Improving dynamic stability and inter-area power transfer using FACTS controllers

Presence of low frequency oscillations is one of the most important issues in power system dynamic analysis. Damping of these oscillations has to be ensured in an effective manner so that the system dynamics remains stable under a range of operating scenario. Both Power System Stabilizer (PSS) and Flexible AC Transmission system have been used for this purpose in the past. Before analyzing the dynamics of a large power system it is helpful to reduce the system to an equivalent one. So, this thesis starts with the dynamic reduction of a local utility system. A two step reduction method is employed to obtain the equivalent system. Simulation software PSS/E is used to conduct the first step of reduction process. The dynamics of the reduced system in its current state is studied and an improvement in the damping feature of the overall system is achieved by tuning the PSS parameters based on an eigenvalue based objective function. Beside this, a Single Machine Infinite Bus (SMIB) system, the 3 machine WSCC system and the 10 machine New England System is considered to study the damping effect of PSS and Thyristor Controlled Series Capacitor (TCSC) on system low frequency oscillation. The tuning problem in these cases is formulated as an Integral of Time weighted Absolute Error (ITAE) based objective function minimization task for both PSS and TCSC. Particle Swarm Optimization (PSO) is then used to solve the optimization problem. The results show that the properly tuned PSSs can successfully damp out the low frequency oscillations and incorporation of TCSCs help to improve the oscillation in line power flow. This feature of TCSC can be used to increase the limit of line power transfer in a multi-area power system. The outcome also confirms the effectiveness of the methodology employed in obtaining the equivalent of multi-machine power system.