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Control Systems
Stability

Practice questions from Stability.

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Q#1 Stability GATE EC 2025 (Set 1) MCQ +2 marks -0.66 marks

Consider the polynomial

. Let  be defined as follows.

 is the number of roots of  with negative real parts.

 is the number of roots of  that are purely imaginary.

 is the number of roots of  with positive real parts.

Which one of the following options is correct?

, and

, and

, and

, and

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Q#2 Stability GATE EC 2024 (Set 1) MCQ +1 mark -0.33 marks

In the feedback control system shown in the figure below .

R(s), Y(s) and E(s) are the Laplace transforms of r(t), y(t), and e(t), respectively. If the input r(t) is a unit step function, then ________.

 does not exist, e(t) is oscillatory

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Q#3 Stability GATE EC 2024 (Set 1) MCQ +2 marks -0.66 marks

Consider a unity negative feedback control system with forward path gain  as shown.

The impulse response of the closed-loop system decays faster than  if

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Q#4 Stability GATE EC 2022 (Set 1) MCQ +2 marks -0.66 marks

Consider an even polynomial  given by

 

where  is an unknown real parameter. The complete range of  for which  has all its roots on the imaginary axis is

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Q#5 Stability GATE EC 2020 (Set 1) NAT +1 mark -0 marks

The loop transfer function of a negative feedback system is

 

The value of , for which the system is marginally stable, is________.

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Q#6 Stability GATE EC 2019 (Set 1) NAT +2 marks -0 marks

Consider a unity feedback system, as in the figure shown, with an integral compensator  and open-loop transfer function 

Where. The positive value of K for which there are exactly two poles of the unity feedback system on the  axis is equal to __________ (rounded off to two decimal places).

\\169.254.160.58\Kreatryx\DATA\Gate 2019\ECE\ECE Solution Digram\47.jpg 

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Q#7 Stability GATE EC 2017 (Set 1) MCQ +2 marks -0.66 marks

Which one of the following options correctly describes the locations of the roots of the equation on the complex plane?

Four left half plane (LHP) roots

One right half plane (RHP) root, one LHP root and two roots on the imaginary axis  

Two RHP roots and two LHP roots  

All four roots are on the imaginary axis

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Q#8 Stability GATE EC 2017 (Set 2) NAT +2 marks -0 marks

A unity feedback control system is characterized by the open-loop transfer function

. The value of k for which the system oscillates at 2 rad/s is ___________

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Q#9 Stability GATE EC 2016 (Set 1) MCQ +1 mark -0.33 marks

Match the inferences X, Y, and Z, about a system, to the corresponding properties of the elements of first column in Routh's Table of the system characteristic equation

X: The system is stable ...            

Y: The system is unstable ...

Z: The test breaks down ...          

P: ... when all elements are positive

Q: ... when any one element is zero

R: ... when there is a change in sign of coefficient

X–>P, Y–>Q, Z—»R

X–>Q, Y–>P, Z—>R

X–>R, Y–>Q, Z–>P

X–>P, Y–>R, Z—>Q

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Q#10 Stability GATE EC 2016 (Set 1) NAT +2 marks -0 marks

The transfer function of a linear time invariant system is given by

The number of zeros in the right half of the s-plane is_______________

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Q#11 Stability GATE EC 2016 (Set 1) MCQ +2 marks -0.66 marks

The first two rows in the Routh table for the characteristics equation of a certain closed-loop control system are given as

The range of K for which the system is stable is

-2.0 < K < 0.5

0 < K < 0.5

2.0 < K < ∞

0.5< K < ∞

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Q#12 Stability GATE EC 2015 (Set 1) MCQ +2 marks -0.66 marks

A plant transfer function is given as

. When the plant operates in a unity feedback configuration, the condition for the stability of the closed loop system is

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Q#13 Stability GATE EC 2014 (Set 4) MCQ +2 marks -0.66 marks

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

K = 2 and a=0.75

K = 3 and a=0.75

K = 4 and a=0.5

K = 2 and a=0.5

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Q#14 Stability GATE EC 2014 (Set 4) NAT +2 marks -0 marks

Consider a transfer function   with p a positive real parameter. The maximum value of p until which  remains stable is _____.

