Nondestructive Characterization of RBSOA of High-Power Bipolar Transistors

Reverse-bias safe operating area (RBSOA) of high-power Darlington transistors is characterized using a 120 A/1000 V nondestructive reverse-bias second breakdown tester designed and fabricated at Virginia Polytechnic Institute and State University. Elaborate RBSOA characteristics are generated with different forward/reverse base drives and collector current levels. The effects of elevated case temperature and second-base drive on RBSOA of four-terminal Darlington devices are also discussed.     

FGH95粉末盘材料热/机械疲劳和等温低周疲劳断裂行为研究

对粉末冶金盘材料 FGH95进行了同相位 ,温度循环为 3 5 0℃到 60 0℃的热 /机械疲劳试验和 60 0℃的等温低周疲劳试验。考察了两种载荷波形下材料的循环应力响应行为和高温疲劳断裂机理以及载荷波形对疲劳寿命的影响。研究结果表明 :同相位热 /机械疲劳寿命比上限温度的等温低周疲劳寿命短。该材料在高温应变疲劳的循环应力响应行为与应变水平的大小以及循环载荷波形有关。试样的微观断口分析显示了在高温应变疲劳试验中同时存在疲劳、蠕变和氧化损伤。在同相位热 /机械疲劳载荷下 ,穿晶 +沿晶断裂为疲劳断裂的主要特征 ;在等温低周疲劳载荷下 ,裂纹主要为穿晶萌生与扩展      

A maximum power transfer battery charger for electric vehicles

A battery charger is described that uses an on-line microcontroller to maximize its output power. This is done by always operating at either the maximum allowable input current or the thermal limit imposed by the charger itself. In this case the thermal limit is determined by the junction temperatures of the two main insulated gate bipolar transistors (IGBTs). Since direct measurement of these temperatures is impractical, they must be calculated by a computer algorithm that uses various on-line measurements. Experimental results for an 8 kW charger indicate a reduction in the bulk charging time of about 26% when used with a set of NiFe batteries.     

ZCS-PWM boost rectifier with high power factor and low conduction losses

A new single-phase high power factor rectifier is proposed, which features regulation by conventional pulsewidth modulation (PWM), soft commutation, and instantaneous average line current control. A new zero-current-switching PWM (ZCS-PWM) auxiliary circuit is configured in the presented ZCS-PWM rectifier to perform ZCS in the switches and zero-voltage-switching (ZVS) in the diodes. Furthermore, soft commutation of the main switch is achieved without additional current stress by the presented ZCS-PWM auxiliary circuit. A significant reduction in the conduction losses is achieved, since the circulating current for the soft switching flows only through the auxiliary circuit and a minimum number of switching devices are involved in the circulating current path and the proposed rectifier uses a single converter instead of the conventional configuration composed of a four-diode front-end rectifier followed by a boost converter. Seven transition states for describing the behavior of the ZCS-PWM rectifier in one switching period are described. The PWM switch model is used to predict the system performance. A prototype rated at 1 kW, operating 60 kHz, with an input ac voltage of 220 V/sub rms/ and an output voltage 400 V/sub dc/ has been implemented in laboratory. An efficiency of 97.2% and power factor near 0.99 has been measured. The analysis and design of the control circuitry are also presented.     

Design Considerations for Differential Low-Level Junction FET Commutators

The many advantages of junction field-effect transistors (FET) in commutation applications have prompted a serious effort to extend the technology without sacrificing performance and, in many areas, to realize an improvement over low-level commutator performance attainable by more conventional electronic means (especially Bright switches), so that these devices may be employed in general application, high-accuracy, low-level commutation. This paper is devoted to a generalization of knowledge recently gained during the development of such equipment, which will aid potential designers and users in their understanding and application of low-level FET commutators. A discussion of device characteristics is offered as the starting point of design. A number of topics are then discussed, including offset drift and scatter, gain drift and scatter, source and amplifier loading, crosstalk, and common-mode rejection. Also, several useful design guidelines, in the form of generalized expressions, are derived or furnished for the reader's use. Finally, in order to lend veracity to the design techniques suggested, the performance data of a low-level FET commutator developed following these techniques are offered for consideration.     

