The aim of this study is to present, compare and improve the options of power transmission for tidal current arrays. The potential to generate low or zero carbon power from the world’s tides is increasing as technology moves forward. The technically available tidal current energy resource, the resource that can be captured using existing technology, in the United Kingdom can supply a significant amount of the UK electricity demand. Even though tidal current devices have similarities to offshore wind turbines in many aspects, a number of characteristics differentiate the approach needed regarding power transmission and drive-train design. Some of these characteristics are: predictable direction and speed of the tidal current, predetermined available area in a tidal channel, less swept area due higher density of water, continuous underwater operation and smaller distances to shore. This thesis is based on the hypothesis that tidal current energy can be harnessed using today’s technology in an efficient manner. Technology progression never stops and as new materials and methods become available the cost of utilising tidal current energy will drop in the years to come. However, the research question that has to be asked is whether using today’s technology tidal arrays can be an alternative source of electrical power. In order to respond to this research question electromechanical models of tidal current devices have been developed in detail, from resource to the grid connection, using mathematical linear and non-linear programming in MATLAB/Simulink. The tidal models developed include the tidal resource, the tidal turbine with pitch control, geared induction and synchronous generators, the power electronics with the generator controller, the grid side controller, the cables for power transmission, the filters and the grid connection. All the modelling aspects of this study are presented in Chapter 3. Single tidal current devices were compared using different generator technologies, squirrel cage induction generator or permanent magnet synchronous generator, and different location of the power converters, in the nacelle near the generator or many kilometres apart from the generator. Regarding the generator technology, results showed that even though differences are minor, the permanent magnet synchronous generators are more efficient. Regarding the location of the power converters results showed that positioning the power converters in the nacelle always yields fewer electrical losses but component accessibility is minimised due to the underwater operation of the tidal current device. A key focus aspect of the study is the power transmission option with onshore converters which is presented in detail. Using this concept it is possible to generate electricity from tidal current devices but at the same time keep the highest possible system reliability despite the continuous underwater operation. This concept has been used in the first demonstration tidal current arrays developed by Andritz Hydro Hammerfest. What is more, data provided by Andritz Hydro Hammerfest were utilised in order to validate the simulation models. In this study a step forward is taken regarding the concept of keeping the converter dry and controlling the tidal current generator from afar. An algorithm is developed to design power harmonic filters for systems that use long distance controls. Power harmonic filters allow the long distance control system to operate reliably under all conditions but generate significant electrical losses. The power harmonic filter design algorithm presented in this thesis estimates the exact filter parameters so that the filter ensures maximum system reliability and generate minimum possible losses. In addition tidal array topologies using this concept are developed. The final part of this thesis compares a number of different tidal array topologies based on resource to grid efficiency and component accessibility for maintenance. Results showed that when tidal current devices are clustered per four turbines on offshore platforms it is efficient to use as many clusters as possible connected to a single cable whose both ends are connected to the grid. Locating the power converters in the nacelle yields fewer electrical losses compared to locating the power converters on the offshore platform. However, the difference is minimised because the distance between the tidal current device and the offshore platform is the least possible. Having the power converters on an offshore platform is beneficial in terms of accessibility for maintenance and operation because they are not underwater. The results and the methodology from this thesis can be extended to other offshore renewable energy systems such as the wind and wave. In addition, this study can be used as a stepping stone for decision making by tidal current developers.

