Comparative analysis on the stability mechanism of droop control and VID control in DC microgrid

Voltage resonance and fluctuation deteriorate the stability of DC microgrids (DC-MGs) and restrict their popularization. Conventional droop control cannot suppress voltage fluctuation and damp oscillations. Therefore, new control methods, namely, droop+filter control and virtual inertia and damping control, are proposed. These methods differ owing to the addition of low pass filter (LPF) and virtual inertia loop. In this study, the stability of these control methods is investigated comprehensively to understand their differences arising from the use of LPF and inertia loop as well as the underlying dynamic stability mechanism. The leading causes of voltage instability in DC-MGs regulated by droop control are first presented. Subsequently, control methods for solving this issue are compared and their simplified small-signal models are constructed. Based on eigenvalue analysis, the DC-MG is equivalent to a third-order system. Different control effects can be acquired by changing the control parameters and the location of the eigenvalues; furthermore, they can be used to understand the dynamic stability. Eigenvalue analysis can provide parameter design guidelines. Finally, the simulation results verify the validity of the theoretical analysis.