Recent issues such as priority access of renewable resources recommended by European energy directives and increase the electricity trading among countries lead to new requirements on the operation and expansion of transmission grids. Since AC grid expansions are limited by legislative issues and long distance transmission capacity, there is a considerable attention drawn to application of HVDC transmission grids on top of, or in complement to, existing AC power systems. The secure operation of HVDC grids requires a hierarchical control system. In HVDC grids, the primary control action to deal with power or DC voltage deviations is communication-free and local. In addition to primary control, the higher supervisory control actions are needed to guarantee the optimal operation of HVDC grids. However, the implementation of supervisory control functions is linked to the arrangement of system operators; i.e. an individual HVDC operator (central structure) or sharing tasks among AC system operators (distributed structure). This thesis presents distributed control of an HVDC grid. To this end, three possible supervisory functions are investigated; coordination of power injection set-points, DC slack bus selection and network topology identification. In this thesis, all three functions are first studied for the central structure. For the distributed solution, two algorithms based on Alternating Direction Method of Multipliers (ADMM) and Auxiliary Problem Principle (APP) are adopted to solve the coordination of power injection. For distributed selection of DC slack bus, the choice of parameters for quantitative ranking of converters is important. These parameters should be calculated based on local measurements if distributed decision is desired. To this end, the short circuit capacity of connected AC grid and power margin of converters are considered. To estimate the short circuit capacity as one of the required selection parameters, the result shows that the recursive least square algorithm can be very efficiently used. Besides, it is possible to intelligently use a naturally occurring droop response in HVDC grids as a local measurement for this estimation algorithm. Regarding the network topology, a two-stage distributed algorithm is introduced to use the abstract information about the neighbouring substation topology to determine the grid connectivity. / <p>QC 20170306</p>

Les réseaux de transport d’électricité multi-terminaux à courant continu se révèlent être la solution adéquate pour une intégration massive d’énergie renouvelable dans les réseaux alternatifs existants. En effet, les réseaux en courant continu sont capables de transmettre de manière efficace des niveaux de puissance élevés sur de très longues distances par rapport aux réseaux alternatifs car, à partir d'une certaine puissance à transmettre, il existe une distance limite à partir de laquelle la transmission d’énergie en courant alternatif perd sa compétitivité face à la transmission en courant continu. L'un des principaux défis liés au développement de ces réseaux de transport d’électricité à courant continu ou Supergrid, concerne leur protection contre des défauts de type court-circuit sur des liaisons en courant continu. . Dans ce travail de thèse, un nouveau concept de stratégie de protection des réseaux en courant continu à haute tension en cas de défaut court-circuit est proposé. La stratégie repose sur une philosophie de protection ayant comme priorité la suppression du courant de défaut avant l’isolation de la liaison en défaut. Elle est basée sur l’utilisation de disjoncteurs mécaniques à courant continu sans avoir recours à des limiteurs de courant de défaut. Une séquence de protection primaire ainsi que deux séquences de sauvegarde en cas de défaillance de disjoncteurs ont été développées, testées et validées à l’aide de simulations de transitoires électromagnétiques et de simulations temps-réel. En outre, les algorithmes des relais de protection ont été implémentés avec l'aide de l’outil d’analyse fonctionnelle descendante SADT (Structured Analysis and Design System). Cette thèse a été effectuée dans le cadre du SuperGrid Institute, une plate-forme de recherche collaborative visant à développer des technologies pour les futurs réseaux de transport d'électricité et regroupant l'expertise d'industries telles que GE Grid Solutions et les laboratoires de recherche publique comme le laboratoire de génie électrique de Grenoble (G2Elab). / Multi-terminal High Voltage Direct Current (MTDC) grids,have been proven to be an adequate solution for massive integration of renewable energy power to existing High Voltage Alternating Current (HVAC) grids. Indeed, HVDC grids are capable of transmitting efficiently high level of power over very long distances compared to HVAC grids since, from a certain power to be transmitted, there is a limited distance from which the AC power transmission loses its efficiency and becomes very costly compared to DC power transmission. One of the main challenges related to the development of theses multi-terminal HVDC grids, or Supergrids, concerns their protection against DC short-circuit faults. In this thesis, a new concept of protection strategy for MTDC grids in case of permanent short-circuit fault on a DC cable has been proposed. The strategy is based on the non-selective fault clearing philosophy where the priority is given to the suppression of the fault current before isolating the faulty transmission line. The strategy is based on mechanical DC breakers and no fault current limiting devices are used. A primary protection sequence as well as two back-up sequences in case of breakers operation failure have been developed, tested and validated through Electromagnetic Transient (EMT) and Real-Time (RT) simulations. Also, algorithms to be implemented on protective relays have been designed with the help of the Structured Analysis and Design System (SADT). This PhD thesis has been performed in the frame of the SuperGrid Institute, a collaborative research platform aiming to develop technologies for the future electricity transmission network and bringing together the expertise of industries such as GE grid solutions and public research laboratories as the Grenoble Electrical Engineering Laboratory (G2Elab).