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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Resonance-enhanced optical nonlinearity in the Weyl semimetal TaAs

The second-order conductivity of a material, σ (2) , relating current to the square of electric field, is nonzero only when inversion symmetry is broken, unlike the conventional linear conductivity. Second-order nonlinear optical responses are thus powerful tools in basic research as probes of symmetry breaking; they are also central to optical technology as the basis for generating photocurrents and frequency doubling. The recent surge of interest in Weyl semimetals with acentric crystal structures has led to the discovery of a host of σ (2) -related phenomena in this class of materials, such as polarization-selective conversion of light to dc current (photogalvanic effects) and the observation of giant second-harmonic generation (SHG) efficiency in TaAs at photon energy 1.5 eV. Here, we present measurements of the SHG spectrum of TaAs, revealing that the response at 1.5 eV corresponds to the high-energy tail of a resonance at 0.7 eV, at which point the second harmonic conductivity is approximately 200 times larger than seen in the standard candle nonlinear crystal, GaAs. This remarkably large SHG response provokes the question of ultimate limits on σ (2) , which we address by a new theorem relating frequency-integrated nonlinear response functions to the third cumulant (or "skewness") of the polarization distribution function in the ground state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Orientation-Dependent Distortion of Lamellae in a Block Copolymer Electrolyte under DC Polarization

Lithium-salt-doped block copolymers have the potential to serve as solid electrolytes in rechargeable batteries with lithium metal anodes. In this work, we use small-angle X-ray scattering (SAXS) to study the structure of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) doped with bis-(trifluoromethylsulfonyl)amine lithium salt (LiTFSI) during direct current (dc) polarization experiments in lithiu-lithium symmetric cells. The block copolymer studied is nearly symmetric in composition, has a total molecular weight of 39 kg mol -1 , and exhibits a lamellar morphology at all studied salt concentrations. When ionic current is passed through the electrolyte, a salt concentration gradient forms that induces a spatial gradient in the domain spacing, d. The dependence of d on distance from the positive electrode, x, was determined experimentally by scanning the incident X-ray beam from one lithium electrode to the other. By studying the two-dimensional (2D) SAXS patterns as a function of azimuthal scattering angle, we find that lamellae with PS/PEO interfaces oriented perpendicular to the flow of ionic current (LAM ⟂ ) swell and contract to a greater degree than those with interfaces oriented parallel to the current direction (LAM || ). While domains with the LAM ⟂ do not provide direct conducting pathways between the electrodes, our analysis suggests that they play an important role in establishing the salt concentration gradient necessary for sustaining a large ionic current through greater expansion and contraction.

25 ENERGY STORAGE↗
DOE OSTI2022

Enhanced Depolarized Electro-Membrane System (EDEMS) for Direct Capture of Carbon Dioxide from Ambient Air (Final Report)

The goal of this final project report is to summarize the work conducted on project DE-FE0031962. In accordance with the Statement of Project Objectives (SOPO), the University of Kentucky Center for Applied Energy Research (UK CAER) (Recipient) developed an intensified process to capture CO2 from ambient conditions (400 ppm CO2). The process combines low-temperature solvent-aided membrane capture with electrochemically-mediated solvent regeneration to simultaneously capture ambient CO2 while regenerating the solvent. The technology employs only two primary units (regenerator and absorber/contactor) while generating high purity hydrogen as a co-product that can be sold, used for energy storage, or cost-saving depolarization of the direct air capture (DAC) system during the grid peak demand, allowing for flexible operation. When depolarization is employed, the operating voltage is reduced by more than 1 V. Since the technology is powered directly by DC electricity, it can seamlessly tie in with power sources like solar cells without the need for AC/DC converters, therefore allowing for a remote operation to further mitigate greenhouse gas generation toward deploying a negative carbon emissions technology that is completely decoupled from the carbon emissions from the power source for the DAC unit. The project results verified that UK CAER’s integrated approach addressed the complexities of incumbent DAC systems by demonstrating at ambient conditions, including (1) low gas-side pressure-drop facile CO2 capture via a membrane contactor with in-situ generated hydroxide as capture solvent, (2) multi-functional electrochemical regenerator for hydroxide regeneration, CO2 concentration and hydrogen production, and (3) depolarization using cathode-produced hydrogen to reduce energy requirement. The EH&S Assessment of the process did not identify any obvious concern for the bench-scale operation and no apparent barriers to implementing UK CAER’s carbon capture and solvent regeneration system at a larger scale.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2022

