Method, device and medium for searching fault chains of power grid with flexible direct access to receiving end

Abstract

The present invention relates to a method, device, and medium for searching for fault chains in a receiving-end power grid containing flexible direct current (FDC), and relates to the field of power grid security. The method comprises: step S1: constructing an electromagnetic, electromechanical, and mechanical co-simulation model; step S2: performing simulation based on the electromagnetic, electromechanical, and mechanical co-simulation model, and calculating, based on the simulation data, a comprehensive vulnerability index for each AC line in the receiving-end power grid, wherein the comprehensive vulnerability index is obtained by the change in the hybrid multi-infeed short-circuit ratio, a DC commutation failure voltage recovery capability metric, a node voltage offset, and a power flow transfer entropy; and step S3: sorting all AC lines from largest to smallest according to the comprehensive vulnerability index, selecting the first AC line as the starting point of the fault chain, and searching for the fault chain using the electromagnetic, electromechanical, and mechanical co-simulation model. Compared with the prior art, the present invention has the advantages of reflecting the response process of conventional DC and flexible DC control systems and improving the accuracy of fault chain search.

Description

Technical Field

[0001] The present invention relates to the field of power grid security, and in particular to a method, device and medium for searching a fault chain of a power grid with flexible direct access to a receiving end. Background Art

[0002] Compared to pure AC systems, AC / DC systems carry a higher risk of severe cascading failures. For conventional HVDC (line commutated converter-based high voltage direct current) transmission, a cascading failure in the AC system could cause it to shut down and exit operation, exacerbating the risk of power outages.

[0003] Therefore, it is necessary to search for fault chains in AC / DC systems. For example, Chinese patent CN114640122A discloses a simulation method for the evolution path of cascading faults in AC / DC power grids. This method generates an initial cascading fault set for a self-set fault, determines the probability of a DC line blocking and a severe overload on the remaining AC lines in the next prediction phase, and generates a fault set for the next prediction phase. Using the disconnection rule for the number of reserved lines, n, the fault line for the next phase is selected until the termination condition is met, generating a set of cascading fault evolution paths. Furthermore, the number of reserved lines is appropriately selected, and while ensuring the search accuracy of the fault evolution path, the possibility of multiple simultaneous DC faults is considered to output the final cascading fault evolution path.

[0004] However, traditional fault chain search methods, including the above methods, do not take flexible DC transmission into consideration. Therefore, the cascading fault search process of AC / DC systems taking flexible transmission into account will be different from that of conventional AC / DC systems.

[0005] To address this phenomenon, some existing technologies, such as the document "A Method for Searching Cascading Fault Chains in AC / DC Hybrid Systems," consider the impact of flexible DC systems during the fault chain search process. However, this method uses an electromechanical simulation model for the DC model. This oversimplified electromechanical transient model cannot accurately reflect the response of conventional DC and flexible DC control systems, making it particularly difficult to identify continuous commutation failures in conventional DC. Furthermore, the derivation of key indicators is overly simplistic and fails to consider the reactive power support role of flexible DC systems. Summary of the Invention

[0006] The purpose of the present invention is to solve the defects of the above-mentioned prior art and to provide a method, device and medium for searching for fault chains in a power grid with flexible direct access to the receiving end.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A method for searching for fault chains in a power grid with flexible direct access to a receiving end, comprising:

[0009] Step S1: constructing an electromagnetic and electromechanical joint simulation model;

[0010] Step S2: Simulating based on the electromagnetic and electromechanical joint simulation model, and calculating based on the simulation data a comprehensive vulnerability index of each AC line in the receiving-end power grid, wherein the comprehensive vulnerability index is obtained by the hybrid multi-infeed short-circuit ratio change, the DC commutation failure voltage recovery capability metric, the node voltage offset, and the power flow transfer entropy;

[0011] Step S3: Sort all AC lines from large to small according to the comprehensive vulnerability index, select the first AC line as the starting point of the fault chain, and search to obtain the fault chain by combining the electromagnetic and electromechanical joint simulation model.

[0012] The comprehensive vulnerability index is obtained by weighted summation of the hybrid multi-infeed short-circuit ratio change, the DC commutation failure voltage recovery capability metric, the node voltage offset and the power flow transfer entropy.

