Field-Oriented Design of Notching and Mechanical Stress Relieving Grooves for Rotors in Flat Wire Permanent Magnet Machines

In this paper, a novel field-oriented design method is proposed for the rotor of the flat wire permanent magnet machine, focusing on both rotor surface notching and stress relieving grooves. Based on the field-oriented method, the spatial contribution of the rotor surface positions on both key radial force and torque is revealed and based on which the q-axis notching method is proposed for the PM rotor. However, the q-axis notching will raise the maximum-mechanical-stress issue for the rotor. Therefore, the stress relieving grooves are designed and optimized based on the load path analysis method. The PM rotor optimized based on the field-oriented method could suppress the torque ripple from 22.8% to 9.9% and the key radial force is reduced by 93.3% from 2717 N/m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> to 153 N/m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, whilst the maximum-mechanical-stress is reduced from 387 MPa to 369 MPa, ensuring the safe operation of the PM rotor.