Characteristics of sub-synchronous oscillation in grid-connected wind farm system

With the rapid development of wind power, wind turbines are accompanied by a large quantity of power electronic converters connected to the grid, causing changes in the characteristics of the power system and leading to increasingly serious sub-synchronous oscillation (SSO) problems, which urgently require the generalized classification and characterization of the emerging oscillation problems. This paper classifies and characterizes the emerging types of SSO caused by grid-connected wind turbines to address these issues. Finally, the impact of the typical system parameters changes on the oscillation pattern is analyzed in depth to provide effective support for the subsequent suppression and prevention of SSO.

THE LIMIT CYCLE BIFURCATIONS OF A WHIRLING PENDULUM WITH PIECEWISE SMOOTH

This paper deals with the problem of limit cycles for the whirling pendulum equation x=y,y=sin x(cosx-r)under piecewise smooth perturbations of polynomials of cos x,sin x and y of degree n with the switching line x=0.The upper bounds of the number of limit cycles in both the oscillatory and the rotary regions are obtained using the Picard-Fuchs equations,which the generating functions of the associated first order Melnikov functions satisfy.Furthermore,the exact bound of a special case is given using the Chebyshev system.At the end,some numerical simulations are given to illustrate the existence of limit cycles.

Sub-synchronous frequency domain-equivalent modeling for wind farms based on rotor equivalent resistance characteristics

The equivalent simplification of large wind farms is essential for evaluating the safety of power systems.However,sub-synchronous oscillations can significantly affect the stability of power systems.Although detailed mathematical models of wind farms can help accurately analyze the oscillation mechanism,the solution process is complicated and may lead to problems such as the“dimensional disaster.”Therefore,this paper proposes a sub-synchronous frequency domain-equivalent modeling method for wind farms based on the nature of the equivalent resistance of the rotor,in order to analyze sub-synchronous oscillations accurately.To this end,Matlab/Simulink is used to simulate a detailed model,a single-unit model,and an equivalent model,considering a wind farm as an example.A simulation analysis is then performed under the sub-synchronous frequency to prove that the model is effective and that the wind farm equivalence model method is valid.

Overview of Sub-synchronous Oscillation in Wind Power System

Nowadays with the improvement in the degree of emphasis on new energy, the wind power system has developed more and more rapidly over the world. Usually the wind plants are located in the remote areas which are far from the load centers. Generally series compensated AC transmission and high voltage DC transmission are made use of to improve the transmission capacity as two main effective ways which can solve the problem of large scale wind power transmission. The paper describes the three kinds of impact varieties and impact mechanisms in the sub-synchronous oscillation phenomena of wind power system based on doubly fed induction generator (DFIG) wind generators. At last, we point out the important problem that should be stressed in the wind power system.

Research on the Sub-synchronous Oscillation in Wind Power Connected to Series Compensated Power System and its Influencing Factors

When wind farms,which is based on double fed induction generator(DFIG),are connected to the series compensation power system,the phenomenon of sub-synchronous oscillation(SSO)may occur.In order to study the sub-synchronous oscillation in wind power connected to series compensated power system and its influencing factors,we used RT-LAB to establish a simulation model concerning wind power connected to series-compensation power system.This model take a wind power connected to series compensation power system in north China as prototype.All influence factors of wind power SSO are simulated and analyzed by using time domain analysis method.The simulation results show that the effects of wind speed,series compensation degree and proportional control coefficient of rotor side converter(RSC)are most obvious.

Gas Temperature Distribution and Fluctuation in a Lab-Scale Fire Whirl

Fire whirls cause an increase in fire damage. This study clarified the unsteady behavior of fire whirls, considering that instantaneous changes in the temperature and flame shape of fire whirls can affect the damage to the surrounding area. Numerical simulations of a lab-scale flame that simulates a fire whirl were performed to investigate the changes in gas temperature and velocity fields under various fuel inflow velocities. The flow field was obtained by solving a continuity equation and a three-dimensional Navier-Stokes equation, and the turbulence was resolved using a large eddy simulation. A chemical equilibrium partially premixed combustion model was used, and radiation effects were considered. The time-averaged gas temperature distribution along the burner central axis revealed that the gas temperature decreased monotonically from upstream to downstream. The time-averaged velocity distribution along the burner central axis showed that the velocity decreased as one moved downstream, but the decrease was uneven. The time variation of the gas temperature demonstrated that the higher the fuel inflow velocity, especially near the burner, the greater the gas temperature flutter. Furthermore, the larger the fuel inflow velocity, the larger the flame swell and wobble. The results showed that the fuel inflow velocity affected temperature fluctuation and flame undulating movement.

