Impact of control system on small‐signal stability of hybrid multi‐infeed HVDC system

Abstract

This paper focuses on the impact of control system on small-signal stability of the Hybrid Multi-Infeed HVDC(H-MIDC) system, in which the Line-Commutated-Converter based HVDC (LCC-HVDC) and Voltage-Sourced-Converter based HVDC (VSC-HVDC) links feed into an AC system in close mutual proximity. A comprehensive linearized small-signal model is developed for an H-MIDC system. Based on the eigenvalue analysis and participation factor analysis, the inherent oscillatory modes of the H-MIDC system are revealed. Then, the impact of the most sensitive control system parameters on the least-damped modes are investigated. The studies show that (i) the proportional gains of PLL functions of LCC and VSC stations, and AC voltage outer loop controller of VSC station are highly coupled, and presents the most sensitivity to the least damped modes; (ii) parameters of PLL in LCC station, and outer loop of AC voltage control and PLL in VSC station can highly impact the damping of the oscillatory modes and even cause instability, and (iii) smaller PLL gains in LCC and VSC stations, and smaller proportional gain of AC voltage control of VSC station are preferable and can enhance damping of dominant modes.