双馈风机低电压穿越励磁控制技术研究

发布时间：2018-04-04 19:54

本文选题：双馈异步发电机　切入点：低电压穿越　出处：《华中科技大学》2014年硕士论文

【摘要】：随着自然环境的不断恶化和不可再生能源的过度消耗，人类面临着环境污染和能源危机等重大难题，清洁与可再生能源的发展因此备受瞩目。风能作为应用最广的可再生能源之一，受到了越来越广泛的关注。近年来，风力发电在电力能源中所占的比重越来越大，对于电网的影响也日益显现。为此，各国都制定了相应的并网准则，其中一个就是低电压穿越要求(LVRT)，即在电网电压发生一定的跌落故障下，保持风机不脱网运行，并为电网提供一定的无功支撑。双馈感应发电机(DFIG)所需的变流器容量小，可实现有功、无功独立调节，是风力发电的主流机型。然而，由于双馈风机定子与电网直接相连，易受电网电压波动的影响，其在严重故障下的LVRT性能很不理想。现有的LVRT方案主要分为轻微故障下改进变流器控制策略和严重故障下增加硬件两种方式。增加硬件主要是在转子侧投入Crowbar电阻泄能，并封锁变流器。Crowbar的投入会导致转矩脉动并吸收无功，并且不合适的切除时刻会导致更严重的暂态过程。而改进励磁控制策略无需增加额外的硬件，在故障期间可以对暂态过程进行一定的控制，，减小电磁振荡和转矩脉动。现有的改进励磁控制策略一般需要磁链的准确观测和相序的快速分离，不易实现，并且存在较大的转矩脉动。本文从故障下的暂态过程入手，分析了过压、过流的机理，并从转子侧端口等效阻抗的角度，根据端口的电压电流特性将转子侧变流器(RSC)等效成一个阻抗。本文分析了现有的低电压穿越控制策略在电气特性方面的统一性，并从简单的物理原理解释了其作用机理，从而归纳出了评判某种控制策略可行性的一个标准。根据对转子电流需求的深入分析和楞次定律的理解，提出了一种反向电流跟踪控制策略，并给出了合理的参数选取原则。该策略具有明确的物理意义，控制结构简单，而且理论上能消除转矩脉动。反向电流跟踪控制策略的效果在MATLAB/Simulink(许可证号:11111-11111-02011-44270)中进行了仿真验证。最后本文设计搭建了一套10kW双馈风力发电系统，并配备了一台电网电压跌落故障发生器，通过电网故障实验验证了本文所提出的低电压穿越控制策略的有效性。该策略具有以下特点： 1.结构简单，原理清晰； 2.控制策略易于切换； 3.有效抑制转矩脉动。在深度故障下，保持不脱网运行和向电网发出无功是相矛盾的。因此需要考虑何时改变控制目标，在度过了最严重的暂态过程之后为电网提供无功支撑。
[Abstract]:With the deterioration of the natural environment and the excessive consumption of non-renewable energy, mankind is faced with environmental pollution and energy crisis, so the development of clean and renewable energy has attracted much attention.As one of the most widely used renewable energy, wind energy has attracted more and more attention.In recent years, wind power plays a more and more important role in electric power, and its influence on power grid is becoming more and more obvious.For this reason, all countries have formulated the corresponding grid connection criteria, one of which is the low voltage traversing requirement (LVRTT), that is, keeping the fan running without the grid and providing certain reactive power support for the power network under the condition of a certain drop fault of the grid voltage.The converter required by doubly-fed induction generator (DFIGG) is of small capacity, can realize active power and independent regulation of reactive power, and is the mainstream model of wind power generation.However, because the stator of doubly-fed fan is directly connected to the power grid, it is easy to be affected by the voltage fluctuation of the power network, and its LVRT performance is not ideal under the serious fault.The existing LVRT schemes are mainly divided into two ways: improving converter control strategy under slight fault and adding hardware under severe fault.The main reason for increasing the hardware is to put Crowbar resistance into the rotor side and block the input of the converter .Crowbar will lead to torque ripple and absorb reactive power, and the improper cutting time will lead to more serious transient process.The improved excitation control strategy can control the transient process without adding additional hardware and reduce the electromagnetic oscillation and torque ripple.The existing improved excitation control strategy generally requires the accurate observation of flux and the fast separation of phase sequence, which is difficult to achieve, and there is a large torque ripple.In this paper, the mechanism of overvoltage and overcurrent is analyzed from the transient process of fault. From the point of view of the equivalent impedance of the rotor side port, the rotor side converter RSC is equivalent to an impedance according to the voltage and current characteristics of the port.In this paper, the unity of the existing low voltage traversing control strategy in the electric characteristic is analyzed, and the mechanism of its action is explained from the simple physical principle, and a criterion for judging the feasibility of a certain control strategy is concluded.According to the deep analysis of rotor current demand and the understanding of Lenz's law, a reverse current tracking control strategy is proposed, and the reasonable parameter selection principle is given.The strategy has clear physical meaning, simple control structure and can eliminate torque ripple theoretically.The effectiveness of the reverse current tracking control strategy is verified by simulation in MATLAB / Simulink (license number 11111-111-02011-44270).Finally, a 10kW doubly-fed wind power generation system is designed and built, and a voltage sag fault generator is equipped. The effectiveness of the proposed low-voltage traversing control strategy is verified by the power network fault experiment.The strategy has the following characteristics:1.Simple structure, clear principle;2.The control strategy is easy to switch;3.Effectively restrain torque ripple.Under the condition of deep fault, it is contradictory to keep the grid running and to issue reactive power to the power grid.Therefore, it is necessary to consider when to change the control objectives and provide reactive power support to the power network after the most severe transient process.
【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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