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Q#15 Stability GATE EC 2014 (Set 3) NAT +2 marks -0 marks

The characteristic equation of an LTI system is given by. The number of roots that lie strictly in the left half s-plane is ______.

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Q#16 Stability GATE EC 2008 (Set 1) MCQ +2 marks -0.66 marks

A certain system has transfer function, where  is a parameter. Consider the standard negative unity feedback configuration as shown below.  

21.jpg

Which of the following statements is true?

The closed-loop system is never stable for any value of.

For some positive values of , the closed loop system is stable, but not for all positive values.

For all positive values of , the closed loop system is stable.

The closed loop system is stable for all values of , both positive and negative.

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Q#17 Stability GATE EC 2008 (Set 1) MCQ +2 marks -0.66 marks

The number of open right half plane poles of  is

0

1

2

3

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Q#18 Stability GATE EC 2006 (Set 1) MCQ +2 marks -0.66 marks

The positive values of “K” and “a” so that the system shown in the figure below oscillates at a frequency of 2rad/sec respectively are

1, 0.75

2, 0.75

1, 1

2, 2

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Q#19 Stability GATE EC 2004 (Set 1) MCQ +2 marks -0.66 marks

The open loop transfer function of a unity feedback system is .

The range of K for which the system is stable is

13 > K > 0

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Q#20 Stability GATE EC 2004 (Set 1) MCQ +2 marks -0.66 marks

For the polynomial

, the number of roots which lie in the right half of the s-plane is

4

2

3

1

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Q#21 Stability GATE EC 2002 (Set 1) MCQ +2 marks -0.66 marks

The system shown in Figure remains stable when

k < -1

-1 < k < 1

1 < k < 3

k < -3

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Q#22 Stability GATE EC 2002 (Set 1) MCQ +2 marks -0.66 marks

The characteristic polynomial of a system is . The system is

stable

marginally stable

unstable

oscillatory

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Q#23 Stability GATE EC 2001 (Set 1) MCQ +2 marks -0.66 marks

The feedback control system in Figure is stable

 

For all

Only if

Only if

Only if

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Q#24 Stability GATE EC 2001 (Set 1) MSQ +2 marks -0 marks

Consider the feedback control system in Figure.

 

Transfer function of the system

Characteristic equation of the system

The system is stable for K>0

The system is stable for K<0

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Q#25 Stability GATE EC 2000 (Set 1) MCQ +2 marks -0.66 marks

A system described by the transfer function  is stable. The constraints on  and k are.

,

,

,

,

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Q#26 Stability GATE EC 1999 (Set 1) MCQ +2 marks -0 marks

The loop transfer function of a feedback control system is given by

,

Using Routh-Hurwitz criterion, determine the region of K-T plane in which the closed-loop system is stable.

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Q#27 Stability GATE EC 1998 (Set 1) MCQ +1 mark -0.33 marks

The number of roots of  in the left half of the s-plane is

zero

one

two

three

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Q#28 Stability GATE EC 1998 (Set 1) MSQ +2 marks -0 marks

The characteristic equation of a feedback control system is

(i) Determine the range of K for the system to be stable.

(ii) Can the system be marginally stable? If so, find the required value of K and the frequency of sustained oscillation.

(i)

(ii)  &

(i) K<1.49

(ii) K=-1.49 &

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Q#29 Stability GATE EC 1997 (Set 1) MSQ +2 marks -0 marks

The figure shows the block diagram representation of control system. The system in block A has an impulse response. The system in block B has an impulse response. The block ‘K’ amplifies its inputs by a factor k. For the overall system with input  and output

21.jpg

Transfer function, When k=1

Impulse response when K=0

values of k for which the system becomes unstable

k<-2

values of k for which the system becomes unstable
k>-2

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Q#30 Stability GATE EC 1993 (Set 1) MCQ +2 marks -0.66 marks

If , then all the roots of this equation are in the left half plane provided that

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