One of the challenging issues with the Microgrid is that the bidirectional power flow providedby the distributed generator (DG) which modify the fault current level. Furthermore, theinverter based-renewable energy source (IB-RES) limits the total fault current contributionto the grid due to its thermal capability. Since Microgrid should be able to operate in gridconnectedand islanded mode, protection strategies are needed to solve this challenging issue.By only having IB-RES and battery storage system, the fault condition and normaloperation cannot be distinguished. Apart from fault clearing issue, there is a consideration tostudy the fault isolation in the Microgrid under the limited fault current provided by IB-RES.To have fault isolation capability, the intelligent electrical device (IED) is needed. The firststep is to find a method that can detect a fault under the fault level modification constraint.This thesis presents a zero and negative sequence current protection to detect a fault.However, to make it selective, this protection will be applied directionally. It is common thatthe distribution grid has unbalanced load operation, thus providing zero and negativesequence component in the grid. To apply the directional zero and negative sequence currentprotection, the unbalanced load flow is simulated to distinguish the fault and normaloperation under unbalanced load condition.Safety and regulation are discussed briefly in this thesis. It is important that each of theIB-RES has fault ride-through (FRT) capability that follows a regulation. However, thisregulation is expected to have a coordination with the proposed protection in the Microgridso the reliability, selectivity, and sensitivity can be achieved in grid-connected and islandedmode. This thesis shows the coordination between fuses, IED, and inverter FRT capability.After providing a protection strategy, the adaptability of the proposed protection isassessed regarding of Microgrid expansion. The result shows that by applying the schemeand following the grading margin requirement that is presented in this thesis, the Microgridexpansion will not disrupt the proposed protection coordination. Since it is known that thedistribution grid is expanding its load capacity and microgeneration in continuous basis, it isconvenient that the proposed protection in the IED is expected to be adaptable, means that ithas a fixed IED setting when the grid is expanded. The analysis is performed by electrical transient analysis program (ETAP) and MatlabSimulink. The short circuit analysis, sequence-of-operation, and unbalanced load flow aresimulated by ETAP, while the protection stability is simulated by Matlab Simulink. / Ett problem som finns med microgrid är att de distribuerade produktionsgeneratorerna harett dubbelriktat effektflöde som modifierar felströmmen. Dessutom, inverterbaseradeförnyelsebara energikällor (IB-RES) begränsar det totala felströmsbidraget på grund av desstermiska kapacitet. Eftersom microgrids ska vara operativ vid både anslutning till externt nätsamt önätsdrift behövs skyddsstrategier för att kunna hantera fel, speciellt vid önätsdrift.Om endast IB-RES och batterilager används kan feldrift och normal drift inte särskiljas.Bortsätt från felhantering är det viktigt att studera felbortkoppling för microgrid underbegränsad felström som fås av IB-RES. För att kunna åstadkomma felbortkoppling behöveren IED (från engelskans Intelligent Electronic Device). Det första steget är att finna en metodför att kunna detektera fel under fel nivå modifiering. Denna avhandling tittar på att användanoll- och minusföljds ström sekvensskydd för att detektera fel. För att göra skyddet selektivtkommer det att titta på riktningen av effektflödet. I distributionsnät är det vanligt att haobalanserade laster vilket medför noll- och negativa sekvenskomponenter i nätet. För atttillämpa riktningsskydd för noll och negativ sekvens ström simuleras ett obalanserateffektflöde för att särskilja på feldrift och normal drift vid obalanserad last.Säkerhet och förordningar diskuteras kortfattat i denna avhandling. Det är viktigt att varjeIB-RES har en feltålighet som följer vissa förordningar. Denna förordning förväntassamordna det föreslagna skyddet i micronåt så att pålitlighet, selektivitet och känslighet kanåstadkommas vid nätanslutning och önätsdrift. Denna avhandling visar samordningen mellansäkringar, IED och feltåligheten för växelomriktare.Anpassningsförmågan för det föreslagna skyddet bedöms med avseende på expansion avmicrogrid. Resultatet visar att en expansion av ett microgrid inte kommer att störa denföreslagna samordningen om skyddsmetoden och tidsfördröjningskravet som presenteras idenna avhandling följs. Eftersom det är känt att distributionsnätet kommer att fortsätta ökasin lastkapacitet och mikrogenerering, är det lämpligt att skyddet förväntas varaanpassningsbart vilket innebär att det har en fast IED inställning när nätet expanderas.Analysen genomförs med mjukvarorna electrical transient analysis program (ETAP) ochMatlab Simulink. Kortslutningsanalysen, arbetssekvensen och obalanserad lastflödesimuleras av ETAP, medan skyddsstabiliteten simuleras av Matlab Simulink.

