Computation of harmonic stray losses of induction motors using adaptive time stepping finite element method together with externally coupled circuits

The precise computation of stray losses in induction motors is still a difficult problem to machine designers. This paper describes a method for evaluating harmonic stray losses in nonskewed induction motors. The model used by the authors couples the finite element electromagnetic equations with external electrical circuit equations. The sets of equations are solved by discretizing the time at short intervals in conjunction with the motion of the rotor mesh. With Fourier series analysis, the time harmonics of the fields are then obtained. The harmonic stray losses are subsequently evaluated according to the distribution of the harmonic fields. The results obtained, by using a computer program being developed, produces results which have very good correlation with test data. To reduce CPU time, an adaptive time stepping method was explored in the developed software. A new method to estimate the local truncation error at each time step is also presented in this paper. The method presented in this paper not only needs no extra CPU time, but the accuracy of the solution is also improved.