This paper presents innovative methods to resolve the two challenges that occur when using a switched reluctance motor (SRM) as a traction motor for a compact electric vehicle (EV). Electric vehicles (EVs) are seeing a rise in popularity today and the demand for further advancement of EV technologies will continue to grow. Induction motors and interior permanent magnet motors (IPMs) are most commonly used traction motors for EVs. In this project, we focused on the development of a switched reluctance motor (SRM) as an alternative motor for compact EVs, leveraging the following benefits of SRMs:
1) SRMs, which require no permanent magnets, have no drag torque, enabling clutchless motor applications, and 2) SRMs demonstrate high efficiency in the high-speed rotation range. In applications of SRMs as EV drivers, however, there are two challenges to be resolved. The first challenge is that SRMs have significant torque ripples due to the principle of torque generation. As a measure to reduce these torque ripples, we have developed an effective commutation control system (Slope control of current command values) which changes current command values in a linear fashion. This system helps reduce torque ripples to approximately 40% at a maximum. The second challenge is to develop a cruise control system, which is indispensable for autonomous driving, while very few EVs equipped with SRMs are capable of cruise control. The developed cruise control system has resolved this challenge by optimizing the transition timing between power running control and regenerative braking, as proven by the road test results of a compact EV with the developed SPM maintaining a constant speed in uphill and downhill road conditions. With these two approaches, the developed SRM offers a practical solution to the insufficient torque issue and the cruise control challenge in SRM applications to compact EVs.
