Silicon carbide (SiC) is a semiconductor that provides significant advantages for high-power and high-temperature applications thanks to its wide bandgap, which is several times larger than silicon. The resulting high breakdown field, high thermal conductivity and high intrinsic temperature (well above 600 °C) allow high temperature operation of SiC devices and relaxed cooling requirements. In particular, SiC bipolar junction transistors (BJTs) are suitable for high temperature integrated circuits (ICs), due to the absence of a gate oxide. This work focuses on design, fabrication and characterization of the first 4H-SiC integrated circuits realized at KTH. It deals with basic bipolar ICs suitable for high temperature and low voltage applications. Operation up to 300 °C of low-voltage 4H-SiC NPN bipolar transistors and digital integrated circuits based on emitter coupled logic (ECL) has been demonstrated. In the temperature range 27 - 300 °C stable noise margins of about 1 V have been achieved for a 2-input OR-NOR gate operated on -15 V supply voltage, and an oscillation frequency of about 2 MHz has been observed for a 3-stage ring oscillator. The possibility of realizing PNP transistors and passive devices in the same process technology has also been investigated. / QC 20120131

The work done in this thesis focuses on the impact of transmission impairments in high speed optical networks. Specifically it focuses on the impact of nonlinear impairments in long haul fiber optic data transmission. Currently deployed fiber optic transmission networks are running on NRZ OOK modulation formats with spectral efficiency of only 1 bit/symbol. To achieve spectral efficiency beyond 1 bit/symbol, fiber optic communication systems running on advanced modulation formats such as QPSK are becoming important candidates. The practical deployment of QPSK based fiber optic communication system is severely limited by Kerr-induced nonlinear distortions such as XPM and XPolM, from the neighboring NRZ OOK channels. In this thesis we focus on the impact of nonlinear impairments (XPM and XPolM) in fiber optical transmission systems running on QPSK modulation with both differential and coherent detection. The dependence of impact of nonlinear impairments on SOP, baud rate of the neighboring NRZ OOK channels and PMD in the fiber, is analyzed in detail through numerical simulations in VPItransmission Maker®. In this thesis we also analyze digital signal processing algorithms to compensate linear and nonlinear impairments in coherent fiber optic communication systems. We propose a simplification of the existing method for joint compensation of linear and nonlinear impairments called "digital back propagation". Our method is called "weighted digital back propagation". It achieves the same performance of conventional digital back propagation with up to 80% reduction in computational complexity.In the last part of the thesis we analyze the transmission performance of a newly proposed hybrid WDM/TDM protection scheme through numerical simulation in VPItransmission Maker®. The transmission performance of the hybrid WDM/TDM PON is limited by impairments from passive optical devices and fiber optical channel. / <p>QC 20120514</p>

In this master thesis, a new distributed multi-agent optimization algorithm is introduced. The algorithm is based upon the dual decomposition of the optimization problem, together with the subgradient method for finding the optimal dual solution. The convergence of the new optimization algorithm is proved for communication networks with bounded time-varying delays, and noisy communication. Further, an explicit bound on the convergence rate is given, that shows the dependency on the network parameters. Finally, the new optimization algorithm is also compared to an earlier known primal decomposition algorithm, with extensive numerical simulations.

Wireless Sensor Networks are nowadays becoming increasingly popular. Due to their low cost, ease of deployment and application, they oer robust solutions in a variety of elds. In this context, localization is one of the most important functionalities that can be implemented. The analysis of existing antennas that could suit a light, small, and energy-ecient sensor and the analysis and design of localization algorithms have been studied in this work. Indoor localization in a smart home poses certain challenges in comparison with the existing and successfully implemented large scale outdoor localization systems, due to the shadow fading eects and the notable dierences among the indoor environments. This work has focused on localization based on channel parameters estimation and received signal strength. This oers versatility, since no previous knowledge of the indoor environment is required, and cheap deployment. A review of existing methods in this area is oered and two classical and robust approaches, least squares estimation and log-likelihood maximization are combined to obtain new algorithms that can statistically improve the performance in terms of bias and variance of the error. The results of this work can be applied to the development of cheap and robustly optimized algorithms. Furthermore, the analysis of the antennas for this context sets the needs that new lines of future investigation and development of sensor devices can address.

