风电并网系统次同步等幅振荡机理与特性分析

Mechanism and characteristics analysis of sub-synchronous constant amplitude oscillation in wind power grid connected systems

针对直驱风电并网系统次同步等幅振荡形成机理及限幅环节动作对振荡特性的影响问题,基于时域模型复现了因直流电压外环比例积分(PI)调节器输出限幅饱和引起的次同步等幅振荡现象,重点分析了限幅环节对系统动态特性的影响.基于特征值分析法,从限幅饱和后直流电压环失效所获得的物理降阶系统的角度,解释了限幅环节动作后直驱风电并网系统发生次同步等幅振荡原理.结果表明:直流电压外环PI调节器输出限幅环节周期性陷入饱和会显著影响系统的动态行为;限幅环节周期性陷入饱和过程中伴随系统周期切换,主导次同步振荡模态随之切换,次同步等幅振荡特性表现为发散振荡和衰减振荡的耦合,而不是传统意义上阻尼比为零的等幅振荡.

In response to the formation mechanism of sub-synchronous constant amplitude oscillation in direct drive wind power grid connected systems and the impact of limiting link actions on oscillation characteristics,based on a time domain model,the phenomenon of sub-synchronous constant amplitude oscillation caused by saturation of the output limiting amplitude of the DC voltage outer loop PI regulator was replicated,with a focus on analyzing the impact of the limiting link on the dynamic characteristics of the system.Then,based on the eigenvalue analysis method,from the perspective of the physical reduction system obtained from the failure of the DC voltage loop after amplitude limiting saturation,the principle of sub-synchronous equal amplitude oscillation in the direct drive wind power grid connected system after the action of the amplitude limiting link was explained.The results indicate that the periodic saturation of the output limiting link of the direct current(DC)voltage outer loop proportional integral(PI)regulator will significantly affect the dynamic behavior of the system.During the periodic saturation process of the limiting link,the system undergoes periodic switching,and the dominant sub-synchronous oscillation mode undergoes switching.The sub-synchronous constant amplitude oscillation characteristic exhibits a coupling of divergent oscillation and attenuated oscillation,rather than the traditional constant amplitude oscillation with zero damping ratio.