Design of 2-phase 4/2 SRM for torque ripple reduction

This paper presents an optimization design process of a 2-phase 4/2 SRM (Switched Reluctance Motor) for a high speed air-blower to reduce a torque ripple. The desired air-blower is unidirectional application, and requires a wide positive torque region without torque dead-zone in the conventional 2-phase SRM. In order to get a wide positive torque region without torque dead-zone during phase commutation, asymmetric inductance characteristic with non-uniform air-gap is considered. Based on the output torque analysis at each rotor position, the air-gap is optimized to reduce torque ripple while rotating. The optimized air-gap in one position cannot consider the previous air-gap effect in the previous rotor position. So, the output torque cannot be fully satisfy the target torque in the first optimization process. In order to satisfy the target torque and to reduce the torque ripple, the second optimization process is implemented with the considerations of the first output torque. The second target torque is determined by the torque error of the first output torque and target torque of the first step. From this optimization sequence, the final air-gap according to the rotor position can be determined to satisfy the torque ripple requirement. The proposed high speed 4/2 SRM is verified by FEM analysis.