【摘要】 风电并网系统的次同步振荡现象具有频率漂移的特征。该文从风速变化影响模式间相互作用的角度解释了频率漂移的原因。首先,推导风电机组受风速影响的振荡模式:双馈风机定转子绕组和转子侧换流器电流内环控制主导的次同步振荡模式的频率;直驱风机直流电压外环主导的振荡模式的留数。然后,推导两输入两输出系统中振荡模式之间发生强相互作用的条件——开环模式耦合。最后,基于双馈风机-串补输电系统和混合风电场并网系统算例,采用模式分析和非线性仿真,演示了风速变化过程中模式交互作用的强弱变化导致的频率漂移的现象。由此得出,风速的随机性使得开环模式耦合条件具备了随机性,在时变场景下模式间的不利交互作用使得弱阻尼或负阻尼次同步振荡模式的频率是动态变化的,由此出现了频率漂移的现象。更多还原

【Abstract】 Frequency drift is the significant feature of subsynchronous oscillation in wind turbine generator intergrated power system. The paper examined the frequency drift from the perspective of modal interaction affected by the variation of wind speed. First, two subsynchronous oscillation modes of wind turbine generator affected by wind speed were presented. One is the oscillation mode dominated by the stator and rotor windings and rotor-side converter current inner control loop of doubly-fed induction generator and its frequency depends on the wind speed. The other is the oscillation mode dominated by the DC voltage outer loop of direct-drive permanent magnetic synchronous generator and its residue is affected by the wind speed. Then, open-loop modal coupling condition was derived to reveal the mechanism of strong interaction between two oscillation modes of double-input double-output system. Finally, based on a doubly-fed induction generator intergrated series compensated power system and a wind farm intergrated power system, modal analysis and nonlinear simulation were adopted to demonstrate the frequency drift caused by the change of the degree of modal interaciton with the variation of wind speed. The main conclusion of this paper is that the randomness of wind speed makes the open-loop modal coupling condition random and the adverse interaction between oscillation modes in time-varying scenarios makes the frequency of the weakly or negatively damped subsynchronous oscillation mode change dynamically, thus the phenomenon of frequency drift appears.更多还原