Power sharing strategy in parallel operation of inverters for distributed power system under line impedance inequality

In this paper, a reactive power sharing method is proposed for the operation of multiple distributed generation units. When the line impedance is unbalanced, accurate reactive power sharing is challenging with conventional current sharing or droop control strategies. This paper describes the effect of the unequal line impedances on the reactive power sharing accuracy, especially for mainly inductive line impedance. The proposed method compensates the impedance effect by modifying the droop slope and is shown to be effective through two parallel 1MVA units. The accuracy of the reactive power sharing is improved by 26.7% and 42.5% for each DG unit in the grid-connected mode and 11.9% in the islanding mode.