Line Voltage Control of Induction Motor for Increase Its Efficiency in Stable Area

Regular induction motors operate at a constant value of voltage. They operate from zero external load to rated value. At low loads, motors works with reserve of the power. At low loads, motor can work with lower voltage, with lower current (lower power losses) and higher power factor (cos φ). In the paper, we consider theoretical basics of reduction of idle current and increase power factor in idle mode operation. We consider speed controller by changing value of motor voltage. With this controller, we can reduce idle current and increase its power factor. In addition, we consider current controller for limiting starting current by decreasing voltage during motor start, and reduction idle current with improved power factor in idle steady state conditions. Voltage change includes controlled (thyristor) rectifier or pulse width modulated converter of voltage. Controllers can include speed or current feedbacks. We consider digital model of induction motor with different controllers. Results of modeling shows decreasing idle current with improved power factor in case with the speed controller. In case with current controller, it is limited starting current and reduced idle current with improved power factor in idle mode operation. Suggested controllers, can find application in the regular induction motor drives. This property of induction motor need take in account in frequency control drives.