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Master of Science / Department of Electrical and Computer Engineering / Alexei Nikitin / Balasubramaniam Natarajan / It has been shown that the performance of communications systems can be severely limited by non-Gaussian and impulsive interference from a variety of sources. The non-Gaussian nature of this interference provides an opportunity for its effective mitigation by nonlinear filtering. In this thesis, we describe blind adaptive analog nonlinear filters, referred to as Adaptive Nonlinear Differential Limiters (ANDLs), that are characterized by several methodological distinctions from the existing digital solutions. When ANDLs are incorporated into a communications receiver, these methodological differences can translate into significant practical advantages, improving the receiver performance in the presence of non-Gaussian interference. A Nonlinear Differential Limiter (NDL) is obtained from a linear analog filter by introducing an appropriately chosen feedback-based nonlinearity into the response of the filter, and the degree of nonlinearity is controlled by a single parameter. ANDLs are similarly controlled by a single parameter, and are suitable for improving quality of non-stationary signals under time-varying noise conditions. ANDLs are designed to be fully compatible with existing linear devices and systems (i.e., ANDLs’ behavior is linear in the absence of impulsive interference), and to be used as an enhancement, or as a simple low-cost alternative, to state-of-the-art interference mitigation methods. We provide an introduction to the NDLs and illustrate their potential use for noise mitigation in communications systems. We also develop a digital implementation of an ANDL. This allows for rapid prototyping and performance analysis of various ANDL configurations and use cases.

It is well known that a crucial factor determining the transmission capacity with regards to the voltage stability limit of a stressed power system, is the limitation of field and stator current of overexcited generators. These limiters are commonly referred to as overexcitation limiters (OEL) and stator current limiters (SCL). This thesis investigates the representation of overexcitation limiters and stator current limiters in the Swedish power system and how they could be implemented in the power system simulator PSS/E. Dynamic simulations in PSS/E are performed to investigate and validate differences between model types and parameters. The thesis compares different types of limiters and presents a representative set of parameters based on the documentation and implements them into PSS/E. The result from the study is a recommendation to migrate to limiter model MAXEX2 for generators without stator current limiters. The MAXEX2 model uses an inverse time characteristic which is becoming more common in installed voltage regulators. This feature makes it possible for extended use of generators before limiter action is applied. The MAXEX2 model is also possible to tune into a fixed time delay to represent older types of limiters.

In today’s technological world, electrical energy is one of the most important forms of energy and is needed directly or indirectly in almost every field. Increase in the demand and consumption of electrical energy leads to increase in the system fault levels. It is not possible to change the rating of the equipment and devices in the system or circuits to accommodate the increasing fault currents. The devices in electronic and electrical circuits are sensitive to disturbance and any disturbance or fault may damage the device permanently so that it must be replaced. The cost of equipment like circuit breakers and transformers in power grids is very expensive. Moreover, replacing damaged equipment is a time and labour consuming process, which also affects the reliability of power systems. It is not possible to completely eliminate the faults but it is possible to limit the current during fault in order to save the equipment and devices in the circuits or systems. One solution to this problem is to use a current limiting device in the system. There are many different types of approaches used for limiting fault currents Two different approaches to limit fault currents have been discussed by the author. One is Passive Magnetic Current Limiter (MCL) and another is High Temperature Superconductor Fault Current Limiter (HTSFCL). Both are passive devices and they do not need any sensor or external sources to perform their current limiting action. The first device consists of two ferrite cores and a permanent magnet which is sandwiched between the two saturated cores and it is called Magnetic Current Limiter. Experimental results with the MCL in circuit are discussed. Both field and thermal models of the MCL have been simulated using finite element software, FEMLAB. The demonstration of the High Temperature Superconductor Fault Current Limiter (HTSFCL) in power systems has been explained. The MATLAB simulation of the HTSFCL has been done and the results with and without the fault are shown. Power System Analysis Toolbox (PSAT) software has been used to locate the optimum or the best location of HTSFCL in a nine bus system. It has been shown that it is possible to find a solution that limits the fault current in power systems. Depending on the size of the system, either the MCL or the HTSFCL can be implemented. The location of the HTSFCL is to be carefully selected to achieve optimum results.