Watching Polarons Move in the Energy and Frequency Domains Using Color Impedance Spectroscopy

The hybrid electronic–ionic transport property of π-conjugated polymers enables new (opto)electrochemical device constructs for energy conversion and storage and biosensing applications. One major challenge is separating the energy and frequency dependence of Faradaic events–those involving charge transfer and the redox processes of the conjugated backbone–from the non-Faradaic components, such as ionic motion. Herein, we combine optical spectroscopy with electrochemical impedance spectroscopy (EIS) to resolve the frequency response of ionic–electronic coupling as a function of electrochemical doping potential. First, using EIS, we identify two different frequency regimes resulting in potential-dependent capacitive elements on the order of ~10 μF/cm 2 in a high-frequency regime and ~50–150 μF/cm 2 in a low-frequency regime. Given the larger magnitude and greater potential dependence, we posit that polaronic motion is more likely to occur at low frequencies (<1 kHz) and overlaps with ionic motion. The use of color impedance spectroscopy (CIS) enables observation of polaronic motion with frequency modulation. We observe that higher doping potentials show a greater motion of polarons above the DC-bias baseline concentration for onset in electrochemical doping, but all potentials considered demonstrate a critical frequency at which the polaronic motion is “frozen” (~40 Hz). Furthermore, this critical information obtained from CIS in highly dielectric environments offers a unique figure of merit for future studies on electronic–ionic coupling by which to compare across polymer/electrolyte interfaces, including the role of a charge-supporting electrolyte, a solvent, and alternative Faradaic processes (e.g., electrocatalysis).

36 MATERIALS SCIENCE↗
DOE OSTI2026

Ferrimagnetic Order in Tetragonal Antiperovskite Mn3GeN

The crystal and magnetic structures of the nitride antiperovskite M⁢n3⁢GeN reveals ferrimagnetic order stemming from a distorted kagome-derived lattice of the Mn atoms. Polycrystalline M⁢n3⁢GeN was synthesized via a solid-state reaction and characterized using neutron powder diffraction, dc magnetometry, and first-principles calculations. Rietveld refinement reveals near-stoichiometric composition (M⁢n3⁢Ge⁢N0.992⁢(7)) adopting a tetragonal 𝐼⁢4/𝑚⁢𝑐⁢𝑚 structure at 𝑇=500K and below, featuring axially distorted and tilted [NM⁢n6] octahedra that result in a buckled Mn kagome lattice. On heating, the tetragonal distortion and octahedral tilt angle decrease continuously before transitioning to the cubic 𝑃⁢𝑚⁢3⁢𝑚 antiperovskite phase at 𝑇≈527K. Neutron diffraction and magnetometry together reveal noncollinear ferrimagnetic ordering. For 30K≤𝑇≤500K, the magnetic structure is described by magnetic space group 𝐼⁢𝑏⁢𝑎′⁢𝑚′ (72.544), with inequivalent Mn1 and Mn2 sublattices that couple antiferromagnetically to yield a net moment. Density-functional theory-based calculations show that the different local moments originate from the bandwidths associated with distinct Mn–N bond lengths. Temperature-dependent refinements reveal distinct differences in the thermal disordering profiles of the Mn1 and Mn2 sublattices. These findings reveal a subtlety in the magnetic and structural behavior of M⁢n3⁢GeN, highlighting the interplay between structural distortions, magnetic ordering, and electronic structure in kagome-derived antiperovskite materials.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Modular HF Isolated MV String Inverters Enable a New Paradigm for Large PV Farms

