Studies On Voltage Fluctuation And Flicker Casued By Integrated Wind Power

Because the wind speed and wind direction are stochastic, and the generation of wind turbines is proportional to the cube of wind speed and depends on wind turbine characteristics, of course, it is unstable. This fluctuant power will affect the power quality of the imbedded grid, such as voltage fluctuation and flicker. My attention in this thesis is focused on modeling of voltage fluctuation and flicker caused by integrated wind power, and methods of the voltage fluctuation evaluation and flicker measurement. The main works of this thesis are: (1) An equivalent wind speed model is established in this thesis considering the effect of tower shadow and wind shear, and the torsion oscillation caused by the gravity deviation between different blades is analyzed. Based on the simulation results of a practical wind turbine, the characteristics of periodical power fluctuation caused by different factors are presented. (2) Study on modeling of constant speed and variable speed wind turbines. The dynamic wind turbine models with the imbedded grid parameters, established in this thesis, can be used to evaluate the voltage fluctuation caused by wind power. (3) An analysis method to simulate voltage fluctuation at all the nodes of a grid with wind farms is established in this thesis, called 'Equivalent current source with power frequency and fixed amplitude'. The current in this method can be with various forms. It can be used in practice as long as they can be demodulated. (4) Using time-varying dynamic phasor principle to calculate the voltage fluctuation. The time-varying dynamic phasor models of power line parameters are established, and a simulation is made in this thesis for a grid with wind farms using the models. The models established in this thesis can be used to calculate not only the voltage fluctuation resulting from operating wind farms but also the transient voltage caused by wind turbine switching. (5) A flickermeter model based on IEC standard is established in this thesis, in which an amendatory block is added that brings comparatively higher precision. This model can be used to measure the flicker produced by integrated wind power properly. In addition, the discrete method used for calculation of flicker caused by wind power is introduced, and the discrete method model is established in this thesis.