Proposal and Machine Characteristics of a Self-Cooling SRM for Electric Hand Tools

Abstract

Electric hand tools must be low cost and require minimal maintenance. To achieve these demands, a switched reluctance motor (SRM) is expected to be used as an electric hand tool motor as an alternative to a brushless DC Motor (BLDCM). The SRM is suitable for electric hand tools owing to its low manufacturing cost. However, the SRM has a disadvantage in that its torque density is lower than that of the BLDCM. Therefore, the SRM needs to add a higher current than the BLDCM to achieve the same output torque. Moreover, the winding temperature quickly increases owing to the large copper loss. To overcome this problem, this paper proposes a self-cooling SRM. The proposed SRM can realize the same output torque and the same volume as a BLDCM system including a fan. Additionally, the proposed SRM can slow the increase in winding temperature by increasing the motor volume and through the self-cooling effect. In this study, the performance of the prototype self-cooling SRM is verified through simulations and experiments.