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This thesis investigates issues affecting grid synchronisation of VSC-HVDC systems with particular regard to, but not limited to, offshore wind power generation during the complex but potentially serious behaviours following solar storms. An averaged value model (AVM) for the contemporary modular multilevel converter (MMC) based VSC-HVDC system is developed and is used in combination with different phase-locked loop (PLL) models and the unified magnetic equivalent circuit (UMEC) transformer model to assess the impacts of geomagnetically induced current (GIC) on grid synchronisation of an offshore VSC-HVDC system. GIC is DC current flowing in the earth caused by strong geomagnetic disturbance events. GIC enters the electric utility grid via the grounded transformer neutral and can cause severe saturation to transformers. This in turn causes disruptions to grid synchronisation. The main contribution of this thesis is that effects of GIC are studied using the UMEC transformer model, which can model saturation. The assessment leads to the development of enhanced fundamental positive sequence control (EFPSC) which is capable of reducing the stress on the system during GIC events. The methods developed can also be applied to other non-symmetrical AC events occurring in VSC-HVDC such as single-phase faults. Additional contributions of the thesis are:A mathematical model of the MMC is derived and forms the foundation of the AVM. The AVM is verified against a detailed equivalent-circuit-based model and shows good accuracy. The PLL is the essential component for grid synchronisation of VSC-HVDC system. Different PLLs are studied in detail. Their performance is compared both qualitatively and quantitatively. This appears to have been done for the first time systematically in the public literature. The UMEC model is verified using hand calculation. Its saturation characteristic is matched to a predefined B-H curve and is also verified. The verifications show that this model is capable of modelling transformer saturation and thus is suitable for this study. The consolidation of the AVM, PLL, UMEC, GIC and EFPSC provides an insight into the how the MMC based VSC-HVDC system behaves under severe geomagnetic disturbances and the possible methods to mitigate the risks and impacts to the power grid.

This thesis investigates the effects of High Voltage Direct Current (HVDC) lines andmulti-terminal grids on power system small-disturbance stability in the presence ofoperational uncertainties. The main outcome of this research is the comprehensiveprobabilistic assessment of the stability improvements that can be achieved through theuse of supplementary damping control applied to HVDC systems.Power systems are increasingly operated closer to stability boundaries in order toimprove their efficiency and economic value whilst a growing number of conventionalcontrolled power plants are being replaced by stochastic renewable generation sources.The resulting uncertainty in conditions can increase the risk of operational stabilityconcerns and should be thoroughly evaluated. There is also a growing necessity toexplore the potential improvements and challenges created by the introduction of newequipment, such as HVDC systems. In recent years, HVDC systems have become moreeconomically competitive and increasingly flexible, resulting in a proliferation ofprojects. Although primarily installed for power transmission purposes, their flexibilityand controllability can provide further benefits, such as the damping of persistentoscillations in the interconnected networks.This work contributes to a number of areas of power systems research, specificallysurrounding the effects of HVDC systems on the small-disturbance stability oftransmission networks. The application and comprehensive assessment of a Wide AreaMeasurement System (WAMS) based damping controller with various HVDC systemsis completed. The studies performed on a variety of HVDC technology types andconfigurations – as well as differing AC test networks – demonstrate the potential forHVDC-based Power Oscillation Damping (POD). These studies include examinationsof previously unexplored topics such as the effects of available modulation capacity andthe use of voltage source converter multi-terminal HVDC grids for POD. Followingthese investigations, a methodology to probabilistically test the robustness of HVDC based damping controllers is developed. This methodology makes use of classificationtechniques to identify possible mitigation options for power system operators whenperformance is sub-optimal. To reduce the high computational burden associated withthis methodology, the Probabilistic Collocation Method (PCM) is developed in order toefficiently identify the statistical distributions of critical system modes in the presenceof uncertainties. Methods of uncertain parameter reduction based on eigenvaluesensitivity are developed and demonstrated to ensure accurate results when the PCM isused with large test systems. Finally, the concepts and techniques introduced within thethesis are combined to probabilistically design a WAMS-based POD controller morerobust to operational uncertainties. The use of the PCM during the probabilistic designresults in rapid and robust synthesis of HVDC-based POD controllers.

The aim of the thesis was minimize the planned cost of construction of the electricity network in North Africa and the Arabian peninsula between solar power plant in Desertec project. The work is divided into three chapters. The first chapter is devoted Desertec concept, its key technologies, benefits and barriers. Another chapter is devoted to the theory of graphs. It consists of an introduction to graph theory, minimum spanning tree and Steiner tree. The third practical chapter is devoted to reduction of the initial projected cost of constructing Electric Supply network using Steiner tree and its modifications. It also addresses the issue of valuation of edges and nodes to which it is necessary to include a number of factors such as energy capacity to be transmitted, the type of transmission medium, environmental conditions, geomorphological aspects and other safety regulatory requirements.

