Power System Stability Improvement with Flexible A.C. Transmission System (FACTs) Controller

Transient stability is important from the view point of maintaining system security that is the incidence of a fault should not lead to tripping of generating unit due to loss of synchronism and the possibility of a cascaded outage leading to system black out. TCSC allows the fundamental capacitive reactance to be smoothly controlled over a wide range. The TCSC controller can be designed to control the power flow, to increase the transfer limits or to improve the transient stability. The TCSC controller can provide a very fast action to increase the synchronization power through quick changing of the equivalent capacitive reactance to the full compensation in the first few cycles after a fault, hence subsequent oscillations are damped. In the present work TCSC controller for single machine infinite bus (SMIB) and multi-machine power system is designed using SIMULINK (a software tool associated with MATLAB). Multi-machine power system with turbine and governing system is modeled. Modeling is done for system with TCSC controller. Effect of TCSC controller parameter variation on rotor angle is also studied. A detailed analysis is conducted for the proposed controller for different fault clearing time. It has been observed that TCSC controller can improve the stability margin significantly. TCSC controller provides variable impedance, which is required for the compensation. The presented controller is suitable only in capacitive zone. For the transition from a capacitive vernier mode to bypass mode the TCSC controller can be modeled with detailed dynamics.