双馈风电系统虚拟同步控制的阻抗建模及稳定性分析
Impedance Modeling and Stability Analysis of Virtual Synchronous Control Based on Doubly-fed Wind Generation Systems
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摘要: 双馈风电系统在弱电网条件下与电网交互作用带来的稳定性问题凸显,采用虚拟同步控制策略为电网提供频率支撑的同时可能存在小扰动稳定性问题。该文针对虚拟同步控制下双馈风电系统的并网稳定性问题,提出一种dq旋转坐标系下输出阻抗建模的稳定性分析方法。首先,基于双馈风电系统的虚拟同步控制策略,利用小扰动分析方法,推导计及功率外环的双馈风电系统的阻抗模型。其次,获取虚拟同步控制下双馈风电系统输出阻抗特性,并通过基于模型的频率扫描方法进行比较验证。最后,利用广义奈奎斯特判据,分析不同电网强度和控制参数对虚拟同步控制下双馈风电系统稳定性的影响,并通过时域仿真结果进行对比验证。结果表明,由于功率外环作用,虚拟同步控制下双馈风电系统可能存在低频段稳定性风险,通过适当增大虚拟惯性时间常数和虚拟阻尼系数可提高其并网运行的稳定性。Abstract: The stability problem of interaction between doubly fed induction generator（DFIG） based wind generation systems and the weak grid is highlighted, however the virtual synchronous control based DFIG wind generation systems may have small disturbance stability problem while providing frequency support for the weak grid. Aiming at the grid-connected stability problem of the virtual synchronous control based DFIG, this paper proposed a stability analysis method by using the output impedance modeling in dq rotating coordinate system. Firstly, considering the impact of the power loop, the impedance model of virtual synchronous control based DFIG was derived by using the small disturbance analysis method. Secondly, the output impedance characteristics of the virtual synchronous control based DFIG were obtained and validated by model-based frequency scanning method. Finally, the influence of different grid strengths and control parameters on the stability of the virtual synchronous control based DFIG was analyzed by using the generalized Nyquist criterion（GNC）, and the results were compared and verified by time domain simulation. The results show that due to the power loop, the virtual synchronous control based on DFIG may have low frequency stability risk.By appropriately increasing the virtual inertia time constant and virtual damping coefficient, the stability of the grid-connected operation can be improved.
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