Ingeniero Civil Eléctrico / En esta memoria se analiza el comportamiento eléctrico de una futura interconexión entre Chile y Perú, identificando inversiones necesarias que permitan una integración eléctrica segura entre ambos sistemas eléctricos de potencia. Un enlace internacional como el mencionado, presenta desde una perspectiva técnica dos particularidades a considerar. En primer lugar, la diferencia de las frecuencias de operación de ambos países (60 Hz en Perú y 50 Hz en Chile) implica que necesariamente la conexión es del tipo asíncrona mediante tecnología en corriente continua. Por otra parte, el grado de desarrollo de la red cerca de la frontera por el lado de Perú, es mayor al de Chile, donde Perú cuenta con líneas de doble circuito en 500kV hasta Moquegua, inmediatamente al norte de Tacna (150 km a la frontera). Mientras que del lado chileno se cuenta con líneas de 220 kV de simple circuito hasta Parinacota (Arica) y de doble circuito en Tarapacá y Lagunas, y próximamente Nueva Encuentro Crucero en 500 kV (a 460 km de la frontera). Mediante el uso de una base en DIgSILENT que integre ambos sistemas, se simulan los principales modos de operación, determinando el comportamiento del sistema conjunto en estado normal y ante contingencias simples, identificando las inversiones y políticas operacionales para implementar, a fin de asegurar una operación confiable y que cumpla con las exigencias de las normas eléctricas de ambos países. Se unifican los modelos de los sistemas eléctricos SING, SIC y SEIN (Perú) con un enlace HVDC entre las subestaciones Montalvo y Kimal (Nueva Encuentro Crucero) y se crean 5 distintos escenarios de operación, bajo los cuales se simulan contingencias simples para evaluar la evolución del sistema conjunto, el desempeño del bipolo HVDC y el cumplimiento de las normas técnicas. El enlace HVDC, de algo más de 610 km, junto con los refuerzos para la convergencia del flujo, representan una inversión estimada de 610 MMUSD. Mientras que para mejorar el desempeño ante las contingencias simuladas, se propone reforzar el sistema de 500 kV en ambos países. Se identificaron como peores escenarios de operación, luego de refuerzos incluidos, el de transferencia de 1500 MW desde Perú hacia Chile, y el de transferencia de 1000 MW desde Chile hacia Perú, ambos bajo hidrología seca con demanda máxima. Operar con menos centrales hídricas despachando disminuye la inercia con la que cuenta el sistema conjunto, lo que se traduce en un comportamiento degradado de la operación conjunta de los sistemas eléctricos de ambos países frente a contingencias simples. El sistema unificado soporta la caída de un polo del enlace HVDC, incluso retorna a valores de estado Normal. También es capaz de reponerse ante la desconexión de generación en la mayoría de los escenarios de operación simulados

Power Systems most often operate in the margins of stability limits. With power grids becoming even more automated now, Phasor Measurement Units (PMU’s) and Phasor Data Concentrators (PDC’s) become essential for real-time control of the system. Since PMU’s are time synchronized, the phasors can be compared at the substations, studied for any faults and analyzed at the same time. These PMU’s report the measured magnitude, phasor angle of voltages and currents in real synchronized time in different locations. One good way to measure these quantities is to use the Discrete Fourier Transform (DFT) and analyze the signal as a digital signal. However with transients and noise present in the input signal, DFT might not be the best approach for measurement and/or protection. With the IEEE C37.118 (Standard for Synchrophasor for Power Systems) 2011 version emphasizing on the importance of the two classes of PMU’s- P-class for Protection and M-class for Measurement; every vendor now has to label their products with one of these classes. There is a high precision required for P-class PMU’s whereas a good reporting rate for M-class. Recently The North-American Synchrophasor Initiative (NASPI) and Western Electricity Coordinating Council (WECC) also gave filtering specifications and frequency response of an industry compliant PMU. This thesis discusses the various frequency estimation algorithms, which are compliant with the NASPI/WECC standards. Further such an algorithm is implemented on ABB proprietary hardware and tested against dynamic tests.

