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Abstract In this study, dense bulk iron nitrides (FexN) were synthesized for the first time ever using spark plasma sintering (SPS) of FexN powders. The Fe4N phase of iron nitride in particular has significant potential to serve as a new soft magnetic material in both transformer and inductor cores and electrical machines. The density of SPSed FexN increased with SPS temperature and pressure. The microstructure of the consolidated bulk FexN was characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID) magnetometry. XRD revealed a primary phase of Fe4N with secondary phases of Fe3N and metallic iron. Finite element analysis (FEA) was also applied to investigate and explain localized heating and temperature distribution during SPS. The effects of processing on interface bonding formation and phase evolution were investigated and discussed in detail to provide insight into fundamental phenomena and microstructural evolution in SPSed FexN. Graphic abstract

Future high-density power electronics applications may require high-temperature optoelectronic devices for gate drive. Thus, a systematic study of optoelectronic material from 10 to 800 K has been performed to understand the potential of the high-temperature operation of optoelectronic devices. The temperature dependence of the photoluminescence (PL) of indium gallium nitride/gallium nitride multiple quantum wells was studied. The integrated PL intensity dropped by an order of magnitude at 800 K compared to 10 K. The spontaneous emission quantum efficiency was calculated from the power-law relation linking the integrated PL signal and the excitation pump power. The validation of the traditional ABC model for solid-state lighting is extended to 800 K. This paper demonstrates the feasibility of developing high-temperature optoelectronic devices, which have operating temperatures over 500 K.

Novel multilayered FeSiCrB-Fe x N (1 = 2-4) metallic glass composites were fabricated using spark plasma sintering of FeSiCrB amorphous ribbons (Metglas 2605SA3 alloy) and Fe x N (1 = 2-4) powder. Crystalline Fe x N can serve as a high magnetic moment, high electrical resistance binder, and lamination material in the consolidation of amorphous and nanocrystalline ribbons, mitigating eddy currents while boosting magnetic performance and stacking factor in both wound and stacked soft magnetic cores. Stacking factors of nearly 100% can be achieved in an amorphous ribbon/iron nitride composite. FeSiCrB-Fe x N multilayered metallic glass composites prepared by spark plasma sintering have the potential to serve as a next-generation soft magnetic material in power electronics and electrical machines.

This paper compares the long-channel and short-channel 3300-V, 5-A silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) manufactured by GeneSiC regarding static characteristics and short-circuit (SC) sustaining capability. Their saturation currents were measured up to 2200-V drain bias at different gate voltages. The SC withstand times of two types of devices were measured at 2200-V drain voltage and 1S-V gate voltage. Their SC test results were compared with 1200-V SiC MOSFETs from four different manufactures, which suggested that SiC MOSFETs with longer channel length should have longer sustaining times in a SC event. In addition, the device dynamic characteristic was evaluated. A comprehensive simulation program with integrated circuit emphasis (SPICE) model was developed based on the device test results.

The paper proposed a novel three-phase single stage AC-DC converter for grid energy storage applications. Variable-frequency (VF) and dual-phase-shift (DPS) modulation are utilized in this Dual-Active-Bridge (DAB) converter to realize power-factor correction (PFC) and zero voltage switching (ZVS). An optimal control is applied to reduce switching loss and increase system efficiency. The prototype is tested to verify the novel control. An efficiency of 96.5% is achieved at 6.6 kW power

Commercial light emitting diode (LED) materials - blue (i.e., InGaN/GaN multiple quantum wells (MQWs) for display and lighting), green (i.e., InGaN/GaN MQWs for display), and red (i.e., Al0.05Ga0.45In0.5P/Al0.4Ga0.1In0.5P for display) are evaluated in range of temperature (77–800) K for future applications in high density power electronic modules. The spontaneous emission quantum efficiency (QE) of blue, green, and red LED materials with different wavelengths was calculated using photoluminescence (PL) spectroscopy. The spontaneous emission QE was obtained based on a known model so-called the ABC model. This model has been recently used extensively to calculate the internal quantum efficiency and its droop in the III-nitride LED. At 800 K, the spontaneous emission quantum efficiencies are around 40% for blue for lighting and blue for display LED materials, and it is about 44.5% for green for display LED materials. The spontaneous emission QE is approximately 30% for red for display LED material at 800 K. The advance reported in this paper evidences the possibility of improving high temperature optocouplers with an operating temperature of 500 K and above.

