Misalignment tolerance improvement of loosely coupled transformer with ferromagnetic materials via genetic algorithm

Abstract

In wireless power transfer (WPT) systems, misalignment between the primary and secondary coils can decrease the transmission efficiency of the loosely coupled transformer (LCT). Adding ferromagnetic materials or a relay coil is an effective solution for efficiency and misalignment tolerance improvement if extra eddy current loss and hysteresis loss on the ferromagnetic materials or the conduction loss caused by the relay coil is well controlled. The effect of ferrite cores on the transmission efficiency of two‐coil and three‐coil LCTs is analysed from the perspective of loss. By finite element analysis, the dimension of ferrite cores is optimised via the genetic algorithm to improve the efficiency and misalignment tolerance of the LCT. Optimal ferrite core dimension is also verified in a 1‐kW WPT prototype, and experimental results show that, after optimisation, transmission efficiency of the two‐coil LCT can be improved by 2.681% and 8.930% under alignment and the 200‐mm misalignment, and with the proposed control strategy, transmission efficiency of the LCT is always above 94.925% under various misalignment conditions.