Modeling and Control of Wind Generation and Its HVDC Delivery System

As the most developed renewable energy source, wind energy attracts the most research attentions. Wind energy is easily captured far away from the places where wind energy is used. Because of this unique characteristic of the wind, the generation and delivery systems of the wind energy need to be well controlled. The objective of this dissertation work is modeling and control of wind generation and its High Voltage Direct-Current (HVDC) delivery system. First of all, modeling of the Doubly-fed Induction Generator (DFIG)-based wind farm is presented including dynamic models of the wind turbine, shaft system and DFIG. Detailed models of the rectifier and inverter of HVDC are given as well. Furthermore, a control scheme for rotor-side converter (RSC) and grid-side converter (GSC) is studied. A control method for the HVDC delivery system is also presented. Secondly, wind farms are prone to faults due to the remote locations. Unbalanced fault is the most frequent. Therefore, fault-ride through (FRT) of an ac connected DFIGbased wind farm is discussed in this dissertation. Dynamic responses of the wind farm under unbalanced grid conditions are analyzed including rotor current harmonics, torque pulsation and dc-link voltage ripples. Coordinated control strategy is proposed for DFIG under unbalanced fault. Thirdly, when a wind farm is connected to remote ac grids through HVDC, active power balance between DFIG-based wind farm and HVDC delivery needs to be obtained. In other words, the power delivered through HVDC should balance the varying wind power extracted from the wind farm. Therefore, control methods of DFIG and HVDC are modified. A coordinated control scheme is proposed to keep the power balance. The transmitted power through HVDC is regulated by adjusting the firing angle of the converter under dif-