计及直流链路动态耦合效应的双馈风电机组谐波阻抗模型

Harmonic Impedance Model of DFIG Considering Dynamic Coupling Effect of DC Link

双馈风电机组的大量并网会给电网带来谐波谐振等电能质量问题,研究此类问题的关键在于建立准确有效的风机谐波模型。传统的双馈风电机组谐波阻抗模型的建立通常基于理想的直流链路电压,然而在风机实际运行中,变流器交直流侧交互作用会导致直流链路电压出现动态耦合谐波成分,且两侧变流器谐波可通过直流链路双向传递,进而产生耦合,即存在直流链路动态耦合效应,从而影响风机谐波阻抗模型的准确性。为此,提出一种计及直流链路电压动态的谐波建模方法,将直流链路的谐波影响以及由此带来的变流器之间的谐波耦合进行解析,得到了计及耦合特性的背靠背变流器谐波阻抗模型,并与感应电机的阻抗模型整合,进而建立了双馈风电机组的谐波阻抗模型,同时还揭示了直流链路动态效应对双馈风机谐波阻抗的影响机理。最后,通过时域仿真以及实验平台有效验证了所建立谐波阻抗模型的准确性及理论分析的正确性。

The increasing integration of the double-fed induction generator(DFIG)brings power quality problems like harmonic resonance to power systems.The key to study this problem is to establish an accurate and effective harmonic model of the DFIG.Traditionally,the DFIG is modeled as an impedance with the assumption of an ideal dc-link voltage.However,the DC link voltage will also experience harmonic ripples when the ac side of the converter meets harmonics.Further,because the grid-side converter(GSC)and the rotor-side converter(RSC)share the dc-link capacitor,there exists a harmonic coupling between the GSC and the RSC.Therefore,this paper presents a more accurate harmonic model of DFIG which takes the impact of the dc-link harmonics into consideration.A coupled harmonic model of the back-to-back VSC is analytically established and is integrated with the linear harmonic model of the induction generator to form the harmonic model of the DFIG.In this proposed model,the influence mechanism of the DC-link dynamic effect on the harmonic impedance of the DFIG is revealed,and the harmonic coupling between the back-to-back converters is analyzed.Finally,the accuracy of the harmonic impedance model and the correctness of theoretical analysis are verified by time-domain simulation and lab experiments.