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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Cogging Torque Minimization in Transverse Flux Machines

This paper presents the design considerations in cogging torque minimization in two types of transverse flux machines. The machines have a double stator-single rotor configuration with flux concentrating ferrite magnets. One of the machines has pole windings across each leg of an E-Core stator. Another machine has quasi-U-shaped stator cores and a ring winding. The flux in the stator back iron is transverse in both machines. Different methods of cogging torque minimization are investigated. Key methods of cogging torque minimization are identified and used as design variables for optimization using a design of experiments (DOE) based on the Taguchi method. A three-level DOE is performed to reach an optimum solution with minimum simulations. Finite element analysis is used to study the different effects. Two prototypes are being fabricated for experimental verification.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2018

SiC MOSFET Based Power Module Design and Analysis for EV Traction Systems

Wide bandgap (WBG) power semiconductor devices, specifically silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) have gained attention from electric vehicle (EV) system developers due to well-known superior properties in comparison to industry standard silicon (Si) based MOSFETs and insulated-gate bipolar transistors (IGBTs). In this work, a power module design based on SiC MOSFETs in a segmented two-level, three-phase inverter topology with 125 kW peak output power and 30 kHz switching frequency is presented. Three different SiC MOSFET die options are analyzed according to experimentally obtained operating conditions of a commercial EV traction system. Substrate design of the power module for multi-die layout, heat sink design, and integration of a segmented phase leg module are presented. Finite-element electrical and thermal analysis of the proposed system are presented and discussed.

Gurpinar, Emre↗
DOE OSTI2019

Medium Voltage (13.8 kV) Transformer-less Grid-Connected DC/AC Converter Design and Demonstration Using 10 kV SiC MOSFETs

Medium voltage (MV) power converters using high voltage (HV) Silicon Carbide (SiC) power semiconductors result in great benefits in weight, size, efficiency and control bandwidth. However, challenges still exist on the components design considering HV insulation and noise immunity requirements in the MV SiC based power converter. A 5-level MMC based transformer-less grid-connected dc/ac converter is developed for 13.8 kV medium voltage grid using 10 kV SiC MOSFETs. The key components, including gate driver with high dv/dt immunity and fast reliable protection, isolated power supply with low parasitic capacitance, voltage/current sensors with high noise immunity, and passives following related insulation standard are provided. A 25 kV dc-link phase-leg is demonstrated, and the experimental results are presented.

Ji, Shiqi↗
DOE OSTI2022

A Half-Bridge On-State Voltage Sensor for In-Situ Measurements

Current prognostics for life expectancy of power semiconductors utilize off-line measurements of the on-state resistance. Presented is a half-bridge (HB) on-state voltage (VON) sensor capable of being utilized for in-situ measurements enabling continuous and real-time monitoring of the on-state resistance. The design provides a single VON measurement output that contains independent VON information of both high and low side devices in a HB leg. The measurement output is referenced from the middle point of the HB and combines the two complementary VON sensing outputs. This system reduces the number of components, required number of analog signal processing circuits, and ADC channels for in-situ health monitoring of a power electronics system. These reductions will facilitate integration of the VON sensor with the gate driver board and achieve low system profile. The experimental results demonstrate the proposed VON measurements while switching with inductive and resistive loads.

Roy, Chondon↗
DOE OSTI2020

Comparison of Dead-Time Effects in a WPT System Inverter for Different Fixed-Frequency Modulation Techniques

In this paper, a comparative study of the dead-time effects in a wireless power transfer (WPT) system inverter is performed for different fixed-frequency control techniques. The dead-time is provided between the complementary switching instances of the inverter phase-legs to ensure safe operation of the input power source. Under certain operating conditions, the dead-time results in waveform distortions or voltage-polarity reversal (VPR) at the inverter output. The VPR affects the switching characteristics, harmonic spectrum, switching losses, and output voltage/power of the system. A detailed analysis of the dead-time effect on the WPT system parameters such as output voltage and output power is conducted for the different fixed-frequency control strategies (i.e., traditional phase-shift control, asymmetrical clamped-mode, and asymmetrical duty-cycle control). Furthermore, the impact of dead-time on the inverter switching losses is compared for the different control strategies.

