Direct current system fault ride-through and recovery capability evaluation method, device, equipment, medium and product

Abstract

The invention relates to a direct current system fault ride-through and recovery capability evaluation method and device, equipment, a medium and a product. The method comprises the following steps: determining the low voltage ride through capability of the multi-terminal embedded direct current system under the condition that a three-phase grounding short circuit fault occurs in an alternating current power grid; after the three-phase grounding short-circuit fault of the alternating-current power grid is removed, the alternating-current voltage recovery capability is determined; determining the power regulation capability of the multi-terminal embedded DC system under the condition that the N-2 fault occurs in the AC line; the N-2 fault comprises that when one alternating current transmission line breaks down, the other parallel or associated line also breaks down; and comprehensively evaluating the fault ride-through and recovery capability of the multi-terminal embedded DC system according to the low voltage ride-through capability, the AC voltage recovery capability and the power regulation capability. Therefore, various different fault scenes can be comprehensively considered, the fault ride-through and recovery capability of the multi-terminal embedded direct current system is evaluated from multiple indexes, and the accuracy of an evaluation result is remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power systems, and in particular to a DC system fault ride-through and recovery capability evaluation method and device, computer equipment, computer readable storage medium and computer program product. BACKGROUND

[0002] With the development of new energy technology, the receiving end AC power grid may need to withstand a high proportion of new energy access and / or intensive feeding of EHVDC.

[0003] At present, the conventional DC system (Line-Commutated Converter-Based High-Voltage Direct Current, LCC-HVDC) is prone to commutation failure when the AC fault occurs, resulting in active power interruption and reactive power impact, which seriously threatens the safety of the power grid. Although the DC system (Voltage Source Converter-based Multi-Terminal Direct Current, VSC-MTDC) has the advantages of no commutation failure and fast power regulation, there is a lack of systematic evaluation method for the fault ride-through and recovery capability of the multi-terminal embedded scene. SUMMARY

[0004] Therefore, it is necessary to provide a DC system fault ride-through and recovery capability method, device, computer equipment, computer readable storage medium and computer program product capable of accurately evaluating the fault ride-through and recovery capability of the multi-terminal embedded DC system facing AC grid faults.

[0005] In a first aspect, the present application provides a DC system fault ride-through and recovery capability evaluation method, which comprises:

[0006] In the case of a three-phase ground fault of the AC power grid, the low voltage ride-through capability of the multi-terminal embedded DC system is determined;

[0007] After the three-phase ground fault of the AC power grid is removed, the AC voltage recovery capability is determined;

[0008] In the case of N-2 fault of the AC line, the power regulation capability of the multi-terminal embedded DC system is determined; the N-2 fault includes: when one AC transmission line fails, another parallel or associated line also fails;

[0009] According to the low voltage ride-through capability, the AC voltage recovery capability and the power regulation capability, the fault ride-through and recovery capability of the multi-terminal embedded DC system is comprehensively evaluated.

[0010] In one of the embodiments, the method for determining the low voltage ride through capability of the multi-terminal HVDC system in the case of three-phase ground fault of the AC power grid comprises:

[0011] determining the actual output active power of the multi-terminal HVDC system during the three-phase ground fault of the AC power grid;

[0012] evaluating the active power retention rate of the multi-terminal HVDC system during the ride through according to the ratio between the actual output active power and the rated active power;

[0013] determining the short circuit current margin according to the upper limit of the circuit breaker breaking capacity and the effective value of the short circuit current at the time of the fault;

[0014] determining the low voltage ride through capability of the multi-terminal HVDC system according to the active power retention rate during the ride through and the short circuit current margin.

[0015] In one of the embodiments, the method for determining the AC voltage recovery capability after the three-phase ground fault of the AC power grid is removed comprises:

[0016] determining the voltage stiffness according to the ratio between the AC bus voltage recovery value after the fault is removed and the rated voltage;

[0017] determining the reactive power compensation rate according to the ratio between the output reactive power of the multi-terminal HVDC system and the reactive power deficiency of the AC system;

[0018] determining the AC voltage recovery capability according to the voltage stiffness and the reactive power compensation rate.

[0019] In one of the embodiments, the method for determining the power regulation capability of the multi-terminal HVDC system in the case of N-2 fault of the AC line comprises:

[0020] determining the thermal stability margin according to the maximum transmission capacity and the actual transmission capacity of the line;

[0021] determining the power transfer amount of the multi-terminal HVDC system in the case of N-2 fault according to the DC power of each terminal before and after the fault;

[0022] determining the power regulation capability of the multi-terminal HVDC system according to the thermal stability margin and the power transfer amount.

[0023] In one of the embodiments, before the fault ride through and recovery capability of the multi-terminal HVDC system is comprehensively evaluated according to the low voltage ride through capability, the AC voltage recovery capability and the power regulation capability, the method further comprises:

[0024] The evaluation index system for establishing the fault ride-through and recovery capability of the multi-terminal embedded DC system comprises: primary indexes and secondary indexes; the primary indexes comprise at least one of a fault ride-through capability, a voltage recovery capability and a power regulation capability; and the secondary indexes comprise at least one of an active power retention rate, a short-circuit current margin, a voltage stiffness, a reactive power compensation rate, a thermal stability margin and a power transfer amount.

[0025] The analytic hierarchy process is used to determine the weight corresponding to each primary index and each secondary index.

