Methodologies for estimating the inertia constant of a power system

Instantaneous power contribution is an intrinsic behavior of conventional Electrical Power Systems (EPS). Immediately after a disturbance, whole set of generators and motors deliver their kinetic energy stored in their rotating masses (inertial response). However, incorporation of distributed generation imposes new challenges related to reliability and stability of EPS. Replacement of conventional generators by those connected by power electronics leads to a decrease of system's rotational inertia. Reduction of the Inertia Constant (IC) mainly influences on frequency stability, resulting in faster and less damped frequency deviations than in conventional networks that could lead to EPS collapse. One way to counteract this issue is by providing virtual inertia controlling the DC / AC converters of the non-conventional generators. For covering the initial lack of power it is necessary to provide an instantaneous power reserve, generally coming from Energy Storage Systems (ESS). For dimensioning both, the power reserve and the ESS capacity, it is essential to know the system's IC and estimate how much additional inertia should be provided to prevent the system from collapsing in the face of future contingencies. This paper reviews different existing methodologies for estimation of IC of electrical networks, studying their characteristics and accuracy of their results. This analysis is aimed at having the bases to establish a methodology for sizing the necessary power reserve.