State-Space Modeling and Analysis of Distributed Secondary Control of DC Microgrids

In conventional DC microgrids (µGs) that have multiple parallel power sources connected to the DC bus, the problem of voltage regulation and current sharing is inherent. Therefore, control methods, such as droop control, have been mainly used in the primary and secondary control layers. While droop control allows current sharing between multiple parallel µG sources, it causes a deviation from the nominal voltage at the DC bus. To address this challenge, a secondary controller is proposed to simultaneously guarantee proportional current sharing while maintaining the DC bus voltage at the nominal value. A distributed approach is utilized in this paper to avoid the single-point failure of centralized controllers and enhance plug-and-play capability. A state-space approach is used to formulate the DC-µGs to aid controller design and analyze its stability. MATLAB/Simulink is utilized to simulate the formulated state-space model of the DC-µGs and the proposed secondary control strategy.