A Battery/Ultracapacitor Hybrid Energy Storage System for Implementing the Power Management of Virtual Synchronous Generators

Renewable energy sources (RESs) have been extensively integrated into modern power systems to meet the increasing worldwide energy demand as well as reduce greenhouse gas emission. As a result, the task of frequency regulation previously provided by synchronous generators is gradually taken over by power converters, which serve as the interface between the power grid and RESs. By regulating power converters as virtual synchronous generators (VSGs), they can exhibit similar frequency dynamic response. However, unlike synchronous generators, power converters are incapable of absorbing/delivering any kinetic energy, which necessitates extra energy storage systems (ESSs). Nonetheless, the implementation and coordination control of ESSs in VSGs have not been investigated by previous research. To fill this research gap, this letter proposes a hybrid ESS (HESS) consisting of a battery and an ultracapacitor to achieve the power management of VSGs. Through proper control, the ultracapacitor automatically tackles the fast-varying power introduced by inertia emulation while the battery implements the remaining parts of a VSG and only compensates for relatively long-term power fluctuations with slow dynamics. In this way, the proposed HESS allows reduction of the battery power fluctuations along with its changing rate. Finally, experimental results are presented to validate the proposed concept.