Modified droop control for improving adaptive virtual impedance strategy for parallel distributed generation units in islanded microgrids

Abstract

This paper proposes a control strategy to improve adaptive virtual impedance performance. The proposed method compensates voltage drop across the output impedances of distributed generation (DG) units, intensified due to the use of virtual impedance, and regulates the voltage of busses feeding microgrid-connected loads in a desired level. In addition, it preserves the advantages of adaptive virtual impedance strategy, including proper active and reactive power sharing and decreased circulating current among parallel DGs. To compensate voltage drop proportional to load variation, the reference voltage used in the droop control strategy is adaptively regulated. To evaluate the performance and efficacy of the proposed control strategy, it was implemented on an islanded microgrid with two DGs. Simulation results show that the proposed strategy makes a compromise between control objectives, including appropriate power sharing, compensation of voltage drop, and reduction of circulating current.