Robust Dynamic Watermarking for Cyber-Physical Security of Inverter-Based Resources in Power Distribution Systems

Grid-connected inverter systems that are important for increased utilization of renewable energy are vulnerable to cyberattacks. Malicious agents can attack a system by providing false measurements of sensed signals, such as power available/generated, or the grid current to sabotage the inverter control system. To defend against such attacks, we propose a technique of dynamic watermarking that superimposes a small secret signal onto the actuator signal and raises an alarm when the purported measurement data returned from the sensors do not contain appropriate transformations of the secret watermark. In this article, a robust attack detector is introduced, which does not require either knowledge of the variance of the ambient sensor noise or a model of the system. We develop an additional test that is not only impervious to sensor noise variance but can also be used to distinguish malicious attacks from sensor unreliability due to changing levels of sensor noise. We also show that a data-driven system identification of the switching inverter system can be employed in the dynamic watermarking tests. We present both simulation and experimental results from a grid-connected photovoltaic (PV) system, which show that the resulting robust dynamic watermarking method can detect malicious attacks on inverter control systems.