The “Modular HF Isolated MV String Inverters Enable a New Paradigm for Large PV Farms” project focuses on exploring alternative power converter and system-level plant configurations to achieve the lowest cost and highest energy output for a given solar plus storage (e.g., PV + battery) plant, including the use of medium voltage (MV) collection while taking into account detailed models of all elements. To realize this objective, four approaches were utilized (i) employ a novel Medium Voltage String Inverter (MVSI) topology (soft switching solid state transformer – S4T) to convert 1000 Vdc to 4.16 kVac; (ii) plant collection using standard, low-cost overhead MV distribution network; (iii) enable energy storage integration without additional converter cost to achieve dispatchability of the PV resource; and (iv) provide advanced functionality (autonomous operation, track ISO signals for dynamic balancing and ancillary services, and PV farm operation as a virtual grid resource). Subsequently and in alignment with the previously mentioned approaches, the project was structured in five efforts (i) S4T MVSI simulation and design; (ii) system analysis and storage optimization; (iii) financial analysis; (iv) power converter prototype build and test; and (v) regulatory and commercial impact study. The outcomes provided by each effort can be summarized as follows (i) Project explored the use of MV AC distribution architecture for hybrid PV+storage utility-scale PV farms; (ii) Detailed loss and LCOE analysis for AC and DC side BESS architecture, including multiple converter topologies, as well as for proposed MVSI/MDCT systems; (iii) MVSI was built and holds promise but needs lower-cost high-voltage Si-C devices, which does not seem possible in the near term; (iv) MDCT provides a simpler modular building block – validated through HIL and farm level modeling, simulation and experimental validation; (v) 300 kVA MDCT prototype built and tested, technology is being commercialized; and (vi) Regulatory model of utility building PV plants, where PV panels are treated as DC generation (IPP), seems viable and can allow improved grid integration.

14 SOLAR ENERGY↗
DOE OSTI2022

Superconducting Shuttle-Flux Shift Register for Race Logic and Its Applications

Here this paper presents a superconducting, magnetically-coupled, shuttle-flux shift register (SF-SR) that stores single flux quantum (SFQ) pulses. This shift register has a DC bias operating margin of ±34% at 10 GHz, with a power dissipation of 3.6 μW and 38% fewer Josephson junctions (JJs) when scaled up to multiple stages compared to a data flip-flop (DFF) based shift register. The clock input is inductively coupled and is independent from the data input. We then present three applications for our SF-SR. In the first application, we add two non-destructive readout (NDRO) cells to construct a buffer that temporarily stores the temporal information of a series of race logic (RL) pulses. The second application is a pseudo-random number generator based on a linear function shift register (LFSR). The third application is N parallel SF-SRs that can act similar to a deserializer or instead can emulate a single SF-SR of N times higher clock frequency. These three applications motivate deep shift registers with many shifting intervals, which our SF-SR can implement with fewer JJs and lower power consumption compared to DFF-based shift registers.

42 ENGINEERING↗
DOE OSTI2021

Quantifying Properties for a Mechanistic, Predictive Understanding of Aqueous Impact on Aging of Medium and Low Voltage AC and DC Cabling in Nuclear Power Plants

