Search NASA⌕ Search

SEARCH · Search NASA

Results for “DC function”

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.

At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Effects of 12-Crown-4 ether on the ionic conductivity and electrode kinetics of electrolytes in polyethylene oxide

Results are described of investigations of the electrical and electrochemical properties of thin films of polyethylene oxide (PEO) electrolytes with and without 12-Crown-4 ether (12Cr4) as a function of temperature and in the frequency regime 100 kHz-0.1 Hz. These measurements were made for LiCF3SO3, LiBF4, and LiClO4 salts. At a given temperature, the bulk conductivity, sigma, (S/cm), for a particular salt, depends on the 12Cr4 concentration with sigma reaching a maximum at about 3 mM 12Cr4. Of the three salts studied, the sigma is the highest for PEO/LiBF4 with 3 mM 12Cr4. The ac and dc measurements yield a lower charge transfer resistance for 12Cr4-incorporated samples than for samples without. Plating/stripping of Li occurs at a potential closer to Li(+)/Li for 12Cr4 samples than those without. The conductivities of a thin (about 100 microns) and a thick (400 microns) films are similar.

Nagasubramanian, G.↗
NASA NTRS2014

Electrical Characterization of 4H-SiC JFET Wafer: DC Parameter Variations for Extreme Temperature IC Design

This work reports DC electrical characterization of a 76 mm diameter 4H-SiC JFET test wafer fabricated as part of NASA's on-going efforts to realize medium-scale ICs with prolonged and stable circuit operation at temperatures as high as 500 degC. In particular, these measurements provide quantitative parameter ranges for use in JFET IC design and simulation. Larger than expected parameter variations were observed both as a function of position across the wafer as well as a function of ambient testing temperature from 23 degC to 500 degC.

Microelectronics↗
DOE OSTI2019

Evidence of long-range ferromagnetic order and spin frustration effects in the double perovskite La 2 CoMnO 6

We present a comprehensive study on the magnetic structure, dynamics, and phase evolution in the single phase double perovskite La 2 CoMnO 6 . The mixed valence state due to oxygen deficiency is verified by x-ray photoelectron spectroscopy and confirms a double ferromagnetic transition observed in dc magnetization. Neutron diffraction reveals that the magnetic structure is dominated by long-range ferromagnetic ordering, which is further corroborated by a critical exponents analysis of the paramagnetic to ferromagnetic phase transition. An analysis of the magnetization dynamics by means of linear and nonlinear ac magnetic susceptibilities marks the presence of two distinct cluster-glass-like states that emerge at low temperatures. The isothermal entropy change as a function of temperature and magnetic field (H) is exploited to investigate the mechanism of stabilization of the magnetic phases across the H – T phase diagram. In the regime of the phase diagram where thermal energy is sufficiently low, regions of competing interactions due to local disorder become stabilized and display glasslike dynamics. The freezing mechanism of clusters is illustrated using a unique probe of transverse susceptibility that isolates the effects of the local anisotropy of the spin clusters. Here, the results are summarized in a H – T phase diagram of La 2 CoMnO 6 from these data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2015

Real-Time On-Board Airborne Demonstration of High-Speed On-Board Data Processing for Science Instruments (HOPS)

The project called High-Speed On-Board Data Processing for Science Instruments (HOPS) has been funded by NASA Earth Science Technology Office (ESTO) Advanced Information Systems Technology (AIST) program since April, 2012. The HOPS team recently completed two flight campaigns during the summer of 2014 on two different aircrafts with two different science instruments. The first flight campaign was in July, 2014 based at NASA Langley Research Center (LaRC) in Hampton, VA on the NASA's HU-25 aircraft. The science instrument that flew with HOPS was Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) CarbonHawk Experiment Simulator (ACES) funded by NASA's Instrument Incubator Program (IIP). The second campaign was in August, 2014 based at NASA Armstrong Flight Research Center (AFRC) in Palmdale, CA on the NASA's DC-8 aircraft. HOPS flew with the Multifunctional Fiber Laser Lidar (MFLL) instrument developed by Excelis Inc. The goal of the campaigns was to perform an end-to-end demonstration of the capabilities of the HOPS prototype system (HOPS COTS) while running the most computationally intensive part of the ASCENDS algorithm real-time on-board. The comparison of the two flight campaigns and the results of the functionality tests of the HOPS COTS are presented in this paper.