This final thesis project is done at the Control Laws EXPERTISE Team at the Auto Flight Control Systems Department of THALES Avionics in Toulouse. The division currently works for both aircraft and helicopter manufacturers. An autopilot (AP) for use in commercial aircrafts must be certified by national authorities; in the EU this body is named European Aviation Safety Agency (EASA). For landing there are different certification standards. The first standard is called CAT I which is used when weather conditions prevents the pilot from seeing the runway during the initial approach. The CAT IIIa on the other hand is the standard needed when the weather conditions are so adverse that the pilot cannot see the runway markings until 50 ft over the ground. This project aims to investigate the possibility to upgrade a given aircraft from a CAT IIIa to a CAT IIIb EASA certification. The CAT IIIb includes the CAT IIIa with an AP controlled runway rollout. The work includes the following: System analysis Proposition of a control law Implementation in non linear Simulink model Mock-up: Simulation visualization with synchronized Flight Mode Annunciator (FMA) and Primary Flight Display (PFD) The primary objective is not to search for the optimal solution for a CAT IIIb upgrade but rather to identify the eventual problems that will be encountered due to system architecture and rollout dynamics. First a system analysis is done. Here important information about the architecture is found. For example there is no connection between the nose wheel command and the auto flight system, which will be necessary, and some parts in the Fly-By-Wire (FBW) system have to be disconnected during the rollout. Also important is an analysis of the ground reaction model made by the client i.e. calculation of friction coefficients and forces. Next step is to develop a control law and a linear model for the rollout is therefore made. The absolute speed is supposed to be the rudder and the nose wheel, we obtain a 2nd degree state space model with the yaw rate r [rd/s] and the lateral speed Vy [m/s] (AC - coordinates) states. Since the rudder only gives effect at relatively high speeds (over ≈100 knots) and the nose wheel due to stability only can be used at low speeds (under ≈50 kn) this can be seen as two different systems and one control law can be developed for each command. The commands are then distributed proportionally between these speeds. The maximal deviation from the runway for the nominal flight case with 15 knots of crosswind is acceptable. However, it does not converge until rather late in the rollout. Simulations with stronger crosswind and head wind have been made with good results. Wet runways or less landing mass seem to be the most degrading cases. At touch down a yaw bar appears in the FPD and shows the control target of the AP. The FMA is complemented with the mode rollout during that phase. The connection with the simulator makes it possible for the viewer to understand the relation between the different phases and the AP logics. The control law is stable for the nominal case and even for different masses and runway conditions. However, when these variables are changed simultaneously unstable behavior appears. The phase just after touchdown should be improved. The FMA and PFD with proper annunciation synchronized with the flight simulator enable the uninitiated to understand the CAT IIIb operation.

Studying plants under controlled environmental conditions is a key component of current research. This thesis concentrates on the study of plant growth under nutrient-limiting conditions. The first objective is the design and construction of a prototype of a system which is able to supply nutrient solutions of prescribed time-dependent concentration to laboratory plants. The system, once configured via a PC, operates fully automatically without the need for human interference. The hardware setup is made of basic electric components, solenoid pinch valves, mixing pumps and metering pumps while the software is implemented in NI LabVIEW. In addition a dynamic model of plant growth is deployed for investigating possible influence on growth with help of the designed system. The focus hereby lies on investigating effects on RGR and steady-state growth during the exponential phase of plant growth.

