Characterization of the Rotor Magnetic Field in a Brushless Doubly-Fed Induction Machine

The large increase in wind generation could improve the final development of wind systems with brushless doubly-fed induction machines (BDFIM) as an alternative to the doubly-fed asynchronous machines. For this reason, a detailed study of several aspects of the BDFIM design, as well as of its rotor configuration, is absolutely essential. In this paper, the authors present an alternative formulation of the BDFIM operating principle in synchronous mode. Besides the basic equation of the machine operation, it presents as main advantage the precise characterization of all the magnetic field components in a BDFIM with idealized stator windings and an idealized rotor cage. Based on this formulation, the paper provides a standard that may be used to compare the fields created by different real BDFIMs. This standard has been validated by laboratory tests.      

Performance of a Five-Phase Induction Machine With Optimized Air Gap Field Under Open Loop $V$/$f$ Control

The paper assesses the steady-state performance of a five-phase induction machine fed by a modified open loop constant volt/hertz ($V$/$f$) control method, which imposes a trapezoidal induction waveform in the air gap under varying load conditions. The trapezoidal air gap induction is achieved through the imposition of an appropriate combination of the third harmonic and fundamental stator voltages. This harmonic combination is determined from the steady-state model using a mathematical optimization procedure, which allows to obtain the optimal weighting factors for each harmonic component. The optimized reference voltages lead to a trapezoidal air gap induction, which allows a better iron utilization and higher output torque for the same rms stator current when compared to sinusoidal air gap induction. The resulting air gap induction is obtained from the induced voltage of a full pitch search coil placed in the air gap. The proposed control scheme was successfully simulated and implemented on a five-phase prototype machine running under different load conditions. Experimental and simulations results show an increase in the torque/ampere relationship for loads above $hbox{50}%$ when compared to the conventional $V$/$f$ method using only the fundamental current and air gap induction. A comparison between the simulation and experimental curves presents a very good agreement that confirms and validates the parameters and model used.      

Two-Step Method for Identification of Nonlinear Model of Induction Machine

A two-step method is applied for parameter identification of a saturated electromechanical model of an induction machine (IM). The k-factor cross saturation technique is used to account for iron saturation. Balanced and unbalanced short-circuits armature current waveforms of this machine are less sensitive to variations in the mechanical parameters. Conversely, any change in these parameters has a strong impact on the start-up test. Accordingly, in the proposed estimation method, the online double-line-to-neutral short-circuit test is performed to estimate the electrical parameters of the machine and the results obtained are then used to compute the mechanical parameters from the starting test. The good agreement of the estimated results with actual data attests to the effectiveness and suitability of the proposed algorithm in computing the electromechanical parameters of these machines.     

基于摄动法的表贴式永磁电机转子偏心空载气隙磁场计算

采用摄动法解析计算表贴式永磁电机转子偏心空载气隙磁场,以无量纲的偏心扰动量作为摄动变量,可解决表贴式永磁电机内转子结构和外转子结构的转子偏心磁场解析问题。根据气隙区域及永磁体区域的边界条件求解拉普拉斯方程和泊松方程,通过矢量磁位推导出气隙磁通密度的解析表达式,进而应用麦克斯韦应力张量法计算不平衡磁拉力,并将解析法结果与有限元法结果进行比较,发现二者一致性较好,验证了该方法的正确性和有效性。     

无刷双馈感应电机耦合电路模型仿真研究

无刷双馈电机是一种特殊结构的电机,只需较小的变流器容量即可实现多种运行模式的变速运行,同时由于其没有电刷和滑环装置,相比普通双馈感应电机具有更高的稳定性和更低的维护成本,在风电领域被认为有潜力可以替代双馈电机作为风力发电机的主流机型,同时可以应用在变载恒速工况下.无刷双馈电机的控制策略是目前的主要研究方向,而要实现高性...     

