Analysis of enhancing SCR and power transfer capacity in renewable energy systems via grid-forming MMC

The active power transfer capacity of renewable energy grid-connected systems is constrained by the short-circuit ratio (SCR). In weak grid scenarios, renewable energy plants may fail to deliver their rated power output. In this article, an equivalent analysis model for new energy grid-connected systems is proposed. The power transfer limitation of renewable energy plants is analyzed, considering the voltage constraints and the converter current constraints. Moreover, grid-forming control is adopted to improve SCR of the grid, thereby enhancing the voltage support strength and the power transfer capacity. Finally, the experimental results verify the analytical method and the theoretical analysis. After the adoption of grid-forming control, the active power transferred by renewable energy plants is increasing from 0.7 p.u. to 1 p.u. in weak grid. The results of this article are beneficial for enhancing the power transfer capacity of renewable energy systems in weak grid conditions.