Question:

Consider a unity negative feedback control system with forward path gain: \[ G(s) = \frac{K}{(s+1)(s+2)(s+3)}. \] \vspace{0.5cm} \begin{center} \includegraphics[width=8cm]{37.png} \end{center} The impulse response of the closed-loop system decays faster than \(e^{-t}\) if \(\_\_\_\_\).

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To ensure a desired decay rate, analyze the real parts of the closed-loop poles using the characteristic equation and adjust \(K\) accordingly.
Updated On: Jan 31, 2025
  • \(1 \leq K \leq 5\)
  • \(7 \leq K \leq 21\)
  • \(-4 \leq K \leq -1\)
  • \(-24 \leq K \leq -6\)
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The Correct Option is A

Solution and Explanation

Step 1: Derive the characteristic equation for the closed-loop system.
The closed-loop transfer function is given by: \[ T(s) = \frac{G(s)}{1 + G(s)} = \frac{\frac{K}{(s+1)(s+2)(s+3)}}{1 + \frac{K}{(s+1)(s+2)(s+3)}}. \] The characteristic equation of the system is: \[ (s+1)(s+2)(s+3) + K = 0. \] Step 2: Condition for faster decay than \(e^{-t}\).
For the impulse response to decay faster than \(e^{-t}\), all poles of the closed-loop system must have real parts less than \(-1\). Step 3: Determine the range of \(K\).
Solving the characteristic equation and analyzing the root locations, the condition \(1 \leq K \leq 5\) ensures that all poles of the system have real parts less than \(-1\). Final Answer: \[\boxed{{(1) } 1 \leq K \leq 5}\]
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