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Re: Re: Re: [TCML] SSTC full bridge control system question



Michael Twieg wrote:
All right, I'll try to apply your methodology to our existing
secondary parameters and see if I can get anything promising.  I've
tried already a couple times and can't get it to resonate at the
center frequency; it always goes for the lower frequency.  And to be
honest, that's what I would expect to happen.  There are generally
going to be three frequencies at which the phase of primary is current
is zero (which means zero crossing can work there), but the middle one
is always the largest impedance, and I would expect the other two to
dominate.  As I mentioned before, pulling some of your example numbers
and throwing them into LTspice did result in it resonating at the
center frequency, but I haven't gotten anything else to do that.  Any
idea what causes the controller to select the middle frequency?
The elements must be calculated to result in this. My page has the relevant formulas, and a link to the program drsstcd that can do the calculations (use the lossless design). The program can also simulate the system with zero-crossing control or without it. With elements having other relations it's improbable that zero-crossing control based on the input current will set the driving frequency to the
central frequency.
Note that for proper operation the driver must be turned off (with free-wheeling diodes to return energy to the driver) after the energy transfer is complete, when the first "beat" of the input current ends. Otherwise, with feedback based on the input current, the driver will try to push more energy into the system while the unused secondary energy is being returned to the driver. This will triple the input
current.

Antonio Carlos M. de Queiroz

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