RMxprt在三相异步电动机中的2D电磁场分析

RMxprt是基于电机等效电路和磁路的设计理念来计算、仿真各种电机模型,具有建立模型简单快捷、参数调整方便等优点,同时具备一定的设计精度和可靠性。针对如何才能更好地计算仿真三相异步电动机,求解二维和三维有限元件这一问题。文中以一台三相异步电动机为蓝本,分析RMxprt模块在三相异步电动机的2D电磁场的应用。将实验计算结果与有限元结果进行横向对比,误差仅0.366 2%,符合工程需要。     

垂直套管环隙内汽液固三相流动沸腾传热的实验研究

符号表C。固体颗粒在液q热通量kw／mZu。固体颗粒与液体中的含量voL％，液体汽化游热kJ／kg体的滑移速度m／s小固体颗粒直径mm或mTi流体温度”CP；液体的密度kg／m’D实验段当量直径mm或mTw加热壁面温度“CP。固体颗粒的密度kg／m’h传热膜系数kw／m’K。1循环液速m／sH液相粘度mPa。k液体导热系数W／inK1前言自MatchL．P．等人首次将固体颗粒引入换热器应用于地热利用山后，对这种流化床换热器的研究开始增多【‘－‘］。研究结果均表明，固体颗粒的引入，可显著强化传热，并有较好的防垢抗垢性能。本文的研究是在液体在垂直套管环…     

Three-phase behavior in a mixed nonionic surfactant system

The effect of monodisperse solubilities of each surfactant in an excess oil phase on the three-phase behavior was investigated in a water/octaethyleneglycol dodecyl ether (R₁₂EO₈)/tetraethyleneglycol dodecyl ether (R₁₂EO₄)/heptane system. The mid temperature of the three-phase region is defined as the HLB temperature. The HLB temperature is largely skewed to higher temperature in a dilute region due to the difference in the distribution of each surfactant between excess oil and microemulsion (surfactant) phases forming the three-phase body. Taking account of the monodisperse solubilities, the equation for the HLB temperature was obtained on the basis of geometrical calculation of a particular three-phase triangle. The equation well describes the three-phase behavior for a mixed surfactant system in a space of compositions and temperature.In the mixed surfactant system, the monodisperse solubility of R₁₂EO₈ in oil phase forming a three-phase body is monotonously increased with the rise in temperature, whereas that of R₁₂EO₄ is first increased and then is decreased. Consequently, the sum of both solubilities does not change greatly in a wide range of temperature.     

基于三维空间矢量算法的三相四桥臂逆变器的研究

对于传统得三相三桥臂逆变电源,当三相负载不对称时,负载中性点电位将会发生漂移,输出三相相电压不再对称,使得负载不能正常工作。三相四桥臂逆变电源,在三相三桥臂的基础上增加一个桥臂作为三相负载的中性点,通过对四个桥臂上下开关的状态进行控制,实现输出三相对称且稳定的相电压。文章主要分析了三相四桥臂逆变器主电路的拓扑结构,在探讨三维空间矢量算法的基础上实现了仿真。仿真结果表明该方案可获得良好的控制特性。     

Propagation of pressure waves in a three-phase medium of cluster structure

The propagation of a step-shaped shock wave in a liquid is investigated experimentally. The liquid contains spherical three-phase clusters (liquid, solid balls, gas bubbles). A comparison of the experimental data on the velocity and wave structure with calculations with the use of the Boussinesq equation for a three-phase cluster medium is made. It is shown that the sound speed in a three-phase medium of cluster structure is higher than in a homogeneous three-phase medium.     