Kavimandan, Utkarsh↗
DOE OSTI2021

Constant Frequency ZVS PWM Converter

In this paper, a simple yet novel buck or boost adaptive zero-voltage switching (ZVS) converter topology is proposed for soft switching pulse-width modulation (PWM) dc / dc converters. The converter is designed for the high switching frequency that can achieve high efficiency by reducing switching losses for the entire load range at low and high power. Besides, the output at the load terminals is maintained by a PWM signal at a fixed switching frequency, a phase shift signal between converter ports (legs) controls the system circulating current in order to provide the ZVS condition in all load conditions. With the proposed controller, the converter, thus, is suitable for high switching frequency and high-power applications with the small volume. The proposed dc / dc converter operation is analyzed, designed, and confirmed by simulation results for 240 V input, 400 V / 5 A output, and 200 kHz operating frequency at full load.

Asa, Erdem↗
DOE OSTI2026

A Novel Low-Profile High-Efficiency Three-Phase Matrix Transformer

High step-down isolated DC-DC conversion from an 800 V DC bus to low-voltage, high-current outputs is required in automotive auxiliary converters and data center power supplies. In such applications, conventional transformer-based converters require large turns ratios, which increase winding resistance, leakage inductance, and magnetic height. This paper proposes a novel low-profile three-phase matrix transformer that realizes a large effective voltage ratio through flux division among multiple secondary legs, without increasing the physical turns count of each winding. As a result, the proposed structure reduces copper usage and transformer height while preserving the voltage conversion capability of a conventional three-phase transformer. Finite element analysis shows that the proposed design reduces magnetic height by 27%, ferrite volume by 34%, and copper volume by 28%. Circuit-level simulations of an 800 V/12 V,3 kW CLLLC dual-active-bridge converter further show that the lower winding resistance reduces total system loss by 91% and increases DC-DC efficiency from 82.6% to 97.6% at 3 kW output.

Inoue, Shuntaro [ORNL] (ORCID:0000000262637627)↗
DOE OSTI2017

Synthetic Fiber Capstan Drives for Highly Efficient, Torque Controlled, Robotic Applications

Here this paper describes the design and performance of a synthetic rope on sheave drive system. This system uses synthetic ropes instead of steel cables to achieve low weight and a compact form factor. We demonstrate how this system is capable of 28-Hz torque control bandwidth, 95% efficiency, and quiet operation, making it ideal for use on legged robots and other dynamic physically interactive systems. Component geometry and tailored maintenance procedures are used to achieve high endurance. Endurance tests based on walking data predict that the ropes will survive roughly 247,000 cycles when used on large (90 kg), fully actuated bipedal robot systems. The drive systems have been incorporated into two novel bipedal robots capable of three-dimensional unsupported walking. Robot data illustrate effective torque tracking and nearly silent operation. Finally, comparisons with alternative transmission designs illustrate the size, weight, and endurance advantages of using this type of synthetic rope drive system.

42 ENGINEERING↗
DOE OSTI2017

Investigation of HTS Twisted Stacked-Tape Cable (TSTC) Conductor for High-Field, High-Current Fusion Magnets

Here, the critical currents of a twisted single-tape were measured at 4.2 K in fields up to 17 T. It was confirmed that the critical current of a twisted-tape was similar to that of a flat tape in c-axis fields. Based on the single-tape critical-currents, a 40-tape (4-mm width) twisted stacked-tape cable (TSTC) conductor was experimentally evaluated at fields up to 17 T at 4.2 K. It was found that the Lorentz load degradation of the TSTC conductor was negligible at the end of a cyclic test. The TSTC cabling method has been considered to be suitable for developing a high-field high-current REBCO conductor for magnet applications as well as power transmission cables. A method to fabricate the inner legs of a D-shape toroidal field coil using a TSTC conductor has been discussed. This method allows the conductor to properly resist the transverse Lorentz load and mitigate ac loss issues by adopting a parallel-HTS-tape flat cable configuration where necessary.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

A Low Loss, Fast Ramp HTS Solenoid Prototype for Compact Spherical Tokamaks

To explore AC loss characteristics of commercial Bi-2212 conductors made in the USA, a small ohmic heating (OH) prototype coil is being developed for compact tokamaks using high performance Bi-2212 wires newly manufactured by Bruker EST. Here, the goal is to build and test Bi-2212 prototype coils for fast ramp central solenoid (CS) operation of spherical tokamaks (ST). For a ST pilot plant, one of the key challenges is the tight space available for CS in a center column where in-board legs of the toroidal field (TF) and OH coils are assembled into a cryostat with a few millimeters clearance. A high current density Rutherford cable consisting of 17 legacy Bi-2212 wires, a contribution of the US Magnet Development Program (MDP), was fabricated at the Lawrence Berkeley National Laboratory (LBNL) for the development of fast ramp CS magnets in the ST Advanced Reactor (STAR) designed by PPPL. Characterization of the new and legacy HTS wires is presented, along with the coil design wound directly with new wire, and a Rutherford cable-wound solenoid using the legacy wire. A comparison of AC losses is made based on expected performance for a fast ramp ST operation. The HTS cable and cabled coil fabrication issues such as the heat treatment, coil mandrel design, assembly and 2212 quench characteristics are discussed, along with a test plan for CS design validation.

