Multiplicative Watermarking for Replay Attack Detection in Distributed DC Microgrids

In distributed energy systems and networked control systems, the integration of communication layers increases vulnerability to cyber-attacks, which can lead to severe operational consequences. Watermarking has emerged as a prominent solution for detecting cyber-attacks. This paper investigates a multiplicative watermarking scheme based on sensor output to address replay attacks in distributed DC microgrids. The proposed scheme employs a pair of finite impulse response (FIR) filters to encrypt and decrypt the sensor output, integrated with unknown-input observers (UIO) for attack detection. Theoretical analysis demonstrates how the multiplicative watermarking enhances the observer's ability to detect attacks by amplifying residual signals. The effectiveness of the proposed method is validated through simulations on a four-area DC microgrid system.