Wireless power transfer (WPT) via magnetic induction is an emerging technology thatis a result of the significant advancements in power electronics. Mobiles phones cannow be charged wirelessly by placing them on a charging surface. Electric vehicles cancharge their batteries while being parked over a certain charging spot. The possibleapplications of this technology are vast and the potential it has to revolutionise andchange the way that we use today’s application is huge.Wireless power transfer via magnetic induction, also referred to as inductive powertransfer (IPT), does not necessarily aim to replace the cable. It is intended to coexistand operate in conjunction with the cable. Although significant progress has beenachieved, it is still far from reaching this aim since many obstacles and design challengesstill need to be addressed. Low power efficiencies and limited transfer rangeare the two main issues for IPT. A tradeoff is usually associated with these two issues.Higher efficiencies are only achieved at very short transmission distances, whereastransferring large amounts of power at large distances is possible but at reduced efficiencies.This thesis addressed the limitations and design challenges in IPT systems such aslow efficiency and short transmission range, in addition to poor power regulation andcoil displacement and misalignment sensitivity. Novel circuit topologies and designsolutions have developed for DC/AC inverters and DC/AC rectifiers that will allowfor increased performance, higher efficiencies and reduced sensitivity to coil misalignmentsand displacements.This thesis contributes in four key areas towards IPT. Firstly, a detailed mathematicalanalysis has been performed on the electric circuit model of inductively coupled coils.This allows for better understanding on how power is distributed amongst the circuit’selements. Equivalent circuit representations were presented to simplify the designprocess of IPT systems. Secondly, a review of the different classes and configurationsof DC/AC inverters that can be used as primary coil drivers in IPT systems werepresented. Class E DC/AC inverters were mathematically analysed in great detail andtheir performance as primary coil drivers in IPT systems was investigated. Thirdly,novel electronic tuning methods were presented to allow Class E primary coil driversto operate at optimum switching conditions regardless of the distance between thecoils of an IPT system and the value of the load. The saturable reactor was used as theelectronic tunable element. Lastly, Class D and Class E AC/DC rectifiers have beenused for the first time in IPT systems. Detailed mathematical analysis and extensiveexperimental results show their superior performance over the conventional half-waveand full-wave AC/DC rectifiers.
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