Re: SSTC, Modes and soft switching

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Antonio Carlos M. de Queiroz" <acmdq-at-uol-dot-com.br> 

Tesla list wrote:

 > Original poster: "Bob (R.A.) Jones" <a1accounting-at-bellsouth-dot-net>

 > As described in my message subject: Mode splitting.  By offsetting the
 > primary and secondary frequencies one of the modes of the split fundamental
 > mode disappears.

I don't see how this could happen...

 > This may be a useful configuration for an SSTC because both the initial
 > transient and the steady state current may be in phase with the drive
 > voltage if its at the frequency of the remaining mode.  Hence soft
 > switching even at the start of a burst may be achievable (assuming no break
 > out)

This is possible, at least in good approximation, even with all the
modes present.

 > I have not yet done the transfer function analysis or transient analysis.
 > Which I will try to do unless someone can point out a problem with this
 > approach or error in my thinking.
 > As always it may well have already been considered.

I have worked out a design approach that appears to work, at least in
simulation:
http://www.coe.ufrj.br/~acmq/tesla/sstc.html
I have written a simulator too:
http://www.coe.ufrj.br/~acmq/programs
I don't like much the consideration that there is a load connected to
the LC network all the time, but the waveforms obtained from the
designed networks without load are not very different during the
rising transient.

 > I believe it has been suggested that from observation of the performance
 > that a system with an offset works better. Has anyone quantified the offset
 > and or got a frequency response of such a system?

What I think that happens is:
- The system always has two different natural oscillation frequencies.
- If the excitation is at one of them, the output voltage can rise
   to very large values, limited only by the Q of the natural frequency,
   but rise to the maximum is initially linear with the time, and
   takes about Q cycles to reach the maximum, what may be too much.
- Fastest rise, to arbitrarily high values in a system with a
transformer,
   can be obtained by excitation somewhere between the natural
frequencies.
- The reason is that this excitation approximates the excitation of a
   system with two identical natural frequencies, at this same frequency.
   This would result in a rise proportional to the square of the time
   instead of just to the time.
- The best excitation frequency is at the geometrical mean of the two
   natural frequencies, if it is assumed that a load is always present
   at the secondary end. The system can then be designed as a band-pass
   filter, or an impedance matching network.
- Without load, the best excitation frequency would be one that puts
   the three frequencies in a ratio of three successive integers, as
   1:2:3, 3:4:5, etc. The output voltage would than be identical to the
   one that can be obtained with an optimally designed magnifier.
   (I have already figured out how to make the design for this case,
   but am still organizing my notes.)

Antonio Carlos M. de Queiroz