Control aspects of a double-input buckboost power electronic converter

Systems in which two or more energy sources combine to supply power to a common load are called hybrid energy systems. Applications of these systems have grown due to their flexibility and reliability. Hybrid energy systems have been successfully implemented in hybrid electric vehicles and wind-solar systems where two or more energy sources share the same load. Double-input (DI) dc-dc power electronic converters (DIPECs) have been gaining popularity in hybrid energy systems due to their reduced component count and control simplicity. In addition, employing DIPECs increases the reliability, stability, and flexibility of the system. In this thesis, a small-signal model for one of the DIPEC topologies, the DI buckboost converter, is developed and compensator design is carried out based on the small-signal model. The compensators are designed to accommodate optimal power sharing between the sources. Theoretically, it is also proven in this thesis that the two inputs of the DI buckboost topology can be independently controlled which gives great flexibility in terms of the compensator design. Time domain analysis of the system is carried out with the compensators included and the results agree with the theoretical analysis. In addition to the small-signal modeling, a new control method called offset time control is also introduced and successfully applied to a DIPEC topology in this thesis. The control scheme is based on adjusting the offset time between the switching commands; which is proven to have a direct impact on the amount of current drawn from each input. Small-signal modeling of the offset time control scheme has been carried out to prove the improvement in the speed of response of the system when the offset time control scheme is applied --Abstract, page iii

Seeking refuge from humanitarian interventions

Over a million migrants and asylum seekers sought refuge in Europe in 2015 – a record which sent the migration crisis to the forefront of the political and social agenda. Behind the crisis lie the large-scale internal conflicts or armed rebellions in countries such as Syria, Afghanistan, Somalia and Iraq. But in order to fully understand why so many are fleeing their native countries, we must examine the causes in more detail – looking in particular at the exponential increase in attacks on civilians, not just by internal parties, but also by third party states, both requested and unsolicited

Interactive optimization of mechanical systems with multiple performance requirements

In the design of mechanical systems, the designer is often faced with the problem of satisfying a number of competing requirements, including light weight and limits on displacements, stresses, and natural frequencies. This usually leads to an optimization problem with weight as the objective and the performance requirements as constraints. It may be desirable, in addition to minimizing weight, to minimize or maximize other performance measures rather than enforcing performance limits;This thesis recast the optimization problem as the minimization of multiple objectives, including performance indices and weight, subject to restrictions placed on the size of the design variables. The thesis also developed an interactive optimization procedure to enable design engineers to bring their skill into play during the optimization process;The procedure transforms the multi-objective problem into a single objective problem by taking the weighted sum of the performance indices and the structure\u27s weight. The weighting factors reflect the relative importance to the designer of the various conflicting objectives. The choice of the weighting factors best suited for the problem is not generally obvious and may require several adjustments before leading to an acceptable design. Thus the procedure is set up so that the designer can choose the weighting factors interactively;Optimization software was developed to provide designers with a decision making tool which is easy to use and provides useful information from which designer can confidently proceed. Since the method uses the NASTRAN for the response and sensitivity calculations, it is applicable to almost any structure which can be modelled using finite elements;Two examples illustrate the power of the technique. The first considers the redesign of an automotive engine block where the challenge was to find a low-weight design which has no natural frequencies in undesirable frequency bands. This problem illustrated the trade-offs between the weight and the natural frequencies, and it demonstrated the interactive process wherein the designer found a combination of the twelve design variables that met performance requirements with a very low weight structure. The second example concerned the redesign of the mounting structure of a heavy-duty truck\u27s exhaust pipe. The structural optimization was stated as finding a low weight structure which satisfied limits on maximum displacements and stresses, and shifted the natural frequencies out of an undesirable band. Again, the design engineer interactively found a very nice solution

