IH technology finds its wide application to melting, welding, hardening, cooking and other fields. IH applications use high current passing through an induction coil to produce a sufficient magnetic field and Eddy current within work pieces. Operating frequency is selected by heating application. Resonant circuits are commonly used in IH application to produce powerful current and high voltage to provide maximum output power to the heating load. Recently, the L-LC resonant topology has been widely introduced for its many advantages.
It is widely known that switching devices can be damaged from NON-ZVS operation and spike current generated during the phase shift angle adjustment with fixed frequency to vary the output power and that when the load parameter is changed due to the workpiece, the temperature is close to the Curie temperature. Therefore, the switching frequency must be controlled when the phase shift angle and load parameters are varied to maintain the ZVS operation and prevent the switching device from spike current.
Ri Nam Jin, a researcher at the Faculty of Automation Engineering, proposed a variable frequency phase shift control (VFPSC) to guarantee the ZVS operation and protect the switch from spike current during the heating process.
The proposed technique achieved more efficient performances than conventional fixed frequency control strategies by eliminating NON-ZVS operation and spike current caused by the change of output power and load and guaranteeing zero voltage switching (ZVS) during output power regulation. The theoretical results were verified experimentally on L-LC resonant inverter.
The experiments to validate the proposed control method were conducted on an induction melting of a 3kg Nickel work piece from room temperature to the melting point of 1 600℃.
© 2021 KumChaek University of Technology