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For a unity feedback control system having an open-loop transfer function

\[G(S) = \dfrac{K(S + 2)}{S^{2}(S^{4} + 7S + 12)}\]

The error constant \(K_p\), \(K_v\) and \(K_a\) respectively are

  • A.\(\infty, \infty, K/6\)
  • B.\(0, 0, K/6\)
  • C.\(\infty, 0, K/6\)
  • D.\(0, \infty, K/6\)

Answer: A

The error constants are \(\infty\), \(\infty\) and \(K/6\), the first option. The system has two poles at the origin, so it is of type 2, and for type 2 the position and velocity constants are infinite.

\[K_p = \lim_{s \to 0} G(s) = \infty\]

\[K_v = \lim_{s \to 0} sG(s) = \infty\]

\[K_a = \lim_{s \to 0} s^2 G(s)\]

\[K_a = \dfrac{2K}{12} = \dfrac{K}{6}\]

The other options give a finite \(K_p\) or \(K_v\), which belongs to a type 0 or type 1 system.

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