Hi all,
I thought I would look at how stable a feedback system is that is oscilating
at the centre frequency . So I looked at the closed loop response assuming
everything is linear including the feedback.
My first go at it with secondary voltage feedback with and with out 90deg
phase shift shows two poles approximately at the up and lower split
frequencies. Which I think means that a DRSSTC will eventually oscillate on
one of those frequencies even if it starts of at the mid point.
I will next try primary current feedback (much more work but that's the one
I am interested in) but I expect the same result. I think the bottom line
is the mid frequency is an unstable operating point and therefore the system
will always move away from it to a stable operating point which are the
split frequency poles if you give it sufficient time.
Robert