This four-part dissertation is essentially concerned with some theoretical aspects of the stability studies of power systems with large penetration levels of distributed generation. In particular, in Parts I and II the main emphasis is placed upon the transient rotor angle and voltage stability. The remaining two parts are devoted to some system-theoretic and practical aspects of identification and modeling of aggregate power system loads, design of auxiliary robust control, and a general qualitative discussion on the impact that distributed generation has on the power systems. One of the central themes of this dissertation is the development of analytical tools for studying the dynamic properties of power systems with asynchronous generators. It appears that the use of traditional tools for nonlinear system analysis is problematic, which diverted the focus of this thesis to new analytical tools such as, for example, the Extended Invariance Principle. In the framework of the Extended Invariance Principle, new extended Lyapunov functions are developed for the investigation of transient stability of power systems with both synchronous and asynchronous generators. In most voltage stability studies, one of the most common hypotheses is the deterministic nature of the power systems, which might be inadequate in power systems with large fractions of intrinsically intermittent generation, such as, for instance, wind farms. To explicitly account for the presence of intermittent (uncertain) generation and/or stochastic consumption, this thesis presents a new method for voltage stability analysis which makes an extensive use of interval arithmetics. It is a commonly recognized fact that power system load modeling has a major impact on the dynamic behavior of the power system. To properly represent the loads in system analysis and simulations, adequate load models are needed. In many cases, one of the most reliable ways to obtain such models is to apply a system identification method. This dissertation presents new load identification methodologies which are based on the minimization of a certain prediction error. In some cases, DG can provide ancillary services by operating in a load following mode. In such a case, it is important to ensure that the distributed generator is able to accurately follow the load variations in the presence of disturbances. To enhance the load following capabilities of a solid oxide fuel plant, this thesis suggests the use of robust control. This dissertation is concluded by a general discussion on the possible impacts that large amounts of DG might have on the operation, control, and stability of electric power systems.

Large-scale deployment of IEEE 802.11 wireless LANs (WLANs) remains a significant challenge. Many access points (APs) must be deployed and interconnected without a-priori knowledge of the demand. We consider that the deployment should be iterative, as follows. At first, access points are deployed to achieve partial coverage. Then, usage statistics are collected while the network operates. Overloaded and under-utilized APs would be identified, giving the opportunity to relocate, add or remove APs. In this thesis, we propose extensions to the WLAN architecture that would make our vision of iterative deployment feasible. One line of work focuses on self-configuration, which deals with building a WLAN from APs deployed without planning, and coping with mismatches between offered load and available capacity. Self-configuration is considered at three levels. At the network level, we propose a new distribution system that forms a WLAN from a set of APs connected to different IP networks and supports AP auto-configuration, link-layer mobility, and sharing infrastructure between operators. At the inter-cell level, we design a load-balancing scheme for overlapping APs that increases the network throughput and reduces the cell delay by evenly distributing the load. We also suggest how to reduce the handoff time by early detection and fast active scanning. At the intra-cell level, we present a distributed admission control that protects cells against congestion by blocking stations whose MAC service time would be above a set threshold. Another line of work deals with self-deployment and investigates how the network can assist in improving its continuous deployment by identifying the reasons for low cell throughput. One reason may be poor radio conditions. A new performance figure, the Multi-Rate Performance Index, is introduced to measure the efficiency of radio channel usage. Our measurements show that it identifies cells affected by bad radio conditions. An additional reason may be limited performance of some AP models. We present a method to measure the upper bound of an AP’s throughput and its dependence on offered load and orientation. Another reason for low throughput may be excessive distance between users and APs. Accurate positioning of users in a WLAN would permit optimizing the location and number of APs. We analyze the limitations of the two most popular range estimation techniques when used in WLANs: received signal strength and time of arrival. We find that the latter could perform better but the technique is not feasible due to the low resolution of the frame timestamps in the WLAN cards. The combination of self-configuration and self-deployment enables the autonomic operation of WLANs.

