A Robust Modified Harmony Search Evolutionary Technique for Transient Stability Enhancement in a Two Machine System Through STATCOM

Nowadays the increasing complexity and dimensionality of modern power systems have given rise to low frequency electromechanical oscillations (LFOs). These oscillations pose a major threat to the stability of power system and cause unnecessary limitations to its smooth operation. For the fast damping of system and successful mitigation of oscillations, Flexible AC Transmission System (FACTS) devices are utilized. Static Synchronous Compensator (STATCOM) is one such versatile shunt connected FACTS device that controls the bus voltage influencing the power flow and enhancing the transient stability of the system very fast because no moving parts are involved. However the PID controller of STATCOM is a linear controller that cannot respond effectively to non linear power system. Hence taking non linearities into account, the PID controller of STATCOM is tuned dynamically with a very robust and powerful meta heuristic optimization technique called harmony search inspired from improvisation process of jazz musician. It is a relatively recent technique that is considered superior because of its easy execution and reduced modifiable parameters. However it also has some noticeable defects like less convergence speed and premature convergence. To overcome the shortcomings of HS, a Modified Harmony Search (M-HS) is proposed in this paper to obtain much better transient as well as dynamic stability results. To justify and validate the effectiveness of M-HS optimized PID in reducing oscillations it is compared and contrasted with HS optimized PID and conventional PID of STATCOM using MATLAB/SIMULINK environment. Furthermore the THD calculation in each case is carried out. The results depict the efficacy and potential of M-HS techniques over HS and conventional PID controller in damping out oscillations and restoring system stability.