Improving the Power Efficiency of a Rotor Flux-Oriented Induction Motor Drive

Abstract

This paper investigates an algorithm for improving the efficiency of a lightly loaded, field-oriented induction motor drive. This is accomplished through determining the optimal torque per flux ratio (or the slip frequency command) necessary for obtaining the desired flux position and high-efficiency requirement. A closed form for the optimal torque per flux ratio has been derived in terms of the motor speed besides the equivalent circuit parameters. Compared to the conventional rated flux control method, it is found that the power efficiency of a 3-HP motor has been improved by more than 12% when operating at a quarter of rated load. It is worthy to indicate that, with negligible core losses, the torque per flux ratio will have a constant value independent of the motor speed. Inspecting the parameters of different motor sizes (0.25-100 hp), it has been detected that this value lies in the narrow range 0.67-0.75. Computer simulations have been carried out to evaluate the proposed method. The results show that an efficiency improvement has been achieved, especially at light loads, along with the high dynamic performance obtained through applying the field orientation concept.

Keywords:

• Vector Control
• Induction Motor Efficiency