Novel Adaptive Virtual Impedance-based Droop Control for Parallel Operation of AC-DC Converter for DC Distribution

The AC-DC converter, which connects the AC grid to the DC grid in the microgrid, is a critical component in power sharing and stable operation. The AC-DC converters are connected in parallel for increased transmission capacity. In parallel connected AC-DC converter, due to the line impedance deviation or sensor error, a deviation occurs in the output voltage of each converter, which cause a circulating current. A general solution to this problem is droop control based on virtual impedance. Since the conventional droop control selects the virtual impedance as the dominant value compared to the line impedance, it has a problem of generating sag of the DC bus voltage by having a large secondary control compensation value. In this paper, an appropriate virtual impedance selection algorithm is proposed to reduce the voltage sag of DC bus by reducing the secondary control compensation value, and the validity of the proposed algorithm is verified through PSIM simulation.