Method, system, device and medium for evaluating transient voltage stability capability of receiving end power grid improved by synchronous generator

Abstract

The application provides a method, system, device and medium for evaluating transient voltage stability of a receiving end power grid supported by a synchronous generator, and belongs to the technical field of power system transient voltage stability. The method comprises the following steps: S1, performing multi-port Thevenin equivalence on the receiving end AC system from the DC transmission bus side and the new energy grid-connected bus side respectively; S2, based on the receiving end AC system after multi-port Thevenin equivalence, calculating the multi-infeed transient short-circuit ratio of the DC transmission bus and the multi-infeed transient short-circuit ratio of the new energy grid-connected bus; S3, determining the weight of different faults, the weight of the DC transmission bus and the weight of the new energy grid-connected bus based on the response of the receiving end AC system to the fault set, and calculating the comprehensive short-circuit ratio of the DC transmission bus and the comprehensive short-circuit ratio of the new energy grid-connected bus; S4, constructing an index system based on the comprehensive short-circuit ratio of the DC transmission bus, the comprehensive short-circuit ratio of the new energy grid-connected bus and the loss of the receiving end AC system; and S5, based on the index system, combining the subjective and objective combined weight and the TOPSIS improved by prospect theory, and comprehensively evaluating the transient voltage level of the receiving end AC system supported by the synchronous generator. The application improves the transient stability margin of the voltage of the DC transmission bus and the new energy grid-connected bus, and reduces the operation risk of DC blocking and new energy unit off-grid after power grid fault disturbance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system transient voltage stability, and in particular to a method, system and device for evaluating transient voltage stability of a receiving-end power grid improved by a synchronous generator, and a medium. BACKGROUND

[0002] Due to the reverse distribution characteristics of renewable energy and load centers, the problem of large-scale clean energy delivery is currently solved by extra-high voltage direct current transmission. The development and construction of new energy in the receiving-end power grid is rapid, and the peak output of new energy accounts for more than 50% of the proportion of electricity load at the same time. Therefore, the receiving-end power grid has or will have multiple direct current feed-in and coexistence of new energy operation scenarios.

[0003] However, the direct current feed-in and the access of new energy cause a large number of replacement of conventional generating units in the receiving-end power grid, a decrease in dynamic reactive power capacity of the load center, and a decrease in voltage support capability. At the same time, the direct current system not only does not provide reactive power support during a fault, but also absorbs a large amount of reactive power from the alternating current system during the recovery process.

[0004] Therefore, it is a technical problem to be solved by those skilled in the art to find a method that can not only improve the transient voltage stability of the power grid, but also reduce the risk of direct current blocking and new energy unit off-grid operation after power grid fault disturbance. SUMMARY

[0005] Therefore, the present application provides a method, system, device and medium for evaluating transient voltage stability of a receiving-end power grid improved by a synchronous generator, which can improve the transient stability margin of the direct current converter bus and the new energy grid-connected bus voltage, and reduce the risk of direct current blocking and new energy unit off-grid operation after power grid fault disturbance.

[0006] The technical solution of the present application is as follows:

[0007] In a first aspect, the present application provides a method for evaluating transient voltage stability of a receiving-end power grid improved by a synchronous generator, comprising the following steps:

[0008] S1, multi-port Thevenin equivalence is performed on the receiving-end alternating current system from the direct current converter bus side and the new energy grid-connected bus side, respectively;

[0009] S2, based on the receiving-end alternating current system after multi-port Thevenin equivalence, the multi-feed-in transient short-circuit ratio of the direct current converter bus and the multi-feed-in transient short-circuit ratio of the new energy grid-connected bus are calculated;

[0010] S3, the weights of different faults, the weight of the direct current converter bus and the weight of the new energy grid-connected bus are determined based on the response of the receiving-end alternating current system to the fault set, and the comprehensive short-circuit ratio of the direct current converter bus and the comprehensive short-circuit ratio of the new energy grid-connected bus are calculated.

[0011] S4, constructing an index system based on the comprehensive short-circuit ratio of the DC converter bus, the comprehensive short-circuit ratio of the new energy grid-connected bus and the loss of the receiving end AC system;

[0012] S5, based on the index system, combining the subjective and objective combined weights and the TOPSIS improved by the prospect theory, comprehensively evaluating the transient voltage level of the receiving end AC system supported by the synchronous generator.

[0013] On the basis of the above technical solutions, preferably, the step S3 specifically comprises:

[0014] S31, establishing a power flow analysis and transient stability calculation model of the receiving end power grid in a PSD-BPA power system analysis program, performing transient stability simulation calculation of the power grid based on the receiving end power grid and the fault set to obtain transient voltage data of nodes; wherein the receiving end power grid comprises a receiving end AC system, a DC converter bus, a new energy grid-connected bus and a synchronous generator;

[0015] S32, calculating a transient stability margin index based on a voltage transient response curve of the nodes;

[0016] S33, weighting different faults, the DC converter bus and the new energy grid-connected bus in the fault set, and calculating the weight of different faults and the weight of different buses;

[0017] S34, weighting the transient stability margin index of the bus voltage response to different fault disturbances by using a binomial coefficient method, and calculating the comprehensive short-circuit ratio under the fault set according to the weight of different faults and the weight of different buses.

