Efficiency evaluation of three-phase-induction motors using dual-frequency and sweep-frequency methods of synthetic loading

The recent global emphasis on efficient use of energy has highlighted the need to develop modern techniques for evaluating the efficiency of electric motors. This paper analyses the dual-frequency and sweep-frequency methods of synthetic loading for their use in evaluating the efficiency of three-phase induction motors. Synthetic loading requires no mechanical load to be coupled to the machine under test. The analysis described uses accurate parameters obtained from real machines and a dynamic induction machine model that includes iron loss. The simulated results show that for efficiency evaluation the synthetic loading methods give good agreement with the measured performance. The input voltages and frequencies for the dual-frequency method produced rotor copper losses that were the same as the full load condition, while the sweep-frequency method produced higher rotor copper losses. The iron loss predicted in both methods was approximately 10% higher than the rated iron loss.