基于LCC-MMC的三端混合直流输电系统故障特性与控制保护策略

研究了送端为相控型换流器(line commutated converter,LCC)、受端为2个并联的模块化多电平换流器(modular multilevel converter,MMC)组成的三端混合直流输电系统的交直流故障特性及其控制保护策略。在分析现有故障穿越控制策略的基础上,针对交流侧故障提出整流站LCC最小触发角控制、逆变站MMC最大调制比控制与直流电压偏差控制的协调策略;针对直流线路故障,通过在直流线路两端配置限流电抗器构造边界条件,提取直流线路故障电流暂态突变量以识别故障位置,并采用直流断路器开断故障的方法,可以快速隔离直流线路故障并缩小故障影响范围。最后,在PSCAD/EMTDC中建立混合直流输电系统模型,仿真验证了所提策略的可行性。结果表明,所提控制策略在所联接电网交流故障情况下可相应提高直流系统的输送功率,降低功率输送中断发生的概率;直流线路故障时基于直流断路器的直流电流突变率保护策略能够快速隔离故障,提高供电可靠性。

Fault Characteristics and Control & Protection Strategy of Three-Terminal LCC-MMC Hybrid HVDC Transmission System

This paper studies the AC/DC fault characteristics and control & protection strategies of the three-terminal hybrid DC transmission system with line commutated converter (LCC)-modular multilevel converter (MMC) converters.Based on the analysis of the existing fault crossing control strategy,the coordination strategy of the minimum triggering angle control,the maximum modulation ratio of the MMC and the DC voltage deviation control of the inverter side LCC is proposed for the AC side fault.In order to solve the DC fault,the DC line fault current transient variable can be used to identify the fault location and break the fault by the DC circuit breaker by arranging the boundary condition of the current limiting reactor at both ends of the DC link,which can quickly isolate the DC link fault and narrow the scope of the impact of failure.Finally,a hybrid DC transmission system model is established in PSCAD/EMTDC,and the feasibility of the proposed strategy is verified by simulation.The results show that the proposed control strategy can improve the transmission power of the DC system and reduce the probability of the power transmission interruption when the AC fault condition is rectified.The DC current mutation rate protection scheme based on the DC circuit breaker can quickly isolate the fault,and improve power supply reliability.