[0018] On the basis of the above technical solutions, preferably, the calculation of the transient stability margin index adopts a multi-two table method, specifically comprising:

[0019] establishing a multi-two table (V crk , T crk ) of the duration T crk of the bus voltage drop below a certain voltage value V crk ;

[0020] determining a weight coefficient K k of the kth voltage drop based on the multi-two table;

[0021] calculating the transient voltage stability margin of the bus based on the multi-two table according to the weight coefficient, and the calculation formula is:

[0022]

[0023] wherein η represents the transient voltage stability margin of the bus based on the multi-two table, V min represents the lowest value of the bus voltage during the fault, and VN Indicates the rated voltage of the busbar, k indicates the number of voltage drop, K k represents the weight coefficient of the kth voltage drop, T cr,k Indicates that the bus voltage drops below the voltage value V crk Duration, V cr,k Indicates the voltage threshold of the kth voltage drop, V cr,k-1 represents the voltage threshold of the k-1th voltage drop, K1 represents the weight coefficient of the first voltage drop, V cr,1 Indicates the voltage threshold of the first voltage drop, V R Indicates the recovery level of the bus voltage after the fault ends.

[0024] On the basis of the above technical solution, preferably, the weights of the different faults and the weights of the different buses are calculated as follows:

[0025]

[0026] Among them, W fy represents the weight of different faults, x represents the bus number, y represents the fault number, η xy W represents the transient voltage stability margin of bus x to the yth fault. Bx Indicates the weights of different buses.

[0027] On the basis of the above technical solution, preferably, the calculation formula of the comprehensive short-circuit ratio under the fault set is:

[0028] K WMITSCR =∑ y ∑ x W fy W Bx K MITSCR ;

[0029] K WMITSCR-N =∑ y ∑ x W fy W Bx K MITSCR-N ;

[0030] Among them, K WMITSCR Indicates the comprehensive short-circuit ratio of the DC commutation bus, K MITSCR K represents the transient short-circuit ratio of the multi-infeed DC commutation busbar. WMITSCR-N Indicates the comprehensive short-circuit ratio of the new energy grid-connected busbar, K MITSCR-N Indicates the multi-infeed transient short-circuit ratio of the renewable energy grid-connected node.

[0031] Further preferably, the index system comprises a first sensitivity, a second sensitivity and a third sensitivity, the first sensitivity being a sensitivity of a comprehensive short-circuit ratio of a DC bus to a generator power factor change, the second sensitivity being a sensitivity of a comprehensive short-circuit ratio of a new energy grid-connected bus to the generator power factor change, and the third sensitivity being a sensitivity of a receiving-end AC system loss to the generator power factor change; wherein,

[0032] The calculation formula of the first sensitivity is:

[0033]

[0034] The calculation formula of the second sensitivity is:

[0035]

[0036] The calculation formula of the third sensitivity is:

[0037]

[0038] wherein K WMITSCR is the comprehensive short-circuit ratio of the DC bus, cosθ k is the power factor of the kth synchronous generator, K WMITSCR-N is the comprehensive short-circuit ratio of the new energy grid-connected bus, P loss is the receiving-end AC system loss.

[0039] On the basis of the above technical scheme, preferably, the step S5 specifically comprises:

[0040] S51, forming a data matrix according to the first sensitivity, the second sensitivity and the third sensitivity;

[0041] S52, establishing a judgment matrix of the first sensitivity, the second sensitivity and the third sensitivity, and respectively calculating comprehensive weights of the first sensitivity, the second sensitivity and the third sensitivity in the judgment matrix based on the data matrix; the comprehensive weights comprise subjective weights, objective weights and subjective-objective combined weights;

[0042] S53, based on the subjective weights, the objective weights and the subjective-objective combined weights, using the TOPSIS improved by the prospect theory to evaluate and sort the synchronous generators, so as to obtain the ability of different synchronous generators in the receiving-end AC system to improve the transient voltage stability of the receiving-end power grid.

[0043] In a second aspect, the present application provides an evaluation system for the ability of a synchronous generator to improve the transient voltage stability of a receiving-end power grid, which adopts the evaluation method as described above, and the system comprises:

[0044] A multi-port Thevenin equivalent module is configured to perform multi-port Thevenin equivalent on an AC receiving system from a DC transmission bus side and a new energy grid-connected bus side, respectively.

[0045] A short-circuit ratio calculation module is configured to calculate multi-infeed transient short-circuit ratios of the DC transmission bus and the new energy grid-connected bus based on the AC receiving system after multi-port Thevenin equivalent.

[0046] A comprehensive short-circuit ratio calculation module is configured to determine weights of different faults, weights of the DC transmission bus and weights of the new energy grid-connected bus based on responses of the AC receiving system to the fault set, and to calculate comprehensive short-circuit ratios of the DC transmission bus and the new energy grid-connected bus.

[0047] An index system construction module is configured to construct an index system based on the comprehensive short-circuit ratios of the DC transmission bus, the comprehensive short-circuit ratios of the new energy grid-connected bus and network loss of the AC receiving system.

[0048] A comprehensive evaluation module is configured to perform comprehensive evaluation on a transient voltage level of the AC receiving system supported by the synchronous generator based on the index system, combined subjective and objective combined weights and TOPSIS improved by prospect theory.

[0049] In a third aspect, the present application provides an electronic device, characterized in that comprising: at least one processor, at least one memory, a communication interface and a bus, wherein,

[0050] The processor, the memory and the communication interface complete communication with each other through the bus;

[0051] The memory stores program instructions executable by the processor, and the processor invokes the program instructions to implement the evaluation method as described above.

[0052] In a fourth aspect, the present application provides a computer readable storage medium, characterized in that the computer readable storage medium stores computer instructions, and the computer instructions make the computer implement the evaluation method as described above.

