Variable-Magnetic-Flux Motors for Opening up a World of the New Motor-Drive Technology

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Kazuto Sakai, Toyo University


Saving energy in electrical appliances and electric vehicles (EV) requires a reduction in power consumption of motors. The motors used in these appliances operate at variable speeds. In addition, these motors operate with small load in stationary mode and with large load in start-up mode. A permanent magnet motor can operate with high efficiency at a rated power. However, the efficiency of this motor is lower at small loads or high speeds because a large constant magnetic force leads to a significant core loss. Also, the flux-weakening current to depress voltage at high speed leads to a significant copper loss. Hence, new technologies that control a magnetic force of a permanent magnet depending on the load or speed have been developed. A variable-magnetic-flux motor operates over a wide range of speed with high power and efficiency. This article introduces new motors which can change magnetic flux of permanent magnet.

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