A multioutput LLC-type parallel resonant converter

When an LLC-type parallel resonant converter (LLC-PRC) operates above resonant frequency, the switching transistors can be turned off at zero voltage. Further study reveals that the LLC-PRC possesses the advantage of lower converter voltage gain as compared with the conventional PRC. Based on the analytic results derived, a complete set of design curves from which a systematic design procedure is developed is obtained. Experimental results from a 150-W, 150-kHz, multioutput LLC-type PRC power supply are presented     

AMTEC electrochemical heat-to electricity conversion defies secondlaw

Sacred among the mechanical engineers is the “second law of thermodynamics,” which defines the maximum possible efficiency of an engine that converts thermal energy into mechanical power. The second law value is the difference between the engine's heat-source temperature and its heat-sink temperature, divided by the absolute value of the engine's heat-source temperature. For example, an engine setting on 0° C ice and running on steam from 100°C boiling water is not allowed to have more than 26.8% efficiency. Power-generating violators of the second law efficiency-limit range from horses to fuel cells. They do not burn fuel to generate mechanical or electrical power. The latest second law violator is the alkali-metal thermal-to-electric converter. Its efficiency approaches 25 percent. AMTEC cells and their variations were the topics of 12 papers at the 35^th Intersociety Energy Conversion Engineering Conference (IECEC) in July 2000     

Fuel cell status: 1996

The technology of fuel cells is heating up. A world that, ten years ago, was unaware of the concept can now witness approximately 200 fuel cell units operating in 15 countries. Energy planners and decision makers are becoming aware that, in addition to a continual increase in installations, the reliability of early commercial units is outstanding and the cost is dropping. They have begun to ask whether fuel cells might fit into their future. While the fuel cell concept is simple, determining which type of fuel cell to consider may prove taxing. The multiplicity of fuel cells and their development programs, coupled with the amount of subject material and claims-versus-reality, may seem overwhelming. Fuel cell commercialization activities in North America are the focus of five manufacturers that are developing four types [fuel cells are typed by electrolyte: the 200°C phosphoric acid (PAFC); the 80°C proton exchange membrane (PEM); the 650°C molten carbonate (MCFC); and the 1,000°C solid oxide (SOFC) fuel cells]. Each fuel cell promises the attractive combination of fairly high efficiency and superior environmental performance compared to the presently available fossil-fueled electric generation technologies. As a result, fuel cells are particularly easy to site. There are additional advantages such as: excellent availability; electrical VAR control; quick ramp rate; remote/unattended operation; and redundancy when multiple units are installed. After earlier success in space, fuel cells are being applied to the commercial sector as on-site cogeneration units mostly fueled by natural gas. They are being considered for larger distributed generators (natural gas) and for vehicular power plants (methanol)     

Lithium micro-battery development at the Jet Propulsion Laboratory

Recent successes in the effort to miniaturize spacecraft components using MEMS technology, integrated passive components, and low power electronics have driven the need for very low power, low profile, low mass micro-power sources for micro/nanospacecraft applications. Recent work at JPL has focused upon developing thin film/micro-batteries compatible with temperature sensitive substrates. A process to prepare crystalline LiCoO₂ films with RF sputtering and moderate (<700°C) annealing temperature has been developed. Thin film batteries with cathode films prepared with this process have specific capacities approaching the practical limit for LiCoO₂, with acceptable rate capabilities and discharge voltage profiles. Solid-state micro-scale batteries have also been fabricated with feature sizes on the order of 50 microns     

C/SiC复合材料烧蚀机理和通用计算模型研究

研究了C/SiC复合材料氧化烧蚀机理,发现它们与传统的硅基和碳基材料烧蚀有很大差别。C/SiC的烧蚀取决于氧的分压、表面温度和材料晶态结构及成份,可能出现活性氧化和惰性氧化两种破坏机制。研究了氧化膜的形成和破坏条件,以及氧化膜中氧气的扩散机制,建立了适用于C、Si、SiC和C/SiC(C和SiC可有不同混和比)四种材料烧蚀计算的通用物理数学模型。     

