Analysis,simulation and verification of a bipolar current source power resonant inverter

A high‐frequency bipolar current source resonant inverter introduced in this paper has dramatic zero‐voltage‐switching (ZVS) characteristic. The analytic expressions of the resonant voltage and current are given. It indicates that the resonant waveform is composed of two parts, i.e. the oscillatory component and the stationary component. In special cases, the resonant waveform degenerates into the mono‐frequency component, as presents the graceful sinusoidal wave with very low total harmonic distortion (THD) value. Based on the closed‐form voltage and current, the component stresses on reactive elements are obtained. The impact of different component values and operating frequencies on ZVS feature is also discussed. It should be noted that the ZVS merit may be lost if the components are carelessly selected. The validity of the theoretical analysis has been proven with Pspice simulations and experimental results. Copyright © 2004 John Wiley Sons, Ltd.     

一种数字式彩色电视副载波综合器的设计

介绍一种适于利用电视信号传送标准时间的数字式彩色电视副载波综合器的设计 ,详细介绍了关键电路———数字混频器的组成、工作原理和输入输出波形 .该电路结构简单、性能稳定、可靠性高 .实际应用证明电路的设计是成功的 .该设计思想可以应用于一切输入频率与要求的输出频率之间没有整倍数关系的频率综合电路中 .     

交流同步电动机传动系统在天钢高线厂的应用

介绍了天钢集团高速线材厂精轧机传动控制系统的构成、基本控制原理和控制方式。该传动系统在生产中应用,具有可靠性高、维护量小,调速范围宽的优点。     

Harmonic solution of semiconductor transport equations for microwave and millimetre-wave device modelling

The hydrodynamic transport equations for charges in a semiconductor have been solved for a periodic excitation by means of a harmonic approach, in order to model microwave and millimetre-wave active devices. The solution is based on the expansion of physical variables in a Fourier series in the time domain, and on discretisation in the space domain. A waveform-balance technique in the TD is used to solve the nonlinear equations system. This approach allows for a longer time step with respect to standard TD solutions for most cases of interest, greatly reducing simulation time by at least two orders of magnitude in typical cases. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14: 36–48, 2004.     

Multistage solid-state power amplifier design by a new alternative synthesis technique

For the first time, the numerical real-frequency technique has been applied to the design of a nonlinear power amplifier. This synthesis technique does not require any transistor model by directly using measured large-signal S-parameters of the power transistor device. The double power-frequency dependence of these S-parameters requires the use of a bidimensional interpolation (spline functions). With the Levenberg–Marquardt optimization and large-signal S-parameters, a specific CAD program optimizes the added-power in order to synthesize the matching networks of the PA. The simulated and measured results of two S-band power amplifiers validate the new synthesis approach. © 2004 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14, 87–98, 2004.     

Repair of notched beam under dynamic load using piezoelectric patch

In this paper, the repair of a cracked beam under an external dynamic load employing the electro-mechanical characteristic of piezoelectric material to induce a local moment is presented. Conceptually, an external voltage is applied to actuate a piezoelectric patch bonded on the beam to effect closure of a crack so that the singularity at the crack tip under dynamic load may be decreased. Globally, this has the effect of altering the resonant frequency of the cracked beam towards that of the healthy beam, which is the criterion used for the repair. To demonstrate the repair methodology, a cantilever beam is used as an illustration, where the repair moment coefficient and the voltage required are mathematically derived. The relationship between repair moment coefficient, crack parameters and length of piezoelectric patch is investigated. The difference between the proposed repair criterion and an earlier published criterion for cracked beam under static load is also shown. A numerical example is used to study the effectiveness of the proposed repair methodology and its results are compared with those from 3-D finite element analyses using ABAQUS 6.4 as one means of verification.     

拓宽调速范围的微机PWM变频传动系统

本文对单CPU结构的PWM变频调速系统做了一些探讨。为解决系统中存在的微机计算速度偏低和硬件复杂性问题,较好地处理软件和硬件的配合问题,本文提出了在较少的硬件结构基础上,通过在线设置辅助数据表,实现计算和存贮相结合的PWM方式:在设计中,利用了微机键盘和显示器实现系统管理。为解决电动机低速运行时机械特性变软这一问题,本文提据电动机定子电压和频率的协调控制原则,实现以电动机基波电流和功率因数为反馈信号的协调控制。实验结果表明,所设计的变频调速系统具有较宽的调频范围、较高的电压及频率分辨率,低速带负载能力大为改善,操作灵活方便。     

基于弹性需求的城市间客车开行频率与票价优化

基于两城市间旅客出行弹性需求,研究了客运企业客车开行频率与票价的组合决策优化问题。在综合考虑旅客出行时间调整费用、车内拥挤费用、票价支出以及客运企业运营的固定成本、可变成本、线路的建设维护分摊费用、车票收入的基础上,以旅客和客运企业的系统净收益为目标函数建立了优化模型和求解方法,并就一组特殊旅客出行时间调整费用函数进行了深入讨论和数值计算分析。研究结果为客运企业客车开行频率和票价的组合决策提供了理论依据。     

工频信号相位和幅值测量的新方法

本文提出了一种利用8031单片微机系统测量工频信号的相位和幅值的新方法,此法只需对两个信号进行三次采样后,再经简单的运算,就能得到两个信号的相位差、幅值以及其它许多重要的电量。     

Investigation of rheological properties of TPS modified bitumen

Rheological properties of the virgin bitumen and TPS modified bitumen binders with several percentages of TPS additives were studied.All TPS modified bituminous binders were prepared on a laboratory scale.Dynamic shear rheometer(DSR) strain sweep test was made to measure the linear viscoelasticity areas of various bitumen binders at -20-70 ℃,then temperature sweep test and frequency sweep test were made in the linear viscoelasticity areas.Complex modulus master curves were drawn to analyze and compare various bitumen binders’ rheological properties.Based on the test results,the ideal percentage of TPS additive was brought forward.The results show that TPS modified bitumen binders have more excellent properties at high,medium and low temperatures compared with original bitumen.The dosages of TPS additive are vital to their properties.