控制策略对风力机振动稳定性的影响

研究了控制策略对风力机振动稳定性的影响,揭示了定转速变桨和变转速变桨控制方式对稳定性产生影响的机理,解释了变桨时延改善风力机抗振稳定性的物理意义。研究结果表明,额定功率之下的最佳转速控制有利于提高风力机的稳定性。而额定风速之上的定转速变桨控制方式会使风力机轴向振动失稳。采取变转速变桨控制方式并选取恰当的变桨时间延迟会有效地抑制风力机的失稳振动。变桨时间延迟τ应选择在(25%～75%)T区间内(T为风力机轴向振动的周期),最佳时间延迟为T/2。

The Dynamic Stability of Wind Turbines due to Different Control Strategies

The control strategies have essential influences on the dynamic stability of modern wind turbines.This paper presents a theoretical investigation on this topic.The investigation is motivated by a vibration measurement of 4 wind turbines with capacity of 1.5 MW in a wind park.The wind turbines always get into a violent axial vibration above rated wind speed,which is finally confirmed as an instability event associated with pitch control system.In this paper the mechanisms of control strategies influencing the dynamic stability are revealed,and the stability enhancement by means of time delay in pitch control is ascertained.The results show that the optimum control of rotational speed for maximizing energy capture below rated power will improve the dynamic stability suppressing the axial unstable vibrations of wind turbines.Above rated wind speed,two control modes can be used to keep the power output equal to rated power.One is fixed speed and variable pitch,and another is variable speed and variable pitch.However the control mode of fixed speed and variable pitch can cause unstable axial vibrations of wind turbines,pitch control with variable speed can suppress the unstable vibrations.Additionally an appropriate time delay τ in pitch control can effectively enhance the dynamic stability of wind turbines.The optimum time delay is Topt(T is the period of the axial vibration of wind turbines).