An emergency control has been applied to power systems to avoid cascading outages by making the best use of existing equipment under severe fault conditions. Battery energy storage system (BESS) is one of the attractive equipment for the emergency control according to its growing installed capacity in the current grid. This paper investigates an effective use of BESS for transient stability improvement, and proposes a novel control scheme using wide-area information. The proposed control scheme adopts two stability indices, the energy function and rotor speed of the critical machine, to make it applicable to multi-machine power systems. Besides, it can control active and reactive power injection of the BESS coordinately to make the best use of its converter capacity for the stability enhancement. Digital simulations are conducted on the 32-machine meshed system with multiple BESSs. The results demonstrate that the BESSs controlled by the proposed method can improve the first swing stability and the system damping, and it is made clear how they improve the transient stability of the multi-machine power system. In addition, an impact of the reactive power control on the bus voltages around the installation sites is investigated to discuss a preferable way of their installation.
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