Static voltage stability index analysis method and system during fault period of multiple new energy fields

Abstract

The invention provides a static voltage stability index analysis method and system during a multi-new energy field fault period, and the method comprises the steps: obtaining a static voltage stability index according to the fault type and fault position of a multi-new energy field station access power grid system; establishing a power grid node voltage equation comprising a generator node, a to-be-evaluated new energy node, a residual new energy node, a contact node and a fault node; according to the power grid node voltage equation, analyzing equivalent single-machine grid-connected system equivalent potential and equivalent impedance of a power grid corresponding to the to-be-evaluated new energy node to obtain an equivalent single-machine grid-connected system equivalent circuit of each to-be-evaluated new energy access node; according to the equivalent circuit of the equivalent single-machine grid-connected system, voltage stability weak nodes in the low-voltage ride-through period of the multi-new-energy grid-connected system are obtained through calculation; and performing corresponding optimization processing according to the voltage stability weak nodes during the low voltage ride-through period of the multi-new energy grid-connected system.

Description

Technical Field

[0001] The present application relates to the field of power system analysis, and in particular to a method and system for analyzing static voltage stability indicators during a multi-renewable energy field fault. Background Art

[0002] Today's society has begun to vigorously develop renewable energy and build a power system with new energy as the main body. As the proportion of distributed new energy connected to the power grid continues to increase, the fault characteristics of the power grid will be mainly determined by the new energy power source. Due to the large number of new energy sources and the scattered access locations, the output fault current is affected by its short-circuit fault low voltage ride-through control strategy, which brings difficulties to the short-circuit fault analysis of the new energy power grid. At the same time, there is a problem of static voltage stability during the short-circuit fault low voltage ride-through when a high proportion of new energy is connected to the power grid. Once the static voltage instability occurs, it will lead to the failure of the fault low ride-through and the system oscillation. Therefore, it is very important to study the static voltage stability evaluation method of the high proportion of new energy connected to the power grid. At present, there are few studies on the static voltage stability problem during the short-circuit fault low ride-through of the high proportion of new energy power grid. Most of the literature studies the static voltage stability problem of the new energy connected to the power grid under normal steady-state operation, and proposes impedance modulus margin indicators and short-circuit ratio indicators. However, the power grid is different during short-circuit faults and normal steady-state operation. During short-circuit faults, the new energy power source outputs controlled reactive current components and active current components according to regulations, showing nonlinear controlled current source characteristics, while during normal steady-state operation, the new energy source has constant active and constant reactive characteristics, that is, the PQ node, which is completely different. Therefore, it is necessary to study the static voltage stability problem of a high-proportion new energy power grid during short-circuit faults.

[0003] The existing technology is to evaluate the static voltage stability under normal operation of the power system, mainly using indicators such as impedance modulus margin index and short circuit ratio index; for these indicators, the existing technology mainly uses the following methods to analyze: 1) The calculation method of the critical point of static voltage stability based on the short circuit ratio. The short circuit ratio defines the strength of the external AC power grid relative to the access to new energy, reflecting the relative strength between the voltage support provided by the AC system and the voltage change caused by the grid connection of new energy. According to the concept of static voltage stability, the critical short circuit ratio is derived to judge the strength of the new energy access system and the static voltage stability of the system. 2) The construction method of the static voltage stability index and the static voltage stability domain of the power system: all new energy, load and DC nodes with similar PQ node properties in the power grid are screened, the impedance matrix of the selected nodes is calculated, and the voltage amplitude, active output and reactive output of each node are obtained through power flow calculation; then the static voltage stability criterion is substituted to derive the static voltage stability index under the current operating state; finally, the boundary of the static voltage stability domain is characterized by the critical value of the static voltage stability index, and the stability margin of each node and the node close to the voltage stability limit are observed. 3) The application of impedance modulus margin in static voltage stability under normal operation of new energy access to the power grid is given. Based on the impedance modulus margin, the static voltage stability limit of the access system is given, and the calculation method of the impedance modulus margin index of new energy single-machine and multi-machine systems is given.

[0004] The existing technology mainly focuses on the static voltage stability assessment of normal steady-state operation of renewable energy access to the power grid, but the static voltage stability assessment of the steady state during low voltage ride-through of renewable energy access to the power grid is different from that of the normal steady state. Summary of the invention

[0005] The purpose of this application is to provide a method and system for analyzing static voltage stability indicators during faults in multiple renewable energy fields. For the access of renewable energy power sources to the power grid, a static voltage stability indicator during short-circuit faults based on phase margin is established, and a low-voltage ride-through control optimization strategy for improving static voltage stability is proposed, thereby solving the problem of static voltage stability assessment during low-voltage ride-through when a high proportion of renewable energy sources are connected to the power grid.

[0006] To achieve the above-mentioned purpose, the static voltage stability index analysis method during multi-renewable energy field faults provided in the present application specifically includes: establishing a grid node voltage equation including generator nodes, new energy nodes to be evaluated, remaining new energy nodes, contact nodes and fault nodes according to the fault type and fault location of the multi-renewable energy field station access to the power grid system; analyzing the equivalent potential and equivalent impedance of the equivalent single-machine grid-connected system of the power grid corresponding to the new energy node to be evaluated according to the grid node voltage equation to obtain the equivalent single-machine grid-connected system equivalent circuit of each new energy access node to be evaluated; calculating the voltage stability weak nodes during the low voltage crossing of the multi-renewable energy grid-connected system according to the equivalent single-machine grid-connected system equivalent circuit; and performing corresponding optimization processing according to the voltage stability weak nodes during the low voltage crossing of the multi-renewable energy grid-connected system.