[0053] The evaluation method, system, device and medium of the present application have the following beneficial effects relative to the prior art:

[0054] (1) By calculating the multi-infeed transient short-circuit ratio of the DC converter bus and the new energy grid-connected bus, combined with the loss of the receiving end AC system, a comprehensive evaluation index system is established, the transient voltage stability capability of different synchronous generators in the system is evaluated and sorted, the transient stability margin of the DC converter bus and the new energy grid-connected bus voltage is improved, the operation risk of DC blocking and new energy unit off-grid after grid fault disturbance is reduced, and the influence of generator steady-state reactive power regulation on network loss is considered, which provides a basis for unit selection to improve the transient voltage stability of the system by using synchronous generator reactive power regulation;

[0055] (2) Based on the power network analysis theory and multi-infeed short-circuit ratio, combined with the multi-infeed transient short-circuit ratio of the DC converter bus and the new energy grid-connected bus calculated by the power system electromechanical transient simulation, the transient voltage stability of the receiving end AC system during fault process is quantified, and the ability of the receiving end AC system to withstand DC infeed and new energy access during transient process is evaluated;

[0056] (3) The comprehensive transient short-circuit ratio is calculated by fault set and bus weighting. The weighting method uses the minimum value of node voltage drop, voltage drop specified threshold duration and voltage recovery level. Compared with single binary table and direct calculation of transient voltage integral area, the calculation efficiency can be improved while the bus voltage transient margin is calculated more accurately, so that the weight calculation is more accurate and efficient. BRIEF DESCRIPTION OF DRAWINGS

[0057] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0058] Figure 1 The flowchart of the evaluation method of the present application;

[0059] Figure 2 The bus transient voltage drop multi-binary table and weight coefficient diagram of the evaluation method of the present application;

[0060] Figure 3 The improved IEEE30 node system wiring diagram of the evaluation method of the present application;

[0061] Figure 4 The equivalent diagram of the receiving end AC system from the DC converter bus of the evaluation method of the present application;

[0062] Figure 5This is a transient voltage variation curve diagram of the commutation bus node 3 of the improved IEEE 30-node system under a typical fault condition according to the evaluation method of the present invention. DETAILED DESCRIPTION

[0063] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0064] As those skilled in the art can understand, as an important regulating resource in the system, the synchronous generator can not only fill the active power shortage caused by DC faults, but also provide reactive power support for the system and improve the transient voltage stability of the receiving power grid.

[0065] like Figure 1 As shown, the present invention provides a method for evaluating the ability of a synchronous generator to improve the transient voltage stability of a receiving-end power grid, comprising the following steps:

[0066] S1. Perform multi-port Thevenin equivalence on the receiving-end AC system from the DC commutation bus side and the renewable energy grid-connected bus side respectively.

[0067] Specifically, in one embodiment of the present application, it is assumed that there are N nodes in the receiving-end AC system, of which there are m DC commutation buses and n new energy grid-connected buses, where m <N,n<N;

[0068] Taking the DC commutation bus as an example, assuming that the DC commutation bus m k (k <N)为第k个母线,则其对应的N×1维节点-端口矢量为:

[0069]

[0070] Among them, M k represents the 1×N-dimensional node-port vector corresponding to the k-th DC commutation bus;

[0071] Arranging all node-port association vectors in columns together forms the node-port association matrix of the DC commutation bus with N×m dimensions:

[0072] M D =[M1M2…M m ] (2)

[0073] Among them, M DM represents the node-port association matrix of the DC converter bus, M1 represents the node-port vector corresponding to the 1st DC converter bus, M2 represents the node-port vector corresponding to the 2nd DC converter bus, and Mm represents the node-port vector corresponding to the mth DC converter bus. m M represents the node-port association matrix of the DC converter bus, M1 represents the node-port vector corresponding to the 1st DC converter bus, M2 represents the node-port vector corresponding to the 2nd DC converter bus, and Mm represents the node-port vector corresponding to the mth DC converter bus.

[0074] The m x m order equivalent node impedance matrix of the multi-port Thevenin equivalent circuit of the receiving end AC system viewed from the m DC converter buses is:

[0075]

[0076] wherein, Z eq represents the m x m order equivalent node impedance matrix of the multi-port Thevenin equivalent circuit of the receiving end AC system viewed from the m DC converter buses, represents the transpose matrix of M D , Z represents the node impedance matrix of the original receiving end AC system, and M D represents the node-port association matrix of the DC converter bus.

[0077] Suppose that the original network equation of the receiving end AC system is:

[0078]

[0079] wherein, Y represents the node admittance matrix, represents the node voltage column vector, represents the node injected current column vector;

[0080] The Thevenin equivalent electromotive force is:

[0081]

[0082] wherein, represents the Thevenin equivalent electromotive force, represents the transpose matrix of M D , M represents the node voltage column vector of the original receiving end AC system; and

[0083] Therefore, the multi-port Thevenin equivalent circuit equation is:

[0084]

[0085] wherein, represents the voltage on the DC bus, represents the current on the DC bus.

[0086] It can be understood that the multi-port Thevenin equivalent circuit equation viewed from the n new energy converter buses is the same, and will not be repeated here.

