Application of impedance boundary conditions in finite element analysis of linear motors

Results of performance analysis of a low-speed linear induction motor with a solid steel secondary are presented. The finite element method (FEM) combined with impedance boundary conditions at the surface of secondary steel has been used as a numerical tool. Numerical values of thrust and normal forces compare favorably with experimental data. Linearization of the ferromagnetic material by comparing the surface impedance for linear and nonlinear half-spaces yields good accuracy and reduces cpu time considerably. Application of the impedance boundary condition reduces the FEM mesh size, which substantially reduces the required volume of storage and computing time. The use of the impedance boundary condition is therefore recommended for other electromagnetic problems which involve the penetration of a time-varying field in a conductive nonlinear ferromagnetic medium and in which the skin depth is small compared with the geometry of the problem