[0013] The hybrid multi-infeed short-circuit ratio variation is specifically:

[0014]

[0015] in: For AC lines k Change in short-circuit ratio of hybrid multi-infeed conventional DC line after fault, For AC lines k Conventional DC line before fault i The hybrid multi-feed short-circuit ratio, For AC lines k Conventional DC line after fault i The hybrid multi-feed short-circuit ratio, For conventional DC lines i The self-impedance of the commutation bus, Fault line k Starting bus m The self-impedance, For conventional DC lines i The commutation bus and fault line k Starting bus m The mutual impedance of n is the number of conventional DC lines;

[0016] Conventional DC lines i The short-circuit ratio of the hybrid multi-infeed is:

[0017]

[0018] in: For conventional DC lines i The hybrid multi-feed short-circuit ratio,S ac,i For conventional DC lines i Short-circuit capacity at the grid connection point, For conventional DC lines i The corresponding reactive power compensation in parallel on the converter, For AC lines k Flexible straight line during fault j The maximum reactive power output to the receiving grid can be calculated by hybrid simulation, NVIF i,j For conventional DC lines i With soft straight road j The node voltage interaction factor between i,p For conventional DC lines i Compared with conventional DC lines p The node voltage interaction factor between P dNi For conventional DC lines i The rated active power, P dNp For conventional DC lines p The rated active power, P dNj Soft straight line j The rated active power, P jm is the margin value, Oh V is the set of all flexible straight lines, Oh L is the set of all conventional DC lines.

[0019] The DC commutation failure voltage recovery capability metric is specifically:

[0020]

[0021] in: For AC lines k The measurement value of the voltage recovery capability after DC commutation failure after a fault, is a conventional DC line with DC dynamic characteristics under AC line fault k i Commutation failure critical voltage, For AC lines k Under fault conditions, conventional DC lines i The commutation bus voltage, t i For conventional DC lines i The time to recover to the critical voltage of commutation failure after a fault, t 0 is the fault start time, and n is the number of conventional DC lines.

[0022] The step S3 comprises:

[0023] Step S3-1: Sort all AC lines according to the comprehensive vulnerability index from large to small to obtain an AC line fault candidate set, and select the first AC line in the AC line fault candidate set as the first-layer fault of the current fault chain;

[0024] Step S3-2: Set the currently selected AC line to three permanent N-1 faults, perform a short-time simulation, and determine whether any undisconnected AC line is overloaded. If so, execute step S3-3; otherwise, execute step S3-7;

[0025] Step S3-3: Add the overloaded AC line to the current fault chain and determine whether there are conventional DC lines with continuous commutation failures. If so, execute step S3-4. Otherwise, determine whether the number of layers in the current fault chain exceeds a preconfigured threshold length. If so, execute step S3-5. Otherwise, execute step S3-6.

[0026] Step S3-4: adding the conventional DC line with continuous commutation failure to the fault chain and blocking the corresponding conventional DC line, and executing step S3-5;

[0027] Step S3-5: Set all faults in the current fault chain as preceding faults, perform a long-time simulation based on the electromagnetic and electromechanical joint simulation model, and add the obtained subsequent faults to the current fault chain to generate a complete fault chain;

[0028] Step S3-6: Select the overloaded AC line and return to step S3-3;

[0029] Step S3-7: Determine whether there is a conventional DC line with continuous commutation failure. If so, execute step S3-4. Otherwise, determine whether the number of layers of the current fault chain exceeds the preconfigured threshold length. If so, execute step S3-5. Otherwise, create and select a new fault chain as the current fault chain, select the next AC line in the AC line fault candidate set that is not included in the fault chain as the next layer fault of the current fault chain, and execute step S3-2.

[0030] The rule for determining whether there is a conventional DC line with continuous commutation failure is: after the first commutation failure, the commutation fails again after a preconfigured time interval.

[0031] The preconfigured time interval is 200 milliseconds.

[0032] In step S3-3, if there are multiple overloaded AC lines, the AC line with the highest overload rate is added to the current fault chain.

[0033] A device for searching for fault chains in a power grid with flexible direct access to a receiving end includes a memory, a processor, and a program stored in the memory. When the processor executes the program, the method described above is implemented.

[0034] A storage medium stores a program, which implements the above method when executed.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. Through electromechanical and electromagnetic hybrid simulation, the response process of conventional DC and flexible DC control systems can be accurately reflected, the failure process of conventional DC continuous commutation can be judged, and the accuracy of fault chain search can be improved.

