电力系统呈现高比例新能源和电力电子设备的发展趋势,大容量远距离的风电外送结构给电网带来了振荡风险。针对直驱风电场(Direct-Drive Wind Forms, DDWFs)经柔性直流输电(Voltage Source Converter based High Voltage Direct Current, VSC-HVDC)外送系统存在的振荡问题,其内部环节间交互作用对系统稳定特性的影响尚未明确。本文首先建立互联系统的小信号模型,通过参与因子确定各模态的主导模块及引发振荡的关键因素。在此基础上,建立考虑带宽约束条件的阻抗模型,解析系统间交互作用产生振荡的机理。最后采用开环传递函数因子分解法将阻抗模型转化为控制器因子相乘的形式,推导出可以显式表述控制环节交互作用本质的系统阻抗解析表达式,进而揭示风机锁相环、各控制环节与柔直控制间的交互作用对次同步及中频振荡的失稳机理;同时分析有功功率以及主电路参数对控制环节交互作用的影响效果,并利用PSCAD/EMTDC仿真验证阻抗模型及机理分析的正确性。
The power system shows the development trend of high proportion of new energy and power electronic equipment, and the large-capacity long-distance wind power transmission structure brings the risk of oscillation to the power grid. With the rapid expansion of wind power installed capacity and project scale, as well as the integration of VSC-HVDC transmission projects, grid-connected wind power systems exhibit multi-mode oscillation characteristics that vary over time and involve interactions between multiple devices across space. These characteristics differ significantly from the oscillation mechanisms of traditional power systems and fundamentally alter the factors influencing stability.
Focusing on the mechanism analysis of these oscillation characteristics in grid-connected wind power systems, this paper investigates a VSC-HVDC connected direct-drive wind farm. First, a state-space model of the interconnected system is constructed, and the eigenvalue method is used to classify the oscillation modes and locate the key links that cause oscillation in the system. Secondly, an impedance modeling method based on transfer function is proposed, considering the influence of PLL dynamic characteristics on the impedance model of direct-drive wind farm, and further tuning the controller parameters according to the bandwidth constraint conditions, and the impedance model with bandwidth as the direct parameter is obtained. Finally, the impedance analytical expression of the system is decomposed, and the interaction process of the internal components is analyzed from a physical perspective. The influence of each control bandwidth parameter on oscillation characteristics is revealed, the underlying cause of interaction is analyzed, and the relationship between active power/main circuit parameters and internal control component interaction is systematically described. This provides a novel approach to evaluate the stability of interconnected systems based on a bandwidth model.
The main conclusions of this paper are as follows: (1) There are sub-synchronous oscillation modes and intermediate frequency oscillation modes in the system of VSC-HVDC connected direct-drive wind farm, both of which are related to D-PMSG power generation system and VSC-HVDC system. Further, a transfer function impedance model considering bandwidth constraints is proposed from the perspective of system impedance, and the Bode diagram method is used to demonstrate the interaction mechanism between the D-PMSG and VSC-HVDC control system. (2) The mathematical mechanism of the instability of grid-connected system caused by the interaction between PLL, voltage outer loop and current inner loop of VSC-HVDC system is discussed. The greater the distance between the PLL bandwidth and the VSC-HVDC inner and outer loop bandwidths, the stronger the interaction between them, increasing the tendency for oscillation amplification. (3) We reveal that the essential reason for mid-frequency band instability in the system is the interaction between the wind turbine side's current loop bandwidth and the VSC-HVDC inner and outer loop control. When the direct-drive current's inner loop bandwidth and the VSC-HVDC's inner and outer loop bandwidths increase cooperatively, the interaction intensifies, which is detrimental to the stability of the interconnected system. 4) The output active power of the D-PMSG and the VSC-HVDC filter capacitance exhibit a similar influence trend in the sub-synchronous and mid-frequency range, and the interaction between the control links is affected by changing the starting position of the low frequency band of the amplitude-frequency characteristic curve.
马燕峰, 韩珊珊, 王子建, 李然, 赵书强. 直驱风电场经柔直外送系统振荡特性及控制环节动态交互作用研究[J]. 电工技术学报, 0, (): 20250460-20250460.
Ma Yanfeng, Han Shanshan, Wang Zijian, Li Ran, Zhao Shuqiang. Study on oscillation characteristics and dynamic interaction of control link of a VSC-HVDC connected direct drive wind farm. Transactions of China Electrotechnical Society, 0, (): 20250460-20250460.
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