Comparison of Time-Harmonic and Transient Finite Element Calculation of a Squirrel Cage Induction Machine for Electric Vehicles

For predicting the performance characteristics of highly utilized induction machines, commonly finite element analysis (FEA) is applied. If only the stationary behavior is of interest, both time-harmonic and transient calculations are feasible. Both procedures offer benefits and drawbacks regarding precision and computing time. In this paper the stationary torque-slip-characteristic of a squirrel cage induction machine for electric vehicle application is calculated by means of time-harmonic and transient FEA. The simulation results are compared to measurements taken on the test bench. For low saturation levels the time-harmonic and transient simulation produce nearly equivalent stationary torque results. For high saturation levels, the commonly used approach for nonlinear time-harmonic calculation is to use a corrected magnetization curve. It is shown that the assumption of sinusoidal time variation of the magnetic field strength usually made in this case results in a torque error increasing with the saturation level for the time-harmonic calculation.

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