Disturbance Observation and Improved MPC Based Harmonic Resonance Suppression Strategy for MMC in Offshore Wind Farms

As considerable offshore wind farms (OWFs) are penetrated into power gird. The capacitive effect of long submarine cable causes serious harmonic resonance problems. An improved control strategy for modular multilevel converter (MMC) in OWF is investigated in this paper. The disturbance observer (DOB), which is used to monitor the variation of various system parameters and grid voltage disturbances, is integrated into the control framework of a dual-vector model predictive control (MPC), which aims at the minimum of the enclosed area between the output and the reference current in a single cycle, which ensures the optimal THD of the output current. The DOB compensates the output current and improves the quality of the AC current, which in turn suppresses the harmonic resonance, and enables active damping and enhances the dynamic response performance. A set of simulations have been performed, and the proposed scheme is verified by hardware-in-the-loop experiments by using RT-LAB. The results indicate that the proposed scheme has high current quality with low THD value, high dynamic performance and interference immunity under sudden current change, inductor parameter mismatch and harmonic injection.