A comprehensive coordinated control strategy of MMC-HVDC system for frequency support and DC overvoltage suppression

To enhance frequency support and fault ride-through capabilities of MMC-HVDC system, an MMC multi-time scale coordinated control strategy considering the regulation dead zone is proposed, which achieves wide-area coordinated complementarity of multiple types of regulatory resources while ensuring system safety. For frequency support requirements at sending-end system, an adaptive control strategy considering a frequency regulation dead zone is proposed for sending-end MMC, and the dead zone value is designed based on the maximum power regulation margin of sending-end system, which reduces disturbance impact while maintaining frequency stability. For frequency support and fault ride-through requirements at receiving-end system, the coupling of frequency, DC voltage, and the inserted number of submodules in MMC is established, a control strategy considering the modulation ratio margin is proposed to improve the inertia support capability of MMC-HVDC. Then, an adaptive control strategy for frequency support and DC overvoltage suppression of sending-end MMC, along with a control mode selection method, is designed, and the DC voltage dead zone value is designed based on the maximum power regulation margin of receiving-end system, which effectively enhances the MMC-HVDC system’s frequency support and fault ride-through capabilities. Finally, the validity of proposed control strategy is verified through real-time digital simulation.