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Predictive (analog) Feedback Element....Musings on Linear Analog op amp

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thermistor-guy:

--- Quote from: Kleinstein on August 30, 2023, 04:34:03 pm ---With control theory such a forward looking element is called feed forward part. It can be quite nice, especially with relatively slow systems, like a thermal system that should follow a temperature profile.

For just an amplifier, there may not be that much need for a feed forward part as the electrical feedback can be very fast.

--- End quote ---

Harold S. Black invented feedforward before he invented feedback.

Feedforward is used in some RF amplifiers, because it avoids feedback instability issues.

I've used feedforward error correction in a 3rd-order digital PLL. It's a useful technique to have in your conceptual toolkit.

Oral history from the man himself: https://ethw.org/Oral-History:Harold_S._Black

RJSV:
Thanks, but even a (likely) impractical suggestion gets provided motivation, especially when I'm rather weak in analog circuits.
   I'm actually reminded of stock market watchers (gamblers).
Predict such and such.  Heck, 5 years ago, I wouldn't have thought to toy around with 'smart' feeds, to a 5 cent analog stage !

langwadt:

--- Quote from: Kleinstein on August 30, 2023, 04:34:03 pm ---With control theory such a forward looking element is called feed forward part. It can be quite nice, especially with relatively slow systems, like a thermal system that should follow a temperature profile.

--- End quote ---

I'd say that it usually makes sense to have feedforward with a thermal system. If you know it take approx X watt to maintain a set temperature it make sense to start with X watt and then let a pid loop handle only the errors

thermistor-guy:

--- Quote from: langwadt on September 01, 2023, 09:43:18 pm ---...
I'd say that it usually makes sense to have feedforward with a thermal system. If you know it take approx X watt to maintain a set temperature it make sense to start with X watt and then let a pid loop handle only the errors

--- End quote ---

It's common for commercial thermal controllers to be self-tuning. They have adaptive feedback, where the control errors are used to adapt the model of the plant.

The practical advantage is you can connect the controller to the plant, and the controller learns what to do. So you don't have to be a controller expert to use it.

Kleinstein:
When speed is not critical the I part of a PID regulator can compensate for the typical output needed. So no advantage of feed forward for a static PID system.  One may get away without the I part and use learned Feed forward instead - still this gives slightly less accurate regulation, though possibly faster on some transients.

The feedforward part is especially helpfull for a dynamic system. So when you want the temperature to follow a given profile and have a good estimate for the added power needed to get a rate of change.

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