Design of Litz Wire for a Slotless High-speed Permanent Magnet Motor with Gramme-ring Windings

The heating problem is a major concern for the design of high-speed permanent magnet motor (HSPMM). This paper first analyzed the copper loss of the litz wires of a slotless gramme-ring-winding HSPMM with gramme-ring windings, combining the analytical and finite-element methods. Then the computational fluid dynamics model was established for thermal analysis. Through the calculation of the loss and temperature field, the strand number and cross-section shapes were finally optimized for litz wires to pursue the minimum temperature rise of the motor, with the methods of DOE and second-order response surface. The proposed optimization process of the design of litz wires is also useful in other electric motors.