Stability Analysis of Wind Turbines under Small and Large Disturbances

The development of various wind turbine concepts in the last decade has been very dynamic and has replaced conventional power generation sources such as coal. As a result, large-scale onshore and offshore wind farms, incorporating hundreds of wind turbines, are increasingly being built across Europe. Nevertheless, the interactions between wind turbines in the same wind farm as well as between wind turbines and the grid have created new challenges to network stability. It is of utmost importance to figure out the sensitivity of wind turbines to different types of disturbances and to understand the control strategies based on grid-forming and grid-following converters.The terms of small and large disturbance in converter-based resources - such as wind turbines - are the same as in traditional power systems with synchronous generators. In small disturbances, the equations that describe the dynamics of the system may be linearized for the purpose of analysis; in large disturbances, linearization is not feasible. Small disturbances can be small load changes like switching on or off small loads, line tripping and small generators tripping, whereas large disturbances can be faults, switching on or off large loads and large generators tripping. This PhD project focuses on the modeling of multi-timescale control dynamics of wind turbines under small and large disturbances of the offshore power network. The ultimate goal of this extended research is a control-design-oriented wind turbine model, which will be capable of characterizing the small-signal and transient stability. The grid-connected voltage-source converter (VSC) of the wind turbine model is the main element of study in this research.