As they are becoming increasingly widespread and at the same time their performance is increasing, wind farms are preferably erected at locations at which there good wind conditions, in particular on coastlines, at sea or in mountainous regions. In many cases, these are areas with only insufficient infrastructure, which applies in particular to wind farms at sea (so-called offshore wind farms), at which there is generally no infrastructure at all yet. This necessitates comparatively long line paths to consumers or to reach high-capacity distribution networks. Therefore, there are often voltage deviations in the case of wind farms with relatively high power feeds. The grid operators have responded to this and demand a greater voltage strength with respect to deviations from the rated voltage to an increasing degree from the wind turbines, wherein this voltage strength should also be provided in the case of operation with a power factor deviating from cos phi=1.
In order to extend the voltage range of the wind turbines, it is known to provide said wind turbines with a tap-changing transformer. In this case, the transformation ratio of the transformer can be changed by means of a switch so that the wind turbine can be matched in this way to different voltages on the upstream grid. Therefore, although a comparatively large voltage range can be covered, the switching times of these on-load tap changers are comparatively long (up to in the minutes range), which is considered to be too slow. In addition, the on-load tap changers are susceptible to wear. In order to avoid this problem, in principle a solution based on semiconductor elements can be provided. However, this has the disadvantage that the semiconductor elements need to be dimensioned so as to be markedly large and are therefore elaborate since the total power is transmitted via said semiconductor elements. For modern powerful wind turbines in the megawatts range, in practice this is barely possible.
USPTO Backgrounds
USPTO Backgrounds