Powder cores have been gained much attention as one of the attractive magnetic cores used in power converters due to their superior features such as high saturation flux density or distributed air gaps. However, powder cores have a unique feature that the relative permeability of the magnetic core varies depending on the magnetic field intensity. However, modeling the variable relative permeability, the design method for powder cores, and computer simulation methods of non-linear inductance are well not discussed in the related literature. Therefore, this paper proposes a novel modeling, magnetic design methods, and simulation technique considering dc superimposition characteristics of powder cores. The modeling method uses a novel model equation representing the behavior of relative permeability under the dc current superimposition condition, which is helpful to evaluate the performance of powder cores and to properly design various magnetic components. Theoretical analysis has been presented and the effectiveness and the validity of the proposed methods are evaluated through simulation and experimental tests.