Digital differentiator-based passivity enhancement scheme for high-frequency resonance suppression in MMC-HVDC system

Inherent control delays and changeable grid operational conditions pose significant challenges to the stability of the Modular multilevel converter-based high voltage direct current (MMC-HVDC) system, inducing the risk of high-frequency resonances (HFR). This paper proposes a passivity enhancement based on the second-order digital differentiator (DD) and lead-lag compensator, ensuring reliable and robust HFR suppression performance even under the resonance frequency drift and fault earthing scenes. First, the passivity-based stability analysis is provided based on the system output impedance model, elucidating the HFR mechanisms and frequency drift problems. Second, the proposed passivity enhancement scheme's control structure and impedance reshaping principle are analyzed to verify resonance suppression ability. Third, the control parameters tuning process and direct realization of differentiator are detailed, reinforcing the stable margin and harmonic rejection ability. Finally, several case studies and simulation results are provided to validate the effectiveness of the proposed passivity-based HFR suppression scheme.