Low Frequency Oscillations (LFO) occur in power systems because of lack of the damping torque .Low frequency oscillations (LFO) are a frequent adverse phenomenon which increase the risk of instability for the power system and thus reduce the total and available transfer capability (TT C and ATC). This brief investigates the damping performance of the static synchronous series compensator (SSSC) equipped with an auxiliary fuzzy logic controller (FLC). This manuscript investigates the damping performance of the Static Var Compensator (SVC) equipped with an auxiliary controller based on Adaptive Neuro-Fuzzy Inference System (ANFIS). First of all, a modified Heffron-Phillips model of the single machine infinite bus (SMIB) system installed with SVC is established. In the following an auxiliary fuzzy logic controller (FLC) for SVC is designed to enhance the transient stability of the power system. Next, an ANFIS based auxiliary damping controller is welldesigned and compared with the FLC. In order to evaluate the performance of the proposed ANFIS based controller in damping of LFO, the SMIB power system is subjected to a disturbance such as changes in mechanical power. The complete digital simulations are performed in the MATLAB/Simulink environment to provide comprehensive understanding of the issue. Simulation results demonstrate that the developed ANFIS based controller would be more effective in damping electromechanical oscillations in comparison with the FLC and conventional proportional-integral (PI) controller.
The dynamic voltage restorer (DVR) is one of the modern devices used in distribution systems to protect consumers against sudden changes in voltage amplitude. In this paper, emergency control in distribution systems is discussed by using the proposed multifunctional DVR control strategy. Also, the multiloop controller using the Posicast and P+Resonant controllers is proposed in order to eliminate the steadystate error response and to improve the transient response in DVR, respectively. The proposed algorithm is applied to some disturbances in load voltage caused by induction motors starting, and a three-phase short circuit fault. Also, the multiloop controller using the Posicast and P+Resonant controllers is proposed in order to improve the transient response and eliminate the steady-state error in DVR response, respectively. The proposed algorithm is applied to some disturbances in load voltage caused by induction motors starting, and a three-phase short circuit fault. Also, the capability of the proposed DVR has been tested to limit the downstream fault current. The current limitation will restore the point of common coupling (PCC) (the bus to which all feeders under study are connected) voltage and protect the DVR itself. The innovation here is that the DVR acts as a virtual impedance with the main aim of protecting the PCC voltage during downstream fault without any problem in real power injection into the DVR. Simulation results show the capability of the DVR to control the emergency conditions of the distribution systems.