A Novel Control Strategy for Grid Forming PV Inverter Integrated with Battery Energy Storage System

It is imperative to convert a traditional renewable energy source (RES)-based inverter from a grid-following configuration to a grid-forming configuration to accommodate the increased penetration of RES-based power generation in the contemporary grid system and to substitute conventional synchronous generators (SGs). The grid-forming photovoltaic (PV) inverter can deliver frequency support, a critical component in ensuring the stability of the power grid. The primary objective of this paper is to introduce a novel AC coupled solution that converts and ensures a seamless transition from a conventional grid-following PV inverter to a grid-forming PV inverter without requiring any adjustments to the PV inverter's internal configuration. In this paper, a battery energy storage system (BESS) is used to provide frequency support and inertia solution to the grid forming system. The novel control of the grid-forming inverter is implemented on the BESS side. The innovative control scheme incorporates both rapid and slow instantaneous power controls. A fast-instantaneous power flow control is implemented for the inertia supply and grid synchronization. On the other hand, frequency droop control is implemented via slow instantaneous power controls. In this system, two crucial fundamental functions are carried out. The first is the rapid frequency response required to resist the frequency variation of the system; the second is the inertia against intermittent PV power.