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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:8183 |
| Date | 27 February 2009 |
| Creators | Wolmarans, Pieter Johannes |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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