Complex Power Sharing is Not Complex

This paper presents a distributed complex power sharing approach that solves the problem of active and reactive power sharing in inverter-based islanded microgrids. Previous state-of-the-art strategies based on droop controls with possibly virtual impedance methods and supplemented with hierarchical schemes may provide poor power sharing due to the R/X ratio and mismatched line impedances, even compromising microgrids stability if droop control parameters are not properly set. The novel control approach, that uses a communication network to exchange data among all inverters to fairly inject power, provides a set of appealing properties. First, it achieves accurate active and reactive power sharing for both resistive and inductive power lines with no additional control cost (avoiding unnecessary power injections), and regardless of load changes and connections and disconnections of inverters. Moreover, it ensures an exponential convergence rate, and the tuning of the control parameters can not compromise microgrid stability. The theoretical development relies on a change of variables that linearizes the complex power dynamics, thus easing the control law design task and providing the means for computing the appropriate amplitude and phase for each inverter output voltage. Selected experimental results on a laboratory microgrid certify the applicability and performance of the proposed control scheme.