Active control of power flow transmission in finite connected plate

The vibration propagation and active control of power flow in finite connected plate structure are studied. The dynamic response of the connected plate is obtained by the wave approach. The active power flow at the junction of the connected plate is suppressed by the feedforward active vibration control. It indicates that the active power flow at the junction of the connected plate cannot be well suppressed by the optimal control force for minimizing the acceleration, but it can be effectively suppressed by the optimal control force for minimizing the active power flow. The small error of the optimal control force has slight effects on the control results.     

对无功功率物理意义的讨论

有功功率和无功功率是电工理论中非常重要的基本概念,有功功率物理意义明确,是瞬时功率在一个周期内的平均值,而无功功率概念模糊,正弦稳态电路中,一端口网络无功功率的值为端口电压有效值与电流有效值及电压与电流相位差的正弦函数三者的乘积,即Q=UIsinφ,有的教材将无功功率解释为网络内部与外部电源能量交换的最大规模,本文通过纯电阻、纯电感和纯电容电路,以及对RL与C并联电路的分析,证实对无功功率的这种解释是有歧义的.     

三相电压型PWM整流器模型预测直接功率控制

通过对三相电压型PWM整流器传统直接功率控制(DPC)引起的开关频率不固定,网侧电流谐波分量高,系统调节时间长等问题的分析,提出一种电压型三相PWM整流器模型预测直接功率控制方法,应用模型预测理论构建目标函数并对目标函数进行求偏导,对下一个采样周期的有功功率和无功功率变化进行预测,将模型预测理论与二阶拉格朗日插值法相结合进行功率修正,实现了有功和无功功率的实际值与预测值的误差最小,并采用空间矢量脉宽调制(SVPWM)产生PWM信号驱动整流器功率开关,实现固定的开关频率;仿真结果表明,本方法具有良好的动态和稳态性能,系统对电感参数的变化不敏感,有效降低了交流测电流总谐波失真(THD),提高了交流侧功率因数。     

Power flow transmission influenced by vibration source impedance for a compound system

I.IntroductionVeryofteninengineeringpracticemachinesareusuallyinstalledonflexiblestructures.Buildingfloors,shipdecks,aircraftfuselages,carortrainChassisarebutafewexamplesthatfallintothiscategory.Themachinetransmitsvibrationtothereceivingstructureandresultsinstructure-bornesoundtransmission.Especiallywhenaheaviermachinerunningathighspeedismoulltedonaflekib1efoundation,thesourceandthereceiverwillpresentsimilardynamiccharacteristicsattheirinterface.Asaresult,theconventionalanalysiscannotbeappli…     

Local sensing/control or global error sensing/control in structural acoustics: A comparison of two techniques influence over sound power

The active control of radiation from large structures is a difficult, though important practical problem. The major reason for the difficulty is the ‘system’ size, as a large number of sensors and actuators are required for successful implementation, thus making it hard to design a robust, efficient system that integrates all sensors and actuators. This work examines the active attenuation of the global error, sound power, from the point of view of two sensing/control strategies that seek to be generalised; thus are applicable to a wide range of applications and are independent of knowledge of structural dynamics. In each approach the idea is that the required hardware can simply be attached, turned on, and immediately being to attenuate global noise. The two strategies are compared based on the level of attenuation of the global error sound power, the attenuation per total control force, and attenuation per actuator (in a structural-acoustic situation). The first strategy is the collocated-decentralised approach, which is built on measuring and controlling local vibration in an attempt to influence the global acoustic error. An alternative approach, termed the hybrid approach is firstly developed. The approach is termed ‘hybrid’ because it is a mix between a fully ‘centralised’ and ‘decentralised’ approach; but still measuring and controlling the global acoustic error directly. The attenuation of sound power is compared for both strategies on two structural sources; using 16 identically placed velocity sensors and 16 secondary point sources, in simulation in an attempt to suggest efficient sensing and control approaches for the global control of sound radiation from large structural sources.     

