O Brasil é um país de dimensões continentais, onde existe uma considerável distância entre a geração e os principais centros de consumo. Dessa forma, o estudo e desenvolvimento de novas tecnologias de transmissão a longas distâncias é de fundamental importância para o desenvolvimento do país. A solução mais utilizada atualmente é a transmissão em corrente alternada. Entretanto a transmissão em corrente continua também é uma solução viável para longas distâncias. O sistema brasileiro é composto principalmente por linhas 500 kV em corrente alternada (também há 230; 345; 440 e 750 kV), bem como em corrente continua (em ±600 e ±800 kV). O presente estudo apresenta uma solução de transmissão em corrente alternada por linhas de 1000 kV, que se mostrou mais econômico na transmissão de potências superiores a 3.500 MW e distâncias de 1400km. Nos próximos anos, a geração de energia elétrica no Brasil será expandida de forma significativa, ocorrerá um aumento principalmente na geração de energia eólica e solar, localizadas em sua maioria na região Nordeste do país. Esse aumento na geração exigirá a transmissão de grandes blocos de energia elétrica por distâncias significativas, devido à falta de proximidade entre a geração e os principais centros consumidores, que estão localizados no Sudeste. Neste estudo, serão mostradas as etapas de definição de condutor economicamente mais adequado e projeto da geometria da torre. Com base nos dados obtidos, será feita a avaliação do desempenho da linha 1000 kV, durante a operação normal de fluxo de carga, curtos-circuitos e estabilidade. / Brazil, a country of continental proportions, have significant distance between the power generation centers and the main consumer centers. In such way, the study and development of new transmission technologies over long distances is of fundamental importance for the development of the country. Nowadays, the most commonly used solution is alternating current transmission. However, direct current transmission is also a viable solution for long distances. The Brazilian system mainly consists of 500 kV alternating current lines (along with 230, 345, 440 and 750 kV) and direct current lines (± 600 and ± 800 kV). This study provides a solution for transmission in alternating current by lines of 1000 kV, which proved to be more economical in power transmission over 3,500 MW and distances beyond 1400km. In the coming years, the electric power generation in Brazil will expand significantly; a boost will take place mainly in wind and solar power generation, located mostly in the Northeast of the country. This generation expansion will require transmission of large blocks of electric power over considerable distances, due to the lack of proximity between generation sites and main consumer centers located in the Southeast. This study will show the setting stages of the most economically applicable conductor and tower geometry design. Based on the data obtained, the performance of the 1000 kV line will be evaluated during the regular load flow operation, short circuits and stability.

Poor settling of solids increases land requirement for tailings containment and imposes severe constraints on the water balance. Consequent to these considerations, the alternating current electrocoagulation (AC/EC) technique emerged as a candidate for enhancing the settling behaviour of suspensions in the mineral, coal and oil sands industries. Hence, a fundamental study of AC/EC was undertaken with aluminum electrodes. Ground silica (d50 = 20 m), which formed a stable suspension, served as the model tailings solid at 5.0 wt % in water. The AC/EC process consisted of two developmental stages: coagulation, marked by pH decrease in the silica suspension; and floc growth, characterized by pH increase from the minimum (i.e., the end of coagulation). AC/EC enhanced the initial settling rate of silica by over three orders of magnitude, and exhibited remarkable flexibility by virtue of the wide range of process parameters that could be optimized. For example, AC/EC can be operated in either the indirect or direct mode. The settling behaviour of bentonite (estimated d50 < 1 m) was more enhanced by indirect AC/EC, while that of silica benefited more from direct AC/EC. Any condition that increased aluminum dosage (e.g., current, retention time), increased the initial settling rate of silica. Over the feed water pH range of 3.0 to 9.1, AC/EC was effective in enhancing the settling behaviour of silica. AC/EC was also effective over a wide range of temperatures (23 to 85C). High electrical energy demand by AC/EC was observed throughout this study. Its optimization was beyond the scope of this work. Dilution of a sample of Syncrude mature fine tailings (MFT) to 4.6 wt % solids sustained a stable suspension. Settling occurred after AC/EC treatment, a crystal-clear supernatant resulted and bitumen was recovered as froth. Entrained solids were easily spray-washed from the froth with water. The settling behaviour of a Luscar Sterco fine coal tailings sample was not augmented by AC/EC, possibly due to contamination by the companys own electrocoagulation operation. After having been stored dry for more than a year, electrocoagulated silica was an effective coagulant for as-received silica and Syncrude MFT. / Chemical Engineering

