SEARCH · Engineering Papers
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Circuit provides forced commutation during starting. Forced commutation circuit diverts current from inverter SCR's and turns SCR's off during commutation intervals. Silicon controlled rectifier in circuit unnecessary when switch S10 replaced by high-current, high-voltage transistor. At present, high-current, low-voltage device must suffice.
The current state of the technology in flywheel storage systems and ancillary components, the technology in light of future requirements, and technology development needs to rectify these shortfalls were identified. Technology efforts conducted in Europe and in the United States were reviewed. Results of developments in composite material rotors, magnetic suspension systems, motor/generators and electronics, and system dynamics and control were presented. The technology issues for the various disciplines and technology enhancement scenarios are discussed. A summary of the workshop, and conclusions and recommendations are presented.
A high voltage power supply is formed by three discrete circuits energized by a battery to provide a plurality of concurrent output signals floating at a high output voltage on the order of several tens of kilovolts. In the first two circuits, the regulator stages are pulse width modulated and include adjustable ressistances for varying the duty cycles of pulse trains provided to corresponding oscillator stages while the third regulator stage includes an adjustable resistance for varying the amplitude of a steady signal provided to a third oscillator stage. In the first circuit, the oscillator, formed by a constant current drive network and a tuned resonant network included a step up transformer, is coupled to a second step up transformer which, in turn, supplies an amplified sinusoidal signal to a parallel pair of complementary poled rectifying, voltage multiplier stages to generate the high output voltage.
The positive intrinsic negative (PIN) diode switch which is designed to protect the receiver from burnout or damage on transmission and channel the echo signal to the receiver on reception is outlined. The receiver must be protected firmly. A schematic diagram of a transformer rectifier (TR-ATR) switch for the Urbana Radar is shown. The T/R switch consists of a half wavelength coaxial cavity with tuning condenser and PIN diodes. Two UM4300 PIN diodes were mounted between the inner and outer conductor. The dc biasing voltage required for the PIN diodes is supplied by a control circuit. On transmission, the PIN diodes are forward biased to about 0.5 amperes. On reception, about 10 volts reverse voltage is applied to the diodes, which produces an initial reverse current to speed the recovery time. The T/R switch characteristics are estimated and the result of testing at different peak transmitter powers from 410 kW to 1500 kW is shown.
The results of evaluation of power semiconductor devices for electric hybrid vehicle ac drive applications are summarized. Three types of power devices are evaluated in the effort: high power bipolar or Darlington transistors, power MOSFETs, and asymmetric silicon control rectifiers (ASCR). The Bipolar transistors, including discrete device and Darlington devices, range from 100 A to 400 A and from 400 V to 900 V. These devices are currently used as key switching elements inverters for ac motor drive applications. Power MOSFETs, on the other hand, are much smaller in current rating. For the 400 V device, the current rating is limited to 25 A. For the main drive of an electric vehicle, device paralleling is normally needed to achieve practical power level. For other electric vehicle (EV) related applications such as battery charger circuit, however, MOSFET is advantageous to other devices because of drive circuit simplicity and high frequency capability. Asymmetrical SCR is basically a SCR device and needs commutation circuit for turn off. However, the device poses several advantages, i.e., low conduction drop and low cost.
The use of more than one remote sensing technique is particularly important for Earth Science applications because of the compositional and textural information derivable from the images. The ability to simultaneously analyze images acquired by different sensors requires coregistration of the multisensor image data sets. In order to insure pixel to pixel registration in areas of high relief, images must be rectified to eliminate topographic distortions. Coregistered images can be analyzed using a variety of multidimensional techniques and the acquired knowledge of topographic effects in the images can be used in photogeologic interpretations.
Circuit maintains arc length on irregularly shaped workpieces. Length of plasma arc continuously adjusted by control circuit to maintain commanded value. After pilot arc is established, contactor closed and transfers arc to workpiece. Control circuit then half-wave rectifies ac arc voltage to produce dc control signal proportional to arc length. Circuit added to plasma arc welding machines with few wiring changes. Welds made with circuit cleaner and require less rework than welds made without it. Beads smooth and free of inclusions.