Comparison of half-bridge off-line, ZCS-QRC and ZVS-MRC

The performance of the half-bridge (HB) zero-current-switched (ZCS) quasi-resonant converter (QRC) and zero-voltage-switched (ZVS) multiresonant converter (MRC) is compared with respect to their efficiency, input voltage range, semiconductor stresses, power density, and reliability. The efficiency of the HB ZVS-MRC at a given nominal input is shown to be highly dependent on the range of the input voltage, and it suffers when the converter has to be designed to cover a wide range. However, this is not the case for the HB ZCS-QRC. Experimental versions of the HB ZCS-QRC and HB ZVS-MRC were designed for the input voltage range from 150 to 350 V and a maximum output power of 100 W, under the same constraints, to facilitate their comparison     

Power Conditioning Systems for High-Power, Airborne, Pulsed Applications

The power conditioning portion of the high-power study that was performed for the Air Force Aeropropulsion Laboratory by the State University of New York at Buffalo is summarized. This effort defines the power conditioning system and critical component developments which will be required to interface the airborne 10-MW to 50-MW sources defined under separate study efforts with certain loads. Power conditioning systems are considered for use with magnetohydrodynamic generators and turbine driven alternators, both conventional and superconducting. The critical components required for each of the power conditioning systems are identified and then analyzed. The component analyses include estimations of development efforts necessary and of specific weights and volumes for components. The primary components considered are transformers (for alternator as well as for inverter use), switches, capacitors, and inductors. Weight algorithms are developed for each of the components. Following the component analyses, subsystems such as inverters and rectifier and filter packages are considered. The data for the various components and subsystems are then utilized for a comparison of the power conditioning techniques to be used with the various power sources. The weights and volumes of power conditioning systems for 8-point designs (8 variations of power, voltage, duty cycle, and total run time) are derived.     

C/ SiC 材料在国外空间光学系统上的应用

C/SiC复合材料具有高的比强度、低的热变形敏感度以及在高低温环境下的适应性,这使其成为目前最具前途的空间光学系统应用材料.本文总结了国外一些国家C/SiC的制备方法及其在空间技术上的具体应用.     

A Comparison of Solar-Cell and Battery-Type Power System for Spacecraft

The electrical power systems of orbiting unmanned spacecraft generally consist of energy-conversion devices in combination with energy-storage and conditioning components. The development of efficient pulse-duration modulation regulators suggests configurations smaller, lighter, and cheaper than conventional dissipative voltage regulators. These savings may or may not be realizable, depending upon the system reliability design goal and amount of redundancy required to meet the goal. Three spacecraft electrical power systems, each containing a solar-cell energy converter and using different voltage regulation schemes, are compared for a common mission specification. Each system is made to meet a given reliability goal by a technique that adds redundant components in a manner that minimizes a system design characteristic such as weight. The reliability design goal is kept constant as mission length is increased, permitting system comparison in terms of weight and cost as a function of time.     

Single-Stage Single-Switch Switched-Capacitor Buck/Buck-Boost-Type Converter

A new dc-dc converter featuring a steep step-down of the input voltage is presented. It answers a typical need for on-board aeronautics modern power architectures: power supplies with a large conversion ratio able to deliver an output voltage of 1–1.2 V. The proposed structure is derived from a switched-capacitor circuit integrated with a buck converter; they share the same active switch. The proposed solution removes the electromagnetic interference (EMI) emission due to the large di/dt in the input current of the switched-capacitor power supplies. Compared with a quadratic buck converter, it presents a similar complexity, a smaller reduction in the line voltage at full load (but less conduction losses due to smaller input inductor current and capacitor voltage), lower voltage stresses on the transistor and diodes, lower current stresses in the diodes, and smaller size inductors. A similar structure using a buck-boost converter as the second stage is also presented. The experimental results confirm the theoretical developments.     