There are many useful guidelines and theories to be found on mixing and mastering. One of these statements is that the monitoring level affects how well one can detect and evaluate the Dynamic Range Compression (DRC) when mixing. However, some of the sources that support this idea are contradictory as to whether a low or high monitoring level is better for this purpose. No previous research on this subject has been found, even though monitoring levels are presumed to be essential for the mixing and mastering engineer. The aim of the study was to investigate if the monitoring level will affect the listeners’ detection threshold for DRC when applied to a vocal track. For this, one higher and one lower monitoring level was chosen, and a simple up-down method was used to obtain the X50 in each monitoring condition, in which these were compared. The results indicate that the monitoring level does not affect the listeners’ threshold of detection for DRC. Moreover, it can be stated that the monitoring level in which the participants had the most habit of working in did not affect the result either. This research can be used to take more informed decisions regarding monitoring levels and to revisit some previous observations.

During several decades of research and development in the field of Magnetically Confined Fusion (MCF) the preferred selection of materials for Plasma Facing Components (PFC) has changed repeatedly. Without doubt, endurance of the first wall will decide research availability and lifespan of the first International Thermonuclear Research Reactor (ITER). Materials erosion, redeposition and mixing in the reactor are the critical processes responsible for modification of materials properties under plasma impact. This thesis presents several diagnostic techniques and their applications for studies of materials transport in fusion devices. The measurements were made at the EXTRAP T2R Reversed Field Pinch operated in Alfvén laboratory at KTH (Sweden), the TEXTOR tokamak, recently shut down at Forschungszentrum Jülich (Germany) and in the JET tokamak at CCFE (UK). The main outcomes of the work are: Development and application of a method for non-destructive capture and characterization of fast dust particles moving in the edge plasma of fusion devices, as well as particles generated upon laser-assisted cleaning of plasma exposed surfaces.  Advancement of conventional broad beam and micro ion beam techniques to include measurement of tritium in the surfaces exposed in future D-T experiments.  Adaption of the micro ion beam method for precision mapping of non uniform elements concentrations on irregular surfaces.  Implementation of an isotopic marker to study the large scale materials migration in a tokamak and development of a method for fast non destructive sampling of the marker on surfaces of PFCs. / <p>QC 20140508</p>

<p>An extensive investigation of front-door protection devices i.e. limiters has been made. The thesis work contains both HPM- and UWB-measurements done on various limiters, in order to characterize them. The measurements show that all limiters are not suitable as protection against HPM- and UWB-pulses. The limiters that were found to provide the best protection are limiters based on diode technologies. PIN- and Schottky-diodes generally shows very good performance and they fulfill many parameters that have been set by FOI. To obtain a full protection it is presumably necessary to use two or more limiters in combination, which complement each other.</p> / <p>En omfattande studie av framvägskopplingsskydd, dvs. limiters har gjorts. Examensarbetet innehåller resultat från både HPM- och UWB- mätningar som har gjorts på olika limitrar för att karaktärisera deras prestanda. Av resultaten från mätningarna kan man se att alla limitrar inte passar som skydd mot HPM- och UWB-pulser. De limitrar som tillhandahöll det bästa skyddet var baserade på olika diodtekniker. PIN- och Schottky-dioder visade sig överlag ha väldigt goda prestanda och de uppfyller många av de parametrar som bestämts av FOI. För att få ett heltäckande skydd är det förmodligen nödvändigt att man använder två eller flera limitrar i kombination, som kompletterar varandra.</p>

No description available.

No description available.

An extensive investigation of front-door protection devices i.e. limiters has been made. The thesis work contains both HPM- and UWB-measurements done on various limiters, in order to characterize them. The measurements show that all limiters are not suitable as protection against HPM- and UWB-pulses. The limiters that were found to provide the best protection are limiters based on diode technologies. PIN- and Schottky-diodes generally shows very good performance and they fulfill many parameters that have been set by FOI. To obtain a full protection it is presumably necessary to use two or more limiters in combination, which complement each other. / En omfattande studie av framvägskopplingsskydd, dvs. limiters har gjorts. Examensarbetet innehåller resultat från både HPM- och UWB- mätningar som har gjorts på olika limitrar för att karaktärisera deras prestanda. Av resultaten från mätningarna kan man se att alla limitrar inte passar som skydd mot HPM- och UWB-pulser. De limitrar som tillhandahöll det bästa skyddet var baserade på olika diodtekniker. PIN- och Schottky-dioder visade sig överlag ha väldigt goda prestanda och de uppfyller många av de parametrar som bestämts av FOI. För att få ett heltäckande skydd är det förmodligen nödvändigt att man använder två eller flera limitrar i kombination, som kompletterar varandra.