A Novel Mixed Control Strategy with Grid-Following and Grid-Forming for Renewable Energy Grid-Connected Inverter

Grid-following (GFL) control features of fast and instant maxim power point tracking (MPPT) is widely applied with the permeation of renewable energy. However, the stability of GFL control is influenced by grid strength. Disturbance of voltage at point of common coupling (PCC) can cause oscillation when GFL converter connected to weak grid. As gird-forming (GFM) control imitates principle of synchronous generator, phase lock loop (PLL) is no longer needed which elevates stability of GFM control under weak grid. However, slow response to power fluctuation makes it hard for GFM to achieve MPPT. Therefore, this paper proposes a novel mixed control strategy with GFL and GFM control which integrates characteristics of GFL and GFM. Participation level of GFL is raised when converter attached to weak gird to improve stability. Participation level of GFM when converter attached to strong gird to achieve MPPT.