Improved Power Sharing Scheme for a Microgrid with Multiple Distributed Generators

Abstract

This paper explores the active and reactive power sharing scheme for the parallel operation of inverter interfaced distributed generators (DGs) in a microgrid system. Applicability of conventional wireless control technique, based on P-f and Q-V droop regulations, is also investigated for the load sharing among the DGs with the help of small signal analysis. The conventional droop technique is found to be ineffective in a distribution system with resistive dominated line. In particular, the reactive power becomes highly uncontrolled with large circulating VAR in the presence of high R/X. The virtual impedance concept proposed in the paper intends to address this problem. The so-called virtual impedance is self-regulated variable aiming to reduce the impedance mismatch thereby eliminating the circulating VAR. Consequently, the scheme provides effective active and reactive power sharing among the DGs by adjusting the magnitude and frequency of the voltage at steady-state. Simulation results presented for the two-DGs microgrid system, confirms the validity of the proposed scheme.