Wireless charging using a separate third winding for reactive power supply

Abstract

In this thesis, three different models of wireless charging systems were investigated theoretically and experimentally. The first model that was evaluated was a basic model of a two winding wireless charging system with a capacitor connected in series with each of the coils. An auxiliary winding was added on top of the transmitter coil in order to provide the reactive power and two different topologies of three winding wireless transfer systems were compared to a basic model. The first three winding model had a capacitor connected in series in the receiver loop and in the auxiliary loop, while the last model of a wireless charging system had a capacitor in every loop. In order to predict the behaviour of each wireless charging system, a simulation in Matlab/Simulink was made, as well as the Bode plot for the transfer function of each system. After some practical measurements, it was found that the best overall efficiency was for a basic two winding model, which was 64%. The three winding model with two capacitors had 57% efficiency, while the model with three capacitors had 61% efficiency. These values are rather low compared to the usual values of the efficiency for a wireless charging system for low power, and the main reason is that there were high copper losses, because Litz wires were not used in the experiment.