Voltage transient evaluation method and device for power system with very high ratio of converters

Abstract

The application discloses a voltage transient state evaluation method and equipment for an extremely high proportion converter power system, wherein the method comprises the following steps: performing simulation analysis on voltage transient state evaluation; calculating node weight coefficients by comprehensively considering the electrical distance from a fault point, power flow contribution degree and node betweenness centrality; combining a transient voltage simulation result, performing weighted calculation on a node level index based on the obtained node weight coefficients, and constructing a system level transient voltage stability evaluation index system; and calculating the overall voltage stability score of the system according to the system level voltage stability evaluation index. The application proposes a set of voltage transient state evaluation indexes and calculation methods for the extremely high proportion converter system, which can quantitatively evaluate the system voltage stability performance and regulation capacity of the power grid under a fault scene, and provides a theoretical basis and technical support for planning and design, operation scheduling, control optimization and the like of the extremely high proportion converter power system. The application can be widely applied to the technical field of power systems.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power systems, in particular to a voltage transient state evaluation method and device for a power system with a very high proportion of converters. BACKGROUND

[0002] In response to the construction goal of "carbon peak and carbon neutral", new energy is widely connected to replace traditional fossil energy, and the proportion of traditional synchronous generators in the system is gradually decreasing. The wide connection of new energy, energy storage systems and DC converters leads to the characteristics of a very high proportion of converters in such systems, and the dynamic characteristics of the system gradually change from synchronous generator dominance to converter dominance. The inherent weak support characteristics of converter equipment and its coupling relationship with the power grid are prone to cause voltage fluctuations, oscillations and even collapse under fault disturbance, and the mechanism of system stability changes compared to the synchronous generator-dominated power grid, which poses a potential threat to the safety and reliability of the power grid.

[0003] In a power system with a very high proportion of converters, the complex cooperative response between high-penetration converters and the coupling of active and reactive power are significantly enhanced, making the system voltage dynamic characteristics under AC / DC disturbance present new changes, and the system voltage stability presents new mechanisms. In terms of voltage transient stability, most existing voltage transient evaluation methods are based on the characteristics of traditional power systems, and do not directly focus on the system-level situation of all node voltages in the system, making it difficult to be directly applied to this new system structure. SUMMARY

[0004] To at least partially solve one of the technical problems existing in the prior art, the purpose of the present application is to provide a voltage transient state evaluation method, device and medium for a power system with a very high proportion of converters.

[0005] The first technical solution adopted by the present application is:

[0006] A voltage transient state evaluation method for a power system with a very high proportion of converters, comprising the following steps:

[0007] Simulate and analyze the voltage transient state evaluation;

[0008] Calculate the node weight coefficient considering the electrical distance from the fault point, the power flow contribution degree and the node betweenness center;

[0009] Based on the obtained node weight coefficient, the node-level indicators are weighted and calculated in combination with the transient voltage simulation results, and a system-level transient voltage stability evaluation index system is constructed;

[0010] According to the system-level voltage stability evaluation index, the overall voltage stability score of the system is calculated.

[0011] Further, the calculation comprehensively considers the electrical distance from the fault point, the power flow contribution degree and the node weight coefficient of the node betweenness, including:

[0012] Define the electrical distance G1 from the fault point, the power flow contribution degree G2 and the node betweenness G3, and comprehensively calculate the node weight coefficient ω:

[0013]

[0014] In the formula, α j is the weight of each factor.

[0015] Further, the expression of the electrical distance G1 from the fault point is:

[0016]

[0017] In the formula, d i is the shortest electrical distance (sum of impedance) from node i to the fault point; max(d) is the maximum electrical distance of all nodes;

[0018] The expression of the power flow contribution degree G2 is:

[0019]

[0020] In the formula, P i is the power flow size of node i; max(P) is the maximum node power generation in the system;

[0021] The expression of the node betweenness G3 is:

[0022]

[0023] In the formula, b i is the betweenness of node i, indicating the contribution of the shortest path passing through the node to the total number of paths; max(b) is the maximum betweenness in the system;

[0024] The calculation formula of the betweenness b i of node i is as follows:

[0025]

[0026] In the formula, σ pq (i) represents the total number of shortest paths passing through node i between node p and node q; p and q are any different nodes in the network, and i is the node for which the betweenness is calculated.

[0027] Further, the system-level transient voltage stability evaluation index system comprises a weighted voltage sag extreme deviation index WVSD, a weighted low voltage recovery time LVRT, a weighted overvoltage duration time OVDT, a weighted voltage recovery steady state time VRST and a weighted steady state voltage deviation index SSVD.

[0028] The overall voltage stability score is calculated as follows:

[0029] S vol = λ1WVSD+ λ2LVRT+ λ3OVDT+ λ4VRST+ λ5SSVD

[0030] In the formula, λ k is a weight coefficient of the kth system-level index.

