真双极MMC-HVDC系统线路过载紧急控制策略

An emergency control strategy for line overload in bipolar MMC-HVDC system

随着直流断路器研究的不断发展,在未来使用直流断路器切除直流故障线路将成为一个可行的方案。但断路器动作后可能会引起线路潮流过载,危及整个直流系统的安全。文章利用真双极模块化多电平换流器直流输电(MMC-HVDC)系统正负极可独立控制的优点,设计了防止线路过载的紧急控制策略。首先推导出直流系统支路开断后的有功功率分布系数,找出可能发生功率越限的线路。然后保持各线路一定的功率裕度,通过功率灵敏度矩阵计算故障极换流站新的功率参考值。最后将减少的功率参考值加载到健康极对应的换流站上,并考虑健康极换流站和线路的功率约束,最大限度地保证交直流系统功率交换的稳定性,减少对交流系统的扰动。该策略能够有效避免潮流校验,提高紧急控制的速度。在PSCAD/EMTDC仿真平台中搭建七端直流模型,对所提控制策略的有效性进行了验证。

With the development of DC circuit breaker research,it will be a feasible scheme to adopt DC circuit breaker to cut off DC fault lines in the future.However,the circuit breaker may cause the line overload and endanger the safety of the whole DC system.In this paper,an emergency control strategy prevents line overload was proposed in this paper.It takes advantage of the independent control of positive and negative poles in bipolar modular multilevel converter based high voltage direct current(MMC-HVDC)system.Firstly,the active power distribution coefficient after opening the branch of the direct current system was deduced,and the line with the potential power limit can be found out.Then,the power margin of each line was maintained,and the new power reference value of the fault pole converter station was calculated by the power sensitivity matrix.Finally,the reduced power reference value was loaded into the healthy pole converter station,and the power constraints of the healthy pole converter station and the line were considered,which maximized the stability of power exchange of AC/DC system and reduced the disturbance to the AC system.The strategy effectively avoids the power flow check and improves the speed of emergency control.The effectiveness of the proposed control strategy was verified by building a plurality of DC models in the PSCAD/EMTDC.