[0087] ​S2. Based on the receiving-end AC system after multi-port Thevenin equivalent, calculate the multi-infeed transient short-circuit ratio of the DC commutation bus and the multi-infeed transient short-circuit ratio of the renewable energy grid-connected bus;

[0088] Specifically, the multi-infeed short-circuit ratio of the DC commutation bus node i' is defined as:

[0089]

[0090] in, represents the short-circuit ratio of multiple infeeds at the DC commutation bus node i', S aci’ P represents the short-circuit capacity of the receiving AC system at the DC busbar node i', deqi’ It represents the equivalent DC rated power at the DC commutation bus node i', U Ni’ represents the average rated voltage of the DC bus node i', I aci’ represents the three-phase short-circuit current of the DC commutation bus node i', P dNi’ represents the rated power of the DC system of the converter station at the DC bus node i', i' represents the specific DC bus node for which the multi-infeed short-circuit ratio is being calculated, j' represents other DC bus nodes except the DC bus node i', and Z i’j’ It represents the element of row i' and column j' of the equivalent node matrix viewed from the DC busbar, Z i’i’ represents the self-impedance of the equivalent receiving AC system node i', Z i’j’ represents the mutual impedance between DC commutation bus node i' and DC commutation bus node j', P dNj’ represents the rated power of the DC system of the converter station at node j'.

[0091] In one embodiment of the present application, it is assumed that at a certain moment, a fault occurs at a node in the receiving-end AC system, causing a voltage drop. At this time, the short-circuit current of the commutation bus node i' is:

[0092]

[0093] Among them, I aci’ It represents the three-phase short-circuit current of DC bus node i', U Ni’ represents the average rated voltage of the DC busbar node i', Z i’i’ represents the self-impedance of the DC commutation bus node i';

[0094] Substituting equation (5) into equation (7) yields the practical calculation formula for the multi-infeed transient short-circuit ratio of the DC commutation bus node i':

[0095]

[0096] in, Z represents the multi-infeed transient short-circuit ratio of the DC converter bus node i', Z Si’i’ Z represents the self-impedance of the DC converter bus node i' when all the synchronous generators in the system are opened after the fault occurs. NEi’i’ Z represents the self-impedance of the DC converter bus node i' when all the synchronous generators in the system are opened after the fault occurs.

[0097] Since the fault at a node in the system will change the voltage and injected current of each node, the short-circuit impedance of each node will also change accordingly, so it is necessary to correct the self-impedance of the receiving end AC system node in real time according to the simulation calculation results of the system.

[0098] S3, determining the weights of different faults, the weight of the DC converter bus and the weight of the new energy grid-connected bus based on the response of the receiving end AC system to the fault set, and calculating the comprehensive short-circuit ratio of the DC converter bus and the comprehensive short-circuit ratio of the new energy grid-connected bus.

[0099] Specifically, step S3 specifically includes:

[0100] S31, establishing a power flow analysis and transient stability calculation model of the receiving end power grid in the PSD-BPA power system analysis program, performing transient stability simulation calculation based on the receiving end power grid and the fault set to obtain transient voltage data of the nodes; wherein the receiving end power grid includes the receiving end AC system, the DC converter bus, the new energy grid-connected bus and the synchronous generator;

[0101] S32, calculating a transient stability margin index based on the voltage transient response curve of the node;

[0102] S33, weighting different faults, the DC converter bus and the new energy grid-connected bus in the fault set, and calculating the weight of different faults and the weight of different buses;

[0103] S34, weighting the transient stability margin index of the bus voltage response to different fault disturbances by using the binomial coefficient method, and calculating the comprehensive short-circuit ratio under the fault set according to the weight of different faults and different buses.

[0104] The present application is based on the power network analysis theory and the multi-infeed short-circuit ratio, and combines the multi-infeed transient short-circuit ratio of the DC converter bus and the new energy grid-connected bus calculated by the power system electromechanical transient simulation, quantifies the transient voltage stability of the receiving end AC system in the fault process, and realizes the ability evaluation of the receiving end AC system in the transient process to withstand the DC infeed and the new energy access.

[0105] In an embodiment of the present application, the equivalent grid-connected capacity of the new energy grid-connected node i is:

[0106]

[0107] wherein, Seqi represents the equivalent grid-connected capacity of the new energy grid-connected node i, S i represents the capacity of the new energy connected at the new energy grid-connected node i, S j represents the capacity of the new energy connected at the new energy grid-connected node j, U i represents the voltage of the new energy grid-connected node i, U j represents the voltage of the new energy grid-connected node j, Z ij represents the mutual impedance of the new energy grid-connected node i and the new energy grid-connected node j, Z ii represents the self-impedance of the new energy grid-connected node i;

[0108] The practical calculation formula of the multi-infeed transient short-circuit ratio of the new energy grid-connected node i is:

[0109]

[0110] wherein, K MITSCR-N represents the multi-infeed transient short-circuit ratio of the new energy grid-connected node i, U N represents the rated voltage of the new energy grid-connected node i, U Ti represents the voltage of the new energy grid-connected node i at a certain time after the fault occurs, U Tj represents the voltage of the new energy grid-connected node j at a certain time after the fault occurs, Z Tii represents the self-impedance of the new energy grid-connected node i after the fault occurs.