[0031] Further, the weighted voltage sag extreme deviation index WVSD is constructed as follows:

[0032] The voltage sag extreme deviation VSED is selected to evaluate the maximum deviation of node voltage sag:

[0033]

[0034] In the formula, v i (t) is the voltage of bus i at time t; is the original voltage of bus i before fault; t f is the system fault time, t c is the system fault clearing time; VSED i is used to measure the severity of voltage sag during the fault, reflecting the transient voltage performance of the system at the time of fault;

[0035] Based on the voltage sag extreme deviation VSED i The penalty value of bus i is defined as:

[0036]

[0037] In the formula, k is a penalty amplitude adjustment coefficient, used to control the influence of the voltage sag degree; v saglim represents the critical value of voltage sag;

[0038] The overall network weighted voltage sag deviation score is used to evaluate the overall voltage sag characteristics of the system; combined with the importance weight of different buses, the system-level comprehensive deviation score of the overall network voltage sag is obtained through weighted summation:

[0039]

[0040] In the formula, ω i ​ωi is the importance weight of bus i, and N is the number of system buses.

[0041] Further, the weighted low voltage recovery time LVRT is constructed as follows:

[0042] Let be the first voltage drop of bus i to v lowlim The time above, be the first voltage recovery of bus i to v lowlim The time above, v lowlim is the critical value of low voltage, then the low voltage recovery time of bus i is defined as:

[0043]

[0044] The low voltage recovery time of all nodes is weighted and summed to obtain the weighted low voltage recovery time LVRT of the whole network:

[0045]

[0046] In the formula, ω i is the importance weight of bus i, and N is the number of system buses.

[0047] Further, the weighted overvoltage duration OVDT is constructed as follows:

[0048] The overvoltage duration of bus i is evaluated in segments It is divided into two parts:

[0049] 1) The duration of bus i voltage between v max and v crit ;

[0050] 2) The duration of bus i voltage exceeding v crit ;

[0051]

[0052] In the formula, k1 and k2 are segmented linear penalty coefficients, v max is the upper limit value of normal operation of voltage, and v crit represents a higher critical value of overvoltage;

[0053] The weighted overvoltage index of the whole network is constructed as follows:

[0054]

[0055] In the formula, ω i is the importance weight of bus i, and N is the number of system buses.

[0056] Further, the weighted voltage recovery steady state time VRST is constructed as follows:

[0057] For each bus i, let be the time when the voltage first falls below v min or rises above v max , be the time when the voltage recovers to steady state and remains stable without deviation; v max be the upper limit of the voltage in normal operation, v min be the lower limit of the voltage in normal operation; the voltage recovery time of bus i is defined as:

[0058]

[0059] The voltage recovery times of all buses are weighted and summed to form the recovery time score of the entire network; the voltage recovery steady state time index is defined as follows:

[0060]

[0061] where ω i is the importance weight of bus i, and N is the number of system buses.

[0062] Further, the weighted steady state voltage deviation index SSVD is constructed as follows:

[0063] Let be the steady state voltage value of bus i after fault; define that after the voltage enters [v min , v max ], and does not leave this range, it is considered to have entered a new steady state; v max be the upper limit of the voltage in normal operation, v min be the lower limit of the voltage in normal operation;

[0064] For buses with steady state voltage below v min or above v max , calculate the steady state voltage deviation penalty factor

[0065]

[0066] The steady state voltage penalty values of all buses are weighted and summed to obtain the steady state voltage deviation score of the entire network:

[0067]

[0068] where ω i is the importance weight of bus i, and N is the number of system buses.

[0069] The second technical solution adopted by the present application is:

[0070] An electronic device, comprising a processor and a memory, the memory storing at least one instruction, at least one program, a code set or an instruction set, the at least one instruction, the at least one program, the code set or the instruction set being loaded and executed by the processor to implement the voltage transient evaluation method for the ultra-high ratio converter power system as described above.

[0071] The third technical solution adopted by the present application is:

[0072] A computer readable storage medium, the storage medium storing at least one instruction, at least one program, a code set or an instruction set, the at least one instruction, the at least one program, the code set or the instruction set being loaded and executed by a processor to implement the voltage transient evaluation method for the ultra-high ratio converter power system as described above.

[0073] The fourth technical solution adopted by the present application is:

[0074] A computer program product or computer program, the computer program product or computer program comprising computer instructions stored in a computer readable storage medium. The processor of the computer device can read the computer instructions from the computer readable storage medium, and the processor executes the computer instructions, so that the computer device executes the voltage transient evaluation method for the ultra-high ratio converter power system as described above.

