Seamless Mode Control Algorithm for a Single-Stage Photovoltaic Virtual Synchronous Generator for Frequency Regulation and Reactive Power Support

High penetration of inverter-based photovoltaic (PV) systems deplete the overall inertia of the grid. One of the alternatives to inertia emulation in grid-tied renewable sources is a virtual synchronous generator (VSG). Hence, the PV source combined with the VSG characteristics performs better in the grid-integrated mode. Due to the maximum power point tracking (MPPT) operation of PV sources, there is no flexibility to change power generation for any change in the grid attributes, such as frequency. Hence, PV systems require additional energy storage to enable frequency regulation in the event of grid frequency changes, incorporating additional costs. In addition, the PV-VSG inverter is not utilized at night. This article presents a seamless mode control algorithm for a single-stage photovoltaic virtual synchronous generator (PV-VSG) system to participate in frequency regulation under grid frequency disturbances without additional energy storage by operating at deloaded MPPT. In addition, the proposed PV-VSG operates as a STATCOM during the night when there is no active power generation. The effectiveness of the proposed controller is verified with the developed experimental prototype of a PV-VSG under changing solar irradiance, temperature, grid frequency deviation, load change, partial shading, and nonlinear load. A seamless transition of the PV-VSG from grid-connected to standalone mode and STATCOM operation during nighttime is also demonstrated. The proposed control algorithm is compared with existing methods with the help of experimental results.