Transient and steady state modelling of inductive power transfer systems

Abstract

Inductive Power Transfer (IPT) is a method and technology through which power is transferred via magnetic fields from a primary power source to one or more galvanically isolated secondary loads. Applications for IPT can be found in situations where power is needed to be delivered to moving loads such as automated factory vehicles, or where galvanic isolation is seen as a great advantage such as outdoor electric vehicle charging. This thesis focuses on the modelling of IPT circuits and aims to develop a methodology through which simple transient and steady state expressions can be derived which contain useful information on the relationship between components and circuit behaviour. This is necessary as complex and intractable expressions result when existing analytical methods are applied, due to the deliberate use of resonant circuits in IPT systems. Envelope modelling is the term given to this new technique. It achieves the goal of producing simplified, yet relevant, expressions by focusing only on the magnitude information at the expense of frequency and phase. This is in direct contrast to general analysis methods which treat magnitude, frequency, and phase as separate variables of equal importance. By reducing the number of unknowns in envelope modelling, the number of variables necessary to describe a system is similarly reduced, thus resulting in simpler equations. Envelope modelling is theoretically shown to be valid in resonant circuits, and is subsequently used to derive transient and steady state expressions for practical IPT systems. The predictions made by these expressions are verified experimentally and shown to be valid. Design equations are thus able to be derived which consider transient behaviour. Envelope modelling is thus shown to be a valuable tool in the analysis and design of IPT systems.