How can HOMER  recognise that rated wind speed, when i just put see performance curve into?

So it's a good question why the maximum wind power output is greater than the reported wind power capacity.  The reason is related to the shape of the power curve and the way HOMER extrapolates from it.  The power curve for that turbine slopes up at 20 m/s where the data end, as you can see in the graph below:

For any wind speed above 20 m/s, HOMER simply extrapolates linearly from the last two points.  That means HOMER expects the turbine output to continue to rise with increasing wind speed above 20 m/s. 

It is a rare power curve that slopes up like that, so usually it is okay to extrapolate from the power curve.