Design of a Controller for Grid Forming Inverter-Based Power Generation Systems

Recently the grid-following inverter-based power generation systems (IBPGSs) dominate over synchronous generators (SGs) in load sharing in some areas of power grids in many countries worldwide. The trend of increasing penetration of IBPGSs to grid results in decreasing number of SGs in operation. This can result in a slowly decreasing system inertia which results in fast dynamics during transient conditions, that may lead to failures of phase-locked loops (PLLs), which are widely used in grid-following IBPGSs. Consequently, the grid-following IBPGS-dominated grids are facing stability issues in their operations. To support these grid-following IBPGSs for their stable operations, a stable grid-forming IBPGS is required that can operate as SGs. In this paper, a grid-forming controller is designed for IBPGSs that can enable IBPGSs to mimic SGs and work as grid-forming inverters that operate like SGs to maintain the grid dynamics suitable for the stable operation of the IBPGSs. For this purpose, a detailed mathematical model of the SG and its associated controller has been used with the proposed grid-forming controller. From the steady-state and transient dynamics, a mathematical relationship between the inertia support from the grid-forming controller and an SG has been developed to control the inverter in the grid-forming IBPGS. The performance of the grid-forming IBPGS during steady-state and transients due to load change, fault, and grid-isolation has been compared with the SG. The simulation results have validated the effectiveness of the proposed controller and grid-forming IBPGSs to help control the voltage and frequency of the IBPGS-dominated power systems.