故障下双馈电机暂态特性分析及撬棒投切策略研究

发布时间：2018-05-30 10:58

本文选题：风力发电 + 双馈电机　；参考：《华中科技大学》2014年硕士论文

【摘要】：随着传统化石能源的日益稀少以及全球气候的不断恶化，以太阳能、风能为代表的新能源越来越受到各个国家的亲睐。中国由于幅员辽阔、风能资源丰富，使得近年来中国的风电产业快速发展，中国已成为全球风电装机容量第一大国。但中国及世界上大多数风电场都集中在偏远地区，例如中国的“三北”（华北、东北、西北）以及东南沿海。这些地区的电网较为薄弱，电网的波动严重影响了风电机组的稳定运行，并且在电网故障引起的电压骤降情况下，风机大面积脱网引起的区域电网频率降低，大量损失出力又将威胁电网的安全运行。因此，现行的风电并网规范中，电网故障时，风电机组自动脱网以自我保护的运行方式不再被允许，并且在故障期间，风机需要向电网提供一定的有功和无功以帮助电网电压恢复。双馈感应电机（DFIG）以其调速范围宽、励磁变频器容量小等优点，成为风电机组中的主流机型。同时，因其与电网半耦合的结构和易受电网波动影响的特点，使双馈电机的低电压穿越技术（LVRT）成为目前工业界和学术界的研究热点。如何提高双馈电机承受深度故障的低电压穿越能力以及在故障期间对电网提供最大程度的支撑具有重要的现实意义。本文首先调研了国内外关于双馈电机故障下暂态特性分析的研究现状，总结了现有的撬棒（Crowbar）投切策略及其优缺点。在双馈电机的数学模型基础上，推导了端口电压发生对称跌落、投入撬棒后，定子磁链、定转子电流的解析表达式，并在表达式的基础上分析了各暂态量的幅值、变化规律等特性。通过对比表达式的计算结果与MATLAB/Simulink中的仿真结果，验证了解析表达式的准确性。从解析表达式中抽离出撬棒阻值与暂态特性的关系，分析了不同撬棒阻值对故障期间系统功率、电磁转矩波动的影响，并结合转子电流峰值计算及直流母线电压钳位效应，给出了一种撬棒阻值的选取方案。该方案将有助于实际工程中选取合适的撬棒参数。通过感应电动势的估算，分析了现有主动控制方法应对电网故障的控制极限，并指出在现有的实际电机参数约束下，撬棒电路在实现深度低电压穿越中的必要性。接着，提出了基于感应电动势估算的撬棒投切策略：当电压突变、转子侧电流超过安全值时，撬棒投入并封锁转子变流器输出，防止变流器过流损坏，同时，实时估算感应电动势的大小，一旦感应电动势低于直流母线电压，即可退出撬棒，切回变流器控制。与现有的撬棒投切策略相比，本文所提出的策略在可靠保护变流器的基础上，更具灵活性，可根据不同的故障深度选择撬棒作用时间，，并且适用于电压阶跃恢复带来的暂态过程。
[Abstract]:With the increasing scarcity of traditional fossil energy and the worsening of global climate, the new energy, represented by solar energy and wind energy, is increasingly popular in various countries. Because of its vast territory and abundant wind energy resources, China has become the largest wind power generation country in the world, because of the rapid development of wind power industry in recent years. But China and most of the world's wind farms are concentrated in remote areas, such as China's "three north" (North, Northeast, Northwest) and southeast coastal areas. In these areas, the power grid is relatively weak, the fluctuation of the grid seriously affects the stable operation of wind turbines, and in the case of voltage sudden drop caused by the fault of the power grid, the frequency of the regional power network caused by a large area of fan de-grid is reduced. A great deal of loss will threaten the safe operation of power grid. Therefore, in the current wind power grid connection specification, when the power grid fails, the self-protection operation mode of the wind turbine automatic disconnection is no longer allowed, and during the failure period, Fans need to provide a certain amount of active and reactive power to the grid to help the grid voltage recovery. Doubly-fed induction motor (DFIGM) has become the mainstream type of wind turbine because of its wide speed range and small capacity of excitation inverter. At the same time, because of its structure of half-coupling with the power grid and the characteristics of easy to be affected by the fluctuation of the power network, the low-voltage traversing technology of the doubly-fed machine (LVRTT) has become a hot research topic in industry and academia at present. How to improve the low voltage traversing ability of the doubly-fed machine to withstand the deep fault and provide maximum support to the power network during the fault period has important practical significance. In this paper, firstly, the research status of transient characteristics analysis of double-fed machine under fault is investigated, and the current switching strategy of crowbar and its advantages and disadvantages are summarized. On the basis of the mathematical model of the double-fed machine, the analytical expressions of stator flux and stator rotor current after the symmetrical drop of port voltage and crowbar are derived, and the amplitude of each transient quantity is analyzed based on the expression. The law of change, etc. The accuracy of the analytical expression is verified by comparing the calculation results with the simulation results in MATLAB/Simulink. The relationship between the Rod resistance and the transient characteristics is analyzed from the analytical expression. The effects of different Rod resistance values on the power and electromagnetic torque ripple of the system during the fault period are analyzed. The peak value of rotor current and the voltage clamping effect of DC busbar are combined with the calculation of the peak value of rotor current and the effect of voltage clamping of DC busbar. A scheme for selecting the resistance of crowbar is presented. This scheme will be helpful to select appropriate parameters of crowbar in practical engineering. Based on the estimation of induction electromotive force, this paper analyzes the control limit of existing active control methods to deal with power grid faults, and points out the necessity of prying rod circuit in realizing depth and low voltage crossing under the constraints of actual motor parameters. Then, a pry-bar switching strategy based on induction electromotive force estimation is proposed: when the voltage changes and the rotor side current exceeds the safe value, the crowbar inputs and blocks the output of the rotor converter to prevent the converter from overcurrent damage, at the same time, The size of induction electromotive force is estimated in real time. Once the inductive EMF is lower than DC bus voltage, it can exit the crowbar and cut back the converter control. Compared with the existing crowbar switching strategy, the proposed strategy is more flexible on the basis of reliable protection converter, and can select the action time of crowbar according to different fault depth. And it is suitable for transient process caused by voltage step recovery.
【学位授予单位】：华中科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM614

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