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Thesis

Master thesis presented:

Saliency-based sensorless control for AC induction machines in wind applications by Geber Villa
Abstract: The master thesis explores the uses of saliency-tracking methods for the sensorless control of induction machines in wind applications in the low speed region. The study is focused on a feasibility analysis of the technique under the typical speed/load conditions. In order to improve the system accuracy as well as extended load operation, decoupling of saturation-induced saliencies is also considered.
Thesis Supervisor: Pablo García Fernández.
Master Course in Electrical Energy Conversion and Power Systems at the University of Oviedo.

Techno-economic analysis of different repowering possibilities for wind turbines by Rahul Kohli
Abstract: This dissertation addresses the issue of the different repowering possibilities for wind turbines, the work was carried out from both technical and economic standpoints to analyze the opportunities and challenges associated with repowering of wind farms. The main objectives were to explored the partial  repowering scenario through rotor blade extension analysis and implementation of a full power rated state of art topology in power conversion stage to existing fixed pitch turbine, the case study is based on Vestas V66 (1.65 MW). The levelised cost of energy model has been developed for partial repowering and the payback period was calculated.
Thesis Supervisor: Cristina González Morán.
Erasmus Mundus Master Course in Sustainable Transportation and Electrical Power Systems at the University of Oviedo.

Electrical energy situation analysis oriented to massive distributed generation penetration in Asturias by Jorge Palacio Sánchez.
Abstract: The aim of this project was searching for new energetic alternatives, especially renewable energies, available at Asturian region to be exploited in the electrical grid. The project aimed to propose several study cases applicable to specific prosumers in the most efficient way, to accomplish with the international commitments that Spain is supposed to reach in future. The contributions include different technical/economical solutions depending of the area of Asturias that is considered.
Thesis Supervisor: Cristina González Morán.
M.S. Industrial Engineering (electrical specialized). University of Oviedo.

Design and construction of an isolated DC to DC switching converter for integration of energy storage systems in power electronic applications 
by Sarah Saeed Hazkial Gerges.
Abstract: With the current trend towards greener energy sources, the integration of Energy Storage Systems (ESS) is the key to sustain the grid against fluctuations of energy generation. This raises a major concern for the inclusion of an efficient, fully controllable power conversion stage to allow an intermediate processing of energy flow. The Dual-Active-Bridge (DAB) converter provides full controllability as well as galvanic isolation. DC-DC Isolated conversion is a critical process in some applications such as Electric (EV) and Hybrid Electric Vehicles (HEV). Also linking ports up in a Multi-port DAB converter via multiport transformer allows for the integration of additional energy sources to the system. This converter can thus be employed in applications ranging from a front-end converter in points of common coupling at facilities, to a high power modular structure used on distribution system levels. The motivation behind the thesis is to study the Dual-Active-Bridge bidirectional dc-dc converter topology, and validate its operation for a 2kW rated power setup. A starting approach for the design procedure, covered in this work, is to employ the converter as a unidirectional power flow converter, supplying a load that resembles the behavior of a typical micro-grid, such as a resistance in parallel with a DC link. Thus, the operation of the converter at rated power can be analyzed, studied and optimized.
Thesis Supervisor: Jorge García.
Master Course in Electrical Energy Conversion and Power Systems at the University of Oviedo.

Design of a Three-port Solid State Transformer for High Power applications by Guirguis Zaki Guirguis Abdelmessih.
Abstract: In this thesis, a Three-Port Active Bridge converter for high power high voltage application is designed. The design includes the Solid state high frequency transformer, and the required reactive elements the series inductors, and the DC-link capacitors. Also the choice of the switches, and the heat sink is defended, and a design of a stack for them is made, this stack will include also the driver boards of the switches and the capacitors with the bus-bars for the DC-link. The thesis also presents a simulation for each part, and a final simulation for the real model containing almost all the losses and parasitics elements. Using simulation based tools, the design for each of the parts and the full converter assembly is achieved. The simulation includes losses calculation and considers the effects of parasitic elements. The selected design is compared versus a Half-Bridge Triple Active Port topology, in order to analyze the differences in terms of efficiency, performance and reliability. Finally a simulation is presented to illustrated the behavior of the full model under the closed loop condition.
Thesis Supervisor: Pablo García.
Master Course in Electrical Energy Conversion and Power Systems at the University of Oviedo.

