一种能够清除直流故障和减少传感器数量的MMC子模块及其特性研究

Research on MMC submodule which can clear DC fault and reduce number of sensors and its characteristics

针对模块化多电平换流器(MMC)的直流故障清除问题,提出了一种新型的局部自均压组合电容型子模块。该子模块的拓扑结构具备故障自清除能力,并且能够利用不同工作模式的投切,自动实现子模块内部电容电压的均衡,即每一个新型子模块只需一个电压传感器对其进行监控。利用MATLAB/Simulink对基于新型子模块的MMC在正常状态和直流侧短路故障状态进行仿真,仿真结果表明相比于传统的N电平m相半桥型MMC需要2m(N-1)个电压传感器和2m个电流传感器,所提出的基于新型子模块的MMC所需电压传感器的数量以及参与控制的电压信号数量均减少一半,降低了系统硬件成本,减少了控制器运算负担,提高了系统稳定性;同时,当系统发生直流侧短路故障时,由于子模块具备故障自清除能力,能够阻断交流系统与故障点的电流通路,实现直流故障的闭锁。

Aiming at the problem of DC(Direct Current)fault clearing of MMC(Modular Multilevel Converter),a novel LSCCSM(Local Self-balancing Combined Capacitor SubModule)is proposed.The topology of SM(SubModule)not only has the ability of fault self-clearing,but also can automatically realize the balance of internal capacitance voltage of SM by using the switching of different working modes,that is,each novel SM only needs one voltage sensor to monitor it.The MMC based on the novel SM in both normal state and DC side short circuit fault state is simulated on MATLAB/Simulink platform.The simulative results show that compared with the traditional N-level m-phase half-bridge MMC,which needs 2 m(N-1)voltage sensors and 2 m current sensors,the number of voltage sensors and the number of voltage signals involved in the control based on MMC with the proposed novel SM are reduced by half,which decreases the system hardware cost,reduces the computational burden of controller and improves the stability of power system.Meanwhile when short circuit fault occurs in DC side,the novel SM can not only block the current path between AC side and the fault point because of the ability of fault self-clearing,but also realize the DC fault blocking.