Performance Comparison of 5-MW Normal and Dual Three-Phase PM Vernier Motors for Ship Propulsion

Despite the fact that conventional three-phase per-manent magnet (PM) motors have dominated the market in recent years, multi-phase PM motors are progressively gaining popularity due to the safety and high-power requirements of certain applications. In this study, a 5-MW fractional-slot permanent magnet vernier motor (PMVM) for ship propulsion is designed and optimized using the finite element method and the non-dominated sorting genetic algorithm (NSGA). For highpower applications, the sub-harmonic components of the stator magnetomotive force (MMF) produce ripple torque, additional core losses and eddy current losses, increasing PM motor losses and the risk of irreversible demagnetization. By implementing dual three-phase in the optimized structure, non-working harmonic components are mitigated and the working harmonics are enhanced, resulting in increased torque, and reduced ripple torque and core loss. Due to the lower current of dual threephase PMVM compared to the normal three-phase PMVM at the same power, improvements to power factor, efficiency and thermal loading can also be realized. The designed dual threephase PMVM has a 44% torque ripple reduction and 7.7% lower copper loss compared with its normal three-phase counterpart. In addition, the performance of the dual three-phase PMVM was also evaluated under a faulty condition when one set of windings was open circuit. The result demonstrates that the machine operates satisfactorily, albeit at a lower power output, under the faulty condition, making it suitable technology for safety-critical applications like ship propulsion.