Studies on ac losses in superconductors have been a subject of great interest for a long time not only as an important topic in fundamental science, but also as a basic requirement for the application of superconductors. A proper understanding of the mechanisms of ac losses and their quantitative knowledge is an essential requirement for any application. Such studies not only yield information on the material parameters crucial for applications but can also provide a test for any possible microscopic theory of superconductivity. The main focus of the current thesis is to understand the mechanisms of ac losses in superconductors and to gain more knowledge on the ac dissipative behavior of type II superconductors. In this thesis we report our investigations on the ac losses in certain type II superconductors at different ranges of frequency through different experimental techniques. We have investigated the ac losses that arise in high Tc superconducting single crystals at rf frequency (8 MHz) using a simple LC oscillator technique. The result shows a surprising ac dissipation behavior in which the loss in the superconducting state is more than the normal state loss. Even though the superconducting state is defined as the zero resistive state, this is true only for dc transport. The ac resistivity studies have been made also on high Tc polycrystalline samples using the standard four-probe technique using a lock-in amplifier (100 kHz). The result shows different ac resistive behavior for samples with different microstructures. Non-resonant microwave absorption (NRMA) studies in MgB2 thin films is reported for the first time. The experiment has been performed using a continuous wave X band EPR spectrometer. The recorded signals give information on the ac losses that occurs at microwave frequency (9.43 GHz). The effects of ac magnetic field on the superconductors have been investigated through a dc four-probe resistivity measurements in the presence of an ac field of different magnitudes applied at different frequencies. Also a simple experimental technique based on the concept of kinetic inductance designed to study the ac losses that arise due to vortex motion is reported. In the following a chapter-wise summary of the thesis is presented.m Chapter 1 surveys the related literature on experimental and theoretical reports on ac losses in superconductors. In this chapter a brief introduction to superconductors is given with an emphasis on the high Tc superconductors. The superconducting materials studied in the thesis are described in detail along with their superconducting parameters and the form of the specimen. The origins of ac losses are discussed with various models proposed so far to explain the ac losses in superconductors. Since most of the ac losses reported in this thesis arise due to the Josephson junctions and vortex motion, they are discussed in detail. The occurrence of Josephson junctions and the various models used to describe the junctions’ characteristics are discussed. The formation of vortices their various forms in layered superconductors and the mechanisms of flux flow and flux creep are discussed. Chapter 2 describes the studies on ac losses in superconducting Bi2Sr2CaCu2O8 single crystals [1,2]. Generally in the superconducting state the dissipation is expected to be less compared with that in the normal state. However, we observe that the ac losses in the superconducting state are larger than the normal state losses. In this chapter we report on the ac losses in superconducting Bi2Sr2CaCu2O8 single crystals at radio frequencies determined from direct measurement of the absorbed power using an rf oscillator [3]. The ac response of Bi2Sr2CaCu2O8 single crystals is investigated as a function of temperature from the measured shift in current and the frequency of the oscillator. The studies are carried out at different rf amplitudes by varying the supply voltage to the oscillator circuit. To understand the magnetic field dependent behavior of ac losses, studies have been performed in the presence of magnetic field of various magnitudes applied parallel to the c-axis of the crystal. In the presence of the magnetic field two peaks are observed in ac losses in the superconducting state as a function of temperature. The presence of the peaks and their behavior are studied in detail by varying the orientation of the applied field with respect to the c-axis of the crystal. The results are discussed in terms of a new model proposed recently by us [4], which explains ac losses as a consequence of cumulative effect of the energy spent in repetitive decoupling of the Josephson junctions and in terms of Lorentz force driven motion of vortices. In Chapter 3, we discuss the ac resistivity behavior of the polycrystalline superconducting samples with different microstructures. Measurement of resistivity is the basic characterization method not only for superconductors but for any material. The superconducting state is defined as the zero resistive state; but this statement is true only for dc and not for ac. The presence of ac resistance in superconductors leads