FFEDBACK INDUCTION HEATER

[radbloke]

Before posting any real material I just wanted to find out if this is the appropriate section to start a post on an induction heater project I have going on??⚡️⚡️ The project which has gone through several iterations utilizes a current control circuit for the primary tank.

[klugesmith]

Most IH discussions have been under Electronic Circuits.

[radbloke]

OK folks, this is a very basic question but something that maybe somebody can answer because I’m not exactly sure what is the best approach – basically the issue is I built an approximately 10 kW induction heater. This is a series LC induction heater using a ferrite coupling transformer to transfer energy to the tank circuit. The coupling transformer is connected to the inverter. One of the outputs of the inverter is connected to the coupling transformer via a DC blocking capacitor, which has a higher value than the value of the tank circuit capacitor. The other output of the inverter is connected directly to the other end of the coupling transformer. Is the DC blocking capacitor really necessary and if so why?

[Anders Mikkelsen]

The bridge output doesn't have any DC component, in the ideal case, but in real life there can be some DC due to mismatched rise and fall times, uneven duty cycle, and other factors. With 400 V bus voltage for example, even just a quarter percent of imbalance will give a volt of DC on the output. And the primary of the transformer has a pretty low impedance at DC, leading to large current flow. If for example the DC resistance is 0.1 ohm, 1 V of DC imbalance causes 10 A of current to flow. In addition to causing losses, this current can saturate your transformer and cause it to draw a large and asymmetrical magnetizing current. So the DC blocking cap is practically always required, or at least strongly recommended.

[radbloke]

Thank you! That is very helpful and a great explanation!