双馈型风电低电压穿越特性分析及撬棒保护模糊优化设计

In recent years, With the developments in wind power generation system, the wind generators tripping resulted from the grids voltage decline has become a major obstacle in the large scale development of wind power generation. In this plan, the transition process and crowbar protection of doubly-fed wind power generator low voltage ride-through are taken as the research objects. By considering the flux saturation and skin effect, the precise mathematical model of doubly-fed wind power generator under Low voltage fault is established and system operating characteristic of low voltage ride-through is analyzed. On this basis, based on fuzzy set theory, according to restrained conditions of engineering in low voltage ride-through, such as the stator and rotor current, DC bus voltage, reactive power, etc, the fuzzy set of crowbar resistance value and switching time are established. A fuzzy objective function (including the reasonable range of converter, DC bus, reactive power, and system mechanical shock), called as satisfaction level for practical engineering applications is proposed, and the symmetry fuzzy optimization method for solving the objective function is given. The crowbar protection designed in this way aims to enhance the whole safety of the system, improve low voltage ride-through ability of wind turbines and reduce adverse impacts on district grid voltage stability with large-scale crowbar switching of wind farms.

近年来，随着风力发电规模和风电机组容量不断增大，电网低电压故障引起风电机组解列成为制约风电产业大规模发展的主要瓶颈。本项目拟以双馈风力发电低电压穿越过渡过程及转子撬棒保护为研究对象，考虑磁链饱和及肌肤效应对风电系统暂态影响，建立精确的故障状态下机组数学模型, 分析暂态响应时风电系统运行特性。在此基础上，基于模糊集理论，根据低电压穿越时定转子电流、直流母线电压、机组无功功率等的工程约束要求，建立撬棒电阻值及撬棒投切时间模糊限制集，提出以安全性（包括变流器，直流母线，机组无功功率，系统机械震荡等的合理范围）为综合指标的模糊优化多目标函数，采用对称模糊优化方法进行求解。以此设计的撬棒保护旨在增强系统故障状态下机组整体安全性，降低风电场在撬棒保护大范围投入后对电压稳定性的不良影响，提高双馈风电低电压穿越能力。

低电压穿越是双馈风力发电机组大规模稳定发展的关键技术，而撬棒保护是提高低电压穿越能力的有效方法之一。本项目对双馈风电机组低电压穿越的暂态过程及转子侧撬棒保护电路进行了理论和实验研究。针对电网电压跌落时定转子电流冲击极易导致双馈电机磁路饱和问题，探讨了主磁路及漏磁路饱和对低电压穿越过程中定、转子电流暂态特性的影响，得出主磁路饱和对系统暂态响应特性影响较小；而漏磁路饱和在拓展低电压穿越过程中系统稳定裕度的同时增加了暂态响应的幅值，不利于双馈机组的安全运行。针对转子侧撬棒保护，首次提出了撬棒电阻多目标模糊优化控制，根据转子电流、电压及撬棒投入后双馈电机从电网吸收的无功功率的工程约束范围建立了撬棒电阻模糊限制集和目标函数，采用遗传算法对该目标函数进行求解得到最优电阻值，从而使双馈风电机组在低电压穿越过程中获得了较高的整体安全裕度及较快的故障电压恢复性能。