# Closed-Loop control system - Control Systems - Exam, Exams for Control Systems. Aligarh Muslim University

## Control Systems

Description: Main points of this past exam are: Closed-Loop Control System, Open-Loop System, Differential Equation, Domestic Central Heating, Electric, Transfer Function, Time-Constant
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Cork Institute of Technology
Bachelor of Engineering (Honours) in Electronic Engineering
- Stage 3
(EELXE_8_Y3)
Autumn 2008
CONTROL SYSTEMS
(Time: 3 Hours)
INSTRUCTIONS:
Each question is worth 25 marks.
You MUST include a list of all MATLAB commands or Simulink diagrams used to
answer a question. Marks will be lost if you fail to do this.
Examiners: Dr. T O' Mahony
Prof. G. Hurley
Dr. S. Foley
Q1. (a) In your own words clearly explain the difference between an open-loop control
system and a closed-loop control system. Include a block diagram illustrating the
difference between an open-loop system and a closed-loop system. Give one
example of an open-loop system and one example of a closed-loop system.
[5 marks]
(b) The thermal response of a domestic central heating system is defined by the
differential equation () 0.003 ( ) 0.02 ( )
dT t Tt Ut
dt
+=
where T(t) is the building
temperature and U(t) is the input signal that switches on/off the electric/gas boiler.
Apply the Laplace Transform to determine a transfer function for this system. What
is the gain of the domestic heating system and what is the time-constant?
[5 marks]
(c) Calculate the closed-loop transfer function for the system illustrated in Figure Q1(c)
for a value of controller gain K = 10. Is the closed-loop system stable for this value
of gain? Generate the response to a unit step input and measure (i) the steady-state
error and (ii) the percentage overshoot. How would you eliminate the steady-state
error in this case?
Plant
Controlle
R(s) U(s)
+
-
Y(s)
K
2
0.6
0.4 0.4ss++
Figure Q1(c)
[15 marks]
Q2. (a) Consider the frequency responses illustrated in Figure Q2(a) and Figure Q2(b).
Figure Q2(a)