A Robust Control Design and Analysis for Modular Multilevel Converters Under Parameter Mismatch

This paper introduces a robust passivity-based controller for a Modular Multilevel Converters (MMC) based on injecting virtual impedances. In this regard, the virtual impedances are injected into MMC's circulating and output current dynamic loops. The proposed method can effectively achieve significant improvement in the dynamic responses of the MMC under parameter variations. This improvement is noticeably increased specifically when suitable sliding surfaces are applied to the dynamics under study. In addition, Robustness of the proposed control technique is enhanced through regulating controllers' coefficients embedded in errors dynamics of the MMC state variables. Simulation results show stable operation with good performance of the MMC under parameters variations. In addition, under mismatch parameters, the MMC output voltage magnitude obtained from the introduced controller can reach less steady-state and transient errors of 0.28% and 0.9% compared to PI controller with errors 1% and 1.6%. Also, Frequency response of MMC output voltage achieved from the proposed control technique can be placed in allowable upper/lower boundaries with maximum frequency errors less than 0.015 Hz. In contrast, the frequency error of MMC output voltage due to the PI controller is 0.025 Hz that is not acceptable.