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*To*: tesla-at-pupman-dot-com*Subject*: Re: More ISSTC theory stuff (l o n g)*From*: "Tesla list" <tesla-at-pupman-dot-com>*Date*: Sat, 12 Jun 2004 10:54:21 -0600*Resent-Date*: Sat, 12 Jun 2004 10:58:11 -0600*Resent-From*: tesla-at-pupman-dot-com*Resent-Message-ID*: <c1rseC.A.MMG.TYzyAB-at-poodle>*Resent-Sender*: tesla-request-at-pupman-dot-com

Original poster: "Antonio Carlos M. de Queiroz" <acmdq-at-uol-dot-com.br> Tesla list wrote: > Original poster: "Steve Conner" <steve.conner-at-optosci-dot-com> > But did you do this simulation assuming a fixed frequency drive, at the > unloaded resonant frequency? This circuit has actually two resonances. The driving frequency for the loaded case is between them. I just kept the same frequency while changing the parameters. > We are now using self-resonant and PLL drive > circuits that adjust the inverter frequency to keep the primary current in > phase with the voltage. The reason being that our IGBTs like zero-current > turn-off. This makes some difference, but the current still increases if the capacitive loading changes, even if the driving frequency is changed to keep the voltage and current in phase. This happens because of the mistuning of the primary and secondary circuits changes the impedance conversion factor. > I _think_ that with one of these drive circuits, the reactive component > would just be forced to go away. Unless the circuit was in a state such that > there was _no_ frequency at which the input impedance was purely resistive, > in which case I have no idea what would happen, but it would probably be > spectacular and expensive. There is always a frequency where the input impedance is resistive. Actually, if the load resistance increases, there are three frequencies where this happens. The normal one, and others at both sides of it. The maximally flat design is the limit case between just one frequency and three where the input impedance is resistive. > I mentioned the L-match thing to Richie Burnett and he tried base-feeding a > resonator straight from the inverter, through a L-match network. His setup > is like an ISSTC in that it shows the desirable dual resonant behaviour (no > "magnetizing current") but also like one of your directly-coupled spark-gap > coils in that the voltage gain n=1. However it seems to perform just as well > as an ordinary SSTC. Yes, it's possible to design the coil in this way. But in this case it's not possible to obtain a maximally flat characteristic on the input impedance ("maximally resistive"). The exact design would be based on a Chebyshev bandpass filter, that also makes the impedance conversion. > I think the inductively coupled ISSTC might still have the advantage for > high powered coils though, since it has an extra untuned transformer (n) to > help with the impedance matching, thus the primary "L-match" can have a > lower loaded Q and hence lower losses. Yes, the required Qs are lower in this case (with transformer). > >I get: In 200 us: 2.4 J > > whoops, it looks like I missed out a 1/sqrt(2) Another way to make this calculation: Consider a square wave with peak amplitude Vmax and a sinusoidal current with peak amplitude Imax: Average power = (1/Pi)*Integral (0, Pi) of Vmax*Imax*sin(x) dx = (2/Pi)*Vmax*Imax. The result is the same of when only the fundamental sinusoids are considered and their rms values are multiplied: Average power = (4/Pi)*Vmax/sqrt(2) * Imax/sqrt(2) = (2/Pi)*Vmax*Imax Antonio Carlos M. de Queiroz

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