Numerical and experimental study of the effects of load and distance variation on wireless power transfer systems using magnetically coupled resonators

This work investigates ways of simulating a series resonant circuit designed to wirelessly transfer power to charge a battery of an electrical vehicle. A common approach assumes the load connected to the power transfer system to be constant and then the wireless link efficiency is studied. In practical engineering applications, however, the load and the distance between coils will vary influencing strongly the efficiency, which may also be affected by the presence of massive conducting or shielding structures in the proximity of the wireless system. Here we study these effects with the help of an equivalent circuit extracted from a full 3D field simulation and correlated with measured results. We reveal that by changing the load resistance the efficiency of the system can be improved, even for a large separation between the two magnetically coupled resonators; however, the maximum efficiency point may not correspond to the maximum power that can be handled by the system. We analyse the primary and secondary voltages and currents in support of the above findings.