problem while tuning PID controller

I try to tune a PID-Controller in Matlab2010b if i use a discrete one i get the error Message "The second input argument of the "d2d" command must be a positive scalar." if i use a continuous one i get "Input to SVD must not contain NaN or Inf." what i have to pay attention that this block works fine? My system can became NaN due to a Sqrt-expression....

Answer 1

[Arkadiy Turevskiy]

What is the purpose of the memory block that you are using at the output of the PID controller? Long story short, that is what creates the problem.

Answer 2

[Arkadiy Turevskiy]

Can you provide the plant model?

Answer 3

[Martin1986]

yes sure i put it on file exchange or you go to here

http://www.gomatlab.de/auslegung-regler-simulink-t21298.html

the file is created on linux with 2010b it is only a part of the system, the massflow(the output which i try to control) will normally have a influence to the 3. input of the subsystem too...

Answer 4

[Yoni]

Hi Martin,

I've had the same problem.

It seems the discrete PID option does not handle a sampling time of "-1" (should have inherited the sampling time it that case)

So the workaround for your problem is to enter your own explicit expression for the sampling time. do not leave it on "-1".

This should eliminate the "The second input argument of the "d2d" command must be a positive scalar."

Cheers, Yoni

[Nail]

Also, simulation time must not be set to "inf".

Answer 5

[Martin1986]

o.O actually this was a try to avoid this problems(and avoid a algebric loop because the starting value must be 0), finally i made some small changes in my Model and than it works also fine ;) i think the block works fine but the debuging is a little bit problematic ;) because if you have a bigger plant it is quite tricky to find the exact cause of the problem