Boost control: Open loop -> closed - why?
08-16-2013, 07:10 AM
#1
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Boost control: Open loop -> closed - why?
I have read a bunch about boost control on the megasquirt and most of the time it tells you to tune open loop first before moving to closed loop. Aside from knowing what duty cycles result in what boost and thus knowing that your EBC is set up correctly, what is the importance? It seems to be mostly irrelevant once you verify the EBC polarity.
I am running closed loop now without ever doing open loop. I am thinking of going back to at least get something reasonable loaded into my MSQ, but I am having a hard time justifying why when my closed loop seems to be working.
I am running closed loop now without ever doing open loop. I am thinking of going back to at least get something reasonable loaded into my MSQ, but I am having a hard time justifying why when my closed loop seems to be working.
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08-16-2013, 07:23 AM
#3
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Boost Control
https://www.miataturbo.net/megasquir...details-60323/
Those to start - for example.
Maybe it's just what most people have done to find success, but I don't think you necessarily have to do open loop.
Closed-loop Tuning Tips This section reviews some tips for tuning closed-loop boost control. Tuning closed-loop boost control should be done in two steps:
- Tune open-loop boost control - In order to make sure that you have the proper polarity set for your valve, and to get a feel for the boost that certain duty cycles yield, it is recommended that open loop boost control is tuned first.
- Set Up Overboost Protection - The closed-loop boost control code uses the maximum boost set in Overboost Protection for some of its internal calculations. This was done purposely so that during the tuning process for boost control, if the settings wildly incorrect, boost will still not climb any higher than the Overboost Protection allows it.
- Tune Proportional-Integral-Derivative (PID) gains - The PID gains are the main controls for how quickly the boost will reach the target, and how close it will remain to the target through the RPM range. Steps for tuning this can be found below.
Those to start - for example.
Maybe it's just what most people have done to find success, but I don't think you necessarily have to do open loop.
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08-16-2013, 10:33 AM
#6
Agree. Would not bother at all with MS3. It has a full PID algorithm that works.
With MS1, the control algorithm is integral-only. Over much of the map, you HAVE to run open loop, otherwise you get integral-windup that causes big boost excursions. That's why the thread title specifically states MS1.
With MS1, the control algorithm is integral-only. Over much of the map, you HAVE to run open loop, otherwise you get integral-windup that causes big boost excursions. That's why the thread title specifically states MS1.
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08-16-2013, 10:58 AM
#7
MS3 dox for you.
Though you said it's already working, for everyone else that finds this thread this is what you should be reading.
Though you said it's already working, for everyone else that finds this thread this is what you should be reading.
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