4H-SiC has physical properties supremely suited for a variety of high power, high frequency and high temperature electronic device applications. To fully take advantage of the material's potential, several problems remain to be solved. Two of the most important are (1) the characterization and understanding of crystallographic defects and their electrical impact on device performance, and (2) the introduction of acceptor dopants, their activation and control of the final distribution of charge carriers. Two main experimental methods have been employed in this thesis to analyze 4H-SiC material with respect to the issues (1) and (2): electron beam induced current (EBIC) and scanning spreading resistance microscopy (SSRM), respectively. EBIC yields a map of electron-hole-pairs generated by the electron beam of a scanning electron microscope and collected in the depleted region around a junction. EBIC is conducted in two modes. In the first mode the EBIC contrast constitutes a map of minority carrier diffusion lengths. Results from these measurements are compared to white beam syncrotron x-ray topography and reveal a one-to-one correlation between lattice distortions and the electron diffusion length in n+p 4H-SiC diodes. In the second EBIC mode, the junction is highly reverse biased and local avalanche processes can be studied. By correlating these EBIC results with other techniques it is possible to separate defects detrimental to device performance from others more benign. SSRM is a scanning probe microscopy technique that monitors carrier distributions in semiconductors. The method is for the first time successfully applied to 4H-SiC and compared to alternative carrier profiling techniques; spreading resistance profiling (SRP), scanning electron microscopy (SEM) and scanning capacitance microscopy (SCM). SCM successfully monitors the doping levels and junctions, but none of these techniques fulfill the requirements of detection resolution, dynamic range and reproducibility. The SSRM current shows on the other hand a nearly ideal behavior as a function of aluminum doping in epitaxially grown samples. However, the I-V dependence is highly non-linear and the extremely high currents measured indicate a broadening of the contact area and possibly an increased ionization due to sample heating. Finite element calculations are performed to further elucidate these effects. SSRM is also applied to characterize Al implantations as a function of anneal time and temperature. The Al doping profiles are imaged on cleaved cross-sections and the measured SSRM current is integrated with respect to depth to obtain a value of the total activation. The evaluation of the annealing series shows a continuous increase of the activation even up to 1950 °C. Other demonstrated SSRM applications include local characterization of electrical field strength in passivating layers of Al2O3, and lateral diffusion and doping properties of implanted boron.

This thesis contributes to the research on optimization algorithms for nonlinear programming, and to the application of such algorithms to nonlinear model predictive control. Regarding the contribution to research on algorithms for nonlinear programming, a novel algorithm is put forward with a complete theory for global and local convergence. This is the main contribution of the thesis. The algorithm, named rFSQP, is a reduced Hessian Feasible Sequential Quadratic Programming method. It remains feasible with respect to nonlinear inequalities at all SQP iterations, but nonlinear equality constraints are treated as in general reduced Hessian SQP methods. The rFSQP algorithm is implemented in MATLAB and tested on a number of small scale problems with encouraging results. However, the algorithm is designed for large scale problems with few degrees of freedom. Some preliminary testing of the algorithm on large scale problems are investigated. The thesis also contributes to the understanding of the relation between sequential and simultaneous reduced gradient methods, and to the understanding of the relation between discretization methods for dynamical systems and the choice of optimization algorithms. The thesis also contributes to model based control approaches of grate sintering. Grate sintering is a complex metallurgical process, where melting of solids and fast gas dynamics give rise to stiff process models, i.e. the "time constants" of the system differ by many decades in magnitude. Hence, application of real-time optimization methods like nonlinear model predictive control to the grate sintering process is challenging. The thesis gives a framework for implementing nonlinear model based control of grate sintering by giving a control objective, a nonlinear model and choosing an appropriate discretization scheme. The thesis gives a reduced order model which is less computationally demanding. Data from industrial experiments are used to adapt the model and to assess the control objective.