Input current shaping techniques for ac-to-dc converters were investigated. Input frequencies much higher than normal, up to 20 kHz were emphasized. Several methods of shaping the input current waveform in ac-to-dc converters were reviewed. The simplest method is the LC filter following the rectifier. The next simplest method is the resistor emulation approach in which the inductor size is determined by the converter switching frequency and not by the line input frequency. Other methods require complicated switch drive algorithms to construct the input current waveshape. For a high-frequency line input, on the order of 20 kHz, the simple LC cannot be discarded so peremptorily, since the inductor size can be compared with that for the resistor emulation method. In fact, since a dc regulator will normally be required after the filter anyway, the total component count is almost the same as for the resistor emulation method, in which the filter is effectively incorporated into the regulator.
Several studies have pointed out that a number of significant differences exist in circulation fields derived from the various Level IIIb analyses. For example, differences in the strength of the January Hadley cell between the GFDL and ECMWF analyses are as large as 35 percent, and there are some locations over the Northern Hemisphere where the 200 mb zonal wind in January differs by 10 m/s between these two analyses. Calculations of the global energy cycle based on the GFDL and ECMWF analyses are significantly different as well. In addition, the uncertain quality of some of the FGGE IIIb moisture and vertical motion fields raises doubts about whether new insights into the role of these fields in the general circulation will be gained from the FGGE data. Overall, therefore, a sense of disappointment emerges that the FGGE analyses have thus far failed to live up to the expectation that they would yield more definitive general circulation statistics. The shortcomings in the Level IIIb analyses need to be rectified before full confidence can be placed in results pertaining to the general circulation that are based on such modern data assimilation approaches.
The bearing development program is summarized for a 25-kWe power conversion subsystem (PCS) consisting of an organic Rankine-cycle engine, and permanent magnetic alternator (PMA) and rectifier to be used in a 100-kWe point-focusing distributed receiver solar power plant. The engine and alternator were hermetically sealed and used toluene as the working fluid. The turbine, alternator, and feed pump (TAP) were mounted on a single shaft operating at speeds up to 60,000 rev/min. Net thermal-to-electric efficiencies in the range of 21 to 23% were demonstrated at the maximum working fluid temperature of 400 C (750 F). A chronological summary of the bearing development program is presented. The primary causes of bearing wear problems were traced to a combination of rotordynamic instability and electrodynamic discharge across the bearing surfaces caused by recirculating currents from the PMA. These problems were resolved by implementing an externally supplied, flooded-bearing lubrication system and by electrically insulating all bearings from the TAP housing. This program resulted in the successful development of a stable, high-speed, toluene-lubricated five-pad tilting-pad journal bearing and Rayleigh step thrust bearing system capable of operating at all inclinations between horizontal and vertical.
A single phase, 440 VRMS, 20 kHz power distribution system with a regulated sinusoidal wave form is discussed. A single phase power system minimizes the wiring, sensing, and control complexities required in a multi-sourced redundantly distributed power system. The single phase addresses only the distribution link; mulitphase lower frequency inputs and outputs accommodation techniques are described. While the 440 V operating potential was initially selected for aircraft operating below 50,000 ft, this potential also appears suitable for space power systems. This voltage choice recognizes a reasonable upper limit for semiconductor ratings, yet will direct synthesis of 220 V, 3 power. A 20 kHz operating frequency was selected to be above the range of audibility, minimize the weight of reactive components, yet allow the construction of single power stages of 25 to 30 kW. The regulated sinusoidal distribution system has several advantages. With a regulated voltage, most ac/dc conversions involve rather simple transformer rectifier applications. A sinusoidal distribution system, when used in conjunction with zero crossing switching, represents a minimal source of EMI. The present state of 20 kHz power technology includes computer controls of voltage and/or frequency, low inductance cable, current limiting circuit protection, bi-directional power flow, and motor/generator operating using standard induction machines. A status update and description of each of these items and their significance is presented.
