Optimal system efficiency operation of an induction motor drive

The efficiency of an induction motor drive can play an important role in energy conservation, especially for hybrid electric vehicle applications. This paper explores the optimal efficiency point of an inverter and induction motor system designed for an electric vehicle. Theoretically, it is shown that the maximum motor efficiency and maximum torque per ampere occur at different slips. Furthermore it is demonstrated that neither of these points is actually the maximum efficiency of the system during most operating conditions. The efficiency gain is not significant at low speed and low torque, but it can be significant at high speed and low torque. The theoretical results are compared with experimental data for a few operating points.