Zhai, Yuhu [Princeton Plasma Physics Laboratory (P↗
DOE OSTI2018

Design of a Modular E-Core Flux Concentrating Transverse Flux Machine

In this paper, a novel E-Core transverse flux machine (TFM) is proposed. The machine has a double stator-single rotor configuration with flux concentrating ferrite magnets and pole windings across each leg of an E-Core stator. E-Core stators with the proposed flux-concentrating rotor arrangement result in better magnet utilization and higher torque density. The machine also has a modular structure facilitating simpler construction. This paper presents a single phase and a two-phase version of the E-Core machine. Case study for a 1 kW, 400 r/min machine for both the single phase and two-phase TFM is presented.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2018

Cogging torque minimization in transverse flux machines

This study presents the design considerations in cogging torque minimization in two types of transverse flux machines. The machines have a double stator-single rotor configuration with flux concentrating ferrite magnets. One of the machines has pole windings across each leg of an E-Core stator. Another machine has quasi-U-shaped stator cores and a ring winding. The flux in the stator back iron is transverse in both machines. Different methods of cogging torque minimization are investigated. Key methods of cogging torque minimization are identified and used as design variables for optimization using a design of experiments (DOE) based on the Taguchi method. A multi-level DOE is proposed as an optimization method to reach an optimum solution with minimum simulations. The case study is analyzed in a two level DOE optimization. Finite element analysis is used to study the different effects. Two prototypes are fabricated for validating the FEA results.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2020

A New Configuration of Paralleled Modular ANPC Multilevel Converter Controlled by an Improved Modulation Method for 1 MHz, 1 MW EV Charger

In this work, a new configuration of the modular multilevel converter (MLC) based on the parallel connection of three-level active-neutral-point-clamped (3L-ANPC) cells as well as its improved modulation method is proposed for 1 MHz, 1 MW electric vehicle (EV) megacharger. In the proposed paralleled modular ANPC-MLC, only six high-frequency silicon carbide (SiC) power switches operating at 333 kHz are required to generate 1 MHz switching frequency spectrum. Moreover, the operating voltage of all power devices is halved, the magnitude of the first switching frequency harmonic cluster is decreased by the factor of five, and the load current is equally distributed between the 3L-ANPC legs by employing the proposed improved modulation method. Hence, the modularity, efficiency, and power density of the proposed converter are notably increased, whereas the value of passive components and the overall switching loss are remarkably decreased. In addition, an optimized design of the one 3L-ANPC cell of the proposed paralleled modular ANPC-MLC for 1 MHz, 1MW EV megacharger using Ansys SIwave, Icepak, and Q3D finite element method platforms is presented and analyzed in detail. The provided experimental results of the down-scaled setup verify the feasibility and viability of the proposed configuration as well as its improved switching pattern.

42 ENGINEERING↗
DOE OSTI2016

Model predictive direct power control for active power decoupled single-phase quasi- Z -source inverter

In this study, the active power filter (APF) that consists of a half-bridge leg and an ac capacitor is integrated in the single-phase quasi-Z-source inverter (qZSI) in this paper to avoid the second harmonic power flowing into the dc side. The capacitor of APF buffers the second harmonic power of the load, and the ac capacitor allows highly pulsating ac voltage, so that the capacitances of both dc and ac sides can be small. A model predictive direct power control (DPC) is further proposed to achieve the purpose of this newtopology through predicting the capacitor voltage of APF at each sampling period and ensuring the APF power to track the second harmonic power of single-phase qZSI. Simulation and experimental results verify the model predictive DPC for the APF-integrated single-phase qZSI.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2014

A High Temperature Silicon Carbide mosfet Power Module With Integrated Silicon-On-Insulator-Based Gate Drive

