James Scofield

Coupled Inductor Characterization for a High Performance Interleaved Boost Converter

Interleaved power converter topologies have received increasing attention in recent years for high power and high performance applications. The advantages of interleaved boost converters include increased efficiency, reduced size, reduced electromagnetic emission, faster transient response, and improved reliability. The front end inductors in an interleaved boost converter are magnetically coupled to improve electrical performance and reduce size and weight. Compared to a direct coupled configuration, inverse coupling provides the advantages of lower inductor ripple current and negligible dc flux levels in the core. In this paper, we explore the possible advantages of core geometry on core losses and converter efficiency. Analysis of FEA simulation and empirical characterization data indicates a potential superiority of a square core, with symmetric 45deg energy storage corner gaps, for providing both ac flux balance and maximum dc flux cancellation when wound in an inverse coupled configuration.

High-frequency design considerations of dual active bridge 1200 V SiC MOSFET DC-DC converter

Silicon carbide (SiC) is more favorable than Silicon (Si) to build high voltage devices due its wider band-gap and higher critical field strength. Especially, the SiC MOSFETs are finding their niche in 1 kV range, which is currently dominated by Si IGBTs. This paper aims at demonstrating high power and high frequency operation of the SiC MOSFETs, as a means to evaluate the feasibility of using SiC MOSFETs for high power density applications. The sample devices chosen for this study are 1200 V, 20 A, SiC MOSFETs co-packed with 10 A JBS diodes — manufactured by the CREE Inc. A dual active bridge (DAB) converter has been built to validate the suitability of SiC devices for high power density converters. The design details of the DAB hardware, and the high frequency transformer used for interfacing both the bridges are given. Experimental results on the DAB at 100 kHz switching frequency are presented. Finally, the device switching waveforms up to 1 MHz are given.

High temperature operation of a dc-dc power converter utilizing SiC power devices

Performance of a 2 kW, 40 kHz, 270 V/500 V boost dc-dc power converter as a function of temperature is reported for the following power semiconductor device combinations: Si MOSFET and Si ultrafast diode, and SiC MOSFET and SiC Schottky diode. The test results clearly demonstrate the possibility of designing 200 degC power converters utilizing SiC power semiconductor devices

200°C Operation of a DC-DC Converter with SiC Power Devices

Design, operation, and performance evaluation of a 180 W, 100 kHz, 270 V/28 V two-transistor forward dc-dc power converter are reported for elevated temperatures up to 200°C. Use of SiC power semiconductor devices, and high temperature powdered ferrite (for magnetics design), and characterization of ceramic (X7R) capacitors leakage current over temperature are presented as well.

Experimental Investigation of DC-Bias Related Core Losses in a Boost Inductor

Soft magnetic components in electronic systems are often subjected to dc bias-flux conditions. These dc bias conditions result in distorted hysteresis loops, increased core losses, and have been shown to be independent of core material. The physical origin of these increased losses is not well understood and there is no simple model that can predict these losses without extensive measurements. Absence of a widely accepted model coupled with the complete lack of dc loss attributes on core manufacturers data sheets result in a requirement to empirically determine loss values for specific design applications. These deficiencies have motivated our efforts to investigate dc bias dependent loss phenomenon in a Fe-based Metglas core inductor operating in a dc-dc boost converter. Since dc flux levels in the core are proportional to the controllable converter load currents, this topology is ideal to study dc-related losses. Inductor core B - H hysteresis loop characterization was accomplished as a function of switching frequency, input voltage, and load current operating conditions and parameters. In this paper, the core loss results were presented as a function of the dc bias conditions, and the results showed that the core losses increased with the pre-magnetized (Bde) fields. As a result of our observations, we have proposed a modification to the conventional Steinmetz loss equation to include the effects of dc pre-magnetization flux in the core.

A comprehensive multi-mode performance analysis of interleaved boost converters

Interleaved power converter topologies have received increasing attention in recent years for high performance applications. In this paper, a comprehensive multi-mode performance analysis is presented for interleaved boost converters operating over the entire duty ratio range (0 ≤ switch duty ratio ≤ 1) under the continuous conduction mode (CCM) and two discontinuous conduction modes (DCMs). With inductor coupling factor and converter loading as parameters, key performance indicators such as the dc voltage gain, input ripple current, inductor ripple current, and output ripple voltage are presented in a normalized form to aid the converter design process. Transitions among the CCM and two DCM modes are clearly defined for the entire switch duty ratio range. Advantages of DCM operation such as reduced switching loss at the expense of undesired ringing are discussed. The comprehensive multi-mode analysis has been experimentally verified using a 250 W, 70 kHz prototype converter unit.

