Fuel cell status, 1994

The high efficiency environmental benefits and other attributes of fuel cells have attracted world-wide attention to the technology. Approximately 250 phosphoric acid fuel cell (PAFC) power units, 35 molten carbonate fuel cell (MCFC) stacks, and 12 solid oxide fuel cell (SOFC) modules have been or are being operated. Total capacity installed or operating is close to 45 MW. Fuel cell development has progressed to where complete power plants have reached nearly 16,000 operating hours and this continues to increase. Developers in the U.S. and Japan have embarked on extensive government and private programs to commercialize the technology in those countries and abroad. By mid-1994, the U.S. sold and shipped to other countries at least 33 PAFC 200 kW plants, 20 675 kW PAFC stacks, two SOFC 25 kW modules, and one MCFC system. Additional units have been produced for the domestic market. There is intense interest in Japan where there are very stringent environmental regulations and fuel prices are high. The fuel cell can respond with its combined attributes of low emissions and relative high efficiency. In Europe, the environmental cleanliness of fuel cell power units holds the promise of preserving the quality of life, motivating support and development of the technology. Canada and Australia have spawned important development programs. Interest continues to increase in other parts of the world. The author reviews the 1994 status and outlines the future development trends in this area     

Jets Downstream of Collisionless Shocks

Space Science Reviews - Particles are accelerated to very high, non-thermal energies in solar and space plasma environments. While energy spectra of accelerated electrons often exhibit a power law,...     

Conception of spacecraft centralized power supply

A reliable power supply for spacecraft is one of the central problems determining the future development of space technology. The traditional solution to this problem implies having an autonomous power plant on board each spacecraft. The most widely used are power plants with solar cells. However, there exists an alternative power supply concept of using a centralized power supply system (CPSS) and power transmission to the user satellites by laser or microwave beams. Use of a CPSS has a number of advantages. In particular, it allows the spacecraft to increase power supply level and service life as well as to decrease the spacecraft mass and cost. However, it sets new physical and technical problems associated with long distance power transmission and requires some changes in spacecraft structure and concepts. The feasibility study of CPSS development and use has to rely on existing or firmly forecastable technologies. An attempt of such an analysis has been done by a group of scientists at Moscow State Aviation Institute during 1994-1996. The very first results have already been published. This paper discusses new results obtained lately regarding a space based CPSS     

Low cost X-band power amplifier MMIC

A family of X-band MMIC power amplifiers using a low cost GaAs pHEMT process is reported. The stepper-based volume 0.5 micron and 0.25 micron GaAs pHEMT processes utilize 4 inter-level metallisation and four dielectric layers for high frequency performance whilst maintaining the economies of scale of 150mm (6") diameter substrates. The fabricated GaAs X-Band PA MMICs exhibit SW to low NY output power under pulsed conditions; 16dB of power gain and power added efficiencies approaching 40%. Excellent repeatability and high yields over a number of wafers have been demonstrated. The design and GaAs process approach taken here with DUV stepper and 150 mm wafer diameter will lead to a significant cost reduction for high performance power amplifier MMICs up to 30GHz.     

Silent energy source for tactical applications

Power source requirements for the Soldier System, which includes all items/equipment worn, consumed, or carried by the soldier in the field for his or her individual use, are discussed. The use of fuel cells, which offer silence and high efficiency, is considered. It is concluded that the proton exchange membrane (PEM) fuel cell coupled with a good hydrogen source offers a very attractive power source for the Soldier System and for other portable requirements needing power in the range of 50 to 500 W     

一种新型航空静止变流器的研究

 提出了一种新型的航空静止变流器方案, 采用分布式电能变换技术, 系统由规格统一、种类有限的印刷线路板构成, 没有高压功率器件, 可以克服目前静止变流器技术能量集中变换和结构复杂等缺点。变流器由4 个推挽正激变换器和4 级级联逆变器组成。分析了系统的工作原理和控制方案。研制的原理样机验证了该静止变流器具有效率高、输出波形质量好、可靠性高、工程实现简便等特点。     

Ultra-lightweight space power from hybrid thin-film solar cells

The development of hybrid inorganic/organic thin-film solar cells on flexible, lightweight, space-qualified, durable substrates provides an attractive solution for space power generation with high mass specific power (W/kg). The high-volume, low-cost fabrication potential of organic cells will allow for square miles of solar cell production at one-tenth the cost of conventional inorganic materials. Plastic solar cells take a minimum of storage space and can be inflated or unrolled for deployment. We explore a cross-section of NASA in-house and sponsored research efforts that aim to provide new hybrid technologies that include both inorganic and polymer materials as active and substrate materials. For NASA applications, any solar cell or array technology must not only meet weight and AMO efficiency goals, but also must be durable enough to survive launch and space environments. Also, balance of system technologies must be developed to take advantage of ultra-lightweight solar arrays in power generation systems.     