The quantitative use of remote sensing satellite images in many applications requires that the geometric distortion inherent in these images be corrected, or rectified, to a desired map projection. The most widely used technique relies on ground control points to empirically determine a mathematical coordinate transformation to correct the geometry. In this paper, using the method of least squares, expressions for the accuracy of the geometric transformation and of the rectification of the satellite image to a map projection are derived. Explicit relations between the global accuracy of the transformation and the number, location, and local accuracy of the ground control points are obtained. The results are applied to the correction of a Landsat MSS image.
A method is described of determining an equivalent circuit for solar cells which have degraded as a result of the formation of a rectifying Schottky barrier at the back contact. An excellent fit of experimental data has been achieved using SCEPTRE with an equivalent circuit derived from the shape of the measured current voltage characteristics. One key parameter of the Schottky barrier diode, the reverse saturation current, can be used to determine the barrier potential. The barrier potential increases as the cell is stressed with 0.5 volts being a typical experimentally determined value for a degraded cell.
Twelve-hour temperature difference (thermal inertia) maps generated by rectifying and registering ascending (day) passes and descending (night) passes of the NOAA-7 Advanced Very High Resolution Radiometer (AVHRR) are compared to vegetation index maps generated from the visible and near IR data from the day pass of that satellite. There appears to be significant and unique information concerning surface characteristics in the temperature difference data on the 1-km scale of the AVHRR. A scatter diagram is provided which shows the pattern of day-night temperature difference compared to vegetation index for irrigated agriculture, dry rangeland, lakes, wet areas and burned rangeland. A detailed description of the techniques employed to provide the day-night temperature maps is provided.
Preliminary experimental results are reported for a diode-pumped Nd:YAG laser employing a tightly focused end-pump geometry. The resonator configuration is planoconcave, with the pumped end of the Nd:YAG rod being coated for high reflection at 1.06 microns. This geometry rectifies nearly all the inefficiencies plaguing side-pumped schemes. This laser is further considered as a candidate for optical communication over the deep space channel.
Twelve hour temperature difference (thermal inertia) maps generated by rectifying and registering ascending (day) passes and descending (night) passes of the NOAA-7 Advanced Very High Resolution Radiometer (AVHRR) are compared to vegetation index maps generated from the visible and near IR data from the day pass of that satellite. There appears to be significant and unique information concerning surface characteristics in the temperature difference data on the 1 km scale of the AVHRR. A scatter diagram is provided which shows the pattern of day-night temperature difference compared to vegetation index for irrigated agriculture, dry rangeland, lakes, wet areas and burned rangeland. A detailed description of the techniques employed to provide the day-night temperature maps is provided.
Attention is given to the orbital accuracy of the Mars Observer (MO) spacecraft throughout its 687 days of mapping (scheduled to commence in 1991). The MO's short period and near circular orbit necessitate a multiorbit analysis in which the spacecraft's motion is strongly perturbed by the local and global gravity field of Mars. This analysis attests to the feasibility of achieving an orbital position accuracy at the level of 2-3 km within the data interval. It is found that Very Long Baseline Interferometric data can rectify a situation in which the position accuracy degrades significantly.
The work is this reporting period was concentrated on electronically calibrating the bolometer detectors. The calibration is necessary for two reasons: first, the power delivered to the rectifying circuit must be known in order to choose a diode with the appropriate barrier height, and second, the power captured by the antenna must be measured if the efficiency of the rectenna is to be divided into antenna efficiency and rectification efficiency. The millimeter wave region operation of the bolometers was simulated with a VHF (10 to 90 MHz) test signal. These detectors are accurate to within roughly 10%. The typical responsivity of the bolometers is 10 volts/watt and the NEP at 20 Hz is 5 times 10 to the minus 9th power W(Hz)-1/2.