Synchronization Stability Analysis and Enhanced Control of Grid-Following Converters under Multi-Timescale Control
Liang Junyang1, Li Hong1, Song Guojie2, Xiahou Kaishun2, Chen Yanming1
1. Guangxi Key Laboratory of Power System Optimization and Energy Technology Guangxi University Nanning 530004 China; 2. School of Electric Power Engineering South China University of Technology Guangzhou 510640 China
Abstract：In the new power systems with increasing penetration of renewable energy and power electronic devices, grid-following (GFL) converters synchronized by a phase-locked loop (PLL) suffer from inadequate damping due to complex control coupling, leading to potential synchronization instability issues. The control loops dominating the dynamic characteristics of the converter can be categorized into DC voltage and AC current timescales, possessing multi-timescale (MTS) features that exhibit strong coupling effects on system damping. However, traditional synchronization stability analysis methods focus on the impact of control on system damping at only one timescale. Thus, the analysis of system synchronous dynamics still needs to be completed. This paper proposes a synchronization stability analysis model, considering the multi-loop control's MTS characteristics. Through sensitivity analysis of system damping, the impact of different operating conditions and control parameters on system synchronization stability is intuitively analyzed. Firstly, a synchronization stability analysis model that considers multiple timescales for GFL converters is established. The coupling paths and damping distribution patterns of each timescale control are revealed. Secondly, the influence of control parameters on damping characteristics is quantified using sensitivity analysis. The dominant factors causing synchronization instability in the system are identified, and their impact on system damping is visually represented through a three-dimensional graph. Additionally, according to the influence of grid impedance change and grid voltage drop on control coupling, the mechanism of system instability under various conditions is analyzed from a damping perspective. Finally, an improved control strategy based on terminal voltage feedforward for damping reshaping is proposed to mitigate the adverse damping effects of MTS control coupling. Simulation and experimental results demonstrate that under weak grid conditions, considering the effects of MTS coupling, step changes in active power reference values, an increase in grid impedance, and voltage drops in the grid can lead to sub-synchronous oscillations in the GFL converter system. The proposed improved control can suppress such oscillations, improving system synchronization stability. The following conclusions can be drawn from theoretical analysis and experiments. (1) The essential nature of the multi-loop control coupling in GFL converters is the frequency band overlap in the timescale, manifesting as MTS characteristics, significantly impacting the synchronization stability of the system. (2) Among the multi-loop control parameters, the dominant factors significantly affecting the system's synchronous characteristics are kp_pll and kp_tvc. Reducing kp_pll or increasing kp_tvc can mitigate adverse damping effects, enhance total system damping, and improve system synchronization performance. (3) Operating conditions, such as an increase in grid impedance, voltage drops in the grid, and internal dq coupling in DC voltage timescales, may exacerbate negative damping effects, potentially causing system synchronization instability. (4) The proposed improved control scheme effectively eliminates the impact of internal dq coupling in DC voltage timescales while significantly reducing adverse damping characteristics, thereby enhancing the synchronization stability of the MTS control system
梁军杨, 李红, 宋国杰, 夏候凯顺, 陈延明. 多时间尺度控制下跟网型变换器的同步稳定性分析与改进控制[J]. 电工技术学报, 2024, 39(22): 7182-7196.
Liang Junyang, Li Hong, Song Guojie, Xiahou Kaishun, Chen Yanming. Synchronization Stability Analysis and Enhanced Control of Grid-Following Converters under Multi-Timescale Control. Transactions of China Electrotechnical Society, 2024, 39(22): 7182-7196.
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2024, Vol. 39 
