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Induction Heater - Series Resonant - uC/PLL Tuning [ReactorForge]

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Josh Campbell

Tue Sept 04 2012, 03:52PM

Registered Member #5258 Joined: Sun Jun 10 2012, 10:15PM
Location: Missouri - USA
Posts: 119

Gabriel35 wrote ...

How are you measuring those waveforms on your scope? Using Differential probes right?

One would think so but no. The my differential probe has been shot for a while, a scope upgrade is in my near future so I'm waiting until then to get new probes. I just isolated the scopes ground and was careful which grounds I connected together with the scope probes. I usually leave my o-scope floating anyway to avoid ground loops.

teravolt

Wed Sept 05 2012, 04:14AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

hi 2bytes I recently aquired some celem caps and I am trying to make a decision on a 4046 circiut and I am interested how you integrated the pll with the micro and did you use a arduino?

it could have other applications for driving other circuits like DRSSTC

what is the advantages of using a micro with the 4046?

Josh Campbell

Sun Sept 09 2012, 05:46PM

Registered Member #5258 Joined: Sun Jun 10 2012, 10:15PM
Location: Missouri - USA
Posts: 119

teravolt wrote ...

hi 2bytes I recently aquired some celem caps and I am trying to make a decision on a 4046 circiut and I am interested how you integrated the pll with the micro and did you use a arduino?

it could have other applications for driving other circuits like DRSSTC

what is the advantages of using a micro with the 4046?

Hey Nathan sorry for the delay, I've been working on a really fun RGB LED project for a client and got side tracked from HV. :)
I'll post my current control schematic and a couple new photos in the OP. Basically I just have the uC inserted as the low pass filter for the PLL. The micro controller takes in the output of the the Phase Comparator I out through a low pass filter. From this we know what the current phase difference is between Fo (inverter drive frequency) and Tce (Voltage across tank the tank capacitor). As I'm sure you already know the tank voltage should lag behind the inverter drive F by 90 degrees at resonance. The uC simply outputs an analog voltage via filtered PWM to feed VCO in on the PLL. This allows us to do much more than a simple low pass filter. Soft starting/stoping, and current control by detuning to name a couple.

The original code was written in C using AVR Studio 6 when I was using the bread board and STK200. I moved to Bascom for the new board once I knew the hardware was working well because it makes it so quick and easy. Although the resulting code is not as optimized imo so I will eventually rewrite the basic for the final product in C.

I'm not a fan of Arduino, I guess because I've been using Atmel products for 10+ years, long before that thing came along. Plus I just make my own boards or have them made for less than the cost of an Arduino. But there is definitely value in them for the beginner or when in a hurry I suppose.

Josh Campbell

Wed Sept 12 2012, 04:40PM

Registered Member #5258 Joined: Sun Jun 10 2012, 10:15PM
Location: Missouri - USA
Posts: 119

BTW Nathan, that's a very nice setup.
Have you tested that push/pull coupling transformer setup yet? Would be interested to see how well that works. What type of cores are those, did you pick them up for this use or just have them lying around? Same thing with the Celem caps, did you source them just for this or just happen upon them? Sure would be nice if those were available as surplus somewhere.

teravolt

Mon Sept 17 2012, 03:04AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

hi Josh, sorry for the delay, I want to do the same thing you are doing but I want to use Raspberry Pi and python to make the same sort of driver.

I haven't applied the driver yet I ame looking at what type of circuit to drive it. I am not shure of what types of cores they are I know they were used for some sort of pulsed transformer aplication and I picked them up as surplus. I have used a signal generator and the resonant frequency is around 10k unloaded. the celems I got on ebay and I snached them up as soon as I soon as I could. The tank circuit has been upraded since the last picture and I will show later I added a mica wrap 3uf+celem 2uf+celem .1uf is my total capacitance. when I get back from yosemite I'll do another picture. what is the resonant freq unloaded. I cind of wanted ti do what Linas did with his

Josh Campbell

Mon Sept 17 2012, 03:26AM

Registered Member #5258 Joined: Sun Jun 10 2012, 10:15PM
Location: Missouri - USA
Posts: 119

HA, I was thinking of using a RasPi in my next version to talk to an FPGA so I could deal with the phase relation ship in real time. Although I think it might be a bit overkill and probably wont use it, a uController to interface with the FPGA is almost always sufficient. But who knows, I did already by this nice case for it from Polycase (highly recommended). Linas might have the better idea, just using a prebuilt controller, a lot of the buck/boost PF correction controllers for florescent lights would work too. They have every feature and more built in that you would need to run an IH. I really just wanted to do it myself in the raw to see what was happening, plus I like PLLs and micro controllers, you know getting your hands dirty and wrapping your mind around the fundamentals.
Have fun in Yosemite (if your going for fun) and keep us updated on your IH!

teravolt

Mon Sept 17 2012, 02:59PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I read some whare that a RPi has lots of interup cycles and that if real time controle is neaded that adruino is better. I am wating for the gert board wich has a aduino chip on it and that could be used to run the 4046 and make adjustments while rpi monitors. FPGA is definatly the way to go it seams. I am realy a newbe when it comes to programing but I know how to hardware. I thought pyton and C and linux are handy to know. maby it is pausible to make a PLL that is aduino based or like you say using a FPGA. micro mixed with analog is good. when I refired to Linas's thread he has some of thos poly caps that you use plus a celem and mixing caps can be tricky. In his setup I think that his poly caps do moast of the work because here XL is 10 times less than the celem and I want to balence it more and I am not shure if it is necisary with the celem. I have wated a long time to find some Celem caps that are afordable.

yosemite is nce and I haven't cought the Haunta Virus hear in curry village yet I hope

teravolt

Wed Sept 19 2012, 01:09AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

Hi Josh, here is a picture of my additions next week I hope to work on the igbt driver

teravolt

Wed Sept 19 2012, 02:14AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

oops sorry for duble poast

Josh Campbell

Wed Sept 19 2012, 03:11AM

Registered Member #5258 Joined: Sun Jun 10 2012, 10:15PM
Location: Missouri - USA
Posts: 119

That's looking great! I'm really interested in your push/pull coupler. Did you see that somewhere else or is that a Nathan original? Also what is that MMC on top of your Celems, are you trying to lower your resonant frequency with those? Or is it a DC filter array or snubber network? Also if that current clamp you have behind your work coil is an iron core you'll melt it, trust me. ;) You'll have to measure tank current by another means, there are a couple methods listed above, unless your running low power of course.

Just noticed you used compression connections, the flare tool is $15-30 and it's worth it. I highly recommend flare connections over compression.

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