Re: Parallel resonant DRSSTC

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Sparktron01@xxxxxxxxxxx 

Hi Sue

What you are mentioning is basically what is termed an 'LCL' inverter 
(Induction Heating Applications).  Using an LCL impedance matching circuit 
to "boost " primary  resonant current (and isolate he**ish peak currents 
for switching devices) is a worthy goal.  The difficulty with such a 
circuit is if there are load "discontinuities" there could be significant 
voltage kickback at the switching devices.  This is a significant design 
issue with high power SS induction heating drivers (100kVA - 1MVA +).  Here 
are several references concerning this topology...

http://www.srt.tu-darmstadt.de/pub/general/publicat/synopsis_PCIM.pdf

Modular, high power SS driver capable that can be scaled as large as your 
pocket book is deep...  ;^D

http://www.powerpulse.net/powerpulse/archive/aa_030501a1.stm
http://www.powerpulse.net/powerpulse/archive/aa_030501a2.stm
http://www.powerpulse.net/powerpulse/archive/aa_030501a3.stm

Design Optimiization Paper for Voltage fed LCL Converter

http://www.richieburnett.co.uk/indheat.html

Richie Burnett's (EXCELLENT!!!!) site with detailed explanation of a LCL 
Induction Heating Converter.  The impedance matching aspect of this design 
(IMHO) should be carefully considered.  Having <100A versus 1kA + going 
through your power devices might improve reliability just a slight 
bit...   ;^D.

I am doing some proprietary IH work at this time (for work  ;^D ), and I 
can provide numerous references that indicate:
1.  The fewer power devices in the power path, the more reliable the 
converter.

2.  A half bridge converter will oustensibly be nearly 2X more reliable (at 
least half as likely to have a destructive DC shoot through event) as a 
full bridge, and are commerically built for IH converters up to 25kVA+.  I 
don't think (at last check) anyone in the WORLD has a SSTC / SS Converter 
that big on the "amateur" level...

3.  Placing a DC buck regulator in series with the half bridge as a high 
speed current limiting/controlling means will also "dramatically" improve 
converter robustness and tolerance to "crazy" loads.  That's why LEPEL, 
Ameritherm, and other major IH manufacturers use this topology for IH 
applications for 100-400kHz, and IGBT converters up to 25 (maybe 50? ) 
kVA.  The only way you will damage an LCL converter of a half-bridge 
topology is if the load "shorts" or you short out the primary (which again 
IMO is highly unlikely).

4.  There are several converter topologies (Neutral Point Clamped [NPC] 
converter), as a half-bridge, may allow operation to "very high" input 
voltages (>1kV).  If you want high power, I truly believe that is the 
direction that MUST be taken.

I hope this information is useful, and Happy New Year to the Tesla List!

Best Regards
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA. USA



> Original poster: Sue Gaeta <sgsparky@xxxxxxxxxxx>
>
> Hi all,
>
> I was curious if anyone has ever tried designing a DRSSTC using a capacitor
> in parallel with the primary rather than in series with it. If something
> like that could work it would have a big advantage that the extreamly high
> primary current would be between the capacitor and primary, and there would
> be almost no current throgh the switching devices.
>
> Has anyone ever thought of something like this, or played with the idea
> with simulation software?
>
> What would be the disadvantage of something like that?
>
> Sue
>
>