Grid connection of wave energy is one of the crucial remaining areas of development towards the commercialization of this renewable energy technology. One of the major challenges with the grid connection of the wave energy technology is power variability. The rapidly changing voltage and power production from very high peaks to lows, increases the complexity for the wave farm developers to reach an agreement with the grid owners to satisfy the grid compliance. Correspondingly, electrical network designs of the offshore wind sector also differ on some key features which includes the power variability, cable lengths, power ratings, connection layouts, sea depths and transmission distances. These differences present new challenges to engineers in adapting technology and knowhow from the wind industry wherever applicable; whereas in parts of the network where power ratings are <2 MW, new designs need to be derived. Hence, power system dynamic modelling of variable emerging wave energy puts a great field of research. CorPower Ocean AB is in the process of developing a 300-kW point absorber type Wave Energy Converter (WEC) that is a commercial fullscale prototype. In this regard, the thesis will discuss the topics of optimization of offshore wave energy electrical networks for farms primarily focused on a 10 MW rating. The modelling for RMS simulation, network efficiency, voltage profile and power quality analysis has been simulated on DIgSILENT PowerFactory. Grid connection compliance for voltage levels, voltage flicker and power factor has been evaluated against local site regulations and parameters for optimal efficiency and better power quality with respect to grid connection is discussed. The impact of grid impedance angle and the wave front incidence angle on the rating of wave farm being connected is also evaluated. The study leads to an optimized electrical layout of a wave farm which can tackle problems such as voltage flicker and varying power. The study also leads to the understanding of better layout for the point absorber with least transmission losses. This study can also be generalized for bigger wave farms in the future which will reduce the complexity and time for wave farms engineers while planning.

Ce travail s’intéresse à l’étude d’un système de pompage turbinage à vitesse variable avec une machine asynchrone doublement alimentée face aux perturbations de réseau électrique. L’objectif est d’assurer la continuité de service de cet élément stabilisateur de réseau électrique de sorte qu’il reste connecté au réseau même en cas de perturbations. Le contrôle du système dans les différentes phases de fonctionnement en mode sain a été tout d’abord développé ainsi qu'une étude de stabilité de système utilisant l’analyse modale. Les différents outils nécessaires pour cette analyse ont été tout d’abord mis en oeuvre. Ensuite, les limites de stabilité du système ont été étudiées tenant compte de la variation de longueur de ligne. Le comportement du système en présence des défauts a été par la suite étudié. Les défauts de réseau considérés sont les défauts symétriques et les défauts asymétriques. Une solution basée sur la modification de la stratégie de contrôle a été adoptée pour le cas des défauts symétriques et une solution basée sur l’ajout d’éléments au circuit de puissance a été adoptée pour les cas des défauts asymétriques. Un dispositif expérimental de 4kW a été mis en oeuvre pour la validation des développements menés dans le cadre de cette thèse. / This work focuses on the study of a variable speed pumped storage system based on a doubly fed induction machine in case of grid disturbances. Thus the main objective is to improve the fault ride through capabilities of this grid stabilizer and to guarantee its connection with the grid even under disturbances. The system control in the different operating phases in healthy conditions is developed and then a system stability study is conducted using the eigenvalue analysis. The system stability limits have been investigated taking into account the variation of grid line length so the grid impedance variation. Then the system behavior under disturbances is analyzed. Theconsidered grid faults are symmetric and asymmetric faults. The investigated fault ride through capabilities of the pumped storage system consist of two solutions, one based on the modification of the control strategy was adopted for the symmetric faults and one based on hardware modification has been adopted for the asymmetric ones. A 4kW laboratory set-up has been developed for experimental validation.