Virtual Energy Storage Operation for Smart Photovoltaic Inverters

Inverter-based resources (IBR) are increasingly adopted and becoming the dominant electricity generation sources in today's power systems. This may require a "bottom-up" change of the operation and control of the employed power inverters, e.g., based on the emerging grid-forming technology and by integrating energy storage. Currently, grid-following and grid-forming inverters are simultaneously seen in power systems, while mostly as demonstration small-scale or medium-scale cases. As such, grid-following inverters should become much smarter and be able to provide various functions to support the power grid in response to static and dynamic disturbances. In this paper, the photovoltaic (PV) inverters are considered to operate as virtual energy storage (VES) to flexibly provide grid support, e.g., short-term frequency control to improve the frequency quality, in the context of more IBR-based power systems. More specifically, the PV inverters are dynamically regulating the active power to "store" or "release" energy to the grid, mimicking the operation of a physical energy storage system. In addition to the grid support, the VES operation can also improve the inverter reliability, and increase the utilization ratio of PV inverters to some extent. Simulation and experimental case studies are presented to demonstrate the VES operation of PV inverters and its effectiveness of inertia support.