功率闭环改造对水电机组性能的影响

机组功率闭环系统中的调速器在“开度调节”模式下运行时,负荷调节稳定性及AGC调节速率达不到电网要求。调速器改为“功率调节”模式后,机组增减负荷比“开度调节”模式更加稳定,功率实发值与功率给定值相差较小,AGC调节速率也能满足电网要求。     

A compact deep-submicron MOSFET gds model including hot-electron and thermoelectric effects

A compact I_ds model with physical drain-conductance (g_ds) modeling for deep-submicron MOSFETs is formulated based on first-principle momentum-/energy-balance equations, which simultaneously includes the hot-electron and thermoelectric effects in a unified compact form with two fitting parameters and one-step extraction. The model has been verified with 0.18-μm experimental data with good g_ds prediction.     

一种适用于航空DC/DC变换器短路限流的控制策略

针对航空变换器在负载短路时需要输出3倍额定电流的要求,提出了一种适用于航空DC/DC变换器短路限流的控制策略。在传统电压-电流双环控制DC/DC变换器的基础上,引入输出电压前馈控制,即将输出电压作为前馈信号,与电流控制器的输出信号相加共同作为调制信号与三角载波交截。通过合理设计前馈系数,保证电流控制器的输出电压在负载短路前后基本保持不变,旁路了PI补偿网络的延时影响,使得短路瞬间占空比即时修正,有效抑制了短路瞬间的电流冲击。小信号建模分析表明,输出电压前馈的引入基本不会影响原双环控制系统的稳态和动态性能。仿真和实验均验证了该控制策略的有效性。     

变压器耦合固态刚管调制器的窄脉冲应用

当前研制固态刚管调制器已经是雷达发射机技术的重要发展方向,不论是直接耦合还是变压器耦合的固态刚管调制器,在许多新型雷达发射机中都得到了应用。文中从开关器件的选择和变压器分布参数两个方面,对变压器耦合固态刚管调制器在窄脉冲应用时的输出波形进行了分析,通过分析和一些验证试验,得到了控制脉冲前沿和过冲的方法。     

基于汽温特性的火电机组过热蒸汽温度控制优化研究

以某台330 MW机组锅炉过热蒸汽温度为研究对象,在分析过热蒸汽温度特性的基础上,构建了以机组负荷为变量的前馈动态补偿函数,并采用Matlab软件对该函数进行了仿真验证.结果表明,以负荷为变量的前馈动态补偿函数较静态补偿函数超调量更小,调节时间短,具有较好的稳定性,可提高过热蒸汽温度的控制品质.     

High-voltage testing on UHV equipment: Overshoot and base curve for oscillating lightning impulse

As the higher impulse testing voltage, residual inductance of the test circuit or the stray capacitance of the test object increases with size. This means that the overshoot superposed on standard lightning impulse voltage would not be neglected because of its larger value during the lightning test. This paper describes the analysis of overshoot and oscillation based on the equivalent circuit containing a residual inductance. The waveform parameters such as relative overshoot magnitude, oscillation frequency are also derived to evaluate the influence of the residual inductance in the impulse testing circuit. The oscillating impulse waveform is related to the base curve of the standard lightning impulse. Furthermore, the base curve for oscillating impulse is proposed by the analysis. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

一种DC-DC开关电源片上软启动电路

提出了一种基于DAC(digital-to-analog converter)控制的数字软启动电路,利用DAC控制和软启动电压检测技术,有效抑制了DC-DC开关电源启动过程中产生的浪涌电流和输出电压过冲,实现了输出电压从零到调整值的平坦上升.在启动完成后启动电路的偏置电流被彻底关断,实现了低功耗没计.该软启动电路采用CMOS器件设计,无需任何外围元件,便于被DC-DC开关电源集成.该电路已成功集成到一款Buck型PWM(pulse width modulation)控制器当中,测试结果表明:在整个负载范围内,DC-DC在启动过程中电感电流平稳变化,输出电压平滑上升、无过冲,启动时间控制在1.2ms.     

Origin of stress overshoot in amorphous solids

Based on the shear-transformation-zone (STZ) theory, we propose a constitutive model for describing homogeneous elastoplastic deformation of amorphous solids where the interaction of shear transformations and free volume dynamics is incorporated. This theoretical model can reproduce the stress overshoot behavior that shows the dependence of strain rate, temperature, STZ population and dilatancy of systems. It reveals that the stress overshoots its steady state value due to the delayed activation of shear transformations that results from the insufficient free volume in the system. However, the subsequent strain softening (stress drop) is attributed to the shear-induced dilatation that is a result of the positive interplay between shear transformations and free volume creation, the latter playing the dominant role. Our analysis also demonstrates that the STZs, as basic carriers of amorphous plasticity, govern the yielding of the system, whereas the free volume dynamics significantly affects the post-yielding behaviors.     

二甲苯吸附分离装置吸附塔压力控制的优化

介绍了二甲苯吸附分离装置模拟移动床工艺技术,针对吸附塔压力控制初期难以满足要求的问题,通过分析工艺过程和压送循环流量控制的特点,对压送循环流量控制进行了优化,解决了压送循环流量在区域切换时无法稳定控制的问题;采用A/B塔塔底压力的交叉控制策略,使得吸附塔压力始终保持稳定,满足控制精度要求。