Electric machines are widely used across a variety of applications. In particular, the cogging torque of a permanent magnet (PM) synchronous motor is a significantly important characteristic in the application of electric power steering (EPS) systems. Accordingly, various optimal design methods are adopted to reduce the cogging torque for an EPS motor. However, in most cases, the measured cogging torque of the EPS motor is much greater than finite element method result, because the additional cogging torque harmonic components are generated by manufacturing tolerances. Especially, the specific harmonic components are produced due to magnetic unbalance by the asymmetry of motor shape which is caused by the tolerances in motor cores or PMs. These components are not eliminated by applying a skew. Thus, in order to reduce the effect of the tolerances, a robust design is needed. In this study, the effect of PM tolerances is studied, and Taguchi robust design is performed to enhance the motor quality regardless of the tolerances.

The rare earth permanent magnet (PM) is widely used for traction motors of hybrid and electric vehicles. These motors have more torque density compared to any other type of motors. However, these PMs have the problems of limited reserves, unstable supply, and high cost. For solving these problems, concentrated flux synchronous motor (CFSM) and multi‐layer interior permanent magnet synchronous motor (IPMSM), using ferrite PMs, are compared in this study. The CFSM and multi‐layer IPMSM are introduced and compared with regard to shape, size, electric parameter, and motor characteristics. In addition, two types of motors are fabricated and tested in order to verify their performance and feasibility. Finally, comparing the merits and demerits, the comparative motor types are estimated in this study.

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We designed and analyzed an interior permanent magnet synchronous motor (IPMSM) to prevent irreversible demagnetization of the permanent magnets (PMs). Irreversible demagnetization of NdFeB PMs mainly occurs due to high temperature, which should thus be minimized. Therefore, it is necessary to reduce the eddy current loss in the PM through optimal design. The shape of the rotor core was optimized using finite element analysis (FEA) and response surface methodology. Three-dimensional (3-D) FEA is required for accurate computation of the eddy current loss, but there is huge time, effort, and cost consumption. Therefore, a method is proposed for indirectly calculating the eddy current loss of PMs using 2-D FEA. A thermal equivalent circuit analysis was used to calculate the PM temperature of the optimized model. For the thermal analysis, the copper loss, core loss, and eddy current loss in PMs were estimated and applied as a heat source. Based on the results, we confirmed the stability of the optimum model in terms of the PM demagnetization.

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