Robustness of a Resonant Controller for a Multiphase Induction Heating System

This paper presents a robustness study of the current control scheme for a multiphase induction heating system. Resonant control has been chosen in order to achieve a perfect current reference tracking in the inductors with different solutions from the literature. A simplified model of the system is given; it is based on data extracted from finite-element software, including a model of the energy transfer between the dc source and the currents. The metal sheet resistivity will change with temperature, inducing some modifications in the system parameters. These disturbances will be rejected by the resonant controllers whose pole and zero variations are investigated. In addition, the tuning method for the resonant controllers is detailed when the sampling frequency/switching frequency ratio is very low. Some specific stability zones are defined for the resonant controller gains. The application is currently developed on a test bench devoted to disc induction heating.