芯片级光钟技术综述

芯片级光钟是一种基于热原子中光频跃迁的新型光钟,近年来随着光子集成技术、激光技术和微机电技术的发展,该类光钟可以实现较小的体积和较高的精度,有望广泛应用于对体积、质量、功耗和精度敏感的各种国防装备中.介绍了国内外芯片级光钟技术的进展情况,阐述了芯片级光钟的相关技术,包括基于双光子跃迁的光频标技术、微制造气室技术和微腔光频梳技术等,分析了影响频率稳定度和准确度的主要因素,最后对芯片级光钟面临的机遇和挑战进行了简要的展望.     

基于MATLAB某型飞机航空直流供电保护研究

在机载直流供电系统保护中,广泛使用的保护装置有熔断器（保险丝）和热断路器（双金属自动开关）,其原因是它们结构简单,且满足航空输配电保护的要求。但是它们本身具有诸多不可克服的缺点,例如熔断器缺乏较集中的过载保护特性且特性不稳定,影响到过载保护的可靠性、熔断时有因过热而爆炸的可能性、部分熔断器因安装位置导致不能目视检查熔断情况及熔断器熔断后在飞行时更新难于操作等等。鉴于这些问题,在过流大、易短路的供电主干线路中使用高可靠性、高稳定性、操作简便、自动化程度高的保护装置对提高飞机供电系统可靠性具有重要意义。提出了某型飞机供电保护方案,在MATLAB平台上实现了模拟仿真,结果表明能够有效地解决线路的短路、过载等故障。     

航空用燃料电池及混合电推进系统发展综述

随着世界范围内碳减排需求的日益增长及长航时飞机的发展需要,高效率的燃料电池航空电推进系统逐渐受到重视,氢能航空的理念被人们所熟知。可使用碳氢燃料的高温燃料电池还可与燃气涡轮组成混合动力系统,发电效率进一步提高至70%。本文首先回顾了燃料电池及燃料电池涡轮混合系统在航空能源、动力系统方向应用概况;接着,概述了几种突破现有涡轮发动机技术瓶颈的新概念混合电推进系统,如发电与推进一体化燃料电池涡轮混合动力系统和无涡轮燃料电池混合推进系统;基于此,本文分析了限制燃料电池混合系统实际应用的关键技术难题,主要体现在混合动力系统功重比较低、大分子碳氢燃料重整技术未突破两方面。     

Global avionics in the future

The following topics are discussed: new batteries for old airplanes; new charge controls for lengthening battery life; fast methods for batteries charging; AC conductance measurement based battery testing; pulse power; bipolar lead-acid batteries vs supercapacitors; Ni electrode cells for spacecraft; worn-out battery disposal; recycling technology; vehicle batteries cost; high energy content batteries; and energy storage for electric utilities     

New architectures for space power systems

Electric power generation and conditioning have experienced revolutionary development over the past two decades. Furthermore, new materials such as high energy magnets and high temperature superconductors are either available or on the horizon. Our work is based on the premise that new technologies are an important driver of new power system concepts and architectures. This observation is borne out by the historical evolution of power systems both in terrestrial and aerospace applications. This paper introduces new approaches to designing space power systems by using several new technologies. Two new architectures are introduced: the current source current intensive system and the articulate system. Basic characteristics of these systems have been investigated. Some aspects of the articulate system architecture, as discussed in this paper can be implemented in the short term. Flexible AC transmission systems which are now undergoing rapid development and implementation, can be regarded as a subset of the family of control methodologies which constitute the realm of articulate systems     

Aircraft Power System Harmonics Involving Single-Phase PFC Converters

AC-DC converters with active power factor correction (PFC) are replacing uncontrolled diode rectification circuits on commercial jet airplanes in order to meet harmonic distortion limits imposed by new airborne electrical system power quality standards. The high line frequency of airborne AC power systems presents a major challenge for the design of PFC converters capable of meeting these standards. This paper investigates a new source of harmonic current distortion and the resulting system power quality problems related to dynamic interactions between PFC converters and the AC source. Experimental results are first presented to demonstrate the existence of such interactions and their effects on system power quality. Analytical and numerical simulation results are then presented to explain why such dynamic interactions can lead to significantly increased harmonic current distortion in steady state operation. Elimination of undesirable system interactions through proper damping of the PFC converter input filter is also presented and its effectiveness experimentally validated.     

