔL A If it is less than zero, it is judged as a phase A fault.

[0155] Scenario 2: Phase selection results for AB fault. An AB fault is set at the midpoint of the line, and the results are shown in Figure 7(a) and Figure 7(b). The resistance and inductance parameters of the two faulty phases (phases A and B) have a coherent change trend. Correspondingly, in the Euclidean distance of the resistance and inductance parameters, AB is the smallest. Equations (11) and (12) can reliably determine that it is a coherent change of AB. Based on this result, it is further verified that only the inductance parameters of phases A and B are negative, and it is determined to be an AB fault.

[0156] Scenario 3: Phase selection results for ABC fault. An ABC fault is set at the midpoint of the line, and the results are shown in Figure 8(a) and Figure 8(b). The resistance and inductance parameters of the fault phases (A, B, and C phases) have a coherent change trend. Correspondingly, in the Euclidean distance of the resistance and inductance parameters, the distances of the three phases AB, BC, and CA are close. By calculating the average distance of the resistance and inductance parameters, it can be seen that the average maximum distances of the resistance and inductance are 0.22 and 0.01. According to formula (9), they are much smaller than the threshold setting, and are judged as three-phase coherent changes. Finally, according to the criterion shown in formula (13), among the inductance parameters, the three-phase parameters are all negative, and it is judged as an ABC fault.

[0157] Scenario 4: The results of the AG fault transition resistance of 300Ω are shown in Figures 9(a) and 9(b). As the transition resistance increases, the trend of synchronous change of the resistance and inductance parameters does not disappear. In particular, according to equations (2) and (3), the inductance parameters are not affected by the transition resistance. Therefore, in Figures 6(a), 6(b) and 9(a), 9(b), the convergence and magnitude of the inductance parameters are almost the same. The adaptive thresholds a and b calculated by equation (12) are 2.6 and 5.4, respectively, which meet the synchronous BC two-phase synchronous change criterion shown in equation (11). Further according to the criterion shown in equation (13), it can be seen that only ΔL A If it is less than zero, it is judged as a phase A fault.

[0158] Scenario 5: Phase selection for different penetration rates and wind-solar ratios, the results are shown in Table 1. Set the penetration rates of 0, 40, 60, 80, and 100 on the power supply side, and set different wind-solar ratios under each penetration rate. Even in the scenario where 100% of the new energy is connected to the power supply side, or there is no new energy on the power supply side (conventional synchronous power supply system), the method of the present invention can select the correct fault phase based on the established synchronization minimization index. It can be seen that the fault phase selection method based on the synchronization minimization of resistance-inductance parameters is not affected by the new energy penetration rate on the power supply side, does not limit the type of power supply, has good flexibility, and can adapt to the scenario of high-proportion new energy bundled transmission.

[0159] Table 1 Phase selection results for different penetration rates and different wind-solar ratios

[0160]

[0161] Scenario 6: Phase selection results at different fault locations. The results of the AG fault at the head end of the line are shown in Figures 10(a) and 10(b). As the fault location changes, the trend of synchronous changes in the resistance and inductance parameters does not disappear. In particular, according to equations (2) and (3), the inductance parameter is not affected by the fault location. Therefore, in Figures 6(a), 6(b) and 10(a), 10(b), the convergence and magnitude of the inductance parameters are almost the same. The adaptive thresholds a and b calculated by equation (12) are 1.7 and 4.1, respectively, which meet the synchronous BC two-phase change criterion shown in equation (11). Further according to the criterion shown in equation (13), it can be seen that only ΔL A If it is less than zero, it is determined to be a phase A fault. The results at the end of the line are similar to those at the head end, with significant coherence minimization features. The adaptive thresholds a and b are 3.2 and 7.2 respectively, and both can be reliably identified as phase A faults.