In grid energy storage systems based on batteries, the interface converter topology plays a significant role in the optimized operation of the system. Among the different types of transformer-less high-power converters, the split battery type modular multilevel converter (SBMMC) has become a promising technology for interfacing the storage system with a medium voltage grid which can also perform battery management. This paper proposes a droop-based control for state of charge (SoC) balancing among the battery packs in SBMMC for a grid-connected battery energy storage system (BESS). First, steady-state analysis of the SBMMC is performed which forms the basis for SoC balancing scheme. Consequently, the droop-based control is applied to balance SoCs among the arms and submodules (SM) by controlling the reference voltages. For SoC balancing among the three phases of the upper and lower arms, appropriate zero sequence voltage (ZSV) is injected to the respective reference voltages of each arm. The proposed SoC balancing method has been validated through simulation results.

The spontaneous emission quantum efficiency (QE) of InGaN/GaN MQWs with different wavelengths was studied using photoluminescence (PL) spectroscopy. The QE was calculated from the power-law relation linking the integrated PL and the excitation pumping power.

In grid energy storage systems based on batteries, the interface converter topology plays a significant role in the optimized operation of the system. Among different types of multi-level converters, cascaded H-bridge converter (CHBC) provides the advantage of utilizing isolated battery pack (BP) with a lower number of series-connected cells and can perform state of charge (SoC) balancing by controlling the power flow to/from each BP. However, the rate of SoC balancing is limited due to low balancing current when the amount of power exchange is low. This paper proposes a new power control method using hybrid modulation strategy with extended operating region (HMSEOR) which enables the CHBC to perform fast SoC balancing at constant current irrespective of the amount of power exchange between the battery system and the grid. The HMSEOR allows power flow from a BP with a higher SoC to a BP with a lower SoC without compromising power exchange with the grid. The performance of the proposed SoC balancing method is validated through real-time hardware-in-the-loop (HIL) simulation and compared with the conventional SoC balancing at unity power factor operation.

A systematic study of wide bandgap (WBG) based light emitting diodes (LEDs) and photodiodes (PDs) were conducted for the assessment of modular integration of optoelectronic devices into power modules. The temperature dependence of the photoluminescence (PL) efficiency of Indium gallium nitride/Gallium nitride (InGaN/GaN) multiple quantum wells (MQWs) material was studied from 10 to 800 K. The photoluminescence efficiency is calculated using the power law relation connecting the integrated photoluminescence signal and the excitation pump power. A peak PL efficiency of 43.97 % was recorded at 800 K. Electroluminescence (EL) study was conducted on Gallium nitride (GaN) based LEDs in the temperature range of 300 – 800 K. An intensity drop of three orders of magnitude is recorded at 800 K as compared to room temperature. The full width half maximum (FWHM) of the spectra was also calculated from the EL measurements. The S-shaped shift of FWHM at high temperature indicates a strong localization effect. High-temperature spectral response analysis of 4H-Silicon carbide (4H-SiC) pn-junction photodiode is performed at zero voltage bias condition. Enhancement of spectral response is observed at higher wavelengths due to increased phonon population at higher temperatures.

In this paper, Triple Active Bridge Converter (TABC) based Cell Level/Sub-Modular level power processing Battery Energy Storage System (BESS) is proposed to provide better efficiency, reliability and safety benefits. One TABC is connected to the two cells/two sub-modules of the battery pack, and all outputs of the TABC’s are connected in series or parallel to achieve the required voltage or current. The main features of the proposed configuration are: to avoid the unnecessary charging/discharging phenomena, providing the isolation, and to improve the optimal power flow of each cell of the battery. Also, secondary voltage compensation and droop based decentralized control scheme is proposed to improve the power-sharing of each TABC and voltage regulation at the battery output under the effect of cable resistance considered. The proposed configuration and control strategy is validated under different loading conditions by MATLAB®, SIMULINK®.

Temperature and power dependent photoluminescence (PL) measurements from InGaN/GaN MQWs has been studied from 77 to 800 K to extract the PL efficiency. The laser powers at maximum quantum efficiency in a wide range of temperatures are calculated.

This paper proposes a Distributed Power Processing based Battery Energy Storage System (DPP-BESS) for improving the performance and reliability of the battery storage system. One dedicated Dual Active Bridge Converter (DABC) is connected to each cell of the battery pack, and all outputs of DABC are connected in a series-parallel combination as per the requirement for dc-link voltage, and power rating of the DPP-BESS. The main features of the system are: to determine the charging/discharging characteristics of different types of battery cells, to avoid the unnecessary discharging/charging phenomena in the battery within one cycle time, providing isolation between cells and the central inverter, and to improve the optimal power flow to/from each battery cell. Operating principle, design optimization, small signal modeling, and control scheme of the system are presented. The performance of the proposed system is validated through simulations in MATLAB®, SIMULINK®.

