Small-Signal Stability Analysis of DC Microgrids

The conventional cascaded control strategies using proportional-integral-derivative controllers often result in high settling times, considerable oscillations, poor voltage regulation, and low bandwidth. This leads to unsatisfactory performance in systems where multiple input variables are each subject to high levels of temporal variability, such as in DC microgrids (MGs) with renewable sources of generation. To overcome these challenges, a new combined control technique including average current mode and PI controllers based on root locus tuning is proposed for DC MGs to maintain small-signal stability. An analytical small-signal equivalent model of DC MG, including the proposed control, is developed to examine the impact of control parameter variations on system dynamics. The stability of the DC MG is assessed to evaluate the effectiveness of the designed controller, while a sensitivity analysis identifies critical parameters affecting system performance. The effectiveness of the proposed control scheme is demonstrated through a comprehensive comparative analysis with a conventional PID controller and a terminal sliding mode controller, which specifically addresses small-signal disturbances. Results demonstrate that the proposed control scheme provides superior robustness against small-signal disturbances, minimises settling time, and eliminates oscillations. Moreover, it offers improved power quality, bandwidth, and voltage regulation compared to conventional methods under both normal operating conditions and in response to small-signal perturbations.