螺旋桨发动机安装系统动力学设计技术综述

随着螺旋桨发动机安装系统国产化研制进程的加快,需要开展相关的安装系统技术研究,而动力学设计是其中的重要组成部分。本文对比分析了不同结构形式安装系统的动态性能特点,进一步从军民用标准规范和工程实践经验出发,归纳了安装系统动力学设计的技术要求,梳理了安装系统动力学设计技术的发展历程和国内外现状,指出国内外差距主要体现在设计理念、关键技术和应用实践经验等方面。在此基础上,展望了螺旋桨发动机安装系统动力学设计技术的发展趋势,为当前及未来螺旋桨发动机安装系统的设计技术研究提供了参考。

特深井钻柱动力学特性模拟与分析

随着钻井深度不断增加,钻柱运动所涉及的力学问题变得更加复杂,钻柱动力学特性模拟及分析可为安全优质高效钻井提供支撑。为了探求特深井钻柱的运动特性,将钻柱运动的控制方程采用Newmark法对时间离散后,运用SOR节点迭代法,对每一时间步的钻柱整体构形进行求解,实现了总长超9000 m的钻柱动力学特性模拟,不仅给出了钻柱4个典型位置的涡动轨迹、涡动速度和横向加速度,还分析了钻柱的粘滑特性。分析结果表明,上部钻柱的涡动及粘滑现象不明显;随着位置下移,出现不规则涡动及不充分粘滑现象;近钻头位置的钻柱会出现较剧烈涡动,也会出现粘滑振动;中性点位置处钻柱的涡动最为剧烈、碰摩严重,可能给钻柱带来安全隐患。研究结果为特深井安全钻井提供了理论依据。

基于空间耦合传输方法的FBG传感器转子涡动测温误差及其影响因素研究

针对电机转子涡动对光纤光栅温度监测系统精度产生的影响,采用光纤光栅(FBG)的传输矩阵理论和自聚集透镜的耦合损耗理论,建立了涡动条件下FBG扫描光谱模型,结合相关试验,研究了扫描光谱的畸变规律及系统测温误差的影响因素。结果表明:涡动导致扫描光谱反射峰发生偏移、3 dB带宽减小,通过协调涡动频率和解调仪扫描频率,使准直器间耦合损耗周期达到FBG光谱扫描时间的10倍以上(q>10)是保证较低测温误差的关键;同时,质心法对剧烈涡动条件下扫描光谱的寻峰效果明显优于高斯曲线拟合法。随着转子端面处的径向位移幅值或轴线偏角幅值的增大,系统的测温误差先缓慢地增大、后剧烈地增大;随着椭圆形轴心运动轨迹轴比的增大,测温误差先剧烈地增大、后缓慢地增大至稳定。当转子径向位移幅值小于200μm、轴线偏角幅值小于0.167°时,在轴比等于3、q值等于10条件下,15次采样试验反映出质心法和高斯曲线拟合法分别令系统的测温误差从2.9℃降低至0.6℃和1.1℃,为监测系统的应用与测温精度的预估提供了依据。

转子运动条件下光纤光栅的扫描光谱特性及测温误差研究

针对基于空间耦合传输方法的电机转子温度监测系统,采用光纤光栅的传输矩阵理论和自聚集透镜的耦合传输理论,建立了转子运动条件下光纤光栅(fiber Bragg grating,FBG)的扫描光谱模型,首先研究了扫描光谱的畸变规律及各算法的寻峰效果,结果表明:转子的涡动导致FBG扫描光谱的反射峰发生偏移,3 dB带宽减小,随着耦合损耗与原始反射峰之间的相位差发生变化,中心波长的最大扫描误差以类似正弦函数的规律发生变化,新反射峰位置由耦合损耗变化速率、FBG原始反射率及其变化速率之间的限定关系决定。协调解调仪扫描速率与转子涡动频率之间的数值关系是减轻光谱畸变的主要方法;此外,相比于半峰法和多种拟合型算法,质心法通过提取畸变光谱的重心也明显地减小了中心波长的扫描误差。然后,通过理论和试验研究了转子涡动频率与解调仪扫描频率对系统测温误差产生的影响,结果表明:随着耦合损耗周期与光谱扫描时间之比(q值)的增加,系统的最大测温误差先剧烈地减小、然后缓慢减小至稳定,令q>10是确保系统的测温误差及其波动较小的最低条件;对于转速小于200 000 r/min的转子(涡动频率小于1 667 Hz),当转子径向振动的幅值小于200μm、轴心轨迹的轴比小于3、轴心线偏转的角度小于0.1°时,采用扫描频率大于760 Hz的解调仪和质心寻峰法可以保证涡动引起的测温误差小于0.3℃,为转子测温系统的实际应用及测温误差的预估提供了依据。