[0075] The beneficial effects of the present application are: the present application proposes a set of voltage transient evaluation indexes and calculation methods for the ultra-high ratio converter system, which can quantitatively evaluate the system voltage stability performance and regulation capacity of the power grid under fault scenarios, and provide theoretical basis and technical support for the planning and design, operation and dispatch, control optimization and other aspects of the ultra-high ratio converter power system. BRIEF DESCRIPTION OF DRAWINGS

[0076] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following introduces the drawings of the related technical solutions in the embodiments of the present application or the prior art. It should be understood that the drawings in the following introduction are only for the convenience of clearly describing part of the embodiments in the technical solutions of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0077] Figure 1 is the architecture diagram of the voltage transient evaluation index system and calculation method in the embodiments of the present application;

[0078] Figure 2It is a transient voltage dynamic curve of an ultrahigh ratio converter power system in an embodiment of the present application.

[0079] Figure 3 It is a schematic diagram of a 5-machine test system of a photovoltaic cluster sending end in an embodiment of the present application.

[0080] Figure 4 It is a system node voltage curve in an embodiment of the present application.

[0081] Figure 5 It is a step flow chart of a voltage transient evaluation method for an ultrahigh ratio converter power system in an embodiment of the present application. DETAILED DESCRIPTION

[0082] The embodiments of the present application are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar notations represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. For the step numbers in the following embodiments, they are only set for the convenience of description and explanation, and the order between the steps is not limited in any way, and the execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0083] In the description of the present application, it should be understood that the orientation description, such as the orientation or position relationship indicated by up, down, front, back, left, right, etc. is based on the orientation or position relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as a limitation of the present application, which indicates or implies that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0084] In the description of the present application, the meaning of several is one or more, and the meaning of multiple is more than two, greater than, less than, more than, etc. are understood as not including the number, and above, below, etc. are understood as including the number. If it is described as first, second, it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the sequence of indicated technical features.

[0085] In the description of the present application, unless otherwise explicitly limited, the words such as setting, installing, connecting, etc. should be broadly understood, and those skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical solution.

[0086] In general, the existing technical problems are as follows:

[0087] 1) The node contribution quantification problem in the transition from node-level indicators to system-level indicators in the system stability evaluation process

[0088] In the construction of the high-proportion converter power system indicator system, the nodes have different influences on the system stability due to the differences in physical location, function and power generation / load characteristics. When transitioning from node-level to system-level indicators, the contributions of each node need to be reasonably quantified to balance the local and global influences, otherwise the system-level indicators may not accurately reflect the status of the key nodes, affecting the evaluation results. How to adjust the weights of each node according to the system characteristics and maintain the scientificity and rationality of the weight distribution is a key difficulty in system-level stability evaluation.

[0089] 2) The comprehensiveness problem of system-level transient voltage stability evaluation indicators for high-proportion converter power systems

[0090] In the high-proportion converter power system, due to the significant differences in dynamic response characteristics between converters and traditional synchronous generators, the existing transient voltage stability evaluation indicators are difficult to comprehensively reflect the dynamic behavior characteristics of the system under disturbance. Compared with traditional power systems, transient power response, voltage fluctuation amplitude and recovery time become important factors for evaluating transient voltage stability in high-proportion converter systems. Therefore, suitable transient voltage stability quantitative evaluation indicators need to be proposed for high-proportion converter systems. At the same time, integrated evaluation of the voltage of all nodes in the system is needed from the system level perspective, so that the evaluation indicators can reveal the voltage response characteristics of the whole system under disturbance, making the dispatching and control decisions more scientific and targeted.

[0091] In view of the existing technical problems, the present application proposes a set of voltage transient evaluation indicators and calculation methods for high-proportion converter systems, which can quantitatively evaluate the system voltage stability performance and regulation capacity of the power grid under fault scenarios, providing a theoretical basis and technical support for the planning and design, operation scheduling, control optimization, etc. of high-proportion converter power systems.

[0092] The system voltage transient evaluation indicator set proposed by the present application has the characteristic that it can comprehensively investigate the propagation degree of voltage drop and the overall voltage recovery of the high-proportion converter system in the process of short-circuit and other large disturbances. The method is to propose a node weight coefficient calculation method that comprehensively considers the electrical distance of the fault point, the power flow contribution degree and the node betweenness center; and based on the node weight coefficient, to realize the weighted integration of the whole system voltage transient, and to propose a set of system-level transient voltage stability evaluation indicators covering voltage instantaneous response and recovery state, which can realize comprehensive and quantitative analysis of the system transient voltage stability.

[0093] Embodiment 1

[0094] As Figure 1 and Figure 5As shown, the embodiment provides a voltage transient evaluation method for a power system with a very high proportion of converters, comprising the following steps:

[0095] S1, simulating and analyzing voltage transient evaluation;

[0096] S2, calculating the node weight coefficient considering the electrical distance from the fault point, the power flow contribution degree and the node betweenness center;

[0097] S3, combining the transient voltage simulation result, based on the obtained node weight coefficient, the node level index is weighted calculated, and the system level transient voltage stability evaluation index system is constructed;

[0098] S4, according to the system level voltage stability evaluation index, the overall voltage stability score of the system is calculated.