To address the gap in knowledge in understanding degradation in relevant service conditions, this project aimed to develop a mechanistic, predictive model of medium and low voltage cable failure based on the primary environmental degradation parameters of aqueous immersion time, temperature, and the oxidation extent. To do so, we took a two-fold approach toward evaluating degradation as related to the aqueous condition. First, we evaluated the chemical, mechanical, and electrical properties of polymers that comprise the cabling insulation under varied aqueous conditions at different temperatures. Secondly, we evaluated the performance of insulation materials under similar accelerated aging conditions in addition to the dielectric breakdown of the cabling under submersion conditions. Thermal oxidation and immersion of LDPE thin films were done using a Parr vessel and the extent of oxidation was monitored using the carbonyl index from ATR-FTIR spectrum, a ratio quantifying the carbonyl functionality produced on the LDPE film surface. Increasing the temperature, oxidation time, and oxygen pressure increased the water-vapor permeability and the carbonyl content. Thermogravimetric analysis of the films confirmed that there is indeed an initial weight loss of the smaller molecular weight molecules and volatiles. At higher temperatures, there is a secondary mass loss. Up to 70°C, the mass loss curves were similar until 80°C, when the aged films decreased at a much greater rate with respect to increasing temperature. This was seen in the 10, 50, 90% weight loss temperatures. The mechanical properties of sheet PP and HDPE as well as injection molded LDPE, HDPE, HDPP dog bones were plotted with respect to the time spent in the Parr vessel during thermal oxidation. For the sheet PP and HDPE, the UTS and the modulus of elasticity decreased while the elongation increased. The injection-molded LDPE, HDPE, and HDPP dog bones experienced a similar trend where the changes in the properties were within experimental uncertainty. This analysis of LDPE in dry and immersive oxygen-rich environments is an important baseline for future experiments looking at other degradation mechanisms. A predictive aging model for low-density polyethylene insulative cable housings was developed. This model revealed a combination of physical and chemical processes which lead to an increase in permeability and a decrease in strength of the insulator. In creating this predictive model, a gap of knowledge in the literature was revealed in two areas: understanding how the crystallinity of a polymer changes with time and visualizing the predicted pores formed through the insulator which leads to failure. Developing and using an adapted ATR-FTIR method, crystallinity was monitored and compared to bulk crystallinity found via DSC. Inhomogeneity in crystallinity changes were observed but the FTIR method but was found to be less reliable. Pore visualization was found utilizing electrical impedance spectroscopy saturated aged polyethylene films with synthesized citrate-capped gold nanoparticles, and chloroauric acid precursor. results indicate a decreasing impedance of the polyethylene films caused by the transport of ions through the film. SEM imaging was then performed for elemental analysis of the films and counter electrodes for the presence of ions. Chloride and gold ions were detected; however, no nanoparticles were found. This gives an estimated pore size of at least 0.3 nm through the aged film. Cyclic submergence of polyethylene and polypropylene in aqueous solutions of copper sulfate and Harrison’s solution were examined. It was discovered that aging in these mixed conditions and at 90°C did cause a small, yet significant increase to tensile strength for both unaged polyethylene and polypropylene. The PE and PP in cycled and submerged conditions did not have tensile strengths significantly different from dry-aged after 16 weeks. For both solutions, it was determined that capacitance increases with both water tree depth and cable temperature and is relatively independent of changing water tree AR. As for resistance, there is no apparent change between depth percentages of 10 and 80 for both solutions. This is because the water tree has not yet entered the conductor and thus there is no shorting current flowing through the tree yet. Between 80 and 100% water tree depth, it is observed that for both solutions there is a rapid decrease in resistance because the tree is now impacting the conductor shield and allowing shorting current to flow through it. The relationship between resistance and temperature was found to be inversed. As temperature increases, resistance decreases for both water tree solutions with distilled water having the most apparent difference across the range of temperatures simulated. With regards to water tree AR, resistance was found to be relatively independent at depth percentages of 10, 50, and 70, but there was some relationship at 100% depth for both solutions. At this depth, as water tree AR increased, resistance was found to also increase. Through the examination of voltage and electric field distribution plots, it was confirmed for EPR cables that increasing water tree depth leads to increasing distortion. The increase in shorting current at 100% depth for aqueous copper sulfate compared to distilled water was also visualized. Lastly, the relationship between shorting current and temperature for narrow water trees was visualized and validated using the distribution plots. This study has led to a better understanding of the effect of cable temperature, water tree solution, and geometry of the tree region on cable degradation. Furthermore, this study has documented simulation results of water tree degradation in EPR MV cables, which had been previously lacking in information. Future work in this area will add frequency into the mix and examine what effect it has on the rate of cable degradation as a result of water treeing. To compliment the work being carried by UMD on different polymer chemistries, harvested medium voltage (MV) cables were selected for accelerated aging study at ORNL. These medium voltage cables are representative of the vintages and materials that are currently in use at existing nuclear power plants (NPPs). These cables were immersed in water at 90°C and energized for a period of two years at elevated voltage. Partial discharge was measured during this period of time to track potential degradation. Unfortunately, due to the absence of failure, the extent of integration between the UMD techniques and the harvested MV insulation was limited. However, based on the findings and from the UMD research in the previous sections on polyethylene and polypropylene, follow-on characterization for harvested MV cable insulation should focus on sample preparation to take advantage of the UMD techniques to better understand mechanistic degradation in MV cable insulations. This would include: 1.) Utilization of solutions and impedance measurement insulation to track permeability in harvested and accelerated aging insulation samples, 2.) Adaptation of gold nanoparticle synthesis for electrical impedance spectroscopy with supporting SEM characterization to study pore formation in harvested and accelerated aged insulation samples, & 3.) ATR-FTIR crystallinity with multiple temperature dependent harvested MV cable insulation under different air and submerged accelerated aging. In addition, low voltage dielectric spectroscopy and high voltage dissipation factor, tan δ, could be implemented as a condition monitoring tool for harvested MV cable insulation in submerged environments.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2021