to losses. In the present work we report on the behavior of ac resistance in the superconductors. The application of a magnetic field and the variation of temperature alter the AC penetration depth of the superconducting sample, which in turn changes the AC impedance associated with it. In this chapter we report the results on the complex AC conductivity that has been measured in two types of polycrystalline YBa2Cu3O7 samples at frequencies starting from 100 Hz to 100 kHz and at temperatures from 10 K to 300 K. In the first pellet which is sintered, the possibility of presence of extrinsic Josephson junctions is less, but a large number of Josephson junctions is present in the second non-sintered pellet. In general it is expected that the AC or the DC resistivity in superconductors should decrease below Tc. In the case of DC resistivity the value of resistance goes exactly to zero and in the case of AC resistivity it keeps on decreasing towards zero with decreasing temperature. But surprisingly we find that in superconducting samples with Josephson junctions, the AC resistivity drops very close to zero at the critical temperature and instead of decreasing it increases slowly with decreasing temperature below the critical temperature. This property is also strongly dependent on the applied AC frequency. Investigation of the above phenomenon gives information regarding the contribution of JJ decoupling towards the AC resistivity of superconducting samples. The observed ac resistive behavior is well fitted with the Ambegaokar-Baratoff model for temperature dependence of critical current in the Josephson junction. In Chapter 4, the possibility of the presence of weak links in the intermetallic superconductor MgB2 is reported. The role of weak links in superconductors has been studied for a long time. Understanding the behavior of weak links has great importance for the applications of superconductors. Presence of weak links in high Tc materials due to its insulating grain boundaries limits the application potential of those materials. These weak links lead to lower critical current density and lower critical field of superconductors and lead to losses. The discovery of superconductivity in the simple intermetallic compound MgB2 has created a lot of interest from both application aspects and of fundamental science. MgB2 differs from high Tc materials and is considered as a potential candidate for applications, because of its high critical current density which arises due to the absence of weak links in MgB2. Absence of weak links is reported in most of the MgB2 literature and only in a very few studies possibility of the presence of weak links is reported. Here, our NRMA studies on the MgB2 thin films show the presence of weak links [5]. NRMA is a highly sensitive, non-invasive technique, which has proven to be a valuable tool for detecting weak links in superconductors and their characterization [6]. In this technique the sample is studied using a continuous wave electron paramagnetic resonance (EPR) spectrometer, by recording the magnetic field dependence of the power absorption. The NRMA studies on the MgB2 thin film shows the presence of weak links and hysteresis in the signal. The origin of weak links is discussed as being due to the presence of oxygen in the grain boundaries. The hysteresis appears because of remnant magnetization and due to the pinning of flux lines when there is a change in the sweeping field direction. The NRMA studies are carried out as a function of temperature, modulation field, microwave power and the scan range and the results are reported in this Chapter. In chapter 5 we report on the resistive behavior of superconducting MgB2 film in the presence of an ac field using a novel technique. In this simple technique the resistive measurements are done using the general four-probe method, but a coil is wound over the sample and connected to an ac source to generate the ac field. The resistivity measurements are carried out as a function of temperature, amplitude and the frequency of ac field. The ac field shifts the Tc towards lower temperature and increases the broadening in transition from normal to superconducting state. In the absence of Lorentz force due to the parallel orientation of ac field with the transport current, we find that Josephson junction decoupling is one of the main origins of resistivity. The results are compared with the resistive behavior of YBCO film. The epitaxial YBCO film which is free from weak links shows a different frequency dependent resistive behavior, which is explained in terms of flux-creep. In the MgB2 film the studies are carried out in the presence of a dc field that is applied perpendicular to direction of transport current in the film along with the presence and the absence of the ac field. The studies show that in superconductors the presence of ac field leads to more loss than that of dc field. Chapter 6 describes a simple experimental technique using the property of kinetic inductance to measure the vortex resistivity arising from the ac current. Since the discovery of the superconductors much attention has been given to the dynamics of the vortices because of their importance from both