How to design phase lead feedback in a tesla coil?

Thread Starter

EthanWu0131

Joined Jan 16, 2024
22
Hello all, I'm working on a tesla coil driver based on the excisting UD2.7(https://www.loneoceans.com/labs/ud27/), and I'm having trouble with the feedback, more specifically the phase lead, below is the feedback circuit of the UD2.7.1713781877746.png
I made my own feedback which is a lot simpler but it gets the job done and drives the half bridge, but it lacks phase lead which leads to hard switching in the half bridge
1713782356962.png
below is the feedback, its pretty basic, L10 is the current transformer(coupled with the primary coil L5).
1713782374607.png
this is the half bridge output waveform, red is the current and green is the voltage, as you can see the feedback works fine but it switches when currents are very high.
1713782339812.png

and below is the current(R) and voltage(G) across the IGBT, the overlap is very bad
1713782897409.png

my question is how do I add phase lead to my feedback, the article I attached at the top suggested a RL filter, but I don't know how and where to put it, since my feedback and the UD2.7's are very different, I am hoping to shift the current to get zero current switching. If anyone is knowledgable about this please tell me how to implement phase lead to my feedback, I would very much appreciate it!

Btw these are all simulated in PSpice.
 
Last edited:

MisterBill2

Joined Jan 23, 2018
18,970
First, the display has way to many cycles displayed to be useful for evaluating the phase delay. two or three cycles can be useful.
Then, think about the relation of the RC time constant relative to the impedance of the IC ( Very great) and the signal source. Add a 100K resistor from the junction of R29 and C30 to get some phase delay. And as I did not do the math, you may need to experiment with the R and C values to get what you want.
 

Thread Starter

EthanWu0131

Joined Jan 16, 2024
22
First, the display has way to many cycles displayed to be useful for evaluating the phase delay. two or three cycles can be useful.
Then, think about the relation of the RC time constant relative to the impedance of the IC ( Very great) and the signal source. Add a 100K resistor from the junction of R29 and C30 to get some phase delay. And as I did not do the math, you may need to experiment with the R and C values to get what you want.
Hi, thanks for responding, I tried changing the RC as you suggested, however it doesn't seem to be making the delay, as I intended the RC to be a part of the voltage clamp(along with the 2 diodes). From what I'm seeing online, most people use a RL filter to make the current lag the voltage thus creating the phase lead, however I'm having issues on how to implement it into my circuit, I tried placing the RL between L10 and the 2 diodes, though it doesn't seem to make any difference, only made the signal worse and unstable.

https://www.loneoceans.com/labs/ud27/, this article has the RL phase lead implemented on another feedback circuit, though because it's quite different from mine I can't copy it.

also below is the simulation with fewer cycles if you need the info.(feedback output(R), half bridge V output(G), I output(B))
1713803725966.png

thanks again!
 

Thread Starter

EthanWu0131

Joined Jan 16, 2024
22
One option could be to reverse the polarity of the winding, to simulate a reversed phase shift.
hi, I tried reversing the polarity, this is how it turned out, the frequency is super high and the waveform is pretty unstable, I don't think this is the correct way to go unless there is something else I need to add to stabalize the signal. I think RL filter might be the best way to go but I'm not sure how to implement it, if you could shed some insight on this I would very much appreciate it!
1713844422506.png
 

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Thread Starter

EthanWu0131

Joined Jan 16, 2024
22
Could you elaborate on that, do you mean I don't need the RL filter, simply adjust the RC values till the waveform is stable? Also can you explain how changing the polarity can create phase lead, and is the phase lead amount adjustable since I need zero current switching, thanks?
 
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