An SDP randomized approximation algorithm for max hypergraph cut with limited unbalance

We consider the design of semidefinite programming(SDP) based approximation algorithm for the problem Max Hypergraph Cut with Limited Unbalance(MHC-LU): Find a partition of the vertices of a weighted hypergraph H =(V, E) into two subsets V1, V2 with ‖V2|- |V1‖ u for some given u and maximizing the total weight of the edges meeting both V1 and V2. The problem MHC-LU generalizes several other combinatorial optimization problems including Max Cut, Max Cut with Limited Unbalance(MC-LU), Max Set Splitting,Max Ek-Set Splitting and Max Hypergraph Bisection. By generalizing several earlier ideas, we present an SDP randomized approximation algorithm for MHC-LU with guaranteed worst-case performance ratios for various unbalance parameters τ = u/|V|. We also give the worst-case performance ratio of the SDP-algorithm for approximating MHC-LU regardless of the value of τ. Our strengthened SDP relaxation and rounding method improve a result of Ageev and Sviridenko(2000) on Max Hypergraph Bisection(MHC-LU with u = 0), and results of Andersson and Engebretsen(1999), Gaur and Krishnamurti(2001) and Zhang et al.(2004) on Max Set Splitting(MHC-LU with u = |V|). Furthermore, our new formula for the performance ratio by a tighter analysis compared with that in Galbiati and Maffioli(2007) is responsible for the improvement of a result of Galbiati and Maffioli(2007) on MC-LU for some range of τ.     

利用FPGA实现三相正弦直接数字频率合成器

利用FPGA芯片及D/A转换器,采用直接数字频率合成(DDS)技术,设计并实现了相位、频率可控的三相正弦信号发生器.正弦调制波的产生采用查表法,仅将1/4周期的正弦波数据存入ROM中,减少了系统的硬件开销.仿真和电路测试表明,输出波形完全达到了技术要求,证明了设计的正确性和可行性.     

基于DSP的静电除尘三相电源调压系统研制

研制了一种基于DSP的静电除尘电源调压控制系统。该控制系统以TMS320F2812为控制核心,能够自动跟踪电场的变化,有效调节中间环节交流电压。实验结果表明,该控制系统能够较好地控制静电除尘电源,大幅度提高除尘效率。     

Identification of bearing dynamic parameters and unbalance states in a flexible rotor system fully levitated on active magnetic bearings

An identification algorithm for the estimation of dynamic parameters of Active Magnetic Bearings (AMBs) and rotor residual unbalances has been presented for a flexible rotor system. The proposed algorithm is suitable for the state of the art rotors that are fully levitated on AMBs. Due to a partial attenuation of unbalance responses by AMBs, difficulty arises in getting the correct estimations from unbalance responses alone, which is not the case with the conventional bearings. For latter bearings responses do reflect real effects of unbalances. Thus, the present algorithm is based both on the measured AMB controlling currents and rotor unbalance responses, and uses these to identify AMB dynamic parameters of each AMB and residual unbalances in flexible rotors at predefined balancing planes. The algorithm is based on the least-squares fit technique in frequency domain. AMB dynamic parameters consist of the force–displacement and the force–current coefficients in two orthogonal transverse directions for each AMB. The finite element method has been used to obtain a unified model of the flexible rotor fully levitated with AMBs for the numerical study, in which the PID controller is used. Numerical simulations have been performed to illustrate the reliability of proposed algorithm. The algorithm is also tested against the measurement noise and modelling errors to investigate its robustness. The proposed algorithm has been finally applied to an experimental data (from Technical University of Darmstadt, Germany) from a fully levitated five-disc flexible rotor test rig with the help of two AMBs. Estimates of AMB dynamic parameters are found to be in close range with that of theoretical values.     

三相异步电动机的选择与维护

三相异步电动机由于其结构简单、坚固耐用、使用和维护方便、效率高等优点,已经发展成为工业、农业生产中应用最广泛的一种动力机械,且随着智能控制技术、单片机、电力电子、交直流调速技术的发展和应用,异步电动机的应用范围正在逐步扩大。合理地选择与使用并能有效地对电动机进行保养与维护,才能保证电动机安全、经济、高效地运行,达到降损节能、提高效率的目的。