Design and performance of an additively manufactured high-Si transformer core
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36 MATERIALS SCIENCE↗
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Assessing Nanocrystalline Pulsed Transformer Core Performance using Maxwell ANSYS
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71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Advances in Processing, Manufacturing, and Applications of Magnetic Materials
Magnetic materials are increasingly important for many green energy technologies. Probably, the best known of these are permanent magnets. They are used to supply a magnetic field and are widely used in actuators, motors, generators, data storage, and sensors. These are “hard magnets,” meaning that they retain a large permanent magnetization (difficult to be demagnetized), which is what makes them so useful in motors where an opposing magnetic field can be used to push against them. A coercivity (resistance to demagnetization) of ~400 Oe (32,000 A/m) or more is typically the threshold value for a hard magnet and is typical of isotropic sintered ferrite (SrFe 12 O 19 ) such as found in many “refrigerator magnets.” Comparably important soft magnets are useful for directing magnetic fields and can be very easily (de)magnetized. As such, they typically have a coercivity < 12.5 Oe (1000 A/m), and specialized very soft magnets can have coercivities < 0.00125 Oe (1 A/m). Some common applications include coil cores, transformer cores, and magnetic shielding. Additionally, they are important for many AC electrical applications such as inductors, filters, and resonators, particularly at high frequencies up to and including microwaves.
36 MATERIALS SCIENCE↗
Flattening the Radial Temperature Profile across the Transformational Challenge Reactor Core
The Transformational Challenge Reactor (TCR) program is demonstrating an agile development approach to advanced nuclear reactor design, which has traditionally utilized a linear design process. In leveraging artificial intelligence, additive manufacturing, advanced materials, and cutting-edge modeling and simulation, the TCR program aims to minimize the high cost and lengthy deployment timelines now standard in the nuclear industry. Within a relatively short period of time, a robust and mature advanced gas-cooled reactor was iteratively designed under the TCR program, using these cutting-edge technologies. The TCR is a 3 MWt gas-cooled microreactor fueled with uranium nitride (UN) tristructural isotropic (TRISO) fuel particles. Though manufactured via traditional means, these UN TRISO particles are loaded into additively manufactured silicon carbide (SiC) cans [4]. Once loaded with TRISO particles, the SiC cans are densified using a chemical vapor infiltration process. The additively manufactured SiC enables significantly more freedom in the design of the fuel form than could ever be achieved using traditionally manufactured SiC. The helium coolant, pressurized to 5 MPa, enters the core at 300°C and nominally exits it at 500°C. Typically, the most thermally limiting components in any reactor design are the fuel assemblies in the core center. To provide a wide thermal margin in these central fuel assemblies, the flow may be biased toward the center of the core to more effectively cool these fuel assemblies with more power deposition and flatten the core’s radial temperature distribution. An analytical fluid model of the TCR core was developed to explore methods for biasing the flow away from the cooler outer fuel assemblies and towards the hotter inner ones. Higher-fidelity models developed in STAR-CCM+ 2020.3.1, a computational fluid dynamics code, were then utilized to verify the analytical model’s findings.