Renewable energy is playing an increasingly significant role in power system operation and stability assessment with its numerous penetration expansion. This is not only brought by its uncertain power output and inverter-based equipment structures but also its operation characteristics like Low Voltage Ride Through (LVRT). It is thus necessary to take these characteristics into consideration and further to find more adaptive schemes to implement them for more effective analysis and safer power system operation. All the aforementioned is based on the accurate identification of the system fundamental information. In this dissertation, a systematic approach is proposed to find the valid system model by estimating the transmission line parameters in the system with PMU measurements. The system transient stability assessment is conducted based on this validated model. The constrained stability region is estimated with Lyapunov functions family based method in the center of angles reference frame considering renewables LVRT as operation limits. In order to integrate the LVRT constraints, a polytopic inner approximation mechanism is introduced to linearize and organize the transformed constraints in state space, which brings much scalability to the whole process. From the voltage stability perspective, an approach to adaptively adjust LVRT settings of the renewable energy sources in the system is formulated to guarantee the system load margin and thus the voltage security. A voltage prediction method is introduced for critical renewable energy sources identification. Estimation methods based on interpolation and sensitivities are developed and conducted for saving computation effort brought by continuation power flows. Multiple test cases are studied utilizing the proposed approaches and results are demonstrated. / Doctor of Philosophy / Renewable energy utilization is continuously rising nowadays. They are clean but highly dependent on natural resources, which causes their uncertainty and intermittence in electric power output. The power system, on the other hand, is designed for schedulable and controllable power generators, which make the traditional methods for system operation and analysis of the system stability much less effective facing the trend of renewables integration. In this dissertation, a series of systematic approaches are proposed firstly identify the system parameters for more accurate system modeling through PMU measurements, then to assess the system transient stability considering the renewable energy sources operation limits, and finally to adaptively adjust these operation limit for improving the system voltage security. The operation limits are transferred into the form in terms of system states. Linearization and approximation methods are also introduced to enhance the scalability of the processes. Multiple test cases are studied with the proposed approaches and the results demonstrate their effectiveness and efficiency.

Obtaining the modal parameters of a deflected and rolling tire represents a challenge due to the complex vibration characteristics that cause the tire's symmetry distortion and the natural frequencies' bifurcation phenomena. The modal parameters are usually extracted using a detailed finite element model. The main issue with full modal models (FEA, for example) is the inability to integrate the tire modal model with the vehicle models to tune the suspension system for optimal ride comfort. An in-plane rigid–elastic-coupled tire model was used to examine the 200 DOF finite difference method (FDM) modal analysis accuracy under non-ground contact and non-rotating conditions. The discrete in-plane rigid–elastic-coupled tire model was modified to include the contact patch restriction, centrifugal force, Doppler, and Coriolis effects, covering a range of 0-300 Hz. As a result, the influence of the contact patch and the rotating tire conditions on the natural frequencies and modes were obtained through modal analysis. The in-plane rigid–elastic-coupled modal model with varying conditions was created that connects any two DOFs around the tire's tread or sidewall as inputs or outputs. The vertical movement of the wheel was incorporated into the in-plane rigid–elastic-coupled tire modal model to extract the transfer function (TF) that connects road irregularities as an input to the wheel's vertical movement as an output. The TF was utilized in a quasi-static manner to obtain the tire's enveloping characteristics rolling over short wavelength obstacles as a direct function of vertical wheel displacement under varying contact patch length constraints. The tire modal model was implemented with the quarter car model to obtain the vehicle response rolling over short wavelength obstacles. Finally, a sensitivity analysis was performed to examine the influence of tire parameters and pretension forces on natural frequencies. / Doctor of Philosophy / The goal of vehicle manufacturers is to predict the vehicle's behavior under various driving conditions using mathematical models and simulation. Automotive companies rely heavily on computational simulation tools instead of real-time tests to shorten the product development cycle and reduce costs. However, the interaction between the tire and the road is one of the most critical aspects to consider when evaluating automobile stability and performance. The tires are responsible for generating the forces and moments that drive and maneuver the vehicle. Tires are complex products due to their intricate design, and their characteristics are affected by many factors such as vertical load, inflation pressure, speed, and a road with an uneven surface profile. Consequently, this project aims to describe the influence of various driving circumstances and load conditions on tire properties, as well as to develop a model that can represent the vertical tire and vehicle behavior while traveling over a cleat under different vehicle loads.

