Primary Frequency Control in a Power System with Battery Energy Storage Systems

This paper addresses the feasibility of a battery energy storage system (BESS) contribution to primary frequency control by simulating its state of charge over several days and by using frequency measurements in the Romanian power system. A BESS correction algorithm has been developed to overcome the average frequency asymmetry which may bring the state of charge to zero or 100%, thus not allowing further primary frequency control due to total discharge or total charge of the storage resource. It is demonstrated that for a number of selected days the algorithm provides good results, the primary frequency control is delivered over entire days, and that a reserve of energy remains in the battery for eventual disturbances in the system, for both over and under frequency needs.