22 GENERAL STUDIES OF NUCLEAR REACTORS↗
Heterogeneous Integration Technologies for High-temperature, High-density, Low-profile Power Modules of Wide Bandgap Devices in Electric Drive Applications (Final Technical Report)
The goal of this project is to develop packaging technologies for making high-temperature, high-density, and low-profile wide-bandgap (WBG) power electronics modules for electric drives. These modules are aimed at enabling the DOE’s University Consortium to reach its 2025 inverter targets of ≥ 100 kW/L and ≤ 2.7 $/kW. The specific objectives are to: design and fabricate SiC half-bridge power modules with double-sided cooling and parasitic inductances < 5 nH, heat flux density > 400 W/cm 2 , and working junction temperature of 200 o C; design, fabricate, and deliver a gate driver with double-sided cooled modules for the construction of a 100 kW/L inverter at Oak Ridge National Lab; and design and prototype intelligent gate drivers with integrated current sensor and a low-profile DC-DC power supply with air-core transformer for testing power modules at 200 o C junction temperature. We followed an iterative technical approach of design, simulation, fabrication, and testing of various versions of modules, current sensors, and power supply. The state-of-the-art silicon carbide devices rated at 1.2 kV and 149 A were packaged by sintered-silver bonding on an aluminum nitride direct-bond-copper substrate for high thermal conductivity, high working temperature, and high joint reliability. Porous silver posts were used to interconnect the device’s source pads to the other direct-bond-copper substrate for low mechanical stresses, ease of manufacturing, and double-sided cooling. A current sensor based on package parasitic inductance was developed to measure switching current. A dynamic feedback scheme was developed to compensate the effect of parasitic resistance and temperature variation. A constant-current class-E dc-dc converter with air-core transformer was developed. Air-core transformer was used due to the unavailability of magnetic core at high temperatures. Gate driver and power supply were integrated with the double-side cooled, high temperature SiC power modules for testing the modules at 200 o C junction temperature. Double-pulse and continuous testing of the integrated technologies validated the design and fabrication of the three component technologies. Throughout the project, we overcame the challenge for design verification caused by low prototyping yield, which then helped train the graduate students, the future workforce, to learn the engineering know-how for low-cost manufacturing of reliable products. Below is a summary of the major accomplishments of this project: development of a prototyping process for fabricating double-side cooled (1200 V, 149 A) SiC phase-leg modules capable of working to 200 o C Tj; simulation and experimental verification of the improvement of thermo-mechanical reliability of the double-side cooled SiC phase-leg module by using rigid encapsulant; design and experimental validation of a current sensor based on package parasitic inductance and a compensation solution for eliminating the effect of parasitic resistance; design and experimental validation of a low-profile power supply with six-output air-core transformer for gate driver; functional demonstration of a SiC phase-leg module integrated with its gate driver, current sensor, and an air-core power supply at 200 o C Tj in a double-pulse switching test setup and Buck converter continuous test setup; successful completion of six PhD and two MS students who are or will work at Apple Inc., Tesla Inc., Wolfspeed Inc., Microchip Inc., Monolithic Power Systems Inc., and LG Magna Inc.
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
Assessment of minnealloy fabrication via three routes
Transformer cores exhibiting higher operating power and improved efficiency are of great interest to electrical utilities, industry, and the de-carbonization effort. Minnealloy, α″-Fe16(C,N)2, a martensite made only of iron, nitrogen, and carbon, has shown the largest saturation magnetization of any soft ferromagnet, 250 emu/g, and tunable magnetocrystalline anisotropy. Given this represents a significant increase in power transferred per cycle compared to legacy transformer core materials, we investigate three novel, industrially scalable routes for fabricating Minnealloy. The martensite phase content is investigated for each route. Vibrating sample magnetometry is used to investigate the change in saturation magnetization and coercivity with respect to the relative content of the desired phase and other iron, iron-nitride, and iron oxide phase impurities. The relationship between structure and magnetic properties of bulk α″-Fe16(C,N)2 is investigated using LDA, PBE, and PBEsol exchange-correlation functionals within the frameworks of Hubbard-corrected density functional theory (DFT+U).
36 MATERIALS SCIENCE↗
Pulsed Transformer Magnetic Core Comparison of Different Materials for Pulsed Power Applications
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Engineering↗
Distributed sensing of electromagnetic components using optical fiber based methods
An OFDR based fiber-optics sensor for distributed real-time temperature rise monitoring of a transformer in operation has been disclosed. The fiber-optic sensor provides an effective solution to monitoring the physical structures of the transformer core, as well as accurately detecting the non-uniform temperature distribution inside the transformer, and thus provides innovative feedback to the transformer design by minimizing the core losses. Additionally, the method may be responsive to the presence of magnetic and electric fields, as well as responsive to various chemical species. The method allows novel approaches to real-time asset monitoring of power transformers while operational.
