This paper proposes an improved analytical stray capacitance model for inductors. It considers the capacitances between the winding and the central limb, side limb, and yoke of the core. The latter two account for a significant proportion of the total capacitance with the increase of the core window utilization factor. The potential of the floating core/shield is derived analytically, which enables the model to apply not only for the grounded core/shield, but also for the floating core/shield cases. Based on the improved model, an analytical optimization method for the stray capacitance in inductors is proposed. Moreover, a global Pareto optimization is carried out to identify the trade-offs between the stray capacitance and ac resistance in the winding design. Finally, the analysis and design are verified by finite element method (FEM) simulations and experimental results on a 100 kHz dual active bridge (DAB) converter.

The photovoltaic (PV) output voltage varies over a wide range depending on operating conditions. Thus, the PVconnected converters should be capable of handling a wide input voltage range while maintaining high efficiencies. This paper proposes a new series resonant dc-dc converter for PV microinverter applications. Compared with the conventional series resonant converter (SRC), a dual-mode rectifier (DMR) is configured on the secondary side, which enables a twofold voltage gain range for the proposed converter with a fixed-frequency phase-shift modulation scheme. The zero-voltage switching (ZVS) turn-on and zero-current switching (ZCS) turn-off can be achieved for active switches and diodes, thereby minimizing the switching losses. Moreover, a variable dc-link voltage control scheme is introduced to the proposed converter, leading to a further efficiency improvement and input-voltage-range extension. The operation principle and essential characteristics (e.g., voltage gain, soft-switching, and root-mean-square current) of the proposed converter are detailed in this paper, and the power loss modeling and design optimization of components are also presented. A 1-MHz 250-W converter prototype with an input voltage range of 17 V-43 V is built and tested to verify the feasibility of the proposed converter. Index terms-PV microinverter, dc-dc converter, series resonant converter, wide input voltage range, 1-MHz frequency.

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Magnetic components are usually assumed relatively reliable in power electronic converters. Nevertheless, with the trend for ever-increasing power density, planar magnetics may need to be designed with reduced margins in terms of thermal and insulation. Wear out or even failure of magnetic components may become an issue in extreme design and operation scenarios. This paper presents the first observations in degradation testing of planar magnetics at high temperatures. It serves to investigate the change of various parameters and identify possible ones as the health indicators of magnetic components for power electronic applications. The degradation testing and characterization results are presented and interpreted.

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