Evaluating the inherent cyber resilience of inverter-based microgrids against PLL attacks under fault conditions

Recently, the concept of inherent cyber resilience has emerged, advocating the use of passive mitigation strategies that leverage the natural dynamics of microgrid components. Prior work has demonstrated that when the phase-locked-loop (PLL) of a grid-following (GFL) inverter is under attack, reducing the droop gain of the closest located grid forming (GFM) inverter effectively mitigates the exhibited voltage sags due to routine load changes. Building on this foundation, this paper first investigates the impact of PLL attacks under major disturbances, such as electrical faults. Simulation studies reveal that fault-induced effects can be magnified, leading to more severe voltage drops, increasing the risk of generator disconnection or even systemwide blackout. Second, it is shown that reducing the droop gain of the GFM inverter effectively restores fault responses to levels observed in an uncompromised system, enhancing system robustness and demonstrating that the concept of inherent cyber resilience remains effective even under fault scenarios.