Passivity-Based Stability Analysis of DC Microgrids Using Physically Decoupled Model

Due to the low inertia and weak damping of the dc microgrid, its stability becomes even more serious and has attracted many investigations. However, as its scale and complexity continue to grow, the effectiveness, reliability, and comprehensiveness of the stability analysis cannot be guaranteed simultaneously. Therefore, this paper proposes a passivity-based stability analysis approach by developing a physically decoupled model. Specifically, for the first time presenting the concept of virtual capacitance in modeling, the dc microgrid is physically decoupled into several low-dimensional subsystems. These subsystems have feedback structures, constituting the physically decoupled model, and the physical meanings of parameters are retained explicitly and completely. Subsequently, a sufficient condition for the stability of the physically decoupled model is derived based on strict passivity and LaSalle's Theorem. Then, by combining optimization theory, the stability domain calculation of multiple subsystems is transformed into a multi-objective optimization problem. The stability impacts of internal circuit and power parameters are evaluated, and the stability boundaries are identified to determine parameter limitations. Finally, numerical and time-domain simulations are carried out to validate the effectiveness and accuracy of the theoretical analysis and the superiority of the proposed method than Lyapunov direct method and TS fuzzy model method.