In a traditional communication system, the coding process is divided into source coding and channel coding. Source coding is the process of compressing the source signal, and channel coding is the process of error protection. It can be shown that with no delay or complexity constraints and with exact knowledge of the source and channel properties, optimal performance can be obtained with separate source and channel coding. However, joint source-channel coding can lead to performance gains under complexity or delay constraints and offer robustness against unknown system parameters. Multiple description coding is a system for generating two (or more) descriptions of a source, where decoding is possible from either description, but decoding of higher quality is possible if both descriptions are available. This system has been proposed as a means for joint source-channel coding. In this dissertation, the multiple description coding is used to protect against loss of data in an error correcting code caused by a number of channel errors exceeding the correcting ability of the channel code. This is tried on three channel models: a packet erasure channel, a binary symmetric channel, and a block fading channel, and the results obtained with multiple description coding is compared against traditional single description coding. The results show that if a long-term average mean square error distortion measure is used, multiple description coding is not as good as single description coding, except when the delay or block error rate of the channel code is heavily constrained. A direct source-channel mapping is a mapping from amplitude continuous source symbols to amplitude continuous channel symbols, often involving a dimension change. A hybrid scalar quantizer-linear coder (HSQLC) is a direct source-channel mapping where the memoryless source signal is quantized using a scalar quantizer. The quantized value is transmitted on an analog channel using one symbol which can take as many levels as the quantizer, and the quantization error is transmitted on the same channel by means of a simple linear coder. Thus, there is a bandwidth expansion, two channel symbols are produced per source symbol. The channel is assumed to have additive white Gaussian noise and a power constraint. The quantizer levels and the distribution of power between the two symbols are optimized for different source distributions. A uniform quantizer with an appropriate step size gives a performance close to the optimized quantizer both for a Gaussian, a Laplacian, and a uniform memoryless source. The coder performs well compared to other joint source-channel coders, and it is relatively robust against variations in the channel noise level. A previous image coder using direct source-channel mappings is improved. This coder is a subband coder where a classification following the decorrelating filter bank assigns mappings of different rates to different subband samples according to their importance. Improvements are made to practically all the parts of the coder, but the most important one is that the mappings are changed, and particularly, the bandwidth expanding HSQLC is introduced. The coder shows large improvements compared to the previous version, especially at channel qualities near the design quality. For poor channels or high rates, the HSQLC provides a large portion of the improvement. The coder is compared against a combination of a JPEG 2000 coder and a good channel code, and the performance is competitive with the reference, while the robustness against an unknown channel quality is largely improved. This kind of robustness is very important in broadcasting and mobile communications. / I tradisjonelle kommunikasjonssystemer kan kodingen deles inn i kildekoding (kompresjon) og kanalkoding (feilbeskyttelse). Disse operasjonene kan ses i sammenheng, og kombinert kilde- og kanalkoding kan gi forbedringer ved begrenset kompleksitet eller forsinkelse, og øke robustheten mot ukjente systemparametre. I avhandlingen vurderes to metoder. I den første er kilde- og kanalkodingen fortsatt delvis separat, men kildekoden er gjort robust mot dekodingsfeil i kanalkoden. Dette gjøres ved flerbeskrivelseskoding (multiple description coding), der kildesignalet representeres med to beskrivelser. Dekoding er mulig fra hver beskrivelse isolert, men høyere kvalitet kan oppnås hvis begge beskrivelsene er tilgjengelig. Ved sammenligning med et tradisjonelt system viser det seg at med hensyn på midlere kvadratisk avvik er flerbeskrivelseskoding som regel mindre bra enn et tradisjonelt system. Direkte kilde-til-kanal-avbildninger er avbildninger fra amplitudekontinuerlige kildesymboler direkte til amplitudekontinuerlige kanalsymboler. En slik metode blir lansert. Der skalarkvantiseres kildesignalet, som antas minneløst, og overføres med ett symbol på en analog kanal, mens kvantiseringsfeilen overføres analogt på den samme kanalen. Systemparametrene blir optimalisert for forskjellige kilder og kanalkvaliteter. Denne koderen gir bra ytelse sammenlignet med andre kombinerte kilde- og kanalkodere, og den er relativt robust mot variasjoner i støynivået på kanalen. Direkte kilde-til-kanal-avbildninger anvendes i en delbåndskoder for stillbilder. Denne koderen, som er basert på tidligere arbeider, blir sammenlignet med en kombinasjon av en JPEG 2000-koder og en god kanalkode, og ytelsen er omtrent like bra som referansen, samtidig som robustheten mot ukjent kanalkvalitet har økt kraftig. Denne typen robusthet er svært viktig i kringkasting og mobilkommunikasjon.

