**Grace Firsta Lukman, Xuan Son Nguyen and Jin-Woo Ahn \***

Department of Mechatronics Engineering, Kyungsung University, Busan 48434, Korea; gracedr@ks.ac.kr (G.F.L.); nguyenxuanson@ks.ac.kr (X.S.N.)

**\*** Correspondence: jwahn@ks.ac.kr; Tel.: +82-51-663-4773

Received: 6 April 2020; Accepted: 28 April 2020; Published: 7 May 2020

**Abstract:** The shift-by-wire (SBW) system in vehicles aims to increase performance, safety, and comfort during driving. Switched reluctance motors (SRMs) are simple, resilient, and require only minimum maintenance; these factors make it a good option for use as an SBW actuator. Inherently, SRM generates a higher torque ripple than other AC machines, which can lead to a deterioration of its function. In this paper, a non-uniform air-gap rotor structure combined with the careful positioning of holes near the pole surface is proposed to reduce the torque ripple. The finite element method (FEM) is employed to analyze the electromagnetic characteristics of the design. The proposed motor is manufactured, and experiments are done to verify the performance. The design alone can reduce the torque ripple by 7% and flatten the torque waveform. The experimental result shows that the proposed motor can achieve the desired performance. The estimated torque ripple from the experiment is 26.65%.

**Keywords:** shift-by-wire (SBW); switched reluctance motor (SRM); non-uniform air-gap; rotor hole placement; torque ripple; rotor structure