A Pulsewidth-Modulated Dc-to-Dc Converter That Utilizes a Small Number of Components

In general, circuit reliability can be enhanced by either incorporating redundancy or by minimizing a circuits component count. Conventional nonregulating converters generally require two active devices, whereas in regulating converters or switching regulators as many as 10 transistors, either integrated or discrete, is not uncommon. A regulating dc-to-dc converter which provides useful regulation and which can be constructed with either two or three transistors is described.     

Effect of earth?s rotation and range foldover on space-based radar performance

Space-based radar (SBR) by virtue of its motion generates a Doppler frequency component to the clutter return from any point on the Earth as a function of the SBR-Earth geometry. The effect of the rotation of the Earth around its own axis also adds an additional component to this Doppler frequency. The overall effect of the rotation of the Earth on the Doppler turns out to be two correction factors in terms of a crab angle affecting the azimuth angle, and a crab magnitude scaling the Doppler magnitude of the clutter patch. Interestingly, both these quantities depend only on the SBR orbit inclination and its latitude and not on the location of the clutter patch of interest. Further, the crab angle has maximum effect for an SBR on a polar orbit that is above the equator. The crab magnitude, on the other hand, peaks for an SBR on an equatorial orbit. Together with the range foldover phenomenon, their overall effect is to generate Doppler spread/splitting resulting in wider clutter notches that degrade the clutter nulling performance of adaptive processing techniques. A detailed performance analysis and methods to minimize these effects are discussed here     

Flyback Converter Output Voltage Stabilization

The expression of the flyback converter output voltage (output power) is derived as a function of the supply voltage, load resistance, transformer ratios, transistor current gain, and base-circuit resistor value. Switching period and duty cycle are also calculated. A converter circuit is designed having stabilized output voltage, with respect to supply voltage, at constant load. The transistor base current is controlled by the supply voltage, via a nonlinear circuit. This feedforward circuit approximates with logarithmic characteristics the ideal hyperbolic dependence of the transistor base current as a function of the supply voltage. The converter has high performance and low cost. A cheaper circuit variant is presented, in which the high-voltage control transistor was eliminated.     

Biphase Sequence Generation with Low Sidelobe Autocorrelation Function

Since Barker-like sequences could not be found for sequence lengths greater than 13, radar system designers have been searching for biphase sequences with discrimination (ratio of the magnitude of the mainlobe to the magnitude of the peak sidelobe of the autocorrelation function of the sequence) greater than 13. We present new results on biphase Legendre sequences for all prime lengths. The results of the paper are as follows. 1) Two lemmas on the symmetric properties of the Legendre sequences are stated and using these lemmas and simple rules of modulo arithmetic, a method is suggested for generating long sequences which does not require multiplications and divisions. 2) From the properties of autocorrelation function of the cyclically shifted Legendre sequence (LS) for prime lengths, a computationally efficient method is evolved for carrying out systematic search for sequences with discrimination greater than 13. The proposed method reduces the computational load by a factor of approximately 16. Using these techniques, we generated codes up to length 1019. In each case we searched for the code which gives the maximum discrimination for that length.     

Analysis of parallel resonant converter operating above resonance

A high-frequency DC-DC converter using a parallel resonant inverter operating above resonance is analyzed using a state-space approach and a constant current model. Closed-form solutions are obtained under steady-state conditions. The analysis shows that with some changes most equations are of the same form as those corresponding to operations below resonance. The analysis is also used to obtain the design curves and to provide a simple design procedure, which is illustrated by a design example. Experimental results obtained with a prototype MOSFET unit (using metal-oxide-semiconductor field-effect transistors as switches and operating above 90 kHz) are presented to support the theory     

