Accurate Determination of Induction Machine Torque and Current Versus Speed Characteristics

The determination of induction machine torque and current speed characteristics relies on methods based on either direct testing or calculation, using a machine equivalent circuit (EC). Both methods may lead to significant errors. As a contribution to a still open discussion, this paper presents the challenges encountered using these methods and an approach is presented in this paper to overcome the inherent challenges. The proposed approach considers saturation, and compensates for skin effect and machine temperature to improve accuracy. Five induction motors of different pole pairs were analyzed and tested to provide the understanding of the underlying issues of predicting torque and current characteristics of induction machines. The findings indicate that, for direct testing, multiple data points closer to nominal voltage are required. In the case of EC modeling, proper correction of the model for temperature and saturation leads to improved prediction of the torque characteristics of general purpose induction machines.