Realization of high-current variable AC filter inductors using silicon iron powder magnetic core

Low-pass filter inductors are widely used in grid-connected power electronic converters. Different magnetic core materials are available for building these inductors. In this paper, the design of an inductor for an industrial-scale 1 MVA high-power three-phase ac-dc converter is reported. Selection of the core material, which depends on trading off between several aspects, is described. Instead of the traditional fixed inductance value for a large current range, the powder core inductor has a nonlinear inductance characteristic which is inversely proportional to the magnetic excitation. The benefits of using this variable inductance characteristic are described and verified by both circuit and magnetic simulation tools. A hardware prototype was built and initial experimental results are illustrated.