[0007] In the above-mentioned method for analyzing static voltage stability indicators during faults of multiple renewable energy fields, optionally, analyzing the equivalent potential and equivalent impedance of the equivalent single-machine grid-connected system of the power grid corresponding to the new energy node to be evaluated according to the power grid node voltage equation to obtain the equivalent single-machine grid-connected system equivalent circuit of each new energy access node to be evaluated includes: according to the power grid node voltage equation, obtaining the node impedance matrix by adding the remaining new energy nodes to the composite sequence network admittance matrix as admittances; analyzing the equivalent potential and equivalent impedance of the equivalent single-machine grid-connected system of the power grid corresponding to the new energy node to be evaluated through the node impedance matrix to obtain the equivalent single-machine grid-connected system equivalent circuit of each new energy access node to be evaluated.

[0008] In the above-mentioned method for analyzing static voltage stability indicators during multi-renewable energy field faults, optionally, obtaining voltage stability weak nodes during low voltage crossing of multi-renewable energy grid-connected systems according to equivalent circuit calculations of the equivalent single-machine grid-connected system includes: obtaining static voltage stability phase deviations and short-circuit fault static voltage stability phase margin indicators of each new energy access node during the low voltage crossing of new energy faults according to equivalent circuit calculations of the equivalent single-machine grid-connected system; and obtaining voltage stability weak nodes during low voltage crossing of multi-renewable energy grid-connected systems by analyzing the static voltage stability phase deviations and short-circuit fault static voltage stability phase margin indicators of each new energy access node.

[0009] In the above-mentioned method for analyzing static voltage stability indicators during multi-renewable energy field faults, optionally, corresponding optimization processing is performed according to the voltage stability weak nodes during the low voltage crossing period of the multi-renewable energy grid-connected system, including: according to the voltage stability weak nodes during the low voltage crossing period of the multi-renewable energy grid-connected system, the static voltage stability is improved based on the calculation principle of the static voltage stability phase margin indicator during the low voltage crossing period of a short circuit fault of the multi-renewable energy field access to the power grid system.

[0010] In the above-mentioned method for analyzing static voltage stability indicators during faults of multiple renewable energy sites, optionally, improving static voltage stability based on the calculation principle of static voltage stability phase margin indicators during low voltage ride-through due to short circuit faults of multiple renewable energy sites connected to the power grid includes: improving static voltage stability by reducing the phase deviation between the equivalent potential in the equivalent circuit of the equivalent single-machine grid-connected system and the node voltage of the renewable energy site to a preset value based on the calculation principle of static voltage stability phase margin indicators during low voltage ride-through due to short circuit faults of multiple renewable energy sites connected to the power grid.

[0011] In the above-mentioned static voltage stability index analysis method during multi-new energy field faults, optionally, reducing the phase deviation between the equivalent potential in the equivalent circuit of the equivalent single-machine grid-connected system and the node voltage of the new energy field to a preset value also includes: obtaining a first ratio based on the ratio between the active component and the reactive component of the current injected by the new energy field; obtaining a second ratio based on the ratio between the resistance component and the reactance component of the equivalent impedance of the equivalent single-machine grid-connected system; when the first ratio is the same as the second ratio, it meets the preset value.

[0012] In the above-mentioned method for analyzing static voltage stability indicators during multi-renewable energy field faults, optionally, obtaining the voltage stability weak nodes during low voltage ride through of the multi-renewable energy grid-connected system through short-circuit fault static voltage stability phase margin indicator analysis of each new energy access node includes: obtaining the voltage stability weak nodes during low voltage ride through of the multi-renewable energy grid-connected system according to the node with the smallest short-circuit fault static voltage stability phase margin indicator.

[0013] In the above-mentioned static voltage stability index analysis method during faults of multiple renewable energy sites, optionally, the calculation of the static voltage stability phase margin index during the low voltage ride-through period of a short-circuit fault in which multiple renewable energy sites are connected to the power grid includes: obtaining the positive-sequence node voltage equation of the decentralized access of multiple renewable energy sites to the power grid, and obtaining the corresponding fault additional impedance according to the type of fault; obtaining the voltage expression of the new energy node to be evaluated by converting the fault additional impedance and the positive-sequence node voltage equation, and obtaining the equivalent single-machine grid-connected system equivalent parameters of the new energy node to be evaluated through the voltage expression; calculating the short-circuit fault static voltage stability phase margin index through the equivalent single-machine grid-connected system equivalent potential and node voltage of each new energy access node.

[0014] In the above-mentioned static voltage stability index analysis method during multi-renewable energy field faults, optionally, obtaining a voltage expression of the new energy node to be evaluated by converting the fault additional impedance and the positive-sequence node voltage equation includes: eliminating the fault node and the contact node in the positive-sequence node voltage equation through the fault additional impedance to obtain a first node voltage equation containing only the generator node, the new energy node to be evaluated and the remaining new energy nodes; equivalently converting the remaining new energy nodes in the first node voltage equation to admittances and adding them to the composite sequence network admittance matrix to obtain a second node voltage equation; eliminating the remaining new energy nodes in the second node voltage equation to obtain the voltage expression of the new energy node to be evaluated.

[0015] The present application also provides a static voltage stability index analysis system during faults of multiple renewable energy sites, the system comprising: an establishment module, used to establish a grid node voltage equation including a generator node, a new energy node to be evaluated, a remaining new energy node, a contact node and a fault node according to the fault type and fault location of the multiple renewable energy sites connected to the power grid system; an analysis module, used to analyze the equivalent potential and equivalent impedance of the equivalent single-machine grid-connected system of the power grid corresponding to the new energy node to be evaluated according to the grid node voltage equation to obtain the equivalent single-machine grid-connected system equivalent circuit of each new energy access node to be evaluated; a screening module, used to calculate the voltage stability weak nodes of the multiple renewable energy grid-connected system during low voltage crossing according to the equivalent single-machine grid-connected system equivalent circuit; an optimization module, used to perform corresponding optimization processing according to the voltage stability weak nodes of the multiple renewable energy grid-connected system during low voltage crossing.

