Mechanism analysis and suppression of bus voltage low frequency oscillation of multi-VSC connected substation

Abstract

Large new energy stations are located in remote areas and integrate into boost substation, which is transmitted to load center through long-distance AC lines. This results in weak electrical connections between boost substation busbar and load center, and causes low-frequency oscillation instability. To reveal the mechanism of low-frequency oscillation, a universal model for low-frequency dynamic analysis of multi-VSC system was established. Focusing on low-frequency dynamics, each VSC and AC power grid were independently established, which is applicable to different quantities of grid-tied VSC with various control strategies. Based on the proposed model, the impact mechanism of various factors such as power grid strength, VSC operating point, and coupling interaction of various VSC’s dynamic loops on low-frequency stability of multi-VSC system were revealed by state space analysis. Based on the analysis results, a virtual point of common coupling control strategy was proposed, which takes the voltage of substation busbar as the unified control objective of each VSC. This strategy can effectively suppress the low-frequency oscillations caused by dynamic interaction of different VSC, and a parameter self-tuning function was designed to eliminate errors caused by variation of line parameters. Finally, the correctness of the impact of various elements on low-frequency dynamics is verified through PSCAD/EMTDC simulation based on proposed model, as well as the effectiveness of proposed control strategy for low-frequency oscillation suppression.

Keywords

• multi-VSC system
• universal analysis model
• interaction of dynamic loops
• improving control strategy
• low frequency oscillation suppression