弱电网故障下新能源并网变换器的奇异摄动模型与暂态稳定性分析

Singular Perturbation Model and Transient Stability Analysis of Grid-connected Converter Under Weak Grid Faults

弱电网短路故障下新能源并网变换器易于暂态失稳,但由于并网系统表现高阶、非线性和强耦合等特征,其暂态稳定性分析十分困难。已有研究大多局限于单锁相环系统,即忽略电流控制动态的影响,无法充分反映并网变换器的暂态失稳机理。针对该挑战,该文同时考虑锁相环和电流环的控制动态,研究弱电网故障下并网变换器的暂态稳定性。首先,建立并网变换器接入弱电网的奇异摄动模型,将原高阶模型降阶简化为二个低阶的快、慢子系统。然后,分别采用李雅普诺夫第一法和第二法分析了快、慢子系统的稳定性,由此揭示了工作点、线路阻抗和控制参数等多重因素对暂态稳定性的影响规律,并给出一些参数优化设计的指导原则。最后,通过实验验证了分析结果的正确性。

A grid-connected converter(GCC)is prone to transient instability under weak grid faults.However,it is very difficult to analyze the transient stability of GCC,due to the characteristics of high-order,nonlinear and strong coupling.Most of the existing works only study the phase-locked loop system and ignore the influence of current control,which cannot fully reflect the transient instability mechanism of GCC in weak grid.To cope with the issue,this paper studies the transient stability of GCC under weak grid faults,while considering the control dynamics of PLL and current loop.Firstly,the singular perturbation model of GCC is established,and then the original high-order model can be simplified to the low-order fast and slow subsystems.Afterward,the stability of the fast and slow subsystems is analyzed by Lyapunov’s first and second methods,respectively.On this basis,the effects of various factors on transient stability are revealed,and some guiding principles for control parameter optimization are given.Finally,the analysis results are validated by experiments.