Power transfer capability and bifurcation phenomena of loosely coupled inductive power transfer systems

Loosely coupled inductive power transfer (LCIPT) systems are designed to deliver power efficiently from a stationary primary source to one or more movable secondary loads over relatively large air gaps via magnetic coupling. In this paper, a general approach is presented to identify the power transfer capability and bifurcation phenomena (multiple operating modes) for such systems. This is achieved using a high order mathematical model consisting of both primary and secondary resonant circuits. The primary compensation is deliberately designed to make the primary zero phase angle frequency equal the secondary resonant frequency to achieve maximum power with minimum VA rating of the supply. A contactless electric vehicle battery charger was used to validate the theory by comparing the measured and calculated operational frequency and power transfer. For bifurcation-free operation, the power transfer capability and controllability are assured by following the proposed bifurcation criteria. Where controllable operation within the bifurcation region is achievable, a significant increase in power is possible.

I. Introduction

The magnetic field has been widely used for the transfer of power or information. Traditionally, good coupling is fundamental for effective transfer of significant amounts of power such as in transformers and induction motors. Recently, developments in modern power electronics have enabled many new loosely coupled applications such as contactless battery charging across large air gaps [1]–[3]. Other examples include material handling systems [4]– [6] and people movers [7], where the secondary systems are electrically isolated and move along a long track. Fig. 1. Structure of LCIPT system. Electrical isolation is essential for power supplies in harsh environments such as mining and outdoor systems. The advantages of such loosely coupled inductive power transfer (LCIPT) systems are reliability and low maintenance.