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I am studying chapter 4 of Dorf title Modern Control systems(11 edition)

I am trying to use MATLAB or Labview to implement block diagram for open loop control systems for speed control of an armature controlled DC motor

I have also attached the figure of book

I understand that the rightmost block \$\frac{1}{js+b}\$ will be in feedback with \$K_b\$ block. But what will be the relation of feedback block \$K_b\$ with the two left most blocks (\$1/R_a\$ and \$K_m\$ in series) ?? Independent individual feedback relation with the two left most blocks (\$1/R_a\$ and \$K_m\$ in series) or the series combination of rightmost block \$\frac{1}{js+b}\$ and \$K_b\$ will be in feedback with the two left most blocks (\$1/R_a\$ and \$K_m\$ in series)

snapshot of block diagram

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The term "feeedback" is used when a portion of the output signal is coupled back to the input. Hence, it is important to verify the input node.

In your circuit, we have two inputs: A reference input v(s) and a disturbance input T(s) and two corresponding transfer functions H1=out/v(s) and H2=out/T(s).

  • For H1 the forward gain Hf is the product of all three forward acting blocks with the feedback block Kb.

  • For H2 the forward gain Hf is only the most right block with a feedback chain consisting of all the remaining three blocks.

  • The closed-loop gain in both cases is Hf/(1+loop gain). The loop gain is the same in both cases; it is the product of all four transfer functions.

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