Recently, the enormous growth in personal communications systems (PCS), satellite communication and various other forms of wireless data communication has made analogue frequency control a key issue as the operation frequency increases to the low/medium GHz range. Surface acoustic wave (SAW) and bulk acoustic wave (BAW) electroacoustic devices are widely used today in a variety of applications both in consumer electronics as well as in specialized scientific and military equipment where frequency control is required. Conventional piezoelectric materials such as quartz, LiNbO3 and LiTaO3 suffer from a variety of limitations and in particular medium to low SAW/BAW velocity as well as being incompatible with the IC technology. Thin piezoelectric films offer the great flexibility of choosing at will the substrate/film combination, thus making use of the electroacoustic properties of non-piezoelectric substrates, which widens greatly the choice of fabrication materials and opens the way for integration of the traditionally incompatible electroacoustic and IC technologies. This thesis focuses on the synthesis and characterization of novel thin film materials for electroacoustic applications. A prime choice of material is thin piezoelectric AlN films which have been grown using both RF and pulsed-DC reactive sputter deposition on a variety of substrate materials. A unique synthesis process has been developed allowing the deposition of high quality AlN films at room temperature, which increases greatly the process versatility. The films are fully c-axis oriented with a 1.6° FWHM value of the rocking curve of the AlN-(002) peak. Complete process flows for the fabrication of both SAW and BAW devices have been developed. Electroacoustic characterization of 2 GHz BAW resonators yielded an electromechanical coupling coefficient (kt²) of 6.5%, Q-value of 600 and a longitudinal velocity of 11350 m/s. AlN thin films based SAW resonators on SiO2/Si yielded a SAW velocity of around 5000 m/s and a piezoelectric coupling coefficient (K²) of around 0.3%. Finally, AlN on polycrystalline diamond 1 GHz SAW resonators exhibited an extremely high SAW velocity of 11800 m/s, a piezoelectric coupling coefficient (K²) of 1% and a Q-value of 500.

Economic affordability of services and infrastructures has rapidly become one of the key issues in the evaluation and design of wireless access systems. The provisioning of high data rates, at an ``affordable'' price, constitutes a serious challenge to the structure and management of current and future wireless networks. The management of radio resources, Radio Resource Management or RRM for short, has traditionally been benchmarked mostly by technical merits such as throughput (data delivery capability) and Quality of Service (QoS). When comparing different RRM schemes, the scheme that can deliver more bits per Hertz (unit of bandwidth) or per Euro is often assumed the more efficient. From an economic point of view, however, cost efficiency is not equivalent to profitability. We conjecture that the economic efficiency and profitability can be improved both by better technical efficiency and by better accounting for users' service appreciation and willingness to pay. While we shall, primarily treat the operator's benefit of improved RRM, we will try to improve the RRM by means of being more responsive to the demands of the users. In eight conference and journal papers, we investigate: Provisioning of support for asymmetric traffic, Quality and pricing aware resource management and Creation of forwarding incentive in multihop cellular networks. We show that implementing support for asymmetric links can improve the efficiency of (service) production in Time Division Duplexing (TDD) mode wireless networks with asymmetric traffic. That is, more traffic can be handled with the same system resources. Compared to Frequency Division Duplexing (FDD), TDD offers more flexible use of spectrum resources. The benefits of TDD and support for asymmetric links are readily available for systems providing high-rate spotty coverage. For systems aiming at full coverage and tight reuse, however, proper measures must be taken to control inter-mobile- and inter-base-station-interference. We present the MEDUSA model framework for taking users' service appreciation and willingness to pay into account in performance evaluations of wireless networks with elastic traffic. Assuming that user satisfaction depends on both the quality and the price of the service, numerical experiments show that the economic efficiency of an RRM scheme is affected by the pricing scheme. We also introduce the concepts of speculative resource management to exploit traffic elasticity and improve resource utilisation. With speculative admission control, users with good propagation conditions may be admitted to a full system at the expense of a slight degradation of the QoS of some or all users, if the expected total revenue would thereby increase. Results indicate significant revenue gain with speculative admission control. Service perception aware scheduling was evaluated as a means to improve resource utilisation, but yielded only marginal gain compared to a weighted proportional fair scheduler. For the third area studied in this Thesis, i.e. multihopping in cellular networks, economic efficiency was both the goal and one of the means to achieve it. By means of a resource re-distribution scheme called Resource Delegation we eliminated the bandwidth bottle neck of the relays. We combined Resource Delegation with economic compensation for the energy expenditures of the relays and were able to achieve significantly increased operator revenue with maintained or improved user utility. Assuming that the added complexity of keeping track of reward transactions is negligible, profitability was correspondingly improved. / QC 20101021