Beyon, Jeffrey Y.↗
NASA NTRSDate not supplied

Electric Aircraft Propulsion Power System Impedance Modelling Methodology

This paper describes techniques to be used to model megawatt Electrified Aircraft Propulsion (MW EAP) components, specifically motor/generators and inverters, DC-DC converters, and long power leads; resulting in impedance-based models which require no information from the component manufacturers. A custom curve fitting method is described, and an example power supply model is fit using measured impedance data. A method called subscale measurement, employing measurement equipment which has much lower power capability than the MW EAP system under test, is described, simulated, and used to generate an impedance transfer function model of a load. Finally, stability analysis using a Nyquist based approach is performed on the combined supply and load system, using the generated models.

Megawatt electrified aircraft propulsion↗
NASA NTRS1977

Development of a standardized control module for dc-to-dc converters

The electrical performance of a power processor depends on the quality of its control system. Most of the existing control circuits suffer one or more of the following imperfections that tend to restrict their respective utility: (1) inability to perform different modes of duty cycle control; (2) lack of immunity to output filter parameter changes, and (3) lack of capability to provide power component stress limiting on an instantaneous basis. The three lagging aspects of existing control circuits have been used to define the major objectives of the current Standardized Control Module (SCM) Program. Detailed information on the SCM functional block diagram, its universality, and performance features, circuit description, test results, and modeling and analysis efforts are presented.

Yu, Y.↗
DOE OSTI2018

Effect of the Air Flow Velocity on the Characteristics of a Pulsating Discharge Produced by a DC Power Source

Results are presented from experimental studies of a pulsating discharge produced by a dc power source in subsonic and supersonic cold (T = 150–300 K) air flows at static air pressures in the flow of 40–760 Torr. Two modes of pulsating discharge were implemented experimentally: without and with (from one to five) intermediate breakdowns. The discharge pulsation frequency, the maximum attainable voltage across the discharge gap, the length of the plasma channel, and the electric field in the discharge plasma were studied as functions of the air flow velocity and discharge current.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1981

Preliminary design for a Zero Gravity Test Facility (ZGTF). Volume 1: Technical

The functional requirements and best conceptual design of a test facility that simulates weightless operating conditions for a high gain antenna systems (HGAS), that will broadcast to the Tracking Data Relay Satellites were defined. The typical HGAS defined is mounted on a low Earth orbiting satellite, and consists of an antenna with a double gimbal pointing system mounted on a 13 foot long mast. Typically, the gimbals are driven by pulse modulated dc motors or stepper motors. These drivers produce torques on the mast, with jitter that excites the satellite and may cause disturbances to sensitive experiments. The dynamic properties of the antenna support structure (mast), including flexible mode characteristics were defined. The torque profile induced on the spacecraft by motion of the high gain antenna was estimated. Gain and phase margins of the servo control loop of the gimbal drive electronics was also verified.

Germain, A.↗
NASA NTRS2001

Performance of Power Converters at Cryogenic Temperatures

Power converters capable of operation at cryogenic temperatures are anticipated to play an important role in the power system architecture of future NASA deep space missions. Design of such converters to survive cryogenic temperatures will improve the power system performance and reduce development and launch costs. Aerospace power systems are mainly a DC distribution network. Therefore, DC/DC and DC/AC converters provide the outputs needed to different loads at various power levels. Recently, research efforts have been performed at the NASA Glenn Research Center (GRC) to design and evaluate DC/DC converters that are capable of operating at cryogenic temperatures. This paper presents a summary of the research performed to evaluate the low temperature performance of five DC/DC converters. Various parameters were investigated as a function of temperature in the range of 20 to -196 C. Data pertaining to the output voltage regulation and efficiency of the converters is presented and discussed.

