Wind Energy

174 E. Anahua et al.
Elec. Power Output [kW]
3000
2500
2000
1500
1000
500
0 0 5 10 15 20 25 30 35
Wind speed [m/s]
Fig. 31.1. Typical nonlinearity effects on measured power output data of a WEC
of 2 MW [5]. A complex behaviour is observed by the dynamics response on sudden
changes of wind velocity. The dots are instantaneous measured data and the solid
line is the average power output 〈L(u)〉
around 〈u〉, i.e. small turbulent intensities ti = σu/〈u〉. It is known that
the wind fluctuation distribution presents an anomalous statistics around the
mean value [1], therefore this is again limited. As an improvement, this article
reports that the dynamical behaviour of the power output of a WEC, which
acts as an attractor, can be described by a simple function of relaxation and
noise. We have shown that those two parts describe the power curve properly if
they are calculated from stationary wind measurements. This analysis is very
usefull to describe power curve characteristics for situation with increased
turbulent intensities and it can be easily applied to measured data.
31.2 Simple Relaxation Model
The instantaneous elect. power output of a WEC defined by: L(t) =Lfix(u)
+ ℓ(t) can be described by the following relaxation model [2], see also [6]
ℓ(t) ∝ e| −αt
d
L(t) =−αℓ(t)+g(L, t)Γ (t),
dt