[0026] In one of the embodiments, the comprehensive evaluation of the fault ride-through and recovery capability of the multi-terminal embedded DC system according to the low-voltage ride-through capability, the AC voltage recovery capability and the power regulation capability comprises:

[0027] According to the low-voltage ride-through capability, the AC voltage recovery capability and the power regulation capability, and the weight corresponding to each primary index and each secondary index, a comprehensive score corresponding to the multi-terminal embedded DC system is determined, and the comprehensive score is used to evaluate the fault ride-through and recovery capability of the multi-terminal embedded DC system.

[0028] In a second aspect, the application further provides a device for evaluating the fault ride-through and recovery capability of a DC system, and the device comprises:

[0029] A first determining module is configured to determine a low-voltage ride-through capability of a multi-terminal embedded DC system in the case of a three-phase ground fault of an AC power grid.

[0030] A second determining module is configured to determine an AC voltage recovery capability after the three-phase ground fault of the AC power grid is removed.

[0031] A third determining module is configured to determine a power regulation capability of the multi-terminal embedded DC system in the case of an N-2 fault of an AC line, wherein the N-2 fault comprises a situation that when one AC transmission line fails, another parallel or associated line also fails.

[0032] An evaluation module is configured to comprehensively evaluate the fault ride-through and recovery capability of the multi-terminal embedded DC system according to the low-voltage ride-through capability, the AC voltage recovery capability and the power regulation capability.

[0033] In a third aspect, the application further provides a computer device comprising a memory and a processor, wherein the memory stores a computer program, and the processor implements the following steps when executing the computer program:

[0034] In the case of a three-phase ground fault of an AC power grid, a low-voltage ride-through capability of a multi-terminal embedded DC system is determined.

[0035] determining an AC voltage recovery capability after the three-phase ground fault of the AC power grid is removed;

[0036] determining a power regulation capability of the multi-terminal HVDC system in the case of an N-2 fault of the AC power grid; the N-2 fault includes that when one AC transmission line fails, another parallel or associated line also fails;

[0037] comprehensively evaluating the fault ride-through and recovery capability of the multi-terminal HVDC system according to the low voltage ride-through capability, the AC voltage recovery capability and the power regulation capability.

[0038] In a fourth aspect, the present application also provides a computer readable storage medium, which has a computer program stored thereon, and the computer program is executed by a processor to implement the following steps:

[0039] determining a low voltage ride-through capability of the multi-terminal HVDC system in the case of a three-phase ground fault of the AC power grid;

[0040] determining an AC voltage recovery capability after the three-phase ground fault of the AC power grid is removed;

[0041] determining a power regulation capability of the multi-terminal HVDC system in the case of an N-2 fault of the AC power grid; the N-2 fault includes that when one AC transmission line fails, another parallel or associated line also fails;

[0042] comprehensively evaluating the fault ride-through and recovery capability of the multi-terminal HVDC system according to the low voltage ride-through capability, the AC voltage recovery capability and the power regulation capability.

[0043] In a fifth aspect, the present application also provides a computer program product, which includes a computer program, and the computer program is executed by a processor to implement the following steps:

[0044] determining a low voltage ride-through capability of the multi-terminal HVDC system in the case of a three-phase ground fault of the AC power grid;

[0045] determining an AC voltage recovery capability after the three-phase ground fault of the AC power grid is removed;

[0046] determining a power regulation capability of the multi-terminal HVDC system in the case of an N-2 fault of the AC power grid; the N-2 fault includes that when one AC transmission line fails, another parallel or associated line also fails;

[0047] According to the low-voltage ride-through capability, the AC voltage recovery capability and the power regulation capability, the fault ride-through and recovery capability of the multi-terminal HVDC system is comprehensively evaluated.

[0048] The DC system fault ride-through and recovery capability evaluation method, device, computer equipment, computer readable storage medium and computer program product provided in the embodiment of the present application, by determining the low-voltage ride-through capability of the multi-terminal HVDC system in the case of three-phase ground fault of the AC power grid; determining the AC voltage recovery capability after the three-phase ground fault of the AC power grid is removed; determining the power regulation capability of the multi-terminal HVDC system in the case of N-2 fault of the AC line; the N-2 fault includes: when one AC transmission line fails, another parallel or associated line also fails; thereby the fault ride-through and recovery capability of the multi-terminal HVDC system can be analyzed from three aspects of low-voltage ride-through capability under three-phase ground fault, AC voltage recovery capability, and power regulation capability under N-2 fault of the AC line, ensuring the comprehensiveness and objectivity of the analysis. According to the low-voltage ride-through capability, the AC voltage recovery capability and the power regulation capability, the fault ride-through and recovery capability of the multi-terminal HVDC system is comprehensively evaluated. Thus, various different fault scenarios can be considered comprehensively, and the fault ride-through and recovery capability of the multi-terminal HVDC system can be evaluated from multiple indexes, significantly improving the accuracy of the evaluation result. BRIEF DESCRIPTION OF DRAWINGS

[0049] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related art, the drawings needed to be used in the description of the embodiments of the present application or the related art will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other related drawings can also be obtained without creative labor.

[0050] Figure 1 The principle diagram of the DC system fault ride-through and recovery capability evaluation method provided in an embodiment of the present application;

[0051] Figure 2 The flowchart of the DC system fault ride-through and recovery capability evaluation method in an embodiment;

[0052] Figure 3 The flowchart of the DC system fault ride-through and recovery capability evaluation method in another embodiment;

[0053] Figure 4 The structural block diagram of the DC system fault ride-through and recovery capability evaluation device in an embodiment;

[0054] Figure 5A structural block diagram of a device for evaluating the fault ride-through and recovery capability of a direct current system in another embodiment;

[0055] Figure 6 An internal structural diagram of a computer device in an embodiment. DETAILED DESCRIPTION

[0056] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not intended to limit the present application.

