Design a photovoltaic system based on maximum power point tracking under partial shading

Photovoltaic systems have been given special attention given their long-term potential advantages. Solar panels can produce maximum power at specific operating points called maximum power points (MPP). Solar panels must work at this particular stage in order to ensure that solar panels produce maximum power and maximize efficiency. The performance of the solar photovoltaic unit is strongly affected by the level of radiation, heat and partial shading condition. The partial shedding condition is one of vectors that can affect the PV cell performance. To overcome on this problem, this project proposes photovoltaic system based on maximum power point tracking of partial shading condition. The MPPT algorithm has many methods like P&O and PSO. P&O it had limitation that is not capable to cover the multi-peaks curves. Beside that the PSO method is more effective in partial shading condition. The voltage and current of MSX60 PV module are subjected to various insolation conditions. The Particle Swarm Optimization (PSO) algorithm based MPPT has been implemented to track maximum power partial shading condition. So, in normal condition the power reach 245 W which is higher than the power under partial shading condition that reach 100 W. The PV module is designed using MATLAB/SIMULINK. The accurateness of this simulator is verified with PV module, the result is practiced during normal condition and under partial shading condition meanwhile, multiple curves of I-V and P-V will produce during normal condition and partial shading condition

Nanoscale and macroscale characterization of the dielectric charging phenomenon and stiction mechanisms for electrostatic MEMS/NEMS reliability

