Digitally controlled boost PFC converters operating with large scale load fluctuations

When boost power factor correction （PFC） circuit works with large scale load fluctuations, it is easy to cause a higher total harmonic distortion and a lower power factor because of traditional controllers and inductor cur- rent mode. To solve this problem, this paper proposes a PFC control system, which can operate with load fluctuations up to 1 000 W by using duty cycle feed-forward control theory to achieve smooth switching mode. The duty cycles in the next period of the control system are pre-estimated in the current cycle, which enhances the speeds of AD samplers and switching frequency, and reduces the cost and volume of the equipment to some extent. Introductions of system decoupling and feed-forward of input-voltage greatly improve the system performance. Both theoretical simulation and experimental results prove the advantage of the proposed scheme.     

晶体微粒光致旋转的研究

理论分析了光束具有的自旋角动量传递给晶体并导致其旋转的机理。并以碳酸钙粒子为例从理论上的分析了有效功率,粒子形状和大小,以及粘滞系数对旋转角速度的影响。对实验中如何提高晶体旋转角速度具有一定参考价值。     

LLC谐振式DC/DC变换器的研究与实现

基于基波分析法（ FHA）对LLC谐振变换器进行建模分析,并以此为依据提出一种简化的参数设计方法。该方法根据谐振电路的二端口模型得到归一化工作频率和电压增益的关系,按照规定输入输出的要求确定电压增益后得到谐振工作频率,进而可以得到谐振电路的特性阻抗和谐振腔元件参数。利用Saber软件仿真和硬件实验验证了该方法的有效性,表明所设计的变换器可实现开关管的零电压开通和整流二极管的零电流关断,能够降低开关损耗,提高装置效率。     

TM波的平面波导解法

介质波导具有损耗小和辐射小的特点,广泛应用于光通讯领域。平板波导是一种重要的平面介质波导,其中的TE波和TM波的传输特性,更是为波导器件的设计提供理论支持。本征方程是分析传输特性的重要方程,而TE波较TM波具有相对简单的电磁场连续性边界条件,其本征方程已有详细介绍。从TM波的波动方程出发,推导出三层平板波导TM波的场分布,并根据电磁场的连续性边界条件,逐步推到出它的本征方程。     

光源对于太阳能电池基本特性测量实验影响的研究

本文研究了光源对于太阳能电池基本特性测量实验的影响。分别采用白炽灯和日光灯作为光源，测量了太阳能电池的伏安特性、开路电压、短路电流、最大输出功率、填充因子、光照特性等基本特性。     

La Medusa by Caravaggio: characterisation of the painting technique and evaluation of the state of conservation

The oil painting “La Medusa” executed by Caravaggio at the end of the XVI century on a wooden shield, was investigated by integrated physical–chemical and analytical methodologies in order to obtain scientific data capable of elucidating the state of conservation and the painting technique. Optical (OM) and electronic (SEM-EDS) microscopy, micro-FT-IR spectroscopy, gas chromatography–mass spectrometry (GC–MS) and pyrolysis GC–MS were applied on two microfragments and some organic samples obtained by solvent extraction using the swab cleaning technique. The obtained results indicated that Caravaggio probably reused an old shield as a previous gypsum preparation layer has been detected under the original painting layers. He used white lead, natural earths, verdigris and lead–tin yellow type I mixed with drying oils to paint. The considerable amount of amorphous particles of copper chlorides found in the green pigment verdigris suggests that it could have been produced according to the ancient recipe of verde salsum described by Theophilus. Mordant gilding has been identified on the upper part of the shield that can be related to an abandoned experiment to give the painting a mirror-like reflecting effect. Three different varnishes layers have been detected above the painted surface. The original and restoration varnishes have been identified and they contain a mixture of drying oil, mastic and turpentine and some beeswax. Cleaning tests, performed with different organic solvents, suggest the use of isopropyl alcohol as cleaning agent because it is less efficient in comparison to others solvents; thus it ensures a careful and controlled removal of the varnishes.     

脉幅调制(PAM)逆变器谐波的削减

本文从实用角度出发,在分析了单相逆变器输出矩形脉冲电压的傅氏级数后,推导出与电机交流绕组系数完全相同的谐波削减系数。再根据对谐波削减程度的要求,合理选择组成脉幅调制逆变器的单相逆变器台数和输出矩形脉冲电压宽度缩短角和初相角,从而有效地抑制了输出电压中的谐波分量,简化了滤波电路,设计出一些结构简单,运行可靠,经济实用的脉幅调制(PAM)逆变器。     

基于升频升压五相混合式步进电机驱动器的研究

升频升压驱动方式已广泛应用在混合式步进电机驱动器中,文章介绍了以频压转换芯片LM2097、脉宽控制芯片TL494、调压电路组成的升频升压控制方式,其输出的直流母线电压接步进电机各相的MOSFET功率驱动电路。在驱动器中过压过流保护电路也是必须设计的。     

ELBAS仿真软件在客运专线牵引变压器安装容量确定中的应用

牵引变压器是牵引供电系统的重要设备,其容量确定是牵引供电计算的主要内容。针对沪杭客专,利用ELBAS仿真软件对牵引供电系统进行模拟仿真,根据仿真结果选取合适的安装容量。     

航空铅酸蓄电瓶常用维护术语解析

随着铅酸蓄电瓶在通用航空轻型飞机上的广泛应用,为了保证飞行安全,降低维护成本,各维修单位也越来越重视其日常维护工作,不断完善和规范电瓶的维护程序。正确理解和掌握维护工作中所使用到的常用维护术语,纠正认识上的误区,有助于维护人员能更好地完成电瓶日常维护工作。