[0057] It should be noted that the terms "comprise" and "have" and any variations thereof used in the present application are intended to cover non-exclusive inclusion. The term "and / or" used in the present application refers to one of the schemes or any combination of multiple schemes.

[0058] Although the direct current system has advantages such as no commutation failure and fast power regulation, it mainly relies on a single index (such as short circuit ratio) to evaluate voltage stability, without comprehensively considering power regulation, thermal stability constraints and multi-scheme comparison and selection requirements under multiple fault scenarios, resulting in inaccurate evaluation results.

[0059] In view of the problems in the prior art, the present application aims to provide a method for evaluating the fault ride-through and recovery capability of a direct current system, which analyzes the fault ride-through and recovery capability of a multi-terminal embedded direct current system from three aspects of low voltage ride-through capability under three-phase ground fault, AC voltage recovery capability, and power regulation capability under AC line N-2 fault, and comprehensively analyzes different capabilities by using an analytic hierarchy process method to obtain a complete scheme for evaluating the fault ride-through and recovery capability of a multi-terminal embedded direct current system facing AC grid faults, so as to objectively and accurately evaluate the fault ride-through and recovery capability of a conventional direct current system and a flexible direct current system.

[0060] An exemplary, Figure 1 A principle schematic diagram of the method for evaluating the fault ride-through and recovery capability of a direct current system provided in an embodiment of the present application is shown in FIG. 1. Figure 1 The embodiment can be applied to a multi-terminal embedded direct current system facing AC grid faults and evaluate the fault ride-through and recovery capability thereof. Alternatively, the comprehensive analysis is mainly performed from three aspects of low voltage ride-through capability, AC voltage recovery capability, and power regulation capability under N-2 fault. The method can also be applied to a multi-terminal interconnected grid containing a conventional direct current and a direct current, and evaluate the stability under three-phase ground fault, AC line N-2 fault and other scenarios.

[0061] In an exemplary embodiment, as shown in FIG. 2, Figure 2As shown, a DC system fault ride-through and recovery capability evaluation method is provided, which can include the following steps 201 to 204. Among them:

[0062] Step 201, in the case of three-phase ground fault in AC power grid, determine the low voltage ride-through capability of multi-terminal embedded DC system.

[0063] In the AC power grid, three-phase ground fault is a serious type of fault, which involves three-phase lines in the grid being connected to the ground at the same time, causing current to flow through the grounding path. This kind of fault usually leads to the rapid action of power grid protection devices (such as circuit breakers) to cut off the fault part to prevent further damage or safety accidents. Therefore, it is necessary to analyze the low voltage ride-through capability of multi-terminal embedded DC system in the case of three-phase ground fault in AC power grid.

[0064] Among them, the low voltage ride-through (LVRT) capability refers to the ability of power generation equipment or power electronic devices to continue running without being disconnected from the grid when voltage sag occurs, and in some cases, to provide reactive power to help the system recover voltage. This capability is crucial for maintaining grid stability and reducing the number of repeated grid connections of power generation systems during faults.

[0065] It should be noted that in the DC system, low voltage ride-through capability is very important, especially in renewable energy power generation systems such as wind power and photovoltaic power generation. When the grid voltage decreases, the DC system needs to have certain mechanisms to maintain its operation and avoid system shutdown due to voltage sag.

[0066] For example, during the period of three-phase ground fault in AC power grid, the actual output active power of multi-terminal embedded DC system is determined; the active power retention rate of multi-terminal embedded DC system during ride-through is evaluated according to the ratio between actual output active power and rated active power; the short-circuit current margin is determined according to the upper limit of circuit breaker interruption capacity and the effective value of short-circuit current during fault; the low voltage ride-through capability of multi-terminal embedded DC system is determined according to the active power retention rate during ride-through and the short-circuit current margin.

[0067] Optionally, the active power retention rate η p during low voltage ride-through is calculated as follows:

[0068]

[0069] In the formula: P fantt is the actual output active power of DC system during fault; P rated is the rated active power. The active power retention rate during low voltage ride-through reflects the power retention capability of the system during voltage sag.

[0070] Optionally, the short-circuit current margin λ sc The influence of the DC system on the short-circuit current of the AC bus is measured by the following formula:

[0071]

[0072] In the formula: I limit represents the upper limit of the breaking capacity of the circuit breaker, I fault represents the effective value of the short-circuit current at the time of the fault. When λsc>0, it indicates that the system short-circuit current is not over-limit.

[0073] Step 202, after the three-phase ground fault of the AC power grid is removed, the AC voltage recovery capability is determined.

[0074] The AC voltage recovery capability refers to the ability of the AC power grid to quickly recover to a normal level after a fault in the power system. This capability is crucial for ensuring the stable operation of the power system, as it directly affects the reliability and power supply quality of the power system.

[0075] For example, according to the ratio between the AC bus voltage recovery value after the fault is removed and the rated voltage, the voltage stiffness is determined; according to the ratio between the output reactive power of the multi-terminal embedded DC system and the reactive power deficiency of the AC system, the reactive power compensation rate is determined; according to the voltage stiffness and the reactive power compensation rate, the AC voltage recovery capability is determined.

