Abstract

Cyber-Physical Systems (CPS) are systems that include physical and computational
components linked by communication channels. In a Smart Grid (SG), the power plants and loads
communicate with supervisors (Central Controllers (CC)) for managing the power demand more
efficiently. As such, a smart grid can be regarded as a CPS. The computational components and
communication links of a CPS can be subject to cyber-attacks. Researchers have been exploring
detection and mitigation strategies for various types of cyber-attacks.
An important type of attack is the replay attack for which various strategies based on
watermarking signals have been proposed. One such scheme is based on switching multi-sine
waves as the watermarking signal. This thesis adapts this scheme and develops a design procedure
for detecting replay attacks for smart grids. Specifically, it examines the places in a grid where the
watermarking signal can be injected and presents guidelines for choosing the amplitude and
frequencies of sine waves that suit smart grids.
One of the drawbacks of using a watermarking signal is the additional control cost (i.e.,
decrease in performance). In the context of smart grids, watermarking results in small fluctuations
in delivered power. This thesis extends the single-input-single-output watermarking to a two-input-two-output watermarking scheme for smart grids in such a way to considerably lower grid power
fluctuations due to watermarking. The proposed method is verified using a simulated grid
connected inverter-based plants. Simulation results show that using the suggested strategy, the
effect of watermarking on the overall grid power reduces significantly.