Performance analysis of a multi-mode interleaved boost converter

Interleaved power converter topologies have received increasing attention in recent years for high performance applications. The advantages of coupled interleaved boost converters include increased efficiency, reduced size, reduced electromagnetic emission, faster transient response, and improved reliability. In this paper, a comprehensive performance analysis is presented for a multimode interleaved boost converter operating under the continuous conduction mode (CCM) and two discontinuous conduction modes (DCMs). With inductor coupling factor and converter loading as parameters, key performance indicators such as the dc voltage gain, input ripple current, inductor ripple current, and output ripple voltage are presented in a normalized form to aid the converter design process. Transitions among the CCM and two DCM modes are clearly defined as part of the analysis. Advantages of DCM operation such as reduced switching loss at the expense of undesired ringing are discussed. The analysis presented is experimentally verified using a 250 W, 70 kHz prototype converter unit.

Development of A 4H-SiC CMOS Inverter

In this paper we report the first 4H-SiC CMOS inverter, which was designed to be integrated in the process flow of a 4H-SiC power DMOSFET. The channels of both of the n channel and p-channel MOSFETs of the inverter were 50 um wide by 3 um long. NMOSFET threshold voltage (VTH) ranged from 4.4 V at 25°C to 2.2 V at 250°C and PMOSFET VTH ranged from -4.75 V at 25°C to just under -4 V at 300°C. The transfer threshold voltage (Vm) of the 4H-SiC CMOS inverter was in a very tight range of 2.8 V to 2.9 V over the entire temperature range of 25°C to 300°C when using a drive voltage (VDD) of 10 V.

Femtosecond, two-photon laser-induced-fluorescence imaging of atomic oxygen in an atmospheric-pressure plasma jet

Femtosecond, two-photon-absorption laser-induced-fluorescence (fs-TALIF) spectroscopy is employed to measure space- and time-resolved atomic-oxygen distributions in a nanosecond, repetitively pulsed, externally grounded, atmospheric-pressure plasma jet flowing helium with a variable oxygen admixture. The high-peak-intensity, low-average-energy femtosecond pulses result in increased TALIF signal with reduced photolytic inferences. This allows 2D imaging of absolute atomic-oxygen number densities ranging from 5.8???×???1015 to 2.0???×???1012cm?3 using a cooled CCD with an external intensifier. Xenon is used for signal and imaging-system calibrations to quantify the atomic-oxygen fluorescence signal. Initial results highlight a transition in discharge morphology from annular to filamentary, corresponding with a change in plasma chemistry from ozone to atomic oxygen production, as the concentration of oxygen in the feed gas is changed at a fixed voltage-pulse-repetition rate. In this configuration, significant concentrations of reactive oxygen species may be remotely generated by sustaining an active discharge beyond the confines of the dielectric capillary, which may benefit applications that require large concentrations of reactive oxygen species such as material processing or biomedical devices.

Visible and Infrared Rare-Earth Activated Electroluminescence From Erbium Doped GaN

Room temperature visible and IR light electroluminescence (EL) has been obtained from Er-doped GaN Schottky barrier diodes. The GaN was grown by molecular beam epitaxy on Si substrates using solid sources (for Ga and Er) and a plasma source for N 2 . Transparent contacts utilizing indium tin oxide were employed. Strong green light emission was observed under reverse bias due to electron impact excitation of the Er atoms. Weaker emission was present under forward bias. The emission spectrum consists of two narrow green lines at 537 and 558 nm and minor peaks at 413, 461, 665, and 706 nm. There is also emission at 1000 nm and 1540 nm in the IR. The green emission lines have been identified as Er transitions from the 2 H 11/2 and 4 S 3/2 levels to the 4 I 15/2 ground state. The IR emission lines have been identified as transitions from the 4 I 13/2 and 4 I 13/2 levels to the 4 I 15/2 ground state. EL intensity for visible and IR light has a sub-unity power law dependence on bias current. An external quantum efficiency of 0.1% has also been demonstrated under a reverse bias current of 3.85 mA.