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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
You can't drive a parallel LC circuit with a voltage source inverter! :( It must be operating as a LCLR with the leakage inductance of the transformer as the matching inductor.
I've had a lot of success with pulse-skipping control for DRSSTCs and induction heaters. I dither the gate drive on and off using a flip-flop to switch only complete cycles, to avoid problems with DC offset.
Registered Member #1143
Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721
Steve Conner wrote ...
You can't drive a parallel LC circuit with a voltage source inverter! :( It must be operating as a LCLR with the leakage inductance of the transformer as the matching inductor.
I've had a lot of success with pulse-skipping control for DRSSTCs and induction heaters. I dither the gate drive on and off using a flip-flop to switch only complete cycles, to avoid problems with DC offset.
Yea, i guess i will try to make it with pulse skipping, what should not take much time with stm32f4 already up and running in discovery board add inductor in series to transformer secondary coil and that should solve my problem ? (well, if it's problem) just one question, will PLL be able to lock on resonance only with one impulse? i guess i only need one sense wire for STM32F4 for period counting and one output for PLL to enable/disable (5 leg should work ) two ideas so far: allow low/high signal and calculate frequency from that , at same time allow all impulse i need (lets say i allow 5, wait for 495, so that would be 1% of power, and use while loop for delay to get 495 , and allow 5 periods, wait 495 and so on, only problem it have to be spot on on turning on if LC circuit still have some juice left over.
second would be count LC circuit periods even then i have PLL disabled, for that i need to be able to see oscillations long time after PLL was disabled,so i need to check how long i have ringing in my LC circuit, and if i have more than 100 periods, what would be super :)
Registered Member #599
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
My transformer coupled series resonant induction heater is nowusing 3 phase SCR stack for power control. Control voltage for SCR rectifier is generated from ivnerter output current. Simple and very effective. Driver is locked dead on resonance as its basicly just drsstc driver with interrupter jumped permanently on.
So far 12kW, lots of popped 16A fuses and no problems at all.
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
Linas wrote ...
Uzzors wrote ...
Nope, it uses phase comparator II.
Where is special reason for that or just for layout simplicity ?
Phase comparator 2 causes no phase offset (0 degree shift) from the locked signal. Despite this you do end up with a phase shift in the end, which is adjusted by the potentiometer. I don't know how it works, but it does so quite well so I'm not complaining. I couldn't get a stable 90 degree lock using the XOR comparator.
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+10KW induction heater
