Improvement of Power System Stability Using Coordinated Design of Facts Devices and Excitation Controllers

Abstract

This thesis is concerned with the optimal design of coordinated series Flexible AC Transmission Systems (FACTS) devices with Power System Stabilizer (PSS) in excitation system of power systems for damping out the Low Frequency Oscillations (LFO) and hence improving the system stability during disturbance and steady change of operating conditions during gradual change in load demands. The existence of LFO does not allow the steady state power flow in transmission line and persistence of LFO for long duration may create instability and even cascading outage if sufficient damping action is not taken immediately. Thyristor Control Series Capacitor (TCSC) and Static Synchronous Series Compensator (SSSC) are two series FACTS devices employed in this thesis work for auxiliary power oscillation damping (POD) controller. The work is focused on the improvement of the rotor angle stability that includes small signal stability and transient stability of power systems. Since, the stability depends on the design of FACTS devices and PSS controller, the conventional lead-lag structure of PSS has been modified to classical controller such as PD, PID and fractional PID type PSS for improving the behavior of system characteristics. The linear control theory is used in linearized Heffron-Philips model of power systems to find the closed loop dominant eigen values from which the damping ratio and natural frequency of oscillations are investigated to ensure the effectiveness of the controller. The stability improvement of nonlinear power system has been investigated with Multi-Input and Single Output (MISO) control structure than that of Single Input and Single Output (SISO) structure. Both local and remote control signals are investigated and employed in the proposed controller. It is found that, the remote signal in the analysis of system stability is more effective due to its controllability and observability properties. The work has also been done to construct the remote signal from the availability local signal and applied in co