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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Ultrafast Modulation and Switching of Quantum-Well Lasers using Terahertz Fields

Modulation and switching of semiconductor lasers are important for laser-based information technology. Typically the speed of modulation and switching is limited by interband processes such as stimulated and spontaneous recombinations which occur on a nanosecond time scale. This is why the diode laser modulation has been restricted to tens of GHz. Modulation at higher speed is highly desirable as the information technology enters into the so-called tera-era. In this paper, we study the possibility of utilizing THz-field-induced plasma heating to modulate quantum-well lasers. This is a timely study since, with the advancement of THz solid-state sources and free-electron lasers, THz physics and related technology is currently coming out of its infancy. The investigation of interplaying THz and optical fields is also of intruiging fundamental interest. First, we introduce theoretical plasma heating results for the quantum-well optical amplifier in the presense of an intense half-cycle THz pulse. The heated carrier distributions are then utilized to calculate the THz-pulse-induced change in refractive index and gain profile. Since the electron-hole-plasma is heated using intraband transitions, we circumvent the usual complications due to an overall change in density, and the nonlinear recovery is governed solely by the carrier-LO-phonon interactions, typically 5 ps for a complete recovery. This procedure implies THz and sub-THz switching and recovery rates, respectively; using either gain modulation or index modulation. Plasma heating via steady-state THz fields is also studied. Finally, numerical simulation of a coupled set of equations to investigate the THz modulation based on a simplified model for quantum-well lasers is presented. Our results show that a semiconductor laser can be modulated at up to 1 THz with little distortion with a THz field amplitude at the order of a few kV/cm. Laser responses to a change in THz frequency will be shown. Constraints, practicalities, and applications will be discussed.

Ning, Cun-Zheng↗
NASA NTRS2008

Update on Development of SiC Multi-Chip Power Modules

Progress has been made in a continuing effort to develop multi-chip power modules (SiC MCPMs). This effort at an earlier stage was reported in 'SiC Multi-Chip Power Modules as Power-System Building Blocks' (LEW-18008-1), NASA Tech Briefs, Vol. 31, No. 2 (February 2007), page 28. The following recapitulation of information from the cited prior article is prerequisite to a meaningful summary of the progress made since then: 1) SiC MCPMs are, more specifically, electronic power-supply modules containing multiple silicon carbide power integrated-circuit chips and silicon-on-insulator (SOI) control integrated-circuit chips. SiC MCPMs are being developed as building blocks of advanced expandable, reconfigurable, fault-tolerant power-supply systems. Exploiting the ability of SiC semiconductor devices to operate at temperatures, breakdown voltages, and current densities significantly greater than those of conventional Si devices, the designs of SiC MCPMs and of systems comprising multiple SiC MCPMs are expected to afford a greater degree of miniaturization through stacking of modules with reduced requirements for heat sinking; 2) The stacked SiC MCPMs in a given system can be electrically connected in series, parallel, or a series/parallel combination to increase the overall power-handling capability of the system. In addition to power connections, the modules have communication connections. The SOI controllers in the modules communicate with each other as nodes of a decentralized control network, in which no single controller exerts overall command of the system. Control functions effected via the network include synchronization of switching of power devices and rapid reconfiguration of power connections to enable the power system to continue to supply power to a load in the event of failure of one of the modules; and, 3) In addition to serving as building blocks of reliable power-supply systems, SiC MCPMs could be augmented with external control circuitry to make them perform additional power-handling functions as needed for specific applications. Because identical SiC MCPM building blocks could be utilized in such a variety of ways, the cost and difficulty of designing new, highly reliable power systems would be reduced considerably. This concludes the information from the cited prior article. The main activity since the previously reported stage of development was the design, fabrication, and testing a 120- VDC-to-28-VDC modular power-converter system composed of eight SiC MCPMs in a 4 (parallel)-by-2 (series) matrix configuration, with normally-off controllable power switches. The SiC MCPM power modules include closed-loop control subsystems and are capable of operating at high power density or high temperature. The system was tested under various configurations, load conditions, load-transient conditions, and failure-recovery conditions. Planned future work includes refinement of the demonstrated modular system concept and development of a new converter hardware topology that would enable sharing of currents without the need for communication among modules. Toward these ends, it is also planned to develop a new converter control algorithm that would provide for improved sharing of current and power under all conditions, and to implement advanced packaging concepts that would enable operation at higher power density.

