Optimal efficiency analysis of induction motors fed by variable-voltage and variable-frequency source

The authors discuss the efficiency analysis and experimental data for an induction motor fed by a variable-voltage and variable-frequency (VVVF) source. Nonideal factors (core saturation, source harmonics, and skin effect) affecting the efficiency are included in the analysis to yield practical results from computer simulation. Based on the simulated results, an experimental system, composed of a DC link power converter with a VVVF feature, a dynamometer and a PC/AT, was developed to evaluate the efficiencies of the induction motor from low to rated speed and torque. Both analysis and experimental results indicate that the efficiency with VVVF is superior to that of constant flux operation. Experimental results showed that 10-15% improvement in the efficiency of a 2 hp induction motor at 0.4 per unit load using VVVF can be achieved as compared to the constant flux operation