Communication-efficient distributed secondary control for accurate reactive and harmonic power sharing in stand-alone AC microgrids under switching communication topologies

This study proposes a primary-control-agnostic, communication-efficient, fully distributed secondary-control framework for stand-alone AC microgrids (SAMGs) to achieve accurate and simultaneous sharing of reactive and harmonic power under switching communication topologies (SCTs). The proposed secondary layer relies only on locally available interface signals, including power measurements and voltage-reference channels, and is therefore not tied to a specific primary-control structure. It is instantiated and validated on inverter-based resources operated with unified hybrid control (UHC), in which grid-forming and grid-following functionalities are integrated within a single converter. In droop-controlled SAMGs, mismatched feeder impedances and mixed linear/nonlinear loads can lead to inaccurate reactive and harmonic power sharing, circulating power components, and degraded voltage quality, while SCT-induced link variations further complicate distributed coordination. To address these challenges, the proposed controller injects capacity-weighted voltage-correction signals into the primary-control reference channels through decoupled fundamental and harmonic compensation paths. A dual-threshold event-triggered communication mechanism, combining a state-relative term with a time-decaying offset, reduces redundant neighbor-to-neighbor transmissions while preserving coordination performance. A Lyapunov-based analysis establishes boundedness, consensus convergence, and exclusion of Zeno behavior under connected SCTs. Real-time OPAL-RT experiments on a four-inverter SAMG demonstrate accurate reactive and harmonic power sharing, reduced communication updates, stable voltage and frequency regulation, and robust performance under load changes, reference-power variations, voltage/frequency restoration, and plug-and-play operation.