含风电场的多端柔性直流输电系统小信号建模方法

Small Signal Modeling Method for Multi-terminal Flexible DC Transmission System with Wind Farms

含风电场连接的多端柔性直流输电系统易发生系统失稳现象,构建一个精确的小信号模型分析系统小干扰稳定性是必要的。然而,在建立含风电场的有源直流系统小信号模型时,已有文献大多未对风电场进行建模。据此,文中以平均值模型为基础,在时域下建立了包括风电场在内的直流系统小信号模型。为体现换流器自身损耗,计及直流侧等效桥臂阻抗,提出利用部分直流线路电容简化换流器直流侧模型推导;同时,考虑到风电场接入的影响,引入交流公共耦合点滤波电容。在风电场模型构建上,建立了全功率聚合风电场的小信号模型,与风电场侧换流站构成单个状态空间。算例部分搭建了含风电场三端柔性直流输电系统的小信号模型,与PSCAD模型进行阶跃响应及稳定裕度对比,结果表明所提小信号建模方法能够精确模拟小干扰动态响应,且在系统稳定性分析中性能优越。

Multi-terminal flexible DC transmission system with integration of wind farms is prone to instability,it is necessary to establish an accurate small-signal model to analyze the stability of small disturbances in the system.However,most of the existing research papers do not consider wind farm models when a small-signal model of DC system with source is established.According to the fundamental theory mentioned above,in time domain,a small-signal model of the DC system integrated with wind farm is established based on the average value model.In order to reflect the power losses of converter,the impedance of equivalent bridge arm on DC side is considered and proposed to simplify the DC-side model derivation of the converter by using parts of the DC line capacitance.At the same time,for the purpose of reflecting impacts of the wind farm integration,point of common coupling(PCC)filter capacitors is also considered.In view of wind farm modeling,a small-signal model of the full-powered wind farm is established,which can constitute a single state space with the converter on wind farm side.In the case,the small-signal model of the three-terminal flexible DC transmission system with integration of wind farms is built.Step response and stability margin of the model is compared with the PSCAD model.The results indicate that the proposed small-signal model can accurately simulate the dynamic response of small disturbance,and the superior performance of the model in system stability analysis is shown.