Efficiency control of inverter fed induction motor drives

Induction motor losses at partial loads can be significantly reduced by operating an adjustable frequency drive at the optimum slip which yields maximum efficiency. The present investigation quantifies the potential improvement in induction motor efficiency for both standard and energy efficient motors operating on a six-step voltage-source inverter supply. The analysis employs a comprehensive model of the induction motor which incorporates the frequency - dependent nature of the motor parameters and effects of stray load loss. Efficiency contours are plotted on a torque- speed plane for constant volts/hertz operation and for optimum slip frequency control plotted as a contour map.