Seeds of Peace: Visible Cooperation Between Jews and Muslims in Morocco

A carrefour in various contexts, Morocco stands in a unique position between the Arab world and Israel for several reasons. The country is unique due to the historical presence of Judaism in the region that, over the years, became a Muslim-majority Islamic kingdom. The members of Morocco’s Muslim and Jewish communities coexisted for centuries, albeit with minor hurdles, as did the Muslims and Jews of Palestine. However, political events around the world in the twentieth century led to the rapid departure of Jews from their Moroccan homeland. Today, with so few remaining in Morocco, “Jew” often becomes synonymous with “Israel,” and as a result, relations between Moroccans–mainly Moroccan Muslims–supporting Palestine and their Jewish compatriots become tense. Despite this unfortunate reality, there are still many Muslims and Jews in Morocco who hope for peaceful relations to once again become more widespread. However, during a time when such efforts bring with them the risk of political categorization, stigmatization and silence, how do these movements seek to successfully counter the tensions caused in Morocco by the Israeli-Palestinian conflict? This paper will examine some of the current efforts to encourage mutual understanding between Muslims and Jews in Morocco. By conducting interviews with leaders of peace-building movements, listening to past interviews with and speaking to members of the Jewish community that remains in Morocco, and reading literature discussing Morocco’s past involvement in the Arab-Israeli conflict, I was able to connect these present-day efforts to Morocco’s historical role in peace-building between Israel and Palestine. I hope that this paper will begin to bring to light the potential for creative efforts to encourage widespread cooperation between two of Morocco’s most long-standing cultural communities

Hardware integration of ultracapacitor based energy storage to provide grid support and to improve power quality of the distribution grid

Grid integration of distributed energy resources (DERs) is increasing rapidly. Integration of various types of energy storage technologies like batteries, ultracapacitors (UCAPs), superconducting magnets and flywheels to support intermittent DERs, such as solar and wind, in order to improve their reliability is becoming necessary. Of all the energy storage technologies UCAPs have low energy density, high power density and fast charge/discharge characteristics. They also have more charge/discharge cycles and higher terminal voltage per module when compared to batteries. All these characteristics make UCAPs ideal choice for providing support to events on the distribution grid which require high power for short spans of time. UCAPs have traditionally been limited to regenerative braking and wind power smoothing applications. The major contribution of this dissertation is in integrating UCAPs for a broader range of applications like active/reactive power support, renewable intermittency smoothing, voltage sag/swell compensation and power quality conditioning to the distribution grid. Renewable intermittency smoothing is an application which requires bi-directional transfer of power from the grid to the UCAPs and vice-versa by charging and discharging the UCAPs. This application requires high active power support in the 10s-3min time scale which can be achieved by integrating UCAPs through a shunt active power filter (APF) which can also be used to provide active/reactive power support. Temporary voltage sag/swell compensation is another application which requires high active power support in the 3s-1min time scale which can be provided integrating UCAPs into the grid through series dynamic voltage restorer (DVR). All the above functionalities can also be provided by integrating the UCAPs into a power conditioner topology. --Abstract, page iv

Biocompatibility of Osteoblast Cells on Titanium Implants

Adhesion and proliferation of UMR 106-01 osteoblast cells were studied on various surface modified titanium materials such as polished, sandblasted, anodized and alkaline treated. Anodization of polished surface in Hydrofluoric acid developed nano-tubes, while NaOH treatment produced spongy microporous morphology. Test samples were coated with non-adhesive protein bovine serum albumin and compared with fibronectin coated specimens. The adhesion study lasted for 4 hrs, where osteoblast cells were cultured in serum free medium. Polished titanium, anodized titanium and NaOH titanium have shown similar percentages of cell adherence. The proliferation study lasted for 48 hrs, where cells were initially allowed to adhere to the surface in serum free medium for 4 hrs, followed by a medium change to 10 fatal bovine serum. The specific growth rate after 48 hrs in culture on the polished surface was found to be comparable to the tissue culture plastic, which exhibited a high growth rate. No significant difference was found in cell numbers between polished, anodized and NaOH-Ti, but each has varying cell orientation on the surface. Fluorescence images stained with alkaline phosphatase revealed that polished surface had cells flattened to the surface with short filapodia. Anodized surface had cells uniformly distributed across the surface where as NaOH-Ti displayed cells in colonies. Cells were found bonding to the surface of NaOH-Ti firmly using their filapodia as an anchoring agent. These results suggest that NaOH-Ti provides support in initial hours of implantation and bolsters cell proliferation. All together this process may help to better integrate titanium implant surface