scientific and application point of view. When a magnetic field of amplitude more than Hc1 is applied the type II superconductors enter in to the ‘mixed state’ due to the presence of vortices. In the presence of a current, the vortices experience Lorentz force of magnitude F = J x B normal to the current and the field. The vortices move under the influence of the Lorentz force along its direction which leads to resistivity. The electric field generated by the vortex movement has two components, one acting along the current direction and the other normal to the current direction. But most of the vortex resistivity measurements are carried out either in the presence of high magnetic field or at temperatures closer to Tc due to the limitation of experimental techniques. In this chapter we are reporting a simple experimental technique to measure vortex resistivity with very high resolution even at low temperatures and fields based on the concept of kinetic inductance. Kinetic inductance is the property which arises mostly in superconductors due to the inertial mass of the charge carriers. In our measurement kinetic inductance is measured through a simple four-probe ac impedance technique, which is more commonly used for measuring resistivity. The penetration depth due to vortices is related to their resistivity and from the relation between the measured kinetic inductance and penetration depth vortex resistivity is calculated. In this report we discuss the experimental setup, principle of the method and present the results of our measurements carried out on YBa2Cu3O7 thin films.

No description available.

Submitted to the Department of Electrical Engineering in Fulfilment of the Requirements for the Magister Technologiae in Electrical Engineering at the Cape Peninsula University of Technology SUPERVISOR: E. VOSS NOVEMBER 2013 / The reluctance synchronous machine (RSM) operates on the principle of magnetic reluctance, which is produced through a careful selection of rotor flux barriers and cut-outs. Magnetic reluctivity is the resistance to magnetic flux and can be directly related to the principles of Ohm’s law in electrical circuits. Although reluctance motors have been known for more than 150 years, researchers lost interest when Nikola Tesla’s induction machine (IM) was introduced to industry. Over the last few decades, however, RSMs have shown a lot of potential. They are cheap, robust, reliable, and their rotors can also be used in the stators of IMs. The disadvantage of these machines is an inherently high torque ripple, being the result of its rotor geometry, but the biggest advantage is having a significant reduction in copper losses after the rotor cage has been removed. This advantage drove engineers to investigate, optimise and modify the performance and structure of this machine, which led to the usage of electronic drive systems. The recent advances in technology have allowed researchers to further investigate and modify the design and performance of this special type of machine, with the integration of Finite Element Analysis (FEA) software also making a contribution to the development of the RSM’s current driven systems. The voltage-fed RSM, driven direct-on-line (DOL) from the utility supply, was left in the shadows as the current-fed RSM took reign, but still is, in the author’s opinion, not yet fully analysed. This thesis practically investigates the performance characteristics of the cageless, voltage-fed 3kW RSM in its steady-state operation, under various loads. These performance characteristics are also compared to a RSM driven from a sensorless vector drive (current-fed) to investigate the advantages and disadvantages between the two. Experiments performed on the test bench immediately reveal a limitation to the voltage-fed RSM’s ability to drive higher loads. While the current-fed RSM conveniently reaches 150% of its full-load, the voltage-fed RSM, due to its cageless structure, only reaches 110% of its full-load power. Despite this discovery, the voltage-fed RSM proves to have a lower core loss, harmonic content and torque ripple. Using a FE software package with an integrated source-code, additional parameters such as the dq-axis inductances and currents are also compared and analysed in terms of its reaction to an increase in load. The eddy-current, hysteresis and excess losses are also analysed as well as the harmonic components caused by the geometry of the RSM. For academic purposes, a fair amount of emphasis is placed on the approach to the problem. The preparation for the FE simulation is explained in detail, providing insight into the FE mathematical model as well as parameter acquisition. These parameters include current angle, friction and windage losses, stator resistance, end-winding leakage reactance, core loss and inertia. The results obtained by the FE model are compared to that of the measured results and is found to have an error of only 0.52%. Furthermore, this study attempts to find the feasibility of the voltage-fed RSM’s practicality in modern-day industry. The conclusion is drawn that the voltage-fed RSM could be used as a more elegant alternative to an otherwise over-complicated and over-priced installation.

