Modified control structures for sharing of asymmetrical powers amongst inverter based distributed energy resources.

Renewables interfaced through inverters in microgrids, may be controlled using centralized, decentralized or distributed approaches. The decentralized droop control involves mimicking the performance of a synchronous generator of the power system, so as to share load power proportionately amongst parallel connected sources. When the conventional droop control is used, only the fundamental real powers can be shared in proportion to the source ratings, which does not ensure satisfactory performances in the presence of unbalanced/ asymmetrical loads. Several schemes have been worked upon to achieve proportional load power-sharing with power quality aspects: in the presence of harmonic and unbalanced loads. This paper proposes five modifications for the popular virtual conductance vs. negative sequence power (G vs. Q-) approach, aimed at improving the sharing of the unbalanced currents amongst the sources to improve the power quality and microgrid system reliability. The eigenvalue analysis for determining the parameter range for assuring stability and comparisons with fixed virtual conductance values are discussed. The proposed modifications are discussed and demonstrated through simulations on a two inverter-based distributed generator (DG) system, a modified 13 bus system, and using experimental results on a lab-scale microgrid. • The work presented focuses on the power quality of unbalance in islanded AC microgrid systems and proposes five modifications for the popular G vs. Q- approach, aimed at improving the sharing of the unbalanced currents amongst the parallel connected sources. • The proposed modifications are based on local measurements and do not need communication, network and load estimations • The eigenvalue based small signal analysis for determining the parameter range for assuring stability and comparisons with fixed virtual conductance values are presented. • The proposed modifications are discussed and demonstrated through simulations on a two-inverterbased distributed generator (DG) system, a modified 13 bus system, and using experimental results on a lab-scale microgrid. • An overall improvement in the range of 26.0% to 61.0% was observed across the different cases (enhanced unbalanced power-sharing: before and after activating the proposed control). [ABSTRACT FROM AUTHOR]