A Unified Distributed Digital Control Architecture for Secondary Control in Islanded Microgrids

Abstract

Distributed control theory has gaining momentum for the global stability of modern Micro-grids (MGs), which can be hence regarded as a cyber-physical energy systems in a networked control systems perspective. Besides the benefits, the control over networks poses several issues and, among them, how to preserve stability despite the unavoidable sampling process is one of the most crucial to be addressed for the implementation in real-world scenarios. The paper addresses this concern by introducing a unified digital control architecture for secondary control of inverter-based MGs working in islanded mode, where both frequency and voltage regulations are ensured via fully-distributed sampled-data control protocols. By choosing a small-enough sampling period h > 0, the proposed strategies can ensure a reduction of the communication burden by avoiding a continuous interactions among electrical entities, thus enhancing the efficiency of the MG. Exponential stability of frequency and voltage closed-loop systems is analytically proven via Lyapunov-Krasovskii theory. The derived stability conditions are in the form of Linear Matrix Inequalities (LMIs) whose solution provides the maximum sampling period preserving the global stability. Simulation results, carried out in MATLAB/SimPower Systems, confirm the theoretical derivation.