🚀 go-pugleaf

>In article <1e9hpgINNc8j@iskut.ucs.ubc.ca>, 
>lug@balsam.ppc.ubc.ca (Guoqiano Lu) writes:
>I am using Simulink to simulate continuous-time self-tuning algorithms. 
>Generally it works well except sometimes there are some crazy peaks in 
>the output which is supposed to be smooth. It seems to me that these are 
>due to the numerical intrgration algorithms that SimuLink used. Any one 
>has the same experiences or any suggestions to overcome this problem? 

Numerical integration schemes can cause funny problems, particularly when 
used with something like a self-tuning algorithm.  Variable step integration 
schemes in particular tend to "hunt" in an attempt to converge, particularly 
in simulation that include random noise.  But typically they will only run
slowly and not create "peaks".  To check to see if it is the integration 
scheme and not the self-tuning system, switch to a fixed time step 
integration scheme (like Euler), with a small time step.  (I hope that 
you can switch integration schemes in Simulink.  You can do this in ISI's 
SystemBuild, of which I am familiar).  If this clears up the problem, 
then you know its the integration scheme and you can deal with that issue 
by changing your integration technique.

If you still have the "crazy peaks", all that I can suggest (with the 
given information) is to check to make sure that the self-tuning algorithm 
is "sufficiently excited".  Astrom had published some papers in the early 
1980's about the "bursting" phenomen where a self-tuning or adaptive 
scheme can blow up the varying gains if not receiving the proper system 
excitation.  I've experienced this with self-tuning simulation in the 
past.  Typically this might happen in a simulation during steady
state regulation (non-transient), when the characteristics of the 
system build identified or being tuned to, are not available in the
measurements.

Duane Mattern (mattern@mars.lerc.nasa.gov)	(216)433-8186
Sverdrup @ NASA Lewis Research Center, M/S 77-1, 21000 Brookpark Road
Cleveland, OH 44135