Immunity of grid forming control without energy storage to transient changes of grid frequency and phase

The starting of decarbonization of electric power generation lead to an increase of renewable energy sources and a resulting reduction of conventional high-power plants. Thus, the inertia / stability of the grid is decreasing in many countries. In order to counteract this change grid forming control structures with virtual inertia for inverter based renewable energy sources have been developed in academia. In case of frequency and phase transients the frequency inertia of grid forming control will respond with grid supporting active power transients like synchronous generators would do. This is problematic for frequency and phase drops, if the regenerative power plant is already operating at its maximum active power available from the primary source. This paper describes effective measures to droop based grid forming control to avoid overloads at frequency or phase drops if there is no reserve power available. At the same time the presented measures do allow grid forming behavior to the extend active power reserve is available. Within this work an analytical solution for the power transient due to phase jumps is presented. Simulations and laboratory results with real world parameters confirm the effectiveness of the proposed measures and the coincidence with the theoretical results.