[0037] 2. Combined with electromechanical and electromagnetic hybrid simulation, a search index system for cascading faults in the receiving grid of flexible direct current (VDC) is established. A search process for cascading faults in the receiving grid of wind power via VDC is established. Initial faults are selected based on the proposed hybrid multi-infeed VDC system vulnerability index and AC transmission line index. Short-timescale hybrid simulations are performed, including judgments on overloaded lines and multiple commutation failures. If the judgment criteria are met, the system structure is modified to screen for the next level of faults. The search is terminated when the maximum number of search levels is reached, DC is locked, or the system becomes unstable. This forms a cascading fault chain involving offshore wind power via VDC in the receiving grid.

[0038] 3. It can not only ensure the accuracy of the model but also meet the requirements of large power grid simulation speed. Combined with the proposed cascading fault screening indicators and cascading fault search process, it can realize the rapid and accurate search of cascading faults in the receiving power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic flow chart of the main steps of the method of the present invention;

[0040] Figure 2 Flowchart of the simulation search process. DETAILED DESCRIPTION

[0041] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0042] Example 1

[0043] A fault chain search method for a power grid with flexible direct access to the receiving end, such as Figure 1 Shown, including:

[0044] Step S1: constructing an electromagnetic and electromechanical joint simulation model;

[0045] The electromagnetic and electromechanical joint simulation model is implemented based on electromagnetic transient simulation software, electromechanical transient simulation software and corresponding interface software respectively. Since this part has been recorded in the existing technology, it will not be repeated here.

[0046] Step S2: Simulate based on the electromagnetic and electromechanical joint simulation model, and calculate the comprehensive vulnerability index of each AC line in the receiving-end power grid based on the simulation data. The comprehensive vulnerability index is obtained by the change of the hybrid multi-infeed short-circuit ratio, the DC commutation failure voltage recovery capability metric, the node voltage offset, and the power flow transfer entropy.

[0047] The comprehensive vulnerability index is obtained by weighted summation of the hybrid multi-infeed short-circuit ratio change, DC commutation failure voltage recovery capability metric, node voltage offset and power flow transfer entropy.

[0048] 1) For hybrid multi-infeed short-circuit ratio variation

[0049] According to the definition of equivalent single-node injection current:

[0050]

[0051] in: I eq,xy is a node y To Node x The equivalent current transmitted, Z xy 、 Z xx Node x 、 y The mutual impedance between x The self-impedance. I y Injection node y The current is thus:

[0052]

[0053] in: U x 、 U y They are x 、 y The node voltage, S eq,xy For nodes y To Node x The output equivalent apparent output power, S y For nodes y The apparent power, in addition:

[0054]

[0055] in: P eq,xy 、 Q eq,xy For nodes y For Node x Equivalent active and reactive output. P y and Q y is the active and reactive output power of the transmission line, Δ f xy For nodes x With node y The voltage phase angle difference between , we can get:

[0056]

[0057] The node voltage interaction factor (NVIF) is defined as:

[0058]

[0059] Of which: NVIF x,y For nodes x and nodes y The node voltage interaction factor between them.

[0060] The short-circuit ratio can reflect the grid structure of the receiving power grid and its support capacity for the hybrid multi-infeed DC system, and is an important indicator for evaluating the system voltage stability. An improved hybrid multi-infeed DC short-circuit ratio indicator is proposed:

[0061]

[0062] in: S ac,i For conventional DC lines i The short-circuit capacity, For conventional DC lines i Reactive power compensation in parallel on the corresponding converter. Oh V is the set of all flexible straight lines, Oh DC Aggregate for all conventional DC lines and flexible straight lines. Q eq,i Soft straight line j Equivalent to conventional DC line i The reactive power at P eq,m In addition to conventional DC lines i Other DC lines other than the i The active power at P i For conventional DC linesi Rated output power.

[0063]

[0064] in: Q vr,j Soft straight line j The maximum reactive power output to the receiving grid during the fault period can be calculated by hybrid simulation, NVIF i,j Soft straight line i With conventional DC j The node voltage interaction factors between , in addition:

[0065]

[0066] in: For conventional DC lines p The active power, Soft straight line j Active power, NVIF i,p For conventional DC lines p and conventional DC lines i The node voltage interaction factor between them, when an AC fault occurs at the receiving end, the flexible DC rectifier side converter station takes control measures to stabilize the active power output of wind power, and the active power fluctuation is reflected to the receiving end grid connection point through the flexible DC. P jm express:

[0067]

[0068] In the formula, the margin value P jm Indicates the basic supporting capability of the flexible DC rectifier side to the receiving power grid. S ac,w Offshore wind power grid connection node w The short-circuit capacity at Q vs,j Soft straight line j The maximum reactive support capacity provided by the rectifier side under different control modes. The greater the reactive support on the rectifier side, the greater the margin value. P jm The larger the value, the greater the value. Q vs,j The values ​​of are shown in Table 1:

[0069] Table 1

[0070]

[0071] In Table 1, Q ref，j It is a soft straight road jRectifier side reactive power reference value, U 2 ac,j Soft straight line j Rated voltage of the AC system on the rectifier side, X eq,j Soft straight line j Equivalent impedance of the AC system on the rectifier side.

[0072] After processing, conventional DC lines i The short-circuit ratio of the hybrid multi-infeed is:

[0073]

[0074] in: For conventional DC lines i The hybrid multi-feed short-circuit ratio, S ac,i For conventional DC lines i Short-circuit capacity at the grid connection point, For conventional DC lines i The corresponding reactive power compensation in parallel on the converter, For AC lines k Flexible straight line during fault j The maximum reactive power output to the receiving grid can be calculated by hybrid simulation, NVIF i,j For conventional DC lines i With soft straight road j The node voltage interaction factor between i,p For conventional DC lines i Compared with conventional DC lines p The node voltage interaction factor between P dNi For conventional DC lines i The rated active power, P dNp For conventional DC lines p The rated active power, P dNj Soft straight line j The rated active power, P jm is the margin value, Oh V is the set of all flexible straight lines, Oh L is the set of all conventional DC lines.

[0075] The improved hybrid multi-infeed short-circuit ratio can be calculated through hybrid simulation to more accurately evaluate the reactive power support capability of the flexible DC system to the receiving grid, while fully considering the supporting role of the flexible DC rectifier side on the voltage stability of the receiving grid.

[0076] The closer the electrical distance between the AC line and the DC system commutation busbar, the stronger the coupling effect between the AC and DC. Before and after the AC line fault k occurs, the change in the hybrid multi-infeed short-circuit ratio is defined as:

[0077]

[0078] in: For AC lines k Change in short-circuit ratio of hybrid multi-infeed conventional DC line after fault, For AC lines k Conventional DC line before fault i The hybrid multi-feed short-circuit ratio, For AC lines k Conventional DC line after fault i The hybrid multi-feed short-circuit ratio, For conventional DC lines i The self-impedance of the commutation bus, Fault line k Starting bus m The self-impedance, For conventional DC lines i The commutation bus and fault line k Starting bus m The mutual impedance of n is the number of conventional DC lines;

[0079] The value of the fault line The larger the value, the better the AC line k The greater the impact of post-fault removal on the normal operation of conventional DC lines, the higher the risk of subsequent commutation failure or even DC blocking.

[0080] 2) Voltage recovery capability measurement for DC commutation failure

[0081] Define the DC commutation failure voltage recovery capability metric:

[0082]

[0083] in: For AC lines k The measurement value of the voltage recovery capability after DC commutation failure after a fault, For AC lines k Conventional DC lines taking into account DC dynamic characteristics under fault conditions i Commutation failure critical voltage, For AC lines k Under fault conditions, conventional DC lines i The commutation bus voltage, t i For conventional DC linesi The time it takes to recover to the critical voltage of commutation failure after a fault, t0 is the fault start time, and n is the number of conventional DC lines.

[0084] t i 、 t i0 It can be obtained by hybrid simulation calculation. S k The larger the value, the stronger the AC line k After a fault occurs, the voltage recovery capability of the commutation busbar of the hybrid multi-infeed HVDC transmission system is weaker.

[0085] U icr The calculation formula is as follows:

[0086]

[0087] Where, U icr It is a conventional DC line i The continuous commutation failure voltage threshold; N is the number of single-pole 6-pulse converters; is the extreme arc extinction angle; It is the trigger advance angle corresponding to when the arc extinction angle drops to the limit arc extinction angle during the commutation failure recovery process; is the commutation reactance; and are the rated values ​​of DC voltage and current respectively; the arc extinction angle during the recovery process of commutation failure Controlled by CEAC, and are the proportional coefficient and integral time constant of CEAC respectively; During commutation failure The downward slope of the curve; is the reference value of the arc extinction angle; is the integral constant, which can be obtained from the recovery process of commutation failure and The steady-state value is determined. b 、 k d is a constant term.

