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State modeling of RL circuit

  1. Nov 1, 2013 #1
    Hi.. This is sundaram, I'm trying to learn state space modeling, I'm trying to model the simple RL series circuit, to control/read the current flowing through inductor.

    I could find the way to monitor the voltage across inductor. as below

    x'=(u - Rx)*(1/L)
    y=(u - Rx)

    where:
    x => i (current), x' => di/dt
    R=> resistance & L=> inductance
    u is the applied voltage
    y=> the voltage across inductor


    can any one help me in framing the state space equation to control I

    Thanks in advance..!
    Sundaram..
     
  2. jcsd
  3. Nov 1, 2013 #2

    meBigGuy

    User Avatar
    Gold Member

    I'm too lazy to figure out and rewrite your variables.

    Rewrite it with I, V, and R and subscripts.

    I'm not sure what you mean by state space, but maybe it will be clear when you rewrite the equations.
     
  4. Nov 2, 2013 #3
    hello sundaram...
    you did right... lemme call the current that is flowing through the inductor iL = x1
    using kirchhoff voltage law you got

    x1' = u/L - (R/L)*X1

    to "control" your current you just need to use y = x1

    in MATLAB you can use
    A = [-R/L]
    B = [u/L]
    C = [1]
    D = 0
    sys = ss(A,B,C,D)
    step(sys)
    it will show you the step response of your system using the current as output. :D
     
    Last edited: Nov 2, 2013
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