Construction and Comparison of Models With Different Time Scales For Offshore DC Wind Turbine Using LLC Resonant Converter

ABSTRACT Constructing an all‐DC offshore wind farm with DC power generation, DC collection, and DC transmission is an important direction for the development of offshore wind power. The offshore DC wind turbine generator is the core equipment of the all‐DC wind farm, and establishing its simulation models at different time scales is of great significance for conducting source‐grid coordinated research. Currently, worldwide, the all‐DC offshore wind farm is still in the research and development stage, with no actual engineering applications yet. Existing research mostly focuses on the topology of high‐capacity DC/DC converters suitable for offshore DC wind turbines, often only paying attention to the control characteristics of the DC/DC converter, lacking research on the overall control strategy and the simulation model of the offshore DC wind turbine. This paper first compares several typical schemes of DC collection for offshore DC wind farms, pointing out that the parallel two‐stage voltage boost scheme is the most technically and economically viable at this stage. It then selects a modular combination‐type DC/DC converter topology based on the LLC resonant converter, presents the complete structure of the offshore DC wind turbine using this topology, establishes an electromagnetic transient model of the offshore DC wind turbine based on the LLC resonant converter, and designs its control strategy under small and large disturbances. Through simulation examples, the model's ability to maximize wind energy capture during normal operation and ensure safe and stable operation during faults is verified. Subsequently, based on the average models of the AC/DC converter and the DC/DC converter, an electromechanical transient model of the offshore DC wind turbine is established, its control strategy is designed, and the accuracy of the electromechanical transient model is verified by comparing the simulation results with those of the electromagnetic transient model. Finally, the paper presents the different application scenarios of the two established models at different time scales in the grid‐connected operation research of the offshore DC wind power system and looks forward to the future research focus. The research in this paper can provide a certain reference for the field of modelling and analysis techniques for grid‐connected offshore DC wind power systems.