Power management of virtual synchronous generators through using hybrid energy storage systems

The increasing demand for clean energy necessitates a large-scale integration of renewable energy sources (RESs), which has dramatically changed the paradigm of modern power systems. Conventionally, synchronous generators with rotating reserves are responsible for system frequency regulation. As the penetration of RESs grows, the task of frequency regulation is supposed to be gradually taken over by virtual synchronous generators (VSGs), which are essentially grid-interfaced power converters behaving similarly to synchronous generators. Nonetheless, unlike synchronous generators, VSGs do not possess spinning reserves, and hence, energy storage systems (ESSs) are required in VSGs. However, the implementation and coordination control of ESSs in VSGs have not been investigated. To fill this research gap, this paper proposes a hybrid ESS (HESS) consisting of a battery and an ultracapacitor to achieve the power management of VSGs. During load disturbances, the ultracapacitor tackles the fast-varying power introduced by inertia emulation while the battery implements the remaining parts of VSGs and only compensates for relative 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 illustrate the effectiveness of the proposed concept.