[0099] Based on the perspective of system stability characteristic analysis, the application proposes a set of transient voltage stability quantitative evaluation index system for a power system with a very high proportion of converters, to comprehensively measure the transient voltage stability performance of the system. According to the transient voltage characteristics of the power system with a very high proportion of converters, a node weight coefficient calculation method is proposed, which comprehensively considers the electrical distance from the fault point, the power flow contribution degree and the node betweenness center, to comprehensively reflect the importance of each node in the system, and to provide a basis for system level index calculation.

[0100] Further, a set of stability index system considering the transient state and dynamic recovery characteristics of the system transient voltage is established. On this basis, based on the node weight coefficient, the node level index is weighted calculated, and the system level transient voltage stability evaluation index system is constructed, to objectively evaluate the stability performance of the system as a whole. Finally, by integrating each system level index, the overall voltage stability score of the system is calculated.

[0101] The method of the embodiment is explained and described in detail as follows.

[0102] (1) Node weight coefficient ω i Calculation

[0103] According to the structure and power transmission characteristics of the power system with a very high proportion of converters, a weight calculation method for comprehensively evaluating the importance of nodes in the whole network is proposed. The node weight coefficient is mainly considered based on the following factors.

[0104] a) Electrical distance from fault point G1

[0105] The electrical distance reflects the length of the electrical transmission path from the node to the fault point. The closer the node to the fault point, the more obvious the voltage fluctuation in the transient process. Therefore, according to the network topology, the shortest electrical distance from each node to the fault point is calculated, and the electrical distance is further normalized to a value between [0, 1] to construct the electrical distance G1 from the fault point. The closer the distance, the greater the weight. The formula is as follows:

[0106]

[0107] In the formula, d i is the shortest electrical distance (sum of impedance) from node i to the fault point; max(d) is the maximum electrical distance of all nodes. Through normalization processing, the closer the node to the fault point, the greater G1(i).

[0108] b) Power flow contribution G2

[0109] For a high proportion of converter system, the power coupling relationship between the converter node and the power grid is complex, and the higher the power flow contribution, the greater the impact of the node on the overall power balance of the system. By taking the power flow contribution into the weight coefficient, the nodes with greater contribution to the system power flow are mainly considered in the evaluation process, so that the evaluation results can effectively reflect the impact on voltage stability when the power balance fluctuates. The calculation formula is as follows:

[0110]

[0111] In the formula, P i is the power flow of node i; max(P) is the maximum node power generation in the system. Through normalization processing, the greater the power flow, the greater G2(i).

[0112] c) Node betweenness centrality G3

[0113] In a high proportion of converter power system, some nodes are key transmission channels and may be located at the hub of the system, which not only needs to carry a large power flow, but also needs to respond quickly in disturbance. Its failure and disturbance may lead to a decrease in transmission efficiency or even instability, and its stability performance has a more significant impact on the overall stability of the system. Therefore, it should be given a higher weight in system planning and operation control analysis.

[0114] The betweenness centrality of each node is calculated, and the node with high centrality is given a higher weight. The calculation formula is as follows:

[0115]

[0116] In the formula, b iThe betweenness centrality of node i represents the contribution of the shortest path passing through the node to the total number of paths; max(b) is the maximum betweenness centrality in the system. Through normalization processing, the greater the betweenness centrality, the greater G3(i). The calculation formula of betweenness centrality is as follows:

[0117]

[0118] In the formula, σ pq (i) represents the total number of shortest paths passing through node i between node p and node q; p and q are any different nodes in the network, and i is the node for which the betweenness centrality is calculated.

[0119] Further, according to the characteristics of the system and expert experience, the weights of the above factors are determined as α j = 0.4, α j = 0.3, and α j = 0.3, and the sum of the weight coefficients of each factor is 1. Through the above formula, the importance of each node can be calculated, so as to identify the nodes that have a key influence on the stability of the system, which are used for subsequent system-level index weighting calculation of the evaluation index system.

[0120]

[0121] In the formula, ∑ j α j = 1. Through the above formula, the importance of each node can be calculated, so as to identify the nodes that have a key influence on the stability of the system, which are used for subsequent system-level index weighting calculation of the evaluation index system.

[0122] (2) Voltage stability evaluation index

[0123] As shown in FIG. 2, Figure 2 is the transient voltage simulation curve of an ultra-high ratio converter power system under different types of faults, based on which the voltage stability evaluation index is constructed. Among them, Figure 2 (a) is the dynamic curve of three-phase short-circuit fault, Figure 2 (b) is the dynamic curve of DC single-pole blocking. Figure 2 a) Weighted voltage sag deviation index (Weighted Voltage Sag Deviation, WVSD)

[0124] The voltage sag extreme value VSED is selected to evaluate the maximum deviation of the voltage sag of the node.

