Using the multicontroller to implement a form of closed loop boost control?

[JDG Gt4]

I was wondering if anybody has tried it?

 

I was thinking you could implement it to trim the boost controll solenoid +/- 10-20% by mapping the PSI into one of the multicontrollers and then feeding this back to the special trim on the boost control.

 

Obviously this isn't as good as a full PID controller but it would be able to trim it and hopefully stabalise it a bit more?

[JDG Gt4]

I would like comments from anyone that can remember their University control theory to make sure I haven't implemented something with an inherent instability.

 

While doing some data logging on my daily commute to work, I had a light bulb moment and realised that a type of closed loop system could be implemented in the features that Wolf provides.

 

Implementation:

Below is a screen shot of the boost control configuration screen, with duty cycle Vs RPM. This is the base configuration which in my case was setup to provide Approx 14psi.

 

On the left you can see a range of modifiers they provide such as air temp, engine temp and throttle position which are all handy. Then there is the "Special Trim" where you can choose what signal you map in the last modifier. One of the options is the Boost, psi value.

 

 

Then with boost PSI selected, you can map a +/- percentage to modify the base table by based on the boost. Since I'm aiming for 14psi I have it giving and extra 10% until it reaches 10psi, then it ramps down to 0% at 14psi and then through to -10% at 18PSI.

 

To give an idea, previous testing showed a decrease of 15% duty, dropped the boost to 8-9 Psi from 13-14.

 

 

Result:

The seat of my pants dyno tells me that this made a massive difference to the turbo spool, and comparing these data logs you can see the closed loop control adjusting the boost solenoid duty cycle in the second graph.

 

BEFORE - Open Loop Log: You can see the duty cycle move with RPM as mapped

 

AFTER - Closed Loop Log: here you can see the duty cycle start to decrease as it approaches the preset 14PSI. Closed Loop Control!!

 

This is were it all gets a little control theory.

 

I think what I have implemented here is a form of differential controller (integrator ?).

The greater slope I put on the special trim, the greater I increase the gain on the output of the differential controller. How far should I go with this? The greater the gain the faster the boost response but I believe greater chance of instability and boost overshoot? I guess trial and error.

 

By limiting this to +/-10% for now, I hope to avoid some of this instability but that now make is it a non linear system. Again is this going to give me stability issues?

 

Might be time to crack out the Uni text books

[ktm]

Looks interesting. The slope of your trim line is dependent on the original duty cycle relationship since that is what determines you boost.

 

If you original duty cycle curve is off too much, you'll need a steeper trim curve.

[JDG Gt4]

Here is a better log showing the trim working