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BSVi

Tue Jul 05 2011, 09:05AM

Registered Member #1637 Joined: Sat Aug 16 2008, 04:47AM
Location: Kiev, Ukraine
Posts: 83

Arcstarter, Steve Ward
Sorry, I confused "secondary tank impedance" which is 1/Q with secondary impedance, which is jwL.

GeordieBoy

I don't know if this is running directly off the mains supply?

It is fed from 220->12v linear transformer.

BTW, the capacitance between primary and secondary sides is as low as 12pf.

I'd definitely scratch that off if my life depended on isolation!

You are right! Thank you for pointing that out.

I have my controller board assembled now and it works well (at least, on test rig). I plan to make some power electronics this week, so stay tuned

JimmyH

Sat Jul 09 2011, 07:57PM

Registered Member #358 Joined: Sat Apr 01 2006, 06:13AM
Location: UCSB
Posts: 28

Shurely, the system will be able to supply power (it's drsstc after all), but with lowering Q the current ripple increases. I'm not shure about implications of high current ripple, so that's another thing to find out.

DRSSTCs ain't magic you know! If you drive it at the primary resonance frequency, it'll suck power, but it will have to ring up very high before any power is transferred to the secondary, and the load will be very tuning (ie streamer length) dependent. Steve has been driving his QCW at the other (upper) pole for these reasons. At the upper pole, it'll only pull significant power through a high Z primary tank if the tuning is just right, which it can't be for all frequencies.

Yep, I tried to simulate system with load and saw exactly what you are talking about - the current drops significantly with added secondary load. The solution is obvious - to decrease coupling, but I dont know if it would have "QCW effect" with low coupling.

Decreasing coupling or detuning would fix it in theory, but there are practical reasons to not be running the primary at an effective Q of 1000. The "QCW" effect is dependent only on the voltage history of the topload (for a given geometry, at least). Everything else is screened off so the sparks "can't know".

I think, you mean to increase secondary impedance, but secondary impedance is not something that you can rely on. It varies greatly with steammer loading. So decreased coupling looks like a better solution to me.

Secondary impedance (the amount of topload voltage divided by the circulating current) becomes a lot more stable when its low. If you stick 100 secondaries/toploads in parallel, it'll be much less disturbed by the same spark. This is the same as lowering inductance and increasing capacitance.

There are two advantages of storing the energy in the secondary instead of the primary. The first is that it's easier to come up with a capacitor on the secondary side that can handle the current, the second is that you can always drive the upper pole without tuning issues.

Steve and I didn't settle on this idea because we weren't sure if it'd work with poor regulation, but it might. Just make sure whatever drive setup you choose can pump a half amp into realistically modeled streamers at 50kv before you start actually making the thing.

BSVi

Mon Aug 29 2011, 06:00AM

Registered Member #1637 Joined: Sat Aug 16 2008, 04:47AM
Location: Kiev, Ukraine
Posts: 83

Hi, I'm sorry for being absent for this long. Now I'm ready to return to my design.

Control electronics is ready and functional, but I'm in doubt about resonator design (I know, it's complicated thing). It's great if anybody is eager to help me.

Input data:
I have irg4pc40w transistors with 40amps of constant current rating.
Also, I have nice small toroid with 5pF capacitance

That's all :)

I tried to simulate resonator as shown in attachement. I'm unable to acheive half an amp into 300k load (is it reallistical model of streamer?)

You also need to tune the primary and switch it to operate at the primary zero

How can I do that? Both poles has higher gain, any self-resonating circuit will lock on any of them. Anyway, when I lowering coupling for the system to work, zero dissapears (look at my ac simulation in attachement). If I increase coupling, zero appears again, but streamer current decreses.

As for now, my model pumping 150ma at 42kV into 300k load at 40amp of primary current. the model is also attached.

]resonator.zip[/file]

Mathias

Mon Aug 29 2011, 09:28AM

Registered Member #1381 Joined: Fri Mar 07 2008, 05:24PM
Location: Hungary
Posts: 74

BSVi wrote ...

I tried to simulate resonator as shown in attachement. I'm unable to acheive half an amp into 300k load (is it reallistical model of streamer?)

Not quite, atleast streamer/spark parameters have "time" dependant parts. It's series resistance should drop significantly (from 1Mohm to a few Kohm or an even lower value) if currents start to flow also it's series inductance rises a bit. (but this can be left out of consideration cause the change takes place on the order of a few hunder nH)

Steve Ward

Wed Aug 31 2011, 06:01AM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

For my streamer load model i used something like 2pF per foot of spark length in series with something in the range of 20-50k ohms. With this sort of loading i was able to match my real world measurements for all voltages and currents.

For the resonator, i think since the top voltage is probably going to be low, it cant hurt to go with a short, wide coil form (4.5" PVC would be my choice on a coil this size).