超大功率电推进电源处理单元关键技术研究

针对深空探测等空间任务对超大功率(10kW~100kW范围)电推进系统的需求,通过对国内外超大功率电推进技术的调研,提出了一种50kW超大功率霍尔电推进系统电源处理单元（Power Processing Unit,PPU）设计方案,重点对核心的阳极电源关键技术进行研究,提出了四管Buck-Boost变换器和三相LLC谐振变换器级联的设计方案,为我国超大功率PPU的发展提供了技术参考。     

WARLOC: A High-Power Coherent 94 GHz Radar

This paper describes the development of a high-power, coherent radar system at W-band and discusses potential applications of radars with this new capability. Previous radars in this frequency band were limited by available power-amplifier technology to about 500 W of average power; WARLOC radar represents an increase in power, by 20 times, over previous coherent radars at 94 GHz. This performance improvement is possible due to the development of a gyroklystron amplifier specifically for this and future radars in this frequency band. The gyroklystron amplifier tubes deliver 100 kW peak power and 10 kW of average power at a center frequency of approximately 94 GHz. Other novel features of this radar include the use of highly overmoded waveguides and rotary joints for the transmission of power from the final power amplifier (FPA) to the antenna, and a high-power quasi-optical duplexer. The system uses a relatively large 1.8 m diameter (580-wavelength) Cassegrain antenna, which required the development of an antenna with an rms surface accuracy of 0.0025 in, to obtain long-range detection and identification of small objects. Test data show an antenna gain of 62.5 dB, confirming that the needed surface accuracy was achieved. Two mobile shelters house the radar system, permitting relocation to various test sites. WARLOC is presently operational at the Naval Research Laboratory's Chesapeake Bay Detachment facility, Maryland. It is being employed in radar imaging of airborne and surface objects, and in the scientific study of propagation effects and atmospheric physics phenomena.     

Full bridge ZCS PWM converter for high-voltage high-powerapplications

This paper presents a comprehensive study of a full bridge (FB) zero-current switched (ZCS) PWM converter which is suitable for high-voltage and high-power DC application that achieves ZCS for all active switches, and zero-voltage-switched (ZVS) operation for all diodes on the high voltage side. The given converter utilizes component parasitic parameters, particularly for the high-voltage transformer, and employs fixed-frequency phase-shift control to implement soft-switching commutations. Detailed steady state analysis of the converter power stage is presented for the first time and the major features of the converter's power stage are discussed. Small-signal characteristics are also presented and accompanied by a discussion of the controller design and implementation. A design example is also presented based on the steady state analysis and is validated by simulation. Theoretical and simulated results are in good agreement     

纤维表面状态对C/C-SiC复合材料微观组织和相成分的影响

为了研究纤维表面状态对C/C-SiC复合材料微观组织和相成分的影响,将T300碳纤维在氮气氛围中进行不同温度的热处理后,采用液硅熔渗法制备了C/C-SiC复合材料。采用光电子能谱(XPS)对纤维表面成分进行了分析。结果表明:未处理纤维表面具有较高的氧含量,随着热处理温度的升高,纤维表面氧含量逐渐降低,导致纤维表面含氧官能团数目减少。扫描电镜(SEM)观察发现:未处理纤维增强的C/C预制体,孔隙尺寸较大且孔隙率低;而经1 500℃热处理纤维增强的预制体,孔隙尺寸较小但孔隙率高。随后对C/C预制体进行液硅熔渗处理,并对熔渗反应过程分析发现:由未处理纤维增强的预制体,液硅熔渗反应主要受溶解-沉淀和界面限制的扩散反应过程控制,获得的C/C-SiC复合材料中SiC基体相分布规则且含量较低,同时含有较高的残留Si;而经1 500℃热处理纤维增强的预制体,熔渗反应则主要受溶解-沉淀过程控制,获得的C/C-SiC复合材料中SiC基体含量多且分布较均匀,残留Si含量较少。     

3D针刺C/SiC复合材料螺栓的低成本制备及力学性能

以三维针刺碳毡作为预制体,通过化学气相渗透(CVI)工艺,制备了密度约为1.50～1.60 g/cm3的半成品C/SiC复合材料板材,然后采用专用磨具在半成品复合材料板上按照指定的取样方式切割出螺杆与头部毛坯,并分别对螺杆和头部攻丝,将两者装配在一起形成半成品螺栓,对半成品螺栓CVI致密化并在其表面制备SiC抗氧化涂层,制备出低成本的3D针刺C/SiC复合材料螺栓.提出了C/SiC复合材料螺栓力学性能的测试方法,通过自行设计的夹具,对所制备螺栓的力学性能进行了测试表征,并利用扫描电子显微镜(SEM),对C/SiC复合材料螺栓的拉伸断口形貌进行了观测.结果表明,所制备的螺栓具有较好的抗拉和抗剪能力,室温下螺栓的抗拉强度和剪切强度分别为151.7 MPa和85.6 MPa.     

