Approximate Protocol for Increased Induction Motor Drive Efficiency

For a mechanical operating point, i.e., rotational speed and torque, of an induction motor drive system, there is a combination of applied terminal voltage and slip that minimizes loss in the motor. Over the years, a variety of impressive models and control formulations have better characterized machine and inverter loss mechanisms resulting in closer-to-optimal control actions. However, it is unclear what level of model complexity is required to realize significant efficiency gains. This paper emphasizes the utility of the linear induction motor model with core loss resistance for optimizing slip frequency and increasing drive efficiency. Experimental results show that, for some sample operating points, the simple equivalent-circuit model reasonably estimated the minimum-loss slip frequency of a 0.25 hp squirrelcage induction motor. Sensitivity analysis provides insight to the optimization and helps guide system identification efforts. An example control structure and drive simulation showcases use of the method.