Plug-and-Play Compliant Control forInverter-Based Microgrids

Control of inverter-based microgrids (IBMGs) with power sharing capability is a challenging task due to specific nature of microgrid instabilities. Specifically, droop-controlled microgrids prone to become unstable when the X/R ratio is near unity and the lines are short. Virtual impedance is thought to be one of the promising tools to prevent this type of instability allowing for a broad range of droop coefficients for efficient power sharing between inverters. However, proper sizing of virtual impedance for particular microgrid configuration is still an open question. In this paper, a systematic method for determining the size of virtual impedance in a plug-and-play fashion is proposed for enhancing the stability of the droop modes. Based on the Lyapunov method, concise and simple stability certificates are derived to provide flexible choices of the droop gains for different inverter ratings.The implementation of the virtual impedance with the proposed approach for stability enhancement is verified by both numerical simulation through MATLAB/Simulink and experiment via a small-scale prototype for different scenarios.