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Summary One of the effective approaches to maintain power generation consumption balance during contingencies and therefore transient stability of the system is instantaneous rise of generation power and changing the generators excitation control system. This article proposes an auxiliary droop controller, which can replace generator main controller in order to maintain the transient stability of the system at the time of fault occurrence. Because of its linear structure, the proposed droop controller has a high response speed, so it can well supply the additional power demand given the rapid changes of the electric power demand at the time of fault occurrence. The proposed controller replaces the main controller of the generator that has the most impact on the maintaining system transient stability. Therefore, in the proposed method, first, the most efficient generator of the grid is identified using trajectory sensitivity analysis. Then, to maintain balance between power generation and consumption at the worst time of fault occurrence, the smallest amount of auxiliary controller slope is calculated through trajectory sensitivity analysis. Therefore, under any contingencies occurrence in the system, replacing the main controller with an appropriate auxiliary one will guarantee the transient stability of the system. The affectivity of the proposed method is shown using simulations on the IEEE 33‐bus test system. The simulation results show that the proposed auxiliary control method can lead to the at least 20% increase of critical clearing time (CCT) compared to the conventional droop control method. Furthermore, it is robust against the changes of inertia, up to 5%, as one of the main parameters in the first swing stability of the system.

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