A Method to Detect Man in the Middle Attack (MiTM) on a Grid Following PV Inverter

In this paper, a method to detect a man-in-the-middle attack (MiTM) on a grid following PV inverter is discussed. The control objective of the grid following inverter is to utilize the measurement data from the smart meter to supply the maximum available solar power at any given point to a residential load, while simultaneously preventing any reverse power flow to the grid. Now, a false data injection (FDI) attack is envisioned on the smart meter data (P and Q) communicated to the inverter by malicious actors. In such cases, the FDI can result in the inverter producing more power than the feeder load demand, resulting in reverse power flow into the grid, causing the system to disconnect. The proposed method superimposes a small randomly varying voltage with a unique signature termed as “watermark” into the input inverter DC link voltage and then checks the measurement data returned from the smart meter to contain the appropriate transformation of the secret watermark to detect any possible acts of FDI. A unique characteristic of our method is its ability to inject the watermark signal into the DC link, which is external to the PV inverter. This broadens its applicability to any commercial inverter setup. Communication protocols such as Modbus that could serve as attack points are reviewed. A Hardware-in-the-Loop (HIL) implementation reveals that the method effectively identifies FDI and unobservable FDI such as replay attacks. An experimental 3.5kW PV inverter is currently under test, with outcomes to be disclosed at a subsequent stage.