Ride-hailing platforms (RHP) are sharing economy platforms that connect passengers who need to order a private ride or to share a vehicle with drivers who want to share a ride. However, after rapid growth, major RHPs (e.g., Uber, Lyft, and Didi) have begun to face severe driver shortages. Attracting and maintaining a large driver base is critical to the survival and success of any RHP no matter its size. While practitioners are urging to seek suggestions from academia to prevent driver loss, limited research attention has been paid to RHP drivers’ discontinuance. To fill this gap, this dissertation aims to explore factors that motivate drivers to discontinue using RHPs from the perspective of algorithm unfairness. The algorithm is the boss of ride-hailing drivers as they are matched, paid, and evaluated by various algorithms. While algorithms have the potential to make the ride-hailing process more efficient, they also yield socially biased outcomes which create inequalities and uncomfortable experiences for both drivers and riders which may further influence their decisions to use to not use RHPs. Following the logic, the research question of the current dissertation is “how does algorithm unfairness of RHPs affect drivers’ discontinuance?” Stressor-strain-outcome model and organizational justice theory are adapted to the ride-hailing context based on the contextualization approach to serve as theoretical frameworks of the current study. An online survey is conducted to empirically test drivers’ discontinuance of ride-hailing platforms. Research participants of the studies are recruited by employing the service provided by Prolific. co. Data analysis is conducted by employing the covariance-based structural equation modeling approach by following previously defined approaches. The results support most of the hypotheses. The study is expected to contribute to the current literature on information systems discontinuance, ride-hailing, IT stress, AI-empowered algorithm management, algorithm unfairness, dark side of AI, stressor-strain-outcome model, and organizational justice theory. My dissertation is also expected to offer rich insights into how to retain the user base effectively for practitioners in emerging sharing economy platforms. Moreover, the results of the current dissertation also offer rich implications on how to manage dispersed workforces using AI-empowered algorithms.

In order to reduce emissions and achieve sustainable energy systems, renewable energy is increasingly being integrated into the power grid. However, the integration of renewable energy into the grid poses several challenges, including maintaining a stable power supply under changing and unpredictable conditions. Low Voltage Ride Through (LVRT) assesses a generator's ability to maintain stable voltage during grid voltage drops, which is crucial for renewables due to their low inertia and vulnerability to voltage disruptions caused by changes in wind or sunlight. LVRT requirements are defined by regional grid codes and regulations, which vary in their diversity. A study was conducted using Matlab Simulink to model and simulate the LVRT phenomenon on Siemens Energy's medium gas turbine generator. The entire power system generation system was simulated to observe the system's response and the generator's behavior during LVRT events. A previous gas turbine power plant project in Romania, delivered by Siemens Energy in Finspång, was simulated for analysis and compared against the grid code requirements. The findings indicated that the Siemens Energy gas turbine model SGT-750 satisfies the Romanian LVRT grid code requirements.

