风电系统次同步等幅振荡的机理与特性分析

On Subsynchronous Sustained Oscillation Issues of Wind Power Systems

风电系统并网产生的次同步振荡问题近些年来得到了学术界和工业界的广泛关注。大量现场实测数据表明,风电控制器中的限幅等非线性环节对振荡特性有显著影响,往往导致负阻尼的发散振荡逐步演化为恒幅恒频的等幅振荡,且其幅值难以通过小信号模型解析求得。该文从闭环反馈原理的角度探讨了等幅振荡的产生机理,提出了考虑限幅非线性和dq轴耦合效应的风电并网系统频域传递函数模型,介绍了高维模型降维等效分析的原理与思路,探讨了等幅振荡的产生条件及其幅值、频率特性的解析计算方法,并结合时域仿真验证所提理论的有效性。

The subsynchronous oscillations emerged in grid-connected wind power systems have caused great attention in both academia and industry.Field measurement data have shown that the saturation nonlinearities in the converter control system have a great impact on oscillation characteristics and may lead to a diverging oscillation into a sustained oscillation.The magnitude and frequency of the sustained oscillation can hardly be assessed by small-signal techniques.This paper proposes the occurrence criterion of the sustained oscillation from the perspective of the closed-loop feedback control theory.A frequency-domain closed-loop model of the grid-connected wind farms is established with consideration of saturation nonlinearity and cross-coupling effects between d�and q-axis.Based on the proposed criterion and model,the magnitude and frequency of the sustained oscillation are analytically computed.Time-domain simulation verifies the effectiveness and accuracy of the proposed method.