直流异步联网对送端系统阻尼特性的影响

大型交流电网采用柔性直流系统进行异步联网后,可以完全消除区域系统间的低频振荡,但送端系统内部的低频振荡特性也会发生改变。为探讨送端系统在柔性直流异步联网前后的低频振荡阻尼构成和变化规律,重点分析了负荷、交流联络线功率、运行电压及线路阻抗对系统阻尼的影响,并推导了交流联络线上增加柔性直流输电系统后,换流站不同控制方式及安装位置对送端系统低频振荡阻尼特性及小干扰稳定能力的影响机理,得出了异步联网情形的阻尼系数表达式;最后采用PSASP程序仿真计算进行验证,结果表明柔性直流异步联网能够阻断区域间低频振荡,提升送端系统阻尼特性及小干扰稳定能力,但有可能改变送端系统的区域内振荡模式。

Influence of DC Asynchronous Interconnection on Damping Characteristics of Sending System

Asynchronous grid interconnection in which a flexible HVDC system is adopted can eliminate the inter-area oscillations in large interconnected systems. However, the oscillations inside the sending end system may be affected. To explore the composition and variation of low frequency oscillation damping of sending end in the cases of AC and flexible dc interconnection, firstly, we analyzed the effects of system load, tie line flow, operating voltage and impedance on system damping in detail. Secondly, taking the addition of flexible DC system on AC tie into account, we derived a system damping expression corresponding to different control mode and installation position of DC converter. Thereby, the variation mechanism of low frequency oscillation characteristics and small disturbance stability of sending end system was revealed, and PSASP simulation was used to verify these theories. The results show that the flexible DC interconnection can clear the inter-area low frequency oscillation, improve the damping characteristics and small disturbance stability of sending end system, but it may change the oscillation mode inside the area.