Communication-based distributed secondary control is deemed necessary to restore the state of islanding AC microgrids to set points. As its limited global information, the microgrids become vulnerable to cyber-attacks, which by falsifying the communicating singles, like the angular frequency, can disturb the power dispatch in the microgrids or even induce blackout by pushing the microgrids beyond the safe operation area and triggering the protection. To make the microgrids more cyber secure, adaptive resilient control for the secondary frequency regulation is proposed. It assumes that each converter is communicating with its adjacent converters. With the proposed control, the weight of the communication channel being attacked is automatically reduced, and the more the communicating signals are falsified, the further the weight of that communication channel is weakened. The proposed approach does not rely on attack detection and thereby is easy to implement; Besides, it still works when challenged by a combination of multi-attack signals; Moreover, it applies to multiple communication lines getting attacked cases. Finally, the effectiveness and feasibility of the proposed resilient control scheme are validated by both simulations and experimental results.

In multi-inverter parallel connected islanded micro-grids, reactive power sharing is challenged by the differences in feeder impedance and various controller parameters. In order to address this issue, a virtual impedance reshaping strategy based on the consensus algorithm is proposed in this paper. The proposed method facilitates adaptive modulation of virtual impedance to ensure that it is consistent with the desired value. Notably, the method has the advantage of accurate reactive power sharing even in the presence of communication delays and interruptions. Furthermore, the proposed strategy exhibits resistance to malicious cyber-attacks by integrating an auxiliary controller that reconstructs the propagated information in the face of cyber threats that challenge the integrity of the original signal. Furthermore, this paper introduces an exit strategy that enables data exchange during the system construction phase and subsequently fixes the virtual impedance proportionally. This feature significantly reduces the communication burden. The effectiveness of the proposed control strategy is evaluated through several experimental cases, including accurate reactive power sharing and plug-and-play capability.

Reinforcement of the legacy grid infrastructure will be very costly and thereby unrealistic. Consequently, weak grid connection of electric vehicle (EV) chargers will sooner or later be the case. It may however bring instability issues since the EV chargers that can work well in strong grid conditions usually do not fit the weak grid conditions. Aiming at design guidelines, this digest analyzes the influence of the charger's design on the stability of the grid connection. Simulations and experiments are carried out to verify the analysis results.