Evaluating Power Sharing Performance of Distributed Generators in Microgrids With Hybrid Sources and Mixed Tie-Lines

Abstract

Proportional output power sharing amongst distributed sources in islanded microgrids is necessary to maintain a good voltage profile, avoid tripping of sources and avoid circulating current flows. Underground (UG) cables are popular in densely populated areas and military applications. However, researchers typically consider microgrid networks with overhead lines (OHL) in their studies. This paper examines the power sharing performance among droop controlled inverters and virtual synchronous generators in a system with mixed tie-line configurations i.e., network sections with both OHL and UG cable tie-lines. Furthermore, two proposed control strategies to vary the virtual impedance linearly as a function of the DG output currents are examined for their effectiveness to improve the proportional power sharing. The studies are performed considering a system with four inverter based sources operated with the popularly used <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$L$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$RL$</tex-math></inline-formula> droop controllers through detailed simulations in MATLAB/Simulink. The enhancement of power sharing is verified for both uniform and non-uniform inverter controls, different R/X ratios of the OHL and UG cables, and in a meshed network configuration with different loading conditions. Controller hardware in the loop (CHIL) based experiment validation is carried out in Typhoon HIL with linear, non-linear and induction motor load, showing that proposed control strategy results in enhanced power sharing in addition to damping oscillations due to dynamic loads.