A versatile finite element model of electric machines

A versatile numerical model for the simulation of dynamic operations of electric machines and drives is presented, and the formulations of the model are described in detail. To consider the field changes along the axial direction, the magnetic field equations are derived using the multislice finite element method. A systematic and simple method to couple the arbitrarily connected external circuits with the multislice magnetic fields using the nodal method is also presented. Because the system equations are derived directly from the fundamental formula describing the machine construction, the model can be applied to simulate the operations of an induction motor, synchronous motor, and brushless d.c. motor. The examples reported include a critical study of a synchronous motor with its windings connected in star and delta, the calculation of the interbar current losses in the rotor cage of an induction motor, and the computation and comparison of the stator phase current waveforms of a brushless d.c. motor with its corresponding experimental results. Moreover, the study also includes the estimation and comparison of the output torque profiles of a five-phase synchronous reluctance motor with its two different rotor structures, the computation of the stator current with or without third harmonics, as well as when the rotor has nonskewed or skewed magnetic poles. In other words, a wealth of examples are reported in this paper to illustrate the versatility and superiority of the proposed algorithm when compared to conventional techniques.