Modeling and Emulation of a Synchronous Generator Considering Unbalanced Load Conditions

Power electronics converters can be applied as emulators to mimic different grid components used for system behavior analyses and control validation. Synchronous generators (SGs) are the major sources of electric grids. Converter-based SG emulators have been developed for system stability analysis, fault analysis, and frequency support. However, existing SG emulators have not considered the impacts of load unbalance, which is a common phenomenon in distribution grids and will lead to system-level issues. In this article, a SG emulator considering an actual SG's negative sequence (NS) performance is developed for system analyses under unbalanced load conditions. With different simplifications, a SG can have different orders of electrical models. By deriving the NS performances of different SG electrical models, an appropriate SG electrical model in unbalanced load conditions is selected. Then a novel control diagram is proposed to ensure that the NS performances of the selected model can be fully realized. The derived NS models and the proposed control diagram are verified through simulation first and then validated with a converter-based hardware testbed.