An efficient power control strategy for small fixed-pitch wind turbine to extend the operating range to high wind speed region

This paper deals with the control of small-power wind turbine using fixed-pitch blades. A three-phase permanent magnet (PM) brushless generator is connected to the grid through a double stage converter: active rectifier (VSR) + d.c.-link + inverter (VSI). A very simple and effective control strategy of the generation set (PM generator +VSR) is presented; it is mainly aimed to extend the wind-turbines operation range to high wind-speed region, maintaining the generated electric power constant and equal to its “rated” value. By means of this technique, the cut-off speed can be considerably increased with respect to the usual values on the market, improving the energy production of the considered mini-generation plant during the years. The numerical analysis carried out in the paper shows that the VSR has to be “reasonably” oversized, while the PM generator ratings are not modified, because the overload operations do not produce any dangerous over-heating. The improvements linked to the proposed technique are more evident when the turbine blades are properly designed and when the wind speed frequently exceeds the ordinary values. Moreover, the proposed control algorithm is also able to improve the efficiency of the wind conversion system for wind speed values lower than the rated one.