Unless I missed something, in his paper, he does ask for comments and
criticism.
In the Hammer circuit he is contending he can produce phase shift. In fact,
his adjustment only changes the amplitude of the signal, not the actual zero
crossing point of the signal. If you watch the video you can see this. The
gate drive overshoot is reduced, but the voltage-currtent phase is not
changing when the pot is adjusted, only the zero crossing point ---- and
this is valid for only one particular setting of current not thru the entire
range..
The gate drive overshoot is reduced, but this is valid only for one current
setting. It may be set for a low current, medium current, or high current,
but not all values as the inductance is dynamically changing as the Q factor
(tied directly to inductance for those looking for equations) is dynamically
changing.
Any Tesla coil, RF air core inductor, under dynamic operating conditions
contains an AC resistance in parallel with a DC resistive component. As the
coil heats slightly due to changing dI/dt, the dynamic operating Q of the
circuit changes. If the dynamic Q is changing the inductance is also
dynamically changing. Current and voltage do not reach zero at the same
time due to a phase shift. You can correct phase shift for any particular
value of current, however this value is constantly changing during the ramp
up. You would have to sit there and change the pot value all the time along
with the dynamically changing signal.
His adjustment circuit changes the amplitude not the phase shift of the
circuit.
If you want futher proof, do a nodal analysis on the circuit and you will
see exactly what I am talking about.
If you set the zero crossing value so there is zero current at switching,
and then try to also set this value for the point of maximum current, you
will fail --- at least with this method. As the current is ramping up to
full value,
the IGBTs will overheat due to the phase shift problem.
I'm not just firing out blank comments here to serve no purpose ---- I do
have a solution that can be pursued.
Remember how B&W and color TV receivers always incorporate "delay lines" in
their construction to perfectly sync the signals? This same technique could
be applied to solve this zero crossing problem. Delay lines, or, a
microprocesser accurately tracking the signal could produce outputs that can
adjust phase shift just as is accomplished today in color TV receivers to
get everything in sync. TVs use delay lines not micros for this purpose.
Hammer definitely needs to adjust the gate drive transformer turns to reduce
the overshoot. You can't get it perfect with near zero overshoot, but
certainly better than his scope signals indicate.
Hopefully, this will clear up some of the confusion on this issue.
Dr. Resonance
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