[0076] Optionally, the voltage stiffness K vtg The support capability of the DC system for the AC voltage recovery is evaluated by the following formula:

[0077]

[0078] In the formula: U recovery represents the AC bus voltage recovery value after the fault is removed, U rated represents the rated voltage. K vtg The closer to 1, the stronger the voltage recovery capability.

[0079] Optionally, the flexible DC system can provide dynamic reactive power support after the fault, and the reactive power compensation rate η Q is defined, and the calculation formula is as follows:

[0080]

[0081] In the formula: Q provided represents the output reactive power of the DC system, Q demand represents the reactive power deficiency of the AC system.

[0082] Step 203, determining the power regulation capability of the multi-terminal embedded DC system in the case of N-2 fault of the AC line.

[0083] Wherein, the N-2 fault includes: when one AC transmission line fails, another parallel or associated line also fails.

[0084] It should be noted that in the power system, the N-2 fault also includes the case of simultaneous double or multiple faults (including short circuit and operation) in the system. The purpose of calculating the complex fault is to determine the severity of the fault, set the relay protection device, select the electrical equipment, and analyze the distribution of negative sequence and zero sequence current in the system.

[0085] For example, according to the maximum transmission capacity and the actual transmission capacity of the line, the thermal stability margin is determined; according to the DC power of each terminal before and after the fault, the power transfer amount of the multi-terminal embedded DC system in the case of N-2 fault is determined; according to the thermal stability margin and the power transfer amount, the power regulation capability of the multi-terminal embedded DC system is determined.

[0086] Optionally, the thermal stability margin Φ i The calculation formula is as follows:

[0087]

[0088] In the formula: S max,i represents the maximum transmission capacity of the line, S at,i represents the actual transmission capacity. When Φ i <0, the line flow is out of limit.

[0089] Optionally, the power transfer amount of the multi-terminal DC system under N-2 fault The calculation formula is as follows:

[0090]

[0091] In the formula: P dc,j and P dc,j ′ respectively represent the DC power of the jth terminal before and after the fault.

[0092] Step 204, according to the low voltage ride through capability, the AC voltage recovery capability and the power regulation capability, the fault ride through and recovery capability of the multi-terminal embedded DC system is comprehensively evaluated.

[0093] In this embodiment, the fault ride-through and recovery capability of the multi-terminal embedded DC system can be evaluated from three aspects of low voltage ride-through capability, AC voltage recovery capability and power regulation capability. Alternatively, corresponding weights are set for each capability, and the index values of the three aspects of low voltage ride-through capability, AC voltage recovery capability and power regulation capability are multiplied by the corresponding weights, so that the comprehensive score of the fault ride-through and recovery capability of the multi-terminal embedded DC system can be obtained.

[0094] In the above method for evaluating the fault ride-through and recovery capability of the DC system, the low voltage ride-through capability of the multi-terminal embedded DC system is determined in the case of three-phase ground fault of the AC power grid, the AC voltage recovery capability is determined after the three-phase ground fault of the AC power grid is removed, and the power regulation capability of the multi-terminal embedded DC system is determined in the case of N-2 fault of the AC line. The N-2 fault includes: when one AC transmission line fails, another parallel or associated line also fails. Thus, the fault ride-through and recovery capability of the multi-terminal embedded DC system can be analyzed from three aspects of low voltage ride-through capability under three-phase ground fault, AC voltage recovery capability, and power regulation capability under N-2 fault of the AC line, ensuring the comprehensiveness and objectivity of the analysis. According to the low voltage ride-through capability, the AC voltage recovery capability and the power regulation capability, the fault ride-through and recovery capability of the multi-terminal embedded DC system is comprehensively evaluated. Thus, various different fault scenarios can be considered comprehensively, and the fault ride-through and recovery capability of the multi-terminal embedded DC system can be evaluated from multiple indexes, significantly improving the accuracy of the evaluation result.

[0095] In another exemplary embodiment, as shown in Figure 3 a method for evaluating the fault ride-through and recovery capability of a DC system is provided, which can include the following steps 301 to 306. Among them:

[0096] Step 301, in the case of three-phase ground fault of the AC power grid, the low voltage ride-through capability of the multi-terminal embedded DC system is determined.

[0097] Step 302, after the three-phase ground fault of the AC power grid is removed, the AC voltage recovery capability is determined.

[0098] Step 303, in the case of N-2 fault of the AC line, the power regulation capability of the multi-terminal embedded DC system is determined.

[0099] The specific implementation process and technical effects of steps 301 to 303 in this embodiment can be referred to the related description of steps 201 to 203 in the method embodiment shown in Figure 2 , and will not be described here.

[0100] Step 304, an evaluation index system of the fault ride-through and recovery capability of the multi-terminal embedded DC system is established.

[0101] The evaluation index system includes: primary indexes and secondary indexes; the primary indexes include at least one of the fault ride-through capability, the voltage recovery capability and the power regulation capability; and the secondary indexes include at least one of the active power retention rate, the short-circuit current margin, the voltage stiffness, the reactive power compensation rate, the thermal stability margin and the power transfer amount.

[0102] Step 305, the analytic hierarchy process is used to determine the weight of each primary index and each secondary index respectively.

[0103] The analytic hierarchy process (AHP) is a technique for multi-criteria decision support. This method is particularly suitable for complex problems that are difficult to solve with traditional quantitative methods. It combines qualitative analysis with quantitative analysis to help decision-makers determine the importance of different objectives based on their experience and judgment, and accordingly assigns weights to each scheme to compare the advantages and disadvantages of each scheme.

