Improved Switching Converter Model Using Discrete and Averaging Techniques

The nonlinear modeling and analysis of dc-dc converters has been done by averaging and discrete-sampling techniques. The averaging technique is simple, but inaccurate, as the modulation frequencies approach the theoretical limit of one-half the switching frequency. The discrete technique is accurate even at high frequencies, but is very complex and cumbersome. An improved model is developed by combining the aforementioned techniques. This new model is easy to implement in circuit and state variable forms and is accurate to the theoretical limit.     

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.     

Magnetic Position and Orientation Tracking System

Three-axis generation and sensing of quasi-static magneticdipole fields provide information sufficient to determine both the position and orientation of the sensor relative to the source. Linear rotation transformations based upon the previous measurements are applied to both the source excitation and sensor output vectors, yielding quantities that are linearly propotional to small changes in the position and orientation. Changes are separated using linear combinations of sensor output vectors, transformed to the desired coordinate frame, and used to update the previous measurements. Practical considerations for a head-tracking application are discussed.     

Some early results of the keV plasma experiment on GEOS-1

Some preliminary new results are presented of the keV plasma experiment on GEOS-1. Electrons and ions have been observed to stream along the magnetic field lines in the dayside magnetosphere from the ionospheric side of the satellite towards the equatorial plane during magnetic storms, with streaming velocities corresponding to a kinetic energy of the order of a keV. The opposite streaming velocity has also been seen, but primarily in the ions only and with a smaller flux ratio for the two opposite directions along the field lines. The transition between the two opposite streaming directions, as seen by the satellite, has been found to occur even in a fraction of a second.In magnetic storm conditions azimuthal asymmetries in ion fluxes corresponding to electric field intensities of several tens of millivolts per meter have been observed.     

DO 28飞行试验数据一致性检验

 本文研究DO28试验机飞行试验数据一致性检验及其误差校正。建立了由非线性运动学方程及内容广泛的校正环节构成的一致性检验模型,解决了大地风场重构、测量信号时间延迟估计、ψ转换及测量控制信号的校正。为DO28参数估计提供了可靠、准确的飞行试验数据。     

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     

Fundamental parameters of the W Serpentis stars

Application of digital cross-correlation spectroscopy to the spectra of the W Serpentis binaries SX Cas and RX Cas has allowed an accurate determination of the orbits and rotations of the (mass-losing) K-subgiant secondary components. The distortion of the primary radial-velocity curves due to the influence of the prominent accretion disks in these systems has been modelled to first order. This enables us to estimate k ₁, and thereby the mass ratio q ≈ 0.30, to within ～ ± 20%. The absolute radii of the secondaries are derived independently from the observed rotations and periods, assuming synchronous rotation. They show that the stars fill their Roche lobes, or at least very nearly so. Rough fits to the available photometry shows both primaries to be unevolved mid-B stars; that in RX Cas appears completely obscured by the disk. Preliminary spectroscopic data for W Ser and W Cru show some promise for similar analyses of these systems.     

Filtering of discontinuous processes arising in marine integratednavigation systems

A refined stochastic model for the errors of the Loran-C radio navigation aid is described, and it is shown how this model can be used to improve the performance of integrated navigation systems. In addition to the usual propagation errors, Loran-C time of arrival measurements are occasionally plagued with sudden intermittent errors of a particular magnitude and caused by receiver cycle selection errors. These result in sudden large jumps in the calculated position solution. The Loran-C error has been modeled as the sum of a diffusion process, representing the normal propagating errors, and a pure jump process of Poisson type, representing the cycle selection errors. A simple integrated navigation system is then described, based on the Loran-C model and the standard dead reckoning (heading and speed) system model. Assuming that the observed process is governed by a linear stochastic difference equation, a recursive linear unbiased minimum variance filter is developed, from which the Loran-C and dead reckoning errors, and hence position and velocity, can be estimated     

Gravitation and celestial mechanics investigations with Galileo

The gravitation and celestial mechanics investigations during the cruise phase and Orbiter phase of the Galileo mission depend on Doppler and ranging measurements generated by the Deep Space Network (DSN) at its three spacecraft tracking sites in California, Australia, and Spain. Other investigations which also rely on DSN data, and which like ours fall under the general discipline of spacecraft radio science, are described in a companion paper by Howard et al. (1992). We group our investigations into four broad categories as follows: (1) the determination of the gravity fields of Jupiter and its four major satellites during the orbital tour, (2) a search for gravitational radiation as evidenced by perturbations to the coherent Doppler link between the spacecraft and Earth, (3) the mathematical modeling, and by implication tests, of general relativistic effects on the Doppler and ranging data during both cruise and orbiter phases, and (4) an improvement in the ephemeris of Jupiter by means of spacecraft ranging during the Orbiter phase. The gravity fields are accessible because of their effects on the spacecraft motion, determined primarily from the Doppler data. For the Galilean satellites we will determine second degree and order gravity harmonics that will yield new information on the central condensation and likely composition of material within these giant satellites (Hubbard and Anderson, 1978). The search for gravitational radiation is being conducted in cruise for periods of 40 days centered around solar opposition. During these times the radio link is least affected by scintillations introduced by solar plasma. Our sensitivity to the amplitude of sinusoidal signals approaches 10^-15 in a band of gravitational frequencies between 10^-4 and 10^-3 Hz, by far the best sensitivity obtained in this band to date. In addition to the primary objectives of our investigations, we discuss two secondary objectives: the determination of a range fix on Venus during the flyby on 10 February, 1990, and the determination of the Earth's mass (GM) from the two Earth gravity assists, EGA1 in December 1990 and EGA2 in December 1992.