Virtual shaft control of hybrid energy storage for oscillation suppression by transient energy capture

If the hybrid energy storage device (HESD) with virtual inertia is coupled with synchronous generators (SGs) by a virtual shaft, the stronger transient stability of the power system can be achieved if more transient energy is captured by renewable power generation. In this paper, the conversion relationships between the static energy of the HESD and the kinetic energy of the SG are established. The virtual inertia hidden in the HESD is then explored to obtain the synchronous operation capability. To capture more transient energy from SGs to HESD, a novel virtual shaft is added to the VSG, and moreover, the impacts of HESD coupled with the virtual shaft on system transient stability are analyzed. Using the Hamiltonian energy function, the necessary conditions for improving the transient energy capture efficiency of the HESD are presented, and thus the virtual shaft control strategy of the HESD is proposed to integrate the power support functions for system frequency regulation and power oscillation damping. Finally, a typical test system with high penetration of photovoltaic arrays and HESDs is implemented on a hardware-in-the-loop platform. The results demonstrate that under the proposed control strategy, the transient stability of system frequency and rotor angle can be both significantly improved.