Analysis and Comparison of Printed-Circuit Stator Winding Patterns for Axial Flux Permanent Magnet Machines

Printed-circuit stator windings allow low-profile construction, zero cogging torque, and high power density when used for axial flux permanent magnet machines. Trapezoidal and rhomboidal windings are the two most popular printing patterns. Since the area of printed-circuit boards is limited and the separation between conductor traces is inevitable owing to manufacturing requirements, it is critical to assess winding patterns in terms of their torque-producing capability and board-area utilization. In this paper, we present a detailed analysis of winding patterns and derive a mathematical model that predicts the coil resistance and torque produced by winding patterns. It was found that the trapezoidal pattern produces much larger torque, but the rhomboidal pattern has lower copper losses. The torque produced by the trapezoidal pattern is 81 % larger than that of the rhomboidal torque. However, if the torque is normalized by coil resistance, the trapezoidal pattern is 13 % better than the rhomboidal pattern with the same geometry.