Magnetics for Power Electronic Converters

Magnetics are an integral part of every switching converter. Often, the design of the magnetic devices cannot be isolated from the converter design. The power electronics engineer must not only model and design the converter, but must model and design the magnetics as well. Modeling and design of magnetics for switching converters is the topic of this course. In this module, basic magnetics theory is reviewed, including magnetic circuits, inductor modeling, and transformer modeling. This provides the technical tools needed in the remainder of the course to understand operation of magnetic devices, model their losses, and design magnetic devices for switching converters.

Eddy currents also cause power losses in winding conductors. This can lead to copper losses significantly in excess of the value predicted by the dc winding resistance. The specific conductor eddy current mechanisms are called the "skin effect" and the "proximity effect". These effects are most pronounced in high-current conductors of multilayer windings, particularly in high-frequency converters. This module explains these physical mechanisms and provides practical methods to compute these losses.

The goal of this chapter is to design inductors for switching converters. Specifically, magnetic elements such as filter inductors are designed using the Geometric Constant (Kg) method. The maximum flux density Bmax is specified in advance, and the element is designed to attain a given copper loss. Both single-winding inductors and multiple-winding elements such as coupled inductors and flyback transformers are considered.