基于MMC闭锁与负直流电压无闭锁的综合直流故障限流策略

Integrated DC fault current limiting strategy based on blocking and negative DC voltage non-blocking of MMC

基于模块化多电平换流器(MMC)的柔性直流电网存在抗直流故障扰动能力弱的问题。为此,在无闭锁和闭锁限流的基础上,提出了一种适用于柔性直流电网的无闭锁与闭锁的综合直流故障限流策略。故障发生后,各换流站首先根据直流侧出口电流进行基于负直流电压控制的无闭锁限流,若某换流站由于无闭锁降压限流失效而发生过流,则主动将该换流站闭锁。故障消失或隔离后,无闭锁换流站第一时间恢复正常工作模式,而无须等待重启过程较长的闭锁换流站,以尽量减小系统功率损失。基于MATLAB/Simulink的仿真结果表明,所提综合直流故障限流策略可快速阻断故障电流,并兼顾限流过程的安全性和快速性,最大限度保证系统功率传输,提高了直流电网的抗故障扰动能力。

The flexible DC grid based on modular multilevel converter(MMC)has weak anti-DC fault capability.Therefore,an integrated DC fault current limiting strategy is proposed,which is suitable for non-blocking and blocking flexible DC grid.After the fault occurs,according to the DC-side outlet current,each converter station first carries out non-blocking current limiting based on negative DC voltage control.If overcurrent occurs in a converter station by reduction voltage and invalid current limiting caused by the non-blocking,the converter station is actively blocked.In order to minimize the power loss,the non-blocking converter station returns to normal working mode in the first time right after the fault disappears or is isolated,with⁃out waiting for the blocking converter station with long restart process.Based on MATLAB/Simulink,simu⁃lative results show that the proposed integrated DC fault current limiting strategy can quickly block the fault current and take into account the safety and rapidity of the current limiting process,ensure the power transmission of the system to the maximum extent,and improve the anti-fault capability of DC grid.