Restoration and Grid Integration of Unbalanced and Distorted Distribution System Using Inverter Based Renewable Energy Systems

This paper deals with restoration and grid integration of an unbalanced and distorted distribution system, following a power outage (blackout). In this work, a new control strategy is proposed to enhance the restoration and grid integration capability of the grid forming based inverters consists of unbalanced and non-linear loads. Performance evaluation of grid forming based proposed control scheme is carried out during blackstart of an islanded distribution system. This system encompasses various type of loads like unbalanced and non-linear, as well as induction motor. The objectives are given as follows: (i) maintain the distortion less balanced voltage during restoration, (ii) restore all the loads without significant transient in current, voltage and power, (iii) whenever grid is available, re-synchronize with the grid as soon as possible for better reliability with respect to the loads and without instability. The entire distribution system along with the proposed inverter control is modeled using MATLAB/Simulink platform. The findings demonstrate improved ability of grid-forming inverters to initiate a blackstart and restoration operations, even with unbalanced and non-linear loads. The proposed controller ensures enhanced resiliency and reliability of an unbalanced and distorted distribution system with 100% inverter based renewable energy system during restoration and grid-integration.