【作者】 黄辉；

【导师】 郭育华；

【作者基本信息】 西南交通大学 ， 电气工程， 2016， 硕士

【摘要】 双馈风力发电系统的变流器容量是双馈电机的转差率容量,具有体积小、重量轻、损耗低等特点,因此是目前国内外市场上的主流机型。随着风电场规模的扩大,要求并网的双馈风力发电系统必须具备低电压穿越、抵御电网电压不平衡的影响以及无功补偿的能力,即提高双馈风力发电系统并网适应性。本文结合云南电网电力科学研究院“基于PSCAD的风电机组建模技术及并网适应性研究”科研项目,围绕双馈风力发电系统的变流器控制技术进行了较为深入的研究,主要内容如下：双馈风电发电系统数学模型的建立。综合双馈风力发电系统的风速、风力机、双馈感应电机、机侧和网侧变流器等子系统的数学模型,建立了基于定子磁链定向的双馈电机矢量控制策略和基于电网电压定向的网侧变流器矢量控制策略,在PSCAD环境下建立了单机仿真模型,并通过仿真进行了验证。故障时双馈电机暂态分析和低电压穿越能量吸收方案。通过拉普拉斯变换,推导了双馈电机在电网电压跌落至零时的定、转子故障磁链和故障电流解析式,分析了双馈电机在电网对称跌落时的电磁暂态特性,讨论了在电网电压跌落时,DFIG低电压穿越需要解决的问题,即减小转子故障电流来保护机侧变流器,减小直流母线的过电压来保护中间电容。从减少故障恢复时从电网吸收无功功率的大小和避免直流母线电压上升的角度推导了Crowbar电阻的取值。在PSCAD中从添加外部电路(Crowbar电路和Chopper电路)的角度来实现低电压穿越。电网电压不平衡时变流器的控制策略。在正负序分量分离的基础上,建立了双馈电机在正负序坐标系下的数学模型和瞬时功率模型,得出电网电压不平衡时定子磁链中出现的负序分量是引起电磁转矩、有功功率、无功功率脉动,转子电流畸变,定子电流不对称的根本原因。采用两套控制系统分别控制定子电流的正负序分量,分别实现了机侧变流器抑制定子三相电流不平衡,网侧变流器抑制网侧变流器输出三相电流不平衡的控制目标,并在仿真模型中进行了验证。风电场建模与无功补偿。总结了风电场建模的主要问题和常用的等效方法,以及风电场集群效应对电力系统的正面影响,通过比较用完全聚合法和分群等值法建立的风电场模型得出分群等值法建立的风电场具有较高的准确性。通过改变机侧和网侧变流器的控制策略中功率外环无功分量指令值,使DFIG机侧和网侧变流器具有一定的无功补偿能力,同时介绍了静止无功发生器的基本工作原理和在维持风电场并网点电压稳定性方面的作用,并通过仿真进行了验证。更多还原

【Abstract】 Converter capacity of double-fed wind power generation system is double-fed motor slip capacity with features of small size, light weight, low loss characteristics etc, which has become the mainstream model on the market at home and abroad. With the expansion of the scale of wind power, DFIG system must be equipped with the ability of low voltage riding through, resisting the influence of unbalanced grid voltage and reactive power compensation, namely, to enhance the grid-connection adaptability. Combined with the research project "Modeling and Simulation on Adaption of Grid-Connection Technology for Wind Turbine" authorized by Electric Power Research Institute of Yunnan Grid, converter control strategy of DFIG system was studied. The main contents are as follows:The mathematical model of DFIG system was built. Combined with the mathematical models of wind speed, wind turbine, doubly-fed generator and converters, stator flux oriented vector control strategy of DFIG, grid voltage oriented vector control strategy of grid-side converter were established. A simulation model was established in PSCAD, which was validated by simulation.Transient analysis and LVRT energy absorbing solutions were proposed if grid faults happen. Then the analytical formulas of stator and rotor’s transient flux and current were presented by the method of Laplace transform when stator voltage drops to zero. Besides, electromagnetic transient characteristics of DFIG faced with symmetrical grid voltage drop were analyzed. Reducing the rotor fault current to protect the DFIG-side converter and avoiding the DC bus overvoltage to protect the capacitor are the key issues of LVRT. The value of crowbar resistance was derived from absoring reactive power and avoiding the DC bus overvoltage. LVRT was achieved by employing an external circuit including crowbar and chopper circuit in PSCAD.Moreover, control strategy of converters under the unbalanced grid voltage were established. A mathematical and instantaneous power model of DFIG were established in the premise of positive and negative sequence separation. The negative component of stator flux is the root cause of active power, reactive power and torque pulsation, stator current unbalanced and rotor current distortion when grid is unbalanced. The positive and negative sequence components of the stator current were controlled by the two sets of control systems respectively, which was to suppress the unbalanced three-phase current of stator and grid-side converter, and then simulated in PSCAD.Furthermore, wind farm modeling and reactive power compensation were discussed. The main issues and equivalent methods of wind farm modeling were summarized, as well as the positive impact of wind farm cluster effect on the power system. Compared the complete polymerization and clustering equating methods, the latter has a higher accuracy in the application of wind farms modeling. To make DFIG-side and grid-side converter have reactive power compensation capabilities, reactive power reference values in control strategies of DFIG-side and grid-side converters can be changed. Meanwhile, the basic principle and the function of SVG in the maintenance of the voltage stability between wind farm and grid are also researched, and validated by simulation.更多还原