Fault Detection in the DC Bus System of a Vehicle by Octavian Rotariu.
Abstract: In this thesis, the topic of fault detection in the DC and communication buses of avehicle was addressed. Typical fault detection methods were examined and the most appropriate one for the automotive DC bus was further investigated. More techniques commonly used in aviation are investigated and compared. A Matlab Simulink simulation model for reflectometry techniques (Time Domain, Sequence Time Domain, Spread Spectrum-Time Domain and a new Spread Spectrum Frequency Shift Time Domain Technique) was developed and verified experimentally for Time  Domain Reflectometry in coaxial cables and CAN twisted pair wires. Since in a fault condition an impedance variation occurs which causes different reflections of the voltage wave, it is possible to determine the fault condition and its spatial location in a cable. Different cross-correlation and wavelet analysis digital signal processing techniques were tried out.
Thesis Supervisors: Manuel Alberto Diaz Millan, Pablo García.
Master Course in Electrical Energy Conversion and Power Systems at the University of Oviedo.

Investigations on Reactive Power Compensation for a Double Active Bridge with a Planar Transformer by Javier Gómez-Aleixandre Tiemblo.
Abstract: In the future, the power system will be a set of intelligent grids (smart grids) with the generation close to the demand (micro grids). The ultimate goal will be to accomplish most of the energy demand with clean and renewable sources. The problem of this energy sources is that they are volatile, and thus the generation may not match with the demand in some instants. In order to solve this, energy storage systems are required to absorb the extra power when there is more generation than demand, and releasing it in the other case. The objective of this thesis is to study the interconnection between these grids and the energy storage with an isolated power converter. A first overview around the different possible converters is covered in order to justify the selection: a dual active bridge (DAB). The behaviour of the DAB was then explained under different situations. Especial interest is paid in the effect of the dead time in the behaviour of the converter and the excessive reactive power. Finally, a control of the power flow in this converter is tested with a variable load. It is also tested an algorithm to compensate the effect of the dead time.
Thesis Supervisor: Pablo García.
Master Course in Electrical Energy Conversion and Power Systems at the University of Oviedo.

Transient Frequency Drift Compensation on Weak AC Microgrids Using Energy Storage Interface with Interleaving Bidirectional Power Electronic Converters by Angel Navarro Rodríguez. 
Abstract: Micro-grids are without any doubt the future of electrical grids, advocating for a sustainable and efficient exploitation of the energy sources and the integration of re- newable energies. However, these grids are by nature weak grids, exhibiting a low inertia and high impedance which makes them prone to contingencies that compro- mised the grid quality and stability. The scope of this master thesis is to cover one of these contingencies consisting on the transient frequency drift that occurs when changes in the active power takes place. The low inertia of the generators that com- pose a micro-grid could cause a fluctuation in their rotor speed, which is directly related to the grid frequency due to the applied transient torque. Thus, the present Thesis is focused on the study of a solution based on Energy Storage System (ESS) for transient frequency drift compensation in micro-grids. Such study covers the design and implementation of a power topology and different control alternatives in both, simulations and in an experimental setup, demonstrating the validity of the proposed system.
Thesis Supervisor: Pablo Garcia.

Master Course in Electrical Energy Conversion and Power Systems at the University of Oviedo.