Smart grid has been proposed as an alternative to the traditional electricity grid recently thanks to its advantages of real time control on consumption demands. The latest wireless network, 3GPP Long Term Evolution (LTE), is considered to be a promising solution to interconnecting the smart objects in a smart grid because LTE provides both low latency and large bandwidth. However, the theories and standards for deploying a smart grid are still under study. Furthermore, the performance of LTE network depends on the user devices’ conditions as well as the network service operators. Therefore it is important to analyze the performance of LTE network experimentally. In this master thesis report, the specific requirements in terms of latency and bandwidth were first determined for a hypothetical smart microgrid which consists of several key components, such as one substation/distributed generation, Phasor Measurements Units (PMU) and Advanced Meter Infrastructures (AMI). Then the latency and the peak data rats of the LTE networks provided by two service operators TELE2 and TELIA were investigated and compared. The experimental results show that both latency and peak data rate of the LTE network provided by TELE2 fulfil the requirements for the smart microgrid, while the LTE network provided by TELIA gives a little longer latency. In addition, the simulation results based on a proposed scheduler indicate that the latency can be improved by an appropriate scheduler. This study has proven that LTE network is a promising solution for smart grids.

With today’s increasing railway traffic, the demand for electrical power has increased. However, several railway systems are weak and are not being controlled optimally. Thus, transmission losses are high and the voltage can be significantly lower than the nominal level. One proposal, instead of using an extra HVAC power supply system, is to implement a HVDC supply system. A HVDC supply line would be installed in parallel to the current railway catenary system and power can be exchanged between the HVDC grid and the catenary through converters. This thesis investigates different properties and behaviours of a proposed HVDC feeder solution. An AC/DC unified Optimal Power Flow (OPF) model is developed and presented. Decision variables are utilized to obtain proper control of the converters. The used power flow equations and converter loss function, which are non linear, and the use of binary variables for the unit commitment leads to an optimization problem, that requires Mixed Integer Non-Linear Programing (MINLP) for solving. The optimization problem is formulated in the software GAMS, and is solved by BONMIN. In each case investigated, the objective is to minimize the total active power losses. The results of the investigated cases presented in this thesis, show that the proposed OPF-controlled HVDC solution reduces the losses and provides better voltage profile at the catenary, compared with today’s supply systems.

As signal speed increases and electronic products become progressively smaller,the risks of electromagnetic radiation and interference are also heightened.Ericsson's SCXB, an Ethernet switch card, experiences exactly this problem,with excessive emission levels probably caused by common-mode noise.In this project, a common-mode lter using the electromagnetic bandgap(EBG) structure has been designed and implemented in the SCXB. Unlikeconventional common-mode lters, the common-mode lter is embedded inthe printed circuit board (PCB) beneath the dierential lines. The eect ofthe common-mode lter is assessed by measuring the insertion loss and thepower radiation of a shielded cable connected to the common-mode lter.A compact common-mode lter using an EBG structure has been proposedin this project and this works eectively at 937.5 MHz. One of the resultsfrom the parametric analysis shows that the common-mode lter is suitableto work in a high frequency range due to the smaller structure and the widerbandwidth range. The common-mode lter is constructed with the PCBfabrication process. No additional components are necessary, although morelayers of the PCB's stack up are required in which to embed the common-mode lter.

Networked control systems (NCS) have recently been attracting significant attention as they are easier to monitor and modify and have reduced costs for wiring compared to the standard wired solutions. Wireless systems, on top of these traits, can overcome several physical impossibilities of wiring, i.e. they could enable installing a sensor on a rotating mill. However, wireless communication systems have evident imperfections, such as time-varying delay and packet dropout. The stochastic packet transmission process makes the critical assumptions of classical control theory appear invalid. Therefore new system theory and engineering methodology for NCSs need to be developed. PID Controllers, being simple and effective, overwhelmingly dominate the industrial controllers. It is not far-fetched to believe that, as the migration from wired systems to wireless systems continues, PID controllers will remain the dominant controllers in industry. This study, therefore investigates the application of PID controllers to wireless systems. Two particular control structures from the literature have been examined, followed by a newly developed estimation-based controller structure for networked PID control. Various simulations have been conducted on many types of plants, and the robustness of the system against packet losses and plant uncertainties, among others, have been evaluated. It has been shown that the newly proposed controller structure has a significantly better performance than earlier proposals. The results have been verified by an implementation on a water tank system.