Coordination of D-STATCOM & SVC for Dynamic VAR Compensation and Voltage Stabilization of an AC Grid Interconnected to a DC Microgrid

This article presents a new collaborative control method based on expert decision, proposed for the combined system of an ac grid with a low THD thyristorized static var compensator (SVC), interconnected to a dc microgrid through a distribution static compensator (D-STATCOM) that also works as a bidirectional power converter. The combination of large rating SVC and a low rating D-STATCOM functions as a hybrid compensator for the ac distribution grid. In the combined mode of operation, the D-STATCOM mitigates voltage fluctuations and compensates initial var demands, while the SVC caters to the base var requirements. The D-STATCOM has also been used for integration of a dc microgrid to the utility grid, permitting exchange of power between the grids and thereby reducing voltage fluctuations of both the systems. The proposed collaborative control method based on expert decision can extract the full advantages of the respective subsystems as per demand of the operating condition. This combined system complies with the relevant harmonic standards and can effectively correct system power factor, stabilize bus voltage, and mitigate voltage flicker under fluctuating load conditions. Theoretical analyses with simulation results as well as experimental results show that the proposed system can meet the requirement of continuous dynamic reactive power compensation and voltage stabilization with low cost, high reliability, and large capacity.