[0016] The present application also provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the above method when executing the computer program.

[0017] The present application also provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program for executing the above method.

[0018] The present application also provides a computer program product, comprising a computer program / instruction, which implements the steps of the above method when executed by a processor.

[0019] The beneficial technical effect of the present application is that: a static voltage stability assessment method and index during the low voltage crossing period of short circuit faults caused by a high proportion of new energy access to the power grid are proposed, including two parts: static voltage stability assessment during the low voltage crossing period of short circuit faults caused by a high proportion of multiple new energy sites connected to the power grid, and static voltage stability optimal control strategy during the low voltage crossing period of new energy site faults. Furthermore, the voltage stability degree during the low voltage crossing period of the fault of the new energy access node in the system can be ranked by calculating the index, and the weak nodes of voltage stability during the low voltage crossing period of the fault of the new energy power grid can be understood without simulation, which is of great significance for guiding the safety and stability analysis of the power grid in terms of voltage stability. The proposed static voltage stability optimal control strategy during the low voltage crossing period can effectively improve the static voltage stability during the low voltage crossing period of the fault of the new energy site. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings described herein are used to provide a further understanding of the present application, constitute a part of the present application, and do not constitute a limitation of the present application. In the drawings:

[0021] Figure 1 A schematic flow chart of a method for analyzing static voltage stability indicators during a multi-energy power plant fault provided by an embodiment of the present application;

[0022] Figure 2 A schematic diagram of a fault circuit provided in an embodiment of the present application;

[0023] Figure 3 A schematic diagram of a flow chart for obtaining an equivalent circuit provided in an embodiment of the present application;

[0024] Figure 4 A schematic diagram of a weak node analysis process provided by an embodiment of the present application;

[0025] Figure 5 A schematic diagram of an optimization strategy analysis provided by an embodiment of the present application;

[0026] Figure 6 A schematic diagram of a process for obtaining a short-circuit fault static voltage stability phase margin indicator provided in an embodiment of the present application;

[0027] Figure 7 A schematic diagram of a flow chart for obtaining a voltage expression provided in an embodiment of the present application;

[0028] Figure 8 This is a schematic diagram of an equivalent circuit of a single-machine grid-connected system of a node c to be evaluated provided in an embodiment of the present application;

[0029] Fig. 9 A schematic diagram of voltage phasors of an equivalent single-machine grid-connected system of a node c to be evaluated provided in an embodiment of the present application;

[0030] Fig.10 A schematic diagram of the application process of a static voltage stability index analysis system during a multi-energy power plant fault provided by an embodiment of the present application;

[0031] Fig.11 A schematic diagram of the structure of an electronic device provided in one embodiment of the present application;

[0032] Fig.12 A schematic diagram of the structure of an IEEE 33-node distribution network with multiple renewable energy accesses provided in an embodiment of the present application. DETAILED DESCRIPTION

[0033] The following will describe the implementation methods of the present application in detail in conjunction with the accompanying drawings and embodiments, so that the implementation process of how the present application applies technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly. It should be noted that as long as there is no conflict, the various embodiments in the present application and the various features in the embodiments can be combined with each other, and the technical solutions formed are all within the protection scope of the present application.

[0034] In addition, the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be performed in an order different from that shown here.

[0035] Please refer to Figure 1 As shown, the static voltage stability index analysis method during a multi-energy power plant fault provided by the present application specifically includes:

[0036] S101: according to the fault type and fault location of the multiple renewable energy stations connected to the power grid system, establish a grid node voltage equation including the generator node, the renewable energy node to be evaluated, the remaining renewable energy nodes, the contact node and the fault node;

[0037] S102: Analyze the equivalent potential and equivalent impedance of the equivalent single-machine grid-connected system of the power grid corresponding to the new energy node to be evaluated according to the power grid node voltage equation to obtain the equivalent single-machine grid-connected system equivalent circuit of each new energy access node to be evaluated;

[0038] S103: Calculating the voltage stability weak node of the multi-renewable energy grid-connected system during the low voltage ride-through period according to the equivalent circuit of the equivalent single-machine grid-connected system;

[0039] S104: performing corresponding optimization processing according to the voltage stability weak nodes during the low voltage ride-through period of the multi-renewable energy grid-connected system.

[0040] Specifically, the static voltage stability index analysis method during a multi-energy power plant fault provided by the present application mainly includes two steps, as follows:

[0041] (1) Calculation of the static voltage stability phase margin index during the low voltage ride-through period of a short-circuit fault in a power grid system with multiple renewable energy stations connected.

[0042] (2) The optimal control strategy for static voltage stability during low voltage ride-through when new energy stations are connected to the grid.

[0043] In actual work, the calculation process of the static voltage stability phase margin index during the low voltage ride-through period of short-circuit faults in the power grid system connected to multiple renewable energy stations mainly includes the following processes:

[0044] Establish the grid node voltage equation including the generator node, the new energy node c to be evaluated, the other new energy nodes, the contact node and the fault node; obtain the equivalent single-machine grid-connected system equivalent circuit of each new energy access node to be evaluated; on this basis, calculate the static voltage stability phase deviation during the new energy fault low voltage ride-through and the short-circuit fault static voltage stability phase margin index of each new energy access node, so as to evaluate the system voltage stability during the fault low voltage ride-through. The specific fault circuit diagram is shown in Figure 2 The specific implementation of each step will be described in detail in the subsequent embodiments, and will not be given examples one by one here.