Electromagnetic control of the instability in the liquid metal flow over a backward-facing step

The tile-type electromagnetic actuator (TEA) and stripe-type electromagnetic actuator (SEA) are applied to the active control of the perturbation energy in the liquid metal flow over a backward-facing step (BFS). Three control strategies consisting of base flow control (BFC), linear model control (LMC) and combined model control (CMC) are considered to change the amplification rate of the perturbation energy. CMC is the combination of BFC and LMC. SEA is utilized in BFC to produce the streamwise Lorentz force thus adjusting the amplification rate via modifying the flow structures, and the magnitude of the maximum amplification rate could reach to 6 orders. TEA is used in LMC to reduce the magnitude of the amplification rate via the wall-normalwise Lorentz force, and the magnitude could be decreased by 2 orders. Both TEA and SEA are employed in CMC where the magnitude of the amplification rate could be diminished by 3 orders. In other words, the control strategy of CMC could capably alter the flow instability of the liquid metal flow.     

望远镜主镜气压力驱动器设计

为了获取优异的光学图像质量,大口径天文望远镜通常采用主动支撑结构以校正主镜面形误差。对望远镜主镜支撑系统所需的气压驱动器进行了研究。基于气动原理设计了一种采用滚动膜片结构的气压力驱动器,其中滚动膜片结构用于消除摩擦力的影响,滚珠式力解耦器用于消除侧向力、弯矩的影响。进一步设计了针对气压驱动器带死区的比例-积分-微分(PID)控制算法,以实现对气压驱动器的闭环控制。实验结果表明:气压力驱动器可精确提供主镜控制所需的支撑力,在望远镜高角变化速度达到2°/s时,输出支撑力范围为0～1000N,驱动器支撑力误差仅为满量程的±0.4%。设计的气压驱动器可实现主动支撑力的快速精确输出,能满足天文望远镜主镜主动支撑需求。     

On the design of structural junctions for the purpose of hybrid passive-active vibration control

A theoretical investigation of wave scattering and the active modification of wave scattering at structural junctions is presented. A resonant and a non-resonant Euler-Bernoulli beam are coupled, and an external force is introduced at the junction. The external force is intended for feedforward control in order to manipulate the scattering properties at the junction. The purpose of the investigated control law is to make the junction non-reflective in the case of an incident bending wave. The control effort and the resulting power flow are investigated for different properties of the beams. By introducing damping in the resonant beam all incidence wave power is absorbed either passively, in the resonant beam, or actively, by the force. The results form the basis for a discussion of the possible benefits of using such a configuration for hybrid passive-active vibration control. The results show that for certain ratios of bending stiffness and mass the presented hybrid passive-active solution may offer advantages compared to purely passive or purely active solutions.     

Orthogonal contributor number for the measurement of sound power

Orthogonal contributors to a global error represent a very efficient design method in terms of both sensing and control of noise radiation. In practice the price of a sensing system will be determined by the number of errors it must resolve. Therefore predicting the most efficient way of measuring radiation power is an important problem. Recently work has compared sensing the number of vibration modes to the number of orthogonal contributors to radiated power. The required number of vibration modes was based on the proximity of the structural mode resonance frequency and the excitation frequency. While ultimately this technique will result in a valid estimate of radiated power, it is shown here that the number of structural modes can be minimized by first considering orthogonal radiators based on structural mode amplitudes. Two disturbance cases are considered: a point force and an even disturbance coupling to each structural mode. Also, under these conditions the practicality of estimating the number of orthogonal radiators when it is assumed that each contributor is equal in amplitude is examined. Finally in an attempt to optimism the number of signals to be sensed, a variable error margin for the estimate of power, based on the ratio of the sound power at each frequency to the maximum peak in the considered frequency range is proposed and analyzed.     

