Coordinated power system stability control

Abstract

This thesis proposes a novel power system control framework toward universal type controllers which flexibly respond to all stability problems in a coordinated way. It aims to improve power system stability over a wide range of the anticipated operating region with robustness to different faults. By effectively allocating power system resources, different stability issues in different time frames, including transient angle stability, voltage stability and damping of long-term inter-area oscillations following a disturbance can be maintained. The development of this coordinated control framework, called global control, includes the determination of its control hierarchy, the formulation of stability indices and the evaluation of the performance of different power system controllers. The implementation includes sensing the power system parameters and operating states in real-time, determining the (optimized) switching schedule and the actuation of control commands. The use of power electronic devices in the implementation of global control is emphasized. Various controller models such as Static Synchronous Compensator (STATCOM), Static Reactive Power (VAr) Compensator (SVC), Thyristor Controlled Series Capacitor (TCSC), On-Load Tap Changer (OLTC) and Unified Power Flow Controller (UPFC) and their corresponding control modes have been adopted with refinements in this thesis. In particular, interactions between TCSC, OLTC and SVC are studied. The results show that the power system security would be compromised should the controllers not be properly tuned and coordinated. Under the proposed framework, however, dissimilar controllers like those scattered at different parts of the power system can all be coordinated for power system stability improvement. The two-level control architecture introduced in this thesis separates global coordinated controls from local controls; i.e. coordinated control actions will only be activated and swarm in to rescue the system if any of the pre-defined power system instability indicators are high, e.g. exceeds its threshold value. The original functionality of the local controllers is thus preserved. Optimization routines can also be incorporated into the control framework to maximize the overall stability improvement. This coordinated control framework has been applied in various power systems including the WSCC 3-machine 9-bus (3M9B) test system, the IEEE two-area benchmark system and the 2002 South China power network. The simulation results have shown that the global control schemes are capable of improving various kinds of stabilities and handling multiple contingencies at once. Fast-response power electronic devices play an essential role in enabling the implementation of the proposed control framework. Therefore, an evaluation of some STATCOM designs at circuit level, along with hardware verification of the functionality of the STATCOM in a test power system is performed. Some practical guidelines for .the design of control systems are established. In summary, the results from this thesis suggest that with the proper use of the existing technologies, such as power electronic control devices along with communications and computing technology, it is possible to develop a selfmonitoring, self-correcting and self-healing power system, which guarantees power quality, safety, uninterruptible supply and reliable delivery.

Date of Award	15 Jul 2005
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	S.Y. Hui (Supervisor) & David John HILL (Supervisor)