Les phénomènes de chargement des diélectriques constituent l'un des principaux mécanismes de défaillance des microsystèmes à actionnement électrostatique, ce qui limite la commercialisation de ce type de dispositifs. Par exemple, dans le cas de micro-commutateurs capacitifs ce chargement entraîne des problèmes de collage entre la membrane actionnable et la surface du diélectrique qui recouvre l'électrode d'actionnement. Malgré de nombreux travaux réalisés dans le monde, les phénomènes de chargement des diélectriques sont encore mal compris aujourd'hui et les mécanismes de défaillances associés peu explicités. Par ailleurs de nombreuses méthodes de caractérisation ont été développées afin d'étudier ces phénomènes : capacité/tension dans les micro-commutateurs capacitifs, courant/tension dans les capacités MIM (Métal-Isolant-Métal). Bien que très souvent utilisées, ces méthodes donnent des résultats qui dépendent fortement de la nature du dispositif utilisé. Dans les capacités MIM par exemple, la décharge a lieu en situation de court-circuit et les charges injectées dans le diélectrique sont collectées seulement par l'électrode qui a servi à réaliser l'injection. Cette configuration est l'inverse de celle qui a lieu réellement dans les microsystèmes pour lesquels les charges sont injectées par la membrane actionnable et collectées par l'électrode d'actionnement, puisque la membrane ne touche pas le diélectrique lorsque la tension est supprimée. Par ailleurs les mécanismes de défaillances sont souvent liées à des phénomènes multi-physiques (électrique, mécanique, thermique). Ainsi le chargement des diélectriques peut être couplé notamment à des problèmes de fatigue mécanique de la membrane, ce qui peut fausser les interprétations. Des études récentes ont par ailleurs montré que les phénomènes tribologiques, comme l'adhésion et la friction, sont cruciaux pour les MEMS/NEMS et peuvent affecter radicalement leurs performances. Les micro-commutateurs RF étant basés sur le contact intermittent entre deux surfaces (membrane métallique et diélectrique), la fiabilité des ces composants est également impactée par ces phénomènes de surface. Des études sur la micro-nanotribologie appliquée aux micro-commutateurs RF sont donc nécessaires pour comprendre les phénomènes qui se passent aux interfaces et pour coupler ces phénomènes avec le chargement des diélectriques. Les travaux sur le chargement des diélectriques présentés dans ce mémoire sont basés sur la microscopie à force atomique (KPFM, FDC) et permettent de supprimer les inconvénients des méthodes conventionnelles. Le diélectrique étudié est le nitrure de silicium obtenu par PECVD pour des micro-commutateurs RF à contact capacitif. Les méthodes utilisées permettent de réaliser l'étude des diélectriques à l'échelle nanométrique grâce à l'utilisation de l'AFM dont la dimension de la pointe est comparable aux aspérités des microstructures. Différentes structures de tests ont été caractérisées incluant des films diélectriques, des capacités MIM et des micro-commutateurs. La pointe de l'AFM est utilisée pour réaliser l'injection des charges (comme dans le cas d'une aspérité en contact avec le diélectrique), mais également pour mesurer le potentiel de surface et la force d'adhésion. Les résultats obtenus ont été comparés à des mesures de charges et décharges plus conventionnelles sur des capacités MIM et sur des micro-commutateurs RF. Tous ces résultats ont également été comparés à des données de la littérature provenant de différents composants. L'influence de plusieurs paramètres clés sur le chargement des diélectriques a également a également été étudiée. Différentes épaisseurs de SiNx déposées sur de l'or (évaporé et électro-déposé), sur du Titane et sur du silicium ont été analysées. Différents modes d'élaboration du SiNx PECVD ont été utilisés en changeant le ratio des gaz, la température de dépôt, la puissance et la fréquence RF. Des analyses physico-chimiques ont également été menées pour déterminer les liaisons chimiques et les compositions des films de SiNx (FTIR, XPS). Ces données ont été utilisées pour expliquer les résultats électriques obtenus. Différentes conditions de chargement ont également été explorées : amplitude, durée et polarité de la tension, taux d'humidité, contamination dues aux hydro-carbones. Les différents phénomènes tribologiques (adhésion, friction) ont aussi été étudiés à l'échelle nanométrique sous différentes tensions et pour différents taux d'humidité. A partir de ces études, deux principaux mécanismes de collage dans les microsystèmes à actionnement électrostatique ont ainsi été explicités : le chargement des diélectriques et la formation d'un ménisque d'eau. L'interaction entre ces deux mécanismes a également été mise en évidence et a permis de mieux comprendre les phénomènes de collage dans les MEMS à actionnement électrostatique.The reliability of electrostatically actuated micro- and nano-electromechanical systems (MEMS and NEMS) is determined by several failure modes which originate from different failure mechanisms. Among various reliability concerns, the dielectric charging constitutes major failure mechanism which inhibits the commercialization of several electrostatic MEMS devices. In electrostatic capacitive MEMS switches, for example, the charging phenomenon results in shifting the electrical characteristics and leads to stiction causing the device failure. In spite of the extensive study done on this topic, a comprehensive understanding of the charging phenomenon and its relevant failure mechanisms are still missing. The characterization techniques employed to investigate this problem, though useful, have serious limitations in addition to the missing correlation between their results. On the other hand, recent studies show that tribological phenomena such as adhesion and friction are crucial in MEMS/NEMS devices requiring relative motion and could affect their performance. Since the operation of MEMS switch is based on intermittent contact between two surfaces, the movable electrode and the dielectric, critical tribological concerns may also occur at the interface and influence the device reliability. These concerns have not been investigated before, and consequently, micro/nanotribological studies are needed to develop a fundamental understanding of these interfacial phenomena. Also, the multiphysics coupling between the charging phenomena and those expected tribological effects needs to be studied. This thesis addresses the abovementioned weaknesses and presents numerous novel characterization techniques to study the charging phenomenon based on Kelvin probe force microscopy (KPFM) and, for the first time, force-distance curve (FDC) measurements. These methods were used to study plasma-enhanced chemical vapor deposition (PECVD) silicon nitride films for application in electrostatic capacitive MEMS switches. The proposed methods are performed on the nanoscale and take the advantage of the atomic force microscope (AFM) tip to simulate a single asperity contact between the switch movable electrode and the dielectric surface. Different device structures were characterized including bare dielectric films, MIM capacitors, and MEMS switches. In addition, the charge/discharge current transients (C/DCT) and thermally stimulated depolarization current (TSDC) assessment methods were used to study the charging/discharging processes in metal-insulator-metal (MIM) capacitors. A comparison and correlation between the results from the investigated characterization techniques were performed. Moreover, a correlation between the obtained nanoscale/macroscale results and the literature reported data obtained from device level measurements of actual MEMS devices was made. The influence of several key parameters on the charging/discharging processes was investigated. This includes the impact of the dielectric film thickness, dielectric deposition conditions, and substrate. SiNx films with different thicknesses were deposited over metal layers and over silicon substrates to study the effect of the dielectric thickness. The impact of the dielectric deposition conditions was investigated through depositing SiNx films using different gas ratio, temperature, power, and RF modes. To study the influence of the substrate, SiNx layers were deposited on evaporated gold, electrochemically-deposited gold, evaporated titanium layers, and over bare silicon substrates. Fourier transform infra-red spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) material characterization techniques were used to determine the chemical bonds and compositions, respectively, of the investigated SiNx films. The obtained data from these techniques were used to explain the electrical characterization results. The impact of electrical charge injection conditions, which are the voltage amplitude, polarity and duration, was also explored. Finally, the influence of the relative humidity, environment medium, and contaminants on the charging phenomenon was studied. Furthermore, the thesis investigates different tribological phenomena at the interface between the two contacting surfaces of electrostatic MEMS switches as well as their multiphysics coupling with the dielectric charging failure mechanism. The adhesive and friction forces were measured on the nanoscale under different electrical stress conditions and relative humidity levels using an AFM to study different stiction mechanisms. In these devices, stiction can be caused by two main mechanisms: dielectric charging and meniscus formation resulting from the adsorbed water layer at the interface. The effect of each mechanism as well as their multiphysics interaction and impact on the overall adhesion or stiction was quantified. Finally, the impact of the dielectric charging on the friction force between the two contacting surfaces of the switch has been studied

