Design improvement of a new outer-rotor hybrid excitation flux switching motor for in-wheel drive EV

Research and developments of in-wheel motors applied in pure electric vehicles (EVs) propulsion systems have attracted great attention recently. This is due to their definite advantages of great controllability for each independent wheel as well as the availability of more cabin space due to removal of conventional mechanical transmission and differential gears. Moreover, more series batteries can be installed to increase the driving distance. Since the motors are attached directly to the wheel, the major requirements are to have high torque density and efficiency. As one of alternative candidates with high torque possibility, a new design of outer-rotor hybrid excitation flux switching motor for in-wheel drive EV is proposed in this paper. The proposed motor consists of 12 slots of stator poles, and 10 rotor poles, with all active parts are located on the stator. In addition, it has a robust rotor structure which only comprises a single piece of rotor and has a wide range flux control capabilities. Under some design restrictions and specifications for the target EV drive applications, the performance of the proposed machine on the initial design and improved design are analyzed based on 2-D finite element analysis (FEA). The performance of the improved design motor shows that the maximum torque achieved is 81.5% of the target performance, whereas the maximum power has achieved 143.6 kW which is greater than the target value. Thus, by further design refinement and optimization it is expected that the motor will successfully achieve the target performances.