Analysis and Modeling of Planar Concentric Windings Forming Adaptable-Diameter Burners for Induction Heating Appliances

Adaptable-diameter inductors are being implemented in domestic induction hobs in order to increase the range of suitable pot diameters and to achieve the better use of the rated power electronics. Such inductors are arranged by means of several concentric planar windings, usually up to three units, each one of them comprising several litz-wire turns. Currently, one resonant inverter is dedicated to supplying each winding. In this paper, a characterization of these inductors in terms of their impedance matrix is derived. The self-impedance of each winding and those caused by the coupling between them are analyzed. The contribution of this paper lies in the understanding and analysis of the coupling between concentric windings. Unlike transformers, where ideally the magnetic path consists of a lossless material, in domestic induction heating, the vessel is part of the flux path. Consequently, the off-diagonal terms of the impedance matrix have been generalized because they have a resistive component in addition to the classical mutual-inductance component. The analysis presented in this paper 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 their concentric neighbors.