LCC-HVDC's Systematical Impact on Voltage Stability: Theoretical Analysis and a Practical Case Study
Tiankai Lan, Huadong Sun, Wuzhi Zhong, Yiran Jing, Bing Zhao, Jian Xu
Abstract
Line-commutated-converter HVDC (LCC-HVDC) is generally believed to impair voltage stability. While in a China's practical power grid, increase of HVDC power unexpectedly enhances the stability. The phenomenon reveals that existing studies overlook HVDC's systematical impact on the receiving AC system. This paper empirically elaborates how the phenomenon arises, theoretically clarifies the mechanism, and demonstrates its effect on practical system operating. In this paper, systematical features of power grid are visually depicted by two vectors, i.e., network structural vector and power-flow conditional vector. A unified burden rate is proposed to evaluate voltage stability of any AC bus. Impact of HVDC is explicitly expressed by two positive-definite terms and one negative-definite term. The latter of them is overlooked by most existing literatures, and enhances voltage stability by reducing the burden rate. The proposed methodology is validated by simulations with a practical power system in Asia with tens of HVDC infeed and tens of thousands of AC nodes.