Numerical Study of Nonlinear and Transient Behaviors of a Variable Electromotive-force Generator with an Adjustable overlap between the Rotor and the Stator Using the Finite Element Method

A modified generator, referred to as the variable electromotive-force generator, is developed to enhance fuel efficiency of hybrid vehicles and expand operational range of wind turbines. Obtaining a numerical model that provides accurate estimates on the generator output power at different overlap ratios and rotor speeds, comparable with those from experimental results, would expand the use of the proposed modified generator in different applications. The general behavior of the generated electromotive forces at different overlaps and rotor speeds is in good agreement with those from experimental and analytical results at steady-state conditions. Employing generator losses due to hysteresis and eddy currents in a three-dimensional model would generate more realistic and comparable results with those from experiment. In this work, electromagnetic analysis of a modified two-pole DC generator with an adjustable overlap between the rotor and the stator at transient conditions is performed using finite element simulation in the ANSYS 3D Low Frequency Electromagnetics package. The model is meshed with tetrahedral or hexahedral elements, and the magnetic field at each element is approximated using a quadratic polynomial. For a fixed number of coils, two cases are studied; one with constant magnetic properties and the other with nonlinear demagnetization curves are studied.