Probabilistic design of facts device for power system small signal stability enhancement

Under economic and environmental pressures, electric power system becomes more heavily loaded, damping tends to reduce. Electromechanical oscillations occur more often than before, which not only impose unnecessary limitations on power system operation, but also affect system economics and security [1]. FACTs devices have been recognized as an effective means to this problem and to enhance the system performance. Among them, PSS has been recognized as one of the first measures to enhance the damping of power swing [2]. But with increasing transmission line loading over long distance, PSS might not provide sufficient damping. In these cases, other effective solutions are needed. A static VAr system (SVC), with an additional damping control loop, can be used to provide damping to system and increase the system small signal oscillation stability. SVC has good damping effect with the features [3] as: (a) more effective for controlling power swings at higher levels of power transfer; (b) the effectiveness of SVC for power swing damping is dependent on SVC placement. In general damping is most effective when SVC is located near the electrical midpoint of the intertie. In addition, it has been proved that the SVC voltage control has little influence on the improvement of the power system damping [4], and the extra damping control introduced by the SVC can provide the power system with damping and its capability increases at higher levels of load. So in this paper, authors use a simplified SVC model with voltage regulator neglected.