Lostetter, Alexander↗
NASA NTRS2009

Polarimetric Imaging using Two Photoelastic Modulators

A method of polarimetric imaging, now undergoing development, involves the use of two photoelastic modulators in series, driven at equal amplitude but at different frequencies. The net effect on a beam of light is to cause (1) the direction of its polarization to rotate at the average of two excitation frequencies and (2) the amplitude of its polarization to be modulated at the beat frequency (the difference between the two excitation frequencies). The resulting modulated optical light beam is made to pass through a polarizing filter and is detected at the beat frequency, which can be chosen to equal the frame rate of an electronic camera or the rate of sampling the outputs of photodetectors in an array. The method was conceived to satisfy a need to perform highly accurate polarimetric imaging, without cross-talk between polarization channels, at frame rates of the order of tens of hertz. The use of electro-optical modulators is necessitated by a need to obtain accuracy greater than that attainable by use of static polarizing filters over separate fixed detectors. For imaging, photoelastic modulators are preferable to such other electrio-optical modulators as Kerr cells and Pockels cells in that photoelastic modulators operate at lower voltages, have greater angular acceptances, and are easier to use. Prior to the conception of the present method, polarimetric imaging at frame rates of tens of hertz using photoelastic modulators was not possible because the resonance frequencies of photoelastic modulators usually lie in the range from about 20 to about 100 kHz.

Wang, Yu↗
NASA NTRS2007

Electro-Optical Modulator Bias Control Using Bipolar Pulses

An improved method has been devised for controlling the DC bias applied to an electro-optical crystal that is part of a Mach-Zehnder modulator that generates low-duty-cycle optical pulses for a pulse-position modulation (PPM) optical data-communication system. In such a system, it is desirable to minimize the transmission of light during the intervals between pulses, and for this purpose, it is necessary to maximize the extinction ratio of the modulator (the ratio between the power transmitted during an "on" period and the power transmitted during an "off" period). The present method is related to prior dither error feedback methods, but unlike in those methods, there is no need for an auxiliary modulation subsystem to generate a dithering signal. Instead, as described below, dither is effected through alternation of the polarity of the modulation signal. The upper part of Figure 1 schematically depicts a Mach-Zehnder modulator. The signal applied to the electro-optical crystal consists of a radio-frequency modulating pulse signal, VRF, superimposed on a DC bias Vbias. Maximum extinction occurs during the off (VRF = 0) period if Vbias is set at a value that makes the two optical paths differ by an odd integer multiple of a half wavelength so that the beams traveling along the two paths interfere destructively at the output beam splitter. Assuming that the modulating pulse signal VRF has a rectangular waveform, maximum transmission occurs during the "on" period if the amplitude of VRF is set to a value, V , that shifts the length of the affected optical path by a half wavelength so that now the two beams interfere constructively at the output beam splitter. The modulating pulse signal is AC-coupled from an amplifier to the electro-optical crystal. Sometimes, two successive pulses occur so close in time that the operating point of the amplifier drifts, one result being that there is not enough time for the signal level to return to ground between pulses. Also, the difference between the optical-path lengths can drift with changes in temperature and other spurious effects. The effects of both types of drift are suppressed in the present method, in which one takes advantage of the fact that when Vbias is set at the value for maximum extinction, equal-magnitude positive and negative pulses applied to the electro-optical crystal produce equal output light pulses.

