Fast charging of electric vehicles (EVs) requires isolated AC/DC converters with a wide output voltage range of 200V to 1000V. Combining a three-level Vienna Rectifier (VR) with four isolated Dual-Active-Bridge DC/DC Converter (DABC) modules and latest-generation 600V GaN technology enables very high switching frequencies of 560 kHz for the VR and up to 330 kHz for the DABCs. Hence, in this paper an ultra-compact realization of a 10 kW EV charger module with a power density of 9 kW/dm ³ (about 150 W/in ³ ), not including the coldplate, is presented. In this context, a simplified DABC modulation method and straightforward yet accurate (confirmed by experiments) loss models for the DABCs and the VR are introduced, which facilitate a thorough investigation of the optimum synergetic operation of the two stages: For the considered converter, changing the VR operating mode from conventional 3/3-PWM (where the two stages operate rather independently and hence all three VR bridge-legs operate with PWM) to 1/3-PWM (where the DABCs shape the voltage of the shared intermediate DC-link such that always only one of the VR’s three bridge-legs must operate with PWM) results in an advantageous efficiency improvement of up to about 2% over a large part of the output voltage and power range, and in a peak efficiency of more than 97%. Further, the synergetic operation of the two-stage system (VR and DABCs) is experimentally verified for the first time, confirming the modeling results and the efficiency advantage of 1/3-PWM (i.e., 95.4% vs. 95.1% at the rated load of 10 kW and with 500V output voltage). Conducted EMI pre-compliance measurements indicate that the change of the operating strategy from 3/3-PWM to 1/3-PWM only requires minor changes of the EMI filter design.

In the energy distribution grid of electric vehicles (EVs), multiple different voltage potentials need to be interconnected, to allow arbitrary power flow between the various energy sources and the different electrical loads. However, between the different potentials, galvanic isolation is absolutely necessary, either due to safety reasons and/or due to different grounding schemes. This paper presents an isolated three-port DC/DC converter topology, which, in combination with an upstream PFC rectifier, can be used as combined EV charger for interconnecting the single-phase AC mains, the high-voltage (HV) battery and the low-voltage (LV) bus in EVs. The proposed topology comprises two synergetically controlled and magnetically coupled converter parts, namely, a series-resonant converter between the PFC-sided DC-link capacitor and the HV battery, as well as a phase-shifted full-bridge circuit equivalent in the LV port, and is mainly characterized by simplicity in terms of control and circuit complexity. For this converter, a simple soft switching modulation scheme is proposed and comprehensively analyzed, in consideration of all parasitic components of a real converter implementation. Based on this analysis, the design of a $3.6$ $\mathrm{k}$$\mathrm{W}$, 500 $\mathrm{V}$/500 $\mathrm{V}$/15 $\mathrm{V}$ prototype is discussed, striving for the highest possible power density and as low as possible manufacturing costs, by using PCB-integrated windings for all magnetic components. The hardware demonstrator achieves a measured full-load efficiency in charge mode of 96.5% for nominal operating conditions and a power density of $16.4$ $\mathrm{k}$$\mathrm{W}$$\mathrm{L}$⁻¹.

This paper extends the Generalized Steinmetz Equation (GSE) to account for the influence of mechanical stress on ferrite core losses. Experimental measurements are used to quantify the effects of compressive and tensile stresses on the relative permeability and the core losses of different ferrite materials. Mechanical stress is found to significantly affect the core losses, depending on the relative orientation of the magnetic flux density and the applied mechanical stress. Specifically, the losses monotonically increase when the flux and compressive stress vectors are parallel, while perpendicular vectors lead to a more complex response depending on the level of mechanical stress. The measured loss characteristics are translated in an extension of the GSE (X-GSE), which is validated for different ferrite materials, and provides a useful tool for a first rough estimation of the core losses under mechanical stresses. Finally, FEM simulations demonstrate how thermally induced mechanical stresses in a ferrite core can redistribute the magnetic flux and therefore impact the resulting core losses, which underlines the importance of considering the stress dependence of core losses in ferrite, especially in the development of magnetic components to be encapsulated in incompressible materials.

For power electronic converter systems, the cost and the size of the magnetic components are typically limiting factors when it comes to overall production costs and power density. This especially holds for soft-switching high-frequency applications, where a resonant discharge of the output capacitances of the semiconductors relies on sufficient amount of energy stored in the main magnetic components, i.e. inductors or transformers, yielding a substantial increase in their volumes. In this paper, an alternative solution is introduced, where a small auxiliary circuit is used to ensure soft-switching of the power transistors, whereby the aforementioned volume of the main magnetic components can be significantly reduced. The proposed auxiliary circuit provides zero-voltage-switching conditions independent of the applied voltages, the switching frequency and the output power level, without significantly increasing the circuit complexity or the control effort. The concept is first analyzed based on simple analytical calculations and circuit simulations, and is then experimentally verified by means of hardware demonstrators related to a ${3.6kW 250\dots 500V/250\dots500V}$ series-resonant DC/DC converter application. Finally, it is shown that the auxiliary circuit can also be used to pre-charge the output capacitor of a converter system, which allows to further reduce the size of the main magnetic components.

The next-generation industrial environment requires power supplies that are compact, efficient, low-cost, and ultra-reliable, even across mains failures, to power mission-critical electrified processes. Hold-up time requirements and the demand for ultra-high power density and minimum production costs, in particular, drive the need for power converters with (i) a wide input voltage range, to reduce the size of the hold-up capacitor, (ii) soft-switching over the full input voltage and load ranges, to achieve low losses that facilitate a compact realization, and (iii) complete PCB-integration for low-cost manufacturing. In this work, we conceptualize, design, model, fabricate, and characterize a $1.5$ $\mathrm{k}$$\mathrm{W}$, 12 $\mathrm{V}$-output DC/DC converter for industrial power supplies that is required to operate across a wide 300 $\mathrm{V}$–430 $\mathrm{V}$ input voltage range. This module utilizes an LLC-based control scheme for complete soft-switching and a snake-core transformer to divide the output current with a balanced flux among multiple secondary windings. Detailed loss models are derived for every component in the converter. The converter achieves close to 96% peak efficiency with a power density of 337 $\mathrm{W}$ ${\mathrm{in}}^{-3}$ ($20.6$ $\mathrm{k}$$\mathrm{W}$/${\mathrm{d}\mathrm{m}}^{-3}$), excellent matching to the derived loss models, and zero-voltage switching even down to zero load. The loss models are used to identify improvements to further boost efficiency, the most important of which is the minimization of delay times in synchronous rectification, and a subsequent improved $1.5$ $\mathrm{k}$$\mathrm{W}$ hardware module eliminates nearly 25% of converter losses for a peak efficiency of nearly 97% with a power density of 308 $\mathrm{W}$ ${\mathrm{in}}^{-3}$ ($18.8$ $\mathrm{k}$$\mathrm{W}$ ${\mathrm{dm}}^{-3}$). Two $1.5$ $\mathrm{k}$$\mathrm{W}$ modules are then paralleled to achieve 3 $\mathrm{k}$$\mathrm{W}$ output power at 12 $\mathrm{V}$ and 345 $\mathrm{W}$ ${\mathrm{in}}^{-3}$ ($21.1$ $\mathrm{k}$$\mathrm{W}$ ${\mathrm{dm}}^{-3}$) with ideal current sharing between the secondary outputs and no drop in efficiency from a single module, an important characteristic enabled by the novel snake-core transformer.