While there has been considerable research regarding the role of Mobility Hubs in cities and transport networks, significant investment is required to develop these facilities. It is the correlation between investment, new users’ attraction and revenue generation that is the key for a sustainable development of Mobility Hubs and this investment must, therefore, be correctly assessed and targeted. This study aims to develop a methodology to determine the viability of investing in Mobility Hub features, weighing the investment on different Hub features and services against expected potential benefits and revenue generation, addressing the question: Can investment in Mobility Hub features be justified and, if so, which features maximize its expected positive impact? Based on a review of literature and definition of possible Hub features as variables, secondary research data was compiled to enable the analysis of expected impacts of each variable/feature in terms of new user’s attraction and revenue generation, which was then used to develop individual Net Present Value analysis of each feature. The result of these analysis demonstrates and concludes that different Hub features have the potential to generate substantially different investment outcomes, and that each feature should be analyzed individually prior to investment decision. It was also concluded by this research that the proposed assessment methodology can be used for future research on other listed Hub features, albeit with the constraint that primary data will be required when secondary research data is not available.

High penetration of wind energy requires innovations in different areas of power engineering. Methods for improving wind energy and power system interconnection, control, and operation are proposed in this dissertation. A feed-forward transient compensation control scheme is proposed to enhance the low-voltage ride-through capability of wind turbines equipped with doubly fed induction generators. Stator-voltage transient compensation terms are introduced to suppress rotor-current overshoots and torque ripples during grid faults. A dynamic stochastic optimal power flow control scheme is proposed to optimally reroute real-time active and reactive power flow in the presence of high variability and uncertainty. The performance of the proposed power flow control scheme is demonstrated in test power systems with large wind plants. A combined energy-and-reserve wind market scheme is proposed to reduce wind production uncertainty. Variable wind reserve products are created to absorb part of the wind production variation. These fast wind reserve products can then be used to regulate system frequency and improve system security.

La thèse concerne l'instabilité des couches minces et en particulier à la délamination des couches sur substrat rigide. La première partie du travail s'intéresse aux contraintes résiduelles dans les couches minces de molybdène déposées par pulvérisation cathodique. Elle a permis d'étudier et développer des couches fortement compressives pour la délamination. Dans la seconde partie du travail ces couches fortement contraintes sont utilisées pour provoquer la délamination par cloquage d'un empilement contenant une interface faible. La propagation ainsi que la morphologie des délaminations ont été étudiés. Les paramètres qui affectent la morphologie des délamination sont identifiés et permettent la construction d'un diagramme de phase. Dans la dernière partie du travail un modèle numérique couplant flambage d'une plaque mince et zone cohésive est développé afin de modéliser le phénomène de délamination par cloquage. Les résultats obtenus par la méthode des éléments finis sont en accord avec les expériences.

Avec le développement de l’éolien, les prescriptions techniques de raccordement de cette technologie obligeront le maintient de sa connexion lors d’incidents sur la tension du réseau électrique. L’enjeu pour le gestionnaire du réseau est de pouvoir utiliser tous les générateurs pour garantir la stabilité du système électrique.A partir d’un modèle dynamique d’une éolienne à base de Machine Asynchrone à Double Alimentation (MADA), une commande vectorielle améliorée a été proposée en prenant en compte la dynamique du flux statorique engendrée par la chute de tension. Les performances supérieures en terme de maintient de la production ont été établies par comparaison avec la méthode de commande classique. Son domaine d’utilisation a été également déterminé.Pendant les creux de tension importants, une protection matérielle (crowbar) est implémentée avec un contrôle de la démagnétisation de la MADA. En outre, de la puissance réactive peut être produite à la fois par la MADA et par le convertisseur connecté au réseau électrique au cours de la défaillance du réseau.Un contrôle vectoriel à hystérésis des courants pour les deux convertisseurs électroniques multiniveaux est proposé et évalué pour améliorer la réponse dynamique de ces convertisseurs et pour réduire les effets des variations des paramètres sur les performances de la commande. Selon la durée du défaut, des objectifs différents de contrôle doivent être réalisés en priorité pour empêcher des surintensités rotoriques et pour fournir de la puissance réactive. Une reconfiguration complète du dispositif de commande de cette éolienne est détaillée pour renforcer le maintient de la production éolienne lors de défaillances / With the massive development of wind energy, the technical requirements for connecting this technology will require the improvement of the fault ride-through capability of grid-connected wind turbines. The task for the grid system operator is to use all generators to ensure the stability of the electrical system.From a dynamic model of a Doubly Fed Induction Generator (DFIG) based wind generator, an improved vector control has been proposed by taking into account the dynamics of the magnetic flux, which are generated by the voltage dip. The higher performances have been established by comparison with the conventional control method. The operation domain was also determined.During serious voltage dips, a hysteresis control scheme of the active Crowbar is proposed to protect the system within a demagnetization method of the DFIG. Moreover, additional reactive power can be produced both by the MADA and the grid-side converter in order to support the electric network during the grid fault.A space vector hysteresis current control strategy of both three-level converters is proposed to improve the dynamic response of the system and to reduce the parameter variation effects on the control performanceDepending on the grid fault duration, different control objectives have to be achieved with priority to restrain the rotor over-current or to supply reactive power. Then the reconfiguration scheme of the control strategies of high power DFIG wind turbine system is proposed to enhance the fault ride-through capability of the DFIG system. With this specific methodology, the DFIG can stay connected and can supply maximal reactive current during voltage dips to help voltage recovery

