Distributed Secondary Control for Average Voltage Recovery and Current Sharing of DC MGs via a Fully Actuated Error Model

The modeling problem of converter-based multibus direct current (DC) microgrids (MGs) and the conflict between voltage regulation and current balancing in such MGs have been a hot topic of interest. Voltage regulation is essential for ensuring the stability and power quality of MGs, while current sharing is a reflection of the MGs' ability to coordinate power and is critical to extend the lifespan of the generation units. However, due to the presence of line impedance, currents no longer have the freedom of regulation under consistent voltages across the buses. Additionally, existing models have failed to strike a good balance between accuracy and simplicity in describing DC MGs, resulting in rare research on model-based secondary control. With this in mind, this article develops a DC MG error model containing the dynamics of both the circuit and inner control loops via the fully actuated system theory. Further, a distributed optimal control is proposed based on this model. Compared to existing studies, the suggested error model captures the power characteristics of MGs while possesses a simple structure. For regulation tasks of voltage recovery and precise current allocation, this article unifies these two into a single integrated regulation error, offering a novel approach to address their conflict. Subsequently, the stability of the closed-loop MG system is given. Furthermore, this article includes a consensus analysis of current sharing and a tracking analysis of the average voltages. Finally, a laboratory-scale MG prototype equipped with photovoltaics and batteries is developed to validate the effectiveness of the proposed method.