The dynamic stability analysis of wind turbines under different control strategies

The control strategies have influences on the dynamic stability of modern wind turbines. This article presents a theoretical investigation on this topic. The investigation is motivated by a vibration measurement of wind turbines in a wind farm. The mechanisms of control strategies influencing the dynamic stability have been discussed and the stability enhancement by means of time delay in pitch control is investigated. The results show that the optimum control of rotational speed for maximizing energy capture below rated power can improve the dynamic stability by suppressing the axially unstable vibrations of the wind turbines. At above rated wind speed, the control mode of fixed-speed variable-pitch can cause unstable axial vibrations of the wind turbines; variable-speed variable-pitch can suppress the unstable vibrations. Additionally an appropriate time delay in pitch control can effectively enhance the dynamic stability of wind turbines.