Claims

1. A fault phase selection method for renewable energy bundled transmission lines based on the minimum coherent characteristics of resistance and inductance parameters, characterized by The following steps are involved: Step 1: Establish an equivalent RLC network on the opposite side of the single-ended measurement signal; Step 2: Analyze the characteristics of the fault phase and the non-fault phase respectively; Step 3: Analyze the resistance and inductance parameter characteristics of the receiving system; Step 4: Construct the phase selection characteristics of the coherent minimization of the resistance and inductance parameters; Step 5: Calculate the resistance and inductance parameters of the RLC network by using the recursive least squares method RLS; Step 6: Establish fault phase selection criteria.

2. According to claim 1, the fault phase selection method for new energy bundled transmission lines based on the minimum coherent characteristic of resistance and inductance parameters is characterized by: In step 1, the single-ended measurement signal of the power supply side line is used as a reference to construct an equivalent RLC network on the opposite side, wherein the line is equivalent to a series-parallel combination of R, L, and C, the receiving end system is equivalent to a passive impedance, and the power supply behavior is described by the numerical change of the resistance and inductance parameters; in steady state, the parameters of the equivalent RLC network have the following relationship: In formula (1), subscript 0 represents the parameters of steady-state operation before the fault; R', L', C' represent the resistance, inductance, and capacitance parameters of the equivalent RLC network respectively; R, L, C represent the resistance, inductance, and capacitance parameters of the line respectively; R e(0) and L e(0) They respectively represent the equivalent resistance and inductance parameters of the receiving system before the fault.

3. According to claim 2, the fault phase selection method for new energy bundled transmission lines based on the minimum coherent characteristic of resistance and inductance parameters is characterized by: In step 2, for the fault phase, the equivalent R, L, and C parameters after the fault can be derived from the fault network: Where R', L', and C' represent the resistance, inductance, and capacitance parameters of the equivalent RLC network, respectively; R1 and R2 represent the line resistance on the left and right sides of the fault point, respectively; R e represents the equivalent resistance of the receiving end system after the fault; A represents the resistance additional coefficient on the right side of the fault point; L1 and L2 represent the line inductance on the left and right sides of the fault point respectively; L e represents the equivalent inductance of the receiving end system after the fault; B represents the additional inductance coefficient on the right side of the fault point; R f is the transition resistance; ω is the rated angular frequency; It can be seen that in formula (3), no matter what the fault location and transition resistance are, the numerator is always smaller than the denominator, so the coefficient B is always less than 1; while A will be affected by R f , L e , and the impact of fault location; For the non-fault phase, since its topological structure is the same as before the fault, the equivalent parameters of resistance, inductance and capacitance are expressed in the same way as in formula (1); Since the capacitive reactance of the capacitor is much larger than the value of the resistor and inductor, it can be seen from equations (1) and (2) that the difference in the parameters of the equivalent RLC network after the fault is reflected between R and L, and C remains unchanged. Therefore, only the characteristic changes of R and L are concerned in the following.

4. According to claim 3, the fault phase selection method for new energy bundled transmission lines based on the minimum coherent characteristic of resistance and inductance parameters is characterized by: In step 3, it can be obtained through the analysis of step 2 that the equivalent resistance and inductance parameters of the fault phase are related to the equivalent impedance parameters of the infinite system at the receiving end; taking the steady-state power flow direction of the line as the reference positive direction, during steady-state operation, the power absorbed by the infinite system at the receiving end can be equivalent to a positive impedance; and after the fault, the infinite system at the receiving end reversely supplies power to the fault point, and there are differences in the resistance and inductance parameters between the phases.

5. According to claim 4, the fault phase selection method for new energy bundled transmission lines based on the minimum coherent characteristic of resistance and inductance parameters is characterized by: In step 3: (1) Fault phase: Since the infinite receiving system supplies reverse power to the fault point, and the fault phase current provided by the infinite receiving system is the largest, R e and L e Significant drop compared to before the failure; At the same time, due to reverse power supply, the polarity is reversed, R e and L e Tends to be negative after a fault; (2) Non-fault phase: In actual operation, considering the mutual inductance and coupling factors of the line, the current of the non-fault line may fluctuate slightly. Therefore, the R e and L e Small change compared to before the failure; In summary, the behavior of the resistance-inductance parameters of the infinite system at the receiving end can be described from the two aspects of numerical value and numerical polarity. It can be seen that the fault phase tends to a smaller negative value, while the non-fault phase remains basically unchanged compared to before the fault.