Cell-level power processing in battery packs can provide better efficiency, reliability and safety benefits. As part of a broader investigation of how dual-active bridges can be used for such processing, a secondary voltage control and droop control strategy have been examined for the distributed power processing based battery (DPPB) energy storage system. The control strategy is divided into primary cell-level control with high gain droop and secondary voltage control and stability analysis. The performance of proposed control strategy is validated under different loading conditions by MATLAB®, SIMULINK®. The control strategy improves the power sharing of each cell in a DPPB, and voltage regulation of DPPB output.

A technique to characterize interface traps near the minority carrier band for wide bandgap metal-oxide-semiconductor (MOS) capacitors at room temperature is presented. The method uses photogeneration of minority carriers and transient analysis of the subsequent photocapacitance decay to evaluate trap response times. The technique is demonstrated using n-type substrate 6H- SiC/SiO2 MOS capacitors to extract interface trap density (Dit) ranging in energy from 0.2 to 0.8 eV above the valence band edge (Ev) and trap cross sections from 0.4 to 0.7 eV above Ev. For the given material system, traps near Ev exhibit significant differences between n-and p-type substrate MOS capacitors.

Interest in improving energy security and reducing carbon emissions have led to significant investment in renewable power generation such as wind and solar. However, the intermittent nature of these energy sources necessitates the implementation of grid-level energy storage systems to provide the base-line power that is currently provided by non-renewable sources (coal, nuclear, etc.) Significant investment in improved transmission capability (e.g. high-voltage DC) will also be required to deliver power from potentially remote generation and storage locations to heavily-populated urban areas where demand is highest. Portable energy storage systems are also likely to play a role. Power electronics is the common element linking energy generation, storage, and consumption. For example, inverters are required to transform DC power from photovoltaic arrays or battery-based storage into AC power suitable for grid transmission, and Flexible AC Transmission Systems (FACTS) are necessary to efficiently control the flow of power in a “smart grid” implementation [1]. Power semiconductor switching devices are at the heart of all power electronics systems. While Si-based devices have been effectively utilized for many years, emerging devices based on the wide-bandgap semiconductor Gallium Nitride (GaN) offer potentially disruptive improvements in efficiency, thermal management, and system complexity. Several DOEsponsored programs at Sandia National Laboratories are currently addressing the issues associated with the implementation of wide-bandgap power electronics from the systems level, through the circuit and device level, down to the material and atomic level, where we investigate the fundamental defects responsible for performance and reliability of this emerging technology. This talk will thus be in two parts. The first part will discuss the systems-level motivation for moving to widebandgap power devices, while the second part will discuss some of the detailed work we are doing to solve the reliability problems currently facing GaN-based power devices. GaN has been a popular and extensively studied material for Radio-Frequency (RF) applications. RF AlGaN/GaN High Electron Mobility Transistors (HEMTs) aim to achieve large piezoelectric polarization and the highest possible channel density by utilizing a high Al molefraction in the AlGaN barrier layer. However, for power devices, achieving high breakdown voltage is not possible with very high channel electron density. Also, the high mechanical strain due to large lattice mismatch is detrimental to device reliability under the harsh operating conditions of a power device. Therefore, a reduced Al molefraction becomes necessary to adapt the AlGaN/GaN HEMT to high-power applications. In this work, the effects of reducing the Al molefraction in the AlGaN layer on the charge trapping behavior (and hence the stability) of the device are studied. This charge trapping is recoverable, and is thus distinct from reported permanent failure modes such as the inverse piezoelectric effect [2]. The effect of surface passivation and the interplay of surface charge on breakdown voltage is a key factor in the optimization of the design and processing of the device. HEMTs utilizing Al0.15Ga0.85N and Al0.26Ga0.74N barriers, both with and without surface passivation, are studied. Various experimental techniques are utilized to characterize charge trapping centers in the devices. Previous studies have shown the presence of multiple trapping and detrapping components in AlGaN/GaN systems [3]. For relatively shallow traps, the current-transient-based multiple exponential method [4] is employed (Figure 1). For deeper traps, emission following exposure to monochromatic light of variable wavelength is used (Figure 2). Additionally, the spatial location of charge traps is studied by measuring the surface potential within the device using Kelvin Force Microscopy (KFM). The combination of these techniques provides a comprehensive picture of the traps responsible for electrical degradation and instability in AlGaN/GaN power HEMTs. Such instability is one failure mechanism that ultimately limits the implementation of these GaNbased devices in grid-level power switching applications.