Modeling of resonant inverters with high harmonic content using the extended describing function method

This paper analyzes the extended describing function technique (EDF) for modeling a resonant power converter applied to induction heating applications. Since in this specific application operating conditions may be far from resonance, this paper is focused on extending the model to several harmonics and verifying its validity range. The main goal is to obtain accurate control-to-power transfer functions which predict the resonant inverter small-signal behaviour. A simulation test bench is proposed and evaluated for measuring the open-loop duty cycle and frequency-to-power transfer function plots from time domain simulations of the switching model. Finally, the accuracy of the model is analyzed.