Majority of loads on AC mains are induction motors. Certain industries like tea, these motors will be lightly loaded for most of the time. If the torque requirements can be met with reduced stator applied voltage, substantial energy saving is possible in induction motors. With reduced voltage, stator will be subjected to reduced flux. In this paper, different control strategies to operate the induction motor at maximum efficiency are compared. An on-line efficiency optimization controller is proposed for induction motor. In this, the controller searches for a minimum stator current by changing the control variable (stator voltage). The controller can be used effectively to applications with frequent changes of torque. An 8 switch PWM three phase AC chopper is used to control the stator voltage. Duty ratio of the AC chopper is varied to get optimum voltage. A complete simulation of the system is carried out in SIMULINK of MATLAB environment. Experimental validation in open loop is done on a laboratory model set up using MOSFET switches in the power circuit.

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Induction motor efficiency search method current minimization