Voltage Control for Nonlinear DC Microgrids via a Fully Actuated System Approach

Except for purely resistive loads, DC microgrids (MGs) interfaced with boost or buck converters typically feed multistage power converters via a common bus. A notable class within this framework is the tightly regulated point-of-load (POL) converter, which behaves as a constant power load (CPL) within its control bandwidth. Considering the challenges posed by the negative incremental impedance characteristics of CPLs on MG stability, this article establishes a second-order fully actuated (SOFA) model for nonlinear MGs incorporating CPLs and proposes a fully actuated (FA) voltage regulator based on a disturbance estimator. The proposed approach accounts for both known and unknown CPL scenarios, including load variations that are not previously identified. Furthermore, a closed-loop MG system with FA control under parameter perturbation is analyzed based on singular perturbation theory. In this study, the first-order under-actuated MG system containing CPLs is transformed into an SOFA system by means of techniques such as state transformation, system dimension reduction, and system order augmentation. Compared to the existing methods, the proposed FA controller, based on this system model, features a straightforward and easy-to-implement structure, which makes the parameterized design of the controller possible. Finally, the effectiveness of the proposed method for achieving voltage tracking as well as system stability is confirmed through abundant experimental cases conducted on a built hardware MG platform.