[0125]

[0126]

[0127] In the formula, v i (t) is the voltage of bus i at time t; is the original voltage of bus i before the fault; t f is the system fault time, and t cSystem fault clearance time. VSED i Used to measure the severity of voltage sag during faults, reflecting the transient voltage performance of the system at the time of fault.

[0128] Based on the voltage sag extremum VSED i Define the penalty value of bus i For:

[0129]

[0130] In the formula, k is the penalty amplitude adjustment coefficient, used to control the influence of voltage sag degree; v saglim represents the critical value of voltage sag, taking v saglim = 0.4. For the voltage of each bus, if the voltage sag deviation is greater than v saglim , it is punished according to specific rules, and the bus with voltage sag deviation less than v saglim is not punished.

[0131] The overall voltage sag characteristics of the system are evaluated by using the weighted voltage sag deviation score of the whole network. Combined with the importance weight of different buses, the system-level comprehensive deviation score of the whole network voltage sag is obtained by weighted summation, reflecting the overall voltage stability of the system.

[0132]

[0133] In the formula, ω i is the importance weight of bus i, and the detailed calculation method is described in the above (1) part.

[0134] b) Weighted Low Voltage Recovery Time (LVRT)

[0135] Low voltage recovery time is used to evaluate the process of power system from voltage sag to voltage recovery after fault occurs, reflecting the response speed and recovery ability of the system to fault. The shorter the low voltage recovery time, the better the stability of the system, which can recover to normal operation faster; the longer the time, the slower the recovery of the system, and the weaker the voltage support ability.

[0136] Let be the time when the voltage of bus i first falls to v lowlim below, be the time when the voltage of bus i first recovers to v lowlim above, v lowlim represents the critical value of low voltage, taking v lowlim = 0.8, then the low voltage recovery time of bus i is defined as:

[0137]

[0138] To get the low voltage recovery time score of the whole system, the low voltage recovery time of all nodes can be weighted and summed up to get the weighted low voltage recovery time LVRT of the whole network. The formula is as follows:

[0139]

[0140] c) weighted Over-voltage Duration Time (OVDT)

[0141] Over-voltage Duration Time reflects the length of time during which the voltage of the power system exceeds the safe range during faults or disturbances, especially the damage to equipment and the impact on system stability. Prolonged high voltage can cause damage to equipment insulation and seriously affect system safety, so it is very important to evaluate the over-voltage duration time.

[0142] Segmented evaluation of the over-voltage duration time T of bus i i IVDT It is divided into two parts:

[0143] 1) The duration of the voltage of bus i between v max and v crit ;

[0144] 2) The duration of the voltage of bus i exceeding v crit ;

[0145]

[0146] In the formula, k1, k2 are piecewise linear penalty coefficients, where k1 < k2, indicating that the greater the penalty for the more serious over-voltage. v max is the upper limit value of the voltage in normal operation, generally 1.1 p.u. v crit represents a higher critical value of over-voltage, taking the value of 1.3 p.u. The weighted over-voltage OVDT index of the whole network is constructed as follows:

[0147]

[0148] d) weighted Voltage Recovery Steady-state Time (VRST)

[0149] Voltage recovery time is used to measure the time it takes for the voltage of the power system to return to the normal operating range (less than v min or greater than v maxthe length of time to recover to steady state after the disturbance. This index reflects the voltage recovery capability of the system after being disturbed.

[0150] For each bus i, let be the time when the voltage first falls below v min or rises above v max . be the time when the voltage recovers to steady state and remains stable without deviation; v max be the upper limit of the normal operating voltage, v min be the lower limit of the normal operating voltage; the voltage recovery time of bus i is defined as:

[0151]

[0152] To evaluate the voltage recovery time of the entire system, the voltage recovery times of all buses are weighted and summed to form the overall network recovery time score. The steady-state voltage recovery time index is defined as follows:

[0153]

[0154] e) Weighted Steady-State Voltage Deviation (SSVD)

[0155] Let be the steady-state voltage value after the fault of bus i; define the voltage entering the range [v min , v max ] and not leaving this range as entering a new steady state. For buses with steady-state voltage below v min or above v max , calculate the steady-state voltage deviation penalty factor

[0156]

[0157] To obtain the overall steady-state voltage deviation score of the system, the steady-state voltage penalty values of all buses can be weighted and summed to obtain the overall network steady-state voltage deviation score:

[0158]

[0159] (3) Index Integration

[0160] According to the above system-level voltage stability evaluation indexes, the overall voltage stability score of the system is calculated as follows:

[0161] S vol = λ1WVSD+ λ2LVRT+ λ3OVDT+ λ4VRST+ λ5SSVD

[0162] where λkis the weight coefficient of the kth system-level index, which is obtained using the entropy method. k vol is the overall voltage transient score of the system. Using this overall score, the stability characteristics of all nodes in the system during the transient process can be evaluated, and the smaller the value, the more stable the system, and vice versa.

