Stationary and traveling hot spots in the catalytic combustion of hydrogen in monoliths

In the course of catalytic combustion of hydrogen (1-5% H₂ in air) in monolith reactors, strongly localized stationary and traveling hot spots arise in response to a sudden and persistent rise of gas flow velocity. Such hot spots may occur, e.g. in a catalytic converter following the acceleration of a car or in a catalytic combustor as a result of a load increase. This phenomenon is illustrated by simulations using a two-phase reactor model. The temperature overshoot of the adiabatic limit is typically of the order of the adiabatic temperature rise itself.The following mechanism underlies this behavior. Light fuel is supplied to the catalytic wall by fast diffusion (in the direction perpendicular to flow), while the heat released by reaction is removed from the wall by the slower, mixture-averaged heat conduction. This leads to accumulation of heat at the catalytic surface that eventually saturates at high temperatures. The hot spots may exhibit intricate dynamics, propagating downstream or upstream, or they may remain stationary. The direction of propagation depends on the relative strength of convective downstream and conductive upstream contributions to the overall displacement of reaction fronts. Generally, the hot spot tends to drift downstream at low flow velocities, remain stationary at intermediate flow velocities, and drift upstream at high flow velocities.     

无源软开关电路拓扑的研究

提出一个研究无源软开关电路的新技术方法;其特征是对基本的单管隔离型PWM DC/DC变换器进行类比分析,由此直接导出可行的缓冲能量再生复位电路.该新方法能使DC/DC PWM硬开关变换器转变为软开关变换器.以新型Boost无源软开关变换器为例,进行了电路理论分析与中功率样机的实验测试;结果表明此新变换器具有较宽的软开关工作范围、较低的电应力、较小的缓冲元件量值等特点.由此认为,这种研究方法推导简单、物理意义清晰,还能深入地研究无源软开关的新电路拓扑.     

The experimental research of a digital sampling signal converter

The sensitivity and rise time of a transient characteristic of a digital sampling signal converter are experimentally researched. The sampling converter is built at a clocked tunnel-diode comparator.     

A systematic review of robust control strategies in DC microgrids

This paper provides a comprehensive and systematic review of robust control strategies in DC microgrids. Microgrids gain worldwide attention in decades regarding its effective and feasible integration of distributed generations (DGs). Getting rid of frequency synchronization and reactive power problem, the DC microgrid is superior to its ac counterparts in stability, flexibility and complexity. The recent efforts were mainly directed toward developing the feasibility of implementing DC microgrids on kinds of specific application scenarios. DC microgrids design-related aspects such as the system architecture and topology, voltage levels, operation and control framework, stability analysis method, and protection challenge have been studied in a deep degree. In this paper, operation and control framework in both grid-connected (grid-forming) mode and islanding (grid-following) mode will be focused, to provide the guideline where we currently stand on the migration path from the overwhelming fully AC microgrids to a more flexible DC microgrids. Besides, the impediments against stability and effectiveness of DC microgrids and representatively proposed solutions will be discussed.     

超导储能装置用GTO PWM电流型变流器模块方阵

本文提出一种ＧＴＯＰＷＭ电流型变流器模块的连接方法。Ｎ×Ｎ个变流器模块组成一个方阵,通过适当地设计调制信号和载波信号的相位,该方阵能够实现特大功率变换,且网侧谐波得到抑制。由于ＰＷＭ主要用来实现功率的调节,因此ＧＴＯ仅需工作在较低的开关频率。本方案只需用Ｎ个移相变压器,就能获得６Ｎ２脉波变流器的特性。通过仿真,将变流器模块方阵与经典变流器模块直接并列结构作了比较。     

三相电压型低谐波PWM整流器主电路参数间的关系

三相电压型低谐波PWM整流器主电路的多个参数之间的关系较为复杂，在仿真和实验中，若给出的参数不合理，则变换器不能正常工作，从而给仿真和实验带来一定困难。文章在考虑了输入电阻的情况下，给出了功率因数角为任意值时，主电路各参数和控制参数间的稳态关系及一些参数的约束关系。上述关系对于分析和设计被研究电路具有很好的指导意义，文中的公式通过了仿真验证。     

Buck调节器大信号稳定性分析方法探讨

本文以Buck调节器为例，对如何分析其出现的典型非线性大信号振荡现象作了一些有益的探索，以对电路的稳定性分析及工作机理有更好的理解。     

Microprocessor controlled three-way catalyst efficiency monitoring system

The present paper describes a new design for a microcontrolled three-way catalyst efficiency monitoring system. The system is based on the Motorola 68HC11e2 microprocessor and utilizes the differential signal from a pair of thermocouples installed at the catalyst outlet and inlet sections. This signal is processed in real time using an appropriate statistical algorithm and the corresponding results are compared to experimentally determined limiting values to assess the current state of the catalyst efficiency during driving conditions. The result of this comparison is presented on an LCD display as an A, B, C, or FAIL catalyst condition signal. The system can be readily installed and can operate on new and used cars provided that the type of catalyst used has been experimentally tested to provide the necessary limiting values that characterize its relative levels of efficiency. It can also be reprogrammed and calibrated via a RS232C serial interface.     

基于LabVIEW的浑浊度数字化测试仪设计

本文将虚拟仪器技术与光频转换器件TSL230B相结合,设计新型浑浊度数字化测试仪.阐述该系统的工作原理、硬件构成及软件设计方案;实现浑浊度的自动在线测量.实验结果表明,该仪器数据处理能力强,图形化显示直观,保存与打印结果方便,测量的重复性好,精确度高.     

基于PCI总线的高速大容量数据采集卡

介绍了一种基于PCI总线的高速大容量数据采集卡的设计原理与实现。该采集卡由预处理电路、A／D转换器、同步动态随机存储器(SDRAM)、高频时钟发生器、集成于FPGA芯片的PCI接口控制器和SDRAM控制器组成。它通过PCI总线接口与计算机连接，可完成400MHz／s实时数据采集、512MB实时数据存储。