计及控制响应的多端混合直流输电系统短路电流近似计算方法

doi:10.19595/j.cnki.1000-6753.tces.230281

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摘要

多端混合直流输电系统故障发展迅速、短路电流水平超标问题严重,换流站高度非线性特征使现有短路电流求解忽略了控制系统的响应过程且多依赖于建模仿真结果,无法得到短路电流的具体解析式实现故障特性的定量分析计算。为此本文提出三种兼顾准确性与计算复杂程度的系统模型简化措施,并在此基础上提出计及控制系统作用的短路电流复频域近似求解方法,利用Pade逼近以及分段线性化法对模型进行降阶处理,通过拉普拉斯逆变换求得短路电流的时域解析式。最后,基于PSCAD/EMTDC对不同故障距离、过渡电阻以及故障类型进行了仿真分析。结果表明,该方法能在故障的暂态阶段（10 ms内）对短路电流有较为准确地刻画,能为直流保护定值整定、断路器额定容量选取、直流输电控制策略切换以及系统规划设计等提供重要依据。

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	李杭泽
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关键词 ：短路电流计算, 控制系统, 网络等值, 多端混合直流输电, 线路故障

Abstract：

The hybrid DC transmission system, which gives full play to the advantages of conventional DC and flexible DC, has become a research hotspot in the fields of long-distance transmission and renewable-energy grid connection. However, HVDC transmission lines are long and the working environment is complex, resulting in high fault probability. Once a short-circuit fault occurs on the DC line, it will generate fault current several times the rated current within 10ms, exposing the whole system to a serious overcurrent risk and threatening the sTab.operation of the system. In addition, the highly nonlinear characteristics of the converter station make the existing short-circuit current solutions ignore the response process of the control system and rely on the modeling and simulation results. It is impossible to obtain the specific analytical formula of the short-circuit current to realize the quantitative analysis and calculation of the fault characteristics, which brings difficulties to the protection and design of DC control systems and restricts the development of hybrid DC transmission technologies. Therefore, considering control response, an approximate calculation method for short-circuit current of multi-terminal hybrid DC transmission systems is proposed.
First, three system model simplification measures are proposed, which take into account both accuracy and computational complexity, including port processing, non-fault-pole discharging-loop processing and AC system processing. Second, the system topology model and control model are modeled. Based on the fault-component network, the short-circuit current is obtained regardless of the action of the control system, and then the corrected current under the control action is obtained by using this calculation result. The two are superimposed to obtain the final complex frequency domain analytical formula for the short-circuit current, and the inverse Laplace transform is used to obtain the time-domain solution for the short-circuit current. The proposed method corrects the trigger angle of the LCC side, using Pade approximation and piecewise linearization method to reasonably reduce the order of short-circuit current model, which takes into account the calculation accuracy and efficiency, to effectively avoid the problem that the inverse Laplace transform cannot be solved due to the high order of complex frequency domain expression. Finally, based on PSCAD / EMTDC, the simulation analysis on different fault distances, transition resistance and fault types is carried out.
It can be concluded that, the proposed method can accurately describe the transient characteristics and trend of the fault current at the outlet of each converter station before the blocking of the MMC station, obtaining the analytical expression of the fault current which provides a quantitative calculation method of fault current for power grid planning, equipment parameter selection and protection setting. In addition, the transient current increment considering the control characteristics of the converter station is less than that without considering the control characteristics. Therefore, the fault transient characteristics can be quickly analyzed and judged by using the fault current calculation results without considering the control. Finally, it can be concluded that, in terms of calculation efficiency, the proposed method does not have the problem of excessive computational complexity due to the order reduction. The calculation error is mainly related to the factors neglected or simplified in the calculation process, including the approximate equivalent processing of the model, the approximate fitting process of the waveform and the accuracy reserved when the intermediate variables are obtained, but the overall relative error is still controlled within 10% to meet the accuracy requirements of fault current calculation.

Key words： Short-circuit current calculation control system network equivalence multi-terminal hybrid HVDC transmission line fault

收稿日期: 2023-03-12

PACS:

TM713

基金资助:

国家自然科学基金资助项目(51877084)

通讯作者: 戴志辉男,1980年生,教授,博士生导师,研究方向为电力系统保护与控制。E-mail：daihuadian@163.com

作者简介: 李杭泽男,1999年生,硕士研究生,研究方向为直流输电系统保护与控制。E-mail：925449790@qq.com

引用本文:

李杭泽, 戴志辉, 石旭, 杨明玉. 计及控制响应的多端混合直流输电系统短路电流近似计算方法[J]. 电工技术学报, 0, (): 230281-230281. Li Hangze, Dai Zhihui, Shi Xu, Yang Mingyu. Approximate Calculation Method of Short-Circuit Current of Multi-Terminal Hybrid DC Transmission System Considering Control Strategy. Transactions of China Electrotechnical Society, 0, (): 230281-230281.

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