Bipolar nickel-metal hydride batteries for aerospace applications

Electro Energy Inc. (EEI) is developing high power, long life, bipolar nickel-metal hydride batteries for aerospace applications. Bipolar nickel-metal hydride designs allow for high energy and high power designs with a 25 percent reduction in both weight and volume as compared to prismatic and/or cylindrical Ni-MH designs. Utilizing a sealed wafer cell design EEI has demonstrated a 1.2 kW/kg power capability. Prototype designs have achieved 70 Wh/kg. Designs studies show 80 Wh/kg are achievable with EEI's state-of-the-art technology. The sealed wafer cell is the building block for EEI's high power and high voltage bipolar batteries making the assembly easy and significantly lower in cost. Satellite and aircraft batteries are being developed which provide high power and long life. Sealed cells now show excellent rate capability and life. Cells tested in a low earth orbit (LEO) cycle have reached 9000 cycles and continue on test. High power, bipolar battery designs are ideal in applications where using conventional aerospace battery technology would require excessive capacity; weight and volume, thereby reducing usable payload on the vehicle     

银膜的原子氧剥蚀效应及其防护的试验研究

 空间太阳电池板作为空间飞行器电源系统的重要组成部分,它的正常工作对飞行器的运行起着非常重要的作用,而作为互连片的银材料,可能会与空间环境中的原子氧发生反应,生成不导电的氧化物,从而影响空间太阳电池板的有效寿命。本文在原子氧效应地面模拟试验设备中,对银以及镀有不同防护层的银膜进行了原子氧效应地面模拟试验研究,对试验前后试样的外观、质量进行了比较,获得了银在设备中的反应特点,同时对不同防护镀层的有效性进行了验证,为银互连片在空间太阳电池板上的应用及其防护提供了设计依据。     

Radioisotope powered AMTEC systems

Alkali Metal Thermal to Electric Converter (AMTEC) systems are being developed for high performance spacecraft power systems, including small, General Purpose Heat Source (GPHS) powered systems. Several design concepts have been evaluated for the power range from 75 W to 1 kW. The specific power for these concepts has been found to be as high as 18-20 W/kg and 22 kW/m³. The projected area, including radiators, has been as low as 0.4 m²/kW. AMTEC power systems are extremely attractive, relative to other current and projected power systems, because AMTEC offers high power density, low projected area, and low volume. Two AMTEC cell design types have been identified. A single-tube cell is already under development and a multi-tube cell design, to provide additional power system gains, has undergone proof-of-principle testing. Solar powered AMTEC (SAMTEC) systems are also being developed, and numerous terrestrial applications have been identified for which the same basic AMTEC cells being developed for radioisotope systems are also suitable     

民用客机电磁散射特性的研究

利用数值方法对民用客机的电磁散射问题进行了研究,相比各种高频方法,应用矩量法(MOM:Moment Method)可以获得精确的数值结果。本文建立了一种幂级数形式的混合域基函数矩量法的通用公式,该混合基函数基于四边形剖分模型,对三维矢量有效地实现了降维处理,并可用来模拟民用客机的探测的散射特性。     

矢通量分裂-TVD杂交新格式及其应用

在贴体曲线坐标系中,本文提出了一个高分辨率的新格式,它是Steger-Warming的矢通量分裂与Harten的TVD(Total Variation Diminishing)格式的杂交,用于计算跨音速定常流动和捕获激波。典型的跨音速内流和叶栅流的算例表明:在60×15网格下捕获的激波过渡区不超过两个网格,证明其分辨率较高;分析激波附近的数值结果,没出现“低亏、过跳”、伪振荡现象;与实验结果的比较表明,对定常流在无人为附加耗散项的条件下它能给出较高质量无数值波动的激波流场解。     

Voltage-based maximum power point tracking control of PV system

Photovoltaic (PV) generators exhibit nonlinear v-i characteristics and maximum power (MP) points that vary with solar insulation. An intermediate converter can therefore increase efficiency by matching the PV system to the load and by operating the solar cell arrays (SCAs) at their maximum power point. An MP point tracking algorithm is developed using only SCA voltage information thus leading to current sensorless tracking control. The inadequacy of a boost converter for array voltage based MP point control is experimentally verified and an improved converter system is proposed. The proposed converter system results in low ripple content, which improves the array performance and hence a lower value of capacitance is sufficient on the solar array side. Simplified mathematical expressions for a PV source are derived. A signal flow graph is employed for modeling the converter system. Current sensorless peak power tracking effectiveness is demonstrated through simulation results. Experimental results are presented to validate the proposed method