变速恒频双馈风力发电系统励磁控制策略研究

论文首先总结了目前变速恒频双馈风力发电系统通常采用的定子磁链定向、转子磁链定向和气隙磁场定向控制方式的基本控制原理和存在的一些问题。为了解决这些问题,论文依据双PWM变流器的拓扑结构,设计了基于电网电压定向的矢量控制策略,同时,针对转子侧变流器所要实现的功能,设计了基于定子电压定向的矢量控制策略,最后,论文通过仿真,验证了电压定向的矢量控制策略的正确性。     

直驱变流器网侧双电流环控制仿真研究

针对电网电压跌落情况下风电直驱变流器不脱网运行时,网侧采用单电流环控制导致的不良后果,如直流侧电压二次波动、网侧输出电流谐波含量高等问题,结合直驱变流器的主回路特点,提出网侧采用双电流环控制。分析了双电流环的控制目标,并详细分析了两种控制算法(即滤波法和矢量法)的数学推导过程,最后根据动模实验平台搭建了仿真模型。仿真结果表明:双电流环控制中滤波法优于矢量法,滤波法支持长期稳态运行、直流电压阶跃、功率阶跃,在故障期间,采用双电流环控制(滤波法)的电网电压、电流正弦度较好。     

不平衡及谐波电网条件下双馈风电变流器的改进控制研究

针对双馈风电机组在电网电压不平衡及谐波畸变条件下的故障穿越问题,分析了此类电网故障对机组运行性能的影响,提出了一种双馈机组转子侧、网侧变流器的协同控制方案。通过改进转子侧、网侧变流器的矢量控制算法,抑制了双馈感应电机的电磁转矩波动,降低了机组输出总有功功率的波动,获得了对称、正弦的机组输出电流。仿真结果表明,所述控制方案能够显著改善双馈风电机组在此类电网故障条件下的运行性能,从而提高机组的故障穿越运行能力。     

利用BESS提高双馈风电机组低电压穿越能力

该文详细介绍了双馈风电机组基于电流解耦的转子侧和网侧变流器矢量控制方案以及转子侧变流器的Crowbar滞环控制保护方法;在分析电池特性的基础上建立了电池储能系统(BESS)的数学模型及其串级控制策略;结合算例仿真表明在双馈风电机组的直流侧安装BESS装置可以有效维持电网故障期间直流侧母线电压的稳定,从而提高风电机组的低电压穿越能力。     

风力发电系统中PWM整流器脉宽调制方法的研究

近年来,离网型风力发电(isolated WECS)引起了人们的广泛关注,为了获得可靠平稳的负载电压,风力发电机侧整流器的控制至关重要.针对PWM整流器的动态响应问题,首先分析了当前主流的三相电压型PWM整流器(VSR)的拓扑结构、数学模型及控制策略,然后通过公式推导引出了基于电网电压定向的矢量控制策略,最终在基于Matlab Simulink平台搭建了三相VSR仿真模型,分别用正弦脉宽调制(SPWM)与空间矢量脉宽调制(SVPWM)方法进行了仿真研究.研究结果表明,基于电网电压定向的矢量控制能够有效控制PWM整流器,获得稳定的直流母线电压,同时空间矢量脉宽调制方法能够有效改善VSR动态性能,为离网型风力发电系统的研究提供了有力参考.     

基于IPM的三相SVPWM变流器实验平台

给出了三相SVPWM变流器的拓扑结构和旋转坐标系下的低频模型,分析了SVPWM变流器的工作原理,并基于其离散数学模型比较了电压定向的空间矢量控制和无差拍电流控制的工作性能。基于IPM和数字处理器TMS320F28335,介绍了系统的闭环控制和软硬件设计思想,实现全数字化SVPWM变流器实验平台的搭建。     

一种基于电网对称故障下DFIG的改进矢量控制策略

提出了一种电网对称故障下DFIG的改进矢量控制策略。给出了同步速ω1旋转坐标系中DFIG风电机组的等效模型,据此设计出以d轴磁链定向的网侧、转子侧PWM变换器矢量控制方案,并对其进行改进,然后对改进后的策略进行仿真。仿真结果表明,改进后的控制策略,使系统具有更好的不间断运行能力。     

采用异步电机的42V汽车起动/发电机系统

论述基于异步电机和PWM变流器串联构成的42V汽车起动/发电机系统,采用转子磁场定向矢量控制方法使电机带动发动机顺利起动,并在电机发电时有效控制变流器的输出电压,着重分析了系统从起动到发电的四种状态并进行了仿真实验,结果表明该系统具有良好的性能。     

基于双馈风力发电机网侧变换器的控制研究

双馈电机(DFIG)在风力发电系统中的应用日趋广泛,在风速变化时要实现变速恒频运行和最大风能追踪,网侧变换器的控制研究十分重要。为了使网侧变换器的功率双向流动、功率因数可调、输入电流接近理想正弦波、输出直流侧电压可调,设计了一个基于电压定向矢量控制的整流器,并在Matlab/Simulink上验证分析结果,仿真结果证明了设计的正确性。     

大功率直驱风力发电系统直流侧电压复合控制策略

在开发大功率直驱型风力发电双脉宽调制（PWM）变流器的过程中,为有效抑制由于电机侧有功功率及电网电压的突变而导致的直流侧电压的大幅波动,提出了一种闭环控制与前馈控制相结合的直流侧电压复合控制策略,即在电流控制环中引入机侧有功功率和电网电压前馈控制。仿真实验有效验证了该方法的可行性。研究结果表明,这种控制策略与传统单纯的直流侧电压闭环控制相比,有更快的响应速度和更强的抗扰性能,有效地提高了系统的鲁棒性。     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

ANGULAR DISTORTION ALLOWABLE VALUE AND ASSESS METHOD OF WELD ON COKE TOWER

A graph as the new engineering method for estimate the safety of bulging deformation of coke tower is proposed. Through stresses analysis of circumferential weld of coke tower and comparing the stresses produced by pressure with heat stress of steady state, residual stress, bending stress produced by both itself weight and wind loads, it showed that the stresses produced by pressure on the angle distortion are the main factor of equivalent stress of the combined stress. After comparing four kinds of stress controlling conditions, the relation to stress with depth of angular distortion, grade of curvature of angular distortion and half of region of angular distortion has been inferred. Graph of deformation allowable value of coke tower for different condition by angular distortion and half of region of angular distortion has been plotted. The five steps for its engineering use have been explained. The lighter the grade of curvature is, the larger of bulge allowance, may be, and the bigger of depth of angular distortion may pose too. For the coke tower with a popular structure of Dg 5 400 mm×28 mm, the result by graph is nearly more than the result of two formulas formed by other research, the error is less than 7.0%. But, the graph can be easily applied to different size of angular distortion.