Test 3 - Control System | Electronics and Communication (ECE)

Description: Topic wise test 3 for Control System (ECE) of GATE Electronics and Communication
Number of Questions: 20
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Tags: Control System
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The magnitude plot of a rational transfer function G (s) with real coefficients is shown below. Which of the following compensators has such a magnitude plot?

  1. Lead compensator

  2. Lag compensator

  3. PID compensator

  4. Lead-lag compensator


Correct Option: C
Explanation:

PID compensator is used in feed back control system.

Which one of the following polar diagrams corresponds to a lag network?


Correct Option: D
Explanation:

The pole-zero given below corresponds to a

  1. Law pass filter

  2. High pass filter

  3. Band filter

  4. Notch filter


Correct Option: C
Explanation:

The feedback system shown below oscillates at 2 rad/s when

  1. K = 2 and a = 0.75

  2. K = 3 and a = 0.75

  3. K = 4 and a = 0.5

  4. K = 2 and a = 0.5


Correct Option: A
Explanation:

null

Given G(s) H(s) = $\dfrac{K}{s(s+1)(s+3)}$. The point of intersection of the asymptotes of the root loci with the real axis is

    • 4
  1. 1.33

    • 1.33
  2. 4


Correct Option: C
Explanation:

Centroid is the point where all asymptotes intersects.

$$ \sigma = \dfrac{\sum Real \ of \ Open \ Loop \ Pole - \sum Real \ Part \ of \ Open \ Loop \ Pole}{\sum No.\ of \ Open \ Loop \ Pole - \sum No.\ Part \ of \ Open \ Loop \ zero} \\ = \dfrac{-1-3}{3} = -1.33 $$

Direction: The Nyquist plot of a stable transfer function G (s) and its closed loop system in the feedback configuration are shown below.

Which of the following statements is true?

  1. G (s) is an all-pass filter.

  2. G (s) has a zero in the right half plane.

  3. G (s) is the impedance of a passive network.

  4. G (s) is marginally stable.


Correct Option: B
Explanation:

The plot has one encirclement of origin in clockwise direction. Thus G(s) has a zero is in RHP.

The transfer function of a phase-lead compensator is given by Gc = $\dfrac{1+3T_s}{1+T_s}$, where T > 0. What is the maximum phase shift of the compensator?

  1. $\dfrac{\pi}{2}$

  2. $\dfrac{\pi}{3}$

  3. $\dfrac{\pi}{4}$

  4. $\dfrac{\pi}{6}$


Correct Option: D
Explanation:

Group I gives two possible choices for the impedance Z in the diagram. The circuit elements in Z satisfy the conditions R2C2 > R1C1. The transfer functions $\dfrac{V_0}{V_i}$represents a kind of controller.

Match the impedances in Group I with the type of controllers in Group II.

  1. Q - 1, R - 2

  2. Q - 1, R - 3

  3. Q - 2, R - 3

  4. Q - 3, R - 2


Correct Option: B
Explanation:

The signal flow graph of a system is shown in figure. The transfer function $\dfrac{C(s)}{R(s)}$ of the system is

  1. $\dfrac{6}{s^2+29s+6}$

  2. $\dfrac{6s}{s^2+29s+6}$

  3. $\dfrac{s(s+2)}{s^2+29s+6}$

  4. $\dfrac{s(s+27)}{s^2+29s+6}$


Correct Option: D
Explanation:

Consider the Bode magnitude plot shown in the fig. The transfer function H(s) is

  1. $\dfrac{s+10}{(s+1)(s+100)}$

  2. $\dfrac{10(s+1)}{(s+10)(s+100)}$

  3. $\dfrac{10^2(s+1)}{(s+10)(s+100)}$

  4. $\dfrac{10^3(s+100)}{(s+1)(s+10)}$


Correct Option: C
Explanation:

The asymptotic Bode plot of a transfer function is as shown in the figure. The transfer function G(s) corresponding to this Bode plot is

  1. $\dfrac{1}{(s+1)(s+20)}$

  2. $\dfrac{1}{s(s+1)(s+20)}$

  3. $\dfrac{100}{s(s+1)(s+20)}$

  4. $\dfrac{100}{s(s+1)(1+0.05s)}$


Correct Option: D
Explanation:

A control system with a PD controller is shown in the figure. If the velocity error constant KV = 1000 and the damping ratio $\xi$= 0.5, the values of KP and KD are

  1. Kp = 100, KD = 0.09

  2. Kp = 100, KD = 0.9

  3. Kp = 10, KD = 0.09

  4. Kp = 10, KD = 0.9


Correct Option: B
Explanation:

Consider a linear system whose state space representation is x and (t) = Ax (t). If the initial state vector of the system is x (0) =$ \left[ \begin{array} \ 1 \\ -2 \end{array} \right] $, the system response is x (t) = $ \left( \begin{array} \ e^{-2t} \\ -2 e^{-2t} \end{array} \right) $. If the initial state vector of the system changes, the system response becomes x(t) = $ \left[ \begin{array} \ e^{-t} \\

  • e^{-6} \end{array} \right] $.

