Advanced Current-Limiting and Power-Sharing Control in a PV-Based Grid-Forming Inverter Under Unbalanced Grid Conditions

Grid-forming (GF) inverter technology is a novel and evolving concept for systems with high penetration of renewables. The integration of these grid-independent units with the existing conventional generators and gradually replacing them should contribute to stabilizing the power grid. Several control strategies are proposed in order to design GF inverters to emulate the kinetic energy and the self-synchronization features of synchronous machines with robust control on voltage and frequency to deal with the dynamic issues of the grid. In this article, a photovoltaic (PV)-based GF inverter with a modified virtual synchronous machine control in parallel with a battery supported inverter with an enhanced droop control is considered to operate under non-ideal grid voltage conditions and in the isolated mode of operation. The control methodology encloses a PV synchronous generator, along with the nonlinear feedback linearization current-limiting control with voltage ride-through capabilities. They enable the GF PV inverter and the grid-following battery inverter to provide active and reactive power to the load during unbalanced grid conditions seamlessly. A hardware cosimulation environment in Simulink using the software tool of Piecewise Linear Electrical Circuit Simulation (PLECS) and System Generator from Xilinx is applied to evaluate the operation of the controller and verify its flexibility and effectiveness in different case studies.