Permanent magnet motors capable of pole-changing without changing the connection of the windings for high efficiency

To realize energy saving in electrical appliances and electric vehicles, it is necessary to reduce the power consumption of motors operating at variable speeds. We developed a technique that changes the poles of a permanent magnet (PM) motor depending on the speed. Here, we propose a novel PM motor that changes the number of poles without changing the winding connections and discuss its basic configurations and principles. Pole-changing is accomplished using the d-axis current of the proposed motor for magnetization. Our analysis results confirm that the pole-changing PM motor reduces iron loss by 36% over a conventional PM motor and increases efficiency over a wide range of speeds. Hence, the proposed motor is suitable for use in variable-speed drive systems to achieve high performance and efficiency.