Multiphase Resonant Inverter With Coupled Coils for AC–AC Induction Heating Application

In this article, a multiphase resonant inverter with vertical aligned coupled coils is proposed for an induction heating application, in which the proposed phase-shift control strategy improves the system power capability. The model for an <inline-formula><tex-math notation="LaTeX">$n$</tex-math></inline-formula> coil arrangement is developed using the impedance matrix approach, which allows a circuit representation by means of dependent sources. Each coil is part of a series resonant tank fed by a half-bridge inverter. In particular, the developed converter is evaluated for an <inline-formula><tex-math notation="LaTeX">$n=2$</tex-math></inline-formula> case, which is composed by two coils, whose commutation states and the typical waveforms for zero voltage switching operation are addressed in detail. Extensive SPICE simulations are accomplished for validating the analytical model under switching frequency, and duty cycle and phase-shift modulations are contrasted. The model parameters of the coils are obtained applying a nonlinear regression from the experimental data provided by an impedance analyzer. Afterwards, the system feasibility is corroborated using a 2-kW prototype with 97% maximum efficiency under wide load conditions for the aforementioned modulations.