Jawaharlal Nehru Technological University Hyderabad
Jawaharlal Nehru Technological University Hyderabad B.Tech III CONTROL SYSTEMS ENGINEERING Previous Question Paper (October - 2020 - R13)
Answer any five questions. All questions carry equal marks.
Main
Explain the closed loop control system with different examples. List out its merits and demerits.
Answer
A closed loop control system is a system in which the control action is dependent on the output of the system. It uses a feedback mechanism to compare the actual output with the desired input (reference) to generate an error signal, which is then used by the controller to minimize the error.
Examples include:
- Automatic Temperature Control: An air conditioner uses a thermostat to sense room temperature and adjust cooling to maintain a set point.
- Speed Control of DC Motor: A tachometer measures output speed and feeds it back to the controller to maintain constant speed under varying loads.
Merits:
- High accuracy due to feedback.
- Reduced sensitivity to parameter variations and external disturbances.
- Improved bandwidth and stability control.
Demerits:
- Complex design and construction.
- Higher cost compared to open-loop systems.
- Risk of instability or oscillations due to feedback.
Determine the transfer function of the system given in Figure 1.
Answer
Since the figure was not provided in the prompt, the general procedure to determine the transfer function for a closed-loop system is as follows:
- Identify the forward path gain G(s) and the feedback path gain H(s) from the block diagram.
- Apply the standard closed-loop transfer function formula for a negative feedback system:
If the feedback is positive, the denominator becomes 1 - G(s)H(s). Simplify the resulting expression by performing algebraic manipulation to obtain the final transfer function in the form of a ratio of two polynomials in s.
The block diagram of the multi loop system shown in Figure 2; find the closed transfer function using signal flow graph technique.
Answer
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Derive the time domain specifications of second order system with unit step input.
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The open loop transfer function of a unity feedback system is characterized as:
Find the steady state error for unity step, unity ramp and unity acceleration inputs. Also find the damping factor and natural frequency of dominant roots.
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Define the steady state error and error constants with respect to unit step, unit velocity and unit acceleration inputs. How the steady state errors can be reduced.
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State and explain the Routh’s stability criterion.
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Draw the root locus for the given open loop transfer function.
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The open loop transfer function of unity feedback system is given by:
Using Routh’s criterion, determine the values of K and T which will correspond to a stable system.
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A unity feedback control system has an open loop transfer function given by:
Draw Nyquist diagram and test the stability.
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State the advantages and disadvantages of state space approach for analysis and design of control systems.
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Obtain the state model of the system described by the transfer function:
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