Taguchi robust optimum design for reducing the cogging torque of EPS motors considering magnetic unbalance caused by manufacturing tolerances of PM

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.