双馈风机经VSC-HVDC接入弱受端系统运行特性分析

基于电压源换流器的高压直流输电(VSC-HVDC)是远距离风电并网的理想方案,同时可用于联接弱受端系统,但双馈风机经VSC-HVDC能够馈入多弱的受端系统仍待深入研究,有必要提出基于短路比的指标来衡量所能接入的受端系统。对此,基于定功率控制下VSC的稳定运行约束,分析系统稳态的临界运行点,总结出临界短路比的求解步骤。在此基础上,结合双馈风机的控制方程,详细讨论了风电场出力、弱交流系统等效阻抗和临界短路比的关系。仿真分析发现,受双馈风机无功特性的影响,接入受端系统的临界短路比未能达到理论值,引入基于无功补偿的有效短路比作为受端系统的强弱判断指标,使得所提临界短路比求解方法在此工况下依然成立。

Operating Characteristics Analysis of DFIG Connected to Weak Receiving System via VSC-HVDC

VSC-HVDC has been applied to the transmission of long-distance grid-connected DFIG wind farms, and its self-commutation capability can also be used to connect to weak receiving systems. However, when the DFIG is used as a power generating source to access the VSC transmission system, its operational characteristics and the stability of the access receiving systems remain to be further studied. In this paper, the constraint conditions such as tidal current solution and safe and stable operation criterion are considered comprehensively. The method for obtaining the critical value of the connected receiving systems is proposed. The impact of the DFIG on the VSC accessing weak receiving system and its effects are analyzed. The ESCR based on reactive power compensation is introduced as the judgment index of the strength of the receiving system under such conditions. Finally the effectiveness of the proposed method and indicators is verified by computer simulation study.