Controlled magnetic devices in power electronic applications

Abstract

Almost all power electronic converters require magnetic devices and some properties of the converters can be controlled with magnetics. New magnetic materials enable implementation of magnetic control of converters also in high switching frequency applications. The presented paper gives an overview about controllability of magnetic devices in theory and practice, simulation approaches and examples. The focus is on electrically controllable magnetic devices. This means that an additional control winding is wound on or integrated into the magnetic core of the device. This additional winding is used to control the inductive behavior of the device by injecting a current. The different basic control approaches of magnetic devices are explained theoretically and demonstrated experimentally by laboratory prototypes. Several controllable magnetic devices were tested in order to evaluate the applicability of the different control methods. The control techniques were demonstrated also with different core materials to address different applications. Especially ferromagnetic alloys and ferrite materials are in focus of the investigation. Moreover, first approaches for the modelling and simulation of controllable magnetic devices are given in the paper.

Review of Flux Interaction of Differently Aligned Magnetic Fields in Inductors and Transformers

“…According to [2], there are three different methods of superposing magnetic fields in inductors and transformers. They differ in terms of the auxiliary winding's design, which is either wound on the magnetic core or introduced into it through drill holes.…”

“…FIGURE 1: Core section with main winding and additional auxiliary DC bias winding [2] the permanent magnet can be magnetized in its opposite direction. This case could occur e. g. in a fault situation of the application.…”

“…Core section with main winding and auxiliary DC bias winding introduced to the core through drill holes orthogonal to the main flux [2] are either orthogonal or parallel to the main flux depending on the position of the considered section around the drill hole. Regarding the parallelly aligned sections, the auxiliary bias flux is either aligned in the same or opposite direction.…”

“…Core section with main winding and auxiliary DC bias winding introduced to the core through drill holes parallel to the main flux [2] fields and fluxes should not affect each other. The coupling between both coils should theoretically be zero, whereby mathematical description and calculations become significantly simpler.…”

“…The presented results show significant reductions of the 3rd as well as the 5th and 7th harmonic. The concept has been developed through several prototypes (see [2]) and applied in a demonstrator for reactive power management in distribution grids (medium-voltage grids) to compensate reactive power feed-in of renewable energy sources (see [121]).…”