CHAPTER 1
1.0 INTRODUCTION
Speed control is the intentional
changing of the speed of a motor for a specific purpose or work process. This
was done manually by an operator before now, but with the advent of powerful
electronic elements like thyristor, Bipolar Junction Transistor (BJT),
Insulation Gate Bipolar Transistor (IGBTs), Metallic Oxide Semiconductor Field
Effect Transistor (MOSFET), etc it is now possible to actualize this speed
control automatically.
There
are two broad classification of the speed control of a D.C motor: Armature-Voltage control scheme and field
flux control scheme. To control the motor above its based speed, the field-flux
control scheme is used, while Armature Voltage Scheme is used for speed below
its rated speed. D.C motors have numerous domestic and industrial applications
(e.g crane control, electric vehicle control, conveyor belt etc). For the
purpose of this design, the armature-voltage control scheme using MOSFET would
be used.
1.1 TECHNICAL BACKGROUND OF STUDY
This
project is designed specifically as a dc motor speed control system using
MOSFET. The circuit consists of six units:
i.
A 24V dc power source unit
ii.
Voltage regulator unit
iii.
Pulse Width Modulation (PWM) generator
unit
iv.
Signal amplifier unit
v.
MOSFET unit
vi.
24V D.C Source
The
24V D.C power source is the main power source to the circuit. The voltage
regulator regulate the voltage to 9V that powers the Pulse Width Modulation
(PWM) Generator (NE555 Timer), which generate the PWM signal needed to fire the
MOSFET The signal amplifier, amplifies the PWM signal which in turn is used to
fire the MOSFET that drives the D.C Motor. The firing angle of the MOSFET are
altered by altering of the pulse width of the PWM signal which in turn, alters
the voltage of the PWM signal going to the MOSFET and thus varies the armature
voltage and speed of the D.C motor.
1.2
STATEMENT OF PROBLEM
This design deals with how to control the
speed of a D.C Motor using MOSFET. The speed control unit should be able to
vary the speed of the D.C Motor from minimum to maximum. To achieve this is not
an easy task, especially in the area of handling the semi-conductor electronic
devices like the MOSFET Transistors, NE555 Timer etc. If there is any wrong procedure
or handling in the process of constructing the hardware, the semi conductor
devices would be destroyed. Thus
absolute care must be taken to ensure that the semi-conductor devices would
still work within their rated specification
1.3 DESIGN AIM AND OBJECTIVES.
The
main aim of this design is to design and a speed control unit of a D.C
Motor. It involves research phase, design
phase of a prototype of the design. The prototype should be able to vary the
speed of the 24V D.C Motor, from minimum to maximum speed.
These
are the objectives to be accomplished in this design:-
1.
To design an efficient speed control
system of a D.C Motor using MOSFET
2.
Construction of the design prototype.
The
prototype should be able to vary the speed of a 24V D.C Motor from minimum to
maximum
1.4 SIGNIFICANCE OF THIS DESIGN.
· To
design a prototype speed control unit
· To
design a speed control unit to power a dc motor of 0.25amps
1.5 DESIGN METHODOLOGY
This is a detailed design procedures which discuss
the parts to be designed and some other functional parts, stating clearly the
design criteria and few assumptions. The design parameters determined shall
serve as a criteria for various dimensions and calculations during design.
The
speed control unit consist mainly the following
· The
protection unit
· The
oscillator unit
· MOSFET
unit
· DC
motor unit
1.6 ORGANIZATION OF THE DESIGN
Chapter
1 introduces the background of the research work and information relating to
the design of this work. Chapter 2 deals with literature review and the
description of all the components used in the design . Chapter 3 contains the
design methodology. The results and analysis is in Chapter 4. Then the
conclusion and recommendation is presented in Chapter 5.
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