Effects of large solar zenith angles and cloud cover on underwater irradiance

Le processus de la photosynthèse nécessite l'énergie de la lumière solaire et, dans l’océan, se déroule essentiellement dans la couche euphotique. Outre les autres variables (à savoir la chlorophylle a et les paramètres photosynthétiques), une connaissance appropriée du champ lumineux en termes de rayonnement incident disponible sur la photosynthèse (PAR) à un emplacement, une profondeur et une heure et une date donnés, est requise par les modèles d'écosystème marin. Le travail inclus dans cette thèse examine comment des angles de zénith solaires plus grands et différentes conditions nuageuses caractéristiques des régions de haute latitude, en particulier dans l'Arctique, peuvent affecter la précision des estimations de l'éclairement de surface et dans la colonne d’eau. L’accent est également mis sur les variations du champs lumineux à haute fréquence liées à la nébulosité sur les estimations de la productivité primaire. Les PAR de surface estimés à partir de différents modèles ont été comparés à des mesures en série chronologique in situ à haute fréquence de données de PAR d'une bouée située en mer Méditerranée. Nous avons examiné comment les incertitudes dues aux angles de zénith solaires plus grands, en conditions nuageuses variables, pouvaient affecter la précision des estimations de l'éclairement de surface. La méthode de classement objectif a été utilisée pour identifier les meilleures méthodes. Le produit PAR de la NASA-Ocean Biology Processing Group (OBPG) a montré les meilleures performances globales, tandis que les PAR basées sur la méthode de la table de conversion (LUT) ont présenté les meilleures performances en termes de différence carrée moyenne, de biais sous ciel clair et également par temps couvert. D'autres méthodes basées sur des formulations empiriques ont montré la troisième meilleure performance par temps clair, tandis que par temps nuageux, elles présentaient de plus grandes incertitudes. Trois méthodes testées par faible ensoleillement ont montré des incertitudes allant jusqu'à 50% dans toutes les conditions du ciel. Les performances du modèle dépendent des propriétés et des produits de nuage...The process of photosynthesis requires the energy from sunlight and takes place essentially in the euphotic layer of the oceans. In addition to other variables (i.e., chlorophyll a and photosynthetic parameters) a suitable knowledge of light field in terms of photosynthetically available radiation (PAR) at any given location, depth and time is an important input parameter required by marine ecosystem models. The work included in this thesis examines how larger solar zenith angles, different cloud conditions that are characteristic features of high latitude regions, especially in Arctic, might affect the accuracy of surface irradiance estimates. Further, main focus was on the effects of high frequency variations in the light field on primary production. Surface PAR estimated from different models were compared with high frequency in situ time series measurements of PAR a buoy located in Mediterranean Sea. It was examined how uncertainties due to larger solar zenith angles under varying cloud conditions might affect the accuracy of surface irradiance. Objective ranking method was used to identify the best methods. Methods tested under low sun elevations exhibited uncertainties as large as 50% under all sky conditions. Model performances were dependent on cloud properties and products. Accuracy of a semianalytical model for coefficient of vertical diffuse attenuation of surface irradiance (kd!) based on optical properties inherent to the water itself (absorption and scattering), and solar zenith angle was examined under larger solar zenith angels and cloud conditions. Extensive radiative transfer simulations were performed to quantify the uncertainties due to large solar zenith angles and clouds on the estimates of diffuse attenuation coefficient. The uncertainties under both these conditions are due to the variability in the proportions of direct and diffuse parts of the total irradiance reaching the surface and in the water column. Also, an improved model parameterization proposed to estimate !"# under large solar zenith angels and cloud conditions was evaluated with Arctic in situ data exhibited good performances..

Power Sharing in a Double-Input Buckboost Converter using Offset Time Control

Multi-input power electronic converters have been gaining popularity in applications such as renewable energy sources and hybrid electric vehicles due to their reduced component count. In this paper, a new control method is introduced and successfully applied to a double-input buckboost converter to adjust the power supplied by each one of the sources. The control scheme is based on controlling the offset time between the switching commands while switching frequency is kept constant. Theoretically, it is proved that the offset time between the switch commands has a direct impact on the amount of current drawn from each source. The proposed control method has a very fast dynamic response and improves the stability of traditional controllers. Simulation results agree with the theoretical analysis