[0163] The above method is further described below in conjunction with the accompanying drawings and specific examples.

[0164] (4) Example

[0165] A 5-machine test system for a photovoltaic cluster sending end is built, which includes 5 0.8 kV photovoltaic cluster equivalent models, which are respectively boosted to 5 50 w collection stations via 5 transformers with a transformation ratio of 0.8 / 35 kV, 35 / 230 kV, and 230 / 525 kV, and then transmitted to a flexible converter station for external transmission. A PSCAD / EMTDC electromagnetic transient simulation model architecture is built and fault simulation is performed. The system network of this example is radial, and the overall architecture is shown in Figure 3 . The voltage stability performance of the 13 marked nodes is studied.

[0166] The transient fault simulation conditions are set as follows: a three-phase short circuit fault occurs near the flexible converter station side in the test system, the total simulation time is set to 20 s, the fault occurs at t f = 15 s, and the fault is removed 10 ms after the fault occurs. The total photovoltaic output is set to 8000 MW in scenario 1 and 9000 MW in scenario 2, and the stability evaluation index is calculated and analyzed according to the transient simulation results.

[0167] 4.1) Node weight coefficient calculation

[0168] First, the node weight coefficients of the 13 marked nodes in the entire system are calculated. The electrical distance G1, power flow contribution G2, and node betweenness centrality G3, and the node weight coefficient are shown in Tables 1 and 2, respectively. Since the system power flow size is different under different photovoltaic output modes, the calculated G2 is different.

[0169] Table 1: Node weight coefficient results table for scenario 1 (PV8000MW)

[0170]

[0171] Table 2: Node weight coefficient results table for scenario 2 (PV9000MW)

[0172]

[0173] ​

[0174] 4.2) Stability index calculation results

[0175] The system voltage stability index is calculated as shown in Table 3:

[0176] Table 3: System voltage stability index results table

[0177]

[0178] 4.3) Index comprehensive integration

[0179] The entropy method is used to determine the weight of the above index, and the result is shown in Table 4:

[0180] Table 4: Voltage stability index weight table

[0181]

[0182] According to the weight calculation result, the system overall voltage stability score is calculated, and the result is shown in Table 5:

[0183] S vol = λ1WVSD+ λ2LVRT+ λ3OVDT+ λ4VRST+ λ5SSVE

[0184] Table 5: System overall voltage transient score table

[0185]

[0186] The voltage simulation curve diagram of the two scenes is drawn as shown in Figure 4 It can be seen intuitively that the overall voltage stability effect of scene 1 is better than that of scene 2, and the system overall voltage transient score is much smaller than that of scene 2, verifying the rationality of the index calculation method proposed in the present application.

[0187] In summary, the present application has at least the following advantages and beneficial effects compared with the prior art:

[0188] 1) A node weight coefficient calculation method for ultra-high proportion converter power system transient voltage stability evaluation is proposed

[0189] The present application aims at the reasonable quantification of the contribution of different nodes in the transition from node-level stability evaluation index to system-level stability evaluation index in the process of establishing the voltage stability index system of the very high ratio converter power system, and proposes a node importance weight calculation method which comprehensively considers the electrical distance of the node from the fault location, the power flow contribution and the node betweenness centrality. By assigning a scientific and reasonable weight to each node, the contribution of the node in the overall stability of the system is more accurately reflected, thereby improving the accuracy and reliability of the system-level index evaluation.

[0190] 2) Propose a set of system-level transient voltage stability evaluation index and calculation method covering voltage transient response and recovery state

[0191] The present application formulates a transient voltage stability evaluation index system for the very high ratio converter power system, and proposes a transient voltage stability evaluation method based on the system-level perspective. The method defines voltage evaluation indexes from multiple angles such as transient response and recovery state characteristics, including weighted voltage drop extreme deviation, low voltage recovery time, overvoltage duration, voltage recovery steady-state time and steady-state voltage deviation. Based on the node weight coefficient, a system-level weighting method is proposed, which obtains the system-level evaluation index by weighting calculation of the node-level index, so as to ensure that the overall evaluation of the whole system voltage transient response is more representative. Finally, the system-level indexes are integrated to obtain the overall voltage stability score of the system.

[0192] Embodiment 2

[0193] The embodiment of the present application also provides an electronic device, which comprises a processor and a memory, and the memory stores at least one instruction, at least one program, a code set or an instruction set. Figure 5 As shown in a voltage transient evaluation method for a very high ratio converter power system.

[0194] It can be understood that the memory can include a random access memory (RAM) and a read-only memory (ROM). Optionally, the memory includes a non-transitory computer-readable storage medium. The memory can be used to store instructions, programs, codes, code sets or instruction sets. The memory can include a program storage area and a data storage area, wherein the program storage area can store instructions for implementing an operating system, instructions for at least one function, instructions for implementing the above-mentioned various method embodiments, etc.; and the data storage area can store data created according to the use of the server, etc.

