Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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)

    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..!
  2. jcsd
  3. Nov 1, 2013 #2


    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)
    it will show you the step response of your system using the current as output. :D
    Last edited: Nov 2, 2013
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook