Analysis and Suppression of DC-Side Oscillations in MMC Grid-Connected Systems

With the increasing penetration of power electronic devices in power systems, oscillations resulting from dynamic interactions between devices have become increasingly prominent. This paper investigates DC-side oscillation issues arising from grid-connected Modular Multilevel Converters (MMC). Firstly, an MMC impedance model is developed to analyze the mechanisms behind DC-side oscillations. Subsequently, a DC-side oscillation suppression strategy based on impedance phase optimization control is proposed, in which an impedance phase correction module is integrated with the conventional notch filter to compensate for MMC impedance phase deviations specifically. This effectively enhances the phase margin and suppresses oscillations in the system. Simulation results validate the effectiveness of the proposed method, demonstrating that it significantly improves system stability and provides rapid dynamic response.