[0111] As shown in Figure 2 , the horizontal coordinate is time t, and the vertical coordinate is voltage V. In an embodiment of the present application, the calculation of the transient stability margin index adopts a multi-two table method, which specifically includes:

[0112] A multi-two table (V crk , T crk ) of the duration T crk of the bus voltage drop below a certain voltage value V crk is established;

[0113] The weight coefficient K k of the kth voltage drop is determined based on the multi-two table; the formula is:

[0114]

[0115] wherein, K n represents the weight coefficient of the nth voltage drop, V N represents the rated voltage of the bus, V cr,n represents the voltage threshold of the nth voltage drop, T cr,n represents the duration of the nth voltage drop below the voltage threshold V cr,n ;

[0116] The transient voltage stability margin of the bus based on the multi-binary table is calculated according to the weight coefficient, and the calculation formula is:

[0117]

[0118] wherein η represents the transient voltage stability margin of the bus based on the multi-binary table, V min represents the minimum value of the bus voltage during the fault, V N represents the rated voltage of the bus, k represents the serial number of the voltage drop, K k represents the weight coefficient of the kth voltage drop, T cr,k represents the duration that the bus voltage drop is lower than the voltage value V crk , V cr,k represents the voltage threshold of the kth voltage drop, V cr,k-1 represents the voltage threshold of the k-1th voltage drop, K1 represents the weight coefficient of the 1st voltage drop, V cr,1 represents the voltage threshold of the 1st voltage drop, V R represents the recovery level of the bus voltage after the fault ends.

[0119] Further, the weight calculation formula of different buses of the sum of the weights of different faults is:

[0120]

[0121]

[0122] wherein W fy represents the weight of different faults, x represents the bus number, y represents the fault number, η xy represents the transient voltage stability margin of the bus x to the yth fault, W Bx represents the weight of different buses.

[0123] In an embodiment of the present application, the fault includes three-phase short circuit, two-phase short circuit, single-phase short circuit, etc.

[0124] Further, the calculation formula of the comprehensive short-circuit ratio under the fault set is:

[0125] K WMITSCR =∑ y ∑ x W fy W Bx K MITSCR (16)

[0126] K WMITSCR-N =∑ y ∑ x W fy W Bx K MITSCR-N(17)

[0127] wherein K WMITSCR represents the comprehensive short-circuit ratio of the DC converter bus, K MITSCR represents the multi-infeed transient short-circuit ratio of the DC converter bus, K WMITSCR-N represents the comprehensive short-circuit ratio of the new energy grid-connected bus, K MITSCR-N represents the multi-infeed transient short-circuit ratio of the new energy grid-connected node.

[0128] The application calculates the comprehensive transient short-circuit ratio through a fault set and bus weighting. The weighting method used utilizes the minimum value of node voltage drop, voltage drop specified threshold duration and voltage recovery level. Compared with single binary table and direct calculation of transient voltage integral area, the method can more accurately calculate the bus voltage transient margin while improving the calculation efficiency, thereby more accurately and efficiently realizing weight calculation.

[0129] S4, constructing an index system based on the comprehensive short-circuit ratio of the DC converter bus, the comprehensive short-circuit ratio of the new energy grid-connected bus and the loss of the receiving end AC system.

[0130] Specifically, the index system includes a first sensitivity, a second sensitivity and a third sensitivity. The first sensitivity is the sensitivity of the comprehensive short-circuit ratio of the DC converter bus to the change of the power factor of the generator. The second sensitivity is the sensitivity of the comprehensive short-circuit ratio of the new energy grid-connected bus to the change of the power factor of the generator. The third sensitivity is the sensitivity of the loss of the receiving end AC system to the change of the power factor of the generator. Wherein,

[0131] The calculation formula of the first sensitivity is:

[0132]

[0133] The calculation formula of the second sensitivity is:

[0134]

[0135] The calculation formula of the third sensitivity is:

[0136]

[0137] wherein K WMITSCR is the comprehensive short-circuit ratio of the DC converter bus, cosθ k is the power factor of the kth synchronous generator, K WMITSCR-N is the comprehensive short-circuit ratio of the new energy grid-connected bus, P loss is the loss of the receiving end AC system.

[0138] S5, based on the index system, and combined with the subjective and objective combined weight and the TOPSIS improved by the prospect theory, the transient voltage level of the synchronous generator supporting the receiving end AC system is comprehensively evaluated.

[0139] Further, the step S5 specifically comprises:

[0140] S51, forming a data matrix according to the first sensitivity, the second sensitivity and the third sensitivity;

[0141] S52, establishing a judgment matrix of the first sensitivity, the second sensitivity and the third sensitivity, and based on the data matrix, respectively calculating the comprehensive weight of the first sensitivity, the second sensitivity and the third sensitivity in the judgment matrix; the comprehensive weight comprises a subjective weight, an objective weight and a subjective and objective combined weight;

[0142] S53, based on the subjective weight, the objective weight and the subjective and objective combined weight, using the TOPSIS improved by the prospect theory to evaluate and sort the synchronous generators, so as to obtain the ability of different synchronous generators in the receiving end AC system to improve the transient voltage stability of the receiving end power grid.

[0143] In an embodiment of the present application, the rows of the initial data matrix represent indexes, and the columns represent different synchronous generators.

[0144] In an embodiment of the present application, the judgment matrix R of the three indexes is established according to the opinions of L-bit experts, and the calculation formula of the subjective weight of each index in the judgment matrix is as follows:

[0145]

[0146] wherein, δ l represents the subjective weight of the lth index, R ln represents the element of the lth row and the nth column in the judgment matrix, and L represents the L-bit expert suggestion.

[0147] The initial data matrix X is standardized to obtain the normalized data matrix X s , and then the objective weight of each index is calculated:

[0148]

[0149] wherein, I τ represents the information entropy of the τth index, p μω represents the proportion of the element of the μth row and the ωth column in the normalized data matrix X s , x rt represents the element of the rth row and the τth column in the normalized data matrix X s , v τ represents the information utility value of the τth index, and ε τObjective weight of the τth index, v u Information utility value of the u th index;

[0150] The calculation formula of the subjective and objective combined weight is:

[0151]

[0152] Wherein, w τ Subjective and objective combined weight of the τth index, δ r Subjective weight of the r th index, δ τ Subjective weight of the τth index, ε r Objective weight of the r th index, ε τ Objective weight of the τth index.

