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A Stable and Computationally Efficient Spatial Harmonic Model for Predicting the DC Winding Induced Voltage in WFSF Machine

In order to predict the DC winding induced voltage in the wound field switched flux (WFSF) machine with consideration of the impact of current harmonics in both DC winding and AC windings, the field-circuit coupling method based on the high-fidelity spatial harmonic (SH) model is applied in this paper. However, it is found that the inductance-based SH model of the WFSF machine is unstable in dynamic operation, as the model suffers from the numerical instability due to the high condition number of the inductance matrix caused by the magnetic coupling among d-, q-axis and the DC winding, resulting in prediction errors of the d-, q-axis flux-linkages, and that of the DC winding. To solve this problem, a flux-linkage-based SH model is proposed for the WFSF machine in this paper, and the simulation results show that the proposed flux-linkage-based SH model can operate stably in dynamic operation. In addition, the calculation speed of the flux-linkage-based SH model is 147 times faster than the inductance-based one, due to the exemption of the calculation of the partial derivation equations.