Design of a decentralized non-linear controller for transient stability improvement under symmetrical and unsymmetrical fault condition: A comparative analysis with SSSC

The efficacy and robustness of a nonlinear Power System Stabilizer (NPSS) in comparison with that of a series controlled FACTS device, the Static Synchronous Series Compensator (SSSC), is evaluated in this paper, to reinforce the transient stability of a multi-machine power system. The proposed controller is powered to control the three main parameters affecting the stability of the system; namely rotor angle, slip, and power output in a coordinated manner. A nonlinear feedback law is proposed in this work in order to make an effective comparison of transient stability with that of an existing nonlinear controller, which converts a nonlinear power system into closed loop decentralized linear time varying systems. The proposed feedback controller has been designed using linear quadratic regulator to stabilize the decentralized linear time varying systems. The performance of the proposed method has been tested on a 3-machine, 9-bus WSCC system in presence of SSSC device, and a 4-machine, 10-bus system. Its validity is examined for detailed model of generators through time domain simulation.