[0153] In an embodiment of the present application, the improved TOPSIS based on prospect theory specifically includes:

[0154] The expected value of each index is given for m indexes to form an expected matrix Q.

[0155] Based on the original data matrix X, the index value and the expected matrix are standardized, and the formula is as follows:

[0156]

[0157] Wherein, x eq The element value of the e th row and the q th column in the standardized original data matrix X, q g The element value of the g th column in the standardized expected matrix Q, Q h The original element value of the h th column in the expected matrix Q;

[0158] The loss matrix S is calculated, and the calculation formula is as follows:

[0159]

[0160] Wherein, s cy The element value of the c th row and the y th column in the loss matrix S;

[0161] The prospect value matrix V is calculated by using the loss matrix S, and the calculation formula is:

[0162]

[0163] Wherein, V fq The element value of the f th row and the q th column in the prospect value matrix V, λ represents the loss aversion coefficient, α represents the risk coefficient of the income, and β represents the risk coefficient of the loss.

[0164] In an embodiment of the present application, when the risk coefficient a is 0.88 and the loss avoidance coefficient β is 2.25, the analysis result of the prospect theory is close to the decision result caused by the actual decision maker's psychology of the gains and losses.

[0165] In an embodiment of the present application, the specific steps of the improved TOPSIS of the prospect theory are as follows:

[0166] First, the positive and negative rational points are selected, and the calculation of the positive ideal point and the negative ideal point of the dth index is as follows:

[0167]

[0168] wherein, represents the positive ideal point of the dth index, represents the negative ideal point of the dth index, V sd represents the element of the s th row and the d th column in the prospect value matrix V;

[0169] For the z th synchronous generator, the distance between the z th synchronous generator and the positive ideal point and the negative ideal point is calculated:

[0170]

[0171] wherein, represents the weighted Euclidean distance between the z th synchronous generator and the positive ideal point, w τ represents the weight of the d th index, represents the weighted Euclidean distance between the i th synchronous generator and the negative ideal point;

[0172] According to the distance between each scheme and the positive ideal point and the negative ideal point, the closeness degree of each scheme can be calculated and sorted:

[0173]

[0174] wherein, d z represents the relative closeness degree of the z th synchronous generator.

[0175] The present application calculates the multi-infeed transient short-circuit ratio of the DC converter bus and the new energy grid-connected bus, combines with the loss of the receiving end AC system, establishes a comprehensive evaluation index system, realizes the evaluation and sorting of the transient voltage stability capability of different synchronous generators in the system, improves the transient stability margin of the DC converter bus and the new energy grid-connected bus voltage, reduces the operation risk of DC blocking and new energy unit off-grid after power grid fault disturbance, and at the same time, takes into account the influence of generator steady-state reactive power regulation on the loss of the grid, thereby providing a basis for the selection of units for improving the transient voltage stability of the system by using synchronous generator reactive power regulation.

[0176] In an embodiment of the present application, in order to verify the evaluation method of the synchronous generator for improving the transient voltage stability of the receiving end power grid coexisting with multi-infeed DC and new energy, the improved IEEE30 node system example is applied for simulation research.

[0177] As shown in Figure 3 , compared with the standard IEEE30 node system, in the improved IEEE30 node system provided by the present application, the synchronous generators at node 11 and node 13 are replaced with wind turbine generators, and a photovoltaic power station is additionally arranged at node 9. Two DC lines are infeed at node 3 and node 7. The capacity of the DC line and the new energy unit is as shown in Table 1. In addition, the synchronous generator capacity of node 1, node 2, node 5 and node 8 is 300MW, and the initial power factor is 0.9. It can be seen that the improved IEEE30 node system is a typical receiving end power grid coexisting with multi-infeed DC and new energy access.

[0178] As shown in Figure 4 , taking the DC converter bus as an example, the multi-port Thevenin equivalent of the receiving end AC system of the multi-infeed DC receiving end power grid from the converter bus is equivalent to the equivalent system, and the DC line rated power and new energy unit capacity are shown in Table 1:

[0179] Table 1

[0180]

[0181] The PSD-BPA establishes the power flow analysis and transient stability calculation model of the improved IEEE30 node system, and carries out transient stability simulation calculation based on typical faults. The selected typical faults are: {three-phase short circuit, single-phase short circuit, two-phase short circuit, two-phase to ground short circuit, three-phase line break, two-phase line break, single-phase line break, DC blocking, and DC power reverse}. Taking the converter bus node 3 as an example, the transient voltage change curve of node 3 under different faults is shown in Figure 5 , the horizontal coordinate is time, unit is cycle, and the vertical coordinate is voltage, unit is per unit (p.u.).

[0182] According to the simulation calculation results, the weights of different severe faults and the converter bus and the new energy grid-connected bus are calculated as shown in Tables 2 and 3.

[0183] Table 2

[0184]

[0185] Table 3

[0186] busbar node 3 node 7 node 9 node 11 node 13 weight value 0.4892 0.5108 0.3475 0.3075 0.3450

[0187] As can be seen from Table 2, the weight values of three-phase short circuit, two-phase short circuit and two-phase-to-ground short circuit are high, and the influence on the transient voltage stability of the system is large, and the weight values of DC blocking and DC power reversal and other DC faults are small, because the system has sufficient active power reserve and reactive power support capability, so the influence of DC fault on the transient voltage stability of the system is smaller than that of three-phase short circuit and two-phase short circuit fault.