翼型绕流的洛伦兹力控制机理

在翼型上翼面壁面附近流场中形成的流向洛伦兹力,可提升翼型的升力减小阻力,然而制约其推广应用的主要瓶颈是极为低下的控制效率,为提高洛伦兹力的控制效率,需研究其控制机理.以翼型绕流的洛伦兹力控制为例,利用双时间步Roe格式及水槽对其进行数值及实验研究.结果表明:洛伦兹力的控制效果随着来流速度的增加而下降,升力增幅和阻力减幅与来流速度大小呈反比关系,但升力增加和阻力减小的规律不变,都是升力先急剧增加随后缓慢增加,而阻力先急剧减小然后再缓慢增加,基本原因为升力和阻力先受洛伦兹力推力的影响而分别增加和减小,随后洛伦兹力作用增加翼面壁面摩擦力,导致升力减小和阻力增加,流向洛伦兹力还导致翼型壁面压力下降,增加翼型升力和压差阻力;壁面摩擦力导致的升力降幅比壁面压力变化导致的升力增幅小,壁面压力变化起主导作用;洛伦兹力推力对阻力的降幅比压差阻力的增幅大,洛伦兹力推力起主导作用,因此阻力减小.     

薄镜面面形主动校正技术研究

采用12个主动支撑点对口径400 mm薄实验镜进行面形主动校正,使用Zygo干涉仪测量面形误差,主动支撑点的力促动器由位移促动器和力传感器组成。分别测量单个促动器的响应函数,由各促动器的响应函数组成刚度矩阵,然后用阻尼最小二乘法计算各支撑点的校正力。实验中分析主动支撑结构对各项Zernike形式像差的校正能力,并选择了7项像差进行校正。经过5次校正,使初始状态下1.16λ(λ=0.632 8μm)RMS面形精度达到0.13 RMS,接近镜面抛光后的精度。     

大口径天文薄镜面磨制试验

介绍了采用薄镜面主动支撑技术来加工大口径天文薄镜面的试验情况。试验镜为一弯月型球面反射镜．直径为Ф1035mm,镜面曲率半径为3220mm,径厚比约为40：1。在磨制过程中,有55个分离支撑点支撑存镜子背面。支撑点的位置与支撑力的大小通过有限元分析计算确定,其中3个为固定支撑点．另外52个为主动支撑点。每个支撑点位置设置了力促动器,调节力促动器加力的大小。可以主动改正镜面的低频误差。加工后最后达到的面形精度：λ=632．8nm,面形误差(RMS)小于等于λ／21．5,局部高频误差(RMS)小于等于λ／23。试验证明所采用的方法适合于大口径天文薄镜面的加工。     

在COIL中碘量变化与激光功率波形的关系

 针对碘量在一定范围内变化对激光功率影响不敏感,采用碘量变化的方法,通过对大量的250mmol/s列管式射流氧发生器的出光实验的分析,得到了激光功率波形随碘量变化的实验规律。这一实验结果可用于根据功率波形变化来调节最佳碘量。并对其机理进行了理论分析。     

离体射流对S809翼型气动性能的影响

在Re=5×10⁶的条件下,分别在S809翼型前缘点附近不同位置处设置离体射流装置,改变射流动量的大小和射流口宽度,探究其对S809翼型气动性能的影响。并通过流场分析,研究这种流动控制手段有效的物理机理。结果表明:在射流装置位置和射流口宽度固定时,射流动量的大小对控制效果影响显著;在S809翼型表面附近设置微小离体射流装置后,即使关闭射流(射流动量为零时),也具有一定的流动分离控制效果;当射流动量逐渐增大时,射流能明显的减小流动分离泡的大小,降低阻力系数,同时可以有效提升升力系数,使得翼型的气动性能得到进一步显著提升。值得指出的是,射流口宽度与射流装置的位置对流动控制效果也具有一定的影响。     

基于SOGI-FLL算法的油田电网动态无功补偿对策研究

为了解决油田无功补偿装置爆电容现象,本课题在现有无功补偿装置存在问题的基础上,提出了采用晶闸管投切电容器与静止无功发生器相结合的补偿方案。将SOGI－FLL算法应用于电压精准锁相和无功功率的准确计算中,其结果分别用于确定matlab仿真模型中晶闸管投切电容器的投入时刻和提供静止无功发生器的控制参考信号,从而实现谐波和无功电流的有效控制。仿真结果表明,该方案不仅实现了无功功率的有效补偿,而且进一步降低了油田配电网无功损耗,提高了功率因数。     