Comparison of a CFD Analysis and a Thermal Equivalent Circuit Model of a TEFC Induction Machine With Measurements

For a totally enclosed fan-cooled induction machine, two methods of numerical analysis are compared with measurements. The first numerical method is based on computational fluid dynamics (CFDs) and the second one uses a thermal equivalent circuit (TEC). For the analysis based on CFD, a 3-D induction machine including housing is modeled. The numeric solution of the flow equations is determined for stationary temperature distributions. For the TEC, a discretized one-and-a-half-dimensional model of the induction machine is considered. With the TEC model, stationary and transient operating conditions can be simulated. Measurement results are determined by iron–copper–nickel sensors embedded in the stator winding and the housing, as well as by an IR sensor for measuring the rotor temperature. With these measurement signals, stationary and transient operating conditions can be analyzed. For stationary operating conditions, additionally, the housing temperatures are determined by an IR camera. The investigated simulation and measurement methods reveal different local and global temperatures, and thus, only certain aspects and characteristics of the obtained temperatures can be compared. Nevertheless, certain conclusions can be drawn from comparing these aspects considering the actual restrictions of each of the applied methods.      

Thermal Performance Prediction in the Air Gap of a Rotor-Stator Configuration: Effects of Numerical Models

This study is dedicated to a numerical investigation of convective heat transfer on the rotor surfaces of a rotor-stator configuration that is typically found in large hydro-generators. The computational fluid dynamics calculations with two turbulence modelling approaches are used to predict the flow structure and heat transfer in the air gap of the rotor-stator configuration. The steady state mixing plane approach is employed at the interface to couple the rotor and stator components. Results s...     

Capacitors Required for Maximum Power of a Self-Excited Single-Phase Induction Generator Using a Three-Phase Machine

This paper aims to determine the optimal capacitors required for maximum output power of a single-phase self-excited induction generator (SEIG), using a three-phase machine feeding inductive as well as capacitive loads. The generator consists of a three-phase star-connected induction machine with three capacitors and a single-phase load. The algorithm, which gives directly the values of the optimal capacitors for the maximum power output and the maximum power available, has been developed using the steady-state model of the SEIG and sequential unconstrained minimization technique (SUMT). The variations of the maximum power output with power factor (pf) of loads (both inductive and capacitive) and speed of the SEIG have been presented. The voltage regulation of the generator is small due to the effect of the two series capacitors. Experimental results have shown the effectiveness and accuracy of the developed algorithm.     

气密性试漏机校准研究

气密性检测设备已普遍应用于发动机制造行业,是保证零部件质量的重要手段,中国气密性检测技术起步较晚,没有对气密性试漏机建立校准规范,对泄漏量检测缺乏可溯源的国家标准.本文以企业零部件生产线上使用的气密性试漏机为研究对象,通过对气密性试漏机结构原理的分析,确定了气密性试漏机校准项目,选购了压力校验仪和流量计,形成了气密性试漏机校准规程.解决了气密性试漏机无校准规范的问题,确保了泄漏量量值的准确.     

电磁感应加热器在吹膜机组上的应用

电磁感应加热器具有加热迅速、温度控制实时准确等特点,应用于塑料吹膜机组上,不但能改变传统电阻丝加热方式工艺落后、高耗能等现状,而且还能使吹膜机组料筒树脂易于塑化,使薄膜产品性能明显提高;同时电磁感应加热器也具有使用寿命长、维护简单、功率大、安全可靠的特点,起到了节约电能和降低环境温度的作用。     

密封间隙内气体流动对气缸动力特性影响的试验研究

在密封试验台上进行了密封泄漏率与密封间隙内气体流动对气缸动力特性影响的试验,并开发了气缸频响函数测试系统.通过测试气缸脉冲激励下的振动响应,求出了不同转速、不同进气压力下的气缸传递函数,分析了充气前后气缸共振频率的变化,并应用对数衰减率法评估了系统阻尼特性.结果表明:充气前后气缸的共振频率变化很小,但会对系统阻尼造成较大影响;随着进气压力的提高,系统阻尼系数增大;随着转速的加快,系统阻尼系数减小.     

电站锅炉冷热一次风道改进及一次风流场均匀性分析

为了解决安徽淮南某电厂中速磨煤机前一次风道动压、静压和温度分布不均造成一次风量测量不准的问题,对冷一次风道加装混流器和在混合段弯头加装导流叶片,利用数值模拟软件FLUENT,采用Realizable k-ε湍流模型对该厂4种工况(40%THA、50%THA、75%THA和100%THA)下一次风道内流动进行模拟,根据传递误差公式分析动压和温度均匀性对风量测量的影响。结果表明:一次风道经过改进,4种工况下动压相对标准差在40%THA时最大降低5.1%,在50%THA和100%THA最小降低3.1%;温度相对标准差在40%THA时最大降低3.8%,在100%THA时最小降低1%;4种工况下测量面的动压和温度均匀性都有所提升;流量的传递误差在50%THA时最大降低0.902 kg/s,在40%THA时最小降低0.377 kg/s,检测点处流量偏差除40%THA减小不明显外,其他3种工况减小显著。     

