Applications of rare-earth permanent magnets in electrical machines: from motors for niche applications to hybrid electric vehicles

The advent of modern rare-earth permanent magnets, which have a magnetic energy product up to an order of magnitude greater than those of Alnico and ferrite magnets, with high remanence and coercive force, has resulted in improved performance of many devices and products. Modern rare-earth magnets, especially neodymium-iron-boron, when combined with technological advances in power and control electronics, computational techniques based on finite-element methods, and new generation soft magnetic materials, have had a major impact on electric machine design. These technologies have resulted in state-of-the-art electrical machines that are compact, of high efficiency, and high torque and power outputs per unit volume. Such machines have been integral to the success of a number of mass market consumer applications, for example computer disk drives, camcorders, CD and DVD players etc. Several innovative electrical machines are reviewed that have been developed by the CSIRO Division of Telecommunications and Industrial Physics and by the Faculty of Engineering, University of Technology, Sydney, (UTS), for a number of niche applications. In each case the machine pushes the boundary of electric machine design, and results in a machine that has unique features, such as compactness, high efficiency or high torque per unit volume. These attributes are in large part a benefit of the use of rare-earth permanent magnets. Machines discussed include a sheep shearing hand-piece, a direct drive actuator, an implantable centrifugal blood pump, a motor for a solar powered racing car and a permanent magnet generator for a series hybrid electric vehicle. All use neodymium-iron-boron magnets on the rotating part of the motor and a three phase winding on the stationary part (or “stator”).