[0195] The processor can include one or more processing cores. The processor connects various parts within the entire server by various interfaces and lines, executes various functions of the server and processes data by running or executing instructions, programs, code sets or instruction sets stored in the memory, and calling data stored in the memory. Alternatively, the processor can be implemented in at least one of a hardware form of a digital signal processing (DSP), a field-programmable gate array (FPGA), and a programmable logic array (PLA). The processor can be integrated with one or several combinations of a central processing unit (CPU) and a modem. Among them, the CPU mainly processes operating systems and application programs; the modem is used to process wireless communication. It can be understood that the above-mentioned modem can also not be integrated into the processor, but can be realized by a single chip.

[0196] Since the electronic device is an electronic device corresponding to the voltage transient state evaluation method for the very high ratio converter power system of the embodiment of the application, and the principle of solving problems of the electronic device is similar to the method, the implementation of the electronic device can be referred to the implementation process of the above-mentioned method embodiment, and the repeated parts will not be described here.

[0197] Embodiment 4

[0198] The embodiment of the application further provides a computer readable storage medium, wherein at least one instruction, at least one program, a code set or an instruction set are stored in the storage medium, and the at least one instruction, the at least one program, the code set or the instruction set are loaded and executed by a processor to realize a voltage transient state evaluation method for a very high ratio converter power system as shown in Figure 5

[0199] ​Those skilled in the art can understand that all or part of the steps of various methods in the above embodiments can be completed by instructing the relevant hardware through a program, and the program can be stored in a computer readable storage medium, including Read-Only Memory (ROM), Random Access Memory (RAM), Programmable Read-only Memory (PROM), Erasable Programmable Read Only Memory (EPROM), One-time Programmable Read-Only Memory (OTPROM), Electrically-Erasable Programmable Read-Only Memory (EEPROM), Compact Disc Read-Only Memory (CD-ROM) or other optical disk storage, magnetic disk storage, magnetic tape storage, or any other medium that can be used to carry or store data which can be read by a computer.

[0200] Since the storage medium is a storage medium corresponding to the method for voltage transient state evaluation of an ultra-high ratio converter power system in the embodiments of the present application, and the principle of solving the problem is similar to the method, the implementation of the storage medium can refer to the implementation process of the above-mentioned method embodiments, and the repeated parts will not be described again.

[0201] Embodiment 5

[0202] In some possible implementation manners, various aspects of the method of the embodiments of the present application can also be implemented in the form of a program product, which includes program codes for causing a computer device to execute the steps of the method for voltage transient state evaluation of an ultra-high ratio converter power system according to various exemplary embodiments of the present application described above in the specification when the program product is run on the computer device. Wherein, the executable computer program codes or "codes" for executing various embodiments can be written in a high-level programming language such as C, C++, C#, Smalltalk, Java, JavaScript, Visual Basic, Structured Query Language (for example, Transact-SQL), Perl, or in various other programming languages.

[0203] It should be understood that various aspects of the application can be implemented in hardware, software, firmware or a combination of them. In the above embodiments, various steps or methods can be implemented in software or firmware which is stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, and in another embodiment, any of the following technologies, known in the art, or their combination, can be used: discrete logic circuitry having logic gates for implementing logic functions upon an application of data signals, application-specific integrated circuits having appropriate combinational logic gates, programmable gate arrays (PGA), field-programmable gate arrays (FPGA), and so on.

[0204] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Also, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples, without contradiction.

[0205] The above embodiments are only for the purpose of illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the essence of the present application should be covered within the protection scope of the present application.

Claims

1. A method for voltage transient assessment for power systems with very high ratio converters, characterized in that, The method comprises the following steps: a simulation analysis is performed on voltage transient evaluation; a node weight coefficient is calculated by comprehensively considering an electrical distance from a fault point, a power flow contribution degree and a node betweenness centrality; a system-level transient voltage stability evaluation index system is constructed by combining a simulation result of transient voltage and performing a weighted calculation on a node-level index based on the obtained node weight coefficient; an overall voltage stability score of the system is calculated according to the system-level voltage stability evaluation index; the calculation of the node weight coefficient by comprehensively considering the electrical distance from the fault point, the power flow contribution degree and the node betweenness centrality comprises: The electrical distance G1 from the fault point, the power flow contribution G2 and the node betweenness centrality G3 are defined, and the node weight coefficient ω is calculated comprehensively i : In the formula, α j is the weight of each factor; ω i is the node weight coefficient and the importance weight of the bus i; an expression of the electrical distance G1 from the fault point is: In the formula, d i is the shortest electrical distance from node i to the fault point; max(d) is the maximum electrical distance of all nodes; an expression of the power flow contribution degree G2 is: In the formula, P i is the power flow size of node i; max(P) is the maximum node power generation in the system; an expression of the node betweenness centrality G3 is: where b i is the betweenness centrality of node i, representing the contribution of the shortest paths passing through this node to the total number of paths; max(b) is the maximum betweenness centrality in the system; Betweenness centrality b of node i i The formula for calculating b is as follows: In the formula, σ pq (i) represents the total number of shortest paths passing through node i between node p and node q; p and q are any different nodes in the network, and i is the node for which the betweenness centrality is calculated.

