Modeliranje in analiza magnetnih komponent v močnostnih DC-DC pretvornikih : doktorska disertacija

slovenian

doktorska dela

2014

eddy currents   finite element method   high power DC-DC coverters   high power density   hysteresis   imbalanced magnetic flux   inhomogenous magnetic flux distribution   lumped element model   magnetic components   modeling   saturation prevention

Univerza v Mariboru, Fakulteta za elektrotehniko računalništvo in informatiko

This thesis describes various modeling techniques, analyses and prevention methods for imbalanced and inhomogeneous distribution of magnetic flux inside the magnetic components of high power DC-DC converters. Two techniques for detailed modeling of the discussed magnetic components are presented in detail. In the first technique the finite element method is used, where the detailed finite element model is adequately coupled with the circuit model of the DC DC converter, and where also the properties of active and passive converter components are described adequately. The direct coupling between both models based on modified nodal analysis is presented. The second technique for detailed modeling of magnetic components is based on the lumped parameter method. This way the topological as well as hysteresis properties of the magnetic subsystem are taken into account. Further, a magneto-dynamic model of soft magnetic steel sheets is presented, where the interdependence between eddy currents and magnetic field inside soft magnetic steel sheets is taken into account. The parameters of circuit models that are difficult to determine, are determined using optimization algorithm differential evolution. This thesis also presents overviews and analyses of sources regarding imbalanced and inhomogeneous distribution of magnetic flux inside the magnetic cores of transformers inside DC-DC converters. An imbalanced magnetic field is a consequence of the drift of the magnetic flux inside the transformer core. Inhomogeneous distribution of magnetic field is however a consequence of inadequate distribution of transformer windings along the transformer's magnetic core. These discussed phenomena can cause both saturation of the transformer core, and generally leads to lower efficiencies, power densities and operating reliabilities of such devices. Further, active and passive methods for prevention of the discussed phenomena are presented in detail. It is recognized that the imbalance of the magnetic flux can be prevented both with active as well as passive methods, where inhomogeneous distribution of magnetic flux can be reduced only by passive measures. Methods and sensors for determining magnetic flux imbalances and saturation inside the magnetic components are also presented, where the sensor in the form of a magnetic bridge is presented in detail. Based on this sensor an active technique for preventing of saturation of transformers' cores is presented, which uses hysteresis control of magnetic flux inside the transformer core. At the end of the thesis the discussed problems are analysed with the numerical calculations based on the derived models, which are validated with measurements.

07.08.2023