A permanent magnet AC machine structure with true field weakening capability

New doubly salient machines in which the field excitation is developed by stationary or mounted permanent magnets has recently been undergoing development at the University of Wisconsin. Because of the unique geometry of the stator, these permanent magnets are readily accessible. Therefore, for experimental purposes, simple iron blocks are used to ´short´ a large portion of the permanent magnet flux and thus reduce the back EMF developed within the machine. However, for practical applications, field weakening schemes involving miniature linear actuators or high torque stepper motors are being explored. Preliminary experimental results show that a substantial reduction in the back EMF can be readily obtained thus lending credibility to the concept of weakening fields produced by stationary permanent magnets.