Investigation of a staggered dual-rotor wound field synchronous motor for offshore wind turbine full-scale testing platforms

The development of high-fidelity testing platforms for offshore wind turbines necessitates drag motors capable of emulating complex marine operating conditions while maintaining ultralow torque ripple. This paper proposes a staggered dual-rotor wound field synchronous drag motor (WFSDM) system for 25 MW full-scale land-based testing platforms targeting large-capacity offshore wind turbines. The research follows a structured approach: firstly, the theoretical model of the WFSDM is introduced, and its dimensions and structural parameters are determined according to design requirements using the D²L method. To enhance average torque and minimize torque ripple, the rotor structure undergoes further optimization through a multi-objective genetic algorithm. Following this, an analysis of the electromagnetic performance of the optimized WFSDM is conducted. To meet the testing requirements of 25 MW wind turbines, a staggered salient poles assembly of dual-rotor is proposed, which reduces torque ripple to 1.31% while maintaining an average torque output of 34.82 MNm. Finally, the mechanical analysis results are verified to ensure that both the stator and rotor structures comply with safety requirements and possess sufficient safety factors. The staggered dual-rotor WFSDM addresses critical challenges in offshore turbine testing and provides a scalable solution for next-generation offshore wind technology validation, bridging the gap between laboratory testing and real-world marine deployment.