COUPLED FINITE ELEMENT AND EXTENDED-QD CIRCUIT MODEL FOR INDUCTION MACHINE ANALYSIS

The design of high-performance squirrel-cage induction motors (IMs) entails the capability to predict the motor efficiency map with high accuracy over an operating range. In particular, modeling high-frequency rotor bar currents becomes important for loss analysis in high-speed applications. In theory, it is possible to analyze an IM using time-stepping finite element analysis (TS-FEA); however, this is not viable due to computational limitations. To bridge this gap, we set forth a computationally efficient method to predict the rotor cage loss. This is achieved by coupling magnetostatic FEA with an extended qd-circuit model of the cage. The circuit model is derived in a synchronously rotating reference frame. The proposed IM model includes the effects of saturation, winding and slot harmonics, as well as nonuniform current distribution in the rotor bars. The proposed model is validated by comparing the estimated cage loss and computational effort against a 2-D nonlinear TS-FEA.

The proposed electromagnetic model is finally coupled to a linear thermal model to predict IM performance over an operating range and the results are validated using experiments. The proposed model is further extended to identify detailed flux density waveforms in the iron to estimate core loss. The flux density waveforms are obtained by conducting a set of magnetostatic FEA studies using the derived rotor bar currents.