Energy functions for FACTS devices with an energy-storage system

An energy-storage system (ESS) can provide additional capabilities for FACTS devices in dynamic power-flow control, and in this way improve electric-power system stability. In order to assess their influence on the system's dynamic behavior or to determinate the device's control strategy using direct methods, proper energy functions for these devices are needed. In this paper the energy functions for the whole spectrum of FACTS devices with an ESS have been developed. For each of the devices various energy functions were proposed according to the control strategy applied. The energy functions were constructed as additional terms that can be added to any existing structure-preserving energy function (SPEF). Tests within a single-machine infinite-bus system proved the correctness of the proposed energy functions. The application of new energy functions was demonstrated on the problem of transient-stability assessment. Copyrighi (C) 2006 John Wiley & Sons, Ltd.