BoostcontrolWithTargetBasedReference (2013-06-23 17:40:04)

New Boostcontrol strategy allows even easier configuration since firmware 1.2.9

Overview

PID can be configured to switch to PD when boost is way too low, or to PI when boost is too high


Mattias Sandgren was kind to contribute some documentation embryo - will be moved to [VT help] at "birth-time"

Begin by setting the "Boostcontrol PID integral limit" to 0 and adjust the "refDC Table vs boost target" so that you get a good starting point for enabling the PID regulated boost controller.

Apply max DC until

To shorten turbo spool time you can apply the maximum dutycycle allowed. This can only be done up to a certain limit below the boost target, set this limit here. This must be kept low enough to avoid an initial boost target overshoot that the PID regulation will not be able to stop.

PD control (far from target)

PI control (close to target)

PID overlap range

Boost P, I, D

Boost control PID integral limit

Set how large the integral is allowed to build up. This value is what is added/subtracted to the reference dutycycle in order to reach boost target. In effect setting this to 0 will disable the boost control PID regulation completely and you will just send reference dutycycle to the boost control valve.

(needs some explanation of how much x of max is, like what is normal limit, etc)

Boost PWM maximum value

Limit the maximum dutycycle the boost control valve receives.

Boost PWM minimum value

Limit the minimum dutycycle the boost control valve receives.


Copied from IRC discussions :

Overlap is PID mode, where its far enough from target to still might need the D term

PD is for not winding the integral up when too far from target

PI is close to target (its now control range)

when close to target, PI only is used, as D wouldnt make any big difference anyway

so it can be used with higher settings from far away, still not messing with close to target control

What is the buildup range and control range?

Buildup integral is frozen and control derivate is disabled. It means "too far from target, probably not physically possible to reach, don't build up a integral error" and disabling D term "close enough to target, error for P is small, so no D needed".

Overlap is PID

P is not active between max dc and buildup

Buildup = I frozen outside this range

buildup enables PD

control is PI

between buildup and maxduty there is referece only

Future ?

the buildup range might go, just enabling PD from maxduty

its easier to find the optimal P if its scaled in kpa / %

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(may2013 FPhil)This is what I get from above, I hope that is correct

DOMAIN zero to maxDCmaxDC to BuildUpBuildUp to CntrlCntrl to TargetTarget to ? (Overlap)
STRATEGYDC ?? PD PI PID
PARAMS PWMmin & maxid & I limitid & I limit id & I limit
What happen if for some reasons boost enter the Cntrl to Target domain at fast increase? one can then expect a large overshoot.

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My way is start tune with quite large PID values and low boost with slope RefDc table where bottom row is W-gate minimal pressure and top row - aprox 30Kpa above my maximum boost expectations. Bottom line filled with 0...10, top line - 60...100 - spring dependant, Interpolation inbetween. With PID enabled it is easy to fill Ref DC table with correct values just by reading the log file. Wise way is match row boot value with current target - then actual BoostDC represent DC values for table. Overshoot or slow buildup can be achieved by table increase or decrease respectively.

What is good in new strategy - it allows much larger Integral values.

First WOT run with boost valve off [minimal pressure] is helpful for further tuning. GintsK.

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Can Vemstune be made to represent the PID values for proper PID tuning for boost control? ItĀ“s extrememly important when setting up boost control to know which value is what without having to bring out the calculator every time and the values currently used are not documented either. Same actually goes for all PID loops currently available and that will be available in the future.

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Gunni -

IĀ“m writing a complete boost control guide for VEMSĀ“s new setup, but have found the following bug.

"I" value influences the Integral limit and thus the total possible DC% that the I value is able to give. This is completely wrong in my oppinion. The Integral limit should not be influenced by the I value but only work as a limit irregardles of what the I value is. The I should only function as the rate of windup to the limit based on amount of error.

I have detailed so far the operation of getting to a final boost target in a flow chart and then getting to a final BoostDC% but need more information about the PID values

So far I can see

P value:

Approximate P_DC% = 0.314 * P * ErrorKpa/100

I value:

I values behaviour is a mystery as the scale of 0-255 is hard to reference to I_DC% as the update rate is unknown and the windup per error is also hard to quantify. Please detail and explain so I can include in the guide.

D value :

No sense of behaviour as scaling and rate is unknown.

This needs detailing.

PID 0-255 scaling:

Ideally would be removed and engineering scaling implemented instead even if itĀ“s a drop down menu with 255 pre selected values or Vemstune automatically rounds down or up to the nearest allowed value like is seen in many places already.

Boost PID output NEEDS LOGGING. Is there a reason why this is not logged or loggable?

More questions

Are the PD and PI controls also functional in the same sense if MAP is above the target and not just below the target?

PD control:

If PD control is set to 20kpa and PI control to 10kpa, at what point does the D control disable?

PI Control:

If PI Control is set to 10kpa and PID overlap range is set to 6kpa at what point does D disable ?

Note : if PI Control is higher then PD control then PI control is disabled until PD control is within range seemingly allowing PID control from that point until some unknow point.

PID overlap range:

What does "forever" mean. Does 6kpa mean that PID is enabled when TargetError is within 6kpa of target?