Farr, William↗
DOE OSTI2018

Hybrid memory module bridge network and buffers

Systems, apparatuses, and methods for implementing a hybrid memory module bridge network and buffers are disclosed. A system includes one or more host processors and multiple memory modules. Each memory module includes a relatively low pin count, high-bandwidth serial link to one or more other memory modules to perform inter-memory data transfers without consuming host-memory bandwidth. In one embodiment, a first memory module acts as a cache and a second memory module acts as the main memory for the system. The traffic between the host and the first memory module utilizes a first interface, and the cache traffic between the first and second memory modules utilizes a second interface. Cache line fill and writeback transfers between the first and second memory modules occur in parallel with timing-critical cache demand accesses from the host, in a latency-tolerant and buffered manner, without interfering with the cache demand accesses.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

A Coordinated Compensation Strategy for Module-Mismatch of CHB-PV Systems Based on Improved LS-PWM and Reactive Power Injection

Here, the cascaded H-bridge (CHB) converter has become a promising candidate topology for utility-scale photovoltaic systems thanks to merits like modular structure, distributed maximum power point tracking (MPPT), and direct distribution grid access without medium-voltage transformers, etc. However, module-mismatches arising from non-ideal elements like partial shading and parameter variations pose a technical challenge for such systems. If not dealt with properly, module-mismatches can lead to adverse effects like unbalanced dc-link voltages of the modules, distortion of grid current, reduced power generation, etc. Conventional methods, such as reactive power compensation and level-shifted pulse-width modulation (LS-PWM) based compensation, can alleviate this issue, but their performances are still limited by the allowable modulation range of power converters. In this paper, a compensation strategy combining reactive power compensation with a novel modulation method is proposed to extend the operating range in terms of module mismatch. Experimental results on a 2.4kW/208V single-phase setup are presented and have demonstrated that the proposed method can not only ride through a larger range of module-mismatches but also improve solar power utilization and system efficiency owing to reduced switching events, non-compromised MPPT, and less required reactive power.

42 ENGINEERING↗
DOE OSTI2025

Field‐Relevant Degradation Mechanisms in Metal Halide Perovskite Modules

Field testing, failure analysis, and understanding of degradation mechanisms are essential to advancing metal halide perovskite (MHP) photovoltaic (PV) technology toward commercialization. Here, we present performance data from up to 1 year of outdoor testing of MHP modules in Golden, Colorado. The module encapsulation architecture and encapsulant materials have a significant impact on module reliability, with modules containing a polyolefin elastomer (POE) in addition to a desiccated polyisobutylene (PIB) edge seal outlasting modules with only a PIB edge seal or PIB blanket. Nondestructive and destructive characterization of the field-tested modules points to module scribes and interfaces as areas of potential mechanical weakness and chemical migration, resulting in shunt pathways and increased series resistance. Finally, indoor accelerated stress testing with light and elevated temperatures is performed, demonstrating failure with similar scribe degradation signatures as compared to the field-tested modules. In conclusion, under both outdoor testing and light and elevated temperature conditions, electrochemical corrosion between the copper electrode and the mobile iodine ions appeared dominant, with a significant progression at the scribes that is speculated to result from an interplay between the initial laser damage and joule heating from enhanced ion diffusion under bias.

14 SOLAR ENERGY↗
DOE OSTI2020

Validation of Advanced Photovoltaic Module Materials and Processes by Combined-Accelerated Stress Testing (C-AST)

Tessolar module technology was developed to allow the incorporation of 5 incremental module material innovations. Combined, these innovations may improve the efficiency and durability of the standard silicon cell module. The innovations evaluated are: electrically conductive adhesive (ECA) replacing soldering of tabbing ribbons, light-capturing ribbon (LCR), silicone encapsulant, 2 mm front glass with backsheet, and a polymer-composite module frame. Tessolar-constructed individually encapsulated cells incorporating the material innovations are used to assemble 60-cell modules. 2 x 2 cell mini-modules of the same materials were produced for combined-accelerated stress testing (C-AST). C-AST results demonstrate that the 2 x 2 cell mini-module of Tessolar construction out-performed mini-modules using both ECA with EVA and standard solder with EVA constructions in power production over 108 cycles of testing.

