Induction motor is a high efficiency electrical machine when working closed to its rated torque and speed. However, at light loads, there is no balance between copper and iron losses, which results in considerable reduction of efficiency for induction motor drive. The part load efficiency and power factor can be improved by making the motor excitation adjustment in accordance with load and speed. In this paper, an efficiency optimization controller of induction motor drive system, based on searching the value of stator voltage that maximizes the efficiency, will be developed. Then, the validity of the proposed controller and the performance of the drive system have been analyzed by simulation results. To reduce the slip at light loads and low frequencies, a slip compensator has been introduced. 

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