[0104] For example, first define the primary indexes: fault ride-through capability (A1), voltage recovery capability (A2) and power regulation capability (A3); and define the secondary indexes: active power retention rate (B1), short-circuit current margin (B2), voltage stiffness (B3), reactive power compensation rate (B4), thermal stability margin (B5) and power transfer amount (B6).

[0105] 1) Under the A1 index, determine the weights of B1 and B2, and satisfy the sum of B1 and B2 being 1; under the A2 index, determine the weights of B3 and B4, and satisfy the sum of B3 and B4 being 1; and under the A3 index, determine the weights of B5 and B6, and satisfy the sum of B5 and B6 being 1.

[0106] 2) According to the actual needs of the AC-DC power grid, determine the weights of A1, A2 and A3, and satisfy the sum of A1, A2 and A3 being 1.

[0107] 3) Combining the above two steps, the standard weight coefficients of B1 to B6 indexes are obtained, and the sum of B1 to B6 is 1.

[0108] Step 306, according to the low voltage ride-through capability, the AC voltage recovery capability and the power regulation capability, the fault ride-through and recovery capability of the multi-terminal embedded DC system is comprehensively evaluated.

[0109] Exemplarily, according to the low-voltage ride-through capability, the alternating-current voltage recovery capability and the power regulation capability, and the weight corresponding to each first-level index and each second-level index, a comprehensive score corresponding to the multi-terminal embedded DC system is determined, and the comprehensive score is used for evaluating the fault ride-through and recovery capability of the multi-terminal embedded DC system.

[0110] In this embodiment, the fault ride-through and recovery capability of the multi-terminal embedded flexible DC system is analyzed from three aspects of the low-voltage ride-through capability under three-phase ground fault, the alternating-current voltage recovery capability, and the power regulation capability under alternating-current line N-2 fault, and the comprehensive analysis of different capabilities is performed by using the analytic hierarchy process method, so as to obtain an accurate evaluation result of the fault ride-through and recovery capability.

[0111] Exemplarily, in order to help understanding, the above DC system fault ride-through and recovery capability evaluation method is applied by taking the 2040 summer big data of East China Power Grid as an example and using BPA simulation software.

[0112] Firstly, the setting of the multi-terminal embedded DC system is described.

[0113] (1) DC type: 2 return LCC-HVDC (A, B), 2 return VSC-MTDC (C, D);

[0114] (2) Rated voltage: ±800kV (LCC), ±500kV (VSC);

[0115] (3) Feeding power: A 7200MW, B 6400MW, C 1200MW, D 3000MW.

[0116] Secondly, the fault scene setting is described.

[0117] For three-phase ground fault:

[0118] 1) Simulation conditions

[0119] Fault location: a certain 500kV bus in Shanghai;

[0120] Fault duration: 0.1s;

[0121] Evaluation object: C, D.

[0122] 2) Key calculation

[0123] Active power retention rate: (C), evaluated as 70.8 points;

[0124] Short-circuit current margin: , evaluated as 65.9 points;

[0125] Voltage stiffness: , evaluated as 95 points;

[0126] Reactive power compensation rate: , evaluated as 80 points.

[0127] For AC line N-2 fault:

[0128] 1) Simulation conditions

[0129] Fault line: Huliantang-Hunanqiao double-circuit line is removed;

[0130] Evaluation index: thermal stability margin Φ, power transfer amount Δ Ptrans .

[0131] 2) Key calculations

[0132] Thermal stability margin of a certain 500kV line: , evaluated as 50 points;

[0133] Power transfer amount after fault: , evaluated as 90 points.

[0134] Further, the standard weights of each index are determined according to the analytic hierarchy process:

[0135] According to the actual needs of the power grid, the weights of A1, A2 and A3 are determined as: 0.3, 0.4, 0.3.

[0136] Among them, the weights of B1 and B2 under the A1 index are 0.4 and 0.6 respectively; the weights of B3 and B4 under the A2 index are 0.5 and 0.5 respectively; the weights of B5 and B6 under the A3 index are 0.4 and 0.6 respectively.

[0137] Therefore, the standard weights of the six secondary indexes can be determined by the analytic hierarchy process as: 0.12, 0.18, 0.2, 0.2, 0.12, 0.18.

[0138] Finally, the total evaluation score is calculated as: 0.12x70.8+0.18x65.9+0.2x95+0.2x80+0.12x50+0.18x90=77.558 points.

[0139] It should be understood that the method provided by the embodiment is applicable to the fault ride-through and recovery capability evaluation of multi-terminal interconnected power grid containing conventional DC and flexible DC in the scenarios of three-phase ground fault, AC line N-2 fault, etc., and the evaluation result considers the influence of multiple indexes, so that the final evaluation result is more objective and accurate.

[0140] It should be understood that although the steps in the flowcharts involved in the above embodiments are shown in sequence according to the arrows, the steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, the execution of the steps is not strictly limited in sequence, and the steps can be executed in other orders. Moreover, at least some of the steps in the flowcharts involved in the above embodiments can include multiple steps or multiple stages, which are not necessarily executed at the same time, but can be executed at different times, and the execution order of the steps or stages is not necessarily sequential, but can be alternately executed with at least some of the other steps or steps or stages in the other steps. It can be understood that the steps in different embodiments can be freely combined as needed, and various non-contradictory schemes formed by the combination are within the scope of protection of the present application.

