Design and optimization of 3-kW inductive power transfer charging system with compact asymmetric loosely coupled transformer for special applications

摘要

Inductive power transfer (IPT) technology has become popular in wireless charging applications. Compared with the traditional 3-kW wireless charging application, the diameter for the primary coil and the secondary coil in this special design are required to be smaller than 260 and 110 mm, respectively. In order to achieve this target, an approach to design and optimize the loosely coupled transformer (LCT) is proposed to match the strict geometry limitation, while achieving the high conversion efficiency. Different from the traditional design method, the low resonant current and voltage stress are considered as the input of the design flowchart, especially the LCT. Thus, the overall conversion efficiency can be improved. Based on series-series (S-S) compensation topology, the parameter range of the LCT is determined by analyzing transformer-based equivalent model. To achieve the desired coil size, an asymmetric LCT with single-layer primary coil and three-layer secondary coil is designed and optimized by the proposed approach. Furthermore, the closed-loop controller with narrow frequency variation range is design to realize constant current (CC) charge and constant voltage (CV) charge. A 3-kW IPT charging prototype is built to demonstrate the validity of the proposed method. Experimental results show that the peak efficiency from input to battery load is 95.69% at 3-kW output power in the transition point from CC mode to CV mode.