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*To*: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>*Subject*: Re: [TCML] understanding DRSSTC*From*: "Udo Lenz" <udo_lenz@xxxxxxxxxxxxxx>*Date*: Thu, 14 Feb 2013 10:18:56 +0100*Delivered-to*: teslaarchive@xxxxxxxxxx*Delivered-to*: tesla@xxxxxxxxxx*Dkim-signature*: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mx.aol.com; s=20121107; t=1360833563; bh=AmXKFxZIdZpFdQpYUWyaqDN0ib8QgqMl/iMvikqgNac=; h=From:To:Subject:Message-ID:Date:MIME-Version:Content-Type; b=FX5df4FdzR8ohm2kQrmb0YAnirC4+MKuzzpdPDjktxOlqUnk1i+qVao56qLV+0Ib5 SaXglX2dybe9Gaw1Eed4PN4Tjbzjb1yB3f9btAkgCK5wd5ikf0si5glIUhhve2fCAN wXPOsc+mJ41Gs44tCHh7G9IgDTSfUtvvD6ClUiCo=*List-archive*: <http://www.pupman.com/pipermail/tesla>*List-help*: <mailto:tesla-request@pupman.com?subject=help>*List-id*: Tesla Coil Mailing List <tesla.pupman.com>*List-post*: <mailto:tesla@pupman.com>*List-subscribe*: <http://www.pupman.com/mailman/listinfo/tesla>, <mailto:tesla-request@pupman.com?subject=subscribe>*List-unsubscribe*: <http://www.pupman.com/mailman/listinfo/tesla>, <mailto:tesla-request@pupman.com?subject=unsubscribe>*References*: <510781E7.22222.26F033@xxxxxxxxxxxxxxxxxxxxx>, <AA15AC9F78E74F4BB90E4A656780F965@UdosLaptop><51175855.6319.ABCD7@xxxxxxxxxxxxxxxxxxxxx><5117FA4D.9000708@xxxxxxxxx><B3EC473009924A27960726D175D02CAE@UdosLaptop> <511AC087.1040709@xxxxxxxxx>*Reply-to*: Tesla Coil Mailing List <tesla@xxxxxxxxxx>*Sender*: tesla-bounces@xxxxxxxxxx

Hi Antonio,

I wrote a document with some simulations of a DRSSTC, designed withthe method that I have developed:http://www.coe.ufrj.br/~acmq/tesla/drsstcexcitation.pdfThe central frequency can be made to match the secondary resonantfrequency.If you run at this frequency, the operating frequency will be equal tothe secondaryfrequency and this will give you the highest possible power transferto the secondary.In my simulations this was close, but not exact. The secondary resonanceis at 283886 Hz and the driving frequeny is 294427 Hz.The result with excitation at the secondary resonance results inslightly slower output rise and the full beats in the unloaded casedisappear.The pole frequencies can never coincide with the secondary frequencydue to thecoupling, so that running at their frequencies will require moreprimary currentto achieve a given power transfer.. I believe, this is what you observed.I agree.But the central frequency has disadvantages: Consider a simple seriestank.If you drive it below the resonant frequency the current phase willlead theinput voltage. A PLL circuit would detect that and increase thefrequency.The central frequency has the opposite behaviour. There a drop in thefrequencyleads to a current lagging the voltage. The PLL wouldn't lock on to it. The pole frequencies on the other hand show the "normal" behaviour.But this system has two resonances. Looking at the frequency response ofthe system, what I see is:At the poles the input impedance is never purely resistive, and ispurely reactive in the unloaded case,inductive above and capacitive below.At the central frequency the input impedance is purely resistive, withany resitive load at the output.Greater load widens the frequency range where the input impedance isapproximately resistive.

I agree. I've carelessly equated the terms "pole frequency" and "ZCS frequency". As you have shown, they are not identical.. You should be able to run a coil with ZCS (i.e.the input being purely resistive) in the vicinity of the pole frequencies.

A PLL controlled by the input current would lock correctly. There isjust a possible problem, becauseas in the unloaded case there are full beats of the input current, andif the driver is not turned offafter the first beat, the PLL will invert the operation of the driver,causing a great increase in the inputcurrent. In the lightly loaded case this also happens. A PLL would notlock at the pole frequencies. Itwould move the driving frequency to the central frequency automatically.You could invert the feedback of the PLL, so that it locks onto thecentralfrequency, but I think, this is a fragile mode of operation, since theinvertedphase relation holds only between the poles. A glitch or a ground arcmight throwthe PLL off.It's really confuse what to do with a PLL if the system is designed to acertain maximum number ofcycles per burst and allowed to exceed this number. I am a bit scepticalabout the use of a PLL in thesesystems with short bursts. It would be useful only in really longbursts, because of the number of cycles required tolock. And note that the ambient has heavy interferences.Under heavy arc loading the central frequency will disappear. I believethis to happen at about Qsec = 1/k In your simulation with k=0.12 thatwould be around Qsec = 8.I've made measurements of arc load at 70kVpeak (at about 200kHz) andthey give aload resistance of about 100k. With the parameters you used, Qsecwould drop toabout 2 with a 100k load.I don't see it disappearing with any load. In the sense that the inputimpedance remains always resistive.What happens with heavy load is that the two resonances become dampedand both move to thecentral frequency, resulting in just one peak in the voltage gain.

The center frequency at light loads and the central frequency at large loads have different properties. The first one will be more inductive below it and more capacitive above. The latter one is the other way around, behaving like a pole. So the frequency with the first behaviour does not exist anymore at large loads. A PLL, which corrects the frequency according to the phase between primary current and voltage can only lock onto one of these frequencies. It will be driven away from the other one.

My measurement was made under QCW conditions,so that the arc had time to grow to its final size. With short burst,I'd expect the arc loadto be smaller. Nevertheless low Qsecs don't seem to be exotic. Underthese conditions you'llhave only one ZCS frequency with a "normal" frequency-phase shiftrelation. An invertedPLL will fail then.With heavy load, as I said above, the two peaks disappear, and a PLLwould really make the systemoperate at a pole frequency, because both pole frequencies areidentical, at the central frequency(with different Qs).If you are using a PLL, compare the frequency where it operates at theend of a long burstwith arc load with the two pole frequencies of the unloaded system. It'strue that arc load addscapacitance to the secondary and changes the tuning of the system, so Iwould expect the finalfrequency to be somewhere below the central frequency. Or you canoperate the system withsmall arcs, so the unloaded tuning is preserved.

In the case of a heavily loaded system with only a single ZCS frequency, this frequency will be close to the primary resonant frequency. The secondary resonance will be wide at this point, as you have stated above, so that the value of that frequency will not matter as much as in the lightly loaded case. Udo _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla

**Follow-Ups**:**Re: [TCML] understanding DRSSTC***From:*Antonio Queiroz

**References**:**Re: [TCML] understanding DRSSTC***From:*Udo Lenz

**Re: [TCML] understanding DRSSTC***From:*Herwig Roscher

**Re: [TCML] understanding DRSSTC***From:*Antonio Queiroz

**Re: [TCML] understanding DRSSTC***From:*Udo Lenz

**Re: [TCML] understanding DRSSTC***From:*Antonio Queiroz

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