ELEC5303 Week 1: Computer Control System Design: Course Overview

1
ELEC5303 Week 1 Computer Control System Design
Course Overview

• Lectures on text
• Computer Controlled System Theory and Design by
  Astrom and Wittenmark, 3rd edition, Prentice Hall
  (1997) ISBN 0133148998.
• Digital Signal Processing using Matlab, Vinay K.
  Ingle and John G. Proakis, 2nd Edition, Thomson,
  (2007) ISBN 0495073113
• Tutorials on exercises in text
• 2 to 3 exercises per week totaling 30 of total
  course mark.
• Final Exam worth 70 of total course mark.

2
Tutorials

• Start in week 3
• Exercises based on text and lectures
• Tutorial for help, to submit exercises and to get
  exercises marked.
• Exercises marked by tutor.
• 30 of course mark

3
Computer Control System

• y(t) AND u(t) continuous time signal
• A-D analogue to digital converter
• Conversion done at sampling times tk
• Computer interprets converted signal y(tk) as
  a sequence of numbers
• Computer then processes the measurements using an
  algorithm and gives a new sequence of numbers
  u(tk)
• The sequence is then converted to an analogue
  signal by a D-A converter.
• Events synchronized by real time clock in the
  computer.
• Computer controlled system contains both
  continuous time signals and sampled (discrete
  time) signals. Such systems are also called
  Sampled Data Systems

4
A schematic diagram of a computer controlled
system.
5
Computer Control Theory

• Using computers to implement controllers has
  advantages
• There are no problems with accuracy or drift
  (evident with analogue implementation)
• Very easy to have sophisticated calculations in
  the control law
• Easy to include logic and nonlinear functions
• Use tables to store data

6
Computer Control Theory

• Times when measure signal is converted to digital
  form are called sampling instants
• Time between successive samplings is called
  sampling period and is denoted by h.
• Periodic sampling is normally used.
• You could sample when the output signals have
  changed by a certain amount or use different
  sampling periods for different loops in the
  system (called multi-rate sampling).

7
Computer Controlled Systems

• A schematic diagram of a computer controlled
  system.
• The system consists of
• Process
• Sampler together with Analogue to Digital (A-D)
  converter
• Digital to Analogue (D-A) converter with a hold
  circuit
• Computer with a clock, software for real time
  applications, and control algorithms
• Communication network

8
Computer Controlled Systems

• The process is a continuous time physical system
  to be controlled.
• The input and the output of the process are
  continuous time signals.
• The AD converter is converting the analogue
  output signal of the process into a finite
  precision digital number depending on how many
  bits or levels that are used in the conversion.
• The conversion is also quantized in time
  determined by the clock. This is called the
  sampling process.
• The control algorithm thus receives data that are
  quantized both in time and in level. The control
  algorithm consists of a computer program that
  transforms the measurements into a desired
  control signal.
• The control signal is transferred to the DA
  converter, which with finite precision converts
  the number in the computer into a continuous time
  signal. This implies that the DA converter
  contains both a conversion unit and a hold unit
  that translates a number into a physical variable
  that is applied to the process.

9
Computer Controlled Systems

• The communication between the process, or more
  accurately the AD and DA converters, and the
  computer is done over a communication link or
  network.
• All the activities in the computer controlled
  system are controlled by the clock with the
  requirement that all the computations have to be
  performed within a given time.
• In a distributed system there are several clocks
  that have to be synchronized.
• The total system is thus a real time system with
  hard time constraints.

10
Schematic diagram of a computer controlled system
11
Discrete Time signals using Matlab

• a discrete-time signal, which is a, number
  sequence, where the up-arrow indicates the sample
  at discrete instance in time, n 0.
• A correct representation of x(n) would require
  two vectors, one each for x and n. For example, a
  sequence x(n) 2,I,-1,0, I,4,,3,7 can be
  represented in MATLAB by

12
Unit sample sequence
13
Unit step sequence
14
Real-valued exponential sequence and
Complex-valued exponential sequence
15
Sinusoidal sequence
16
Signal addition
17
Signal multiplication
18
For week 2

• No tutorials in week 2
• Tutorials start in week 3
• Do tutorial in week 3
• First homework is due in week 4 tutorial class
• Read Chapter 1 of Digital Signal Processing using
  Matlab