Analysis and Design of a PM-assisted Wound Rotor Synchronous Machine with Reluctance Torque Enhancement

Abstract

In this paper, a novel structure is proposed for a wound rotor synchronous machine with a small ferrite magnet in each rotor pole. The key is to achieve a higher reluctance torque term and also acquire torque-angle approaching that would allow the field torque and reluctance torque to reach maximum values at the closed current phase angle for efficient production of the average total torque. The assisting ferrite magnet in the proposed model helps compensate the q-axis flux while keeping the d-axis flux unchanged as much as possible, for enhancing reluctance torque and power factor. Meanwhile, the assisting ferrite magnet makes an asymmetrical magnetic flux distribution to close the current phase angles between the maximum of the field torque and the reluctance torque. Moreover, the related parameters of the assisting ferrite magnet in the proposed structure were determined by optimal techniques using the Kriging method and genetic algorithm. In addition, the potential for demagnetization of the assisting magnet was analyzed and the results verified that this would not affect the motor output performance. Finally, prototypes were manufactured for the experiments to verify the principle analysis and finite element analysis results.