I. INTRODUCTION
Wind turbines are the most common wind energy conversion
systems. Even though they are able to compete with
fossil fuels at some favorable areas, it is necessary to develop
the technology in order to gain an edge on a big scale and
reduce the power production price. On the individual wind
turbines, the production price can be reduced by maximizing
the generated power and minimizing the dynamic loads,
thereby increasing the energy production on the life span of
the turbine. However because of the aerodynamics interaction
[1], maximizing wind turbine powers individually does not
lead to a maximized power on the wind farm scale. For
example in an early work [2], the authors have shown a
wind farm controller can in fact increase the energy. Different
methods for maximizing the produced power of a wind
farm is suggested. For example in [3] and [4] the wake
interaction is minimized by finding suitable tip speed ratio
and pitch angle for individual wind turbines. The results
show an increase in the produced power compared to the
normal operation case. In [5] and [6] the focus has also
been on wind farm control taking loads into account. In [4]