Grid frequency and voltage support using PV systems with energy storage

An optimized operating scheme for a utility connected community based photovoltaic (PV) system is described. The system can participate in grid ancillary services like frequency and voltage regulation functions based on the Smart Grid framework The proposed model comprises of a PV plant with Li-ion batteries coupled to the grid with the help of a three phase inverter. A two-way communication between the PV plant and the grid is assumed. The PV/storage plant provides constant updates on its current kW/kVar capability and the grid transmits the demand for specific amounts of power and for specific lengths of time. The battery charging energy can originate from either the PV system or the grid depending on the prevailing energy prices. The batteries are discharged when two conditions are met: the grid requests energy from the community-based PV system and if the PV system itself fails to meet the requested kW or kVar demand. The PV plant and the battery storage are integrated with the grid with the help of dc-dc and dc-ac converters in such a way that bi-directional flow of active and reactive powers can be achieved. Controllers integrating energy sources respond to the received signals and attempt to fulfill the grid demand. The system response is almost instantaneous and thus can be very helpful in frequency and voltage regulation.