Performance and structural load analysis of small and medium wind turbines operating with active speed stall control versus pitch control

The objective of this paper is to investigate the performance pitch and active speed stall control, and their impact on the structural loads of small and medium wind turbines (SMWTs). Large wind turbines use blade pitching to limit the power at high wind speeds. For SMWTs, the cost and complexity of a blade pitching system are not justified, so that passive yaw, stall control, or a furling tail mechanism is used instead. However, the choice of a proper control concept is not straightforward for SMWTs. In this regard, it is important to take into account that the control strategy has a significant impact on the structural loads. Reducing the structural loads results in a longer lifespan and ensures the safe operation of the wind turbine in stormy wind gusts or fierce winds. In this study, a 10 kW wind turbine is operated with different control strategies to investigate the corresponding loads, both in uniform and turbulent winds. The simulation results show that controlling power around the rated value is feasible and stable for both control strategies. However, active speed stall control increases the bending moments at the blade root, while it lightens the tower base moments, in contrast to the pitch control.