This paper presents the design and analysis of a high-density two-stage battery charger for mid-power applications like small electric vehicles and high-performance laptops utilizing gallium nitride (GaN) power devices. In addition to adherence of maximum junction temperatures, a thermal analysis is carried out for in-housing operation, which is particularly critical for fanless wall chargers. Design measures include calorimetric semiconductor selection, half-bridge miniaturization, thermally conductive epoxy resin and reference-based convection modeling for thermally optimized component placement using 3D-stacking. Furthermore, the remaining optimization potential of the charger is estimated by virtual prototyping. A 170 W hardware prototype is developed and tested, achieving a two-stage power section efficiency of 95.4 % with a maximum switching frequency of 550 kHz. This results in a power density in open-housing operation of 1.6 kW / dm. Using epoxy resin, copper and graphite heat spreaders, an in-housing operation power density of 1.1 kW / dm is achieved with minor reduction of output power due to surface temperature constraints.

A detailed accuracy analysis of calorimetric measurements for benchmarking wide bandgap power transistors under soft-switching operation is presented. This paper will present a deeper insight into this method and propose enhancements to ensure higher accuracy of the extracted switching energy by evaluating the whole measurement and calculation chain. Furthermore, the confidence level for the switching energy can be derived for each measurement and the most critical errors of the presented measurement chain can be identified. A benchmarking of the soft-switching energies of different SiC and GaN devices is presented, compared to other work and discussed.

Virtual prototyping, multiobjective optimization, and design automation are increasingly being used to meet the growing demands of modern power electronic applications in terms of efficiency and power density. These concepts are based on accurate loss models of the power semiconductors used. While for hard-switching, the double pulse test is an established electrical characterization method, soft-switching losses can only be determined by calorimetric measurements. Despite significant improvements in using transient approaches, calorimetric characterization of soft-switching loss energy is very time-intensive and requires complex measurement setups. This article presents a new automated calorimetric method with thermal impedance calibration that enables rapid and noninvasive switching loss measurements. Using ultrafast transient measurements and accelerated cooling phases in between, soft-switching loss maps can be determined based on hundreds of individual readings. The proposed measuring method is validated against hard-switching electrical double pulse test measurements. The method achieves a maximum error of $1.9 \,\%$ for the total loss measurement from $1-9 \,\mathrm{W}$ and an average measurement error of $16.5 \,\%$ for the soft-switching energy from $1-4 \,\mu \mathrm{J}$ of wide bandgap power semiconductors. In addition to comparing the results of different semiconductor technologies for use in a charger application, the manufacturers' simulation models are also analyzed with respect to soft-switching energy.

This work presents a novel approach for the optimization of a self-oscillating power converter (Royer converter) based on GaN HEMTs for inductively coupled wireless power transfer applications. By combining gallium nitride high electron mobility transistors (HEMT) as power transistors and depletion-mode (silicon) transistors as control transistors, not only the better intrinsic performance of GaN is used, but also all auxiliary supply voltages can be omitted in comparison to the standard silicon transistor-based Royer converter. This paper describes the functional principle with the aid of a simulation based on an inhouse extended power transistor model and optimized transistor parameters. Then it gives insight into the novel prototype and demonstrates the operation at a resonance frequency and an output power of up to 500 kHz and 90 W at 30 V input voltage with peak efficiencies above 94% for the whole wireless power transfer system. Finally, the limitations and further optimizations for such Royer converter systems will be discussed.

Silicon carbide (SiC) MOSFETs are increasingly used in automotive applications due to their ability to operate at high frequencies and power levels, with high partial-load efficiency. However, gate-switching instability (GSI), which describes cycle-dependent degradation of the threshold voltage due to bipolar gate-switching, poses a major reliability concern. While extensive research exists on this phenomenon’s influence on static characteristics, such as on-resistance and threshold voltage, the impact of GSI on switching losses remains largely unexplored. This work provides a detailed analysis of this degradation mechanism on hysteresis, gate charge, capacitances, and switching losses. Key parameters, including drain current, drain voltage, and both positive and negative gate-to-source voltages, are examined to develop an aging-dependent switching loss model. The results show that after ${10}^{{12}}$ switching cycles at 18/–9 V gate–source voltage stress, turn-off losses slightly decrease in a planar 1.2 kV, 63m $\Omega $ SiC MOSFET. Furthermore, a current-dependent increase in turn-on losses is observed. Further analysis reveals that the degradation in threshold voltage is directly proportional to the increase in switching losses and can be effectively modeled by a decrease in the overdrive voltage for turn-on and an increase in the overdrive voltage for turn-off. Finally, the influence of degradation on switching and conduction losses is evaluated for a typical mission profile, yielding 2.2% degradation at 15V and 1% at 18V positive gate–source voltage.