purpose of state-space with pid

Hi everyone! I am having problem that when I connect state space block to PID and take its output as feedback in simulink I get a plot that converges at reference value; now I have to do the same job in mfile I have done the coding for pid but I am not getting idea that; what is the purpose of state space connected with pid so that I can write code for it.

Answer 1

[Azzi Abdelmalek]

clear,close
%your model and its input output
mot=tf(1,[1  1]),
model=ss(mot);
[F,h,c,d]=ssdata(model);
model.u='u'
model.y='y'
%your pid controller
r=pid(5,1/0.05,10)
r.u='e'
r.y='u'
%adding a reference r with som2=r-y
som1 = sumblk('e = r - y');
%global model with all conneection
modelg=connect(som1,r,model,'r','y')
%simulation
step(modelg)

[azan]

Sir its giving error at model y='y' and the statement of error is 'Invalid property name y'

[Azzi Abdelmalek]

the first code or the second? have you control system toolbox?

[azan]

First code sir and I am having control system toolbox.

[Azzi Abdelmalek]

clear then run my code and tell me which line is making error

[azan]

ok Sir and what about 'P' in your code?

[Azzi Abdelmalek]

first, did the first code work or no?

[azan]

first code didn't work,however your code is running but I am not sure of the value P

[Azzi Abdelmalek]

p is the disturbance signal added to your output, you can set it to zero

[Azzi Abdelmalek]

I've tested the two codes, they both work

[azan]

And sir I have to give input from my sensor and compare it with my reference value.Sir I need to know where that input value will be in this code.

[Azzi Abdelmalek]

why are 'nt you using simulink? how are you connecting your sensor to your computer and matlab?

[azan]

actually instead of sensor my image processing code is dong the job and it is done in mfile

[azan]

strange but even your code is not running for p=0

[Azzi Abdelmalek]

forget a disturbance signal look at the edited answer

[azan]

It is still not working at model.y='y'

[Azzi Abdelmalek]

which version of matlab are you using?

[azan]

matlab 7.8(2009)a

[Azzi Abdelmalek]

when you click on >>model

what do you get?

[azan]

a = x1 x1 -1

b = u1 x1 1

c = x1 y1 1

d = u1 y1 0

[Azzi Abdelmalek]

know, when you click model.u and model.y what is the result?

[azan]

Sorry sir I couldn't get this what do you mean by clicking model.u and model.y? Now the error is 'Invalid property name "y". Type "help ltiprops" for more information on valid LTI properties.'

[Azzi Abdelmalek]

azan have you copied and past my code or what? because I see in your error message , model y (it's no my code) it's model.y (you missed a dote)

[azan]

No it was just a typing mistake.I have written model.y Infact I have just copied your code

[Azzi Abdelmalek]

I can't explain what is going on, because, whe I run my code it works fine

[azan]

Thank you sir for your time and effort I will try to figure it out

[azan]

Sir code is working now and the issue was I had to write like this model.inputname='u' model.outputname='y'

[azan]

Sir can you now tell me where is that input(e.g 6 taken from image processing part) in this code which I have to compare with the reference value