The wells air turbine for wave energy conversion

The wave energy devices currently in operation in the United Kingdom and India and those that are to be built in Europe are based on the principle of the oscillating water-air column. In these devices the pneumatic energy of the oscillating air column is converted to mechanical energy of rotation by a Wells turbine. A monoplane (single plane) Wells turbine can absorb only a certain maximum pneumatic pressure amplitude due to tip speed limitations. For wave energy devices which produce large amplitudes of pneumatic pressure a biplane Wells turbine with or without guide vanes can be used. The prediction methods currently available and parameters controlling the aerodynamic performance of the Wells turbines are reviewed. Some novel techniques to improve the performance of Wells turbine are suggested.     

Cosmic-Ray Modulation in the Heliosphere A Phenomenological Study

The heliospheric cosmic-ray network–Pioneer 10/11, Voyager 1/2, Ulysses and IMP 8 have provided detailed observations of galactic and anomalous cosmic rays over a period of time that now exceeds 25 years and extends to heliocentric distances beyond 65 AU. These data, when compared over consecutive 11 year solar cycles, clearly establishes the existence of a 22-year cosmic ray modulation cycle that is dominated by the 11-year solar activity cycle but is strongly influenced by gradient and curvature drifts in association with the tilt of the heliospheric neutral current sheet as well as the mediation of the enhanced magnetic turbulence above the solar poles. Over successive solar minima these effects manifest themselves in the remarkable differences in the energetic particle time histories, in the magnitude and sign of the radial and latitudinal intensity gradients and in the changes in the energy spectra of anomalous cosmic rays as a function of heliocentric distance.From solar minimum to solar maximum the long term modulation is principally a combination of two solar related phenomena, the cumulative effect of long-lived global merged interaction regions (GMIRs) and gradient and curvature drifts in the interplanetary magnetic field. For the periods when positive ions flow in over the solar poles and out along the heliospheric current sheet, the modulation of ions is dominated by GMIRs. When this flow pattern is reversed it is found that drifts are an important but not dominant factor for cosmic ray modulation with the current sheet related drift effects decreasing with increasing rigidity R, heliolatitude and heliocentric distance. Over a single solar cycle these conclusions are confirmed at 1 AU by comparing the relative modulation of cosmic-ray helium nuclei and electrons.     

Inherent Overload Protection for the Series Resonant Converter

The overload characteristics of the full bridge series resonant power converter are considered. This includes analyses of the two most common control methods presently in use. The first of these uses a current zero crossing detector to synchronize the control signals and is referred to as the ? controller. The second is driven by a voltage controlled oscillator and is referred to as the ? controller. It is shown that the ? controller has certain reliability advantages in that it can be designed with inherent short circuit protection. Experimental results are included for an 86 kHz converter using power metal-oxide-semiconductor field-effect transistors (MOSFETs).     

Safety tests of lithium 9-volt batteries for Navy applications

COTS batteries are relatively inexpensive, readily accessible, and extremely versatile. These attributes allow the military to save time and money during the research and development stages. Of these COTS batteries, a 9-Volt (9 V) lithium/manganese dioxide battery is the subject of this paper. This 9 V battery has the ability to provide a low magnetic signature, which is very important to the Navy for many applications, Also, it is Underwriters Laboratories (UL) listed at the unit level; however, these UL tests cannot be directly related to the safety of these 9 V batteries when they are combined in various series and parallel configurations. Naval Surface Warfare Center (NSWC) Carderock was tasked to rate the safety of several such specialized battery packs. It was found that packs consisting of two 9 V batteries in parallel were relatively safe, experiencing no violent behavior. Battery packs with six 9 Vs in parallel vented and deformed the 9 V batteries, but no smoke or flames were noticed. A battery pack with thirty 9 V batteries, 2 in series with 15 legs, experienced venting, smoke, and flames under certain circumstances, After testing, the six and thirty 9 V packs were required to include the addition of various safety devices     

分布式信任模型在嵌入式Internet中的应用研究

为了充分利用嵌入式设备的联合处理能力,嵌入式设备之间必须进行一系列的合作.信任是人们进行社会交往的基础,人们之间的信任关系在不断地更新和传递.依据这种原理,提出了一种基于社会信任关系的协同工作分布式网络模型.嵌入式Internet系统中的设备在协作过程中,互相之间逐步形成了一种相互信任的关系,这种关系以信任表的形式存在本地端点中,并通过不断地自学习来修改信任表.给出了信任模型的建立过程以及信任参数的更新和传递算法,应用实例表明了模型的有效性.     

