Analysis of Output Current Characteristics for Higher Order Primary Compensation in Inductive Power Transfer Systems

Constant output current is desirable for some wireless power transmission applications such as charging batteries and driving light-emitting diodes. Converters having an inherently small output current fluctuation versus variations of load and coupling are attractive solutions since such converters can be controlled to achieve constant current with minimum control efforts. In this paper, the impedance conditions and the output current characteristics for different compensation types are presented. It is shown that the types of compensation producing load- and coupling-independent output current at the designed operating point as well as having a unimodal dependence of the output current on coupling would achieve better output current performance against variations of load and coupling. The sensitivities of the output current to parameter variation of typical compensation types are quantitatively analyzed and compared. Analytical results indicate that the primary parallel-series and secondary series compensation, which produces output current that exhibits a unimodal relationship with coupling and is nearly immune to coupling variation at the designed operating point, has the smallest output current fluctuation versus variation of the coupling coefficient. Finally, a comparison of experimental results of different types of compensation is presented for verification.