As to the pole/zero issue. Yes, the poles have more gain, but it seemed possible to either use a PLL, or just a VCO, to start the system off at the Fzero frequency. With no streamer load the primary current will be tiny and very distorted, so this is where the VCO would have to just power through and keep switching at some specified frequency. After the streamer starts to pull more energy from the secondary, the inverter current should increase and start looking more sinusoidal. At some point along here it seemed feasible to start using primary current feedback to maintain good ZCS, and the system should keep oscillating at this frequency as the pole frequencies should not really be present after so many cycles. Admittedly, this is not a real simple approach, and i dont think anyone knows yet whether or not it will work all that well. Id probably stick with the pole operation for now if you want to get it up and running quickly.

BSVi

Wed Aug 31 2011, 03:26PM

Registered Member #1637 Joined: Sat Aug 16 2008, 04:47AM
Location: Kiev, Ukraine
Posts: 83

Hi! Thank you for your answers. I'v done quite a lot of simulations today.

I dont want to bother with tuning to zero - it's too complicated and requires me to remake my control board, so I'll tune my coil to pole.

Its not obvoious to me which pole to use. Common logic tells me that it's better to tune to lower pole - when spark grows, it detunes secondary lower, so both coils stays tuned. But simulation shows that secondary influences primary and as spark grows primary goes lower. From secondary/primary current ratio it's better to tune to the upper pole. When transition from upper to lower pole tuning occurs, overal gain expirienses dip at zero's frequency - that's (from my point of view) another drawback of tuning to the upper pole.

I can't also came up with coupling. The coupling doest influences anything much and that surprises me. Now I use 0.2 coupling.

Now my settings are (with 22mH/10.35p secondary):

Secondary is, as you suggested, 4.5''*9'' crowned with my 5pf toroid

. Coupling is 0.2.

For higher pole I use: 5n MMC, 50uH primary: 676mA into streammer / 85amps of primary current
For lower pole I use: 5n MMC, 70uH primary: 596mA into streammer / 48amps of primary current

Lower pole variant has higher impedance, so I also will be able to control current more smoothly.

I'm a newbie in resonator design, so forgive me if all i'm saying is a one huge mistake

Attached is my current resonator design. I use two 2p/35k networks to switch betwen 0/1/2ft sparks by cutting wires :)

Goodchild

Wed Aug 31 2011, 05:44PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

I think Steve has his QCW tuned the same way I do, but I found that the best performance was at the upper pole.

I also like the upper pole because I can drive at the magic >350KHz and don't have to make a supper small secondary with very little windings. A helping part of this is the higher coupling, as this drives the 2 poles farther apart making it possible to have even a high drive freq without making a small secondary. This is the main reason I like the upper pole.

Eric

BSVi

Wed Aug 31 2011, 07:55PM

Registered Member #1637 Joined: Sat Aug 16 2008, 04:47AM
Location: Kiev, Ukraine
Posts: 83

Goodchild, the bad thing is that PS QCW differs from plain QCW - it can't have such a high coupling.

>magic >350KHz
What's magic in >350kHz? I tought that increasing frequency is the mean to make coil smaller so it doesn't occuply half of living room.

Goodchild

Wed Aug 31 2011, 10:59PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

BSVi wrote ...

Goodchild, the bad thing is that PS QCW differs from plain QCW - it can't have such a high coupling.

>magic >350KHz
What's magic in >350kHz? I tought that increasing frequency is the mean to make coil smaller so it doesn't occuply half of living room.

I'm not so sure that I entirely agree with what Steve said about the system having to be low coupling in order for it to have low current ripple. It should be a high Q system but from the research I have done I have a slightly different opinion on it. I am in the process of building a very similar driver for my QCW that uses large IGBT and a similar control setup to yours to control current.

Although it's any one's guess at this point how the system will react in the "real world" all we have to go on at the moment is simulations. My simulations suggest that even with a high coupling and losses you can still achieve reasonable current ripple if you keep the impedance and Q high.

yes >350KHz seems to be the magic freq to drive the resonator at. Any lower and you will begin to experience branching of the sparks. This has been shown on the QCW and also with many VTTC as well. The higher you go in frequency the straighter the sparks seem to get.

BSVi

Thu Sept 01 2011, 02:15PM

Registered Member #1637 Joined: Sat Aug 16 2008, 04:47AM
Location: Kiev, Ukraine
Posts: 83

I'm not so sure that I entirely agree with what Steve said about the system having to be low coupling

I think Steve is right - the secondary has high loss this loss is transfered to primary by coupling. The less coupling the less loss in primary - the less loss the higher Q, the higher Q the smoother current control.

I am in the process of building a very similar driver for my QCW that uses large IGBT and a similar control setup to yours to control current

If you need any schematics, models, pcbs or firmwares from my project to shorten your developement, just tell :)

with a high coupling and losses you can still achieve reasonable current ripple if you keep the impedance and Q high.

You cant have high losses and keep Q high - that mutually exclusive things.

Now I want you to take a look at my resonator design and tell - is it a good starting point? I just do not want to make it in vain.

So here are specs:

Secondary is, 4.5''*9'' crowned with my 5pf toroid . Coupling is 0.2.

For higher pole: 5n MMC, 50uH primary: 676mA into streammer / 85amps of primary current
For lower pole: 5n MMC, 70uH primary: 596mA into streammer / 48amps of primary current

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