Wireless Charger for Hand-held Mobile Devices

Abstract

This thesis describes the design and prototyping results of a low power wireless power transfer (WPT) system. In particular the design and testing of a transmitter.

Firstly, existing research is discussed and it is found that a significant part of this discusses higher power transfer systems. Here lies the challenge for this thesis: to find an efficient way of transferring a low amount of power wirelessly, with a significant distance between the transmitter and the receiver. Also, existing WPT standards were investigated and their shortcomings are discussed.

Secondly, the design of the transmitter is discussed. It starts out with the fundamental and circuit theory behind wireless power transfer. With this, it is found that tuning capacitors can greatly increase the efficiency of the system. Next, the design of the components in the coupled coils system is discussed, with calculations on equivalent series resistance for different frequencies. Furthermore, the functional block diagram consists of an oscillator, gate driver and inverter circuit and its design choices are discussed. The design concludes with a frequency optimization and simulation results.

Lastly, the design has been built and tested. A transmitter efficiency of 93.4 % has been reached at a coupling of around 0.1. This is at a distance of 20 millimeters. Further improvements may be done with the gate-driver. Control techniques may also prove beneficial for future work.