Electric power system inertia online identification method and system based on ARMAX model

The invention provides an electric power system inertia online identification method and system based on an ARMAX model, common faults of a power grid are decomposed into pulse disturbance and step disturbance based on common commutation failures and direct current locking faults in an electric power system, and an inertia identification method based on pulse response and an inertia identification method based on step response are provided. After parameter identification is carried out based on actually measured active power and frequency data, different order determination (or order reduction) is carried out on a system model according to different disturbance forms: if the disturbance is pulse disturbance, parameter identification is carried out and a balance truncation method is adopted to judge whether the disturbance can be reduced to 1 order, and if so, pulse response is reserved and applied for further inertia time constant identification; if not, the system model of the order is abandoned; and if the