考虑PLL和接入电网强度影响的双馈风机小干扰稳定性分析与控制

Small Signal Stability Analysis and Control of Double-Fed Induction Generator Considering Influence of PLL and Power Grid Strength

国内外风电事故表明:风电经远距离线路外送时,系统容易在发生扰动的过程中出现频率为几到几十Hz的功率振荡现象,且其振荡原因难以用传统同步发电机小扰动振荡的机理完全解释。考虑到风电机组主要通过锁相环与电网之间实现功率耦合,从而锁相环动态特性将会影响系统小干扰稳定水平。该文首先建立了含有锁相环动态特性的双馈风电机组–无穷大系统的动态模型;采用特征值分析研究了风机不同运行状态下其接入电网强度变化对风电系统中各个振荡模式的影响规律;然后通过复转矩分析理论解释了风电系统的失稳机理,研究结果表明:锁相环振荡是导致风电系统并入弱电网系统发生小扰动失稳的主要原因。最后,提出一种基于相位补偿的风电机组阻尼控制器来抑制该振荡现象,仿真验证了其有效性。

Wind power accidents occurred in the world show that wind power delivered by a long-distance transmission line system will be excited power oscillations with frequency in range from several tens to hundreds Hz by disturbances. Moreover, this oscillation reason cannot be able to fully explain by the small signal oscillation theory of synchronous generator. Since the wind turbine mainly realizes the coupling between itself and power grid through the phase-locked loop （PLL）, the dynamic characteristics of the PLL will seriously affect the small signal stability of power system. This paper established a single double-fed induction generator （DFIG） infinity-bus model considering the dynamic characteristics of PLL, and analyzed the characteristics of small signal stability under different operating conditions and various power grid strengths. The analysis results show that： PLL oscillation is the main reason leading to small signal instability of a weak power system grid integration of wind power. Finally, a damping controller based on phase compensation was proposed to suppress oscillation instability problem. Simulation results verify the validity of the analysis results and proposed damping controller.