Coordinated power control of unified power flow controller and its application for enhancing dynamic power system performance

Abstract

This thesis focuses on reporting my research study on a problem area relating to use of Unified Power Flow Controller (UPFC) for coordinating load flow in power systems so as to enhance their static and dynamic performance by having more secure and economical operation and higher dynamic stability margin. UPFC is considered as one of the most promising devices for implementing the Flexible AC Transmission System (FACTS) concept. Although development of UPFC is still on an infant stage, probing into its impact on power system operation is actively pursued and significant effort has been devoted to put it forward as a practical FACTS device and as a challenging academic research object. In order to consider UPFC as a basic power system element, it has to be involved in associated load flow computation essentially for power system control analysis and operational planning. An up front problem for design engineers is therefore pointing to a need to modify existing load flow program so as to accommodate interactions of UPFCs. A lot of research output start coming out but their computational efficiency are not high enough. In this regard, I propose two methods to perform the UPFC embedded load flow calculation to cater for two different types of application. The first one caters for analyzing direct control of load flow on transmission lines with embedded UPFCs. In this type of problem, active and reactive power of the lines, as well as the magnitude of bus voltages are priori given. The load flow solution can then be obtained and enables the UPFC parameters to be determined with a significantly improved computational efficiency. The second one works in contrary to the first one by which parameters of UPFCs are given before hand and the load flow calculation is performed for conforming a feasible operation. It can be regarded as an indirect load flow control calculation which is useful in planning stage for incorporating UPFC into existing system and/or carrying out various optimization processes. The next major contribution of my research project reported on the thesis relates to determination of optimal location of UPFCs which is practically important when coming to decision-making for installing and implementing the devices. As an extension on the use of the load flow calculation model, I develop an optimizing technique for identifying optimal location of UPFCs using Augmented Lagrange Multipliers method. At last but not the least, I develop a dynamic model of UPFCs embedded power system for which dynamic performance analysis is carried out. Coordinated power control strategy is derived to show that UPFC can play an important role in mitigating power system oscillations and enhance dynamic stability margin of the system.