Towards single-chip radiofrequency signal processing via acoustoelectric electron–phonon interactions

Abstract The addition of active, nonlinear, and nonreciprocal functionalities to passive piezoelectric acoustic wave technologies could enable all-acoustic and therefore ultra-compact radiofrequency signal processors. Toward this goal, we present a heterogeneously integrated acoustoelectric material platform consisting of a 50 nm indium gallium arsenide epitaxial semiconductor film in direct contact with a 41° YX lithium niobate piezoelectric substrate. We then demonstrate three of the main components of an all-acoustic radiofrequency signal processor: passive delay line filters, amplifiers, and circulators. Heterogeneous integration allows for simultaneous, independent optimization of the piezoelectric-acoustic and electronic properties, leading to the highest performing surface acoustic wave amplifiers ever developed in terms of gain per unit length and DC power dissipation, as well as the first-ever demonstrated acoustoelectric circulator with an isolation of 46 dB with a pulsed DC bias. Finally, we describe how the remaining components of an all-acoustic radiofrequency signal processor are an extension of this work.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Laser-induced fluorescence measurements of ion fluctuations in electron and ion presheaths

Electrostatic flow-driven instabilities have been predicted in the presheath region of low-temperature plasmas for both ion and electron rich sheaths. The ion-acoustic fluctuations that arise from these instabilities can influence transport through an enhanced collision rate. In this work, ion fluctuation spectra were measured using laser-induced fluorescence (LIF) in the presheath region for both sheath polarities. Furthermore, the non-invasive nature of LIF compared to that of probes is particularly valuable for these measurements because the sheath and presheath around a probe may generate their own flow-driven instabilities, which obscure the measurement. Measurements were made using a recently implemented field programmable gate array-based system able to measure ion fluctuation spectra up to 1 MHz using a two-point correlation function technique. Narrow bandwidth ion fluctuations were observed near 0:46 f pi (460 kHz) for both sheath polarities, where f pi is the ion plasma frequency. The observed fluctuations were significantly stronger in the electron sheath case and were observed over a larger volume of plasma. Fluctuations were measured in the ion sheath case at locations far enough from the sheath that linear theory predicts stability, suggesting that ion-acoustic instabilities generated in the relatively small unstable region near the boundary reflect from the sheath and perturb a much larger volume of the plasma. This is expected to affect probes with both ion and electron rich sheaths, meaning any dc biased probe may effectively act as an ion-acoustic wave antenna. These measurements are consistent with the recent theory and particle-in-cell results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Modular DC circuit breaker with integrated energy storage for future DC networks

A T-breaker is an all-in-one solution for dc microgrid fault protection, power flow control, and power quality improvement. A T-breaker features a modular multilevel “T” structure with integrated energy storage devices. The two horizontal arms of the T-breaker realize fault current breaking, load voltage compensation, and power flow control; and the vertical arm of the T-breaker realizes shunt compensation. The configuration provides excellent voltage scalability and relaxes the requirements on the switching signal synchronization during fault transients. The local energy storage in sub-modules eases the fault energy dissipation requirement placed on the traditionally-adopted surge arrestors. The modular multilevel structure also offers immense control flexibility for all types of targeted functions of the provided T-breaker.