Le sommeil est un état de conscience faisant preuve d’un vaste potentiel au niveau clinique. Par exemple, le sommeil est devenu un outil dans le diagnostic précoce de certains processus dégénératifs au sein du cerveau, ainsi que dans le traitement de différents troubles physiologique et psychologiques. Son potentiel pourrait même être augmenté via la stimulation cérébrale. Bien que le cerveau soit un centre de communication majeur, la recherche en sommeil s’est principalement centrée sur des mesures statiques du sommeil. L’étude des patrons de communication entre les différentes régions du cerveau nous permet pourtant d’inférer sur leur utilité fonctionnelle chez l’humain. Et si ces patrons de communication permettaient une compréhension plus intégrée des changements du sommeil à travers la vie et de leurs conséquences au cours du vieillissement? Cette thèse permet d’étudier, sous un angle dynamique et novateur, l’interaction de l’activité neuronale et la modulation expérimentale du sommeil au cours du vieillissement normal. À l’aide de l’électroencéphalographie, la connectivité fonctionnelle cérébrale est évaluée à l’échelle des stades et des cycles de sommeil, de l’onde lente elle-même, ainsi que sous une perspective expérimentale grâce à la stimulation transcrânienne par courant alternatif. Les résultats des deux premières études démontrent les changements au niveau de la connectivité cérébrale en sommeil au cours du vieillissement, tandis que la troisième étude démontre la possibilité de moduler cette connectivité, ainsi que les oscillations cérébrales, chez la population âgée. À l’échelle des stades de sommeil, le cerveau des personnes âgées est plus connecté lors du sommeil lent profond et moins connecté lors du sommeil lent léger, comparativement aux jeunes adultes. Ces différences d’âge sont d’ailleurs plus importantes en début de nuit. Nos résultats démontrent aussi une diminution de connectivité associée à la phase de dépolarisation de l’onde lente chez la population âgée, comparativement aux jeunes adultes. Chez ces derniers, une augmentation marquée de la connectivité pendant l’onde lente est observée. La connectivité au cours de l’onde lente est aussi affectée par la présence d’un fuseau de sommeil en simultané, suggérant soit le mixte de leurs réseaux ou la mise en place de ceux du fuseau. Nous démontrons également, grâce à l’utilisation de métriques novatrices, la présence de deux types d’ondes lentes avec une dynamique de connectivité qui leur est propre, suggérant qu’elles soient impliquées dans des processus fonctionnels distincts. Pendant une sieste, l’utilisation de la stimulation transcrânienne par courant alternatif a aussi permis de moduler les fuseaux de sommeil, leur couplage avec l’onde lente ainsi que la connectivité fonctionnelle des individus âgés. Ces résultats, bien que modestes, démontrent l’aspect prometteur de la modulation non-pharmacologique du sommeil. Non seulement cette thèse fournit une vision intégrée des changements de connectivité fonctionnelle au cours du vieillissement, mais elle démontre qu’il est possible de moduler le sommeil des personnes âgées à des fins ultimement thérapeutiques. Le manque de flexibilité des différents réseaux des personnes âgées pourrait être à la base, entre autres, des changements au niveau de la consolidation de la mémoire. Les implications de nos résultats pourraient être pertinentes à l’étude des processus de plasticité ayant lieu au cours du sommeil. / Sleep is a state of consciousness which shows a great potential in the clinical field. For instance, sleep has become a tool in the early diagnosis of certain neurodegenerative processes, as well as in the treatment of various physiological and psychological disorders. Its potential could even be increased via brain stimulation. Although the brain is a major communication center, sleep research has mainly focused on static measures of sleep. The study of the patterns of communication between the different regions of the brain nevertheless allows us to infer on their functional utility in humans. What if these patterns of communication allowed a more integrated understanding of sleep changes throughout life and their consequences during aging? This thesis investigates, from an innovative and dynamic angle, the