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Rare-earth magnets of high-energy products have been widely used to improve the efficiency, as well as the power and torque per unit weight, of permanent-magnet machines. In addition to the drawbacks of limited resources and high prices, the rare-earth magnet may risk irreversible demagnetization during field weakening or malfunctioning in machine operation. To solve this problem, we investigate the antidemagnetization property due to the flux shunt mechanism and hybrid magnetomotive force in a permanent-magnet direct-current motor. The hybrid magnetomotive force is provided by low-grade permanent magnets and additional field windings, between which are ferromagnetic media that shunt the adjustable magnetic flux in the machine. We performed an optimal machine design and verified it with a finite-element analysis. We fabricated a prototype, and the experimental results show that machine efficiency and torque are increased by increasing the current of the field winding and that machine speed can be extended by reducing the field current. Finally, we proved that the antidemagnetization mechanism is effective by investigating the reduction of back electromagnetic force after demagnetization.
Date of Publication: Nov. 2010