Designing a PI controller

Discussion in 'Homework Help' started by glorimda, Nov 11, 2012.

  1. glorimda

    Thread Starter New Member

    Oct 12, 2011
    I'm doing my homework, and encountered a problem.


    The problem is the one as attached. It includes a part of solution that I don't understand.

    I've known that when designing the PI controller, we start from D(s) = (Kp + Ki/S)

    The condition of the PI controller is, firstly, unity DC gain.

    So the way I started is setting D(0) = 1, but couldn't proceed anymore cuz there is 1/s

    in D(s), also it is obviously different from the solution.

    The second way was setting whole transfer function of the system Gcl(0) = 1,

    but couldn't find the right solution.

    According to solution, it approaches Kp and Ki separately.

    And it uses (G(0)/(1+Kp*G(0))=1), but I can't understand this.

    Could somebody help me out??