[0088] 3) For node voltage offset

[0089] The AC transmission line vulnerability index refers to the impact of an AC line fault on the power flow and reactive power balance of other lines in the receiving grid. The AC transmission line vulnerability index is divided into node voltage offset and power flow transfer entropy.

[0090] The node voltage offset is defined as:

[0091]

[0092] Where, U a0 、 U ak AC lines k Communication nodes before and after the fault a The voltage per unit value of the AC line k After the fault, if the AC node a Voltage per unit value U ak When it is lower than 0.8, the node is considered to be seriously affected by the fault. S Represents a collection of nodes of this type. D k The larger the value, the more serious the node voltage drop is, and the greater the impact on the local reactive power balance of the system. k The degree of impact on node voltage and system reactive balance after a fault.

[0093] 4) For the power transfer entropy

[0094] The power flow transfer entropy reflects the degree of balance of the power flow carried by an AC line in other AC lines after the line is disconnected due to a fault. It is used to evaluate the impact of the power flow transfer of the disconnected line on the system. The calculation formula is as follows:

[0095]

[0096] in:

[0097]

[0098] Where, L k Indicates AC line k After disconnection, the system's power flow transfer entropy; C is a constant with a value of 1; β c,k Indicates AC line k After disconnection, the AC line c Margin ratio; α c,k Indicates AC line c The proportion of the margin ratio of the system to the total margin ratio; m c0 、 m c,k Respectively represent the AC lines before and after the AC line k is disconnected c The load factor, m cmax For AC lines c The warning load rate is set to 0.9; l is the total number of AC lines.

[0099] To highlight the AC line k When the power flow carried by the line exceeds the warning load power, this paper performs weighted processing on the power flow transfer entropy, where P c,k For AC lines k After the AC line is removed c The transmission power, P cmax For AC lines c Warning load power.

[0100]

[0101]

[0102] The greater the system's power transfer entropy, the better the AC line k The more reasonable the transfer power generated after the removal is distributed in other AC lines according to the margin ratio, the more balanced the load rate distribution of the system; otherwise, it means that the AC line k The resulting current surge can easily lead to overloading of other lines or even over-limit failures.

[0103] Step S3: Sort all AC lines in descending order according to the comprehensive vulnerability index, select the first AC line as the starting point of the fault chain, and search the fault chain by combining the electromagnetic and electromechanical joint simulation model. In this embodiment, Figure 2 As shown, specifically including:

[0104] Step S3-1: Sort all AC lines according to the comprehensive vulnerability index from large to small to obtain an AC line fault candidate set, and select the first AC line in the AC line fault candidate set as the first-layer fault of the current fault chain;

[0105] Step S3-2: Set the currently selected AC line to three permanent N-1 faults, perform a short-time simulation, and determine whether any undisconnected AC line is overloaded. If so, execute step S3-3; otherwise, execute step S3-7;

[0106] Step S3-3: Add the overloaded AC line to the current fault chain and determine whether there are conventional DC lines with continuous commutation failures. If so, execute step S3-4. Otherwise, determine whether the number of layers in the current fault chain exceeds a preconfigured threshold length. If so, execute step S3-5. Otherwise, execute step S3-6.

[0107] Step S3-4: adding the conventional DC line with continuous commutation failure to the fault chain and blocking the corresponding conventional DC line, and executing step S3-5;

[0108] Step S3-5: Set all faults in the current fault chain as preceding faults, perform a long-time simulation based on the electromagnetic and electromechanical joint simulation model, and add the obtained subsequent faults to the current fault chain to generate a complete fault chain;

[0109] Step S3-6: Select the overloaded AC line and return to step S3-3;

[0110] Step S3-7: Determine whether there is a conventional DC line with continuous commutation failure. If so, execute step S3-4. Otherwise, determine whether the number of layers of the current fault chain exceeds the preconfigured threshold length. If so, execute step S3-5. Otherwise, create and select a new fault chain as the current fault chain, select the next AC line in the AC line fault candidate set that is not included in the fault chain as the next layer fault of the current fault chain, and execute step S3-2.

