Zero-voltage-switching (ZVS) of dual active bridge (DAB) converter and its range extension have been studied intensively. However, this paper proves that the external inductance location, i.e. placing on which side of the transformer, does affect the ZVS operation due to transformers' parasitic capacitances, in particular at a high switching frequency of higher than 1 MHz. Thus, this paper, for the first time, gives the mathematical model of the resonant transition during the dead time and thereby analyzes partial hard switching under different modulation schemes with consideration of transformer's parasitic capacitances. From the analysis of ZVS operation, the solution of splitting the interfacing inductance and placing them on both sides of the transformer is proposed and its associated methodology of selecting these inductances is introduced. It extends the ZVS for all the switching devices, therefore, enhance the efficiency or move losses away from the critical semiconductor devices. Finally, the theoretical analysis is verified by the experimental results from a 1 MHz Gallium Nitride (GaN) based DAB converter prototype.

Abstract-In this paper, an improved power flow model for dual active bridge (DAB) converters with phase-shift modulation is introduced. Based on the analysis and the accordingly derived equations, a power plateau phenomenon, in which the phase shift loses its power-regulating capability, is investigated. Moreover, it is found that this power plateau phenomenon leads to an inversed power flow characteristic in some specific regions compared to the models reported in previous literature. The characteristics of the power plateau and its occurring conditions are derived and analyzed in depth. The calculations, simulations and analyses have been verified by experiments.

Abstract-Developing bidirectional dc-dc converters has become a critical research topic and gains more and more attention in recent years due to the extensive applications of smart grids with energy storages, hybrid and electrical vehicles and dc microgrids. In this paper, a Partial Parallel Dual Active Bridge (P 2 DAB) converter, i.e. low-voltage (LV) side parallel and high-voltage (HV) side series, is proposed to achieve high voltage gain and low current stress over switching devices and transformer windings. Given the unmodified P 2 DAB power stage, by regulating the phase-shift angle between the paralleled active bridges, the power equations and voltage gain are then modified, and therefore the operation range can be extended effectively. The operating principles of the proposed converter and its power characteristics under various operation modes are studied, and the design constraints are discussed. Finally, a laboratory prototype is constructed and tested. Both simulation and experimental results have verified the proposed topology's operation and design.

This paper presents a lossless power flow model and an improved power flow model of the Partial Parallel Dual Active Bridge (P 2 DAB) dc-dc converter with single-phase-shift modulation (SPSM). The improved model considers the dead time and the parasitic elements. A GaN based P 2 DAB converter prototype is built to verify the models. The lossless model is more accurate than the other at small phase shift region, while the improved one is more accurate at medium and large phase shift region. The cause of the errors are discussed, and the solution to improve the accuracy is provided. Moreover, the improved model provides more details about the power flow characteristics than the lossless model.

The magnetoelectric (ME) composite with the flux concentration effect is designed, fabricated, and characterized for detecting weak ac magnetic-field. The high-permeability Fe73.5Cu1Nb3Si13.5B9 (FeCuNbSiB) foils act as flux concentrators and are bonded at the free ends of traditional ME laminates. With the improved ME responses in the proposed ME composite based on the flux concentration effect, the output sensitivities under zero-biased magnetic field can reach 7 V/Oe and 15.8 mV/Oe under the resonance frequency of 177.36 kHz and the off-resonance frequency of 1 kHz, respectively. The results indicate that the proposed ME composites show promising applications for high-sensitivity self-biased magnetic field sensors and ME transducers.

Abstract-In order to achieve low switching frequency range and high efficiency for a wide-input LLC resonant converter, a new hybrid control combining pulse-frequency modulation (PFM) and phase-shift pulse-width modulation (PS-PWM) is proposed. In the new control, the LLC converter has two operation modes, i.e PFM and PFM+PS-PWM. The new control scheme and operation principle is analyzed deeply, and then efficiency optimization can be carried out by the proposed design procedure for the resonant tank of LLC converter. Finally, a prototype is developed with input voltage range from 22V to 45V, and rated power of 250W and output voltage of 380V. The experiment shows that the peak efficiency of LLC converter reaches to 96.2%, and verifies the proposed control scheme, design.

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