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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.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Analysis and Control of a Three-Port Converter with High-Frequency AC Link for Hybrid Unmanned/Autonomous Aerial Vehicles

In this study, a three-port resonant converter with a high-frequency isolation link for hybrid unmanned/autonomous aerial vehicle (UAV/AAV) applications is analyzed. The rectified engine-generator set output supplies the first input ports while the other is connected to a battery energy storage system. Input ports consist of half-bridge high-frequency inverters, whereas output port utilizes a semi-bridgeless active rectifier. This rectifier is formed by replacing rectifier low-side diodes with active switching devices. A phase-shift duty-cycle control is implemented for switching signals to regulate the power share and flow between ports. The proposed control system implemented achieves zero voltage switching (ZVS), reduces switching losses, and minimum current flow optimization ensures regulation in a wide range of output power. Compared to the existing bidirectional pulse width modulation (PWM) converters, the proposed system decreases the number of power conversion stages and provides centralized control without needing communications between the ports. The proposed control technique operating in closed-loop control achieves the power flow between ports under various load conditions. Finally, theoretical analysis demonstrates the proposed converter’s viability and laboratory experimental validations at 500 W full power.

33 ADVANCED PROPULSION SYSTEMS↗
NASA NTRS1979

Switching transients in high-frequency high-power converters using power MOSFET's

The use of MOSFETs in a high-frequency high-power dc-to-dc converter is investigated. Consideration is given to the phenomena associated with the paralleling of MOSFETs and to the effect of stray circuit inductances on the converter circuit performance. Analytical relationships between various time constants during the turning-on and turning-off intervals are derived which provide estimates of plateau and peak levels during these intervals.

Sloane, T. H.↗
NASA NTRS1999

Comparative Wide Temperature Core Loss Characteristics of Two Candidate Ferrites for the NASA/TRW 1500 W PEBB Converter

High frequency core loss and magnetization properties of commercial type MN8CX and PC40, high resistivity, MnZn based, power ferrites are presented over the temperature range of -l50 C to 150 C, at selected values of peak flux density (B (sub p)). Most of the data is at 100 kHz, with some data extended to 200 and 300 kHz for the MN8CX. Plots of the specific Core loss against temperature exhibit the minimal characteristic of such ferrites. These plots show that the MN8CX is optimized for minimum loss at about 25 C, whereas the PC40 is optimized at about 80 C. At the points of minimum loss and for the same B (sub p), the MN8CX has roughly half the losses of the PC40 at the lower flux densities. This loss ratio continues down to cryogenic temperatures. However, above about 80 C the losses are practically equal. The lowest 100 kHz loss recorded, 50 mW/cm3 for the MNGCX at a B (sub p) of 0.1T, equals that of a very low loss, Co based, transverse magnetically annealed, amorphous ribbon material. Except possibly at lower B (sub p) or much higher frequencies, these ferrites are not competitive for low losses over a wide temperature range with certain specialty amorphous materials. Permeability is computed from a linear model, plots against temperature are presented and again compared to the specialty amorphous materials.

Niedra, Janis M.↗
NASA NTRS1973

Eight-channel telephone telemetry system

Portable telemetry system uses conventional telephone link which eliminates mailing or messenger service between physician and analyst. Transmitter is used by physician; receiver is used by analyst. Each unit is inductively coupled to its respective telephone set, transmitter converting EEG into audio frequency and receiver converting this frequency back to EEG.

Smith, R.↗
NASA NTRS1982

A study of the high frequency limitations of series resonant converters

A transformer induced oscillation in series resonant (SR) converters is studied. It may occur in the discontinuous current mode. The source of the oscillation is an unexpected resonant circuit formed by normal resonance components in series with the magnetizing inductance of the output transformers. The methods for achieving cyclic stability are: to use a half bridge SR converter where q0.5. Q should be as close to 1.0 as possible. If 0.5q1.0, the instability will be avoided if psi2/3q-1/3. The second objective was to investigate a power field effect transistor (FET) version of the SR converter capable of operating at frequencies above 100 KHz, to study component stress and losses at various frequencies.

Stuart, T. A.↗
NASA NTRS1995

Simplified Digital Down-Converters

Design of digital frequency down-converters simplified by eliminating need for both high-speed number-controlled oscillators (NCOs) and mixer-multipliers, and implementing functions via multiplication coefficients of finite-impulse-response (FIR) filters. Simplification depends on particular choices of operating frequencies. Simplified designs implemented with commercial FIR integrated circuits.

Sigman, Elliott H.↗
NASA NTRS1988

A versatile power converter for high-frequency link systems

A single-phase HF link appears to be an attractive alternative to the dc link commonly used in power conversion systems. Here, a power converter suitable for one-step conversion of the single-phase HF link voltage to the three-phase LF voltages typically required for interfacing with system sources and loads is proposed. The converter utilizes zero-voltage switching principles to minimize switching losses and an easy-to-implement technique of pulse-density modulation for the control of the amplitude, frequency, and waveshape of the synthesized LF signals. Adaptation of the proposed topology for power conversion to single-phase ac and dc voltage or current outputs is shown to be straightforward. The feasibility of the proposed power circuit and the control technique has been experimentally verified.

