Efficiency testing of motors powered from pulse-width modulated adjustable speed drives

This is a report of efficiency testing of an induction motor powered from three different pulse width modulated adjustable speed drives. The motor was operated at a range of speeds and torques, and each drive was operated at the highest, lowest, and an in-between carrier frequency. The motor was a typical NEMA design B motor, and the drives were typical, industrial scalar drives using the default volts/Hz setting. The testing showed that the drive efficiencies remained above 90% until torque was lowered to below 20% of rated torque. Combined motor and drive efficiencies remained above 80% until speeds or horsepower loads were lowered to below 20% of rated torque. The test was performed using a unique data acquisition scheme that permitted acquisition of a large number of torque settings for each speed selection.