14 SOLAR ENERGY↗
DOE OSTI2021

Reliable Power Rating of Perovskite PV Modules

As the perovskite technology is ramping up into commercialization, reliable and accurate power rating of large-size perovskite modules becomes a prominent aspect for its future deployment in the PV market. It is known that the performance calibration of perovskite PV devices is very challenging due to its complex dynamic response during a conventional current-voltage (IV) measurement. PV researchers have previously proposed several steady-state performance calibration methods to reliably extract PV efficiencies, but mostly focus on small area research-type cells. In this paper, we emphasize the importance of reliable performance calibration on large-size perovskite modules. Extending the NREL Cell and Module Performance (CMP) group's steady-state performance calibration protocol (i.e., Asymptotic P MAX Scan) for perovskite cells to modules, we justify the necessity of reporting steady-state efficiencies for perovskite cells and discuss the challenges of applying this protocol to modules. We also present our protocol for Maximum Power Point Tracking (MPPT), which is a technique often used for performance calibration of perovskite cells and modules, and show a comparison between MPPT and Asymptotic P MAX . Using MPPT we demonstrate the interplay between metastability and degradation in perovskite modules, and emphasize the necessity to develop preconditioning protocols for stabilizing these devices. Our aim is to promote development of consensus protocols for performance calibration of perovskite modules, and to advance their credible power ratings, which will be beneficial to the growth of perovskite technology in the PV market.

perovskite↗
DOE OSTI2024

State-of-the-Art Medium- and High-Voltage Silicon Carbide Power Modules, Challenges and Mitigation Techniques: A Review

Silicon carbide (SiC) power modules have been demonstrated potential for improving power density and efficiency for low-voltage power electronics systems. This has resulted in a paradigm shift toward development of medium-voltage and high-voltage (MV/HV) SiC power modules to revolutionize the future power grid and transportation systems. However, designing MV/HV SiC power modules involves significant design challenges due to higher blocking voltage and exacerbation of side effects due to high switching dv/dt and di/dt of SiC devices-concerns that may not be as critical as in low-voltage module development. This article reviews the development of state-of-the-art MV/HV SiC power modules, ranging from 3.3 kV to 40 kV, from both industry and academia. First, a discussion on SiC modules based on voltage level is presented. This is followed by a discussion of challenges associated with designing and testing MV/HV modules- including parasitic controls, electromagnetic interference (EMI), partial discharge, and thermal management-and the corresponding mitigation approaches from various perspectives. We conclude with a summary of major findings and future directions for the development of MV/HV modules.

EMI↗
DOE OSTI2021

A Double-side Cooled SiC MOSFET Power Module with Sintered-silver Interposers: I. Design, Simulation, Fabrication, and Performance Characterization

Planar, double-side cooled power modules are emerging in electric-drive inverters because of their low profile, better heat extraction, and lower package parasitic inductances. However, there is still concern about their reliability due to the rigid interconnection between the device chips and two substrates of the power module. In this paper, a porous interposer made of low-temperature sintered silver is introduced to reduce the thermo-mechanical stresses in the module. A double-side cooled half-bridge module consisting of two 1200 V, 149 A SiC MOSFETs was designed, fabricated, and characterized. By using the sintered-Ag instead of solid copper interposers, our simulation results showed that at a total power loss of 200 W, the thermo-mechanical stress at the most vulnerable interfaces (interposer-attach layer) was reduced by 42 % and in the SiC MOSFET by 50 % with a trade-off of only 3.6 % increase in junction temperature. The sintered-Ag interposers were readily fabricated into desired dimensions without post-machining and did not require any surface finishing for die-bonding and substrate interconnection by silver sintering. Here, the porous interposers were also deformable under a low force or pressure, which helped to accommodate chip thickness and/or substrate-to-substrate gap variations in the planar module structure, thus simplifying module fabrication. Experimental results on the electrical performance of the fabricated SiC modules validated the success of using the porous silver interposers for fabricating planar, double-side cooled power modules.

42 ENGINEERING↗
DOE OSTI2018

Two-Layer Anti-Reflection Coatings with Optimized Sub-Bandgap Reflection for Solar Modules

The efficiency of a crystalline silicon solar module decreases as its operating temperature rises. Module cooling is possible via selective reflection of sub-bandgap photons so that they are not parasitically absorbed. Selecting from a library of common dielectrics, we numerically optimize the design of two-layer mirrors at the outer glass surface of a crystalline Si solar cell module. The mirrors are designed to maximize the annual energy yield of a module by both reflecting light below the bandgap and enhancing the transmission of light above the bandgap. Combined ray-tracing and finite element simulations determine the power output and temperature of the module over time. Since any two-layer mirror would replace a conventional single-layer glass anti-reflection coating on the module glass, we study the ability of a two-layer structure to improve on a single-layer coating. The best two-layer designs improve the annual energy yield over a module with a glass anti-reflection coating and reduce the module operating temperature.