[0141] Based on the same inventive concept, the embodiments of the present application also provide a DC system fault ride-through and recovery capability evaluation device for implementing the above-mentioned DC system fault ride-through and recovery capability evaluation method. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme described in the above method, so the specific limitations in one or more DC system fault ride-through and recovery capability evaluation device embodiments provided below can refer to the limitations of the DC system fault ride-through and recovery capability evaluation method described above, and will not be repeated here.

[0142] In one exemplary embodiment, as shown in Figure 4 A DC system fault ride-through and recovery capability evaluation device is provided, comprising: a first determination module 401, a second determination module 402, a third determination module 403, and an evaluation module 404, wherein:

[0143] The first determination module 401 is configured to determine the low voltage ride-through capability of the multi-terminal embedded DC system in the case of a three-phase ground fault of the AC power grid.

[0144] The second determination module 402 is configured to determine the AC voltage recovery capability after the three-phase ground fault of the AC power grid is removed.

[0145] The third determination module 403 is configured to determine the power regulation capability of the multi-terminal embedded DC system in the case of an N-2 fault of the AC line; the N-2 fault includes: when one AC transmission line fails, another parallel or associated line also fails.

[0146] The evaluation module 404 is configured to comprehensively evaluate the fault ride-through and recovery capability of the multi-terminal embedded DC system according to the low voltage ride-through capability, the AC voltage recovery capability, and the power regulation capability.

[0147] The first determining module 401 is configured to determine the actual output active power of the multi-terminal embedded DC system during the three-phase ground fault of the AC power grid, evaluate the active power retention rate of the multi-terminal embedded DC system during the ride-through according to the ratio between the actual output active power and the rated active power, determine the short-circuit current margin according to the upper limit of the breaker interruption capacity and the effective value of the short-circuit current at the time of the fault, and determine the low-voltage ride-through capability of the multi-terminal embedded DC system according to the active power retention rate during the ride-through and the short-circuit current margin.

[0148] The second determining module 402 is configured to determine the voltage stiffness according to the ratio between the AC bus voltage recovery value after the fault is removed and the rated voltage, determine the reactive power compensation rate according to the ratio between the output reactive power of the multi-terminal embedded DC system and the reactive power deficiency of the AC system, and determine the AC voltage recovery capability according to the voltage stiffness and the reactive power compensation rate.

[0149] The third determining module 403 is configured to determine the thermal stability margin according to the maximum transmission capacity and the actual transmission capacity of the line, determine the power transfer amount of the multi-terminal embedded DC system in the case of N-2 fault according to the DC power of each terminal before and after the fault, and determine the power regulation capability of the multi-terminal embedded DC system according to the thermal stability margin and the power transfer amount.

[0150] In this embodiment, the low-voltage ride-through capability of the multi-terminal embedded DC system is determined in the case of the three-phase ground fault of the AC power grid, the AC voltage recovery capability is determined after the three-phase ground fault of the AC power grid is removed, and the power regulation capability of the multi-terminal embedded DC system is determined in the case of N-2 fault of the AC line. The N-2 fault includes that when one AC power transmission line fails, another parallel or associated line also fails. Thus, the fault ride-through and recovery capability of the multi-terminal embedded DC system can be analyzed from the three aspects of the low-voltage ride-through capability under the three-phase ground fault, the AC voltage recovery capability, and the power regulation capability under the N-2 fault of the AC line, so as to ensure the comprehensiveness and objectivity of the analysis. The fault ride-through and recovery capability of the multi-terminal embedded DC system is comprehensively evaluated according to the low-voltage ride-through capability, the AC voltage recovery capability, and the power regulation capability. Thus, various different fault scenarios can be considered comprehensively, and the fault ride-through and recovery capability of the multi-terminal embedded DC system can be evaluated from multiple indexes, so as to significantly improve the accuracy of the evaluation result.

[0151] In another exemplary embodiment, as shown in Figure 5 a DC system fault ride-through and recovery capability evaluation device is provided, and based on the device shown in Figure 4 the device can further include:

[0152] The evaluation index system establishing module 405 is configured to establish an evaluation index system of the fault ride-through and recovery capability of the multi-terminal embedded DC system, and the evaluation index system comprises: primary indexes and secondary indexes; the primary indexes comprise at least one of a fault ride-through capability, a voltage recovery capability and a power regulation capability; and the secondary indexes comprise at least one of an active power retention rate, a short-circuit current margin, a voltage stiffness, a reactive power compensation rate, a thermal stability margin and a power transfer amount.

[0153] The weight determining module 406 is configured to determine the weight corresponding to each primary index and each secondary index respectively by using an analytic hierarchy process.

[0154] For example, the evaluation module 404 is specifically configured to: determine a comprehensive score corresponding to the multi-terminal embedded DC system according to the low-voltage ride-through capability, the AC voltage recovery capability and the power regulation capability, and the weight corresponding to each primary index and each secondary index, and use the comprehensive score to evaluate the fault ride-through and recovery capability of the multi-terminal embedded DC system.

[0155] The above modules in the DC system fault ride-through and recovery capability evaluation device can be realized by software, hardware and a combination thereof in whole or in part. The above modules can be embedded in or independent of a processor in a computer device in a hardware form, or can be stored in a memory in a computer device in a software form, so as to be called and executed by a processor to perform the operations corresponding to the above modules.

