Control of Energy Storage Equipped Shunt-connected Converter for Electric Power System Stability Enhancement

Licentiatavhandling, 2012

Flexible AC Transmission System (FACTS) controllers, 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 FACTS controllers family, the Static Synchronous Compensator (STATCOM) is a key device for the reinforcement of the stability in an AC power system. The STATCOM provides transient stability enhancement (TSE) and Power Oscillation Damping (POD) by controlling the voltage at the point of common coupling by using reactive power injection. This thesis investigates the application of the STATCOM with energy storage (here named E-STATCOM) to improve the dynamic performance of the power system. In particular, the focus of this work is on the development of a cost-effective control system for the E-STATCOM for POD and TSE. This is achieved using a signal estimation technique based on a modified Recursive Least Square (RLS) algorithm, which allows a fast and selective estimation of the low-frequency electromechanical oscillations in the measured signals during power system disturbances. The output of the POD and TSE controllers are active and reactive power references that are to be injected by the E-STATCOM. The performance of the POD and TSE controllers is validated both via simulation and through experimental verification. The robustness of the control algorithm against system parameter changes is verified through the tests. It is shown that with the selected input signals for the controller (based on local measurements), the E-STATCOM is able to guarantee a uniform stability enhancement regardless of its location in the power network.