Oscillation Analysis and Control in Offshore Wind Power MMC-HVDC Grid-Connected System

The high voltage direct current transmission technology, widely implemented in offshore power grid-connected projects, has recently attracted significant attention due to oscillation-related challenges. This paper analyzes the influence of zero-sequence current control strategy in modular multilevel converters on the dynamic stability of offshore wind farms integrated with MMC-HVDC grid-connected system. Firstly, the MMC impedance model incorporating zero-sequence circulation controller dynamics is established using harmonic state space method. Subsequently, the influence of zero-sequence circulation controller implementation on system stability is systematically analyzed. The analytical results demonstrate that zero-sequence circulation controller integration effectively increases the bridge arm resistance, enhances the system damping, and suppresses the impedance resonance peak in MMC islanded control mode. Finally, a parameter optimization scheme for zero-sequence circulation controller is proposed from the perspective of damping enhancement, with simulation results validating the theoretical analysis and demonstrating the effectiveness of the proposed approach.