[0156] In an exemplary embodiment, a computer device is provided, which can be a terminal, and an internal structure diagram of the computer device can be as shown in Figure 6As shown in the figure. The computer device includes a processor, a memory, an input / output interface, a communication interface, a display unit and an input device. Among them, the processor, the memory and the input / output interface are connected through the system bus, and the communication interface, the display unit and the input device are connected to the system bus through the input / output interface. Among them, the processor of the computer device is used to provide computing and control capability. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operating system and the computer program in the non-volatile storage medium to run. The input / output interface of the computer device is used to exchange information between the processor and the external device. The communication interface of the computer device is used for wired or wireless communication with external terminals, and wireless communication can be realized through WIFI, mobile cellular network, Near Field Communication (NFC) or other technologies. The computer program is executed by the processor to realize a direct current system fault ride-through and recovery capability evaluation method. The display unit of the computer device is used to form a visually visible picture, which can be a display screen, a projection device or a virtual reality imaging device. The display screen can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer device can be a touch layer overlaid on the display screen, or a key, trackball or touchpad arranged on the shell of the computer device, or an external keyboard, touchpad or mouse, etc.

[0157] Those skilled in the art can understand that, Figure 6 The structure shown in the figure is only a block diagram of part of the structure related to the scheme of the present application, and does not constitute a limitation on the computer device to which the scheme of the present application is applied. The specific computer device can include more or fewer components than those shown in the figure, or combine certain components, or have a different component arrangement.

[0158] In one exemplary embodiment, a computer device is provided, comprising a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the following steps:

[0159] In the case of three-phase ground fault of the alternating current power grid, the low voltage ride-through capability of the multi-terminal embedded direct current system is determined; after the three-phase ground fault of the alternating current power grid is removed, the alternating current voltage recovery capability is determined; in the case of N-2 fault of the alternating current line, the power regulation capability of the multi-terminal embedded direct current system is determined; the N-2 fault includes: when one of the alternating current transmission lines fails, the other parallel or associated line also fails; according to the low voltage ride-through capability, the alternating current voltage recovery capability and the power regulation capability, the fault ride-through and recovery capability of the multi-terminal embedded direct current system is comprehensively evaluated.

[0160] In one embodiment, the processor, when executing the computer program, also implements the following steps:

[0161] During a period of a three-phase ground fault of the alternating current power grid, an actual output active power of the multi-terminal embedded direct current system is determined; an active power retention rate of the multi-terminal embedded direct current system during the period of the fault ride-through is evaluated according to a ratio between the actual output active power and a rated active power; a short-circuit current margin is determined according to an upper limit of a breaking capacity of a circuit breaker and an effective value of a short-circuit current at the time of the fault; and a low-voltage ride-through capability of the multi-terminal embedded direct current system is determined according to the active power retention rate and the short-circuit current margin.

[0162] In one embodiment, the processor, when executing the computer program, also implements the following steps:

[0163] A voltage stiffness is determined according to a ratio between a recovery value of the alternating current bus voltage after the fault is removed and a rated voltage; a reactive power compensation rate is determined according to a ratio between an output reactive power of the multi-terminal embedded direct current system and a reactive power deficiency of the alternating current system; and an alternating current voltage recovery capability is determined according to the voltage stiffness and the reactive power compensation rate.

[0164] In one embodiment, the processor, when executing the computer program, also implements the following steps:

[0165] A thermal stability margin is determined according to a maximum transmission capacity and an actual transmission capacity of the line; a power transfer amount of the multi-terminal embedded direct current system in the case of an N-2 fault is determined according to direct current powers of each terminal before and after the fault; and a power regulation capability of the multi-terminal embedded direct current system is determined according to the thermal stability margin and the power transfer amount.

[0166] In one embodiment, the processor, when executing the computer program, also implements the following steps:

[0167] An evaluation index system of the fault ride-through and recovery capability of the multi-terminal embedded direct current system is established, the evaluation index system including: primary indexes and secondary indexes; the primary indexes including: at least one of the fault ride-through capability, the voltage recovery capability and the power regulation capability; the secondary indexes including: at least one of the active power retention rate, the short-circuit current margin, the voltage stiffness, the reactive power compensation rate, the thermal stability margin and the power transfer amount; and weights corresponding to each primary index and each secondary index are respectively determined by using an analytic hierarchy process.

[0168] In one embodiment, the processor, when executing the computer program, also implements the following steps:

[0169] A comprehensive score corresponding to the multi-terminal embedded direct current system is determined according to the low-voltage ride-through capability, the alternating current voltage recovery capability and the power regulation capability, and the weights corresponding to each primary index and each secondary index, the comprehensive score being used to evaluate the fault ride-through and recovery capability of the multi-terminal embedded direct current system.

[0170] In one embodiment, a computer readable storage medium is provided, having stored thereon a computer program, which when executed by a processor implements the method steps of the various embodiments described above.

[0171] In one embodiment, a computer program product is provided, comprising a computer program which when executed by a processor implements the method steps of the various embodiments described above.