基于潮流追踪的电网同步性能优化及鲁棒性分析

采用二阶类Kuramoto模型对电网进行合理建模，分别应用临界同步耦合强度和平均同步误差来描述电网的同步能力和鲁棒性.研究发现，发电机的功率分配对线路的传输功率影响较大，而电网中高负荷线路越多，网络越难同步.基于这一发现，首先在发电机功率均匀分配（EG）方式下，计算出每条线路的传输功率，然后基于潮流追踪算法提出一种发电机功率非均匀分配（TG）方式，即在发电总量不变的情况下，增大枢纽发电机节点的功率，减小边缘发电机节点的功率.该发电机功率分配策略可以在一定程度上降低网络的临界同步耦合强度，减小平均同步误差，改善电网的同步性能和鲁棒性.     

关于流体流动的最大输出功率及效率

1引言传统有限时间热力学研究的模型为仅考虑温差传热的内可逆卡诺热机。事实上，存在有限势差（温度差、化学势差、压力差、电压差等）的各种装置均可应用类似分析。流体流动作功与温差传热热机间的类比性最早由Bajan[1]发现，Radcenco[2]进一步作了研究．最近，Bejan[3-4]用内可逆热机的研究方法分析了流体流动的最大功率输出问题。本文基于非线性压力流阻关系导出流体流动功率输出与效率关系，并导出了最大功率输出及其相应的效率界限，由此发现Bejan[3-4]的结果是不正确的。2物理模型和性能分析考虑图1所示活塞、气缸装置。活塞在压差…     

Optimization of the number and the positions of error sensors in adaptive active sound control

l.lntroductlonRcccntly,inthcapplicationoractivcsoundcontrol,thetcchniqucofadaptivcfiltcrhasbeenincommonuseforcontro1systcmandithasbccnrealizedbyfastDSP(digitalsignalproccssing).Espcciallyinthcactivcsoundcontro1inspace,thiskindofcontrolsystemcansurmountthcdiflicu1tywhichiscauscdbythecomplicatcdacoustica1cnvi-ronmentandthevariationofmanyphysica1parameters.ThcreIbrcitprovidesapossibiIi-tyforthepracticaluscsoractivcsoundcontrol.Thisdis1inguishingfcaturchasbccnprovcdbyboththeoryandcxperimentl'].T…     

稳态强磁场装置电源系统并联直流有源滤波器的实现新方案

结合串联型有源滤波器和并联型PWM有源滤波器的特点,提出了并联型线性调整有源滤波方案。介绍了该有源滤波器的结构及其工作原理,对其具体的实现方案进行了分析设计。就该直流有源滤波器进行了建模仿真,模拟结果证实了其参数设计是合理的,基于所提出的方案,研制了一台实验原型。实验结果表明,该滤波器具有良好的滤波效果。     

Dielectrophoresis flow control in microchannels

The control of flow in microscale is one of the most important problems in microfluidic devices, which in particular, are used as micro heat exchangers. The use of electric field is one of the efficient methods of control of dielectric liquid flow in microscale. The electric field influences liquid flow by the EHD force which affects liquid behaviour in terms of the flow rate and pressure.The EHD force consists of three components: the first is the electrostatic force due to free charges present in the liquid, the next one is the force due to the gradient of permittivity of material, and the third one is caused by the change in the electric field intensity.The EHD force is used also in many commercial devices, for example EHD pumps or dielectrophoretic separators. An own approach to apply the EHD force to control the liquid flow rate is presented in this paper. Authors paid a close attention to the dielectrophoresis effect. Dielectric liquid in a non-uniform electric field tends to drift/migrate towards the region of high electric field intensity. With decreasing the electrode dimensions, the dielectrophoresis force becomes relatively stronger. For the dimensions under 400 μm the dielectrophoresis phenomenon can be used for control and actuation of the liquid flow in microchannels. The originally developed design of such flow controller is presented in this paper. The experimental investigations covered flow rate measurement of 2-propanol in microchannel flow controller with application of AC field. It was showed that the dielectrophoresis phenomenon could effectively control the flow. The results for distilled water are also comparatively discussed in the paper.