Les variateurs de vitesse modernes sont exclusivement basés sur l’utilisation de moteurs triphasés alimentés par des onduleurs à modulation de largeur d’impulsion (MLI). La plupart des applications modernes de la variation de vitesse, comme les ascenseurs, les grues et les machines-outils sont caractérisées principalement par un rapport élevé entre la puissance crête et la puissance moyenne et une forte demande de freinage à la puissance nominale. Dans les variateurs de vitesse ordinaires, l’énergie de freinage, qui est de l’ordre de 30 à 50% de l’énergie consommée, est dissipé dans une résistance. Outre les problèmes « énergétiques », les interruptions et dégradations de la tension d’alimentation ainsi que la qualité du courant d’entrée et la fluctuation de la charge, sont d’autres questions à aborder et à résoudre.Le super-condensateur dédié aux applications de conversion de puissance est ainsi proposé. Un variateur de vitesse équipé avec des super-condensateurs est présenté dans la thèse. Les super-condensateurs, interconnectés par un convertisseur DC-DC sont utilisés pour stocker et ré-injecter l'énergie de freinage. De plus, le convertisseur DC-DC contrôle le courant du redresseur et la tension du bus DC. Le THD du courant d’entrée est ramené à 30%. La tension du bus DC est élevée et en permanence contrôlée et lissée indépendamment de la charge et de la variation de la tension réseau. Pour terminer, les pics de puissance peuvent être lissés. La solution présentée est analysée théoriquement et vérifiée par un ensemble de simulations et expérimentations. Les résultats sont présentés et commentés / Modern controlled electric drives are exclusively based on three-phase motors that are fed from three-phase pulse width modulated (PWM) inverters. Most of modern controlled electric drive applications, such as lifts, cranes and tooling machines are characterized by high ratio of the peak to average power, and high demand for braking at the rated power. In ordinary drives, the braking energy, which represents 30-50% of the consumed energy, is dissipated on a braking resistor. Apart from the “energetic” issue, the mains interruption and degradation, the input current quality and the load fluctuation are additional issues to be addressed and solved.The ultra-capacitor dedicated for power conversion applications has been discussed. In comparison to electrochemical batteries, the ultra-capacitors have higher power density and efficiency, longer life time and greater cycling capability. This makes the ultra-capacitor an excellent candidate for power conversion applications.A new electric drive converter equipped with the ultra-capacitor is presented in the dissertation. The ultra-capacitor with an inter-connection dc-dc converter is used to store and recover the drive braking energy. Moreover, the dc-dc converter controls the rectifier current and the dc bus voltage. The drive input current THD is reduced to 30%. The dc bus voltage is boosted and controlled constant and ripple free regardless on the load and the mains voltage variation. Moreover, the drive input peak power can be smoothed. The presented solution is theoretically analysed and verified by set of simulations and experiments. The results are presented and discussed