Dynamic DC-Bus Voltage Control of Induction Hardening System Under Load Temperatures from Ambient to Beyond Curie Point

In this work, the DC-bus voltage level control of an industrial induction hardening system is studied for reduced load modeling including non-linearities on the electrical behavior. The power converter consists of 3-stage electronics: PFC rectifier, DC-DC converter, and high-frequency inverter, respectively. The power transferred to the load is controlled by varying the DC-bus voltage level of the inverter which works at a fixed frequency close to the self-resonant frequency of the load. The control variable is the output current of the inverter which strongly depends on the characteristics of the load composed of a coil and a workpiece. This load is typically modeled as a series RL-circuit. However, its values strongly depend on the frequency as well as the temperature of the workpiece and the magnetic field levels of the coil. The main characteristics of the load will be calculated from FEM-tool simulation including non-linearity dependencies. These results will be used to obtain a reduced model of the load capturing the main characteristics of its behavior in a wide range of temperatures from ambient to beyond the Curie temperature of the material. Finally, a full Simulink model with a reduced order load will be tested in an experimental setup.