A modular multilevel converter-based composite power quality compensation system

This paper presents a composite power quality compensation system, which is developed based on a modular multilevel converter (MMC). A decoupled current control is proposed for the lower and upper arms of the MMC to reduce the switching losses of the system. The submodules (SMs) in the upper arm of the modular multilevel converter are only used to compensate the fundamental frequency active power, while the SMs in the lower arm of the MMC are used for compensation of fundamental frequency reactive power and harmonic components. Thus, the carrier frequency of the upper arm can be much lower than that of the lower arm which leads to less power losses. A decoupled control scheme of ac-side current and the circulating current of the MMC are proposed to achieve the control objectives discussed in this paper. The proposed control strategy is finally verified by MATLAB/Simulink simulations.