基于定子Crowbar电路的双馈风力发电系统低电压穿越技术研究

发布时间：2018-08-25 11:09

【摘要】：风力发电在整个电力系统中装机容量和发电量所占比例日益提高。双馈风电机组定子侧直接与电网相连,转子侧通过容量较小的变流器与电网相连,这种特殊的拓扑结构导致双馈风电机组在电网电压跌落故障期间具有较为复杂暂态特性,定转子绕组出现大电流,直流母线电压骤升,威胁变流器的安全运行乃至引起双馈风电机组脱网运行。本文主要研究定子Crowbar电路的低电压穿越技术。首先对双馈风力发电系统的基本组成、运行原理进行阐述分析;结合基本运行原理分析了电网电压发生对称跌落故障下,双馈风力发电机组的暂态响应。给出电网电压对称跌落时转子故障电流的解析式,定转子绕组参数、机端电压跌落深度、转差率以及转子侧变流器输出的电压等因素影响着转子故障电流的大小。然后给出了定子Crowbar电路模式切换的低电压穿越方案,进一步分析了双馈风力发电机组模式切换过程中,转子暂态电流响应特性;给出电网故障期间,定子Crowbar电路接入系统,双馈风电机组切换至感应发电机组模式下,系统的有功功率与无功功率可通过两侧的变流器控制。该方案能有效地抑制转子暂态电流和直流母线电压的波动,无功功率的注入有利于电网电压的恢复。接着,在考虑故障期间系统存在不平衡转矩的条件下,确定了定子Crowbar电路临界阻抗选取的计算方法;详细分析电磁转矩、转子转速、定子Crowbar电路阻抗之间的关系;同时,结合转子侧变流器的控制策略,给出了一种实时跟踪定子电流变化的控制策略。最后经仿真验证表明,所改进的方案均能有效地改善双馈风力发电系统的低电压穿越能力。
[Abstract]:Wind power generation in the whole power system the proportion of installed capacity and electricity generation is increasing. The stator side of the doubly-fed wind turbine is directly connected to the power grid, and the rotor side is connected to the power network through a converter with small capacity. This special topology leads to the complicated transient characteristics of the double-fed wind turbine during the voltage drop fault of the power network. The large current in stator and rotor windings and the sudden rise of DC bus voltage threaten the safe operation of converter and even cause the double-fed wind turbine to run off the grid. In this paper, the low voltage traversal technique of stator Crowbar circuit is studied. Firstly, the basic composition and operation principle of doubly-fed wind power generation system are described and analyzed, and the transient response of doubly-fed wind turbine under symmetrical drop fault of grid voltage is analyzed in combination with the basic operation principle. The analytical formula of rotor fault current, the stator and rotor winding parameters, the drop depth of terminal voltage, the slip rate and the output voltage of rotor side converter are given. Then, the low voltage traversing scheme of stator Crowbar circuit mode switching is given, and the transient current response characteristics of rotor during the mode switching process of doubly-fed wind turbine generator are analyzed, and the stator Crowbar circuit access system is given during the fault period of power network. When the doubly-fed wind turbine is switched to the induction generator mode, the active and reactive power of the system can be controlled by the converter on both sides. This scheme can effectively restrain the fluctuation of rotor transient current and DC bus voltage, and the injection of reactive power is beneficial to the restoration of grid voltage. Then, considering the unbalanced torque of the system during the fault period, the calculation method of the critical impedance of the stator Crowbar circuit is determined; the relationship among the electromagnetic torque, rotor speed and the impedance of the stator Crowbar circuit is analyzed in detail; at the same time, the relationship between the electromagnetic torque, the rotor speed and the impedance of the stator Crowbar circuit is analyzed in detail. Combined with the control strategy of rotor side converter, a control strategy of tracking stator current change in real time is presented. Finally, the simulation results show that the improved scheme can effectively improve the low voltage traversing capacity of the doubly-fed wind power system.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM614

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