基于负直流电压控制的MMC快速无闭锁故障穿越策略

A Fast Non-blocking Fault Ride-through Strategy for MMC Based on Negative DC Voltage Control

传统半桥子模块无法阻断直流短路电流,基于新型子模块的闭锁式故障穿越策略则存在换流器不可控、系统重启过程复杂等缺点,降低了模块化多电平换流器的可靠性。为此提出了一种基于负直流电压控制的无闭锁故障穿越策略,在直流侧短路后通过调制波下移将直流电压控制为负值,从而实现直流故障电流的快速清除。此外,针对无闭锁故障穿越过程中输出正负电平子模块之间电容电压不均衡的问题,提出了双排序控制算法以实现电容电压的快速均衡,同时设计了从故障发生至换流器重启整个过程中系统的无闭锁故障穿越流程。基于Matlab/Simulink的仿真结果表明,基于负直流电压控制的无闭锁穿越策略可快速阻断直流故障电流,在此过程中子模块电容电压保持均衡,可实现换流器的快速重启。

The half-bridge sub-module cannot block DC short-circuit faults,and the blocking fault ride-through strategy has the disadvantages of getting the converter out of control and complexing the system restart process,which reduces the reliability of the modular multilevel converter.Therefore,a non-blocking fault ride-through strategy based on negative DC voltage control is proposed.In the strategy,after DC side short circuit fault occurs,the DC voltage is controlled to be negative by moving down the modulation wave,so as to realize the rapid removal of DC fault.In addition,to solve the problem of unbalanced capacitor voltage between output positive and negative level submodules in the process of the non-blocking fault ride-through,a double-sequencing control algorithm is proposed to realize the rapid equalization of capacitor voltage of submodules.At the same time,a systematic non-blocking fault ride-through strategy from DC fault to the restart of converter station is designed.The simulation results based on MATLAB/Simulink show that the non-blocking ride-through strategy based on negative DC voltage control can quickly block the DC fault current,and the capacitor voltage of the submodules remains a balance,which can realize the quick restart of converter.