Investigation of Dual Stator Spoke Type Vernier Machine for EV Application

Recently, vernier machines have been nominated for EV applications numerously [1]-[3]. The attractive features of vernier machine for EV applications are a reduction of volume due to the removal of gearbox [4], and high power density owing to magnetic gear effect, also called as vernier effect. However, one of the critical issues for vernier machine on EV application is the low power factor. To enhance power factor of vernier machine, various methods and topologies were suggested continuously [5]. Especially, one stator-spoke type vernier machine was suggested to increase power factor with the use of flux focusing effect. However, it had flux bypass issue that reduced vernier effect [6]. To solve the issue, dual stator spoke type vernier machine (DSSTVM) uses dual stator to permit flux as additional flux path [7]. DSSTVM eventually realized flux focusing effect to boost torque thus high power factor. However, the study of DSSTVM had been limited to the combination of 12 slots and 20 poles [8]. In this paper, the comparative study of different slot/pole combination DSSTVMs with different winding configurations to find a suitable model for the EV application is done. Power density per volume and weight is a critical feature for light weighted EV. Additionally, good flux weakening capability for wide speed range and high efficiency for less energy usage is required for future EV application. Hence, comparisons of different models of DSSTVM with the aspect of back-emf, torque, power density, power factor, loss, and efficiency are done. The top priority of the work was to find the best model for EV application in overall performance and to discover various trade-off relationships for each machine with differences they are given. Finite element method (FEM) analysis is utilized for the overall performance comparison