Mutual Impedance of Small Ring-Type Coils for Multiwinding Induction Heating Appliances

This paper proposes a model of the mutual impedance between ring-type coils used in domestic induction hobs. Recent developments in these appliances have focused on flexible cooking surfaces, including adjustable-size or total-active surfaces. Flexible cooking surfaces are implemented by means of several small ring-type closely arranged coils, each one supplied by a resonant inverter. The basic winding is a ring-type circular small coil, whose self-impedance has been reported previously. In this paper, the coupling between coils in terms of impedance is derived. The coils are modeled as axisymmetric current density distributions with parallel revolution axes. The mutual impedance between the coils is obtained considering two media representing the load and the ferrite, respectively. Experimental measurements have been performed to validate the results.