复杂弱电网中并网变流器系统稳定性的分析测评与增强控制

Grid-connected converter is the key equipment in the future power distribution network and micro-grid, but the uncertainty of the grid impedance affects the converter’s stability, and hence threaten the stability and reliability of the power grid. This project intends to study the impedance frequency characteristics of complex weak grid and its influence on the stability of grid-connected converters, and explore ways improving the control system stability margin of the grid-connected converter, with the help of theoretical analysis, digital simulation and experiment. Finally, the theoretical basis and key technologies for enhancing the converter's stability will be provided..The impedance frequency characteristics in a wide frequency range of low-voltage complex weak grid will be investigated by analyzing and testing of actual grids, the equivalent circuit and its parameter estimation method of low-voltage grid will be provided for the stability analysis of grid-connected converters. For the converters with different type of grid-connecting filter, the influence mechanism of grid impedance and voltage feed-forward on the converter’s stability will be clarified, and the relations between the converter stability and the grid impedance will be revealed. In the consideration of line distributed parameters between converters, the stability analysis model of distribution grid with multi dispersed-installed converters will be established. Using neural network modeling method, the relationship between the control error sequence and the stability margin of the converter will be formulated, and an improved model predictive control strategy based on online correction of predictive model will be proposed in order to enhance the converter’s ability to adapt to the complex weak grid.

并网变流器是未来配电网/微电网的关键设备，其稳定性受到复杂弱电网下电网阻抗不确定性的影响，进而威胁到电网的稳定与可靠运行。本项目拟结合理论分析、仿真和实验，研究复杂弱电网的阻抗频率特性及其对并网变流器稳定性的影响，探索提高并网变流器控制系统稳定裕度的方法与途径，为增强变流器控制系统的稳定性提供理论依据和关键技术。.通过电网络分析与实测互证，探讨低压复杂弱电网在宽频范围内的阻抗频率特性，确定面向并网变流器分析的低压电网等值电路和参数估计方法；针对不同的并网滤波器结构，阐明变流器稳定性受电网阻抗和电压前馈影响的内在机理，揭示电网阻抗结构与参数对变流器稳定性的影响规律；计入弱电网的线路分布参数，建立多变流器分散并网系统的稳定性分析模型；利用神经网络建模方法，建立变流器控制目标误差序列与稳定裕度的关系，据此提出基于模型在线校正的变流器模型预测控制策略，增强并网变流器对复杂弱电网的适应能力。

并网变流器是未来配电网/微电网的关键设备，其稳定性受到复杂弱电网下电网阻抗不确定性的影响。本项目结合理论分析、仿真和实验，研究了弱电网下并网变流器系统的稳定性分析方法和增强控制策略，为增强并网变流器系统的稳定性提供了理论依据和关键技术。. 通过并网变流器系统的控制框图变换，分析了采用电网电压前馈策略的并联变流器系统在弱电网条件下的稳定性，指出变流器数字控制延迟是弱电网下电网电压前馈控制导致系统不稳定的主因，在此基础上提出了在前馈环路进行相位超前补偿、对前馈信号进行带通滤波、对前馈信号进行衰减、通过控制虚拟电网电阻等弱电网下的稳定性增强控制策略；基于变流器的诺顿小信号等效模型，利用阻抗比函数分析了弱电网下多变流器模块并联系统的稳定性，指出并联模块数越多，系统等效短路比SCR越小，系统稳定裕度越低；改进了并网变流器的模型预测控制，建立了逆变器的李雅普诺夫稳定性约束条件，并将其作为变流器最优电压矢量选择的必要条件，实现了保证并网变流器稳定运行先决条件下的控制目标优化；针对分布式变流器系统并考虑电网分布阻抗参数，提出了多模块串行级联系统的三种稳定性分析方法，基于变流器的二端口网络模型，推导出级联系统等效阻抗比函数与各级相邻模块输出输入阻抗比的对应关系，简化了级联系统的稳定性分析。. 建立了相应的实验平台，研究结论均通过了仿真和实验验证。