| The advancements in the power grid due to integration of new technology arises concerns regarding its reliability in terms of performance and security. On one hand, the gradual shift towards renewable energy sources leads to rise in uncertainty in terms of control and demand satisfaction. On the other hand, the integration of communication devices in order to make the grid smart increases its vulnerability to malicious activity. Automatic Generation Control (AGC), which is needed to maintain the system frequency and inter-area exchange, has an important priority in both the concerns. With rising shares of renewables and retiring of fossil-fuel based generation, a grid almost entirely served by renewables is a highly possible scenario. In such cases, the impact of an attack on the grid is likely to be influenced by the effect of renewables. Although previous research conducted crucial studies of malicious cyber events on the power grid, analysis in the presence of renewables is still at a nascent stage. As a contribution, this thesis presents an attack-defense analysis on the AGC operation of the power grid under varying conditions of renewables. It has two main contributions -- determination of the influence of renewables during an attack and development of an effective algorithm for defense.;First, this thesis discusses a cyber-attack on the AGC algorithm with various levels of renewable penetration, to analyze the effect of an attack with renewables. The results confirm that the impact of a cyber-attack will be increasingly aggravated by displacement of conventional generation with renewables. Then an algorithm for AGC using a PID based approach aimed at reducing the impact is proposed. From the experiments, the proposed algorithm is shown to reduce the impact of the attack. Secondly, an algorithm for attack mitigation is designed and its performance is analyzed for both the AGC algorithms. The various factors tested are its effectiveness in reducing the impact on the system, and its adverse effects on AGC operation during normal conditions and contingency response. The results show that the algorithm could mitigate the attack without having a negative impact on normal AGC operation. The contingency response analysis shows that during events resulting in a significant change in generation-load balance, the response could be adversely affected by the mitigation. The experiments were conducted using the Power Cyber CPS security testbed at Iowa State University.;The thesis further briefly discusses the prospective research considering various developments in the power grid, renewables and attack vectors. |
