Frequency-dependent modelling of domestic induction heating systems using numerical methods for accurate time-domain simulation

Domestic induction heating systems are usually modelled as an electrical equivalent composed of the series or parallel connection of an equivalent resistor and inductor. This model allows obtaining useful time-domain results in order to extract design conclusions for the power electronic converter. However, this model neglects the dependence of the equivalent electrical parameters with frequency. This dependence becomes a key parameter when the induction system varies the excitation frequency with the purpose of adapting the output power. In order to overcome this limitation, this study proposes a modelling strategy to take into account the influence of frequency divided into two steps. First, the frequency-dependent impedance is obtained by means of a finite-element analysis tool. Afterwards, a passive network composed of several inductors and resistors in series and parallel connection are used to fit the frequency response of the induction load. The proposed strategy allows obtaining a more accurate model of the induction heating load. Moreover, as there is no need to build previous prototypes, the design process is optimised. The feasibility of this proposal has been tested by comparing time-domain simulations with oscilloscope measurements in a real domestic induction heating system.