Induction heating generators are series resonant inverters (SRI) or parallel resonant inverters (PRI) in which the resonant tank consists of an induction coil and a capacitor. They are used to heat metals to be welded, melted, brazed or hardened.
In order to regulate the output power, SRI uses a diode bridge rectifier as a DC voltage source, and employs frequency (FC), phase-shift (PS) variation or pulse density modulation (PDM). These power control schemes, however, may result in an increase of switching losses and electromagnetic noise because it is impossible for switching devices to be always turned on and off under zero-current condition.
Therefore, only MOSFET inverters can be used in high-frequency induction heating applications. Nevertheless, isolated-gate bipolar transistors (IGBTs) are preferred in high-power industrial applications.
Ri Nam Jin, a researcher at the Faculty of Automation Engineering, has proposed an induction heating system of 15kW and 30kHz for industrial applications, which uses a novel control scheme based on a PS IGBT full-bridge SRI that allows us to significantly improve its reliability by increasing the lifetime of IGBTs.
In this power control mode, load adaptive variable frequency regulation and automated dead-time management are performed simultaneously in order to ensure that the inverter ensures zero voltage switching at all power levels and load conditions.
The comparative study between the proposed method and standard PS power control has demonstrated the effectiveness of the proposed one.
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