3-D FEM Calculation of Electromagnetic Properties of Single-Phase Induction Machines

In comparison with three-phase induction machines, modern single-phase induction machines normally have skewed rotors, but show an elliptic magnetic field during start-up. In order to properly model the start-up of such a machine, this three-dimensional (3-D) characteristic has to be accounted for. This leads to the application of the 3-D finite-element method. This paper will introduce a new approach to model and analyze the start-up of such a single-phase machine, with the aim of higher computational efficiency. Furthermore, this paper will discuss how symmetries, both in the circumferential direction and along the motor shaft, can be exploited despite the skewing. This is achieved through transforming (rotating) the cutting plane, doubling the skewing angle, and increasing the rotor conductor conductivity. The analysis is carried out on a small two-pole 100-W machine used for household appliances. The theoretical results are compared with experimental results for six rotors; each with a different skewing angle.