Re: Feed Forward / Slop compensation

--------quote----------------------------- Feedforward is a method used to reduce the effect of a disturbance on the output without running into trouble with oscillations.

-------- end quote-----------------------------

1) Don't you mean input not output otherwise it would be feed back? Could you give me a circuit example? Sorry its hard with no attachment possibility on this forum, could you provide me with a link to a feedforward circuit diagram?

--------quote----------------------------- Slope compensation is a method used to prevent oscillations in converters such as the classic booster where the inductor current is continuous. ACII art: L1 D1 ---)))))----+---->!------+-- Output ! ! O Q1 === C1 / ! ! GND GND While Q1 is on, current builds up in L1 but no current goes through D1. This means that turning on Q1 sooner or for longer to increase the output voltage actually reduces the output voltage in the short term. This can lead to oscillation in any servo loop which has a high bandwidth. In a "voltage mode" PWM, this is prevented by reducing the bandwidth.

-------- end quote-----------------------------

Have you not just described Right half plane zero in your continuous current boost circuit not slope compensation? Continuous current Boost and fly back converters can only be stabilised by heavily damping the voltage element of the feedback loop, be it current mode control or voltage mode control.

-------- quote----------------------------- Now imagine that the pilot suddenly opens the throttles

-------- end quote-----------------------------

The Line in the PSU is the throttle, yes? Are you a piolet and engineer?!

-------- quote----------------------------- Feed forward in this case is an input taken from the throttle setting The Line deviation in a PSU

-------- end quote-----------------------------

I think this is the same as below, from my first post:

-------- quote----------------------------- In another document (circuit diagram in fact) they pull up and down on the current sense pin magnitude depending on the rectified line voltage

-------- end quote-----------------------------

From what you have said I think feed forward takes a quantity (line voltage) and compensates the fast current control system before the slow voltage control system knows what has happened, this has the effect of changing the slope of the primary current, but using a real quantity as apposed to a fixed ramp graphical method of controlling the primary currents slope.

Am I making any sense?

I should have said "effect of a disturbance somewhere as seen on the output". The "on the output" applies only to where you look for the effect.

I explained the problem slope compensation is fixing. I was trying to make clear where the problem is. It is in the fast feedback path of the current sense not in the voltage feedback path.

You have missed the point. The current mode control loop without slope compensation will oscillate even if you integrate the voltage path to death. The current comparitor to the pass transistor is a fast feedback path.

The Line input is like the throttle but the Line input is much less of a problem than the throttle.

I don't want to get on the plane regardless of which seat. As a result becoming a pilot wasn't really an option.

You are making sense but you still seem to have topics confused. Put slope compensation in one room and feedforward in a different one. The feedforward usually won't be changing the ramp. It normally will change the other leg of the current sense comparitor. Since the comparitor looks at the difference, instead of raising one you can lower the other.