FEM-based optimization of the airgap of smoothing inductors

In the paper, the 2-D finite element method implemented with FLUX software was employed to finding the optimal airgap of smoothing inductors with resistive load. The optimal design of nonlinear saturable inductors depends on the power converter characteristics and on the load. The optimal airgap is usually a standard value according to catalog data. The working conditions of the smoothing inductor may require an optimal airgap slightly different of the standard value. It can be determined through an optimization method around the standard value, to obtain the best performances. Similar previous researches were achieved with an optimization tool based on time domain numerical simulation using a model implemented with the powerful circuit simulator SPICE. The best smoothing effect of the inductor is equivalent to the minimum value of the ripple load current corresponding to the optimal airgap. The 2-D finite element method was used to determine the ripple load current depending on the airgap which was set as objective function of the optimization problem. The numerical simulation was performed in transient magnetic regime coupled with electric circuit, taking into account the nonlinearity of ferromagnetic core. To solve the optimization problem, the region elimination method was chosen that best fits to the unconstrained optimization problems with unimodal one-dimensional objective functions. The interval halving procedure has been employed to accelerate the optimization process and acceptable results were obtained.