[0188] The index values of different synchronous generators obtained by combining the weight values of different faults and different busbars are shown in Table 4. Among them, S Dk and S Nk are the sensitivities of the power factor change of the generator to the multi-infeed transient short circuit ratio of the converter bus and the multi-infeed transient short circuit ratio of the new energy grid-connected bus respectively, and both are more optimal index; S Lk is the sensitivity of the power factor change of the generator to the loss of the receiving end AC system, which is a more optimal index.

[0189] Table 4

[0190] node 1 node 2 node 5 node 8 [SA Dk ]]> 5.32 7.15 6.03 6.67 [SA Nk ]] 7.46 9.14 7.21 8.94 [SA Lk ]] 21.75 23.79 19.86 20.37

[0191] According to the index values, the comprehensive evaluation result is: node 2> node 8> node 5> node 1. That is, the ability of the synchronous generator of node 2 to improve the transient voltage stability of the system is stronger.

[0192] The application provides an evaluation system for a synchronous generator to improve the transient voltage stability of a receiving end power grid, which adopts the evaluation method described above, and comprises:

[0193] A multi-port Thevenin equivalent module is configured to perform multi-port Thevenin equivalent on the receiving end AC system from the DC converter bus side and the new energy grid-connected bus side respectively;

[0194] A short circuit ratio calculation module is configured to calculate the multi-infeed transient short circuit ratio of the DC converter bus and the multi-infeed transient short circuit ratio of the new energy grid-connected bus based on the receiving end AC system after multi-port Thevenin equivalent;

[0195] A comprehensive short circuit ratio calculation module is configured to determine the weights of different faults, the weight of the DC converter bus and the weight of the new energy grid-connected bus based on the response of the receiving end AC system to the fault set, and to calculate the comprehensive short circuit ratio of the DC converter bus and the comprehensive short circuit ratio of the new energy grid-connected bus;

[0196] An index system construction module is configured to construct an index system based on the comprehensive short circuit ratio of the DC converter bus, the comprehensive short circuit ratio of the new energy grid-connected bus and the loss of the receiving end AC system;

[0197] The comprehensive evaluation module is configured to perform comprehensive evaluation on the transient voltage level of the synchronous generator supported receiving end AC system based on the index system, in combination with the subjective and objective combined weight and the improved TOPSIS of the prospect theory.

[0198] The application provides an electronic device, comprising: at least one processor, at least one memory, a communication interface and a bus; wherein the processor, the memory and the communication interface complete mutual communication through the bus; the memory stores program instructions executable by the processor, and the processor invokes the program instructions to implement the evaluation method as described above.

[0199] The application provides a computer readable storage medium storing computer instructions, which make the computer implement the evaluation method as described above.

[0200] The above only describes the preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for evaluating the ability of a synchronous generator to improve the transient voltage stability of a receiving power grid, characterized in that: The following steps are involved: S1, perform multi-port Thevenin equivalent on the receiving end AC system from the DC commutation bus side and the renewable energy grid-connected bus side respectively; S2. Based on the receiving-end AC system after multi-port Thevenin equivalent, calculate the multi-infeed transient short-circuit ratio of the DC commutation bus and the multi-infeed transient short-circuit ratio of the renewable energy grid-connected bus; S3. Determine the weights of different faults, the weight of the DC commutation bus, and the weight of the renewable energy grid-connected bus based on the response of the receiving-end AC system to the fault set, and calculate the comprehensive short-circuit ratio of the DC commutation bus and the comprehensive short-circuit ratio of the renewable energy grid-connected bus; S4. Construct an index system based on the comprehensive short-circuit ratio of the DC commutation bus, the comprehensive short-circuit ratio of the new energy grid-connected bus, and the receiving-end AC system loss; S5. Based on the index system and combined with the subjective and objective combined weights and the improved TOPSIS of prospect theory, a comprehensive evaluation is conducted on the transient voltage level of the AC system at the receiving end of the synchronous generator support.

2. The method for evaluating the ability of a synchronous generator to improve the transient voltage stability of a receiving-end power grid according to claim 1, wherein: Step S3 specifically includes: S31. Establish a power flow analysis and transient stability calculation model for the receiving-end power grid in the PSD-BPA power system analysis program, perform grid transient stability simulation calculations based on the receiving-end power grid and the fault set, and obtain transient voltage data at the node; the receiving-end power grid includes the receiving-end AC system, DC commutation bus, renewable energy grid-connected bus, and synchronous generator; S32. Calculating a transient stability margin index based on a voltage transient response curve of a node; S33. Weighting different faults, DC commutation buses, and new energy grid-connected buses in the fault concentration to calculate weights of different faults and weights of different buses; S34. The binomial coefficient method is used to assign weights to the transient stability margin index of the bus voltage response to different fault disturbances, and the comprehensive short-circuit ratio under the fault set is calculated based on the weights of different faults and the weights of different buses.