14 SOLAR ENERGY↗
DOE OSTI2023

Analyzing photovoltaic module mechanics using composite plate theories and finite element solutions

Deflection and stress calculated from an experimentally validated, high-fidelity finite element model (FEM) of a photovoltaic module experiencing mechanical load was compared to results from a simplified FEM treating the module laminate as a homogenized composite using a rule of mixtures approach, and further compared to analytical calculations treating the module as a Kirchoff-Love flat plate. The goal of this study was to determine the error incurred by analyzing module mechanics with varying levels of simplification, since resolving the aspect ratios of a module is computationally expensive. Homogenized FEMs were found to underpredict peak deflection under a 1.0 kPa load by between 13 and 19% for lower and upper bound application of the rule of mixtures. However, module shape was captured, implying that a useful replication of a resolved model could be achieved with a reduced, calibrated material stiffness. Homogenized stress results captured glass layer tensile stress components to within 46 to 52% at a sample location of interest, though agreement was poor through the remainder of the laminate due to the lack of material resolution. For plate theory, deflection was overpredicted by 45 to 67% for upper and lower bound homogenizations, and frame-adjacent module shapes were not adequately replicated. Stress results mirrored FEM trends but magnitudes were not well correlated to resolved model values. These results support the use of homogenized laminate models for module shape derivation, though resolved models remain necessary for stress analyses. The accuracy of plate theory was found to be inadequate for most applications.

14 SOLAR ENERGY↗
NASA NTRSDate not supplied

Design and Analysis of Convolutional Neural Network for RF Signal Modulation Classification for In-Orbit Deployment

To effectively transmit data to and from satellites requires a complex and robust RF communication system. Commonly, several different types of signal modulations may be required to maximize satellite efficiency depending on a variety of unexpected channel impairments. We propose a neural network algorithm capable of learning these RF signal modulations using a supervised learning technique designed for low power, high-efficiency in-orbit deployment. The work presented demonstrates a convolutional neural network (CNN) capable of learning and recognizing a set of modulation schemes commonly used to transmit RF information. We are capable of recognizing the modulation scheme from the I and Q data channels directly, with no preprocessing or data conversion required other than breaking the incoming signal into a set of uniform normalized samples. We perform a network design and size analysis, showing that reasonably high accuracy can be obtained using networks with a relatively low number of trainable parameters. Given that a user of a system such as this may wish to receive a signal using a modulation scheme that the network has not previously learned, we demonstrate that transfer learning can learn new modulation schemes by retraining only the fully connected layers in the CNN. Thus, this type of network would excel in outer space deployment using high-efficiency transfer learning hardware. Modulation recognition can be performed through rapid feedforward computation, and the CNN training process is significantly simplified when learning new modulations is required.

CNN↗
DOE OSTI2021

Reliable Power Rating of Perovskite PV Modules: Preprint

As the perovskite technology is ramping up into commercialization, reliable and accurate power rating of large-size perovskite modules becomes a prominent aspect for its future deployment in the PV market. It is known that the performance calibration of perovskite PV devices is very challenging due to its complex dynamic response during a conventional current-voltage (IV) measurement. PV researchers have previously proposed several steady-state performance calibration methods to reliably extract PV efficiencies, but mostly focus on small area research-type cells. In this paper, we emphasize the importance of reliable performance calibration on large-size perovskite modules. Extending the NREL Cell and Module Performance (CMP) group’s steady-state performance calibration protocol (i.e., Asymptotic PMAX Scan) for perovskite cells to modules, we justify the necessity of reporting steady-state efficiencies for perovskite cells and discuss the challenges of applying this protocol to modules. We also present our protocol for Maximum Power Point Tracking (MPPT), which is a technique often used for performance calibration of perovskite cells and modules, and show a comparison between MPPT and Asymptotic PMAX. Using MPPT we demonstrate the interplay between metastability and degradation in perovskite modules, and emphasize the necessity to develop preconditioning protocols for stabilizing these devices. Our aim is to promote development of consensus protocols for performance calibration of perovskite modules, and to advance their credible power ratings, which will be beneficial to the growth of perovskite technology in the PV market.

