Application of Series Compensation to Improve the Voltage Stability and Power Quality of Wind Farms

Abstract

This thesis deals with the dynamic responses of fixed-speed and variable-speed wind turbines (WTs) in terms of voltage stability and power quality issues using series compensation in both a transmission and distribution network. The main power quality aspects, such as voltage sag, flicker and harmonics, due to uneven power production by intermittent wind sources are presented, with static and dynamic voltage stability analyses under normal and contingency periods conducted. The latest regulations enforced by different utilities on wind power plants are studied and the impacts of power system modelling on stability analysed. Compensating devices, wind farms and loads are considered harmonics generating sources and are modeled according to the international standards. Both short-term and long-term flicker emissions of fixed-speed wind turbine (FSWT) and doubly-fed induction generator (DFIG) based wind farms are presented using series compensation while voltage sag analysis is carried out using failure data. To enhance transmission efficiency series compensation is implemented to utilise full transmission assets by reducing voltage drops in a long transmission line and feeder as most WTs are remotely located to obtain suitable wind conditions, and loss in a transmission line degrades the voltage profile of the network. Like the shunt compensation, series compensation can increase transient voltage stability and, to some extent, contribute to local voltage regulation. The case studies presented in this thesis illustrate the contributions of wind power plants and voltage source converter (VSC) based series compensation on the fault levels of symmetrical and asymmetrical faults. From stability and power quality analyses, the cases studied show that large-scale wind power penetration substantially degrades the voltage stability but that series compensation can enhance the collapse margin and reduce flicker and the sensitivity of bus voltage to reactive power, as well as improve both dynamic and transient voltage stability, including providing effective fault ride-through (FRT) support.