WHIRL SSA:一种基于高级中间表示的优化结构

中间表示对编译器的性能、效率和可扩展性都起着决定性作用.Open64编译器采用一种树型结构的中间表示WHIRL,能表示各种高级控制流结构,但不能显式的提供数据流信息.本文基于WHIRL对SSA(Static Single Assignment)进行扩展,提出了一个新的优化结构WHIRL SSA.WHIRL SSA通过将SSA信息标注在WHIRL节点上,显式的为数据流分析提供使用-定义(UD)信息.相比于传统的数据流信息构建方法,WHIRL SSA提供了更精确、有效的数据流信息.本文讨论了WHIRL SSA的设计与实现和基于WHIRL SSA的优化.

离心空压机波箔气体轴承设计及实验研究

针对功率26 kW、主轴径22 mm的氢燃料电池离心空压机,设计波箔动压气体轴承;在搭建的实验台上进行轴承静动态特性实验和耐久性实验,得到轴承滞回曲线和静态刚度曲线,以及空压机轴系升降速振动三维频谱图、30 000~95 000 r/min下的时域图。实验结果表明:研发的波箔动压气体轴承静态刚度与轴承位移具有非线性特性;空压机启停100 000余次后,平箔表面仅有轻微磨损,波箔高度几乎无变化,表明轴承具有良好的耐久性;转子振动以基频为主,全转速范围内主振幅为1μm左右,无明显低频和高频振动;两级气浮轴承离心空压机实验最高工作转速可达95 000 r/min,并且表现出良好的热力性能。

BWDSP SIMD指令的WHIRL中间表示生成研究

WHIRL是Open64采用的一种通用的中间表示,支持多种高级语言和多种目标机。Open64的后端优化工作都是基于WHIRL设计的。BWDSP是一款支持SIMD指令的数字信号处理器,SIMD指令能够提高该处理器的指令并行性。SIMD优化也需要产生WHIRL中间表示,本文对如何产生BWDSP SIMD指令的WHIRL中间表示进行了研究,并在BWDSP的编译器OCC上得以实现。

聚焦于碰摩诱导的非规则形貌套管磨损分析

由于钻磨铣作业管柱刚度低且受力情况复杂,发生涡动时不可避免会碰摩套管,诱导套管产生不连续、随机的磨损,降低井筒安全性。为研究碰摩磨损对套管安全性的影响规律,基于转子动力学理论建立了钻磨铣作业钻柱有限元动力学模型,得到钻柱涡动轨迹及钻柱涡动诱发的套管碰摩特征;同时建立了碰摩磨损体积计算模型,考察转速、钻压对碰摩诱导的套管磨损的影响规律;将碰摩磨损缺陷引入套管模型,采用应力集中比值分析碰摩磨损缺陷对套管承载性能的影响规律。研究结果表明:钻磨铣作业期间钻柱对套管的碰摩主要发生在下部钻具组合处,表现为不连续性碰摩和连续性碰摩2种形式;转速、钻压与碰摩磨损程度呈正相关关系;碰摩磨损缺陷的偏磨率、开口大小及数量会对套管承载性能产生不同的影响。研究结果可为由碰摩诱导产生的套管磨损分析及井筒完整性评价提供理论依据。

Multi-blade rubbing characteristics of the shaft-disk-blade-casing system with large rotation

Blade rubbing faults cause detrimental impact on the operation of aeroengines. Most of the existing studies on blade rubbing in the shaft-disk-blade-casing(SDBC) system have overlooked the elastic deformation of the blade, while some only consider the whirl of the rotor, neglecting its spin. To address these limitations, this paper proposes a dynamic model with large rotation for the SDBC system. The model incorporates the spin and whirl of the rotor, enabling the realistic reproduction of multiblade rubbing faults. To verify the accuracy of the SDBC model with large rotation and demonstrate its capability to effectively consider the rotational effects such as the centrifugal stiffening and gyroscopic effects, the natural characteristics and dynamic responses of the proposed model are compared with those obtained from reported research and experimental results. Furthermore, the effects of the rotating speed, contact stiffness,and blade number on the dynamic characteristics of the SDBC system with multi-blade rubbing are investigated. The results indicate that the phase angle between the rotor deflection and the unbalance excitation force increases with the increasing rotating speed,which significantly influences the rubbing penetration of each blade. The natural frequency of the SDBC system with rubbing constrain can be observed in the acceleration response of the casing and the torsional response of the shaft, and the frequency is related to the contact stiffness. Moreover, the vibration amplitude increases significantly with the product of the blade number under rubbing, and the rotating frequency approaches the natural frequency of the SDBC system. The proposed model can provide valuable insight for the fault diagnosis of rubbing in bladed rotating machinery.