41 EE - Solar Energy Technologies Office (EE-4S)↗
DOE OSTI2022

Short-Lived Modules Need to be Efficient, Lightweight, and Circular for the Energy Transition

Deployment projections for decarbonizing the grid predict 1.75 TW of PV is needed in the United States by 2050. This entails a cumulative demand of 97 million metric tonnes of virgin materials for c-Si modules. These material needs are extraction and energy intensive, making them a key target for improving PV sustainability. Emerging PV technologies, such as perovskites, are targeting 15-year modules, high efficiencies, and circular designs. Previous analysis found that by just modifying the life expectancy to 15 years (keeping target c-Si efficiencies and BOM), an additional 1.4 TW of replacement modules are required to maintain capacity, increasing virgin material demand by 1.75x unless >95% closed-loop recycling is maintained. This study examines the effect of achieving higher efficiencies with thin-film designs and a 15-year expectancy. Higher efficiencies and thin film designs can decrease deployment and material demands, making the level of circularity more attainable. If BOM mass is reduced by 50%, closed-loop recycling rates need to be >80% to reduce virgin material demands compared to a 35-yr c-Si module. If module efficiencies are 30%, closed-loop recycling rates can be reduced to 65%. This efficiency increase also reflects that 1500 million fewer modules can be deployed, however, this is still 2000 million more modules than a 35-year module needs to deploy to achieve energy transition targets, and no PV technology is closed-loop recycled for all component materials.

circular economy↗
DOE OSTI2022

Photovoltaic Module R&D Considerations for Soiling Mitigation

Photovoltaic (PV) modules work best in the sunniest environments. Unfortunately, often the sunniest places also have substantial amounts of airborne "dust" that deposits on the front surface of the modules and blocks the sunlight; reducing energy output. In fact, natural soiling has reduced the energy output of PV systems since the technology was first used, and viable mitigation strategies have remained elusive ever since. With the ever-increasing deployments around the world, especially in dusty environments, soiling is becoming a billion-dollar problem, worldwide. While substantial work has been done to examine and resolve some of the issues with PV soiling, often mitigation comes down to physically cleaning the modules. However, a more systematic evaluation of the different module properties correlations to soiling mitigation needs to be done. In many instances, the causal connections between module properties and soiling are simply not known. This lack of knowledge results in a substantial increase in time and effort to evaluate and qualify appropriate soiling mitigation protocols based on site specific issues and the intrinsic module properties that are typically not optimized for mitigating soiling in a given environment. Thus, module property protocols and/or standards are needed to more quickly help identify appropriate module and site-specific mitigation.

mitagation↗
DOE OSTI2023

Thermal behaviors of ethylene vinyl acetate encapsulants in fielded silicon photovoltaic modules

Aging of silicon photovoltaic (PV) module packaging is one of the greatest limiters of PV module service lifetimes. Module characterization typically focuses on power degradation metrics, which do not convey the complexities of often simultaneous degradation mechanisms. In this work, PV modules with pristine references and known fielding histories were investigated by non-destructive and destructive methods. Modules from Canadian Solar, Mission Solar, and Hanwha Q-Cells were fielded for up to three years; select modules were removed from fielding each year for coring to allow for characterization of the encapsulant. Modules are commonly encapsulated with two protective layers of partially-crystalline ethylene vinyl acetate (EVA) polymer that must undergo a crosslinking reaction to achieve desired properties. The extent of crystallinity of the encapsulants as studied by differential scanning calorimetry showed differences between manufacturers and over time. Some encapsulants showed different magnitudes of crystal sizes which changed after fielding; encapsulants with the monodisperse crystal sizes did not change with fielding. This is due to differences in thermal history. In conclusion, these results have implications for stress development during module aging, since EVA crystal melting and crosslinking reactions can result in encapsulant density changes.

36 MATERIALS SCIENCE↗