Elbuluk, Malik E.↗
DOE OSTI2023

Grid-Forming PV Inverter: Technology Development and Microgrid Applications

Presently, excluding residential backup power applications, grid-forming (GFM) inverters are commercially available for battery energy storage system (BESS) and some PV plus battery systems but not yet for stand-alone PV. This tech update investigates the control design for GFM PV inverter, especially the control required to provide active power reserve and to stabilize the dc link voltage. Subsequently, the use cases of GFM PV plants in utility-level microgrids are discussed considering fully inverter-based microgrids (i.e., with PV and BESS) as well as mixed-source microgrids (i.e., with PV and diesel generator). Scenarios where active power up-reserve from GFM PV plants is beneficial are illustrated. Moreover, requirements and specifications for GFM PV plant, especially for its active power reserve function are developed. In addition, stability of an example utility-level microgrid with two GFM PV plants and a diesel generator is analyzed to shed light on the potential unstable interaction between multiple GFM resources and the countermeasures. This research aims to advance GFM PV technology to offer more flexibility in microgrid design. With GFM PV available, depending on the level of reliability required, cost-benefit analysis, etc., the GFM BESS or diesel generator may be sized smaller while leveraging the full potential of PV generation inside the microgrid.

14 SOLAR ENERGY↗
DOE OSTI2023

Superconductivity and magnetic and transport properties of single-crystalline CaK ( Fe 1 – x Cr x ) 4 As 4

Members of the CaK (Fe 1–x Cr x ) 4 As 4 series have been synthesized by high-temperature solution growth in single-crystalline form and characterized by x-ray diffraction, elemental analysis, and magnetic and transport measurements. The effects of Cr substitution on the superconducting and magnetic ground states of CaKFe 4 As 4 (T c = 35 K) have been studied. These measurements show that the superconducting transition temperature decreases monotonically and is finally suppressed below 1.8 K as x is increased from 0 to 0.038. For x-values greater than 0.012, signatures of a magnetic transition can be detected in magnetic measurements with the associated features in the transport measurements becoming detectable for x ≥ 0.038. The magnetic transition temperature increases in a roughly linear manner as Cr substitution increases. A temperature-composition (T – x) phase diagram is constructed, revealing a half-dome of superconductivity with the magnetic transition temperature, T*, appearing near 22 K for x ~ 0.017 and rising slowly up to 60 K for x ~ 0.077. The T – x phase diagrams for CaK (Fe 1–x T x ) 4 As 4 for T = Cr and Mn are essentially the same despite the nominally different band filling; this is in marked contrast to T = Co and Ni series for which the T – x diagrams scale by a factor of 2, consistent with the different changes in band filling Co and Ni would produce when replacing Fe. Superconductivity of CaK (Fe 1–x Cr x ) 4 As 4 is also studied as a function of magnetic field. A clear change in $H^{'}_{c2}$ (T)/T c , where $H^{'}_{c2}$ (T) is dH c2 (T)/dT, at x ~ 0.012 is observed and probably is related to a change of the Fermi surface due to magnetic order. Further, coherence length and the London penetration depths are also calculated based on H c1 and H c2 data. Both of them as a function of x show changes near x = 0.012, again consistent with Fermi surface changes associated with the magnetic ordering seen for higher x-values.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1979

Data pattern sensitivity in tracking performance of an AC coupled Costas loop with hard-limited in-phase channel

This paper is concerned with data pattern sensitivity in carrier tracking performance of an AC coupled Costas loop with a suppressed BPSK signal. The signal amplitude suppression factor is derived as a function of data 'asymmetry ratio' - the ratio of '1's to the total number of bits in a period of a periodic signal. For an asymmetric pattern, the effect of AC coupling is noticeable whereas there is almost no effect for symmetric square wave. The tracking performance with an asymmetric pattern is worse than that with a symmetric pattern. However, it is also shown that as expected, the tracking performance of a DC coupled loop with an asymmetric pattern is better than that with a symmetric pattern.

