Evaluation of Inverter-based Grid Frequency Support using Frequency-Watt and Grid-Forming PV Inverters

Currently, the majority of grid-connected PV sources operate in current-control mode, which is known as grid-following control. The ability of grid-following sources to provide ancillary services to the grid is relatively limited due to their inability to directly control voltage and frequency. On the other hand, voltage-controlled inverter known as grid-forming source can be seen as a controllable voltage source behind a coupling reactance, which is much like a synchronous generator. Grid-forming sources allow for direct control of voltage and frequency. In this paper, the performance of grid-following PV sources and grid forming PV sources are compared in providing frequency support in an islanded power system. The study is completed using validated bulk grid model of the Hawaiian island of Oahu. Simulation results indicate that PV inverters with grid-forming control have the potential to provide a robust frequency control on this islanded power system.