Accurate Modulation Voltage Tracking With Reduced Switching Frequency for Modular Multilevel Converters in Offshore Wind Power Systems

In recent years, modular multilevel converter (MMC) technology has become a cornerstone of offshore wind power development. To optimize MMC system performance, this paper proposes an enhanced control scheme, where the number of inserted submodules (SMs) per phase is dynamically adjusted according to real-time capacitor voltage fluctuations to enable precise tracking of the modulation voltage reference. Circulating currents are intrinsically suppressed, reducing arm inductance by 95.6%. In addition, the proposed scheme optimizes SM sequencing by leveraging historical SM switching states, achieving 42.6% switching frequency reduction. Furthermore, an arm energy balancing control is implemented to ensure precise energy equilibrium across the MMC arms. The effectiveness of the proposed strategy is validated through PSCAD/EMTDC simulations of an offshore wind farm integrated via a point-to-point high voltage DC (HVDC) link.