A novel homopolar electrodynamic bearing, together with a suitable permanent magnet drive, have been developed for high-speed applications where low losses and high reliability are essential and exclude the use of ball bearings, and yet where active magnetic bearings offer a too complex system solution. Considered applications are small turbomolecular vacuum pumps, and maintenance free flywheels for energy storage in remote telecom and satellite systems. Other upcoming areas where these bearings offer interesting technical and economic solutions are compressors for fuel cells and heat pumps, applications which normally suffer from short bearing lifetime. Unlike active magnetic bearings, forces are produced in electrodynamic bearings without any control electronics, thanks to stabilizing eddy currents induced by permanent magnets. In the novel homopolar concept eddy current losses are reduced to a minimum using a homopolar design with ring magnets instead of multipole or Halbach arrays. Currents and forces are simulated using steady state 3D-FEM analysis, which can take velocity into account using an implemented Minkowski transform. From these results an analytical model has been developed, and the results are compared. The results are converted into useful rotordynamic data that is easily understood by machine engineers. The bearing has been experimentally tested in a rebuilt turbomolecular vacuum pump up to 90,000 rpm. Bearing forces have been accurately measured on a specially designed spring suspended scales, in which the bearing rotor is powered with the permanent magnet drive. Comparison of measured data with results from the 3D-FEM analysis shows excellent agreement. / QC 20101026

This report describes the development of a sample loader for my diploma work at Q-linea AB in Uppsala. The sample loader will replace the process of loading fluid samples into Q-linea’s instrument for biomolecule analysis. The earlier process was done by hand and was a time consuming and inefficient task. The work was initiated with a design phase where an overview of the system was created. The sample loader will be receiving text commands from a PC that coordinates all the subsystems like pumps and lasers on the analysis instrument. The commands will be translated by a microcontroller into the correct movement of the samples needed to load them. Most of the work was put down into developing the software responsible for handling communications and actuation of a couple of stepper motors. Lastly a circuit board was designed and manufactured, ready to be mounted into the existing instrument. The result was a working prototype which now is used in the daily work at Q-linea. It is subject for further development and in the future it will be shipped as a part of the finished biomolecular analysis instrument from Q-linea.

Detta är en rapport över mitt examensarbete som utfördes för Motion Control AB i Västerås. Uppgiften bestod i att ta fram en prototyp för en handhållen ljudlokalisator för döva. Projektet har inneburit arbete med allt från marknadsundersökningar till lödning. Projektet innehåller såväl analog elektronik som programmering. Mycket tid gick åt till själva förarbetet, kanske lite väl mycket då det kändes som halva tiden gick åt innan jag kunde komma igång och arbeta. Jag lyckades få fram en prototyp där allt fungerade förutom mikrofonerna, de visade sig vara för känsliga för att löda för hand. Dock så har projektet varit mycket lärorikt och intressant. / This is a report of my thesis work carried out for Motion Control AB in Västerås. The task was to develop a prototype for a handheld sound localizator for the deaf. The project has involved working with everything from market research to soldering. The project includes both analog electronics as well as programming. Much time was spent on the preparatory work, maybe a little too much when it seemed like half the time was spent before I could get started and work. I managed to get a functional prototype except for the microphones, as they proved to be too sensitive to solder by hand. However, the project has been very educational and interesting.