A series facts controller as a voltage fluctuation mitigation equipment : an experimental investigation
This research project addresses the mitigation of voltage fluctuations using a series-connected power electronics-based controller, which belongs to the family of Flexible AC Transmission Systems (FACTS) controllers. These are emerging technologies which have been under continuous development for over a decade, and are now available to the electricity supply industry world-wide, helping to ameliorate a wide range of power system phenomena, to increase power transfers and stability margins. Voltage fluctuation is a complex phenomenon affecting adversely transmission and distribution networks. Bulky fluctuating load, wind farms and large induction motor are the major sources of voltage fluctuations. As the phenomenon propagates, it interacts with other voltage fluctuations contributed by different sources, and affecting neighbouring lighting circuits, giving raise to a phenomenon termed light flicker. To ameliorate such a problem, a well-coordinated operation of advanced voltage mitigation equipment, control strategy and specialised measurements instruments are required. Considerable progress has been made in voltage fluctuations mitigation using shunt FACTS controllers. However, very little work has been reported in tackling the very complex issue of mitigation of voltage fluctuation propagating in the network using series FACTS controllers. To advance this area of research, this project addresses the design and construction of a three-phase scaled-down TCSC prototype and a voltage fluctuations experimental environment, suitable for real-time hardware-in-the-loop testing. The research work carries out a fundamental study of TCSC resonances, which are termed resonance modes. It is found that a non-explicit resonance mode at a=90° exists, and it is termed intrinsic resonance mode. For a well-designed TCSC, only the fundamental and the intrinsic resonance mode should be active. To facilitate the design, a procedure has been identified, based in the synchronisation of resonance modes. To achieve mitigation successfully, a new tailor-made TCSC control strategy, named RT-DIMR, and a flexible virtual flickermeter based on the IEC-61000-4-15 standard are thoroughly developed and integrated under the same real-time computing platform. The RT-DIMR demonstrates its capability for controlling the TCSC under different voltage fluctuation conditions. The lEC-Flickermeter provides online flicker severity indices, information which may be used to asses whether or not the electrical network has been effectively improved. The aim of this research work is to experimentally evaluate the TCSC capabilities to mitigate travelling voltage fluctuations. A scaled-down network and voltage fluctuation sources are constructed to mimic a voltage fluctuations propagation environment. A comprehensive number of experiments are carried out to test the mitigation scheme under a wide range of conditions. The robustness and effectiveness of the mitigation schemes have been thoroughly demonstrated. The newly developed TCSC prototype, scaled-down testing environment and RT-DIMR control strategy recommend themselves not only as an imaginative voltage fluctuations mitigation research tool, but also as a general advanced FACTS research tool.