"Stability analysis" in PID controller design

Discussion in 'Homework Help' started by kdar1987, Feb 6, 2010.

  1. kdar1987

    Thread Starter New Member

    Feb 5, 2010
    Hello everyone, I am new on here. New to be on this forum.

    I have to do mini-project for Control and Robotic System class. I have to design PID controller, from one problem, and then simulate it in simulink.

    On part where it ask to do PID controller design, it states "stability analysis". What exactly I have to do on that part? State when, under what conditions, the system is be stable?
  2. mik3

    Senior Member

    Feb 4, 2008
    For, example state the values of Kp, Kd and Ki which make the system stable at a step input change.
  3. kdar1987

    Thread Starter New Member

    Feb 5, 2010
    Thanks... I have another question..

    So, I need to have ts equal 3 seconds or less. I set it equal to 2.95 sec.
    then I find wn (4/(zts)) and later C1=2zwn and C2=wn^2
    (While z = 0.9)

    For Kp I get something like 0.689
    Kd is 0.2259
    Ki I set to 0 (for PD controller)

    However.. when I simulate it in Simulink.. it seems like that a limit is applies on vertical axis, not horizontal one. Horizontal being ts.

    I tried different values for z and ts and all doing the same.

    Can someone help me? Why I am getting such results?
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    It would be useful if you re-phrased the problem in a more systematic manner and gave a diagram of the system you are trying to control or stabilise. Your design goal is not clear.
  5. kdar1987

    Thread Starter New Member

    Feb 5, 2010
    Sorry.. I found my problem.. I forgot feedback loop...