Ohodnicki, Paul R.↗
Solid State Transformer Architecture and Control Compensation for Common Mode Currents
A high-altitude electromagnetic pulse (HEMP) or similar geomagnetic disturbance (GMD) has the potential to impact the operation of large-scale electric power grids. By introducing low-frequency common-mode (CM) currents, these events can degrade the performance of critical system components, such as large power transformers by introducing CM currents which can lead to magnetic saturation of the transformer core. In this work, a solid-state transformer (SST) is developed to replace susceptible equipment and improve grid resiliency by safely absorbing these CM disturbances. This device will be referred to as a common-mode solid-state transformer (CM-SST). An SST architecture based on a four-legged AC/DC converter is developed. This architecture enables active control of CM signals without disturbing the AC voltages or the real and reactive power delivery capabilities. A system-level model of this architecture is created, and time-domain simulations are performed to evaluate the SST’s performance in response to simulated CM disturbances. A control strategy for mitigating CM current is also investigated. Hamiltonian surface shaping and power flow control (HSSPFC) is used to design a nonlinear controller for the SST’s output inverter. The objectives of the controller are to suppress CM-induced AC current offsets and regulate AC currents to desired setpoints. Nonlinear system analysis is applied to design and validate the controller. Two cases are tested: (a) the proposed four-leg inverter and (b) a standard three-leg inverter. The results show that the proposed controller rapidly mitigates CM disturbances while maintaining high-quality AC current waveforms in the four-leg configuration. Finally, the hardware performance of an SST prototype is evaluated. In particular, the ability of the SST to safely redirect and absorb CM currents is demonstrated, showing how it can protect neighboring conventional transformers in the system. The study confirms that appropriate control laws allow the SST to protect both itself and adjacent transformers during a HEMP or GMD event.
24 POWER TRANSMISSION AND DISTRIBUTION↗
Low modulation index 3-phase solid state transformer
A solid-state transformer (SST) comprises a transformer core, a primary winding, a secondary winding, a primary-side switch bank, and a secondary-side switch bank. Each of the switch banks includes six 4-quadrant switches. The twelve 4-quadrant switches are toggled on and off over six clock cycles in a repetitive sequence with a period that is a function of a desired operating frequency of the transformer. The sequence is configured such that at any given time, 2 of 3 input and output phases are connected to the primary and secondary windings. The SST further includes L-C filter circuits that are configured to filter high-frequency components of current and voltage waveforms such that these components are not back-fed to the electrical mains or delivered to a load. The SST includes a primary-side filter circuit and a secondary-side filter circuit that can each include respective L-C filters for three input or output phases.
Koplow, Jeffrey P.↗
Material Characterization Study of Magnetite Nanocrystals for RF Sensing
Magnetite nanocrystals show promise for electrically small gigahertz frequency applications, which could lead to miniaturizing transformer cores and new sensing technologies. This work presents a rigorous radiofrequency characterization of these nanocrystals using vector network analyzer (VNA) ferromagnetic resonance (FMR) measurements. For the first time, two different average diameters of Fe 3 O 4 nanocrystals are investigated (7.3 and 20.2 nm). When the VNA–FMR results were compared to micromagnetic simulations, the magnetic anisotropy (K 1 ) deviated from the ideal mean orientation value of K 1 /2 to K 1 /80 for the 7.3 nm nanocrystal. In contrast, the obtained magnetic anisotropy in 20.2 nm nanocrystals slightly deviated to K 1 /11 due to less structural deformations. These findings resulted in a newly proposed methodology for an approximate simulation based on VNA–FMR measurements. In addition, this work estimates the approximate amount of nanocrystals needed to measure a useful VNA–FMR spectrum.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Adding multiple electrons to helicenes: how they respond?
An overview of structural responses of helicenes with increasing dimensions and complexity to stepwise electron addition reveals charge- and topology-dependent outcomes ranging from reversible to irreversible core transformations and site-specific reactivity.
Chemistry↗
Toward a Holistic Performance Evaluation of Large Language Models Across Diverse AI Accelerators
Artificial intelligence (AI) methods have become critical in scientific applications to help accelerate scientific discovery. Large language models (LLMs) are being considered a promising approach to address some challenging problems because of their superior generalization capabilities across domains. The effectiveness of the models and the accuracy of the applications are contingent upon their efficient execution on the underlying hardware infrastructure. Specialized Al accelerator hardware systems have recently become available for accelerating Al applications. However, the comparative performance of these AI accelerators on large language models has not been previously studied. In this paper, we systematically study LLMs on multiple AI accelerators and GPUs and evaluate their performance characteristics for these models. We evaluate these systems with (i) a micro-benchmark using a core transformer block, (ii) a GPT-2 model, and (iii) an 1,I,M-driven science use case, GenSLM. We present our findings and analyses of the models' performance to better understand the intrinsic capabilities of AI accelerators. Furthermore, our analysis takes into account key factors such as sequence lengths, scaling behavior, and sensitivity to gradient accumulation steps.
