Static eccentricity (SE) is frequently generated by manufacturing processes. As the nonuniformity of the air-gap length is caused by the SE, the torque ripple and cogging torque increase in the motor. This study analyzes the distorted back electromotive force (EMF) and cogging torque due to SE. Further, a motor design considering SE is performed for stable back EMF and low cogging torque. First, the SE was diagnosed and analyzed using the back EMF and cogging torque measured from the test results of the base model. In addition, the rotor position was calculated using the unbalanced back EMF due to the SE. The calculated rotor position is used when analyzing phenomena due to SE and applied to robust design. Subsequently, robust design optimization was performed to improve the unbalanced back EMF and cogging torque due to SE. Using finite element analysis (FEA) considering SE, the shape of the stator was designed based on the base model. The estimated rotor position from the base model was applied to the optimum model to confirm its robustness from SE’s effects. Finally, the base and optimum models were compared through the test results.

Many studies have been conducted to reduce the cogging torque of electric power steering motors. However, in the mass production of such motors, it is essential to enhance performance robustness in relation to tolerances. For such motors, this work analyzes performance robustness in relation to tolerances by applying a cycloid curve to the surface magnet of the rotor. Applying a cycloid curve to the magnet surface of the rotor is one of several ways to reduce cogging torque. To evaluate the performance of the cycloid curve, we compare it with an eccentric curve. The two curves are compared for the same specifications and evaluated using the indicator, tolerance insensitivity rate, which is used to assess performance robustness in relation to tolerances. The cycloid curve was evaluated to be more robust in relation to tolerances, as compared with the eccentric curve. Finally, an experiment was conducted to validate the robustness of the cycloid curve.

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