Contactless energy transmission with optimal efficiency

The paper describes a theoretical and experimental analysis to aid the design optimization in case of the series resonant converter (SRC) operating with a loosely coupled transformer as in contactless power transfer. The main objective of this work is to give an idea about the more efficient modes of operation of the power stage. This study permits to define design criteria for the power circuit parameters in a normalized form (frequency, characteristic impedance, transformer ratio, etc) in order to optimize the efficiency. The analysis includes also a specially made ferrite transformer with two separately wound half-cores, in order to evaluate analytically and experimentally the changes in magnetizing and leakage fluxes and inductances caused by the distance between the halves. It is shown that at practical values of this distance, the leakage inductance remains almost unchanged. Nevertheless the current distribution between the primary and the secondary windings changes drastically due to the large variation of the magnetizing inductance. The analysis is leading to a set of equations describing these features. A graphically represented solution showing the way to an optimized operation of the converter is the contribution to the design of more efficient converters functioning with loosely coupled transformers.