JNTU
JNTU B.Tech III CONTROL SYSTEMS ENGINEERING Previous Question Paper (March-2021 - R13/R15)
Answer any five questions. All questions carry equal marks.
Main
Write the differences between open loop and closed loop control systems.
Answer
| Feature | Open Loop Control System | Closed Loop Control System |
|---|---|---|
| Feedback | Absent | Present |
| Accuracy | Depends on calibration; low accuracy | High; feedback corrects errors |
| Complexity | Simple and inexpensive | Complex and expensive |
| Stability | Generally stable | May become unstable |
| Sensitivity | Highly sensitive to parameter variations | Less sensitive to parameter variations |
| Maintenance | Easy | Difficult |
Find the transfer function Vc(s)/V(s) of the following electrical system (figure 1).
Answer
For an electrical system consisting of a resistor R and capacitor C in series, the voltage across the capacitor Vc(s) is related to the input voltage V(s) by the voltage divider rule in the s-domain. The impedance of the resistor is R and the impedance of the capacitor is 1/(Cs).
Multiplying the numerator and denominator by (Cs), we obtain the transfer function:
This represents a first-order low-pass filter system where the time constant is defined as τ = RC.
Obtain the transfer function for the following signal flow graph using Mason’s gain formula (figure 2).
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Determine the expression for output response when a standard second order system is excited with a unit step input. Also sketch the responses for various dampings.
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State and explain different error constants in steady state error analysis.
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A unity feedback control system has open loop transfer function G(s) = 5 / [s(s+1)(s+2)]; Find the steady state error if the input r(t) = 5t + 2.
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Sketch the Root-locus for the open loop transfer function G(s) = K / [s(s+1)(s+2)].
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Explain the Routh-Hurwitz criteria to predict system stability. State its limitations.
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Draw the Bode plot for the system whose open loop transfer function is G(s) = 100 / [s(s+10)(s+50)]. Also comment on system stability.
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Obtain the solution for the following state space system ẋ1 = x2, ẋ2 = x3, ẋ3 = -2x1 - 4x2 - 6x3 + u. Given initial values for [x1, x2, x3]T at t=0 are [0, 0, 1]T and 'u' is input variable.
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