Abstract
M.Ing.
In power electronics most applications are custom designed. Even though similar topologies are
used, each application is designed to fit specific requirements. Presently there is a move towards
standard modules that can be connected together to perform the desired power conversion, in
much the same way as IC’s have been used for a few decades now. It is important to ensure that
the modules can work together without performance degradation. The close proximity of active,
passive and logic devices in high power applications dramatically increases the risk of EMI
between the various components. This document describes the design and characterisation of a
planar conducted RF-EMI power line filter to be used between modules and between modules
and power supplies. The filter consists of two sets of transmission lines in parallel. The first is a
high permittivity material with nickel conductors, referred to as the attenuator. The second is a
set of copper conductors that are placed on the outside of the attenuator. The filter must be able
to remove conducted differential mode noise from power line to the module and from the module
tot the power line. The filter dimensions are comparable to the wavelengths that have to be
attenuated. This allows for a possible combination of RF filtering techniques and power line
filtering techniques. The design of the filter and the electromagnetic effects that govern its
behaviour is explained. The transfer characteristic of the filter is made possible by the choice of
materials and their relation to each other. Each material is discussed and evaluated.
Characterisation methods are described and results presented. The influence the materials have
on the performance of the filter and the methods and problems of construction of the filter are
discussed. The construction of the filter and the commercial processes available are discussed.
A prototype filter was built to demonstrate the feasibility of the construction processes. The
performance of the prototype filter was then measured. The various test set-ups for different
applications are explained. Small signal tests in 50 W systems were used to allow for
comparisons with other filter types. The prototype has minimal insertion loss in the pass band
and an average slope of attenuation of 40 dB/decade beyond the corner frequency. The corner
frequency is at 1 MHz. Transmission line theory is used to develop a distributed element model
for the filter using the ABCD-matrix representation of transmission lines. From this matrix an
equivalent P-model can be calculated. Applicable assumptions are made to simplify the
equations and values for a lumped element P-model is calculated. Both models indicate the
importance that the material parameters have on the performance of the simulation results. Good
correlation between the measured performance and simulated performance is established. The
material parameters are sensitive to temperature. A one-dimensional thermal model is presented
to estimate the operating temperature of the filter. It is determined that the attenuation of the
filter is primarily determined by the attenuator. Based on the findings, new attenuator designs
are made in an attempt to improve the performance of the filter. The small signal measurements
of the various designs and the test results under load conditions are compared. A power test is
performed. The filter performance varies as the voltage rating is increased. Finally, a
temperature characterisation is done. The filter is absorptive and heat is dissipated in both the
conductors and the dielectric material. The filter performance is sensitive to the operating
temperature. A summary of the technology and the evaluation of this type of filter are presented
in the conclusion.