模块化多电平换流器混合调制策略

Hybrid Modulation Strategy of Modular Multilevel Converter

针对用于低压系统的模块化多电平换流器(modular multilevel converter,MMC),提出了一种提高较低电平数下换流器输出波形质量的混合调制策略。采用最近电平逼近调制(nearest level modulation,NLM)与脉冲宽度调制(pulse width modulation,PWM)相结合的方法,在每个控制周期,以最近电平逼近的方法形成阶梯波,并在每一个阶梯波上引入PWM控制,形成阶梯波和PWM信号相叠加的换流器桥臂调制信号。该调制策略能够在提高换流器输出的波形质量和减少谐波含量的同时,降低调试算法运算量,有利于控制器的实现。通过对用于10 k V交流系统的9电平换流器进行仿真试验,验证了所提出的调制策略能使换流器具有较好的电压、电流输出波形,证明该调制策略的可行性与有效性。

According to the modular multilevel converter（ MMC） in low voltage system,this paper proposes a hybrid modulation strategy for improving the output waveform quality of MMC in low level. Using the combination of the nearest level modulation and the pulse width modulation（ PWM）,the step wave is formed by the nearest level approximation in each control cycle,and the PWM control is introduced on each step wave in order to form each arm modulation signal which is mixed by step signal and the PWM signal. The hybrid modulation strategy can improve the output waveform quality of the converter,reduce the harmonic content, and reduce the amount of modulation algorithm,which is beneficial to the realization of the controller. Simulation experiments are carried out on a 9 level converter connecting with 10 kV AC system.The simulation results show that the proposed modulation strategy makes the converter have better voltage and current output waveform,which verifies the feasibility and validity of the modulation strategy.