Modeling of adaptable-diameter burners formed by concentric planar windings for domestic induction heating applications

Adaptable-diameter inductors are being implemented in domestic induction hobs in order to increase the range of suitable pot's diameters and to achieve a better use of the installed power electronics. Such inductors are arranged by means of several concentric planar windings, usually up to two or three units, each one of them comprising several Litz-wire turns. Normally, one resonant inverter is dedicated to supply each winding. In this paper, a model of these inductors in terms of their impedance matrix is derived. The self-impedance and the coupling between the windings are analyzed on the basis on the transformer analogy. The analysis also includes the losses in the Litz wires generated by the currents in each winding as well as the losses produced by the windings over its neighbors.