6. The fault phase selection method for new energy bundled transmission lines based on the minimum coherent characteristic of resistance and inductance parameters according to claim 3 is characterized by: In step 4, the R of the infinite system at the receiving end obtained in step 3 is e and L e By bringing the characteristics into step 2, the variation law of the resistance and inductance parameters between the fault phase and the non-fault phase can be analyzed; (1) Non-fault phase: Since the equivalent RLC network structure remains unchanged and the R e and L e Compared with the change before the fault, it is smaller. Finally, it can be seen from the expression of formula (1) that the non-fault equal-value resistance-inductance parameters R′ and L′ represented by the single-ended measurement signal of the power supply side line only have a small change after the fault; (2) Fault phase: For the inductance L' parameter, since the coefficient B is always less than 1 and L e It decreases and tends to be negative. Combining equations (2) and (3), it can be seen that the inductance L' parameter of the fault phase is much smaller than the value of the non-fault phase and the steady state after the fault. At the same time, the change law of L' of the fault phase is significantly different from that of the non-fault phase. For the resistance R' parameter, since the R' of the non-fault phase remains unchanged, the change trend of the resistance R' parameter of the fault phase is different from that of the non-fault phase. In addition, for the inductance parameter L', since the value of the fault phase L' after the fault is much smaller than the steady-state value before the fault, its change is negative; the change of the resistance and inductance parameters in the equivalent RLC network is characterized by the single-ended measurement of the three-phase voltage and current mutation, that is, △L=L′-L ( ' 0) (4); In formula (4): △L is the change of inductance parameter; L' is the inductance parameter after the fault; L ( ' 0) is the inductance parameter before fault.

7. The fault phase selection method for new energy bundled transmission lines based on the minimum coherent characteristic of resistance and inductance parameters according to claim 1 is characterized by: In step 5, the voltage and current mutations measured at the power supply side line port are used as inputs, and the recursive least squares (RLS) method is applied to calculate the change in the resistance and inductance parameters in real time. The voltage and current equation of the single-port network is: Among them, u and i represent the voltage and current mutations on the M side respectively; t represents the time variable, R, L, and C represent the resistance, capacitance, and inductance parameters of the equivalent network respectively; X1, X2, X3, and X4 are the four parameters to be determined output by the RLS algorithm respectively; Rewrite equation (5) into a system linear equation: Y(n)=H(n)X(n) (6); In formula (5), Y(n) represents the dependent variable matrix of the system equation. Based on formula (5), we can know that Y(n) = [u(1)u(2)…u(n)] T , u(1)u(2)…u(n) represent the values ​​of the 1st, 2nd…nth voltage mutation respectively; H(n) is the input matrix, H(n)=[h(1) h(2)…h(n)] T , h(1)h(2)…h(n) represent the values ​​of the 1st, 2nd…nth sampling points in the input matrix respectively; h(n)=[d 2 u / dt 2 du / dtdi / dti]; X(n) is the parameter matrix to be estimated, X(n) = [X1X2X3X4] T ; The recursion and parameter update formula of the RLS algorithm with forgetting factor is: Where n represents the current number of sampling points; λ represents the forgetting factor; K(n+1) represents the value of the gain vector corresponding to the n+1th sampling point; P(n+1) represents the value of the estimated error covariance matrix corresponding to the n+1th sampling point; X(n+1) represents the value of the parameter matrix to be estimated corresponding to the n+1th sampling point; h(n+1) represents the value of the n+1th sampling point in the input matrix; y(n+1) represents the value of the system equation dependent variable matrix corresponding to the n+1th sampling point, that is, the value of the n+1th voltage mutation; P(n) corresponds to the value of the estimated error covariance matrix of the nth sampling point; h corresponds to the value of the parameter matrix to be estimated at the nth sampling point; T (n+1) the transposed vector of the value of the n+1th sample point in the input matrix; The changes in resistance and inductance parameters obtained using RLS are: Among them, △R represents the change of the resistance parameter, and its value is equal to the fourth value X4 of the parameter matrix to be estimated by the RLS algorithm; △L represents the change of the inductance parameter, and its value is equal to the third value X3 of the parameter matrix to be estimated by the RLS algorithm.

