Model Predictive Control (MPC) output lag when Prediction Horizon increases

[CW81]

Hi, 

I programmed a simple MPC example using a model that I obtained via system ID. Eventually, this program will be deployed into CompactRio to perform a real time control. However, when I increase my Np, the output will start lagging. 

I am confused why this is happening,

My program: I am trying to run a Smith predictor architecture using MPC controller instead of PID. Thus there is an additional model running parallel with the the actual plant. At this point, since it is in simulation, both models are assumed to be the same.  

Version: LabView 2009 SP1 

Please advice 

Thank you 

CW

[Pcorcs]

Hi, 

Would it be possible to be more clear on the lagging behavior that you are seeing in the system? What magnitude of Np are you increasing to where this behavior becomes apparent? Is/Are there a specific function that is taking significantly longer to execute given a large enough Np? 

I appreciate your time, and look forward to your follow up.

Cheers, 

[Pcorcs]

You may also want to read through the example outlined in the Control Design Manual:

LabVIEW Control Design User Manual

http://digital.ni.com/manuals.nsf/websearch/73D787E59721B3FE862575BA006E6FA8

LabVIEW Control Design User Manual

http://digital.ni.com/manuals.nsf/websearch/73D787E59721B3FE862575BA006E6FA8

Particularly Chapter 18 has a discussion of the control affect of Np in the MPC system.

[ETS_MONT]

you need to change the discretization time (sampling time to 100 ms)