Analytical Derivation of Efficiency Map of an Induction Machine for Electric Vehicle Applications

Induction machines are used in some electric vehicles, just like PM machines. But machines efficiencies are generally not considered in an accurate way during the sizing of a traction system, especially for multi-machine system. In this paper, an analytical efficiency derivation method for an induction machine is proposed based on loss models. The iron losses and the copper losses are deduced as a function of the losses at the rated point. All the relationships deduced in this paper are finally expressed as a function of torque and speed. An efficiency map of an induction machine is then evaluated only by its basic design parameters. Thus the proposed method can calculate the efficiency map of an induction machine before its design. The proposed method has the properties of fast calculation and acceptable accuracy in the sizing stage. Note that the similar deductions also can be extended for PM machines. This method could be used for the sizing of other multi-machine system in the future.