Optimal Transmission Switching in Power Systems with Large-scale Renewable Resources

In the past decade, there has been a rapid growth for renewable generations in power systems worldwide. However, the natural intermittency of wind and solar causes a variable output for renewable generations in power systems. Under this new situation, the optimal network topology of a power system can vary with time. This research focuses on an emerging topology control technology, optimal transmission switching, to improve the flexibility and efficiency of power systems with large-scale renewable generations. Novel optimization and stability enhancement approaches for optimal transmission switching are developed considering the grid uncertainties caused by the highly variable renewable generations and load fluctuation. Three major problems of optimal transmission switching are resolved in this research. First, novel optimization approaches are developed to calculate accurate switching plans for optimal transmission switching actions. Different from the existing approaches, the proposed approaches are focused on the alternating current optimal power flow for a better accuracy. New elements like renewable generations and energy storage devices are included in the optimization problems. In addition, grid uncertainties are taken into consideration and stochastic programming is used in the decision-making process. A scalable decomposition approach is proposed to solve the stochastic programming problem of the alternating current optimal power flow based optimal transmission switching. Second, transient stability issues in the transmission switching actions are investigated and transient stability enhancement methods are proposed. And a new transient stability index, critical switching flow, is proposed for transmission switching actions. Based on the new quantitative index, a preventive stabilizing redispatch scheme is developed. The proposed scheme considers the grid uncertainties in the day-ahead planning and can be applied to avoid unstable switching actions in the online operation. Third, the cyber-security issues associated with transmission switching actions are analyzed. The potential threat of false data injection attack is discussed. The cyber-attack may compromise the state estimator and make a risky switching action stable in the online stability check. As a result, a catastrophic instability will be led by the cyber-attack. The countermeasure is given to defend the cyber-attack. Numerical results on the different test systems justify the proposed approaches in this research. The developed approaches will facilitate the implementation of optimal transmission switching in the real world