  This paper presents a new distributed control framework to coordinate
inverter-interfaced distributed energy resources (DERs) in island microgrids.
We show that under bounded load uncertainties, the proposed control method can
steer the microgrid to a desired steady state with synchronized inverter
frequency across the network and proportional sharing of both active and
reactive powers among the inverters. We also show that such convergence can be
achieved while respecting constraints on voltage magnitude and branch angle
differences. The controller is robust under various contingency scenarios,
including loss of communication links and failures of DERs. The proposed
controller is applicable to lossy mesh microgrids with heterogeneous R/X
distribution lines and reasonable parameter variations. Simulations based on
various microgrid operation scenarios are also provided to show the
effectiveness of the proposed control method.