[0111] In this embodiment, the rule for determining whether there is a conventional DC line with continuous commutation failure is: after the first commutation failure, the commutation failure occurs again after a preconfigured time interval. Generally, the preconfigured time interval is 200 milliseconds.

[0112] In addition, in step S3-3, if there are multiple overloaded AC lines, the AC line with the highest overload rate is added to the current fault chain.

[0113] Example 2

[0114] The electronic device of the present invention includes a central processing unit (CPU), which can perform various appropriate actions and processes according to computer program instructions stored in a read-only memory (ROM) or loaded from a storage unit into a random access memory (RAM). In the RAM, various programs and data required for device operation can also be stored. The CPU, ROM, and RAM are connected to each other via a bus. An input / output (I / O) interface is also connected to the bus.

[0115] Many components in a device are connected to the I / O interface, including: input units, such as a keyboard and mouse; output units, such as various types of displays and speakers; storage units, such as magnetic disks and optical disks; and communication units, such as network cards, modems, and wireless communication transceivers. The communication unit allows the device to exchange information / data with other devices via computer networks such as the Internet and / or various telecommunication networks.

[0116] The processing unit performs the various methods and processes described above, such as methods S1 to S3. For example, in some embodiments, methods S1 to S3 may be implemented as a computer software program, which is tangibly contained in a machine-readable medium, such as a storage unit. In some embodiments, part or all of the computer program may be loaded and / or installed on the device via a ROM and / or a communication unit. When the computer program is loaded into the RAM and executed by the CPU, one or more steps of methods S1 to S3 described above may be performed. Alternatively, in other embodiments, the CPU may be configured to execute methods S1 to S3 by any other appropriate means (e.g., by means of firmware).

[0117] The functions described above herein may be performed, at least in part, by one or more hardware logic components. For example, and without limitation, exemplary types of hardware logic components that may be used include: field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), application specific standard products (ASSPs), systems on chip (SOCs), complex programmable logic devices (CPLDs), and the like.

[0118] The program code for implementing the method of the present invention can be written in any combination of one or more programming languages. Such program code can be provided to a processor or controller of a general-purpose computer, a special-purpose computer, or other programmable data processing device so that when the program code is executed by the processor or controller, the functions / operations specified in the flow chart and / or block diagram are implemented. The program code can be executed entirely on the machine, partially on the machine, as a stand-alone software package, partially on the machine and partially on a remote machine, or entirely on a remote machine or server.

[0119] In the context of the present invention, machine-readable medium can be a tangible medium that can contain or store a program for use with an instruction execution system, device or equipment or used in combination with an instruction execution system, device or equipment. Machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. Machine-readable medium can include, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared or semiconductor systems, devices or equipment, or any suitable combination of the foregoing. More specific examples of machine-readable storage media can include electrical connections based on one or more lines, portable computer disks, hard disks, random access memories (RAM), read-only memories (ROM), erasable programmable read-only memories (EPROM or flash memory), optical fibers, portable compact disk read-only memories (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0120] If the above functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes various media that can store program code, such as USB flash drives, mobile hard drives, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical disks.

Claims

1. A method for searching for fault chains in a power grid with flexible direct access to a receiving end, characterized in that: include: Step S1: constructing an electromagnetic and electromechanical joint simulation model; Step S2: Simulating based on the electromagnetic and electromechanical joint simulation model, and calculating based on the simulation data a comprehensive vulnerability index of each AC line in the receiving-end power grid, wherein the comprehensive vulnerability index is obtained by the hybrid multi-infeed short-circuit ratio change, the DC commutation failure voltage recovery capability metric, the node voltage offset, and the power flow transfer entropy; Step S3: Sort all AC lines from largest to smallest according to the comprehensive vulnerability index, select the first AC line as the starting point of the fault chain, and search to obtain the fault chain using the electromagnetic and electromechanical joint simulation model; The hybrid multi-infeed short-circuit ratio variation is specifically: in: For AC lines k Change in short-circuit ratio of hybrid multi-infeed conventional DC line after fault, For AC lines k Conventional DC line before fault i The hybrid multi-feed short-circuit ratio, For AC lines k Conventional DC line after fault i The hybrid multi-feed short-circuit ratio, For conventional DC lines i The self-impedance of the commutation bus, Fault line k Starting bus m The self-impedance, For conventional DC lines i The commutation bus and fault line k Starting bus m The mutual impedance, n is the number of conventional DC lines; Conventional DC lines i The short-circuit ratio of the hybrid multi-infeed is: in: For conventional DC lines i The hybrid multi-feed short-circuit ratio, S ac,i For conventional DC lines i Short-circuit capacity at the grid connection point, For conventional DC lines i The corresponding reactive power compensation in parallel on the converter, For AC lines k Flexible straight line during fault j The maximum reactive power output to the receiving grid is calculated by hybrid simulation, NVIF i,j For conventional DC lines i With soft straight road j The node voltage interaction factor between i,p For conventional DC lines i Compared with conventional DC lines p The node voltage interaction factor between P dNi For conventional DC lines i The rated active power, P dNp For conventional DC lines p The rated active power, P dNj Soft straight line j The rated active power, P jm is the margin value, Ω V is the set of all flexible straight lines, Ω L is the set of all conventional DC lines.

