Research And Design Of Flux-modulated Permanent Magnet Vernier Machine For Electric Vehicles

With the growing concerns about environmental issues,electric vehicles are gradually replacing the fossil-fueled vehicles and becoming the future development trend.The in-wheel motors is an important part of the investigation of the electrical vehicles.Higher torque density,higher power density and wider speed range are the priorities of the research of in-wheel motors.This paper focus on the vernier machine,which is a kind of flux-modulated permanent magnet machine.The vernier machine is characterized by high torque density and wide speed range.The modulation process and principals of the vernier machine are introduced and then a few vital equations are presented.In addition,the winding theory and the pole-slot combination are further analyzed.Meanwhile,some common issues of the vernier machine are discussed.In this paper,an in-wheel vernier machine for electric vehicles has been designed and the dimension parameters in the case of different air gap length have been optimized and analyzed.The influence of different parameters on the electromagnetic characteristics can be explained.Then an optimized vernier machine model can be obtained.Moreover,the air gap flux density,no-load characteristic and the load characteristics of the machine are analyzed in details,including electromagnetic property,power torque characteristic curves,power factor,iron loss,efficiency,torque ripple and heat dissipation.Through the design and analysis,the vernier machine features many outstanding advantages.The torque is jointly produced by the constant term of air gap permeance,fundamental effect,and together with the harmonics,which result in larger torque.At the same time,the harmonic frequency of the torque ripple is quite high and its amplitude is small,which leads to the sinusoidal back EMF and negligible torque ripple.Furthermore,wider speed range can be achieved due to the tiny flux linkage.The power factor of the vernier machine is low,and the iron loss is high due to the high frequency.Therefore,when choosing the pole ratio of the vernier machine,all the factors in terms of torque,power factor,iron loss,flux leakage,winding factor should be taken into consideration.