The high-voltage AC-DC-AC power system has large offshore wind farms connected to the offshore AC substation. This offshore AC substation is then connected to the AC grid, which is located on the mainland through the High Voltage Direct Current (HVDC) link. The main function of this whole power system is to transfer the injected AC effective power produced by the wind generation into the AC grid where the end users are connected. However, this transfer is imperfect since a power fraction is either locally stored at the line inductances or is dissipated at the line resistances. Thus, these two contributors of power loss, particularly for a long HVDC link, have to be considered in detail to control the full dynamics accurately. The thesis focuses on the development of a complete method for generating and tracking fast trajectories which allow shifting the operation point of a high voltage AC-DC-AC power system within a short time interval (time scale in the order of 10ms or half of the AC period) without exciting additional transients after reaching the operation point. It is important to note that the full system is controlled by three converter stations placed at the beginning, middle, and end of the system. These converter stations are where the inputs that drive the dynamics act. When considering a high voltage AC-DC-AC power system with a conventional rectifier and the modern converter topology known as Modular Multilevel Converter (MMC) as the inverter along with their corresponding internal dynamics, the control of the system becomes more complicated as a result of the increasing number of state variables that are coupled to each other. Given the complexities of the system under consideration, there is a high possibility of generating an undesirable transient at the final state when the system is driven from one state to another. Therefore, the trajectory design has been carefully developed in order to generate the input needed to achieve a smooth transition to a new steady state without causing any transient and, if possible, in a short time interval. This framework lends itself well for developing a stabilizing feedback that is capabale of compensating for small deviations from the desired operation point. Moreover, the technique described in this thesis is applicable not only to the conventional converters but also to the modern converter topology of MMC, and is very promising for future applications involving a sudden voltage drop in a short time.     «

The high-voltage AC-DC-AC power system has large offshore wind farms connected to the offshore AC substation. This offshore AC substation is then connected to the AC grid, which is located on the mainland through the High Voltage Direct Current (HVDC) link. The main function of this whole power system is to transfer the injected AC effective power produced by the wind generation into the AC grid where the end users are connected. However, this transfer is imperfect since a power fraction is either l...     »