2. The method for voltage transient assessment of power system oriented to very high ratio converter according to claim 1, characterized in that, the system-level transient voltage stability evaluation index system comprises a weighted voltage drop extreme deviation index WVSD, a weighted low voltage recovery time LVRT, a weighted overvoltage duration time OVDT, a weighted voltage recovery steady state time VRST and a weighted steady state voltage deviation index SSVD; the overall voltage stability score is calculated as follows: S vol = λ1WVSD + λ2LVRT + λ3OVDT + λ4VRST + λ5SSVD In the formula, λ k is the weight coefficient of the kth system-level index.

3. The method for voltage transient assessment of power system oriented to very high ratio converter according to claim 2, characterized in that, a construction manner of the weighted voltage drop extreme deviation index WVSD is as follows: a voltage drop extreme value VSED is selected to evaluate a maximum deviation of node voltage drop: where v i (t) is the voltage of bus i at time t; is the original voltage of bus i before the fault; t f is the system fault time, t c is the system fault clearing time; Based on the voltage dip extremum VSED i Defining the penalty value of the bus i is: In the formula, k is a penalty amplitude adjustment coefficient, used to control the influence of voltage drop; v saglim represents the critical value of voltage drop; a system overall voltage drop characteristic is evaluated by using a weighted voltage drop deviation score of the whole network; combined with an importance weight of different buses, a system-level comprehensive deviation score of the whole network voltage drop is obtained by weighted summation: In the formula, ω i is the importance weight of bus i, and N is the number of system buses.

4. The method for voltage transient assessment of power system oriented to very high ratio converter according to claim 2, characterized in that, a construction manner of the weighted low voltage recovery time LVRT is as follows: Let be the time at which the voltage of bus i first falls to v lowlim Let be the time at which the voltage of bus i first recovers to v lowlim Let lowlim be the critical value of low voltage, then the low voltage recovery time of bus i is defined as: Let a weighted summation is performed on low voltage recovery times of all nodes to obtain a weighted low voltage recovery time LVRT of the whole network: In the formula, ω i is the importance weight of bus i, and N is the number of system buses.

5. The method for voltage transient assessment of power system oriented to very high ratio converter according to claim 2, characterized in that, a construction manner of the weighted overvoltage duration time OVDT is as follows: Segmenting the overvoltage duration of a bus i for evaluation It is divided into two parts: 1) Bus i voltage in v max to v crit between t and t+T; 2) Bus i voltage exceeds v crit Duration of time; where k1, k2 are piecewise linear penalty coefficients, v max is the upper limit of the voltage in normal operation, v crit represents the higher critical value of overvoltage; a weighted overvoltage index of the whole network is constructed as follows: In the formula, ω i is the importance weight of bus i, and N is the number of system buses.

6. The method for voltage transient assessment of power system oriented to very high ratio converter according to claim 2, characterized in that, a construction manner of the weighted voltage recovery steady state time VRST is as follows: For each bus i, let be the time at which the voltage first falls below v min or rises above v max , be the time at which the voltage returns to steady state and remains stable without further excursions; v max be the upper limit of the normal operating range of the voltage, v min be the lower limit of the normal operating range of the voltage; a voltage recovery time of the bus i is defined as: a weighted summation is performed on voltage recovery times of all buses to form a recovery time score of the whole network; a voltage recovery steady state time index is defined as follows: In the formula, ω i is the importance weight of bus i, and N is the number of system buses.

7. The method for voltage transient assessment of power system oriented to very high ratio converter according to claim 2, characterized in that, a construction manner of the weighted steady state voltage deviation index SSVD is as follows: Let Vf is the steady state voltage value after the fault of the bus i; the voltage is defined to enter the range [v min , v max ] after the fault of the bus i and not to leave this range to enter the new steady state; v max Vmax is the upper limit value of the voltage in normal operation; min Vmin is the lower limit value of the voltage in normal operation; For a bus with a steady state voltage below v min or above v max , a steady state voltage deviation penalty factor is calculated according to the extent of voltage deviation a weighted summation is performed on steady state voltage penalty values of all buses to obtain a steady state voltage deviation score of the whole network: In the formula, ω i is the importance weight of bus i, and N is the number of system buses.

8. An electronic device, comprising: The electronic device comprises a processor and a memory, the memory stores at least one instruction, at least one program, a code set or an instruction set, and the at least one instruction, the at least one program, the code set or the instruction set is loaded and executed by the processor to realize the method in any one of claims 1 to 7.

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