Wang, Jin↗
DOE OSTI2026

Scattering phase shift in quantum mechanics on quantum computers

Here, we investigate the feasibility of extracting infinite volume scattering phase shift on quantum computers in a simple one-dimensional quantum mechanical model, using the formalism established in the work by Guo and Gasparian [Phys. Rev. D 108, 074504 (2023)] that relates the integrated correlation functions for a trapped system to the infinite volume scattering phase shifts through a weighted integral. The system is first discretized in a finite box with periodic boundary conditions, and the formalism in real time is verified by employing a contact interaction potential with exact solutions. Quantum circuits are then designed and constructed to implement the formalism on current quantum computing architectures. To overcome the fast oscillatory behavior of the integrated correlation functions in real-time simulation, different methods of postdata analysis are proposed and discussed. Test results on IBM hardware show that good agreement can be achieved with two qubits, but complete failure ensues with three qubits due to two-qubit gate operation errors and thermal relaxation errors.

Guo, Peng [Dakota State Univ., Madison, SD (United↗
DOE OSTI2021

Phase diagram of CeSb 2 from magnetostriction and magnetization measurements: Evidence for ferrimagnetic and antiferromagnetic states

Cerium diantimonide (CeSb 2 ) is one of a family of rare-earth-based magnetic materials that exhibit metamagnetism, enabling control of the magnetic ground state through an applied magnetic field. At low temperatures, CeSb 2 hosts a rich phase diagram with multiple magnetically ordered phases for many of which the order parameter is only poorly understood. In this work, we report a study of its metamagnetic properties by scanning tunneling microscopy (STM) and magnetization measurements. We use STM measurements to characterize the sample magnetostriction with subpicometer resolution from magnetic field and temperature sweeps. This allows us to directly assess the bulk phase diagram as a function of field and temperature and relate spectroscopic features from tunneling spectroscopy to bulk phases. Our magnetostriction and magnetization measurements indicate that the low-temperature ground state at zero field is ferrimagnetic. Quasiparticle interference mapping shows evidence for a reconstruction of the electronic structure close to the Fermi energy upon entering the magnetically ordered phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Gradient-Descent-Based Learning Gain for Backstepping Controller and Disturbance Observer of Nonlinear Systems

This paper proposes a gradient-descent-based learning (GL) gain for backstepping controller and disturbance observer (DOB) of nonlinear system. The proposed method consists of the GL gain update law, controller, and DOB. The GL gain update law is proposed to adapt the control gain and DOB gain according to the direction that minimizes the cost function. The mathematical analysis reveals that the GL gain always has a positive sign and upper bound. The controller is designed via a backstepping procedure to track the desired output with GL control gain. The DOB is designed to estimate the unknown external disturbance with the GL DOB gain. Because the control and DOB gains are simultaneously tuned to achieve improved performance, the time consumption for tuning can be reduced. In addition, the peaking phenomenon can be avoided initially by a small initial value of GL gains. The stability of the closed-loop system is guaranteed using the input-to-state stability property. The performance of the proposed method was validated via simulations and experiments using a DC motor.

42 ENGINEERING↗
DOE OSTI2018

50-kW 1kV DC bus air-cooled inverter with 1.7 kV SiC MOSFETs and 3D-printed novel power module packaging structure for grid applications

The traditional heatsink design technologies for forced air-cooling and power semiconductors with low junction temperatures have constrained the converters to be designed with massive heatsinks. The low power losses of WBG device technology and higher junction temperature operation over a wide operating range of power have not been fully utilized with liquid-cooled systems. The other major limitation has also been the traditional power module packaging “stack” approach with baseplate. This paper presents a novel power stage design which involves 1.7 kV silicon carbide (SiC) MOSFETs, a heatsink design with Genetic Algorithm (GA) and built using 3D printing technology, and a novel integrated modular power module for high power density. The air-cooled module assembly has a SiC MOSFET phase leg module with split high-side and low-side switches and a gate driver with cross-talk and short circuit protection functions. The heatsink design was modeled using a co-simulation environment with finite element analysis software and GA in MATLAB and COMSOL. The proposed concepts were verified and validated through experiments at each stage of development. The power stage was evaluated at 800V, 900 V, and 1kV for 20 kHz switching frequency and 50-kW load. The experimental results show that the CEC efficiency is 98.4 %. In addition to the efficiency, a power density of 75 W/in 3 was also achieved.