[0045] Please refer to Figure 3 As shown, in one embodiment of the present application, the equivalent potential and equivalent impedance of the equivalent single-machine grid-connected system of the power grid corresponding to the new energy node to be evaluated are analyzed according to the grid node voltage equation to obtain the equivalent single-machine grid-connected system equivalent circuit of each new energy access node to be evaluated, which includes:

[0046] S301: According to the grid node voltage equation, the node impedance matrix is ​​obtained by converting the remaining new energy nodes into admittance equivalents and adding them into the composite sequence network admittance matrix;

[0047] S302: Analyze the equivalent potential and equivalent impedance of the equivalent single-machine grid-connected system of the power grid corresponding to the new energy node to be evaluated through the node impedance matrix to obtain the equivalent circuit of the equivalent single-machine grid-connected system of each new energy access node to be evaluated.

[0048] For further information, please refer to Figure 4 As shown, in one embodiment of the present application, the voltage stability weak node during the low voltage ride-through period of the multi-new energy grid-connected system is obtained by calculating the equivalent circuit of the equivalent single-machine grid-connected system, including:

[0049] S401: Calculate the static voltage stability phase deviation during the low voltage ride-through period of the new energy fault and the static voltage stability phase margin index of the short circuit fault of each new energy access node according to the equivalent circuit of the equivalent single-machine grid-connected system;

[0050] S402: Analyze the static voltage stability phase deviation and short-circuit fault static voltage stability phase margin indicators of each renewable energy access node to obtain the voltage stability weak nodes during the low voltage ride-through period of the multi-renewable energy grid-connected system.

[0051] For details, please refer to Figure 2 As shown, the specific implementation process of the above embodiment is as follows:

[0052] 1) According to the specific fault types and fault locations that occur when multiple renewable energy stations are connected to the power grid system, the grid node voltage equations including the generator node, the renewable energy node c to be evaluated, the remaining renewable energy nodes, the contact node and the fault node are established.

[0053] 2) Keep the new energy at the key node c to be evaluated, and add the new energy at the remaining nodes to the admittance matrix of the composite sequence network, and further obtain the node impedance matrix to obtain the equivalent single-machine grid-connected system equivalent potential of the key node c to be evaluated looking at the power grid and equivalent impedance The equivalent circuit of a single-machine grid-connected system of each renewable energy access node in a multi-renewable energy grid-connected system with a fault is obtained.

[0054] 3) For the equivalent single-machine grid-connected system equivalent circuit of the key node c to be evaluated, calculate the static voltage stability phase deviation during the low voltage ride-through of the new energy fault and the static voltage stability phase margin index of the short-circuit fault, and take the node with the minimum static voltage stability phase margin index of the short-circuit fault as the weak node of voltage stability during the low voltage ride-through of the multi-new energy grid-connected system.

[0055] In one embodiment of the present application, corresponding optimization processing is performed according to the voltage stability weak nodes during the low voltage crossing period of the multi-renewable energy grid-connected system, including: according to the voltage stability weak nodes during the low voltage crossing period of the multi-renewable energy grid-connected system, the static voltage stability is improved based on the static voltage stability phase margin index calculation principle during the low voltage crossing period of a short circuit fault of the multi-renewable energy station access to the power grid system.

[0056] Among them, improving the static voltage stability based on the calculation principle of the static voltage stability phase margin index during the low voltage ride-through of a short-circuit fault in a power grid system with multiple renewable energy sites can include: based on the calculation principle of the static voltage stability phase margin index during the low voltage ride-through of a short-circuit fault in a power grid system with multiple renewable energy sites, by reducing the phase deviation between the equivalent potential in the equivalent circuit of the equivalent single-machine grid-connected system and the voltage of the renewable energy site node to a preset value, so as to improve the static voltage stability. Obtaining the weak node of voltage stability during the low voltage ride-through of the multi-renewable energy grid-connected system through the short-circuit static voltage stability phase margin index analysis of each renewable energy access node can include: obtaining the weak node of voltage stability during the low voltage ride-through of the multi-renewable energy grid-connected system according to the node with the smallest short-circuit static voltage stability phase margin index.

[0057] Specifically, in this application, an optimal control strategy for static voltage stability during low voltage ride-through due to short circuit faults is proposed for the access of new energy stations to the power grid; the ratio of the active component to the reactive component of the current injected by the new energy station is the same as the ratio of the resistance component to the reactance component of the equivalent impedance of the equivalent single-machine grid-connected system, and the static voltage stability level of the power grid can be improved. The optimal control strategy for static voltage stability during low voltage ride-through due to the access of new energy stations to the power grid; the static voltage stability can be improved by reducing the phase deviation between the equivalent potential in the equivalent circuit of the equivalent single-machine grid-connected system and the node voltage of the new energy station through the calculation principle of the static voltage stability phase margin index during low voltage ride-through due to short circuit faults in the power grid system with multiple new energy stations.

[0058] For further information, please refer to Figure 5 As shown, in one embodiment of the present application, reducing the phase deviation between the equivalent potential in the equivalent circuit of the equivalent single-machine grid-connected system and the node voltage of the new energy station to a preset value further includes:

[0059] S501: Obtaining a first ratio according to a ratio between an active component and a reactive component of a current injected by a new energy field;

[0060] S502: Obtaining a second ratio according to a ratio between a resistance component and a reactance component of an equivalent impedance of an equivalent single-machine grid-connected system;

[0061] S503: When the first ratio is the same as the second ratio, it meets a preset value.

