# Induction heating conditions

Status
Not open for further replies.

#### Antares

##### New Member
Dear Forum,
I am a newbie here... lem me as some questions about the induction heating:

So suppose I have a source of an alternating current of some frequency.
I have a load (parallel resonant LCR circuit).

The frequency of the source matches the frequency of the parallel LCR circuit's resonant frequency. So I have a resonance in my circuit - this means that the voltage accross my parallel circuit is in phase with the current that source is supplying. In this case the power factor of the circuit - Cos(phi)=1 since angle phi is zero.

But when I instert a workpiece into the coil of my LCR circuit... the workpiece affects the inductive characteristics of the coil.. hence changing its unductive resistance (may be also some other parameters) and all this finally changes the resonant frequency to some other frequency. And since my source is working with constant old frequency - I am out of resonance (there is some non-zero degree between voltage and current) so the Cos(phi) is less than one and my power factor is worse.
So to mitigate this problem the "L-Matching" component is intorduced.. with the FINE TUNNING of the matching network (matching coil) it is intended to reduce the angle difference between the feeding voltage and feeding current of my load (LCR)... hence rising Cos(phi) as possible to 1 to match again the resonant condition.

Is my undesrtanding correct ?

Thank you very much for your assistance...

#### Warpspeed

##### Member

The best way to overcome this problem is to make the main high power resonant LCR circuit part of a big very high power oscillator.
The drive power into the tuned circuit is then always in the correct phase relationship, because the drive frequency actually fed back from the output tuned circuit.

When you insert a metal load into your induction heater, the frequency will certainly change, but the circuit continues to drive power into the resonant circuit always with the correct frequency and phase relationship.

This way, the circuit self adjusts in frequency to always operate exactly at resonance, where the efficiency and energy coupling is at maximum.

Last edited:
Status
Not open for further replies.

Replies
1
Views
855
Replies
1
Views
612
Replies
15
Views
14K
Replies
37
Views
9K
Replies
8
Views
1K