Design issues of an IPM motor for EPS

Purpose - The purpose of this paper is to present the design procedure of an interior permanent magnet (IPM) motor used in electric power steering (EPS), and some critical issues which have considerable impacts on the machine's performance are fully discussed before detailed sizing optimization.Design methodology approach - The design specifications are derived according to application overall requirements. Critical issues which have considerable impacts on the machine's performance, such as operation mode, rotor structure and slot pole combination, are analyzed based on literature review. The proposed machine is optimized, and the losses and efficiency are computed, using 2-D finite element analysis (FEA).Findings - Before detailed sizing optimization, machine type selection is fully discussed. Aspects such as brushless ac (BLAC) operation mode, IPM rotor structure and combination of 12-slot 10-pole are quite suitable for EPS application. Consequently, a 12-slot 10-pole sinusoidally excited IPM machine with concentrated windings is selected, since it is convenient to obtain sinusoidal back electromotive force (back-EMF), minimum cogging torque and torque ripple, short end windings and high efficiency, as well as simple rotor assembly. The estimated excellent performance confirms that the proposed machine can be an attractive solution for EPS.Research limitations implications - The excitation current is ideal sinusoidal, while some harmonic components are neglected. Besides, in future, the experimental test should be carried out for validation.Originality value - A reasonable design procedure, where the motor type selection should be first addressed before detailed sizing design, is carried out. A 12-slot 10-pole sinusoidally excited IPM machine with concentrated windings is provided as a quite competitive candidate for EPS application.