Power Calculation for Induction heating devices

[sabu31]

Hi All,

I would like to know how to calculate output power (electrical) of a half bridge series resonant induction heating system. Can this be measured through oscilloscope which has builtin power measurement feature. The main doubt is regarding the phase difference between the load voltage and load current, how to do we know how much is apparent power and how much is real power (used in heating).

Thanks & Regards,

 

[KlausST]

Hi,

how to do we know how much is apparent power and how much is real power

I don´t understand .. because that´s exactly the benefit of a scope view.
You can show both V and I waveforms and visually compare them.
Many scope even provide an X * Y multiplacation for P(t) = V(t) * I(t).

Klaus

 

[Easy peasy]

If you have a DC source you can measure the volts and amps from this - most of this will end up in the load

alternatively you can use a fast scope with maths capability and a good AC current probe - multiply the V & I going to the load and get the real power.

 

[mtwieg]

Depends what you mean by "output power". If you're referring to the total power absorbed by your coil+sample being heated, then you can measure I and V with your scope and calculate power as you described.

Yes, any phase skew between the two will affect the measured power. The higher the Q of the resonant system, the greater this effect will be. You should check this phase skew by testing with a known resistive load first.

It might be better measure I and V across the combined series resonant circuit, that way V and I should be roughly in phase (minimizing reactive power in the measurement). The downside is your measurement will also include losses in the capacitor.

If you are referring specifically to the power into the sample being heated, I don't believe there's a way to measure this directly. Would have to characterize the resistance of the coil, and use that to make a correction to the measurement described above.