During the last century, technological advances have deeply renewed many critical infrastructures, such as transportation networks and power systems. In fact, the strong interconnection between physical process, communication channels, and control systems have led to the new concept of cyber-physical systems.
Next to countless new advantages, these systems unfortunately have also new weaknesses. An example is cyber-attacks: malicious intrusions into the communication channel turned to manipulate data. In this thesis the considered cyber-physical system is a power network where hundreds of eld devices are connected to a control center, which collects data and controls the whole system. A cyber-attack where the adversary model is based on the attacker's knowledge of the network topology and line parameters is considered. This work is focused on one of the features of the control center: the state estimator. After a preliminary analysis of the conventional state estimators with respect to cyber attacks constructed according to this adversary model, new ideas for improving the security of the system are presented. The aim of this thesis is to propose novel state estimators that are both accurate under no cyber-attack, and at the same time able to detect attacks that are undetectable by the conventional state estimator. This mainly involves introducing additional information about the system as constraints in the state estimator, under the assumption that the new information is not available to the adversary.
At the end of the analysis of the new mathematical model of the state estimators, a new denition of undetectable attack is proposed. The functionality of the novel state estimators is demonstrated in numerical experiments, which have been performed on dierent benchmark power networks.
2014. , 113 p.