A field construction technique to efficiently model the dynamic vector forces within induction machines

Using finite element (FE) analysis to model the dynamic vector fields and forces within induction machines requires significant computational effort. Numerous researchers have proposed techniques to reduce the effort such as taking advantage of machine symmetry. Although these techniques have been effective, the required computation remains relatively high, particularly if it is desired to use the model as an integral part of machine design, where numerous model evaluations are required. In this research, a new means to establish the dynamic between stator excitation and vector force output of the induction machine is proposed. Using the so-called Field Construction (FC) approach, the calculated response of a FE model of the machine under single-phase excitation and fixed rotor position is used to establish basis functions of the normal and radial flux densities in the airgap of the machine. The basis functions are then used to construct the magnetic fields and vector forces under arbitrary stator excitation and rotor speed. Using FC, evaluation of the fields and forces produced by an induction machine under alternative excitation strategies can be explored much more efficiently. Indeed, the time required to calculate the dynamic torque on a modern personal computer is reduced from many hours using a FE model to minutes using FC. Of note is that the FC technique has been derived to accept current or voltage as model inputs. In addition, a multi-rate FC technique has been developed to enable efficient modeling of machines connected to power electronic devices. Finally, through evaluation of the basis functions used in the FC, closed-form expressions that relate the basis functions to forces acting inside induction machines have been derived to provide new insight into how forces behave within a machine