[0062] Specifically, for the new energy station connected to the power grid system, the node impedance matrix is ​​used to obtain the equivalent single-machine grid-connected system impedance of the new energy station looking at the power grid. The ratio of the active component to the reactive component of the current injected by the new energy station and the equivalent impedance of the equivalent single-machine grid-connected system The ratio of the resistance component to the reactance component is the same.

[0063] Please refer to Figure 6 As shown, in one embodiment of the present application, the calculation of the static voltage stability phase margin index during the low voltage ride-through period of a short-circuit fault of a power grid system connected to multiple renewable energy stations includes:

[0064] S601: Obtaining a positive-sequence node voltage equation of multiple renewable energy fields decentralized access to the power grid, and obtaining a corresponding additional fault impedance according to the type of fault;

[0065] S602: Obtain a voltage expression of the new energy node to be evaluated by converting the fault additional impedance and the positive sequence node voltage equation, and obtain equivalent single-machine grid-connected system equivalent parameters of the new energy node to be evaluated by the voltage expression;

[0066] S603: Calculate the short-circuit fault static voltage stability phase margin index through the equivalent potential of the equivalent single-machine grid-connected system and the node voltage of each new energy access node.

[0067] Please refer to Figure 7 As shown, the voltage expression of the new energy node to be evaluated is obtained by converting the fault additional impedance and the positive sequence node voltage equation, which includes:

[0068] S701: Eliminating the fault node and the tie node in the positive sequence node voltage equation by using the fault additional impedance to obtain a first node voltage equation containing only the generator node, the new energy node to be evaluated and the remaining new energy nodes;

[0069] S702: Equivalent the remaining new energy nodes in the first node voltage equation to admittances and add them into the composite sequence network admittance matrix to obtain a second node voltage equation;

[0070] S703: Eliminate the remaining new energy nodes in the second node voltage equation to obtain a voltage expression of the new energy node to be evaluated.

[0071] In order to facilitate a clearer understanding of the specific implementation process and method of the static voltage stability index analysis method during a multi-renewable energy field fault provided by the present application, the above-mentioned static voltage stability index analysis method during a multi-renewable energy field fault will be described as a whole below. Relevant technical personnel in the field should know that this example is only an example of the use of the static voltage stability index analysis method during a multi-renewable energy field fault provided by the present application, and does not impose any limitation on it.

[0072] (1) Calculation of the static voltage stability phase margin index during the low voltage ride-through period when multiple renewable energy stations are connected to the power grid system with short-circuit faults.

[0073] For new energy stations that are centrally connected to the same bus or node, multiple new energy sources should be merged into one new energy station. From the perspective of short-circuit current calculation, multiple currents injected into the same node need to be merged into one current, and then the short-circuit fault static voltage stability phase margin index calculation and analysis should be performed.

[0074] For the static voltage stability assessment during a short-circuit fault in a decentralized grid system with multiple renewable energy sites, it is necessary to obtain the equivalent single-machine grid-connected system equivalent circuit of each renewable energy access node, and include the renewable energy equivalents of the remaining nodes as impedances in the node admittance matrix.

[0075] First, we need to obtain the positive-sequence node voltage equations for decentralized access to the power grid for multiple renewable energy stations. Figure 2 The positive sequence node voltage equation is:

[0076]

[0077] In the formula, the subscripts G, c, R, Q and f are the generator node, the new energy node to be evaluated, the remaining new energy nodes, the contact node and the fault node respectively. is the system admittance matrix, and are the node voltage and node injection current vector respectively.

[0078] When a three-phase fault occurs, the fault additional impedance is 0, and the corresponding rows and columns of the positive sequence node admittance matrix are crossed out to obtain the node voltage equation:

[0079]

[0080] Eliminate the contact nodes and get:

[0081]

[0082] When an asymmetric fault occurs, the additional fault impedance is determined by the specific fault type. The positive sequence node admittance matrix eliminates the fault node and can be obtained as follows:

[0083]

[0084] Eliminate the contact nodes and get:

[0085]

[0086] After obtaining the node voltage equation containing only the new energy node to be evaluated, the other new energy nodes and the generator node, the other new energy nodes are equivalent to admittance and added to the composite sequence network admittance matrix to obtain:

[0087]

[0088] Eliminate the remaining new energy nodes and get:

[0089]

[0090] make

[0091]

[0092] Then the voltage expression of the node c to be evaluated is:

[0093]

[0094] Therefore, the equivalent parameters of the single-machine grid-connected system of the node c to be evaluated are:

[0095]

[0096] The equivalent circuit is Figure 8 shown.

[0097] The short-circuit fault static voltage stability phase margin index is calculated through the equivalent single-machine grid-connected system equivalent potential and node voltage of each new energy access node, and the node with the smallest short-circuit fault static voltage stability phase margin index is taken as the weak node of voltage stability during the low voltage ride-through of the multi-new energy grid-connected system fault. The calculation formula for the static voltage stability phase deviation Dq during the low voltage ride-through of the new energy node c fault is:

[0098]

[0099] The static voltage stability phase deviation Dq of the new energy node c during the current fault low voltage ride-through period is calculated c After that, the new energy node c is used to stabilize the limit time Dq cmax =90°, define and calculate the static voltage stability phase margin index of the new energy node c short-circuit fault:

[0100]

[0101] K c When it is greater than 0, the voltage is stable during the low voltage ride-through of the new energy node c fault. After calculating the short-circuit fault static voltage stability phase margin index of all new energy access nodes, the minimum value of the short-circuit fault static voltage stability phase margin index is taken as the stability index for judging the multi-new energy grid-connected system:

[0102] K min =min(K c1 ,…,K ck )

[0103] K min The corresponding new energy node is a node with weak voltage stability during the low voltage ride-through period of the multi-new energy grid-connected system fault. The voltage is stable during the low voltage ride-through period of the multi-new energy grid-connected system fault, then Kmin Should be greater than or equal to 0. When K min Very close to 0, for example K min The range is between [0,0.05]. It can be considered that the multi-renewable energy grid-connected system is in a critical voltage stable state during the low voltage ride-through period. If K min Less than 0, the new energy grid-connected system loses static voltage stability during low voltage ride-through due to faults.

