JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III CONTROL SYSTEMS Previous Question Paper (March - 2021 - R18)
Answer any five questions. All questions carry equal marks.
Main
List the differences between open loop and closed loop systems with suitable examples.
Answer
The primary differences between open loop and closed loop control systems are summarized below:
| Feature | Open Loop System | Closed Loop System |
|---|---|---|
| Feedback | Absent | Present |
| Complexity | Simple and inexpensive | Complex and costly |
| Accuracy | Low; sensitive to disturbances | High; self-correcting |
| Stability | Generally stable | Requires careful design to ensure stability |
| Maintenance | Easy | Difficult |
Examples:
1. Open Loop: An electric toaster. It operates for a fixed duration regardless of the actual browning of the bread.
2. Closed Loop: An air conditioning system. It uses a thermostat to sense the ambient temperature and adjusts the compressor operation to maintain the set temperature.
Obtain the transfer function for armature controlled dc servomotor.
Answer
For an armature-controlled DC servomotor, the electrical and mechanical equations are:
Applying the Laplace transform (assuming zero initial conditions):
Substituting Ia(s) = (Js2 + fs)Θ(s) / Kt into the voltage equation:
The transfer function Θ(s) / Va(s) is derived as:
Neglecting armature inductance (La ≈ 0) simplifies this to a first-order system:
where Km is the motor gain and τm is the mechanical time constant.
What is meant by time response? Explain about (i) Steady-state response (ii) Transient response.
Answer
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Find the steady-state error for unit step, unit ramp and unit acceleration inputs for the following systems:
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List the properties of root locus and sketch the root locus of the unity feedback system with:
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A unity feed-back system is characterized by an open loop T.F G(s) = K / [s(s+10)]. Determine the gain K so that the system will have a damping ratio of 0.5. For this value of K, determine Ts, Tp and Mp for a unit step input.
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Explain clearly the steps involved in the construction of Bode plots of a system with loop transfer function consisting of:
i) An open loop gain K
ii) One pole at origin
iii) One quadratic factor.
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State and explain Nyquist Stability Criterion.
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What is Phase Margin and gain margin? Determine the transfer function whose Bode diagram is given.
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Discuss the procedural steps of lag compensation design in frequency domain.
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Define the terms: i) State variable ii) State transition matrix.
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Obtain the state space representation of the electrical system. Take x1=iL , x2=vc1, x3=vc2, v=u and y= vc2.
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An LTI system is characterized by the homogeneous state equation. Compute the solution of the homogeneous equation assuming the initial state vector.
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The system is represented by the differential equation: ÿ + 5ÿ + 6y = u. Find the transfer function from state variable representation.
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