Stability Analysis of a Droop-Controlled DC Microgrid

Stable operation is a primary performance metric that a DC microgrid system should satisfy. This paper presents a comprehensive stability analysis for a two-converter system attached to a Constant Power Load (CPL) under droop control. The study establishes the stability criteria and calculates the minimum capacitance required for the stable operation of the system. The study considers the virtual inertia incorporated via a low-pass filter (LPF) to avoid sudden voltage fluctuations in the analysis. It is concluded that an optimum value of virtual inertia can reduce the required capacitance for stable operation. Additionally, the paper derives a relation providing the maximum power transfer limit for given system parameters and the effect of virtual inertia on this limit. The results are verified by simulation in MATLAB/Simulink. These findings have practical implications for designing and operating DC microgrid systems, particularly for optimizing virtual inertia for maximum power transfer while ensuring system stability.