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Novel Winding Changeover Method for A High Efficiency AC Motor Drive

AC motors have been used in many applications owing to their wide speed range and their high efficiency. However, the maximum speed of the AC motor is limited by the back electromotive force(BEMF) which is determined by the mechanical parameter of a machine. By using the field-weakening control, it can be controlled above the base-speed, but this method also has its limitation. To extend a speed-range of machine under operation, the studies on the methods of changing mechanical elements that affect the BEMF have been conducted. The mechanical elements which affect the BEMF are number of poles, connection method, and the number of the turns in the winding changeover method. The conventional change over method of the number of the turns requires switch box with diode bridges and a snubber capacitor [7], [8]. These methods could generate the torque ripple by the long transient time occurred by winding-changeover circuit. In this paper, a novel method is proposed to complement the problems of power transmission and torque ripple without the need of the switch box. The experimental results show the reduced transient time when the winding is changed also show that no power transmission occurs since this method does not use the diode bridges and a snubber capacitor.