Compensator MCQ

21. Consider the following statements regarding compensators used in control systems:

  1. For type-2 or higher systems, lag compensator is universally used to overcome the undesirable oscillatory transient response.
  2. In the case of the lag-lead compensator, a lag and a lead compensator are basically connected in parallel
  3. The s-plane representation of the lead compensator has a zero closer to the origin than the pole.
  4. A lag compensator improves the steady-state behaviour of a system while nearly maintaining its transient response.

Which of the statements given above are correct?

  1. ii, iii and iv
  2. i, ii and iii
  3. i and ii
  4. iii and iv
Answer
Answer. d

22. Which one of the following is not a correct reason to select feedback compensation over cascaded one?

  1. No amplification is required as the energy transfer is from higher to lower level
  2. Suitable devices are not available for compensation (series)
  3. It is economical
  4. Provides greater stiffness against load disturbances
Answer
Answer. c

23. Which one of the following is the correct expression for the transfer function of an electrical RC phase-lag compensating network?

  1. $\frac{RCs}{1+RCs}$
  2. $\frac{RC}{1+RCs}$
  3. $\frac{1}{1+RCs}$
  4. $\frac{s}{1+RCs}$
Answer
Answer. c

24. Which one of the following statement is NOT correct?

  1. The transfer function of a lag-lead compensation network is $\frac{(1+sT_1a)(1+sT_2b)}{(1+sT_1)(1+sT_2)}(a > 1, b < 1)$
  2. Bridged T-network is used for cancellation compensation
  3. Phase-lag compensation improves steady-state response and often results in reduced rise time
  4. Compensating network can be introduced in the feedback path of a control system
Answer
Answer. c

25. A property of phase-lead compensation is that the

  1. Overshoot is increased
  2. Bandwidth of closed-loop system is reduced
  3. Rise-time of closed-loop system is reduced
  4. Gain margin is reduced
Answer
Answer. c

26. Indicate which one of the following transfer functions represents phase lead compensator?

  1. $\frac{s+1}{s+2}$
  2. $\frac{6s+3}{6s+2}$
  3. $\frac{s+5}{3s+2}$
  4. $\frac{s+8}{s^2+5s+6}$
Answer
Answer. a

27. The transfer function of a phase lag compensator is given by $\frac{1+Ts}{1+aTs}$ where a > 1 and T > 0. The maximum phase shift provided by such a compensator is

  1. $\tan^{-1}(\frac{a+1}{a-1})$
  2. $\tan^{-1}(\frac{a-1}{a+1})$
  3. $\sin^{-1}(\frac{a+1}{a-1})$
  4. $\sin^{-1}(\frac{1-a}{a+1})$
Answer
Answer. d

28. The Laplace transform of a transportation lag of 5 seconds is

  1. e-5s
  2. e5s
  3. $\frac{1}{s+5}$
  4. $e^{\frac{-s}{5}}$
Answer
Answer. a

29. The transfer function $\frac{V_2(s)}{V_1(s)}=\frac{10s}{s^2+10s+100}$ is for an active

  1. band pass filter
  2. low pass filter
  3. all pass filter
  4. high pass filter
Answer
Answer. a

30. Phase lead compensation

  1. increases bandwidth and increases steady-state error
  2. decreases bandwidth and decreases steady-state error
  3. will not affect bandwidth but decreases steady-state error
  4. increases bandwidth but will not affect steady-state error
Answer
Answer. a

31. The compensator $G_c(s)=\frac{5(1+0.3s)}{1+0.1s}$ would provide a maximum phase shift of

  1. 20°
  2. 30°
  3. 45°
  4. 60°
Answer
Answer. b
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