interaction of neuronal activity and experimental modulation of sleep in normal aging. Using electroencephalography, functional connectivity is assessed at the scale of sleep stages and cycles, at the scale of the slow wave itself, and from an experimental perspective using the transcranial alternating current stimulation. The results in our first two studies demonstrate changes in EEG functional connectivity during sleep in aging while our third study showed the possibility of experimentally modulating functional connectivity as well as brain oscillations in the same population. At the sleep stage scale, the brain of older individuals is more connected during slow wave sleep and less connected during lighter sleep, compared to young adults. These age differences are predominant at the beginning of the night. Our results also demonstrate a decrease in functional connectivity associated with the slow wave depolarization phase in older individuals. In the young ones, brain connectivity associated to a slow wave is markedly increased. Functional connectivity during slow wave depolarization is also affected by the simultaneous presence of sleep spindles, suggesting either the admixture of their networks or the establishment of those underlying spindle occurrence. We also demonstrate, through the use of novel metrics, the presence of two types of slow waves, each endowed with specific connectivity dynamics. This suggests the presence of distinct functional implications. These slow waves types could also be inherently modulated by distinct physiological processes. During a nap, the use of transcranial alternating current stimulation has made it possible to experimentally modulate sleep spindles, their coupling with the slow waves, and functional connectivity in older individuals. These results, although modest, demonstrate the promising aspect of non-pharmacological sleep modulation. This thesis provides an integrated view of functional connectivity changes in aging and also demonstrates the feasibility of experimental sleep modulation in older individuals. The lack of network flexibility that we described in the older population in term of connectivity could underlie changes in sleep-dependent memory consolidation processes. The implications of our results is relevant to the study of sleep-dependent plasticity processes.

Cílem této práce je vývoj světelného zdroje založeného na technologii tlustostěnného elektroluminiscenčního panelu napájeného střídavým napětím (ACPEL). V současné době se jedná se o jedinou technologii založenou na metodách materiálového tisku vhodnou pro přípravu velkoplošných, flexibilních a vzorovaných zdrojů světla. Důraz je v této práci kladen na představení, prozkoumání a odstranění typických problémů, které jsou spojovány s touto technologií. Tyto problémy jsou omezený odstín barvy emitovaného světla a dlouhodobá stabilita elektroluminiscenčního prvku, který je vystaven vlivům prostředí. Rešeršní část dizertační práce je zaměřena na představení a identifikaci depozičních technik, vhodných pro reprodukovatelnou přípravu ACPEL panelů. Dalším cílem je identifikace fyzikálních parametrů, vhodných pro charakterizaci velkoplošných zdrojů světla. Praktickým cílem práce je nalezení vhodné metodologie pro popis a charakterizaci panelů, jakožto plošných světelných zdrojů. Fotometrická veličina jas L a spotřeba elektrické energie P byly vyhodnoceny jako vhodné parametry, určující aplikaci ACPEL panelů. Na modrém panelu bylo dosaženo maximální hodnoty jasu L = 133 cd•m2 při napětí Upp = 500 V a frekvenci f = 1000 Hz. Hodnoty spotřeby elektrické energie, vztažené na jednotkovou plochu panelů zkoumaných v této práci, jsou (7±3) mW. Tyto dosažené hodnoty dělají ze světelných zdrojů založených na ACPEL technologii zajímavé kandidáty pro různé aplikace. Vlivu rostoucí amplitudy a frekvence budícího napětí na dlouhodobou stabilitu panelů je důležitým cílem této práce. Pro popis stability byly zavedeny parametry L50 and L75. Bylo zjištěno, že rostoucí frekvence budícího napětí zkracuje životnost panelů. Laminovaný panel napájený napětím s přibližně trojnásobně vyšší frekvencí vykazoval přibližně třetinové hodnoty parametrů L50 a L75. Nejvyšších hodnot stabilitních parametrů dosahoval panel enkapsulován mezi skleněné pláty – přibližně sedminásobnou hodnotu oproti laminovanému panelu s trojnásobnou frekvencí. Optimální stability panelů lze dosáhnout při nastavení frekvence v rozmezí 400–800 Hz a zapouzdřením mezi sklo. Úzká paleta odstínů barev emitovaného světla je jeden z typických problémů, který dále zkoumán v dizertační práci. Tato práce zkoumá nadějnou metodu, přídavek vhodného materiálu pro konverzi barvy (CCM). Nový derivát diketopyrrolopyrrolu (DPP), absorbující v modré oblasti, byl přidán k modrému fosforu a byl pozorován sedminásobný narůst hodnot absolutního spektrálního ozáření v oblasti vlnových délek odpovídajících maximální emisi CCM materiálu. Jednoduchost přípravy vyvinutých zdrojů světla spolu s velmi nízkou spotřebou a vysokou dobou života dělají z ACPEL panelů zajímavé kandidáty pro podsvícení prvků například v automobilovém průmyslu, pro dekorativní osvětlení, pro „branding“ – zvýraznění reklamních značek.

We demonstrate a new approach for fabricating alternating current driven organic electroluminescent devices using the concept of doping in organic semiconductors. Doped charge transport layers are used for generation of charge carriers within the device, hence eliminating the need for injecting charge carriers from external electrodes. The device is an organic-inorganic hybrid: We exploit the mechanical strength and chemical stability of inorganic semiconductors and combine it with better optical properties of organic materials whose emission color can be chemically tuned so that it covers the entire visible spectrum. The device consists of an organic electroluminescence (EL) layer composed of unipolar/ambipolar charge transport materials doped with organic dyes (10 wt% ) as well as molecularly doped charge generation layers enclosed between a pair of transparent insulating metal oxide layers. A transparent indium doped tin oxide (ITO) layer acts as bottom electrode for light outcoupling and Aluminium (Al) as top reflective electrode. The electrodes are for applying field across the device and to charge the device, instead of injection of charge carriers in case of direct current (DC) devices. Bright luminance of up to 5000 cd m-2 is observed when the device is driven with an alternating current (AC) bias. The luminance observed is attributed to charge carrier generation and recombination, leading to formation of excitons within the device, without injection of charge carriers through external electrodes.

With increased penetration of renewable energy sources, maintaining equilibrium between production and consumption in the world’s electrical power systems (EPS) becomes more and more challenging. One way to increase stability and efficiency in an EPS is to use flexible alternating current transmission systems (FACTS). However, an EPS containing multiple FACTS-devices with overlapping areas of influence can lead to negative effects if the reference values they operate around are not updated with sufficient temporal resolution. The reference values are usually set manually by a system operator. The work in this master thesis has investigated how three different reinforcement learning (RL) algorithms can be used to set reference values automatically with higher temporal resolution than a system operator with the aim of increased voltage stability. The three RL algorithms – Q-learning, Deep Q-learning (DQN), and Twindelayed deep deterministic policy gradient (TD3) – were implemented in Python together with a 2-bus EPS test network acting as environment. The 2-bus EPS test network contain two FACTS devices: one for shunt compensation and one for series compensation. The results show that – with respect to reward – DQN was able to perform equally or better than non-RL cases 98.3 % of the time on the simulation test set, while corresponding values for TD3 and Q-learning were 87.3 % and 78.5 % respectively. DQN was able to achieve increased voltage stability on the test network while TD3 showed similar results except during lower loading levels. Q-learning decreased voltage stability on a substantial portion of the test set, even compared to a case without FACTS devices. To help with continued research and possible future real life implementation, a list of suggestions for future work has been established.

No description available.