Transient Stability Enhancement and Assessment of Systems Comprising Controllable Series Devices

U. Gabrijel and R. Mihali? (Slovenia)


FACTS, transient stability, control strategies, CLF, energy functions, CCT.


In this paper we use the Lyapunov theory to develop control laws for controllable series devices (CSDs) that help improve transient stability. If the resulting bang-bang control strategies are performed a maximum effect on the stability margin enhancement will occur. In our considerations we included the following devices of the FACTS (Flexible AC Transmission System) family: Controllable Series Compensation, Static Synchronous Series Compensation, Phase Angle Regulator and QBT (Quadrature Boosting Transformer). The presented control laws are in accordance with previously developed concepts while the QBT control strategy is new and offers the device’s best utilization in both steady and dynamic operation. Furthermore, we introduce new energy functions that make it possible for the direct method to acquire the critical clearing time (CCT) of a single machine-infinite bus (SMIB) system that includes a CSD. Here the developed control laws are considered. We propose that these energy functions are used in power systems that can be reduced to a SMIB without losing the information about the CSD location (e.g. remote generation or interconnection). Their practical value was validated using a numerical example of a CCT evaluation where only small deviations from the results gained by digital simulations were noted.

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