Effect of coercive force and characteristics of a pole changing permanent magnet motor for variable-speed drive

Energy savings in electrical appliances and electric vehicles can be realized by reducing the power consumption of motors operating for variable-speed drive. In order to reduce the energy consumption of such electrical devices, flux-weakening currents are used to reduce the voltage at high rotational speeds, which leads to significant copper and core losses. To counter this problem, we have developed a new technique that changes the number of poles in a permanent magnet (PM) motor based on the rotational speed. Therefore, we have proposed a PM motor that can vary its electrical machine constants to obtain high efficiency and an extensive rotational speed range. Herein, we describe the structure, pole changing magnetization mechanism, and basic characteristics of a novel pole changing PM motor, and present various characteristics of the motor over a wide rotational speed range. Furthermore, we also discuss the effect on the motor of the coercive force of the variable magnetized permanent magnet. The results of our study show that the proposed motor reduces core loss by about 50%, doubles the rotational speed range of the motor, and demonstrates high efficiency over a wide rotational speed range.