[0172] A person of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiments can be completed by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer readable storage medium. When the computer program is executed, it can include the processes of the above-mentioned embodiments. Any reference to a memory, database or other medium used in the embodiments provided in the present application can include at least one of a non-volatile memory and a volatile memory. The non-volatile memory can include a read-only memory (ROM), a magnetic tape, a floppy disk, a flash memory, an optical storage, a high-density embedded non-volatile memory, a resistive random access memory (ReRAM), a magnetoresistive random access memory (MRAM), a ferroelectric random access memory (FRAM), a phase change memory (PCM), a graphene memory, etc. The volatile memory can include a random access memory (RAM) or an external cache memory, etc. As an illustration but not limitation, the RAM can be in various forms, such as a static random access memory (SRAM) or a dynamic random access memory (DRAM), etc. The database involved in the embodiments provided in the present application can include at least one of a relational database and a non-relational database. The non-relational database can include a distributed database based on a block chain, etc., without being limited thereto. The processor involved in the embodiments provided in the present application can be a general processor, a central processing unit, a graphics processing unit, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, an artificial intelligence (AI) processor, etc., without being limited thereto.

[0173] Any technical features in the above embodiments can be combined, and for the sake of brevity, not all possible combinations are described above, however, any combination of the technical features is deemed to be within the scope of the present application.

[0174] The above embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the patent scope of the present application. It should be pointed out that, for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A method for evaluating the fault ride-through and recovery capability of a DC system, characterized in that: The method comprises: Determine the low voltage ride-through capability of a multi-terminal embedded DC system in the event of a three-phase ground fault in the AC grid; After the three-phase ground short circuit fault in the AC power grid is cleared, determine the AC voltage recovery capability; Determining the power regulation capability of the multi-terminal embedded DC system in the event of an N-2 fault on an AC line; wherein the N-2 fault includes: a fault on one AC transmission line and a fault on another parallel or associated line; The fault ride-through and recovery capabilities of the multi-terminal embedded DC system are comprehensively evaluated based on the low voltage ride-through capability, the AC voltage recovery capability, and the power regulation capability.

2. The method according to claim 1, characterized in that Determining the low voltage ride-through capability of the multi-terminal embedded DC system when a three-phase ground short circuit fault occurs in the AC power grid includes: During a three-phase ground short circuit fault in the AC power grid, determining the actual output active power of the multi-terminal embedded DC system; evaluating an active power retention rate of the multi-terminal embedded DC system during the ride-through period according to a ratio between the actual output active power and the rated active power; Determine the short-circuit current margin based on the upper limit of the circuit breaker's interrupting capacity and the effective value of the short-circuit current during a fault; The low voltage ride-through capability of the multi-terminal embedded DC system is determined according to the active power retention rate and the short-circuit current margin during the ride-through period.

3. The method according to claim 1, characterized in that After the three-phase ground short circuit fault of the AC power grid is cleared, determining the AC voltage recovery capability includes: Determine the voltage stiffness based on the ratio between the AC bus voltage recovery value and the rated voltage after the fault is cleared; Determine the reactive power compensation rate based on the ratio between the output reactive power of the multi-terminal embedded DC system and the reactive power deficit of the AC system; The AC voltage recovery capability is determined according to the voltage stiffness and the reactive power compensation rate.

4. The method according to claim 1, wherein The determining of the power regulation capability of the multi-terminal embedded DC system when an N-2 fault occurs on the AC line includes: Determine the thermal stability margin based on the maximum transmission capacity and actual transmission capacity of the line; Determining a power transfer amount of the multi-terminal embedded DC system in the event of an N-2 fault based on the DC power of each terminal before and after the fault; A power regulation capability of the multi-terminal embedded DC system is determined according to the thermal stability margin and the power transfer amount.

5. The method according to any one of claims 1 to 4, characterized in that Before comprehensively evaluating the fault ride-through and recovery capabilities of the multi-terminal embedded DC system based on the low voltage ride-through capability, the AC voltage recovery capability, and the power regulation capability, the method further includes: Establishing an evaluation index system for the fault ride-through and recovery capabilities of the multi-terminal embedded DC system, the evaluation index system comprising: primary indicators and secondary indicators; the primary indicators comprising: at least one of fault ride-through capability, voltage recovery capability, and power regulation capability; the secondary indicators comprising: at least one of active power retention rate, short-circuit current margin, voltage stiffness, reactive power compensation rate, thermal stability margin, and power transfer capacity; The hierarchical analysis method is used to determine the weights corresponding to each first-level indicator and each second-level indicator.

6. The method according to claim 5, characterized in that The comprehensive evaluation of the fault ride-through and recovery capabilities of the multi-terminal embedded DC system based on the low voltage ride-through capability, the AC voltage recovery capability, and the power regulation capability includes: A comprehensive score corresponding to the multi-terminal embedded DC system is determined based on the low voltage ride-through capability, the AC voltage recovery capability, the power regulation capability, and the weights corresponding to each primary indicator and each secondary indicator. The comprehensive score is used to evaluate the fault ride-through and recovery capabilities of the multi-terminal embedded DC system.

7. A DC system fault ride-through and recovery capability evaluation device, characterized in that: The device comprises: A first determination module is used to determine the low voltage ride-through capability of the multi-terminal embedded DC system when a three-phase ground short circuit fault occurs in the AC power grid; A second determination module is used to determine the AC voltage recovery capability after the three-phase ground short circuit fault of the AC power grid is resolved; a third determining module, configured to determine the power regulation capability of the multi-terminal embedded DC system when an N-2 fault occurs in an AC line; the N-2 fault includes: when an AC transmission line fails and another parallel or associated line also fails; An evaluation module is used to comprehensively evaluate the fault ride-through and recovery capabilities of the multi-terminal embedded DC system based on the low voltage ride-through capability, the AC voltage recovery capability, and the power regulation capability.

8. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 6 are implemented.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 6 are implemented.

10. A computer program product comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 6 are implemented.

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