This paper is focused on core size optimization of power inductors in bidirectional dc-dc converters. It presents an experimental large-signal characterization procedure for power inductors in electric vehicle applications and a method to obtain an inductance reference value for the power inductor in dc-dc converters' simulation studies. It discusses the importance of the inductor design project by describing important constraints such as core size and saturation. The main contribution of this paper is related to the proposed dc flux cancelation technique in the bidirectional converter. A variable inductor prototype is used to replace the power inductor in order to decrease core size by improving the ripple content of the inductor current. The saturation level of the core is controlled by means of an auxiliary winding whether the converter operates in buck or boost mode. Experimental results validate the proposed methodology showing more than 50% reduction in magnetic material for similar current levels.