Comparison of two techniques for two-dimensional finite-element inductance computation of electrical machines

The modelling of electrical machines by equivalent circuits requires an appropriate calculation of inductance values. The energy-perturbation and flux-linkage methods have been devised (and extensively used) to determine inductance values of electrical machines from twodimensional finite-element solutions. That both methods are numerically equivalent and give approximately the same values of inductance is shown. However, the flux-linkage method requires less computation resources and is numerically more robust than the energy perturbation method when two-dimensional calculated fields are used. Hence, it is concluded that the flux-linkage approach should be chosen as the preferred method for two-dimensional inductance calculation of electrical machines. The numerical characteristics and equivalence of the energy-perturbation and flux-linkage methods are demonstrated by calculating the time-varying ‘apparent’ inductances of the stator and rotor field windings of a turbine generator running under transient conditions.