Power System Stability Enhancement Using Shunt-connected Power Electronic Devices with Active Power Injection Capability

Sammanfattning: 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 optionalactive 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 controlalgorithm using local measurements. The selection of local signals to maximize the effectivenessof 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 LeastSquare (RLS) algorithm that extracts the required signal components from measured signals isdeveloped. The estimation method provides a fast, selective and adaptive estimation of the low-frequencyelectromechanical oscillatory components during power system disturbances. Thisallows to develop an independent multimode POD controller, which enables the use of multiplecompensators without any risk of negative interaction between themselves. With the proposedselection of local signals together with the estimation method, it is shown that the use of activepower injection can be minimized at points in the power system where its impact on stabilityenhancement 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 andthrough experimental verification using various power system configurations. The robustnessof 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 useof single or multiple compensators connected at various locations in the power system.