A Detailed Study of Power Flow Solution Techniques with the Inclusion of Distributed Generations and Unbalanced Loads to a Power Network by Therese Uzochukwuamaka Okeke.
Abstract: Owing to the frequent changes to power system networks in recent times, continuous studies are encouraged to ensure short, medium or long term planning & operation of any system is accurately resolved to avoid any shortcoming. This in essence, poses various challenges to power engineers as the most important and effective tool used to monitor their system stability continually encounters newer characteristics that were not previously taken into consideration, in this case, the distribution system. A well-articulated policy from various nations in the past decades, regarding global warming, depletion of conventional fuels and monopolization of rich fuels has greatly refurbished the conventional network we are accustomed to, especially at the distribution level. These policies paved way for renewable energy harnessing, which brought about advantages such as generating power at any location. While its advantages proved useful, it birthed nuisance to the engineers. Nowadays, engineers are concerned about the numerical techniques already in use for solving power flow issues as they now produce divergent solutions when used in these modernised networks.  This thesis will present and compare the various load flow techniques used, both the conventional methods and its variants, and also the recent techniques proposed. It will also present a new model recently proposed by a group of researchers that have reduced the complexity attached to modelling components of power systems.
Thesis Supervisors: Cristina González-Morán, Pablo Arboleya.

Erasmus Mundus Master Course in Sustainable Transportation and Electrical Power Systems at the University of Oviedo.

Abstract: This thesis develops a power reliability-based methodology to be used in a computer tool that assesses the selection of the most convenient power distributed-generation system in residential buildings. To do this a building power demand model is implemented by considering the dwellings’ energy consumption, the number of users per dwelling, the non-occupied periods of the inhabitants and the load’s usage pattern between others aspects. Some study cases are carried out under different scenarios to validate the proposed methodology by studying key reliability indexes that provide relevant information to infer the feasibility of the selected distributed generation. The attained results were very promising as they revealed for every case which were the most suitable power generation configurations to be employed.
Thesis Supervisor: Pablo Arboleya.

Abstract: In this thesis, I developed a computer tool which is able to simulate the electrical energy generation of different generators, such as wind turbines, PV panels, fuel cells or micro turbines, for their employment in residential buildings for self-consumption. This involved the development of the mathematical models, as well as the estimation of some weather conditions such as wind profiles and solar radiation. In addition, the economic analysis, which consists on the comparison between the traditional energy purchase and self-consumption, has been also performed. This thesis is part of a project that also covers the demand modeling and the power reliability analysis of the system. The computer tool has been succesfully tested, by simulating different study cases, obtaining good representative results.
Thesis Supervisor: Pablo Arboleya.

OPGrid: Software Tool Development for Transmission Networks Analysis by Bassam Mohamed
Abstract: This thesis is focused on developing power flow solver based on Matlab tools. The solver is used to investigate the steady state of transmission network under different cases of demand variation. The solver is designed to be flexible and able to handle standard data format for exchanging input and output with other software tools. The active power dispatch can be solved based on three mode Conventional , Optimal and Droop Control. The solver setting and case parameters are organised in single structure to be flexible for configuration and easy for exchange. New data file format is proposed to encapsulate the all case information in single file. The solver is implemented to solve multiple case of demand variation by single call which to automate the analysis process and minimise to iteration time. The mathematical equation model can be selected to be based on conventional admittance matrix or incident matrix methods. The solver results of IEEE test cases have been verified with alternative commercial and scientific tools and they satisfied the required accuracy and performance. The solver is released as open source project to support additional functionality and full customisation for scientific research.
Thesis Supervisor: Pablo Arboleya.
Master Course in Electrical Energy Conversion and Power Systems at the University of Oviedo.

Study on Active Filtering of Current Harmonics Content in Public Lighting Systems by Pablo José Quintana Barcia
Abstract: This Master Thesis is intended to propose a methodology to improve the line current THD of a given distribution line configuration, with multiple non-linear loads (in this case conven- tional line frequency public lighting systems). The control scheme avoids the use of current sensors, aiming for a low-cost implementation of the algorithm. The implementation of these active filters has been considered for a case of study of correction of the harmonic content generated by a given number of 150W HPS lamps. In addition to the HPS lamp, each lamppost has certain microgeneration capability, by means of a dedicated solar PV panel. In order to compare, different control schematics for the active filter would be stud- ied as part of the internship at the Microgrid Lab of the Department of Energy Technology at Aalborg University in Denmark: two power converters for single-phase microgrids in dq and αβ reference frame will be evaluated for the use in the proposed active filter.
Thesis supervisor: Jorge García.
Master Course in Electrical Energy Conversion and Power Systems at the
University of Oviedo.

