Projects:2016s1-196 Wireless Power Transfer
Contents
Project Team
Supervisors:
- Dr Withawat Withayachumnankul
Students
- Hang Yin
- Matt Reynolds
Introduction
Wireless power transfer (WPT) is a technology that exploits magnetic, electric or electromagnetic fields to transmit electric power without conductors. This project aims to develop a magnetic WPT system for charging portable devices. The system consists of an oscillator, an amplifier, two coils, a rectifier and the load.
Motivation
The WPT technology has been widely used, especially power charging for portable devices, medical implants and electric vehicles. However, the contradiction between high efficiency, small size and long distance has limited the commercial applications of WPT. Current applications have to sacrifice one of these parameters. Designers should adjust these parameters carefully to meet the requirements of a specified application. Suitable coil design and frequency selection can also improve efficiency without affecting size and distance [1].
Objectives
Since the developed system shall be able to reach a balance between efficiency, size, distance and output power, the following objectives shall be achieved:
-The output power shall be more than 100 mW.
-The efficiency shall be greater than 60% at a distance of less than 1 cm.
-The system shall be portable. Its size shall be like a common mobile phone.
Previous Studies
The efficiency of some commercial WPT systems has been tested in several studies. Siddabattula [4] reports that current Texas Instrument WPT system achieves 60% efficiency. According to Perzow [5], EPC-9112, a commercial WPT system developed by Efficient Power Conversion Corp, reaches up to 51% efficiency.
Several studies have been performed to improve the efficiency of WPT. Students of the University of Adelaide [1] revealed the main factors that affect efficiency via simulation, optimised coil design and achieved 61% efficiency at 50cm distance by using 50cm coil diameter. Karalis et al. [6] used magnetic resonance and achieved 40% at 2m distance. Zhang et al. [7] designed a omnidirectional WPT transmitter consisting of three orthogonal coils which can transfer power in 3D space.
Method
The coil-to-coil efficiency is first studied. It is demonstrated in section 1.3.3 that the coil-to-coil efficiency depends on the parameters of the coils, including R_1, R_2, L_1, L_2 and k. A model that simulates these parameters is built in Matlab. Using this model, the parameters of the coils which bring a balance between efficiency and output power are found.
Then the whole circuit is designed and construct. At the beginning, a signal generator was used as the oscillator since it is easy to adjust frequency. After the most efficient frequency was found, an oscillation circuit using 555 timer was designed to provide a fixed AC signal.
