Abstract
The thesis first presents the basics influences of wind power on
the power system stability and quality by pointing out the main power
quality issues of wind power in a small-scale case and following,
the expected large-scale problems are introduced. Secondly, a dynamic
wind turbine model that supports power quality assessment of wind
turbines is presented. Thirdly, an aggregate wind farm model that
support power quality and stability analysis from large wind farms
is presented. The aggregate wind farm model includes the smoothing
of the relative power fluctuation from a wind farm compared to a
single wind turbine. Finally, applications of the aggregate wind
farm model to the power systems are presented. The power quality
and stability characteristics influenced by large-scale wind power
are illustrated with three cases. In this thesis, special emphasis
has been given to appropriate models to represent the wind acting
on wind farms. The wind speed model to a single wind turbine includes
turbulence and tower shadow effects from the wind and the rotational
sampling turbulence due to the rotation of the blades. In a park
scale, the wind speed model to the wind farm includes the spatial
coherence between different wind turbines. Here the wind speed model
is applied to a constant rotational speed wind turbine/farm, but
the model is suitable to variable speed wind turbine/farm as well.
The cases presented here illustrate the influences of the wind power
on the power system quality and stability. The flicker and frequency
deviations are the main power quality parameters presented. The power
system stability concentrates on the voltage stability and on the
power system oscillations. From the cases studied, voltage and the
frequency variations were smaller than expected from the large-scale
wind power integration due to the low spatial correlation of the
wind speed. The voltage quality analysed in a Brazilian power system
and in the Nordel power system from connecting large amount of wind
power showed very small voltage variations. The frequency variations
analysed from the Nordel showed also small variations in the frequency
but it also showed that the wind turbines excites the power system
in the electromechanical modes. Concerning the stability analysis,
the study cases showed that large-scale wind power modifies the voltage
stability of the power system and can cause power oscillations. It
is showed here that the reactive power from the wind farms is the
key factor on the voltage stability problem. During continuous operation,
the distributed wind power variations did not give any problems to
the power system stability concerning the power oscillations.
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