Communications in IPT systems

Abstract

Inductive Power Transfer {IPT) is a method of transferring power across an air gap. Based upon the fundamentals of electromagnetism discovered by Ampere and Faraday, IPT takes advantage of the magnetic field around a current carrying conductor to couple energy from an elongated primary track to one or more secondary pickups. The power transfer is contactless, clean and robust and because of this IPT technology can be found in many industrial applications such as vehicle technology, materials handling systems, lighting and medical applications to name but a few. Traditionally the design and optimisation of IPT systems concentrated on the efficient transfer of power for end uses. However as IPT systems are used over an increasing range of applications there has become a need for communication systems, compatible with the power transfer process, to provide system control and data transfer capabilities. Both low bandwidth and high bandwidth communication channels are required and any channel should operate with all of the advantageous characteristics of existing IPT technology. This thesis presents the research undertaken to form both low and high bandwidth communication channels. The low bandwidth channel operates in the VLF band and data rates in the order of 20kbps can be achieved. The channel is formed by dual tuning the existing IPT hardware to two frequencies, one for power transfer and one for communications. Care must be taken to avoid noise caused by the various IPT system components. The high bandwidth channel is created by using ribbon cable transmission line as a distributed antenna along the length of an IPT system. By using newly invented near-field antennas, communications signals in the frequency range of 50 to 500MHz can be injected and received to a11d from the ribbon communications track. There have been two types of near-field antenna created for use on the ribbon cable communications track, these are the inductive and capacitive designs. The inductive design uses magnetic fields to couple signals to the track while the capacitive design uses electric fields. Both antenna types have been comprehensively and successfully tested in IPT environments. The high bandwidth communications channel can also be used to create a position location system for IPT applications. This is achieved by deliberately mismatching the communications track and then using nulls in the resulting standing wave pattern to calculate the location of one or more IPT carriers. The best modems to use on the high bandwidth communications channel are wireless LAN (WLAN) modems, however they operate at 2.4GHz. Modules have been designed and tested which frequency shift the WLAN signal down into the bandwidth of the communications channel. Using these modules data rates as high as 27Mbps can be achieved using standard WLAN operating modes. By taking advantage of the 14 different frequency channels over which WLAN modems can operate and the frequency dependent attenuation rate in a ribbon cable communications track, a cellular communications system has been proposed which would allow a continuous track to be segmented in frequency for an unlimited length. All the goals of the thesis have been met, and there are now various options for adding communications to IPT applications.