Analyse de la diversité inter et intra-spécifique des paramètres de l’architecture des systèmes racinaires chez les Solanacées. Les racines des plantes jouent un rôle important pour garantir productivité et résistance à de nombreux stress. Dans le nouveau contexte agricole, l’importance de ce système racinaire et de sonarchitecture sont remises au premier plan. Notre étude porte sur la dynamique de l’architecture racinaire des solanacées, qui contient un ensemble d’espèces horticoles importantes pour l’alimentation. Notre travail porte sur 32 génotypes, parmi 3 groupes d’espèces: aubergines, piments et tomates.Dans cette étude, nous proposons tout d’abord une analyse de la diversité inter et intraspécifique de l’architecture racinaire à travers l’évaluation d’un ensemble de traits qui sont aussi les paramètres d’un modèle dynamique de simulation (ArchiSimple : Pagès et al, 2012). Cette première évaluation a été faite en pots, en utilisant un milieu très favorable à la croissance des plantes et à l’enracinement. Nous montrons que les traits racinaires choisis présentent en effet des variations d’origine génétique, généralement plus fortes entre espèces qu’au sein des espèces. Nous avons également observé des corrélations entre certains traits qui révèlent des compromis ou des coordinations dans les processus de développement.Pour aller plus loin dans la signification des traits racinaires choisis et leur stabilité vis‐à‐vis des conditions environnementales, nous avons également évalué ces traits en conditions de culture hydroponique. C’est un milieu reconnu comme radicalement différent, intéressant pour les possibilités de visualisation des racines qu’il offre. Un dispositif avec des rhizotrons hydroponiques a été construit spécifiquement pour cette expérimentation. Nous avons confirmé, dans ces nouvelles conditions, les différences d’origine génétique entre les différents génotypes utilisés. De plus, nous avons comparé de manière systématique les valeurs de traits mesurés avec celles de la précédente expérimentation. Certains traits se révèlent stables ou très corrélés (e.g. diamètres, distances interramification)alors que d’autres présentent des différences beaucoup plus fortes (e.g. vitesses de croissance, vitesses d’émergence des racines adventives).Une troisième expérimentation, utilisant différentes combinaisons de greffage entre génotypes, nous a permis d’approfondir la question du contrôle des traits par des interactions au sein de la plante: soit à courte distance au sein du système racinaire, soit à plus longue distance parle système aérien. Deux traits importants ont été étudiés (le diamètre apical et la densité de ramification) en utilisant des combinaisons de génotypes ayant des valeurs contrastées par rapport à ces traits. Il en ressort des réponses très différentes, avec un effet marqué du greffon sur les111RésuméBui H.H. (2015), Diversité inter- et intra-spécifique des paramètres racinaires chez les Solanacées diamètres, révélant qu’une partie au moins du contrôle de ce trait est effectuée par le système aérien, et un effet faible ou inexistant du greffon sur la densité de ramification, révélant un contrôle local de ce trait, par des interactions à courte distance entre les racines. Cette expérimentation par greffage a montré un potentiel très intéressant pour mettre en lumière divers mécanismes de contrôle des traits au sein de la plante entière.Cette étude mérite d’être prolongée par des analyses plus systématiques des déterminismes de variation des traits de l’architecture racinaire, et par des simulations par modèle qui permettront de synthétiser les conséquences des variations de traits sur les performances globales des systèmes racinaires pour la prospection du sol. / Analysis of the inter and intra specific diversity of the parameters of the root system architecture in the Solanaceae.Plant roots play an important role to ensure the productivity and the resistance to manystresses. In new agricultural context, the importance of root system and its architecture are placed tothe forefront. Our study focuses on the root architecture dynamics of Solanaceae, which contains aseries of important horticultural species for the alimentation. Our work was based on 32 genotypesbelonging to three groups of species: aubergines, capsicums, and tomatoes.In this study, we propose firstly an analysis of inter‐ and intra ‐ specific diversity of rootarchitecture through evaluating a set of traits which are also the parameters of a dynamic simulationmodel (ArchiSimple: Pagès et al, 2012). The experiment in pots with a very favorable condition forplant growth and rooting was conducted for the first evaluation. It showed that the selected roottraits present an effect of genetic ‐ originated variations and this effect is usually stronger amongspecies than within species. We also found correlations between certain traits, which revealcompromises or coordinations in the developmental processes.In order to go deeper into the signification of selected root traits and their stability toenvironmental conditions, we also evaluated these traits in hydroponic culture. This environment isradically different, and interesting for its possibilities to visualize the roots. An experimental setupwith hydroponic rhizotrons was specially built for this experiment. In the new conditions, the genetic‐ originated differences between different genotypes used also were found. In addition, wecompared systematically the traits values with those of the previous experiment. Certain traits arestable or highly correlated (e.g., apical diameter, inter‐branch distance), while others are muchdifferent (e.g., root growth rate, emission rate of adventitious roots).In a third experiment, we used different grafting combinations between genotypes todeepen the question of the control of root traits by interactions within plant: either short distancecontrol within root system or long distance control by aerial system. Two important root traits (apicaldiameter and branching density) have been studied by grafting between genotypes which havecontrasting values on these traits. The different responses appear: a significant effect of scion ondiameters, which indicate that at least of this trait is controlled by shoot system, and a weak effect orno effect of scion on branching density, revealing the local control of this trait, by short distanceinteractions between the roots. This experiment showed a great potential of grafting to highlightvarious control mechanisms of root traits within whole plant.AbstractBui H.H. (2015), Diversité inter- et intra-spécifique des paramètres racinaires chez les Solanacées 113This study deserve to be extended by more systematic analysis of determinisms of variationsof root architecture traits, and by using simulation model which allow to integrate the consequencesof traits variations on global performances of root system for prospecting of soil.