| Summary: | The modern power system has undergone a significant transformation in the way it generates electrical energy. Increased levels of renewable generation has resulted in a reduction of conventional thermal plant and as a consequence introduced new challenges for network managers. Monitoring of recent power transfer activity between the regional power systems of Ireland has identified periods of sustained electromechanical mode resonance. As a matter of technical coincidence power pulsations at a frequency that coincides with existing system electrical modes have been detected at fixed-speed wind farms connected to the Northern Ireland power system. Prompted by the prevalence of fixed-speed wind turbine technology in Ireland, analysis carried out by research presented in this thesis sought to establish if low-frequency oscillations created by blade-passing (3-p) phenomenon of grid-connected fixed-speed wind farms are capable of influencing power system small-signal stability either by damping or reinforcing existing electromechanical modes. With the aid of electrical data measurements of grid-connected fixed-speed wind farms, visual-recognition software was developed to extract blade angle information from video frame sequences and correlate it with time-synchronised data. Visual analysis of turbine blade movement identified periods of synchronised blade-passing between groups of turbines that resulted in oscillations of greater magnitude at the wind farm level. A unique wavelet-Prony method developed as part of this investigation was used to characterise blade-passing properties of two fixed-speed wind farms over a full range of outputs. Blade-passing characteristics of both wind farms displayed greater mode amplitudes at rated output but with faster decay times. Eigen-analysis performed on a small inter-connected system with high levels of wind penetration exhibiting 3-p oscillatory modes revealed a significant improvement in intra and inter area mode damping. Studies on a larger system operating under high levels of dynamic system demand however, demonstrated electromechanical mode instability under the influence of blade-passing power pulsations. Based on simulation studies it can be concluded that there is a necessity for blade-passing rotational dynamics to be incorporated in future small-signal analysis especially in studies where there are large concentrations of fixed-speed wind farms.
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