Immunity of Grid-Forming Control Without Energy Storage to Transient Changes of Grid Frequency and Phase

European grid operators in ENTSO-E and others with a significant amount of inverter-based generation are experiencing a reduction in system inertia and short-circuit power. The changes in these key parameters are due to both an increasing number of inverter-based resources and also STATCOMS and HVDC terminals operating in a grid-following mode. Grid-forming control is a promising technology for renewable energy resources to provide appropriate grid support. However, wind energy and photovoltaic units cannot increase their active power output when operating in a maximum power point mode, as it would be needed for full grid-forming operation. Both operating at less than optimum power output or adding storage would increase the cost of generation. This article proposes extensions to the grid-forming control of inverter-based energy resources without energy storage. This would limit grid supporting nature for positive frequency or phase changes only. The proposed extensions give grid-forming control the necessary immunity to negative frequency or phase changes without the need to rely on a fast phase-locked loop or fast current control loops. This proposed control scheme has been used to evaluate the response to grid disturbances given in the ENTSO-E Phase I report of the task force grid-forming control published in April 2024.