Development and implementation of a contactless inductive power transfer Qi compliant system
Document typeMaster thesis (pre-Bologna period)
Rights accessOpen Access
Wireless Power Transfer (WPT) is an emerging technology which has attracted a lot of attention in the current electronic market and its contribution is going to play an important role it in the near future thanks to its wide variety of applications fields and to its interesting features. Ranging from consumer electronics to medical implants devices to robotics to automotive applications, this technology it is used to charge the battery of these devices without wiring connections. The major drawback of currently available wireless power systems is the relatively low efficiency (<70%) mainly because of the receiver AC-DC power conversion. This power conversion has been typically performed with a bridge rectifier because of its simplicity and low cost, but with considerable power losses because of the diodes voltage drop. The main target of this project is to develop a WPT receiver prototype with discrete hardware compliant to the Qi standard replacing these diodes by MOSFET transistors and implementing a switching control for them which increases the efficiency of the rectifier and makes the system reliable. The transmitter is also developed to analyze the whole WPT system and study its behaviour. Therefore, a contactless inductive power transfer is implemented for low (5W) and medium power (15 W) to reproduce the most recent rectifier techniques of the state of art. Two different rectifier control approaches has been performed based on the Zero-crossing Voltage Detection (ZVD) and the Zero-crossing Current Detection (ZCD) methods. With the help of a FPGA the rectifier power switches are controlled using the ZVD and ZCD information. Several experimental results compares the traditional simple rectifier, with the method implemented, showing increasing efficiencies from 68 % up to 83 % for 5 W output power. An even higher efficiencies (over 90 %) for low output power [1 - 2 W].