Torque Performance Improvement of Self-Excited Permanent-Magnet-Free-Synchronous Motor with Rotor Auxiliary Poles Utilizing Space Harmonics

Abstract

In this paper, a synchronous motor is described in which space harmonic power is utilized for field magnetization instead of permanent magnets. The stator has a concentrated winding structure, and the rotor has two different types of winding, i.e., an induction pole (I-pole) winding that primarily retrieves the second space harmonic and an excitation pole (E-pole) winding for the field magnetization. The two coils are connected via a center-tapped full-bridge diode rectifying circuit. The effects of the rotor electromangetomotive force distribution on the d- and q-axis are theoretically discussed. Then, the effect of the auxiliary poles is experimentally verified using a prototype motor in terms of the adjustable speed drive characteristics and the efficiency map. In addition, it is experimentally clarified that the rotor self-inductance and the rotor winding resistance significantly affect the conduction period of the rotor induced current.