3. The method for evaluating the ability of a synchronous generator to improve the transient voltage stability of a receiving-end power grid according to claim 2, wherein: The transient stability margin index is calculated using a multi-binary table method, specifically including: Establish bus voltage drop below a certain voltage value V crk Duration T crk Multi-binary table (V crk , T crk ); Determine the weight coefficient K of the kth voltage drop based on the multi-binary table k ; The transient voltage stability margin of the busbar based on the multi-binary table is calculated according to the weight coefficient. The calculation formula is: Where η represents the transient voltage stability margin of the bus based on the multi-binary table, V min Indicates the lowest value of bus voltage during fault, V N Indicates the rated voltage of the busbar, k indicates the number of voltage drop, K k represents the weight coefficient of the kth voltage drop, T cr,k Indicates that the bus voltage drops below the voltage value V crk Duration, V cr,k Indicates the voltage threshold of the kth voltage drop, V cr,k-1 represents the voltage threshold of the k-1th voltage drop, K1 represents the weight coefficient of the first voltage drop, V cr,1 Indicates the voltage threshold of the first voltage drop, V R Indicates the recovery level of the bus voltage after the fault ends.

4. The method for evaluating the ability of a synchronous generator to improve the transient voltage stability of a receiving-end power grid according to claim 3, wherein: The formula for calculating the weights of different faults and the weights of different buses is: Among them, W fy represents the weight of different faults, x represents the bus number, y represents the fault number, η xy W represents the transient voltage stability margin of bus x to the yth fault. Bx Indicates the weights of different buses, and max indicates the maximum value.

5. The method for evaluating the ability of a synchronous generator to improve the transient voltage stability of a receiving-end power grid according to claim 4, wherein: The calculation formula of the comprehensive short-circuit ratio under the fault set is: K WMITSCR =∑ y ∑ x W fy W Bx K MITSCR ; K WMITSCR-N =∑ y ∑ x W fy W Bx K MITSCR-N ; Among them, K WMITSCR Indicates the comprehensive short-circuit ratio of the DC commutation bus, K MITSCR K represents the transient short-circuit ratio of the multi-infeed DC commutation busbar. WMITSCR-N Indicates the comprehensive short-circuit ratio of the new energy grid-connected busbar, K MITSCR-N Indicates the multi-infeed transient short-circuit ratio of the renewable energy grid-connected node.

6. The method for evaluating the ability of a synchronous generator to improve the transient voltage stability of a receiving-end power grid according to claim 1, wherein: The index system includes a first sensitivity, a second sensitivity, and a third sensitivity. The first sensitivity is the sensitivity of the comprehensive short-circuit ratio of the DC commutation bus to the change in the generator power factor. The second sensitivity is the sensitivity of the comprehensive short-circuit ratio of the new energy grid-connected bus to the change in the generator power factor. The third sensitivity is the sensitivity of the receiving-end AC system network loss to the change in the generator power factor. The calculation formula of the first sensitivity is: The calculation formula of the second sensitivity is: The calculation formula of the third sensitivity is: where K WMITSCR is the comprehensive short-circuit ratio of the DC commutation bus, cosθ k is the power factor of the kth synchronous generator, K WMITSCR-N is the comprehensive short-circuit ratio of the new energy grid-connected busbar, P loss is the AC system network loss at the receiving end.

7. The method for evaluating the ability of a synchronous generator to improve the transient voltage stability of a receiving-end power grid according to claim 6, wherein: Step S5 specifically includes: S51, forming a data matrix according to the first sensitivity, the second sensitivity, and the third sensitivity; S52, establishing a judgment matrix of the first sensitivity, the second sensitivity, and the third sensitivity, and calculating the comprehensive weights of the first sensitivity, the second sensitivity, and the third sensitivity in the judgment matrix based on the data matrix; the comprehensive weights include subjective weights, objective weights, and subjective and objective combined weights; S53. Based on subjective weights, objective weights and subjective and objective combined weights, the synchronous generators are evaluated and ranked using TOPSIS improved by prospect theory, and the ability of different synchronous generators in the receiving-end AC system to improve the transient voltage stability of the receiving-end power grid is obtained.

8. An evaluation system for improving the transient voltage stability capability of a synchronous generator in a receiving-end power grid, characterized in that: The evaluation method according to any one of claims 1 to 7 comprises: A multi-port Thevenin equivalent module is configured to perform multi-port Thevenin equivalent on the receiving-end AC system from the DC commutation bus side and the renewable energy grid-connected bus side respectively; A short-circuit ratio calculation module is configured to calculate the multi-infeed transient short-circuit ratio of the DC commutation bus and the multi-infeed transient short-circuit ratio of the renewable energy grid-connected bus based on the receiving-end AC system after multi-port Thevenin equivalent; a comprehensive short-circuit ratio calculation module configured to determine the weights of different faults, the weight of the DC commutation bus, and the weight of the renewable energy grid-connected bus based on the response of the receiving-end AC system to the fault set, and calculate the comprehensive short-circuit ratio of the DC commutation bus and the comprehensive short-circuit ratio of the renewable energy grid-connected bus; An indicator system construction module is configured to construct an indicator system based on the comprehensive short-circuit ratio of the DC commutation bus, the comprehensive short-circuit ratio of the new energy grid-connected bus, and the network loss of the receiving-end AC system; The comprehensive evaluation module is configured as a TOPSIS method based on an indicator system and combined with subjective and objective combined weights and prospect theory to comprehensively evaluate the transient voltage level of the AC system at the receiving end of the synchronous generator support.

9. An electronic device, characterized in that: include: at least one processor, at least one memory, a communication interface, and a bus, wherein: The processor, memory, and communication interface communicate with each other via the bus; The memory stores program instructions that can be executed by the processor, and the processor calls the program instructions to implement the evaluation method according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that The computer-readable storage medium stores computer instructions, and the computer instructions enable the computer to implement the evaluation method according to any one of claims 1 to 7.

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