Conductance Control for Electromagnetic-Compatible Induction Heating Appliances

The design requirements of induction hobs are strongly restricted by efficiency, heating performance, cost, the generation of acoustic noise, and electromagnetic compatibility (EMC). These two latter topics, cost and EMC, motivated the research presented in this article. The different levels at which the equivalent load of the induction hob is excited generate a variation of the equivalent impedance throughout the grid period even if all the other parameters are kept constant. This can cause a nonsinusoidal consumption of the grid current which goes against the compliance with EMC standards. This article proposes an online controller which controls the conductance seen by the inverter by only modifying the switching frequency throughout the bus period. This greatly reduces the harmonic distortion of the grid current, no matter what is the type of the vessel used. Moreover, it requires neither power-factor correction rectifiers nor any additional circuitry and it has a faster dynamic response with respect to the traditional solutions used in induction hobs due to its higher bandwidth.