Data of frequency, for the real time estimation method

The inertia of a power grid is its first (and fastest)line of defense against variations of the frequency. As such, it isan important indicator for its robustness, in particular, its abilityto recover from faults that would cause a significant frequencydeviation. The increased penetration of renewable energy sourcesand battery storage stations in many electricity grids, that bringin high intermittency and little inertia, causes serious concernsabout stability and robustness. Transmission system operatorsas well as private companies are developing and implementingtools to estimate the inertia available in power grids, so that theycan mitigate the effects of lack of inertia, if needed. We proposea method for the real-time estimation of the total inertia, aswell as equivalent local inertia constants (these will be defined).For this, we partition the grid into several well-connected areas(clusters). The method involves injecting small steps of power(both positive and negative) from energy storage units, in eachof the mentioned areas, and measuring the step response ofthe frequency simultaneously across all points in the system.The steps may be small relative to the capacity of the powergrid, but by averaging over several measurements, we reducethe effect of the noise. Processing the step responses measuredin different points allows eliminating the effect of small interareaoscillations and thus, obtaining total inertia estimates. Weuse a simple grid model to derive our estimation method anddemonstrate its effectiveness in simulations and experimentallyin a microgrid comprising four areas.