Design and research of modular permanent‐magnet DC generator based on magnetic integrated transformer for offshore wind farms

Traditional topologies of all‐DC offshore wind farm raised the voltage by making multiple generators connected in series, which would cause problems of additional enforcement insulation and complex power distribution and voltage control when situations of unbalanced wind speed and potential faults were encountered. A modular permanent‐magnet DC wind generator topology based on the magnetic integrated transformer (MIT) for the offshore wind farm was proposed in this study. The combination of fractional slot concentrated winding direct‐drive permanent‐magnet synchronous generator and MIT directly produced high‐voltage direct current at the end of a generator, which was of strong fault tolerance. Mathematical models of the generator, power electronic converters, and MIT were established. Both power factor correction control strategies of generator winding currents and voltage stability control strategy of generator inner low‐voltage direct current bus were designed. Simulation results demonstrated that the designed generator can achieve smooth transitions during start, variable wind speed and fault processes, and realise the maximum power point tracking, which verify the rationality and feasibility of the proposed topology and strategy, and can provide a useful technical reference for the future all‐DC offshore wind farms.