Application of a hybrid FEM-BEM method to the time response of an electromagnet under imposed terminal voltages

The paper presents a method for the analysis of the motion of an electromagnet armature when given voltages are applied at its terminals. The nonlinearity of the ferromagnetic core is treated by the polarization fixed point method (PFPM), the magnetic polarization correction being performed iteratively in terms of the magnetic field intensity. A hybrid Finite Element Method (FEM) - Boundary Element Method (BEM) technique is employed in order to solve the electromagnetic field problem. The FEM is used for the computation of the field within the ferromagnetic bodies and, independently, the BEM is applied to the outside free space, the coupling between the FEM and BEM domains being performed by an iterative correction of the boundary conditions. The terminal voltages determine the coil magnetic fluxes and, then, the current density is obtained by integrating the vector potential over the coil cross sections. The variation with time of the terminal voltages is also taken into account in the solution of the coupled electro-mechanical problem. The response is determined for terminal voltages applied at various times within a period.