Chinthavali, Madhu Sudhan↗
DOE OSTI2020

Design Paradigm for Modular Multilevel Converter-Based Generator Rectifier Systems

Modular Multilevel Converters (MMC) are being widely considered for medium to high voltage DC applications. Designing such converters through multi-objective optimization is of interest because such an approach allows the trade-off between competing objectives (for example mass and loss) to be explicitly and quantitatively identified. In this work, an optimization based design paradigm for MMC based generator rectifier systems is proposed. Such development typically requires detailed component design and simulation models for the electric machine and converter which are computationally expensive. As an alternative, the proposed work utilizes an electric machine metamodel, inductor metamodel, and high-speed steady-state simulation model for the MMC to facilitate multi-objective optimization minimizing system metrics of interest while satisfying system constraints. A case study is undertaken to demonstrate the functionality of the proposed design paradigm.

42 ENGINEERING↗
DOE OSTI2018

DISTINCT: Diversity in Solar Talent Through INnovative Curriculum and Training: An Integrated Research and Education Approach towards Creating Diversity and Advancing Utility-Scale Solar Technology

The DISTINCT project research objective is to develop an innovative N-port power converter for a utility-scale PV system that is modular, compact and cost-effective and that will enable the integration of a high-frequency, high-voltage solid-state transformer. The novelty of the proposed research is the electrical power conversion architecture using an N-port converter system that replaces the output 60Hz transformer with an integrated high-frequency low-weight solid-state transformer reducing power electronics and BOS costs to meet SunShot goals through modularity and direct high-voltage interconnection. A challenge in direct integration with a 13.8kV line is the high voltage handling capacity of the converters combined with high efficiency operation. The front-end converter for each port is a Neutral-Point Clamped (NPC) Multi-Level dc-dc Dual-Active Bridge (ML-DAB) which allows Maximum Power Point Tracking (MPPT). The integrated high frequency transformer provides the galvanic isolation between the PV and grid side and also steps up the low dc voltage from PV source. Following the ML-DAB stage, in each port, is an inverter with H-bridge configuration or NPC configuration. N number of NPC inverters’ outputs are cascaded to attain the per-phase line-to-neutral voltage to connect directly to the distribution grid (i.e. 13.8 kV). The cascaded inverters have the inherent advantage of using lower rated devices, smaller filters and low Total Harmonic Distortion (THD) required for PV grid interconnection. Our analysis and simulation results show improved performance on cost, efficiency, service life with zero downtime and THD. A comprehensive control scheme is presented to ensure the maximum power from each port and each phase are sent to the grid. A functional prototype of a 2-port converter with ML-DAB and cascaded H-bridges has been designed, built, and tested in a laboratory setup to verify the target technical metrics. The N-port converter system due to its modular structure with individual control per port can be easily adapted to integrate functionalities that go well beyond the conventional grid support functions and mitigates impacts of forecasted fast ramp downs or ramp ups and single-fault conditions by automatic reconfiguration of the output.

14 SOLAR ENERGY↗
DOE OSTI2024

Filterscope Techniques for Parasitic Signal Screening

Here, the filterscope diagnostic uses bandpass filters and photomultiplier tubes (PMTs) to detect specific spectral emission lines. A filterscope was used to measure the W I 400.88 nm line emission as a function of ion energy on the Radio Frequency Plasma Interaction Experiment (RF PIE) for the purpose of assessing W erosion on plasma-facing components (PFCs). Different filter techniques are being explored and compared in order to effectively screen out nearby impurity lines, like the Ar II 401.39 nm line. The effectiveness of these techniques is determined by comparing the measurements to a high-resolution 1.0 m Czerny–Turner spectrometer with 0.012 nm spectral resolution. The ability to filter out nearby impurity emissions is useful when imaging PFCs in fusion devices including divertor and antenna guard limiters. Initial results with a helium plasma show little difference between the two techniques at higher bias voltages. In a helium plasma at lower dc bias voltages, a two-filter technique with filters at two separate wavelengths was shown to be more effective at screening out background signals. Data collected with an argon plasma however show the technique with overlapping filters on the line of interest is a closer match to spectrometer data at lower dc bias voltages.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