Design Optimization of a Direct-drive Wind Generator with Non-rare-earth PM Flux Intensifying Stator and Reluctance Rotor

This paper presents a multi-objective design optimization for a novel direct-drive wind turbine generator. The proposed electric machine topology employs an outer rotor of the reluctance type and a special modular stator including three phase-windings and spoke-type permanent magnets (PMs). Each stator module includes a single coil toroidally wound around the ferromagnetic core. Consecutive stator modules are separated by PMs and include coils belonging to a different phase. An optimization method with three objectives: total power loss, weight, and torque ripple, and with one constraint for a minimum acceptable value for the power factor, is described. The design examples are for a direct-drive generator rated at 3 MW and 15 rpm. The simulation results show that with the proposed topology, which greatly benefits from PM flux concentration and special coils, performance, such as specific thrust, efficiency, "goodness", etc, can be comparable to more traditional synchronous PM designs, but without the need to use rare earth-magnets that have high cost and critical supply. Furthermore, options for using aluminum instead of copper wire to further reduce the weight and cost of winding are investigated and comparative results are discussed.