柔性直流电网直流线路故障主动限流控制

Active Current-Limiting Control to Handle Overhead Line Fault in DC Grid

针对架空线柔性直流电网线路故障,提出了基于混合型MMC的主动限流控制方法,从而降低对直流断路器开断速度、开断容量以及吸收能量的要求,减少直流电网建设成本、提高直流电网可利用率。该文首先研究了换流器的交/直流电压解耦可控性,给出了主动限流控制器的控制架构。为了解决直流故障穿越期间,桥臂电容电压可能会短时越限的问题,提出了在内环直流电流控制器附加直流电流指令动态限幅控制器的方案。提出了主动限流控制策略的一种优化手段—电流目标预设控制,分析了不同控制器延时对主动限流控制的影响。计及主动限流控制,研究了单换流器系统和直流电网故障前后直流故障电流演变机理。最后,分别在单换流器系统和直流电网系统中仿真验证了前文理论分析的正确性的有效性。

To handle line faults in a DC grid, this paper proposed a new method of active current-limiting control（ACLC） based on hybrid MMC. With this active control, breaking capacity requirement of DC circuit breaker（DCCB） will significantly decrease and DC gird investment will be reduced. Firstly, independent controllability of AC/DC voltage of converter is studied. The ACLC control architecture is proposed. To avoid overvoltage of capacitor on each arm during DC fault, a method of dynamically adjusting DC current thresholds is proposed. The ACLC optimization method, i.e., target predetermined control, is put forward. Impact of different controller delay time on the ACLC is analyzed. Transient evolution mechanisms of DC fault current are studied in a single converter system and in DC grid respectively. Finally, validity of the ACLC is verified.