Park, Y. H.↗
DOE OSTI2022

Dynamically robust coordinated set point tracking of distributed DERs at point of common coupling

Low-inertia operation of small-scale power systems, such as a microgrid or a portion of a long feeder, requires careful coordination of the controller performance of the constituting devices. This challenge is exacerbated in microgrids serving the functionalities of a conventional synchronous-based generation unit while comprised of smaller DERs operating mainly interfaced through power electronics converters. This paper builds on the idea of set point modulation and proposes a two-level control strategy that aims to achieve superior performance at the point of common coupling (PCC) of microgrids by combining a local control level with a distributed and coordinated level. Several case studies on both AC and DC systems, the CIGRE low-voltage benchmark system as the AC system and a test DC microgrid, validate the performance of the proposed approach. The real-world applicability of the approach is established via a high-fidelity power hardware-in-the-loop (PHIL) experimental setup and an application case study on grid frequency regulation. The proposed approach enables a microgrid to participate in ancillary service provisions where speed and quality of regulation are critical.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2019

Exchange-correlation thermal effects in shocked deuterium: Softening the principal Hugoniot and thermophysical properties

We investigate Exchange–correlation (XC) thermal effect for transport and optical properties of deuterium along the principal Hugoniot. The study is performed using ab initio molecular dynamics simulations within the Mermin–Kohn–Sham density functional theory. XC thermal effects are taken into account via the temperature-dependent Karasiev–Dufty–Trickey (KDT16) generalized gradient approximation functional [Phys. Rev. Lett. 120, 076401 (2018)]. We reveal that XC thermal effects account for the softening of the Hugoniot at pressures P > 250 GPa and improve agreement with recent experimental measurements. Moreover, XC thermal effects lead to the reflectivity increase by about 2% for shock speeds above 20 km/s. Calculated reflectivity for shock speeds up to 50 km/s is in excellent agreement with recent experimental measurements on the OMEGA Laser System. The dc conductivity is increased by about 4% due to XC thermal effects. The system evolution along the Hugoniot crosses the so-called warm-dense-matter regime, and XC thermal effects must be taken into account to accurately predict the thermophysical properties across warm dense conditions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1980

Gigahertz analog modulation and differential delay of GaAlAs lasers - Temperature and current behavior

Gigahertz analog modulation characteristics of broad-area commercially available GaAlAs lasers have been investigated as a function of temperature and current in the vicinity of the upper frequency limit, where the resonance phenomena occur. The optimum temperature for small-signal amplitude modulation was found to be around -15 C for our particular broad-stripe geometry double-heterostructure laser. The Q was found to increase by a factor of 2 and the bandwidth by about 2%; the external quantum efficiency was maximized in this range. The optimum dc current bias was about 2% above the threshold current. Differential delays have also been measured down to a few picosecond accuracy by a unique phase-angle measurement method using a vector voltmeter. Some of the temperature effects observed may be related to mode changes and multimode and superradiance behavior.

Eng, S. T.↗
NASA NTRS1988

Extinction and backscatter measurements of Antarctic PSC's, 1987: Implications for particle and vapor removal

The temperature dependence is examined of optical properties measured in the Antarctic during 1987 at the 70 mb level (near 18 km), a level chosen to correlate the results with in situ measurements made from the NASA-Ames ER-2 aircraft during the 1987 Airborne Antarctic Ozone Experiment (AAOE). The data set consists of extinction measurements by Sam 2 inside the Antarctic polar vortex from May to October 1987; and backscatter measurements by the UV-DIAL (Ultraviolet Differential Absorption Lidar) system aboard the Ames DC-8 aircraft during selected AAOE flights. Observed trends are compared with results from a revised version of Pole and McCormick's model to classify the PSC observations by Type (1 or 2) and infer the temporal behavior of the ambient aerosol and ambient vapor mixing ratios. The sample figures show monthly ensembles of the 70-mb Sam 2 extinction ratio (the ratio of aerosol or PSC extinction to molecule extinction) as a function of NMC temperature at the beginning (June) and (October) of the 1987 Antarctic winter. Both ensembles show two rather distinct clusters of points: one oriented in the near vertical direction which depicts the change with temperature of the ambient aerosol extinction ratio; and a second cluster oriented in the near horizontal direction whose position on the vertical scale marks a change in particle phase (i.e., PSC formation) and whose length (the extinction enhancement related to that of the ambient aerosol) is an indicator of PSC type.

