RESEARCH ARTICLE
Design of Power Density Improvement by Applying Novel Shape of Slit and Notch to Outer Rib of Rotor of Spoke-type Permanent Magnet Synchronous Motor

In this study, improvement of power density by applying novel shape of slit and notch to outer ribs of a rotor that reduces magnetic flux leakage in outer rib and increases air-gap magnetic flux density for spe PMSM for a washing machine, was investigated.

It is important that motors for home appliance require lower manufacturing cost, high power and high efficiency. In order to increase power, rotor shape is re-designed. In the outer rib of the rotor, magnetic flux leakage occurs by permanent magnet and magnetic flux is saturated which is one of the factors that reduces the power and efficiency. However, if the outer rib is designed to be too thin, the permanent magnet may scatter during high-speed rotation. Therefore, a design considering permanent magnet scattering is necessary. Motor for a washing machine has two operating points that washing mode at constant torque point and dehydrating mode at high-speed point.

For improvement of higher power density, 2-D finite elements analysis was performed to optimize the parameters of the shape of slit and notch to increase the torque. The torque increases by optimizing width and length of slit shape and notch shape. Finally, with the optimized parameters of shape of slit and notch, stack length was adjusted as per torque requirement for a washing machine motor and power density increases considering the safe factor from stiffness analysis.