Principle and basic characteristics of a hybrid variable-magnetic-force motor

Reducing the power consumed by motors is important for energy conservation in the case of electrical appliances and electric vehicles (EVs). The motors used for operating these devices operate at variable speeds. Further, the motors operate with a small load in the stationary mode and a large load in the starting mode. A permanent magnet motor can be operated at rated power with high efficiency. However, the efficiency is low under a small load or at high speeds because the large constant magnetic force results in substantial core loss. Furthermore, the flux‐weakening current that decreases the voltage at high speeds leads to significant copper loss and core loss. Therefore, we have developed a new technique for controlling the magnetic force of a permanent magnet on the basis of the load or speed of the motor. In this paper we propose a novel motor that can vary the magnetic flux of a permanent magnet and clarify the principles and basic characteristics of the motor. The new motor has a permanent magnet that is magnetized by the magnetizing coil of the stator. The results of analysis show that the magnetic flux linkage of the motor can be changed from 37% to 100% and that a high torque can be produced. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(2): 47–57, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22309