[0104] (2) The optimal control strategy for static voltage stability during low voltage ride-through when new energy stations are connected to the grid.

[0105] The voltage at the node of the new energy station in the equivalent circuit of the equivalent single-machine grid-connected system Thevenin equivalent potential The product of the current injected into the grid during low voltage ride-through of the new energy station and the impedance Synthesis, such as Fig. 9 shown.

[0106] The ratio of the active component to the reactive component of the current injected by the new energy station and the equivalent impedance of the equivalent single-machine grid-connected system The resistance component Z r and the reactance component Z x The ratio is the same:

[0107]

[0108] At this time, the voltage at the new energy station Thevenin equivalent potential Static voltage stability phase deviation Dq during fault low voltage ride-through c Equal to 0°, K c Equal to 1, the voltage stability is good.

[0109] The present application also provides a static voltage stability index analysis system during faults of multiple renewable energy sites, the system comprising: an establishment module, used to establish a grid node voltage equation including a generator node, a new energy node to be evaluated, a remaining new energy node, a contact node and a fault node according to the fault type and fault location of the multiple renewable energy sites connected to the power grid system; an analysis module, used to analyze the equivalent potential and equivalent impedance of the equivalent single-machine grid-connected system of the power grid corresponding to the new energy node to be evaluated according to the grid node voltage equation to obtain the equivalent single-machine grid-connected system equivalent circuit of each new energy access node to be evaluated; a screening module, used to calculate the voltage stability weak nodes of the multiple renewable energy grid-connected system during low voltage crossing according to the equivalent single-machine grid-connected system equivalent circuit; an optimization module, used to perform corresponding optimization processing according to the voltage stability weak nodes of the multiple renewable energy grid-connected system during low voltage crossing.

[0110] Specifically, the static voltage stability problem during the low voltage ride-through of short-circuit faults in a distributed grid system with multiple renewable energy stations is analyzed as an example. The evaluation and calculation of the static voltage stability margin index are explained in detail. The difference in the static voltage stability margin before and after the implementation of the optimal control strategy for static voltage stability during the low voltage ride-through of renewable energy station faults is compared. The evaluation implementation process is as follows: Fig.10 As shown, the following steps are included:

[0111] Step 1: Establish a circuit for connecting multiple renewable energy stations to the power grid, set basic parameters of renewable energy power sources, low-voltage control strategies and power grid faults;

[0112] Specifically, Fig.12 The IEEE33 node distribution network shown has 8 nodes connected to distributed renewable energy. Node 1 is connected to an external power supply with an internal impedance of 2 ohms. The reference voltage is 12.66 kV, the reference capacity is 10 MW, and the capacity of distributed renewable energy is 3.8 MW. During the fault low voltage ride-through period, it is assumed that the distributed renewable energy is fully reactive according to the rated current. Assume that a symmetrical fault occurs in the power grid, causing the external power supply voltage to drop from 1.05 pu to 0.2 pu.

[0113] Step 2: Calculate the short-circuit current of renewable energy connected to the grid;

[0114] Specifically, the current amplitude of each distributed renewable energy source is 0.1 pu, and the power factor angle is 0°. The output current of each distributed renewable energy source obtained by short-circuit iteration calculation is shown in Table 1 below.

[0115] Table 1

[0116] node New energy output current / pu node New energy output current / pu 4 -0.3797+0.0148i 22 -0.3719+0.0778i 10 -0.1982+0.3242i 23 -0.3798-0.0110i 15 0.3781-0.0375i 27 -0.2965+0.2377i 20 -0.3778+0.0412i 33 -0.0764+0.3722i

[0117] Step 3: For each new energy power access node, use the equivalent principle of the equivalent single-machine grid-connected system to obtain the equivalent potential of the node looking at the grid during the fault low voltage ride-through period;

[0118] Specifically, the equivalent potential and node voltage of each distributed new energy node entering the power grid are shown in Table 2 below.

[0119] Table 2

[0120]

[0121] Step 4: Calculate the static voltage stability phase deviation during the low voltage ride-through period of the new energy fault corresponding to each new energy access node according to the calculation formula of the static voltage stability phase deviation during the low voltage ride-through period of the new energy fault.

[0122] Specifically, each distributed new energy node calculates the static voltage stability phase deviation during the low voltage ride-through of new energy faults as shown in Table 3 below.

[0123] Table 3

[0124] node Phase deviation / ° node Phase deviation / ° 4 17.1236 22 33.9507 10 34.2297 23 18.8809 15 89.6684 27 21.3196 20 27.5711 33 46.5014

[0125] Step 5: Calculate the static voltage stability phase margin index of each new energy access node during short-circuit fault according to the static voltage stability phase deviation during the low voltage ride-through of the new energy fault.

[0126] Specifically, the short-circuit fault static voltage stability phase margin index calculated for each distributed new energy node is shown in Table 4 below.