8. The fault phase selection method for new energy bundled transmission lines based on the minimum coherent characteristic of resistance and inductance parameters according to claim 7 is characterized by: In the step 6, the resistance and inductance parameters of the three-phase equivalent network calculated in step 5 are used to calculate the Euclidean distance of the resistance and inductance between the three phases to characterize the coherent change trend, and a method for identifying the coherent change trend of symmetrical and asymmetrical faults is constructed, and finally a fault phase selection criterion is established; including: (1) Identification of coherent change trends: The sliding data window is used to calculate the Euclidean distance of the phase-to-phase resistance and inductance parameters as an indicator of the coherent change trend. The calculation is as follows: In formula (8), L mn (n) represents the inductance Euclidean distance between phases m and n at the nth sampling point; the values ​​of m and n are A, B or C; D represents the total number of data points in the sliding data window. Considering the requirement of characteristic smoothness, the total number of data points of one cycle is taken; n represents the nth sampling point; N0 is the sampling point number after the judgment is started; △L m (i) represents the change in inductance parameter of phase m at the ith sampling point in the data window; △L n (i) represents the change in inductance parameter of phase n at the ith sampling point in the data window; The Euclidean distance of resistors is the same as above, just replace L with R, and the calculation is as follows: Among them, R mn (n) represents the resistance Euclidean distance between phases m and n at the nth sampling point; the values ​​of m and n are A, B or C; D represents the total number of data points in the sliding data window. Considering the requirement of characteristic smoothness, the total number of data points of one cycle is taken; n represents the nth sampling point; N0 is the sampling point number after the judgment is started; △R m (i) represents the resistance parameter change of phase m at the ith sampling point in the data window; △R n (i) represents the resistance parameter change of the n-phase at the ith sampling point in the data window. Different coherence change criteria are constructed according to the characteristics of symmetrical and asymmetrical faults. The Euclidean distance of the three-phase parameters of symmetrical faults is small and theoretically close to 0. The criterion shown in formula (9) is constructed to identify symmetrical faults. Among them, D Rmn The three-phase Euclidean distance representing the resistance parameter; the subscripts m and n are phase identifiers, which can be A, B or C; N0 is the sampling point number after the criterion is started; R mn (i) is the resistance Euclidean distance of the i-th sampling point; M is the average value calculation window; D set is the symmetric fault discrimination threshold; The calculation of inductance parameters is similar, replacing R with L; the calculation is as follows: Among them, D Lmn The three-phase Euclidean distance representing the inductance parameter; the subscripts m and n are phase identifiers, which can be A, B or C; N0 is the sampling point number after the criterion is started; L mn (i) is the inductance Euclidean distance of the i-th sampling point; M is the average value calculation window; D set is the symmetric fault discrimination threshold; There is always a trend of synchronous change between two phases in an asymmetric fault, so the synchronous change criterion of an asymmetric fault is: In formula (10), R mn Represents the resistance Euclidean distance between phases m and n; R xy represents the resistance Euclidean distance between the x and y phases; L mn Represents the inductance Euclidean distance between phases m and n; L xy It represents the inductance Euclidean distance between phases x and y; for example, if mn is AB, then xy is BC or CA; a and b are the adaptive comparison coefficients of resistance and inductance respectively; (2) Fault phase selection criteria: Based on the above-identified coherent change phase distinction, the fault phase selection criterion is constructed: Among them, △L p Indicates the change in the inductance parameter of the p phase; △L m represents the change in the inductance parameter of the m-phase; represents the change in the inductance parameter of the n-phase; && represents the logical "AND" operation.

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