The way its future power systems are designed will have significant impact on sub-Saharan Africa's (SSA) aspirations to move from low electricity consumption rates to enhance life quality and further increase economic opportunity. At present, Africa is experiencing higher economic growth rates than other continents (including Asia). And so is its need for electric power. However, all too often the options that are chosen are the ones with lowest risk and that require little coordination. In part, this is because region-wide planning, coordination and institutions are in their infancy. “Low risk” power plants typically include oil generators that can be sited close to loads, other fossil fuel power plants, and hydro plants that can easily be connected to the continent’s grid. However, hydropower production has been limited due to changes in weather and climate and socio-economic impacts. Additionally, its potential has also not been reached as large sites are far from adequate grids. A restructuring of the energy system that considers both the potential for increased geographical integration while moving gradually towards more sustainable electricity generation may hold significant promise. This work considers the potential of another renewable technology namely concentrating solar power (CSP) and connecting supply and demand centers via high voltage direct current (HVDC) power lines. Specifically, the focus is on utility-scale solar power generation to supply the needs of growing urban centers of demand. It develops a Geographic Information System-based (GIS) model with a spatial resolution of 30 arc-seconds to calculate the cost evolution of the electricity produced by different technologies of CSP plants and the costs of grid development to selected centers of demand. The results show that major SSA metropolis can benefit from distant CSP economically attractive to compete with inlaid coal-based generation. In 2010, total imports of coal exceeded 1.4 million short tons with consequent economic and environmental costs. Solar towers plants endowed with thermal storage may become a leading technology for smoothing purposes with zero fuel costs. Furthermore, Africa’s vast solar resources are far from urban centers of demand and a transmission system capable to integrate high levels of renewable energy while improving reliability of supply is required. The results of this study point to the importance of SSA centers to rely on a Super Grid approach to take advantage from CSP least-cost potential and to discontinue expensive traditional sources. Overall, solar corridors can integrate with geographically-wide wind and hydro potentials to create clean energy corridors and encourage a transition towards more sustainable energy systems.

The purpose of this thesis is to examine the potential impact of High Voltage Direct Current (HVDC) innovations on the power industry. A short historical review is provided on the so-called ‘War of the Currents’, which has placed alternating current (AC) as the dominant platform for power transmission. The revival of DC in high voltage transmission is here examined as a reverse salient, as various indicators show that the role of HVDC in the power industry seems to be constantly growing. In this thesis the potential of HVDC to drive industrial change is put to question, and an effort is made to define that change; questions are being addressed such as ‘how likely is HVDC to gain a more important role in power transmission, and what may that role be?’ and ‘how may the power market look like after a wider implementation of HVDC in power systems?’. The competition between ABB and Siemens (and at a lower level Alstom), market leaders in HVDC technologies, is analyzed with specific regard to the pursuit of inventing a HVDC circuit breaker; a technological leap that has been considered necessary for overcoming a number of obstacles to creating a DC grid. As of November 2012, ABB has developed the world’s first HVDC circuit breaker, acknowledged as a technological breakthrough. An attempt is being made to evaluate the impact of this innovation in terms of enhancing ABB’s entrepreneurial activity and granting the company with a competitive edge. Furthermore, the vision of developing DC grids – and thus R&D investments for the invention of a HVDC circuit breaker – is approached as a case of climate change being a main driving force for innovation, since this novel invention promises to make easier the integration of more renewable energy sources in power systems. This co-evolution of environment policy and innovation strategy is examined under the scope of Erik Dahmén’s theory of development blocks. Finally, ABB’s recent innovation is considered a disturbance in the system capable of bringing implications on the market that are here interpreted as a case of creative destruction, based upon Schumpeter’s terminology. In the conclusion section possible threats for Siemens and Alstom are also realized, and the need for them is questioned to go through changes in order to remain competitive, a situation that is here regarded as a case of transformation pressure.

The increasing global participation of wind power in the overall generation ca- pacity makes it one of the most promising renewable resources. Advances in power electronics have enabled this market growth and penetration. Through a literature review, this work explores the challenges and opportunities presented by offshore wind farms, as well as the different solutions proposed concerning power electron- ics converters, collection and transmission schemes, as well as control and protection techniques. A novel power converter solution for the parallel connection of high power offshore wind turbines, suitable for HVDC collection and transmission, is presented. For the parallel operation of energy sources in an HVDC grid, DC link voltage con- trol is required. The proposed system is based on a full-power rated uncontrolled diode bridge rectifier in series with a partially-rated fully-controlled thyristor bridge rectifier. The thyristor bridge acts as a voltage regulator to ensure the flow of the desired current through each branch, where a reactor is placed in series for filtering of the DC current. AC filters are installed on the machine side to mitigate harmonic content. The mathematical modeling of the system is derived and the control design procedure is discussed. Guidelines for equipment and device specifications are pre- sented. Different setups for an experimental framework are suggested and discussed, including a conceptual application for hardware-in-the-loop real-time simulation and testing.

