Improved model for design of permanent magnet machines with concentrated windings

Abstract

In literature, many different expressions for Carter factor can be found leading to confusion. This paper evaluates Carter factor expressions by comparing finite element computations in order to find the most suitable one which can be used in the design of permanent magnet machines. This paper shows limitations of conventional literature of slotting effect in the range of small slot opening. Finite element analysis based results show that calculation of magnetic saturation correction factor based on tooth flux density brings up results more accurate than that based on air gap flux density. The analytical model is improved by incorporating static FEM. This leads to hybrid model. Correction factors for slot opening, fringing and magnetic saturation are calculated online by static FEM model. In order to implement this concept, a static FEM program was developed. The program is able to make geometry model and handle boundary conditions automatically. To speed up the refinement of design results, a nonlinear transient finite solver based on scripts was also developed. Our implementation ensures that design parameters can be changed easily. Nonlinear finite element computations and experiments are compared. They are in very good agreement, with an error in the internal voltage of only 1.5%. Comparison of the analytical models, the proposed model and transient FEM model shows that the proposed model is more accurate in predicting permanent magnet machine behavior than conventional analytical model.