Minimization of converter ratings for MW-scale inductive charger operated under widely variable coupling conditions

This paper proposes a combined design and control method for high power inductive battery charger applications where the coupling conditions vary significantly during operation. The method is aimed at minimizing the worst-case Volt-Ampere requirements of the power electronic converters, by utilizing resonant operation with controlled voltage amplitude at low coupling conditions and out-of-resonance frequency-control for high coupling conditions. The method is applied to the design of a 1MW inductive charger to be used with a battery-electric ferry, demonstrating considerable gain in terms of required converter ratings compared to equivalent systems based on conventional resonant control. Effectiveness and feasibility of the method are validated by experimental measurements from a scaled-down prototype.