Poole, L. R.↗
DOE OSTI2018

Investigation of structural and magnetic properties of rapidly-solidified iron-silicon alloys at ambient and elevated temperatures

In this work, we investigated the ambient temperature structural properties (~300 K) and the ambient and high temperature (up to 900 K) direct current (DC) magnetic properties of melt-spun Fe-x wt.% Si (x = 3, 5, & 8) alloys. The wheel surface speeds selected for the study were 30 m/s and 40 m/s. The thickness, width, lattice parameter, saturation magnetization (MS), and intrinsic coercivity (HCI) of the melt spun ribbons are presented and compared with data in the literature. The ribbons produced at the lower wheel surface speed (30 m/s) were continuous having relatively uniform edges compared to the ribbons produced at the higher wheel surface speed. The thickness and the width of the melt-spun ribbons ranged between ~15-60 μm and 500-800 μm, respectively. The x-ray diffraction spectra of the melt-spun ribbons indicated the presence of disordered α-phase, irrespective of the composition, and the wheel-surface speed. The lattice parameter decreased gradually as a function of increasing silicon content from ~0.2862 nm (Fe-3 wt.% Si) to ~0.2847 nm (Fe-8 wt.% Si). Wheel surface speed was not shown to have a significant effect on the magnetization, but primarily impacted the ribbon structure. A decreasing trend in the saturation magnetization was observed as a function of increased silicon content. The intrinsic coercivity of the melt-spun alloys ranged between ~50 to 200 A/m. Elevated temperature evaluation of the magnetization in the case of Fe-3 & 5 wt.% Si alloy ribbons was distinctly different from the Fe-8 wt.% Si alloy ribbons. The curves of the as-prepared Fe-3 wt.% Si and Fe-5 wt.% Si alloy ribbons were irreversible while that of Fe-8 wt.% Si was reversible. The MS for any of the combinations of wheel surface speed and composition decreased monotonically with the increase in temperature (from 300 – 900 K). The percentage decrease in MS from 300 K to 900 K for the Fe-3 wt.% Si and Fe-5 wt.% Si alloys was ~19-22 %, while the percentage decrease in the same temperature range for Fe-8 wt.% Si alloy was ~26-30 %. It appears that Fe-3 wt.% Si and Fe-5 wt.% Si alloys ribbons are primarily comprised of the α phase (disordered phase) with any minor constituents being beyond the detection limits of the studies performed, while the Fe-8 wt.% Si alloy ribbons are comprised of disordered and regions of short-range ordering.

Elevated Temperature↗
NASA NTRS2003

A High Efficiency DC Bus Regulator/RPC for Spacecraft Applications

DC bus voltage regulation may be required in future high powered spacecraft due to the length of the busses or because they are not generated at precise voltage levels. In these cases the regulation range is often only a few percent increase or decrease, but conventional DC voltage regulators switch all the power passing through them, and this level of power switched determines the size and losses in the regulator. A recently developed concept used a low power DC-DC converter in series with the bs to raise or lower the bus voltage over a small range. This partial power processing technique combines the small size and power losses of the low power converter with the ability to regulate, (over a small range) a high power bus. The Series Connected Buck Boost Regulator (SCBBR) described herein provides bus regulation with an efficiency of 98%. The circuit also provides bus switching and overcurrent limiting functions of a Remote Power Controller (RPC). This paper described the circuit design and performance of a breadboard SCBBR configured as a bus voltage regulator providing plus of minus 40% voltage regulation range, bus switching, and overload limiting.

Birchenough, Arthur G.↗