JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Tech II Year CONTROL SYSTEMS Previous Question Paper (February - 2024 - R16)
Note: i) Question paper consists of Part A, Part B.
ii) Part A is compulsory, which carries 25 marks. In Part A, answer all questions.
iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
Part A
What do you mean by a closed-loop control system?
Answer
A closed-loop control system is a system in which the control action is dependent on the output of the system. It utilizes a feedback mechanism to compare the actual output with the desired input (reference signal), generating an error signal that the controller uses to adjust the process to minimize the difference and maintain the desired performance.
What are characteristics of negative feedback?
Answer
Negative feedback is a fundamental concept in control systems where a portion of the output is subtracted from the input to reduce the error signal. Its primary characteristics include:
- Increased Accuracy: By continuously comparing the output to the reference input, negative feedback minimizes the steady-state error, making the system output more precise.
- Improved Stability: It helps in stabilizing an unstable system by reducing the overall gain and making the system less sensitive to parameter variations and external disturbances.
- Increased Bandwidth: Negative feedback extends the frequency range over which the system operates effectively, allowing for faster response times and better tracking of high-frequency inputs.
- Reduced Sensitivity: The system becomes less dependent on variations in the internal components or gain of the forward path, leading to more predictable performance.
Why are test signals needed?
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Name and define the static error coefficients.
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What is conditional stability?
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Define Phase margin and phase cross over frequency.
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What is a lag-lead compensator?
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How polar plots are useful in finding the stability of a system?
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How do you obtain the characteristic equation of a system from its state model?
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State the properties of state transition matrix.
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Part B
State Masons’s gain formula.
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Obtain the closed loop transfer function of the system whose block diagram is shown in figure 1.
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Write the differential equations governing the mechanical rotational system shown in figure 2 and determine the transfer function.
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Compare the AC and DC servomotor.
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What is the effect of a PD controller on the system performance?
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The open loop transfer function of a unity feedback system is given. Determine the nature of response of the closed loop system for a unit step input. Also determine the rise time, peak time, peak overshoot and setting time.
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What is the effect of a PI controller on the system performance?
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For a unity feedback control system, the open loop transfer function is given. Find the position, velocity and acceleration error constants.
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Sketch Bode plot for the following transfer function and determine the system gain K for the gain cross over frequency to be 5 rad/sec.
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Sketch the root locus of the system whose open loop transfer function is given. Find the value of K so that the damping ratio of the closed loop system is 0.5.
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The open-loop transfer function of a type-2 unity feedback system is given. Design a suitable compensator to meet the following specifications: Acceleration error constant and phase margin.
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Sketch the polar plot of a system given. If the plot crosses the real axis determine the corresponding frequency and magnitude.
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Explain the concept of diagonalization.
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Obtain the state transition matrix for the state model whose A matrix is given.
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Given its state model, how can you determine the stability of a system.
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Obtain the state variable model in phase variable form for the given system.
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