Control Strategy of DC-DC Converter With Diode Rectifier for All-DC Offshore Wind Farms

This paper investigates the control strategy of a DC-DC converter with modular multilevel converter (MMC) and diode rectifier (DR) face-to-face connection structure applied in all-DC offshore wind power system. To address the uncontrollability of the diode rectifier, this paper proposes a grid-forming control strategy based on the interdependencies among active power, reactive power, AC voltage amplitude, and frequency within this topology. The control objective is to enable the MMCs to establish a stable voltage and frequency for the AC system inside the DC-DC converter. Furthermore, the proposed control strategy also realizes the fast regulation of AC voltage and frequency during power fluctuations, contributing to the regular operation of the system under unstable conditions. Simulation results in PSCAD demonstrate the effectiveness of the proposed control strategy under startup and power fluctuation scenarios.