等离子体发生器内高温空气化学反应流场分析

空气在高温环境下会发生离解、电离等化学反应使组分发生变化，从而引起流场状态的改变。以一个低温等离子发生器模型为例，应用数值模拟的方法对七种组分，七个化学反应的流场求解，并与纯空气流场的求解结果进行比较．分析化学反应流场流动和传热的特点。在数值模拟过程中采用了局部热力学平衡流体模型，数值格式用SIMPLEC算法，采用贴体坐标的网格模型。计算结果给出了温度场、速度场及组分变化分布图。     

水轮发电机气隙不均匀对磁场强度及转子 磁极应力变化的影响分析

定子内腔和转子外圆气隙不均匀是大型水轮发电机组的主要振源之一。在定子和转子间产生的不均衡磁拉力,对转子和定子形成转频激扰力。为探讨气隙不均匀与磁场强度及电磁应力之间关系,依据发电机的实际结构,考虑铁心饱和的情况,以局部电磁力计算方法中的局部麦克斯韦应力法和虚位移法为基础,结合有限元软件电磁模块分析工具,对水轮发电机转子对中及偏心的6种工况进行发电机内部整体气隙磁场磁感强度及转子表面应力分析,研究水轮发电机气隙变化对转子磁极应力的影响。     

基于MATLAB钢丝感应加热模型及其温度场特性的研究

在感应加热理论和热传导理论的基础上，建立了钢丝在线感应加热的模型，并基于MATALB得到了此模型的数值解，通过数值解分析了钢丝在感应加热过程中的温度场分布特性。     

感应钢包炉炉壳涡流场的有限元计算

本文从感应钢包炉金属炉壳中涡流场的数学模型出发，利用有限元法分析了炉壳中的感生电流的分布，并计算了不同炉壳分块数下的感应钢包炉炉壳中由径向磁场产生的损耗，由此得出了炉壳损耗与炉壳分块数的关系，并合理地选取了炉壳分块数。     

Development of a Phase-Field Model for Simulating Dendritic Growth in a Convection-Dominated Flow Field

The effect of flow convection is taken into account in the currently developed phase-field model (PFM) for simulating dendritic growth. In previous PFM studies, flow over a stationary object is wrongly predicted since the predicted velocity magnitude near the fluid–solid interface is not negligibly small. To tackle this problem, the Navier-Stokes equations are solved only in the liquid, while zero flow velocity is prescribed in the stationary object. Simulated results are compared with those computed from two previously proposed models to justify the newly proposed phase-field model.     

基于LEAP模型的广州交通领域能耗及空气污染物排放分析

基于长期能源替代规划系统(LEAP)模型,结合情景分析法,模拟广州交通领域未来的能耗及CO、HC、NOx、PM2.5、SO2等主要空气污染物排放趋势,分析广州交通领域的节能及空气污染物排放控制策略.结果表明:综合情景下,到2035年,广州交通领域将较基准情景节能23.06％,CO、HC、NOx、PM2.5、SO2分别减...     

乳化油微爆的统一模型

关于乳化油的微爆在以往的文献中提出过各种计算模型,对油包水与水包油两种乳化油的微爆有不同看法。提出一种油包水与水包油微爆的统一模型并给出了微爆强度的定义,试图对微爆的强弱做定量的描述。通过该模型讨论了一些主要因素,如液滴初始直径,分散相直径及水含量等对微爆强度的影响规律。计算结果表明,该模型的理论预测与实验事实基本一致。另外还讨论了其他因素如添加剂的性质、气体溶解度等的作用。     

反吹系流煤粉燃烧技术对炉内空气动力场影响的试验和数值模拟

对引进型300MW机组四角切向燃烧锅炉实施反吹系流技术改造,进行了冷态模化试验和数值模拟。试验数值结果表明：在原炉上实施一次风反吹技术能够改善内容气动力场,解决炉内各种火侧问题,并且能有效地减小水平烟道入口处的残余余旋转量。