Hiroyuki Kosai

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.

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.

AC Magnetic Heating of Superparamagnetic Fe and Co Nanoparticles

AC magnetic heating of superparamagnetic Co and Fe nanoparticles for application in hyperthermia was measured to find a size of nanoparticles that would result in an optimal heating for given amplitude and frequency of ac externally applied magnetic field. To measure it, a custom-made power supply connected to a 20-turn insulated copper coil in the shape of a spiral solenoid cooled with water was used. A fiber-optic temperature sensor has been used to measure the temperature with an accuracy of 0.0001 K. The magnetic field with magnitude of 20.6 μT and a frequency of oscillation equal to 348 kHz was generated inside the coil to heat magnetic nanoparticles. The maximum specific power loss or the highest heating rate for Co magnetic nanoparticles was achieved for nanoparticles of 8.2 nm in diameter. The maximum heating rate for coated Fe was found for nanoparticles with diameter of 18.61 nm.

High Temperature DC-DC Converter Performance Comparison Using SiC JFETs, BJTs and Si MOSFETs

The performance and characterization of SiC JFETs and BJTs, used as inverter switching devices, in a 2 kW, high temperature, 33 kHz, 270-28 V DC-DC converter has been accomplished. SiC and Si power devices were characterized in a phase shifted H-bridge converter topology utilizing novel high temperature powdered ferrite transformer material, high temperature ceramic filter capacitors, SiC rectifiers, and 10 oz. 220oC polyimide printed circuit boards. The SiC devices were observed to provide excellent static and dynamic characteristics at temperatures up to 300oC. SiC JFETs were seen to exhibit on-resistance trends consistent with temperature-mobility kinetics and temperature invariant dynamic loss characteristics. SiC BJTs exhibited positive temperature coefficients (TCE) of VCE and negative β TCEs, with only a 2-fold increase in on-resistance at 300oC. Both SiC power devices possessed fast inductive switching characteristics with τon and τoff ~100-150 ns when driving the transformer load. The SiC converter characteristics were compared to Si-MOSFET H-bridge operation, over its functional temperature range (30-230oC), and highlights the superiority of SiC device technology for extreme environment power applications.

Hysteresis loss analysis of soft magnetic materials under direct current bias conditions

Direct current bias related hysteresis loss characteristics of three commercially available magnetic materials: (1) an iron based Metglas tape core, (2) a Sendust powder core, and (3) a Mn-Zn based ferrite in both un-gapped and gapped configurations were studied. The measurements are conducted for a fixed external field Hext, a fixed flux swing (ΔB), and a fixed maximum forward magnetization (Bmax) as a function of the external bias field. In all the measurements, a direct correlation is found between permeability and measured loss values as a function of dc bias field. Increased hysteresis losses are measured in the magnetization rotation region in which classical domain theory predicts minimal losses. The observed trends are discussed within the frame work of classical domain theory.

High temperature capacitor performance in a high power, high frequency converter

Evolutionary increases in the demand on aircraft electrical power systems have resulted in the need to develop the next generation of compact, power dense, electrical systems. These systems will utilize robust and efficient high voltage power devices that are operable over an extended temperature range (-55°C to 250°C). Recent advances in SiC power devices and high temperature magnetic and insulation materials have stimulated the development of compact, high switch rate power system components that can operate at higher temperatures. These efforts have highlighted the need to develop capacitor technology for high power, high frequency power filter applications, which can cycle over a wide range of temperatures. Stacked ceramic and wound polymer capacitors are evaluated as output filter capacitors in a high power, high frequency DC-DC converter from 25°C to 200°C. Experimental data are compared with SPICE simulations and thermal modeling to provide a basic understanding of how the capacitor architecture, its electrical and thermal properties, and thermal stability affect its performance.