Single shot surface heating series resonant converter with ZCS and an uncontrolled DC link voltage

The voltage fed, full-bridge, series resonant circuit topology is commonly used for medium frequency, medium power induction heating applications. Different control loops, e.g. constant current, voltage or power, are implemented depending on the application. There are a number of possible switching strategies that can be used to realize this control, e.g. load resonance, swept frequency, phase shift control and burst control. In this paper it is shown that for the power densities and final temperatures used for the surface heating of carbon steel, the load resonant control strategy, but without controlling the DC link voltage, is well suited. The increase in the power obtained at the end of the heating cycle favors the final temperature rise. Experimental results are presented at 50 kHz and well above 10 kW.