The impact of oil shocks on the G-7 countries GDP growth

This study examines the impact of oil shocks on the G-7 countries using the time series data from 1975 to 2007. The pooled model was employed; from the results we found that oil shocks has no negative impact on the G-7 countries, due to the flexible labor markets, improvements in monetary policy and smaller share of oil in production, Indirect Tax Analogy, and flexible inflation targeting regimes.Oil prices, G-7 Countries, GDP growth, Pooled Model

Random patterns in fish schooling enhance alertness: a hydrodynamic perspective

One of the most highly debated questions in the field of animal swarming and social behaviour, is the collective random patterns and chaotic behaviour formed by some animal species, in particular if there is a danger. Is such a behaviour beneficial or unfavourable for survival? Here we report on one of the most remarkable forms of animal swarming and social behaviour - fish schooling - from a hydrodynamic point of view. We found that some fish species do not have preferred orientation and they swarm in a random pattern mode, despite the excess of energy consumed. Our analyses, which includes calculations of the hydrodynamic forces between slender bodies, show that such a behaviour enhances the transfer of hydrodynamic information, and thus enhances the survivability of the school. These findings support the general hypothesis that a disordered and non-trivial collective behaviour of individuals within a nonlinear dynamical system is essential for optimising transfer of information - an optimisation that might be crucial for survival.Comment: 12 pages, 5 figures, 1 tabl

A process chain for integrating microfluidic interconnection elements by micro- overmoulding of thermoplastic elastomers

This paper presents a process chain for in-line integration of microfluidic interconnection elements by a variant of micro-injection moulding (mu IM). A SEBS-based thermoplastic elastomer (TPE) was moulded over polymethylmethacrylate (PMMA) to produce a hybrid microfluidic structure with an aspect ratio of 2. The process chain implemented micro-milling for fabricating micro-structured tool inserts, and mu IM and micro-overmoulding was used for replication. A two-plate mould was used for moulding the substrate, whilst a three-plate mould with a replaceable insert was used for TPE overmoulding. The presented application was an interconnect system for a microfluidic device, which enabled direct fitting of standard tubes into microfluidic substrates. A leakage test showed that the interconnection was leak-proof within a range of flow rates between 0.32 and 0.62 ml min(-1)

The Impact of Oil Prices on the Real Exchange Rate of the Dirham: a Case Study of the United Arab Emirates

This study investigated the impact of oil shocks on the real exchange rate of the United Arab Emirates (UAE) dirham. Time series data were used for the period 1977 to 2007 covering four important oil shocks. Five variables have been used in this study, with the real exchange rate of the dirham as the dependent variable and the gross domestic product per capita, oil price, trade balance, and foreign direct investment inflows as the independent variables. In this study we used the Johansen-Juselius cointegration procedure, and conducted the Granger causality tests based on the VECM. Through this research, we found that a fixed exchange rate to the U.S. dollar is not an appropriate exchange rate regime for the UAE. This is because when the price of oil increases, and with a fixed exchange rate regime, this would lead to rapid growth in GDP and liquidity in the UAE economy. This in turn causes domestic prices to increase, which results in high levels of inflation.oil Prices, real exchange rate, UAE, VAR