Autonomous hierarchical control of dc microgrids with constant-power loads

This paper discusses an autonomous controller to achieve current sharing of parallel connected buck converters in a dc micro-grid with constant power loads. A two stage controller is proposed, where current sharing is achieved with a primary/droop control that requires no communication between the converter modules. The output voltage in the main bus is drooped linearly with respect to the load current supplied by each of the converters. To compensate for the voltage deviations without affecting current sharing, the droop control is augmented by a secondary/voltage regulating control. Asymptotic stability of the equilibrium point with the proposed control input is examined using Lyapunov and conditions to ensure local asymptotic stability of the equilibrium points are derived. Simulations and experimental results are included to verify the analysis.