[0127] Table 4

[0128] node <![CDATA[K c ]]> node <![CDATA[K c ]]> 4 0.8097 22 0.6228 10 0.6197 23 0.7902 15 0.0037 27 0.7631 20 0.6937 33 0.4833

[0129] Step 6: According to the index results of each node, the new energy access node with the smallest index is selected as the weak node of voltage stability during the low voltage ride-through of the new energy power grid fault.

[0130] Specifically, according to the above table, it is easy to know that node 15 is a node with weak voltage stability during low voltage ride-through of new energy grid fault. 15 The indicator is 0.0037, close to 0. Therefore, it can be considered that the voltage stability margin during the low voltage ride-through of the new energy fault system is very low, and the system voltage is critically stable. If the new energy capacity increases or the system voltage drops, the system will be unstable.

[0131] Step 7: Change the low voltage ride-through control strategy of new energy sources at nodes with larger indicators to the optimal control strategy proposed in this application, and calculate the indicators again.

[0132] Specifically, the low voltage ride-through control strategy of the node 15 with the largest phase margin index and the node 33 with the largest phase margin index is changed to the optimal control strategy, and the short-circuit fault static voltage stability phase margin index calculated for each distributed new energy node is shown in Table 5 below.

[0133] Table 5

[0134] node <![CDATA[K c ]]> node <![CDATA[K c ]]> 4 0.8985 22 0.8568 10 0.7310 23 0.9107 15 0.8994 27 0.8126 20 0.8900 33 0.9318

[0135] It can be seen that when the new energy station with larger indicators adopts the static voltage stability optimal control strategy during the fault low voltage ride-through period, the phase margin indicators of all new energy nodes increase and the voltage stability is greatly improved, indicating the effectiveness of the static voltage stability optimal control strategy.

[0136] According to the above embodiments, it can be seen that the indicators provided in this application can accurately calculate the static stability margin of the new energy station during the low voltage crossing of the short circuit fault of the power grid. The calculation method is simple and practical. The static voltage stability optimal control strategy during the low voltage crossing of the fault can effectively improve the static voltage stability during the low voltage crossing. The voltage stability during the low voltage crossing of the fault of the new energy access node in the system can be ranked by calculating the indicators, and the voltage stability weak nodes during the low voltage crossing of the fault of the new energy power grid can be understood without simulation, and the static voltage stability optimal control strategy during the low voltage crossing of the fault of the new energy station is proposed through the indicator principle.

[0137] The beneficial technical effect of the present application is that: a static voltage stability assessment method and index during the low voltage crossing period of short circuit faults caused by a high proportion of new energy access to the power grid are proposed, including two parts: static voltage stability assessment during the low voltage crossing period of short circuit faults caused by a high proportion of multiple new energy sites connected to the power grid, and the optimal control strategy for static voltage stability during the low voltage crossing period of new energy site faults. Furthermore, the voltage stability during the low voltage crossing period of the fault of the new energy access node in the system can be ranked by calculating the index, and the weak nodes of voltage stability during the low voltage crossing period of the fault of the new energy power grid can be understood without simulation, which is of great significance for guiding the safety and stability analysis of the power grid in terms of voltage stability. The proposed optimal control strategy for static voltage stability during the low voltage crossing period can effectively improve the static voltage stability during the low voltage crossing period of the fault of the new energy site.

[0138] Fig.11 A schematic diagram of the physical structure of an electronic device provided by an embodiment of the present invention, such as Fig.11 As shown, the electronic device includes: a processor (processor) 501, a memory (memory) 502 and a bus 503.

[0139] The processor 501 and the memory 502 communicate with each other via a bus 503 .

[0140] The processor 501 is used to call the program instructions in the memory 502 to execute the methods provided by the above method embodiments.

[0141] An embodiment of the present invention further provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the method for analyzing static voltage stability indicators during a multi-energy power plant fault is implemented.

[0142] An embodiment of the present invention further provides a computer program product, which includes a computer program. When the computer program is executed by a processor, the method for analyzing static voltage stability indicators during a multi-energy power plant fault is implemented.

[0143] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0144] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0145] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0146] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0147] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for analyzing static voltage stability index during a multi-energy power plant fault, characterized in that: The method comprises: According to the fault type and fault location of multiple renewable energy stations connected to the power grid system, the grid node voltage equation including generator nodes, renewable energy nodes to be evaluated, remaining renewable energy nodes, contact nodes and fault nodes is established; According to the grid node voltage equation, the equivalent potential and equivalent impedance of the equivalent single-machine grid-connected system of the grid corresponding to the new energy node to be evaluated are analyzed to obtain the equivalent circuit of the equivalent single-machine grid-connected system of each new energy access node to be evaluated; According to the equivalent circuit of the equivalent single-machine grid-connected system, the voltage stability weak node of the multi-new energy grid-connected system during the low voltage ride-through period is obtained; Corresponding optimization processing is performed according to the voltage stability weak nodes during the low voltage ride-through period of the multi-renewable energy grid-connected system.

2. The method for analyzing static voltage stability index during a multi-energy power plant fault according to claim 1 is characterized in that: Analyzing the equivalent potential and equivalent impedance of the equivalent single-machine grid-connected system of the power grid corresponding to the new energy node to be evaluated according to the power grid node voltage equation to obtain the equivalent circuit of the equivalent single-machine grid-connected system of each new energy access node to be evaluated comprises: According to the grid node voltage equation, the node impedance matrix is ​​obtained by equivalently treating the remaining new energy nodes as admittances and adding them into the composite sequence network admittance matrix; The equivalent potential and equivalent impedance of the equivalent single-machine grid-connected system of the power grid corresponding to the new energy node to be evaluated are analyzed by the node impedance matrix to obtain the equivalent single-machine grid-connected system equivalent circuit of each new energy access node to be evaluated.

