MIDC输电系统后续换相失败的抑制措施研究

Study on suppression measures of subsequent commutation failure in MIDC transmission systems

随着直流输送容量不断增加,直流落点越来越密集,多馈入直流(MIDC)输电系统的换相失败问题日益凸显。为降低多馈入直流输电系统换相失败的概率,首先分析了多回直流同时或相继换相失败的根本原因,然后结合常规低压限流(VDCOL)控制,提出了电压补偿式变斜率VDCOL协调控制策略。该控制策略充分利用直流故障电流的变化特点,综合考虑了MIDC输电系统中各回直流自身特性影响因素,选取合理的补偿系数K,使各回直流能在故障后有序且稳定地恢复,从而大大减少后续换相失败的发生。同时根据故障的严重程度选择性地切入K值以达到提高直流系统恢复性能的目的。最后在PSCAD/EMTDC中搭建算例系统及实际系统模型进行仿真验证,结果表明该控制策略能有效降低多馈入直流输电系统的后续换相失败的概率,使各回直流在故障后能够有序地恢复,同时在保证良好的恢复性能的基础上大大提高了多馈入直流输电系统的可靠性。

With the increasing of DC transmission capacity, HVDC connecting points are becoming more and more crowded, and commutation failure becomes increasingly prominent in MIDC transmission systems. To reduce the probability of commutation failure in MIDC systems, this paper first analyzes the fundamental causes of simultaneous or successive commutation failure, and then combing with the tradition VDCOL control puts forward the coordinated control strategy of variable slope VDCOL with voltage compensation. The control strategy takes advantage of the DC current characteristics while fault occurs, considers the influence factors of the DC systems characteristics in MIDC transmission system, and selects the reasonable compensation coefficient K, so that the MIDC systems can be recovered stably after faults, and the occurrence of subsequent commutation failure will be reduced. At the same time, according to the severity of the fault, the K value is selectively introduced in order to improve the recovery performance of the DC systems. Finally the example system and the actual system are built in PSCAD/EMTDC. Simulation results show that the control strategy can effectively reduce the probability of following commutation failure in MIDC transmission systems, and makes all DC system recovery orderly after fault, meanwhile ensures the good recovery performance which can greatly improve the safety and reliability in MIDC transmission systems.