Here we present a board-level integrated silicon carbide (SiC) MOSFET power module for high temperature and high power density application. Specifically, a silicon-on-insulator (SOI)-based gate driver capable of operating at 200°C ambient temperature is designed and fabricated. The sourcing and sinking current capability of the gate driver are tested under various ambient temperatures. Also, a 1200 V/100 A SiC MOSFET phase-leg power module is developed utilizing high temperature packaging technologies. The static characteristics, switching performance, and short-circuit behavior of the fabricated power module are fully evaluated at different temperatures. Moreover, a buck converter prototype composed of the SOI gate driver and SiC power module is built for high temperature continuous operation. The converter is operated at different switching frequencies up to 100 kHz, with its junction temperature monitored by a thermosensitive electrical parameter and compared with thermal simulation results. The experimental results from the continuous operation demonstrate the high temperature capability of the power module at a junction temperature greater than 225°C.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Short-Circuit Characterization and Protection of 10-kV SiC mosfet

This paper presents the characterization of the temperature-dependent short-circuit performance of a Gen3 10 kV/20 A silicon carbide (SiC) mosfet. The test platform consisting of a phase-leg configuration and a fast speed 10-kV solid state circuit breaker, with temperature control, is introduced in detail. A novel FPGA-based short-circuit protection circuit having a response time of 1.5 μs is proposed and integrated into the gate driver. The short-circuit protection is validated through the platform. The short-circuit characteristics for both the hard switching fault and fault under load (FUL) types at various dc-link voltages (from 500 V to 6 kV) are tested and discussed. The saturation current increases with dc-link voltage and achieves 360 A at 6 kV. Different from low voltage SiC devices, there is no current spike in FUL type of fault. The temperature-dependent short-circuit performance is also presented from 25 to 125 °C. The difference of short-circuit waveforms at various initial junction temperatures can be neglected. Here, a thermal model of the 10-kV SiC mosfet is built for the junction temperature estimation during the short circuit and for analysis of the initial junction temperature impact on the short-circuit performance.

10-kV SiC mosfet↗
DOE OSTI2021

The Impact of Inverter Dead-Time in Single-Phase Wireless Power Transfer Systems

In this paper, the effect of the dead-time on a single-phase wireless power transfer system is studied in detail. In practice, the dead-time is always placed between the complementary switching pulses of the inverter phase-leg. At higher operating frequencies, the dead-time issues in the resonant inverter become critical, especially as the power level increases. The detailed analysis of the dead-time on a wireless power transfer system is discussed for different operating conditions of the inverter duty-cycle and power factor. The switching characteristics of the wireless power transfer system inverter are analyzed, and the notch phenomenon that appears at the output of the inverter is also discussed. A notch equation based on the observations is derived to predict the notch occurrence during the system operation. Furthermore, the mathematical expressions are presented for different notch conditions. Subsequently, the effect of the notches on the sensitivity and the power transfer of the series-series compensated wireless power transfer system is analyzed. Finally, the approach is verified experimentally on an 8 kW wireless power transfer system prototype, and the results are compared with the theoretical analysis.

42 ENGINEERING↗
DOE OSTI2018

Active Recycling Control Through Lithium Injection in EAST

The coating of tokamak walls with thin layers of lithium has been demonstrated to reduce plasma recycling from the plasma-facing surfaces and to improve overall plasma performance. These effects, including reduced divertor D α emission, the elimination of edge-localized modes, and increased energy confinement have been observed in multiple experiments when lithium coatings are applied before plasma discharges. However, this coating technology does not extrapolate to future long-pulse devices, since the lithium coatings will be passivated by the continual plasma flux onto the surface. In order to provide active conditioning capability, a new technology has been developed that is capable of injecting lithium powder into the scrape-off layer plasma during plasma discharges, where it quickly liquefies and turns into an aerosol. The use of this “lithium dropper” is under study at the Experimental Advanced Superconducting Tokamak (EAST), where the potential benefits of real-time wall conditioning via lithium injection are being tested. Here, we present an analysis of the recycling characteristics during EAST experiments testing active lithium injection in order to assess recycling reduction and control. Lithium aerosol was injected from the top of the machine, with one system dropping lithium near the X-point and another into the low-field side divertor leg. The injection of lithium into the SOL reduced divertor recycling, as evidenced by reduced D α emission with ion flux measured by probes relatively unchanged. This effect is strongest in the active divertor, confirming the lithium is transported to strongly plasma-wetted areas. Furthermore, quantitative analysis of the recycling changes using the SOLPS edge plasma and neutral transport code indicated a ~20% reduction in recycling coefficient with lithium injection.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