对称单极柔性直流输电系统不对称交流故障解析模型

Analytical Modeling of Asymmetric AC faults in Symmetric Single-Pole MMC-HVDC Power Transmission System

交流故障电流计算尤其在不对称故障情况下对断路器选型和直流保护起到至关重要的作用,然而面向直流保护的交流故障电流计算多依赖于电磁暂态仿真。该方法存在仿真计算耗时长、缺乏物理机理剖析和参数影响因素分析等诸多弊端。为了解决上述问题,本文针对实际对称单极结构柔性直流输电系统的交流不对称故障场景,推导出故障下控制系统响应前桥臂电流与交流线路电流上升速率,以及控制系统响应后交流线路短路电流d轴、q轴正序分量和三相短路电流的解析模型。对比解析模型与实际直流工程的仿真结果,验证故障解析模型的正确性。该研究的重要价值在于无需经过多次电磁暂态时域仿真结果,可以通过理论计算得到交流不对称故障下短路电流的动态过程,最终计算结果可以为控制保护策略的设计提供参考。

The calculation of AC fault current plays an important role in the selection of circuit breakers and DC protection,especially in the case of asymmetric faults.However,the calculation of AC fault current for DC protection mostly depends on electromagnetic transient simulation.The method has several drawbacks such as time-consuming simulation,lack of physical mechanism analysis and parameter influence factor analysis.In order to solve the problems above,this paper derives rising rate of the bridge arm current and AC line current before the response of control system,and the analytical models of the d-axis and q-axis positive sequence components of AC line short-circuit current and three-phase short-circuit current after the response of control system for the AC asymmetric fault scenario in the symmetric single pole MMC-HVDC system.The analytical model is compared with the simulation results of an HVDC engineering project to verify the correctness of the fault analysis model.The significant value of this study is that the dynamic process of the short-circuit current under AC asymmetric fault can be obtained by theoretical calculation without multiple electromagnetic transient time domain simulation results,and the final calculation results can provide reference for the design of control and protection strategy.