Reactive power control of micro-grids using FOSMC for grid code compliance during asymmetrical voltage sags.

• Reactive power control of micro-grids during asymmetrical voltage sags to comply with modern grid code requirements. • Sharing requested reactive power among the grid connected sources in the secondary layer. • Restoring the PCC voltage by independently controlling each phase of the grid connected sources in the primary layer. • Implementing a nonlinear robust fractional-order sliding mode controller in the primary control layer. • Keeping the power quality indexes such as total harmonic distortion (THD) and voltage imbalance factor in acceptable range during LVRT conditions. Application of micro-grids (MGs) as a solution for future energy systems are significantly increasing in recent years. On the other hand, more stringent requirements are added to grid codes (GCs) of low-voltage distribution networks. Accordingly, this paper proposes a low-voltage ride-through (LVRT) control scheme for four-wire multi-source MGs. The novel strategy is composed of two layers for controlling each phase of the grid-connected sources independently. The primary layer contains a reverse-droop function for each phase and fractional-order sliding-mode-control (FOSMC). The secondary layer determines the total requested reactive power for each phase during symmetrical and asymmetrical voltage drops. Then, the mentioned power is shared among the phases of each inverter based on the reactive power-sharing strategy and GC requirements. Based on the proposed grid-following controller, the voltage of faulty phases is compensated by reactive power injection. In addition, power quality indexes are kept in acceptable ranges during abnormalities, and the FOSMC performs better than the conventional methods. The effectiveness of the proposed scheme is verified through offline simulations in MATLAB/Simulink as well as validation by real-time results. [ABSTRACT FROM AUTHOR]