3. The method for analyzing static voltage stability index during a multi-energy power plant fault according to claim 2 is characterized in that: The weak nodes of voltage stability during low voltage ride-through of the multi-renewable energy grid-connected system obtained by calculating the equivalent circuit of the equivalent single-machine grid-connected system include: According to the equivalent circuit of the equivalent single-machine grid-connected system, the static voltage stability phase deviation during the low voltage ride-through of the new energy fault and the static voltage stability phase margin index of the short circuit fault of each new energy access node are calculated; The voltage stability weak nodes of the multi-renewable energy grid-connected system during low voltage ride-through are obtained by analyzing the static voltage stability phase deviation and short-circuit fault static voltage stability phase margin indicators of each renewable energy access node.

4. The method for analyzing static voltage stability index during a multi-energy power plant fault according to claim 3 is characterized in that: According to the voltage stability weak nodes during the low voltage ride-through period of the multi-renewable energy grid-connected system, corresponding optimization processing is performed including: According to the voltage stability weak nodes during the low voltage ride-through period of the multi-renewable energy grid-connected system, the static voltage stability is improved based on the static voltage stability phase margin index calculation principle during the low voltage ride-through period of a short circuit fault of the multi-renewable energy station access power grid system.

5. The method for analyzing static voltage stability index during a multi-energy power plant fault according to claim 4 is characterized in that: Based on the calculation principle of the static voltage stability phase margin index during the low voltage ride-through period of short-circuit fault in the power grid system with multiple renewable energy stations connected to the grid, the static voltage stability is improved, including: Based on the calculation principle of the static voltage stability phase margin index during the low voltage ride-through period of short-circuit fault in the power grid system with multiple renewable energy stations connected, the static voltage stability is improved by reducing the phase deviation between the equivalent potential in the equivalent circuit of the equivalent single-machine grid-connected system and the node voltage of the renewable energy station to a preset value.

6. The method for analyzing static voltage stability index during a multi-energy power plant fault according to claim 5 is characterized in that: Reducing the phase deviation between the equivalent potential in the equivalent circuit of the equivalent single-machine grid-connected system and the node voltage of the new energy station to a preset value also includes: Obtaining a first ratio according to a ratio between an active component and a reactive component of a current injected by the new energy field; Obtaining a second ratio according to a ratio between a resistance component and a reactance component of an equivalent impedance of an equivalent single-machine grid-connected system; When the first ratio is the same as the second ratio, the preset value is met.

7. The method for analyzing static voltage stability index during a multi-energy power plant fault according to claim 3 is characterized in that: Through the short-circuit fault static voltage stability phase margin index analysis of each renewable energy access node, the weak voltage stability nodes of the renewable energy grid-connected system during the low voltage ride-through period are obtained, including: The voltage stability weak nodes during the low voltage ride-through period of the renewable energy grid-connected system are obtained according to the nodes with the smallest short-circuit fault static voltage stability phase margin index.

8. The method for analyzing static voltage stability index during a multi-energy power plant fault according to claim 4 is characterized in that: The calculation of the static voltage stability phase margin index during the low voltage ride-through period of short-circuit faults in the power grid system with multiple renewable energy stations includes: Obtain the positive-sequence node voltage equation of the decentralized access of multiple renewable energy fields to the power grid, and obtain the corresponding additional fault impedance according to the type of fault; The voltage expression of the new energy node to be evaluated is obtained by converting the fault additional impedance and the positive sequence node voltage equation, and the equivalent single-machine grid-connected system equivalent parameters of the new energy node to be evaluated are obtained by the voltage expression; The short-circuit fault static voltage stability phase margin index is calculated through the equivalent potential of the equivalent single-machine grid-connected system and the node voltage of each renewable energy access node.

9. The method for analyzing static voltage stability index during a multi-energy power plant fault according to claim 8, characterized in that: The voltage expression of the new energy node to be evaluated is obtained by converting the fault additional impedance and the positive sequence node voltage equation, including: Eliminating the fault node and the contact node in the positive sequence node voltage equation by the fault additional impedance to obtain a first node voltage equation containing only the generator node, the new energy node to be evaluated and the remaining new energy nodes; The remaining new energy nodes in the first node voltage equation are equivalent to admittances and added into the composite sequence network admittance matrix to obtain the second node voltage equation; Eliminate the remaining new energy nodes in the second node voltage equation to obtain a voltage expression of the new energy node to be evaluated.

10. A static voltage stability index analysis system during a multi-energy power plant fault, characterized in that: The system comprises: Establish a module for establishing a grid node voltage equation including a generator node, a new energy node to be evaluated, a remaining new energy node, a contact node and a fault node according to the fault type and fault location of the multiple new energy stations connected to the grid system; An analysis module is used to analyze the equivalent potential and equivalent impedance of the equivalent single-machine grid-connected system of the power grid corresponding to the new energy node to be evaluated according to the power grid node voltage equation to obtain the equivalent circuit of the equivalent single-machine grid-connected system of each new energy access node to be evaluated; A screening module, used for obtaining voltage stability weak nodes of the multi-renewable energy grid-connected system during low voltage ride-through according to the equivalent circuit calculation of the equivalent single-machine grid-connected system; The optimization module is used to perform corresponding optimization processing according to the voltage stability weak nodes during the low voltage ride-through period of the multi-renewable energy grid-connected system.

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

12. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method according to any one of claims 1 to 9 is implemented.

13. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instructions are executed by a processor, the steps of the method according to any one of claims 1 to 9 are implemented.

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