Emani, Murali↗
Progress in development of pulsed resonant charging power supply for the Spallation Neutron Source extraction kicker PFN system
A conceptual design of the pulsed resonant charging power supply (RCPS) for the beam extraction system of the Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory (ORNL) was previously reported at the 2019 IEEE Pulsed Power & Plasma Science Conference (PPPS 2019) [1]. Development and testing of the prototype supply continued through the year to finalize the design ahead of the Proton Power Upgrade (PPU). Testing revealed reliability issues with the original resonant charging scheme related to the step-up transformer core. Additional components were incorporated into the system, and some of the original prototype components were replaced to improve performance and reliability of the power supply. This paper describes the changes in the resonant charging scheme, presents the results of testing of the improved prototype at full power level, and shows the final design of the RCPS.
Peplov, Vladimir↗
Adrian Portales Coop Internship Report
Using the thesis of W.R. Nolan (cite) as a guide, Cobalt Iron (CoFe) powders were reacted with 0.1 wt.% and 0.2 wt.% phosphoric acid in a 20:1 ratio of acetone to phosphoric acid. The powders were then dried at room temperature. The resulting phosphate coated CoFe was then mixed with 0.75 wt.% of the lubricant N,N' ethylene bis-stearamide (trade name: Acrawax C) and hot pressed to form a consolidated soft magnetic material referred to as CoFeP. With an avenue of synthesis for CoFeP determined, a proper amount of stock was synthesized for continuous “brick” production. While under current optimization, these 1x1 mm magnetic bricks will ultimately be placed and secured along the inside wall of each MK Magnetics transformer core by an appropriate CoFeP dispersed epoxy. As of now each brick has been produced though a pressing and annealing process via square 2x2 cm die. Before a brick is made a pressure calculation is run to ensure the dies maximum operating pressure is not exceeded. Figure 1. ensures the user’s safety by showing that the tons-on-ram required for a 2x2 cm square die to reach 760 MPa is below the point of die failure.
36 MATERIALS SCIENCE↗
Pulsed Sphere Time of Flight Neutron Spectrum Measurements: Blank Run and 1.8 Mean-Free-Path thick Polyethylene Moderating Sphere
From the late 1960s to 1985, Lawrence Livermore National Laboratory (LLNL) undertook a series of ‘pulsed sphere’ experiments for 32 materials involving 148 different experiments using 75 different spheres to measure the neutron leakage spectra for different materials from 14-MeV neutrons generated by 3 H(d, n) 4 He reactions induced by an incident D+ beam from the Insulated Core Transformer (ICT) accelerator at LLNL. This deuteron beam was focused to impinge on tritium loaded onto a titanium substrate within a low mass target assembly placed within the center of a spherical shell constructed from the material of interest. The neutron time of flight was measured at a detector outside a collimator. The program was intended to be comprehensive with numerous targets of various thicknesses spanning the periodic table from H to 239 Pu. Five different neutron detectors were utilized to avoid possible systematic errors due to differences in detector responses. Further, these measurements were designed with the aim that the simple geometry of the measurements could be easily simulated to validate Monte Carlo transport codes and nuclear data libraries. As a result, these benchmarks have been extensively used in the validation of ENDL, ENDF and other libraries. Two experiments selected as benchmark cases in this evaluation are: 1) target assembly without material sphere (blank run), and 2) target assembly with a hollow polyethylene sphere, 1.8 mean free path (mfp) or 16.56 cm thick.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Soft magnetic alloy embodiments for additive manufacturing and geometric structures formed therefrom
Disclosed herein are embodiments of soft magnetic alloy embodiments for use in additive manufacturing and structures fabricated from such alloys. In some embodiments, the fabricated structures comprise a continuous thin wall (or plurality thereof) having a geometry that promotes reduced eddy current losses and other performance enhancements. In some embodiments, the fabricated structures are used to make components, such as transformer cores and/or electric motors.
Plotkowski, Alexander↗
Flattening the Radial Temperature Profile across the Transformational Challenge Reactor Core
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Jessee, Casey J.↗