Analysis of Oscillation Stability and Feasible Region of Parameters in Grid-Connected Direct-Drive Wind Farm with Series Compensation
Ji Yining1, Wang Haifeng1,2
1. State Key Laboratory of Alternate Electrical Power System with Renewable Energy ResourcesNorth China Electric Power University Beijing 102206 China; 2. College of Electrical Engineering Sichuan University Chengdu 610064 China
Abstract：Series compensation devices are widely used in power systems. The wind farms grid-connected system composed of large-scale direct permanent magnet synchronous generator with series compensation has the risk of small interference instability in the sub-synchronous oscillation category. Most of the existing literatures are aimed at doubly-fed wind farms. There are few studies on the PMSGs grid-connected wind farm system through series compensation lines, and most of them are based on simulation analysis, lacking in-depth research on the mechanism and analysis of the relationship between various parameters. At the same time, the stability analysis methods of wind farm grid-connected system generally include impedance analysis and mode analysis. However, the system impedance obtained by impedance analysis method is a sufficient but not necessary condition for system stability, which leads to its limitations. Mode analysis method needs to establish a refined model of electromagnetic transient level of power system. When the model scale is too large, there are some problems such as difficult calculation and longtime consumption. Aiming at the research of the above literatures and existing problems, this paper puts forward a simplified model method and corresponding stability criterion based on different time scales for the stability analysis of PMSG grid-connected wind farm with series compensation lines. Firstly, a full-order model of the system for small signal analysis is established, which can be used to clarify the dominant mode of the system. Then, according to the different time scales studied, each part of the grid-connected system is reasonably simplified and the simplified characteristic equation is solved. Then the analytical stability criteria at different time scales are obtained by using Routh-Hurwitz criterion, and the mechanism explanation of the stability of the system at different time scales is given. Finally, the boundary of the stability criterion is visualized by using the analysis method of feasible region, and the accuracy of the stability criterion is verified by nonlinear simulation. According to the simulation results, when studying the oscillation on the time scale of AC current, the oscillation frequency of the dominant mode of the system is around 38 Hz, and this mode is a phase-locked loop mode, which is unstable with the increase of the equivalent reactance Xc of the series compensation device. Through the analysis of feasible region, the critical stable value of Xc decreases with the increase of xL and increases with the increase of Kp. When studying the oscillation on the time scale of DC voltage, the oscillation frequency of the dominant mode of the system is around 2 Hz, and this mode is the outer loop mode of the grid-side converter, which is unstable with the decrease of the equivalent reactance Xc. Through the analysis of feasible region, the critical stable value of Xc increases with the increase of xL and decreases with the increase of Kpdc. In summary, this paper has the following conclusions: (1) According to the different frequency ranges, this paper simplifies the grid-connected system and lists the simplified characteristic equation. (2) When the grid-connected system oscillates in the time scale of DC voltage, the instability risk of the system decrease with the increase of Xc. However, when the system oscillates in the time scale of AC current, the instability risk of the system increase with the increase of Xc. (3) When the time scale of analysis is different, different parameters have different effects on the critical stability value of Xc.
季一宁, 王海风. 包含串补的并网直驱风电场振荡稳定性及可行域分析[J]. 电工技术学报, 2024, 39(3): 686-698.
Ji Yining, Wang Haifeng. Analysis of Oscillation Stability and Feasible Region of Parameters in Grid-Connected Direct-Drive Wind Farm with Series Compensation. Transactions of China Electrotechnical Society, 2024, 39(3): 686-698.
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2024, Vol. 39 