The system matrix A is

  1. $ \left[ \begin{array} \ 0 & 1 \\ -1 & 1 \end{array} \right] $

  2. $ \left[ \begin{array} \ 1 & 1 \\ -1 & -2 \end{array} \right] $

  3. $ \left[ \begin{array} \ 2 & 1 \\ -1 & -1 \end{array} \right] $

  4. $ \left[ \begin{array} \ 0 & 1 \\ -2 & -3 \end{array} \right] $


Correct Option: D
Explanation:

As shown in previous solution the system matrix is $ \left[ \begin{array} \ 0 & 1 \\ -2 & -3 \end{array} \right] $

The open loop transfer function of a unity feedback is given by $G(s) = \dfrac{3e^{-2s}}{s(s+2)}$

Based on the above results, the gain and phase margins of the system will be

    • 7.09 dB and 87.5�
  1. 7.09 dB and 87.5�

  2. 7.09 dB and - 87.5�

    • 7.09 dB and - 87.5�

Correct Option: D
Explanation:

Consider two transfer functions:

G1 (s) = $\dfrac{1}{s^2 + as +b}$ and G2 (s) = $\dfrac{1}{s^2 + as +b}$

The 3 dB bandwidths of their frequency responses respectively are

  1. $\sqrt{a^2-4b}, \sqrt{a^2+4b}$

  2. $\sqrt{a^2+4b}, \sqrt{a^2-4b}$

  3. $\sqrt{a^2-4b}, \sqrt{a^2-4b}$

  4. $\sqrt{a^2+4b}, \sqrt{a^2+4b}$


Correct Option: D
Explanation:

null

A unity negative feedback closed loop system has a plant with the transfer function G(s) = $\dfrac{1}{s^2 + 2s +2}$ and a controller Gc(S) in the feed forward path. For a unit set input, the transfer function of the controller that gives minimum steady state error is

  1. GC(s) = $\dfrac{s+1}{s+2}$

  2. GC(s) = $\dfrac{s+2}{s+1}$

  3. GC(s) = $\dfrac{(s+1)(s+4)}{(s+2)(s+3)}$

  4. GC(s) = 1 + $\dfrac{2}{s}$+ 3s


Correct Option: D
Explanation:

A ramp input applied to an unity feedback system results in 5% steady state error. The type number and zero frequency gain of the system are respectively

  1. 1 and 20

  2. 0 and 20

  3. 0 and $\dfrac{1}{20}$

  4. 1 and $\dfrac{1}{20}$


Correct Option: A
Explanation:

Consider a linear system with state space representation is x and (t) = Ax (t). If the initial state vector of the system is x (0) =$ \left[ \begin{array} \ 1 \\ -2 \end{array} \right] $, the system response is x (t) = $ \left( \begin{array} \ e^{-2t} \\ -2 e^{-2t} \end{array} \right) $. If the initial state vector of the system changes, the system response becomes x(t) = $ \left[ \begin{array} \ e^{-t} \\

  • e^{-6} \end{array} \right] $.

The eigen value and eigen vector pairs ($\lambda_i, V_i$) for the system are

  1. $ \left( \begin{array} \ -1, & \left[ \begin{array} \ 1 \\ -1 \end{array} \right] \end{array} \right) $and $ \left( \begin{array} \ -2, & \left[ \begin{array} \ 1 \\ -2 \end{array} \right] \end{array} \right) $

  2. $ \left( \begin{array} \ -1, & \left[ \begin{array} \ 1 \\ -1 \end{array} \right] \end{array} \right) $and $ \left( \begin{array} \ 2, & \left[ \begin{array} \ 1 \\ -2 \end{array} \right] \end{array} \right) $

  3. $ \left( \begin{array} \ 1, & \left[ \begin{array} \ 1 \\ -1 \end{array} \right] \end{array} \right) $and $ \left( \begin{array} \ -2, & \left[ \begin{array} \ 1 \\ -2 \end{array} \right] \end{array} \right) $

  4. $ \left( \begin{array} \ -2, & \left[ \begin{array} \ 1 \\ -1 \end{array} \right] \end{array} \right) $and $ \left( \begin{array} \ -1, & \left[ \begin{array} \ 1 \\ -2 \end{array} \right] \end{array} \right) $


Correct Option: A
Explanation:

The open loop transfer function of a unity feedback is given by $G(s) = \dfrac{3e^{-2s}}{s(s+2)}$

The gain and phase crossover frequencies in rad/sec are respectively

  1. 0.632 and 1.26

  2. 0.632 and 0.485

  3. 0.485 and 0.632

  4. 1.26 and 0.632


Correct Option: D
Explanation:

Directions : The Nyquist plot of a stable transfer function G (s) and its closed loop system in the feedback configuration are shown below.

The gain and phase margins of G (s) for closed loop stability are

  1. 6 dB and 1800 respectively

  2. 3 dB and 1800 respectively

  3. 6 dB and 900 respectively

  4. 3 dB and 900 respectively


Correct Option: C
Explanation:

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