Application of the Volterra Series to the Analysis and Design of an Angle Track Loop

A typical function of an angle tracking loop is to keep a radar antenna pointed at a target. The error in pointing is directly related to successful operation of the tracking device; therefore, its behavior is of interest. For a tracker with a general polynomial nonlinearity, an arbitrary initial pointing error, and a bounded deterministic input, a method is developed for finding upper bounds on the magnitude of the tracking error using Volterra series techniques. Convergence regions of the Volterra series are also obtained. Applications of these results are made to a second-order tracking device.     

The Influence of Tilt Angle and Magnetic Field Variations on Cosmic ray Modulation

The maximum inclination of the heliospheric current sheet (the tilt angle) and the magnitude B of the heliospheric magnetic field are often used to characterize cosmic ray (CR) modulation. The relevance of B is likely to be the coupling of the interplanetary diffusion coefficients K to the field magnitude in a relation K∝B ⁻ⁿ. In this paper we study the coupled influence of tilt angle and magnetic field variations on the modulation of cosmic rays at neutron monitor energies for the 1974 mini-cycle and for the onsets of solar cycles 21, 22, and 23. It is suggested that for A>0 polarity epochs, the sensitivity of the CR response to variations in B is partly controlled by the size of the tilt angle, α. The onsets of cycles 21 and 23 exhibit differences, related to phase differences in these parameters. A simple model is used to predict the CR response to variations in B. This revised version was published online in August 2006 with corrections to the Cover Date.     

An efficient active ripple filter for use in DC-DC conversion

When low ripple is required from a switched mode dc-dc converter, dissipative active filters offer an alternative to passive LC and coupled inductor filters. Analytical and experimental results are presented for a simple active ripple filter. The filter employs a pair of current transformers as sensors for feedforward and feedback control and two metal-oxide-semiconductor field-effect transistors (MOSFETs) as cancellation current drivers. Measurements demonstrate good ripple attenuation up to 5 MHz, more than 70 dB being obtained at 100 kHz, the switching frequency of a test converter. The overall efficiency was measured as 95%, with room for further improvement. The filter is suitable for input and output smoothing in dc-dc converters for aerospace and other critical applications     

Behavior of a cycled Ni-Cd battery during pulse discharge

The pulse discharge behavior of a 9-Ah, 6-V nickel-cadmium (Ni-Cd) battery fabricated for the FAST program was studied. The response of the battery voltage to a pulse with a current of 60 A and duration of 10 to 200 ms was measured, along with the capacity remaining at the end of pulse discharge. The maximum drop in voltage at the beginning of the pulse was 505 to 1,049 mV, and battery capacity remained stable     

用矩量法研究直升机高频天线电磁特性的旋翼调制效应

 基于面元模型的矩量法与快速多极子方法结合分析了直升机机载高频通信天线电磁特性的旋翼调制效应。通过三维计算机辅助实体建模技术,建立了一个尺度与真实直升机相当的仿真模型,实现了机体表面网格的自动剖分。应用准静态法和FFT技术,计算分析了旋转桨叶对天线辐射场幅度和频率的调制效应,还分析了桨叶旋转对天线输入导纳和互导纳的影响。计算结果表明,旋转桨叶对直升机机载天线辐射场产生了显著的影响。本方法亦适用于其它类型的直升机和其它具有旋转桨叶的载体上天线电磁特性的分析。