高压钠灯电子镇流器建模与仿真

高压钠灯（HPS）电子镇流器是1个非线性系统,多采用电路模型对其进行设计与分析。为了实现对高压钠灯电子镇流器的闭环控制,需建立其动态数学模型。文中在建立电子镇流器各单元数学模型基础上,综合出整机数学模型。Matlab＼Simulink仿真与实际测量对比表明,本文建立的数学模型准确描述了高压钠灯电子镇流器运行状态,为闭环控制算法建立提供了依据。     

患者被动式外骨骼的构想

针对长期昏迷患者以及高位截瘫患者护理过程繁琐、工作量大等特点,设计一种专门辅助患者进行全身性被动运动的外骨骼装置,以减轻家庭和医护人员的压力。通过从仿生学角度分析外骨骼的功能及结构特点,简要介绍了外骨骼的总体设计、支座的机构设计构想以及关节自由度的确定,并采用CAD二维软件、Inventor三维软件及动力学仿真软件ADAMS等完成了装置的结构设计、机构的受力分析以及虚拟样机的制作,为进一步研究外骨骼装置的机构设计等提供参考依据。     

垃圾渗滤液深度处理混凝剂的选择

城市垃圾渗滤液废水的处理已经形成一定的规模,但其深度处理至关重要。文章选用三种常见的混凝剂在同等条件下对垃圾渗滤液废水进行处理,结果表明,聚丙烯酰胺PAM在用量最少的情况下,对废水的处理效果最好,但其受pH影响较大,价格比较贵;聚合硫酸铁PFS的处理效果比聚合氯化铁PFC好,虽然处理效果不如PAM,但其价格低廉,是一种不错的废水处理混凝剂。     

The effects of pre-treatment with vitamin B6 on memory retrieval in rats

The effects of pre-treatment with vitamin B₆ on memory retrieval in adult male Wistar rats were evaluated using a step-through passive avoidance task. The rats were divided into three groups of 10 each. All animals were fed standard rodent chow. Vitamin B₆ (50 or 100 mg/kg) was administered intraperitoneally (i.p.) every other day for 1 month before training was initiated. Three retention tests were performed to assess the memory of the rats. Vitamin B₆ (100 mg/kg) significantly increased the step-through latency of the passive avoidance response compared with the control in the first retention test of the passive avoidance paradigm (p < 0.05). In addition, vitamin B₆ at 100 mg/kg significantly increased memory retrieval in the second and third retention tests conducted 2 days and 1 week after training, respectively, compared with the control (p < 0.05). These results indicate that pre-treatment with vitamin B₆ potentially enhances memory retrieval.     

西安国网数据中心UPS应用的讨论

采用IGBT整流的无变压器UPS是近十年UPS技术领域的最新发展成果.由于采用了不同的电路拓扑结构,其电气性能于传统的带逆变变压器的UPS有明显的改善.特别是由于输入谐波的改善,显著降低了与其配套的电气系统上的投资.同时,由于无需再使用逆变变压器,UPS的占地面积、重量和使用成本也有效降低了.     

粗粒土大型直剪试验的二维离散元模拟

通过一组强风化玄武岩粗粒土的室内大型直剪试验,获取其强度、变形等宏观参数。并基于颗粒离散元软件PFC2D,采用圆盘模拟土颗粒建立了考虑级配的二维直剪模型,结果表明：黏结半径因子为0．39时,剪应力一剪位移模拟值与试验值相符较好,垂直位移一剪位移模拟值与试验值之间存在一定的偏差;通过参数校正发现圆盘间摩擦系数随着垂直压力增加而增大,其值介于0．15—0．60;剪切过程造成了接触压力的偏转和集中,剪切缝附近圆盘呈不规则的涡状细观运动。     

Current‐fed isolated PFC pre‐regulator for multiple LED lamps with extended lifetime

To emit high‐quality LED light, one or a bin of LED lamp(s) is normally driven by a PWM‐controlled constant current source to minimize device variation and achieve accurate brightness control. Powered from offline AC mains, the front‐end power converters should provide a relatively low DC voltage bus for the inputs of post‐end LED current regulators. To match the long lifetime of LEDs, the whole LED driver (ballast) should work as durably as the LEDs. However, the lifetime of the driver is usually limited by the high‐voltage electrolytic charge storage capacitors used in conventional PFC pre‐regulators. In this paper, our previously proposed resonant current‐fed isolated PFC pre‐regulator is extended to operate in discontinuous conduction mode (DCM). It allows the use of the low‐voltage storage capacitors on the transformer secondary, and therefore extends the overall lifetime of the LED lighting system. A detailed procedure for finding the expected lifetime of the low‐voltage electrolytic capacitor is given. As before, the high‐voltage stress on the main switches, which is typical in current‐fed isolated converters, is reduced substantially by taking advantage of the transformer leakage inductance necessary for resonance. Additionally, high efficiency is ensured by the use of dual non‐cascading structures. Steady‐state state‐space averaging analysis is performed for designing the converter in DCM operation. A prototype converter is built to verify performance of the proposed PFC LED pre‐regulator. Copyright © 2011 John Wiley & Sons, Ltd.     

开关电源专用芯片的选择及其应用

首先介绍PLC810PG型半桥LLC谐振式变换器的基本原理及典型应用．然后阐述HiperPFS系列升压式单级PFC控制器的原理与应用实例,最后对HiperTFS系列双开关正激式和反激式变换器做简要介绍、     

高功率因数三相单管Boost PFC变换器

三相单管Boost功率因数校正(power factor correction,PFC)变换器具有开关管零电流开通、二极管无反向恢复、开关频率恒定、控制简单、成本低等优点,适用于中低功率场合。但在工频周期内占空比恒定,尤其在输入电压较高时,输入电流谐波含量较大、功率因数(power factor,PF)相对较低。分析三相单管Boost PFC变换器的PF值。在此基础上,提出变占空比控制的方法,从而降低输入电流谐波、提高PF值。为了简化电路实现,进一步给出一种拟合占空比的方法。与定占空比控制相比,所提方法还具有输出电压纹波小和效率高等优点。完成一台3kW的原理样机,进行实验验证,实验结果验证了理论分析和参数设计的正确性。     

基于PSpice的单相功率因数校正电路的行为建模与仿真

介绍了带输入前馈的平均电流模式控制单相功率因数校正(PFC)变换器的工作原理。利用PSpice模拟行为建模功能和Boost主电路开关电感模型相结合,建立了平均电流模式控制单相PFC电路的仿真模型。通过对开关器件的等效平均,简化了PFC电路的分析与建模,大大缩短了仿真时间。利用仿真模型,可以分析电路的频域及时域特性。最后,利用UC3854芯片搭建了试验电路。试验结果证明了建模方法的正确性。