An improved method for estimation of inertia constant of power system based on polynomial approximation

Installation of phasor measurement units (PMUs) in a number of Iranian power grid substations has offered a set of precise and coherent information of system quantities, specially at event times. Inertia constant of a power grid is one of the criteria of system stability and is a basis for scheduling of spinning-reserve support generators. Estimation of grid inertia constant necessitates precise information of system frequency at the occurrence of generation rejection or load loss events. This paper presents an improved method based on polynomial approximation for calculation of inertia constant. The power system representative model changes at the events of generation rejection or load loss due to responses of generation units to frequency variations. The proposed method takes into account the non-homogeneous nature of system at the occurrence and during an event, so that the system model variations will not deteriorate the accuracy of estimation. The proposed method is examined to estimate the inertia constant of Iranian power grid using frequency information during generation outages, recorded by PMUs. Experimental results reveal that the new method is more robust compared to existing ones and significantly reduces the sensitivity of derived values to two hazy factors which are the exact event time and the polynomial order of the approximation.