Hybridization of Energy Storage Systems for Grid Support by Means of Bidirectional Power Electronic Converter by Ramy Georgious Zaher Georgious.  
Abstract: This thesis deals with the simulation and real-time emulation in a laboratory setup of an Hybrid Energy Storage System connected to microgirds. The association of Vanadium Redox Flow Battery and Lithium Ion battery permits to take advantage of the characteristics of both Energy Storage Systems obtaining a high energy density, high power density. A general Model of Vanadium Redox Flow Battery is developed. A Vanadium Redox Flow battery and Lithium-Ion battery are connected to DC bus and controllable loads through two bidirectional boast converter. The model of the Vanadium Redox Flow battery is implemented in MATLAB/SIMULINK R . The real-time experimental emulation of the Energy Storage System models and Hybrid Energy Storage System have been validated against PC simulations showing full consistency. The setup of the hardware can be used to test any technologies of batteries.
Thesis Supervisor: Jorge García.
Master Course in Electrical Energy Conversion and Power Systems at the University of Oviedo.


On-Going master thesis:

Voltage Regulator Modeling to Imbalance Reduction of Smart Distribution Systems using Unbalanced Power Flow Model in αβ0 Stationary Reference Frame by Md Rejwanur Rashid Mojumdar.
Thesis Supervisor: Pablo Arboleya. 

Feasibility of Wind-Hydro Power Generation System in Sweden by Chibuike Fidelis Maduko
Thesis Supervisor. Rubén Medina, Pablo Arboleya.

Design, Simulation and Experimentation of a Programmable Two Quadrants Three Phase Load by Geber Villa Fernández.
Thesis Supervisor: Pablo García.

Optimal Allocation of FACTS Devices Using Genetic Algorithm to Improve Power System Security by Shan Huang.
Thesis Supervisor: Pablo Arboleya. 


PhD. Thesis:

Unified (AC/DC) power flow applied to railway networks by Manuel Coto García
Abstract: The thesis adds adds some new contributions to the unified alternating current/direct current (ac/dc) power-flow method that is applied to railway power supply systems. These contributions are mainly focused on the way that the unified power-flow problem is implemented. The authors propose a new technique based on graph theory to model the motion of the trains without varying the system topology and dimensions, as well as the solution vector. Furthermore, a new matrix formulation is developed to provide an easy way of setting out the problem. The combination of these techniques makes the unified ac/dc power flow easier to implement, and the comparison among different instants can directly be done, representing the major contribution of this paper. Finally, as a minor contribution, a new technique based on previous matrix formulation is developed to easily obtain all active and reactive power magnitudes in compact form. 
Thesis Supervisors: Pablo Arboleya, Guzmán Díaz González.

Technical and Economical Analysis of Isolated Microgrids by Ahmed Mohamed Abd el Motaleb
Abstract: Several technical and economic analyses were conducted, re- garding microgrids, such as providing an insight about site matching suitability for droop-regulated microgrids supplied by wind generators, optimizing both energy production and economic performance for isolated microgrids supplied by wind energy and batteries and predicting some stability constraints for generation sources by small signal stability analysis. 
Thesis Supervisors: Cristina González-Morán, Guzmán Díaz González.

Abstract: In many industrial applications, may energy is lost due to the friction among the fixed and moving parts. That friction limits the relative movement speed and the accuracy and also needs for periodic lubrication. However, high speed and precision are fundamental requisites in some applications. For these reasons and due to the need of a reduced energy consumption alternatives are needed. Systems based on magnetic bearings meet these specifications, removing the need of lubrication while allowing high speed and control precision. When applied to rotational movement, there are different topologies which can affect the control system. In this thesis the different existing topologies are compared. An analysis is carried out considering different constraints: size, load capability and electrical losses. Additionally, the distribution of the electromagnetic forces being developed by each topology are analysed as well as the effects of the rotor displacement over the electromagnetic force generation.
Thesis Supervisor: Pablo García, Fernando Briz del Blanco.
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