need help PID boost control M800

Discussion and support for MoTeC's latest generation ECUs

need help PID boost control M800

Postby fetzi on Fri Mar 05, 2010 2:28 am

hello,

i need some help by adjusting boost control on a m800.
i attached a picture where you can see how it actually works.

actual values:
max duty: 100%
min duty: 30%
P Gain: 1
D Gain: 0,1
I Gain: 0

i have no idea which values should be changed.

thanks for your help
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boost.JPG
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Re: need help PID boost control M800

Postby Martin on Mon Jun 28, 2010 8:47 pm

I think you are startin with too much P, and maybe filter the controlled channel. I dont think you MAP signal would be heathy for fueling either, maybe start by filtering it in the input setup or maybe seekeing another place to read it from. Just be careful of overfiltering, that would be even worse.


You also dont have the normal position set.

1. Do normal DC contorl boost control.
2. Log what DC`s give you what boost at various RPMs
Normally you will see no boost increast until you reach a certain DC....or its just very slow to react.
Do ramps with ever increasing DC and log it. Once you have this data you can set up a nice table in the normal position table. You might even specify different normal positions for different aim boost levels.

Then start of with small P gains, and maybe a bit of I (remember to set I clamp values) to slowly change the DC as you are not reacing the target with the low P gain. You have to start with small gains to see that it starts reacting in the direction you want. Keep in increasing till you have good response and maybe even small overshoot. Then intruduce Dgain to stop the overshoot, This will make it more unstable if you add too much D. Same for too much P

The attached picure if of closed loop control. This example could do with a bit more Dgain
Attachments
boost2.jpg
Closed Loop Control
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Re: need help PID boost control M800

Postby AaronM on Thu Jul 29, 2010 8:36 pm

Hello,

I would check for an output mode set incorrectly or some sort of plumbing issue. I not sure if the problem lies in the P,I,D. A closer zoom may help.
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Re: need help PID boost control M800

Postby Scott@FP on Sat Jul 31, 2010 7:39 am

Filter the controlled channel a little more (MAP) filter at 2 or 3.

Normal position is important to getting the last Nth of stable control.

Your WG system needs to be within its normal range of control for what you are targeting, otherwise controlling it is next to impossible, for instance if you used to use a standalone boost control with the same solenoid and your 250 kpaA target resulted in a flat 66% BCS DC the ECU controls will work fine, but if you were at 90% and had minimal control don't expect the ECU PID controls to fix anything.

Start with P of .1 leave I and D at 0.

Increase P .05 at a time until it overshoots target, add some D (.005 increments) until it is overshooting then oscillating to a stable setting, then add some I, say .01 at a try, stop at the minimal amount needed to eliminate overshoot. In some cases you may not need ANY Integral.

Hyperactive (wildly oscillating) BCS DC% and/or WG Position (if you have a sensor on it) are signs that one of the PID settings are way off. The top log graph with the wacko Aux 1 trace looks like one or more of the PID settings are an order of magnitude too high. The log posted by Martin shows a setup that is close to ideal for response.

If you are using MAP/EMAP for fuelling might suggest using Effcy on the X axis instead of RPM of the Normal Position table, as turbine relative backpressure (comp PR vs turbine ER) increases it will take more BCS DC% in nearly a direct ratio, you can pretty much guess what its going to need, low Effcy = more DC%.

Also keep in mind, especially for smaller turbos, once you overspeed the compressor any semblance of good boost control is out the window, don't fight a losing battle. For instance you have an 18 PSIg wastegate and above 6500 RPM it will only put out 14 PSIg manifold pressure at full BCS DC%. Well, its DONE regardless of what you do, you're at the end of the compressor map, don't fight it.
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