Negative Effect Analysis and Multi-Strategy Coordinated Oscillation Mitigation of Offshore Wind Power via a MMC-HVDC Transmission System

Modular multilevel converter-based high-voltage direct current (MMC-HVDC) transmission systems possess distinctive advantages such as massive transmission capacity and flexible control, making them increasingly popular for offshore wind power integration. However, offshore wind power via a MMC-HVDC transmission (OWPMMC-HVDC) system is highly susceptible to wideband oscillations caused by dynamic control interactions. Although traditional strategies can effectively mitigate oscillations within a specific frequency band, they frequently induce new oscillations in non-target bands—a phenomenon defined herein as the negative effect. To clarify the negative effect mechanism, this study first analyzes the impedance characteristics of the OWPMMC-HVDC system under traditional active and passive mitigation strategies. To reveal the damping drift characteristics across the full-frequency band, a multi-strategy coordinated oscillation mitigation approach based on the damping complementary principle is proposed. Finally, the effectiveness and superiority of the proposed coordinated oscillation mitigation strategy are verified through PSCAD/EMTDC electromagnetic transient simulations based on the 1100 MW/± 400 kV OWPMMC-HVDC system. The analysis results demonstrate that compared with the single-strategy approach, the proposed multi-strategy coordinated control successfully solves the negative effect issue. This comprehensively enhances wideband oscillation damping and the stable operation of the system, thus providing a robust oscillation mitigation strategy for practical engineering applications.