Nonlinear primary and supervisory control of DC microgrids for distributed optimal operation with neighbour-to-neighbour communication

In this paper a hierarchical control scheme is proposed for distributed operation of DC Microgrids (MGs) consisting of multiple Distributed Energy Resources (DERs) and local loads with an inherent overvoltage protection for each unit. At the primary control level, the recently proposed state-limiting PI (sl-PI) controller is employed to ensure bounded converter capacitor voltage at all times. At the supervisory control level a non-iterative distributed two-layer MPC approach is proposed, where the system is driven to economic targets calculated according to the load demand. We show the existence of bounds on the voltage dynamics based on ultimate boundedness theory by an appropriate choice of the tuning parameters. Asymptotic stability of the closed loop dynamics is analytically proven and conditions for the recursive feasibility of the supervisory controller are provided based on the inherent robustness properties of nominal MPC. Simulation results are provided to demonstrate the boundedness properties and economic regulation of the proposed control scheme, as well as satisfaction of the operation constraints.