Stochastic Eigen Analysis and Unified Control Mode for Grid-Forming and Grid-Following Inverter Based Resources

A Grid-Forming Converter (GFMC) is a critical part for proper operation of an isolated microgrid (MG). Its aim is to generate voltage reference for rest of the inverter- based resources (IBRs) in the MG just like a traditional slack bus generator. To operate a GFMC in a d-q reference frame, single or dual loop proportional-integral (PI) controller is typically used. However, under system and grid parametric fluctuations, the above controller performs poorly. The voltage source converter (VSC) should operate for grid-tied (GT) as well as stand-alone (SA) mode to function as a grid following converter (GFLC) for power delivery to local loads where each mode has its own control loop. It should be seamless in providing an uninterruptible supply of power to the local load. Hence, for the addressable challenges, a non-linear model of both GFMC and GFLC that covers all system and grid parametric variables is devised along with stochastic eigen analysis. The suggested technique has an accurate model for the converter system which can cope with LC filter resonance and uncertainties more effectively where the need of any passive or active dampening methods is unessential. Simulations and tests were carried out to validate the suggested methodology. The simulation and experimental findings indicate that the suggested control strategy may be utilized to accomplish autonomous and smooth mode transitions even in the presence of norm-bound state uncertainty, as well as to offer resilience against grid impedance, system, and grid parameter fluctuations.