Optimum Vo1tage and Frequency for Polyphase Induction Motors Operating with Variable Frequency Power Supplies

Induction motors with variable frequency are becoming more widely used for variable speed drives. These motors may operate over a wide torque and speed range. By an adjustment in voltage and frequency, a motor can be made to operate at the minimum loss for any torque and speed. Equations and curves are developed to find the voltage and frequency to produce the minimum loss, and also to find the value of the loss. It is shown that for a typical motor, the slip speed should be allowed to increase slightly as required torque increases if minimum loss is to be attained.