Computer Simulations of Optimum Boost and Buck-Boost Converters

The development of mathematical models suitable for minimum weight boost and buck-boost converter designs are presented. The facility of an augumented Lagrangian (ALAG) multiplier-based nonlinear programming technique is demonstrated for minimum weight design optimizations of boost and buck-boost power converters. ALAG-based computer simulation results for those two minimum weight designs are discussed. Certain important features of ALAG are presented in the framework of a comprehensive design example for boost and buck-boost power converter design optimization. The study provides refreshing design insight of power converters and presents such information as weight and loss profiles of various semiconductor components and magnetics as a function of the switching frequency.     

基于单片机的多点温度采集系统设计

随着单片机技术的迅速兴起与蓬勃发展,其稳定、安全、高效、经济等优点十分突出。为了实现多点温度数据的精确采集,采用了一种基于单片机AT89C52为核心的数据采集系统,该系统具有电路简单、功耗低、抗干扰能力强、可靠性高等优点,能够通过DBW热电阻变送器对热电阻随温度的变化而得到的模拟信号进行采集,并通过A/D转换器对模拟信号进行模数转换;同时实现基本的人机对话功能,包括使用按键设定温度报警阀值,通过LED数码直读显示检测点、温度等功能。其温度测量精度可达到1℃。     

Improved ZCS-PWM commutation cell for IGBTs application

An improved zero-current-switching pulsewidth-modulated (ZCS-PWM) commutation cell is presented, which is suitable for high-power applications using insulated gate bipolar transistors (IGBTs) as the power switches. It provides ZCS operation for active switches and zero-voltage-switching (ZVS) operation for passive switches. Besides operating at constant frequency and reducing commutation losses, the proposed ZCS-PWM switch cell has no additional current stress and conduction loss in the main switch. To demonstrate the feasibility of the proposed ZCS-PWM commutation cell, it was applied to a boost converter. Operating principle, theoretical analysis, design guidelines, and a design example are described and verified by experiment results obtained from a prototype rated 1 kW and operating at 40 kHz. The PWM switch model and state-space averaging approach is also used to estimate and examine the steady-state and dynamic character of ZCS-PWM boost converter system. Finally, the application of the proposed soft-switching technique in the dc-dc nonisolated converters is presented.     

无压浸渗法制备SiCp / Al 电子封装基板及其性能

采用无压浸渗法制备出电子封装用高体积分数SiCp/Al复合材料基板,研究了主要合金元素对浸渗过程的影响和SiC体积分数对复合材料热物理性能的影响.结果表明:合金中Mg元素能促进界面润湿,Si元素能减小有害界面反应的发生;随着SiC体积分数的增加,复合材料的热导率和线胀系数都呈下降趋势,当SiC体积分数为65%左右,热导率下降幅度减缓;当SiC体积分数为68%左右时,线胀系数显著降低.     

C/SiC复合材料的制备及加工技术研究进展

碳纤维增强碳化硅陶瓷基(C/SiC)复合材料由于其强度高、硬度大、耐磨损,被广泛应用于工业、航空航天等领域,然而C/SiC复合材料难以被稳定地去除加工。本文综述C/SiC复合材料的常见制备方式及其材料的性能特点。概述C/SiC复合材料的传统机械加工、超声辅助加工、激光加工等加工方法,分析了各种加工方法的材料去除机理、加工精度、常见缺陷及加工过程中存在的问题。传统的机械加工需进一步优选切削刀具材料;超声辅助加工需探究超声振动的刀具与材料之间的耦合作用机制、振动作用下的材料去除机理;激光加工要进一步研究2.5维及3维C/SiC复合材料的激光加工去除机理。在这些研究的基础上进一步采用复合加工的方法,探寻C/SiC复合材料高效、精密、稳定和无损加工的可能性。