Wide Speed Range Operation of Non-Salient PM Machines

Abstract

Non-salient permanent magnet machines are considered poor candidates for flux weakening operations due to their inherent low-inductance characteristics. In this paper, a two-pole 24-slot non-salient PM machine design is proposed that can utilize a winding switching technique to achieve wide speed range operation. A very wide speed range operation (from 3 to 1 ratio to as much as 13 to 1) is demonstrated. This is accomplished by simply rearranging the winding coils on the stator periphery. Moreover, a control strategy is proposed that not only utilizes the flux weakening using winding switching, but also flux weakening using a negative d-axis current to maximize the speed range of the machine. The machine is operated with two inverters to control the current in the machine winding over the entire speed range. A dq model for the machine is also presented. Analytical, simulated, and experimental results are provided to validate the proposed machine drive system.