Empirical Wavelet Transform Based Method for Identification and Analysis of Sub-synchronous Oscillation Modes Using PMU Data

This paper proposes an empirical wavelet transform(EWT)based method for identification and analysis of sub-synchronous oscillation(SSO)modes in the power system using phasor measurement unit(PMU)data.The phasors from PMUs are preprocessed to check for the presence of oscillations.If the presence is established,the signal is decomposed using EWT and the parameters of the mono-components are estimated through Yoshida algorithm.The superiority of the proposed method is tested using test signals with known parameters and simulated using actual SSO signals from the Hami Power Grid in Northwest China.Results show the effectiveness of the proposed EWT-Yoshida method in detecting the SSO and estimating its parameters.

极地冰区船舶推进轴系共振方法的应用

船舶在冰区航行时,推进轴系产生共振现象比在非冰区航行产生共振现象的几率大很多,这是因为冰块对螺旋桨的瞬时载荷非常大,如果轴系设计不当,很容易产生轴系共振现象。轴系振动一般情况分为扭转振动、回旋振动、纵向振动和相互耦合振动。采用有限元仿真计算得到的几种评估冰区船舶推进轴系振动是否共振的方法:通过计算轴系的扭转振动频率、扭矩、扭转应力和放大系数,查看轴系扭转振动是否达到共振现象;通过计算轴系回旋振动频率,查看轴系回旋振动是否达到共振现象;通过计算轴系纵向振动的频率和振幅,查看轴系纵向振动是否达到共振现象。在轴系设计过程中,可以对其进行振动的仿真计算,能有效地、预见性地避免轴系共振。

某57MW汽轮发电机组油膜涡动问题分析与处理

油膜涡动是汽轮机常见故障之一,在运行时发生涡动会对设备造成一定损伤。本文以57MW汽轮发电机组为例,阐述机组在A修后发生#3轴承振动异常上升现象,通过分析振动特征数据、运行调整实验,准确判断出油膜涡动故障。通过轴瓦修刮、中心调整,提高轴承稳定能力,维持合适的油膜厚度,最终消除油膜涡动故障,保障了汽轮发电机组的稳定运行。

Effect of suppressing dust by multi-direction whirling air curtain on fully mechanized mining face

A combined method of numerical simulation and field testing was adopted in this study in the interest of solving the problem of hard to control high concentrate dusts on a fully mechanized mining face.In addition,the dust suppression effect of a multi-direction whirling air curtain was studied in this paper.Under the influence of the wall attachment effect,the compressed air which blows out from the two-phase or three-phase radial outlets on the generator of the air curtain can form a multi-direction whirling air curtain,which can cover the whole roadway section of a fully mechanized mining face.The traditional method of controlling dust is a forcing system with exhaust overlap which has the major disadvantage of lacking a jet effect and consequently results in poor dust control.It is difficult to form the air flow field within the range of L_p5Sr^(1/2).However,due to the effect of this novel system,the radial airflow can be turned into axial airflow allowing fresh air to flow through the length of the heading.The air flow field which is good at controlling dust diffusion can be formed 12.8 m from the heading face.Furthermore,the field measurement results show that before the application of a multi-direction whirling air curtain,the dust concentration is 348.6 mg/m^3 and 271.4 mg/m^3 respectively at the roadway cross-section measurement points which are 5 m and 10 m from the heading face.However,after the application of the multi-direction whirling air curtain,the dust concentration is only 61.2 mg/m^3 and 14.8 mg/m^3,respectively.Therefore,the dust control effect of a multi-direction whirling air curtain is obvious.

Simulation Research on Oil Whirl Fault in a High-speed Rotor-bearing System

Under the sliding bearing support for the rotor-bearing system, the dynamic model of a rotor-bearing system is established under the action of non-linear oil film force. The rotor-bearing system has been studied by the application of nonlinear dynamics theory, and the system＇s response was obtained by the numerical integration approach. The effects of eccentricity, speed, lubricant viscosity, radius gap, bearing length and journal radius on the system＇s response have been studied by using an amplitude-frequency curve, three-dimensional spectrum and bifurcation, which provides a theoretical basis for the diagnosis of the oil whirl fault effectively in the rotor-bearing system supported by a sliding bearing.