Distributed Discrete Robust Secondary Cooperative Control for Islanded Microgrids

It is desirable to develop robust controllers for fast frequency/voltage regulation and active/reactive power sharing in an islanded microgrid with high penetration level of renewable energy sources. This paper proposes a fully distributed discrete two-level control strategy for islanded microgrids. The upper-level control determines the active/reactive power generation references to minimize the overall voltage deviations while achieving accurate active/reactive power sharing. The lower-level control enables the inverter to track the power references by adjusting inverter output voltage magnitude and angle. A flexible finite-step convergence tracking controller, which considers the uncertainties and disturbances, is introduced to improve the robustness and control accuracy. The convergence and optimality of the proposed discrete control algorithm are validated by rigorous analysis. The effectiveness of the proposed distributed control approach is verified by simulation results.