Comparative Study of Small-Signal Stability Under Weak AC System Integration for Different VSCs

Abstract

Voltage source converters (VSCs) with self-commutation ability are suitable to interconnect weak AC systems. This paper conducts a comparative study of the small-signal stability characteristics for three typical VSCs, namely, the two-level VSCs (TL-VSCs), the half-bridge modular multilevel converters (HB-MMCs) and the hybrid MMCs (HY-MMCs), under weak AC system integration with special consideration on both inverter and rectifier operation. The frequency responses based on impedance models are compared using the frequency-domain analysis. The oscillation frequencies and mainly participated state variables of the unstable modes are compared using root locus and participation factor analysis in time-domain. Proper parameter retuning approaches for stability enhancement are proposed. The above analysis is adequately validated by electromagnetic simulations.

Impact of Strength and Proximity of Receiving AC Systems on Cascaded LCC-MMC Hybrid HVDC System

“…Considering the increasing penetration of renewable energy and power electronics, the AC system tends to weaken gradually [12]. Besides, the tripping of AC transmission lines by scheduled maintenance or occasional AC faults may also result in a temporary decrease of the strength of the AC system [13]. Existing literatures reveal that both LCC-HVDC and MMC-HVDC are subjected to instability issue when integrating with a weak AC system [12]- [14].…”

Mechanism analysis of the influence of the strength of the receiving end AC system on the stability of MMC-HVDC system

“…Meanwhile, the high-bandwidth PLL may deteriorate the stability of VSC under a weak system scenario [9]. Accordingly, slowing down the PLL and reducing the PLL bandwidth can improve the system stability [10].…”