La multiplication des projets HVDC de par le monde démontre l'engouement toujours croissant pour cette technologie de transport de l'électricité. La grande majorité de ces transmissions HVDC correspondent à des liaisons point-à-point et se basent sur des convertisseurs AC/DC de type LCC ou VSC à 2 ou 3 niveaux. Les travaux de cette thèse se focalisent sur l'étude, le contrôle et la commande de systèmes HVDC de type multi-terminal (MTDC), avec des convertisseurs de type VSC classique ou modulaire multi-niveaux. La première étape consiste à obtenir les modèles moyens du VSC classique et du MMC. La différence fondamentale entre ces deux convertisseurs, à savoir la possibilité pour le MMC de stocker et de contrôler l'énergie des condensateurs des sous-modules, est détaillée et expliquée. Ces modèles et leurs commandes sont ensuite linéarisés et mis sous forme de représentations d'état, puis validés en comparant leur comportement à ceux de modèles de convertisseurs plus détaillés à l'aide de logiciels de type EMT. Une fois validés, les modèles d'état peuvent être utilisés afin de générer le modèle d'état de tout système de transmissions HVDC, qu'il soit point-à-point ou MTDC. La comparaison d'une liaison HVDC à base de VSCs classiques puis de MMCs est alors réalisée. Leurs valeurs propres sont étudiées et comparées, et les modes ayant un impact sur la tension DC sont identifiés et analysés. Cette étude est ensuite étendue à un système MTDC à 5 terminaux, et son analyse modale permet à la fois d'étudier la stabilité du système, mais aussi de comprendre l'origine de ses valeurs propres ainsi que leur impact sur la dynamique du système. La méthode de décomposition en valeurs singulières permet ensuite d'obtenir un intervalle de valeurs possibles pour le paramètre de"voltage droop", permettant ainsi le contrôle du système MTDC tout en s'assurant qu'il soit conforme à des contraintes bien définies, comme l'écart maximal admissible en tension DC. Enfin, une proposition de "frequency droop" (ou "statisme"), permettant aux convertisseurs de participer au réglage de la fréquence des réseaux AC auxquels ils sont connectés, est étudiée. Le frequency droop est utilisé conjointement avec le voltage droop afn de garantir le bon fonctionnement de la partie AC et de la partie DC. Cependant, l'utilisation des deux droop génère un couplage indésirable entre les deux commandes. Ces interactions sont mathématiquement quantifiées et une correction à apporter au paramètre de frequency droop est proposée. Ces résultats sont ensuite validés par des simulations EMT et par des essais sur la plate-forme MTDC du laboratoire L2EP. / HVDC transmission systems are largely used worldwide, mostly in the form of back-to-back and point-to-point HVDC, using either thyristor-based LCC or IGBT-based VSC. With the recent deployment of the INELFE HVDC link between France and Spain, and the commissioning in China of a three-terminal HVDC transmission system using Modular Multilevel Converters (MMCs), a modular design of voltage source converters, the focus of the scientific community has shifted onto the analysis and control of MMC-based HVDC transmission systems. In this thesis, the average value models of both a standard 2-level VSC and an MMC are proposed and the most interesting difference between the two converter technologies -the control of the stored energy in the MMC- is emphasised and explained. These models are then linearised, expressed in state-space form and validated by comparing their behaviour to more detailed models under EMT programs. Afterwards, these state-space representations are used in the modelling of HVDC transmission systems, either point-to-point or Multi-Terminal HVDC (MTDC). A modal analysis is performed on an HVDC link, for both 2-level VSCs and MMCs. The modes of these two systems are specifed and compared and the independent control of the DC voltage and the DC current in the case of an MMC is illustrated. This analysis is extended to the scope of a 5-terminal HVDC system in order to perform a stability analysis, understand the origin of the system dynamics and identify the dominant DC voltage mode that dictates the DC voltage response time. Using the Singular Value Decomposition method on the MTDC system, the proper design of the voltage-droop gains of the controllers is then achieved so that the system operation is ensured within physical constraints, such as the maximum DC voltage deviation and the maximum admissible current in the power electronics. Finally, a supplementary droop "the frequency-droop control" is proposed so that MTDC systems also participate to the onshore grids frequency regulation. However, this controller interacts with the voltage-droop controller. This interaction is mathematically quantified and a corrected frequency-droop gain is proposed. This control is then illustrated with an application to the physical converters of the Twenties project mock-up.