直驱风电机组与弱电网交互作用稳定分析

网侧变流器作为新能源发电单元与电网的接口，对电网系统的安全稳定运行有着重要影响。以直驱型风电机组网侧变流器为研究对象，采用小扰动数学建模方法，建立了包含锁相环和电压前馈环节的网侧变流器及其控制的数学模型，推导了其dq轴系下动态阻抗解析表达式，发现其阻抗在次同步频带呈负电阻（负实部）特性，与弱交流电网连接存在次同步频带不稳定现象。基于上述现象分析了影响稳定的关键控制参数及其特性，结果表明，增强网架强度、优化锁相环控制参数、增大电压前馈滤波频率可在一定程度上降低系统次同步振荡的风险，最后采用电磁暂态仿真验证了上述分析。

Interactive Stability Analysis between Direct-Drive Wind Turbinesand Weak Power System

As an interface between new energy power generator units and a power grid, the grid-side converter plays an important role in maintaining the safe and stable operation of power system. Based on the grid-side converter of direct-drive wind turbines, a math model of grid-side converter and its control including the phase-locked loop (PLL) and voltage feed-forward control is established in the paper using the small disturbance mathematic modelling method, and the dynamic impedance analytical expression under dq axis is derived. It is found that the impedance has the features of negative resistance (negative real part) in the subsynchronous frequency band and is unstable in subsynchronous frequency band when connected with weak power grid. The key control parameters that influence the system stabilities are analyzed. The results indicate that the subsynchronous oscillation risks can be reduced to some extent through enhancing the power grid strength, optimizing the PLL control parameters and increasing the voltage feed-forward filtering frequency. Finally, the above analytical results were verified by electromagnetic transient simulation.