An improved CPS-PWM method for cascaded multilevel STATCOM under unequal losses

The DC-link voltage balance control scheme is regarded as an essential part when implementing a reliable and stable cascaded multilevel static synchronous compensator (STATCOM). However, the modulation signal modification method, which is the commonly used balancing method, disobeys the precondition of the traditional carrier phase shift pulse width modulation (CPS-PWM) method inevitably. In order to reduce the impact caused by the balancing method, a variable CPS-PWM method is proposed in this paper and weighted total harmonic distortion (WTHD) is adopted as the evaluation index. Simulation and experiment results verify contrastively that after introducing the improved CPS-PWM method, the main harmonic defined in this paper is completely eliminated, the WTHD value is reduced and the output performance is advanced effectively.