Enhanced primary droop controller for meshed DC micro-grids with overvoltage protection

Droop control represents the key grid-forming control strategy in modern micro-grids consisting of multiple distributed energy resources (DERs), implemented at the primary control layer of the hierarchical control architecture. In this paper, an enhanced droop control methodology for meshed DC micro-grids with constant power loads (CPLs) is proposed, which inherits the conventional droop control features and additionally guarantees a crucial overvoltage protection property of each DER unit, independently from each other or the loads. Since one of the main challenges in DC micro-grids is that CPLs introduce negative impedance characteristics that can lead to system instability, in this paper, based on the proposed novel control structure and using nonlinear ultimate boundedness theory, an upper limit for the output voltage is rigorously guaranteed. In addition, asymptotic stability to the desired equilibrium for the closed-loop system is analytically proven, and detailed conditions are derived to guide the control design. Simulation testing is performed for a meshed DC micro-grid to verify the theoretical contribution and the effectiveness of the proposed primary droop controller.