Sood, Pradeep K.↗
NASA NTRS1978

Predicting performance of power converters operating with switching frequencies in the vicinity of 100 kHZ

A model describing the turning-on period of a power switching transistor in an energy storage voltage step-up converter is presented. Comparisons between an experimental layout and the circuit model during the turning-on interval demonstrate the ability of the model to closely predict the effects of circuit topology on the performance of the converter. A phenomenon of particular importance that is observed in the experimental circuits and is predicted by the model is the deleterious feedback effect of the parasitic emitter lead inductance on the base current waveform during the turning-on interval.

Bahler, D. D.↗
NASA NTRS2003

Low-Power Radio-Frequency SiGe Analog-to-Digital Converter

A low-power, radio-frequency analog-to-digital converter (RF-ADC) for soil moisture remote sensing was designed and fabricated. The RF-ADC is the fundamental component used in a direct-sampling digital radiometer, which is proposed to minimize the power dissipation and system complexity for synthetic thinned array radiometer. The circuit was implemented using 0.8 micron 35-GHz silicon germanium BiCMOS technology. The total power dissipation was 222 mW.

Thompson, Willie L, II↗
NASA NTRS1987

Constant-frequency, clamped-mode resonant converters

Two novel clamped-mode resonant converters are proposed which operate at a constant frequency while retaining many desired features of conventional series- and parallel-resonant converters. State-plane analysis techniques are used to identify all possible operating modes and define their mode boundaries. Control-to-output characteristics are derived that specify the regions for natural and forced commutation. The predicted operating modes are verified using a prototype circuit.

Tsai, Fu-Sheng↗
NASA NTRS1970

High-frequency wattage-to-voltage converter

Solid state device, which measures electric power over a wide frequency range, multiplies two electrical input signals to produce an output voltage that is proportional to their product. Quarter-square type of electronic analog multiplier is used.

Vrancik, J. E.↗
NASA NTRS1991

The measurement system of pulse modulated carrier frequency stability and timing jitter

The definition of pulse modulated carrier frequency stability and timing jitter as well as the configuration and synchronous acquisition measurement method of its measurement system. Frequency stability of the pulse modulated carrier is measured with a discrimination technique. The pulse modulated carrier under testing is mixed with a reference frequency synthesizer. A delay line is used to convert the frequency fluctuation mixed IF signal to the voltage fluctuation. The system has the capability to make the phase noise measurement of two port devices on a pulsed carrier using a phase bridge. The noise voltage mentioned above is applied to the data acquisition and processing unit by PC to realize stability measurement. The data acquisition is in the form of pulse synchronization so that the measurement system accuracy is increased. The pulse width is more than 0.3 microseconds. The phase fluctuation variance, sigma, is less than 0.017. The time interval measuring system with high resolution is used to make interpulse timing and pulse width jitters automatic measurement. The pulse width is less than 0.2 ns. The resolution is 0.1 ns. The system is successfully applied to radar measurement.

Li Cheng-Fu↗
NASA NTRS1993

Designing Magnetic Components for High Frequency DC-DC Converters

The conversion process in power electronics requires the use of tranformers and inductors, components which frequenly are the heaviest and bulkiest item in the conversion circuits. They also have a significant effect upon the overall performance and efficiency of the system.

Magnetic Core core geometry soft ferrites cores↗
NASA NTRS1979

Development of high reliability, high frequency power conditioning models of converter regulators

High efficiency conversion, regulation, and filtering techniques are discussed for power using high conversion frequencies; i.e., in the order of 1 to 5 MHz for converters having total output power capability in the order of 20 watts and 200 to 500 KHz for converters having total output powers in excess of 200 watts. Work centered on areas of component selection, material selection, optimization of the various types of circuits required, and the selection of materials for and design of magnetic components. These techniques were then applied to the design of two sample converters, one a medium power instrument type converter and the second a high power converter representative of a primary spacecraft converter regulator. The configuration and performance of the two converters is reported and discussed.

Rochussen, A. W.↗
NASA NTRS1989

High power density dc/dc converter: Component selection and design

Further work pertaining to design considerations for the new high power, high frequency dc/dc converters is discussed. The goal of the project is the development of high power, high power density dc/dc converters at power levels in the multi-kilowatt to megawatt range for aerospace applications. The prototype converter is rated for 50 kW at a switching frequency of 50 kHz, with an input voltage of 200 Vdc and an output of 2000 Vdc. The overall power density must be in the vicinity of 0.2 to 0.3 kg/kW.

Divan, Deepakraj M.↗