Design of an asymmetric rotor pole for wound field synchronous machines

Abstract

This study proposes a novel asymmetric rotor pole design for wound field synchronous machines (WFSMs), which can achieve high saliency ratio and also low torque ripple. The key point is the optimal design of the asymmetric rotor pole with the inverse-cosine-shaped (ICS) plus reverse 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> harmonic shaping. The asymmetric rotor pole can help to improve the average output torque by enhancing the saliency ratio. The reverse 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> harmonic shaping on the rotor pole surface is mainly used to reduce the torque ripple. To certify the effectivity of the proposed design, three-phase 54-slot / 6-pole 4.7kW WFSMs with uniform air gap and with non-uniform air gap shaped by the ICS plus optimum reverse 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> harmonic are utilized as the basic model and referenced model for comparison. For the referenced model, the optimum amplitude of reverse 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> harmonic is preferred as 1/6. Finally, all electromagnetic characteristics of the investigated machines are predicted by the finite-element method (FEM). The highest saliency ratio and comparatively low torque ripple have been verified.