THESIS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Power System Stability Enhancement Using Shunt-connected Power Electronic Devices with Active Power Injection Capability

Power electronic devices such as Flexible AC Transmission Systems (FACTS), both in shunt and series configuration, are widely used in the power system for power flow control, to increase the loading capability of an existing line and to increase the security of the system by enhancing its transient stability. Among the shunt-connected FACTS controllers family, the Static Synchronous Compensator (STATCOM) and the Static Var Compensator (SVC) are two key devices for reinforcing the stability of the AC power system. Among other functions, these devices provide transient stability enhancement (TSE) and Power Oscillation Damping (POD) functions by controlling the voltage at the Point of Common Coupling (PCC) by using reactive power injection. This thesis investigates the application of shunt-connected power electronic devices with optional active power injection capability to improve the dynamic performance of the power system. In particular, the focus of the work will be on developing an effective POD and TSE control algorithm using local measurements. The selection of local signals to maximize the effectiveness of active and reactive power for the intended stability enhancement purpose is described. To implement the control methods, an estimation technique based on a modified Recursive Least Square (RLS) algorithm that extracts the required signal components from measured signals is developed. The estimation method provides a fast, selective and adaptive estimation of the lowfrequency electromechanical oscillatory components during power system disturbances. This allows to develop an independent multimode POD controller, which enables the use of multiple compensators without any risk of negative interaction between themselves. With the proposed selection of local signals together with the estimation method, it is shown that the use of active power injection can be minimized at points in the power system where its impact on stability enhancement is negligible. This leads to an economical use of the available energy storage. Finally, the performance of the POD and TSE controllers is validated both via simulation and through experimental verification using various power system configurations. The robustness of the POD controller algorithm against system parameter changes is verified through the tests. With the proposed control methods, effective stability enhancement is achieved through the use of single or multiple compensators connected at various locations in the power system.