一种基于载波移相调制的模块化多电平换流器冗余策略

A Redundancy Strategy for Modular Multilevel Converter Based on Carrier Phase Shift Modulation

现有载波移相调制(CPS-SPWM)的模块化多电平换流器(MMC)冗余策略在切除故障子模块的过程中冗余子模块电容电压恢复缓慢,针对此问题,本文提出了一种MMC子模块电容电压热冗余策略。该策略在非故障运行状态下,按照一定的时间间隔从所有子模块中按规律选择正常运行个数的子模块,其余子模块则处于冗余状态,以使得所有子模块电容电压都维持在参考值附近。当子模块发生故障时,切除故障子模块,剩余子模块仍按非故障运行状态运行,无需单独为冗余子模块充电。同时针对含有冗余模块的MMC系统,提出了分组预充电策略,在控制系统复杂度较小的条件下,通过调节每组充电的子模块个数,使得所有的子模块电容电压都能够充至额定值。在PSCAD/EMTDC中建立了双端MMC模型验证了所提出策略的有效性与实用性。

In the existing redundancy strategy for modular multilevel converter(MMC)under carrier phase shifting sinusoidal pulse width modulation(CPS-SPWM),the capacitor voltages of redundant submodule should be charged from zero which is slow for the system recovery.To solve this problem,an online redundancy strategy for MMC under CPS-SPWM is proposed in this paper.Firstly,to maintain the reference value of all capacitor voltages,N normal submodules of each arm are selected to be normally triggered through a proposed method with certain time intervals for N+1 level MMC system,and the rest of submodules are bypassed.When some submodules have problems to quit the circuit,the remaining submodules can still be operated by using the proposed method without recharge the redundant submodule.Secondly,based on the redundant MMC system,the packet pre-charging strategy is put forward,in which all the capacitor voltages of submodules can be pre-charged to the rated value with low complexity control system through regulating the number of charged submodules.Finally,simulations in PSCAD/EMTDC show the effectiveness and practicability of the proposed strategy.