1.0.1 What is an Inverter?
An inverter (or
power inverter) is an electronic circuitry that changes direct current (DC) to
alternating current (AC).
Direct current is a
type of current that flows in only one direction. Using the conventional
current flow, direct current is such that electrons leaves the power source
from the positive terminal (usually marked red) and flows through the circuit and then terminates
at the negative terminal (usually marked blue) ofthe power source. Direct
current (DC) is usually gotten from battery cells, solar panels, household
Fig 1.1 Graph of DC
voltage against time
current is one in which current direction changes with respect to time, i.e it
flows in one direction for an amount of time after which it changes direction.
In this case there is no fix polarity for the terminals of the power supply.
This type of current is usually gotten from, public power supply distribution
companies, industrial generators etc.
current graph could take the form of sine wave, square wave, triangular wave,
modified square wave etc. These graphs are shown in fig. 1.2.
Fig. 1.2 Varied
forms of alternating currents (a) sine wave
(b) triangular wave (c) square
wave (d) modified square wave
The power supplied
by industrial generator and public distribution companies is usually pure sine
wave. But commercial inverters could give output ranging from square wave,
modified square wave to pure sine wave. Although pure sine wave is most
preferable for electrical equipments, it is usually costly because of the
technology involved.The modified square wave is predominate in house hold
inverters. This modified sine wave is manageable for electoral equipment
compared of square wave
WORKING PRINCIPLES OF INVERTER
The basic difference
between an AC and a DC source is that, while an AC alternate its current
direction or polarity, a DC has fixed current direction and polarity. The major
work of an inverter therefore is to alternate the polarity of the DC power
Consider fig 1.3
The circuit consists
of a centre tapped step-up transformer, a battery and a switch. When the switch
is such that the negative terminal of the battery is connected topoint A,
current flows in the primary side of the transformer as shown by the curve ”a”.
When this is done the secondary side of the transformer gives power with current
flow in the “a” direction. When the switch is reset to connect to point B and
the negative terminal of battery, the current flow in the primary side of the
transformer is indicated by curve “b”. that of the secondary side is in curve
This arrangement gives out a square wave
output. The switching system could be mechanical or electrical. An example of
an electromechanical inverter switch is a VIBRATOR. Transistors of different
power ratings (depending on the power rating of the inverter) can be used as
switch for the circuits.
A pure sine wave can be realized with a
better technology. This is shown in fig 1.4
Fig1.4 Setup for
pure sine wave inverter
Figure 1.4 Contains
A Battery, two Drivers / Motors, A Belt, Power Amplifier and a Power
The battery supplies
power to the driver A. This causes its blades to rotate. The belt transmits
this rotary motion to driver B. The rotational motion of driver B brings about
and alternating current at the terminals of driver B. This alternating current
is fed into the power amplifier. The power amplifier combines the DC current form the battery and the AC current
from driver B to give an AC with higher power.
While the battery
supplies the power (voltage and current), the AC current from the driver B
causes it to oscillate. The output at the power amplifier is fed into the step-up
power transformer which steps up the voltage from 12 volt to 220 volts
Modern inverters are
mere development of these basic inverter circuit.
Below are some importance of inverter circuit to the
engineering and the world at large;
power sources like solar power and batteries can be used for AC appliances with
the aid of inverters
encourages storage of energy which is used in electroshock weapons and uninterruptible
power supply (UPS)
heating which requires high frequency is made possible using inverters.
to the DC/AC conversion process of
inverters, skin effect, number and size of conductors are reduced which
invariably reduces cost in HVDC transmission
AND APPLICATIONS OF INVERTER
of an Inverter
Inverter dates back
to late nineteen century through the
middle twentieth century. Although the term inverter is attributed to David
Prince who publish an article on inverter in the GE Review (vol. 28, No.10, P. 678 – 81) in 1925,
it is not certain if he was the one who
coined the term.
conversion in its early days was accomplished using rotary converters. As
technology improved, vacuum tubes and gas filled tubes were used as switches
for inverter circuit .
The name inverter can be related to the electromechanical forms
of switching used in its early days.
1.1.2 Applications of Inverter
Inverter circuit is
used in the following areas of electrical
and electronic engineering;
grid and HVDC power transmission
motor speed control
power supply (UPS)
The aim of this project is to design and
construct an inverter.
The objective of
this project is to;
review and design of the inverter: Literatures will be
reviewed to obtain the working principles and circuit diagram after which a
design will be made to ascertain the rating and parameters of the different
components involved in the inverter.
Construction of the inverter: The circuit will be
constructed firstly on a breadboard before soldering.
Testing of the circuit: The circuit will be tested with
appliances according to the calculated rating of the inverter.