2. The method for searching for fault chains in a power grid with flexible direct access to a receiving end according to claim 1, characterized in that: The comprehensive vulnerability index is obtained by weighted summation of the hybrid multi-infeed short-circuit ratio change, the DC commutation failure voltage recovery capability metric, the node voltage offset and the power flow transfer entropy.

3. The method for searching for fault chains in a power grid with flexible direct access to a receiving end according to claim 1, characterized in that: The DC commutation failure voltage recovery capability metric is specifically: in: For AC lines k The measurement value of the voltage recovery capability after DC commutation failure after a fault, is a conventional DC line with DC dynamic characteristics under AC line fault k i Commutation failure critical voltage, For AC lines k Under fault conditions, conventional DC lines i The commutation bus voltage, t i For conventional DC lines i The time to recover to the critical voltage of commutation failure after a fault, t 0 is the fault start time, n is the number of conventional DC lines.

4. The method for searching for fault chains in a power grid with flexible direct access to a receiving end according to claim 1, characterized in that: The step S3 comprises: Step S3-1: Sort all AC lines according to the comprehensive vulnerability index from large to small to obtain an AC line fault candidate set, and select the first AC line in the AC line fault candidate set as the first-layer fault of the current fault chain; Step S3-2: Set the currently selected AC line to three permanent N-1 faults, perform a short-time simulation, and determine whether any undisconnected AC line is overloaded. If so, execute step S3-3; otherwise, execute step S3-7; Step S3-3: Add the overloaded AC line to the current fault chain and determine whether there are conventional DC lines with continuous commutation failures. If so, execute step S3-4. Otherwise, determine whether the number of layers in the current fault chain exceeds a preconfigured threshold length. If so, execute step S3-5. Otherwise, execute step S3-6. Step S3-4: adding the conventional DC line with continuous commutation failure to the fault chain and blocking the corresponding conventional DC line, and executing step S3-5; Step S3-5: Set all faults in the current fault chain as preceding faults, perform a long-time simulation based on the electromagnetic and electromechanical joint simulation model, and add the obtained subsequent faults to the current fault chain to generate a complete fault chain; Step S3-6: Select the overloaded AC line and return to step S3-3; Step S3-7: Determine whether there is a conventional DC line with continuous commutation failure. If so, execute step S3-4. Otherwise, determine whether the number of layers of the current fault chain exceeds the preconfigured threshold length. If so, execute step S3-5. Otherwise, create and select a new fault chain as the current fault chain, select the next AC line in the AC line fault candidate set that is not included in the fault chain as the next layer fault of the current fault chain, and execute step S3-2.

5. The method for searching for fault chains in a power grid with flexible direct access to a receiving end according to claim 4, characterized in that: The rule for determining whether there is a conventional DC line with continuous commutation failure is: after the first commutation failure, the commutation fails again after a preconfigured time interval.

6. The method for searching for fault chains in a power grid with flexible direct access to a receiving end according to claim 5, characterized in that: The preconfigured time interval is 200 milliseconds.

7. The method for searching for fault chains in a power grid with flexible direct access to a receiving end according to claim 4, characterized in that: In step S3-3, if there are multiple overloaded AC lines, the AC line with the highest overload rate is added to the current fault chain.

8. A device for searching for fault chains in a power grid with flexible direct access to a receiving end, comprising a memory, a processor, and a program stored in the memory, characterized in that: When the processor executes the program, the method according to any one of claims 1 to 7 is implemented.

9. A storage medium having a program stored thereon, characterized in that: When the program is executed, the method according to any one of claims 1 to 7 is implemented.

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