当弱电网发生不对称故障时,双馈风力发电机(DFIG)与电网阻抗之间会形成正序和负序间的耦合通路,导致交互作用复杂化.根据并网导则的要求,风力机组需向电网提供正、负序动态无功支撑,但若正、负序电流控制参数设置不合理,系统将面临失稳振荡风险.首先采用谐波线性化方法建立DFIG并网系统的序阻抗模型,分析了正序有功、正序无功、负序无功电流对系统稳定性的影响规律,并对序间耦合致稳机理进行了研究.其次,综合考虑稳定性约束、并网导则约束以及变换器容量限制,对DFIG的运行域进行量化表征.针对DFIG稳定运行域不足的问题,提出一种振荡自适应抑制的锁相环控制方法,实现了对锁相环输入振荡分量的自适应抑制,从而扩展了DFIG的稳定运行域.最后,仿真算例验证了理论分析的正确性以及所提控制方法的有效性.

In asymmetric weak grid, there exists a complex coupling path between the positive- and negative-sequences of the impedance between a doubly-fed wind turbine (DFIG) and the grid, leading to intricate interactions. Since grid codes require wind turbines to provide positive- and negative-sequence dynamic reactive power support, improper settings of these currents may result in system instability and oscillations. Therefore, this paper first develops a sequence impedance model of the DFIG-grid system using a harmonic linearization method, revealing the effects of positive-sequence active current, positive-sequence reactive current, and negative-sequence reactive current on system stability, and analyzes the stability mechanism induced by inter-sequence coupling. Furthermore, considering stability constraints, grid codes, and converter capacity, it characterizes the stable operating domain of the DFIG. To solve the problem of insufficient stable operating range in weak grid, it proposes an adaptive oscillation suppression phase-locked loop (PLL) method, which adaptively suppresses the oscillatory component in the PLL input, thereby extending the stable operating domain of the DFIG. Finally, simulation results verify the correctness of the theoretical analysis and the effectiveness of the proposed control method.