Design of PM brushless motors using iron-resin composites for automotive applications

Abstract

New iron-resin soft magnetic materials are now commercially available for AC magnetic applications. These materials, often referred as dielectromagnetics, generally present relative low values of permeability and induction of saturation, but they possess a lot of advantages, if they are properly used during the design process of motors. The relatively low values of unsaturated permeability are not an important drawback in the case of brushless permanent magnet (PM) motors. In this case, the effective airgap of the magnetic structure is imposed by the length of the magnet which has practically a relative permeability equal to unity. An automotive electric fan composed of a conventional PM DC motor with a mechanical collector has been chosen to illustrate the performances of the motors using these new soft magnetic materials and to validate the author's design methods of brushless PM motors. Two prototypes of brushless PM motors using a dielectromagnetic material are presented, which can advantageously replace the conventional DC motor. These prototypes have concentrated windings rather than distributed windings in order to minimize the volume of copper. The magnetic structure of the first prototype is equipped with small teeth localized between the main poles. With this special arrangement, the experimental results show that the torque performances are the same as in the case of classical structures with distributed windings.