  This paper develops a fully distributed attack-resilient secondary defense
strategies for AC microgrids, addressing more generally unbounded attacks on
control input channels than those addressed in existing literature. The
secondary control of local inverter includes consensus-based voltage and
current regulators utilizing relative information from neighboring inverters.
This distributed control approach relies on localized control and a sparse
communication network, making it susceptible to malicious cyber-physical
attacks that can impair consensus performance and potentially destabilize the
overall microgrid. In contrast to existing solutions that are limited to
addressing either bounded faults, noises or unbounded attacks with bounded
first-order time derivatives, we aim to surpass these constraints and enhance
the defense capabilities of counteracting cyber-physical attacks by enabling
the AC microgrids adopting the proposed strategies to withstand a much wider
range of unbounded cyber-attack signals. Fully distributed attack-resilient
secondary defense strategies are developed for AC microgrids to counteract the
detrimental effects of generally unbounded attacks on control input channels.
Rigorous proofs using Lyapunov techniques demonstrate that the proposed defense
strategies accomplish the uniformly ultimately bounded convergence on frequency
regulation and achieve voltage containment and active power sharing
simultaneously for multi-inverter-based AC microgrids in the face of generally
unbounded attacks. The proposed defense strategies are validated on a modified
IEEE 34-bus test feeder benchmark system incorporating four inverter-based
DERs.
