Saliency ratio and power factor of IPM motors optimally designed for high efficiency and low cost objectives

This study uses formal mathematical optimization techniques based on parametric computationally-efficient models and differential evolution algorithms. For constant-power applications, in the novel approach described, three concurrent objective functions are minimized: material cost, losses, in order to ensure high efficiency, and the difference between the rated and the characteristic current, aiming to achieve wide constant-power flux-weakening range. Only the first two objectives are considered for constant-torque applications. Two types of Interior Permanent Magnet (IPM) rotors in a single and double-layer V-shaped configuration are considered, respectively. The stator has the typical two slots per pole and phase distributed-winding configuration. The results for the constant-torque design show that, in line with expectations, high efficiency and high power factor machines are more costly, and that the low cost machines have poorer efficiency and power factor and most importantly, and despite a common miss-conception, the saliency ratio can also be lower in this case. For constant-power designs, the saliency ratio can be beneficial. Nevertheless, despite a common misconception, when cost is considered alongside performance as an objective, a higher saliency ratio does not necessarily improve the power factors of motors suitable for ideal infinite flux-weakening.