This presentation may help to understand the working principle of inverter.

1. WELLCOME!
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2. WORKING MECHANISM OF
POWER INVERTER
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Oct, 2018
By: Sayed Ahmad Zamir
Kandahar University
Engineering faculty
Energy engineering Department

3. Outline
1. Introduction
2. Inverter
3. AC as an output
4. Working mechanism
5. AC as Sinusoidal
6. SPWM Technique
7. Transistor
8. Comparator
9. Inductor and capacitor
filtration
10. Old method of conversion
11. Types of power inerter
12. Inverter vs. Converter and
UPS
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4. Introduction
 There are two types of power in the world an AC
and DC.
 A DC current is that which has one direction of
flowing current or does not have a frequency,
While AC current has a frequency and changes
the direction of the flowing current our the time.
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5. Cont.
 Although they have their own application, but
some time we need to convert them on each
other.
 To convert the DC into AC, we use an inverter.
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6. inverter
 All of us are familiar with an inverter, and we have
been using it in our daily life.
 An inverter is a electrical circuit capable of turning
DC power in to an AC power statically, while at
the same time regulating the voltage, current and
frequency the signal.
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7. Cont.
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8. AC as an output
 The average value of AC power is zero
 In fact all inverters are produce a square wave
power.
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9. Working mechanism
 To convert a DC
power into an AC
power, lets to look this
circuit which is called
full bridge inverter.
 This circuit consist of
four switches.
 The output is on the
load.
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10. Cont.
 In first stage the S1
and S4 is on.
 The current flow from
positive to negative on
one direction.
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11. Cont.
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12. Cont.
 In the second stage if
we switch on the S3
and S2, the result the
current is flowing from
positive to negative
but, the opposite
direction of as in first
stage without to
change the direction
of source.
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13. Cont.
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14. Cont.
 The result is that, here we applied the voltage on
the load but the direction of the current was
different and the applied voltage on the load was
changed from positive to negative.
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15. Cont.
 If switch once the all switches respectively, here
will be produced one cycle of an AC current.
 If we want to produce a power of 50HZ frequency,
we have to switch on the S1 and S4 for 1/100
second, and then switch on S3 and S4 for 1/100
second, which is so difficult.
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16. Cont.
For half positive voltage
For half negative
voltage
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17. Cont.
 To make this switches on and of at this much high
frequency, we require an electronic based
controller circuit. This may be analog or digital
electronic circuit, which generate the current
pulses for this switches.
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18. AC as Sinusoidal
 The actual alternating current should have form of
sinusoidal wave, whose magnitude increases and
decreases.
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19. Cont.
 But our out pout is a square wave form.
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20. SPWM Technique
 To regulate this
square wave form as
sinusoidal, a
technique is used
which is called
Sinusoidal Pulse
Width Modulation
(SPWM).
 There is the need to
change the width of
pulses, means to vary
the on time of the
switches.20

21. Cont.
 Firstly they are may on for a very small duration,
then their on time may to increase and then it
may to decrease at the same rate.
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22. Cont.
 To do this for half positive cycle, do not turn on T1
and T4 for the complete time. Thy must on and
off.
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23. Cont.
 For half negative cycle T3 and T4 on and off, like
T1 and T4.
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24. Cont.
 The output voltage is positive and negative, and the
width of pulses are very short as compere to the
response time of the load circuit.
 The average value of these pulses will be the
sinusoidal nature.
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25. Cont.
 The transistors are to be used as four switches to
on and off the circuit.
 To average the square waves form to sinusoidal
form, two comparator must be used.
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26. Transistor
 To on and of the
switches as much this
high frequency, the
Transistors must be
used.
 Transistor is a device
made from
semiconductor as
silicon and has a
capability to switch on
and off rapidly.
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27. Cont.
 Has two types
PNP NPN
PNP means positive
negative and positive.
NPN means negative
positive and negative.
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28. comparator
 Comparator is a device which compere the given
voltage to the reference voltage.
 Has many types and we use this for averaging
the output voltage of SPWM.
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29. Cont.
 They are also arranging the (on and of) of
transistor to avid the short circuit. It means that
when the S1 is on the S2 must be off, and also
while the S3 is on the S4 must be off.
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30. Inductor and capacitor filtration
 An inductor is a
device which
conserve energy in
the magnetic field.
 And in an inverter it is
used for current
filtration.
 A capacitor is a device
which conserve
energy in an electric
filed.
 And in it is used for
voltage filtration.
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Capacit
or
Inductor

31. Stepping up the voltage
 To step up the
inverted voltage
commonly from 12
voltsto 220 volts, we
use a transformer.
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32. Old method of conversion
 In the past the changing of current was had been
done dynamically before the invention of inverter
by
 connecting of the DC motor with an AC generator.
 Rotary switch.
 Which were not efficient.
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33. Types of power inverter
I. The square wave inverter: a square wave
inverter is a one of simplest inverter type, which
convert a straight dc signal to a phase shifting ac
signal, but the output is not pure ac, i.e. in the
form of a pure sine wave, but it’s a square wave.
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34. Cont.
II. The modified sine wave inverter: a modified sine
wave shows some pauses before the phase shifting
of the wave, i.e. unlike a square it does not shift it
phase abruptly from positive to negative, or unlike a
sine wave does not make a smooth transition from
positive to negative but brief pauses and them shifts
it’s phase.
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35. Cont.
 Pure sine wave inverter: the electrical circuit of a
pure sine wave inverter is more complex than a
square wave or modified sine waver inverter. Another
way to obtain a sine output is to obtain a square wave
output from a square wave and then modify this
output to achieve a pure sine wave
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36. Inverter vs. Converter and UPS
 Converters and inverters are electrical devices
that both convert power.
 Converters convert the voltage of an electric
device, usually alternating current (AC) to direct
current (DC). On the other
hand, inverters convert direct current (DC) to
alternating current (AC).
 UPS: Uninterruptible power supply (UPS)
provides power in case of power cut. Mostly used
for desktop computers backup and can save
energy for computer from 10 to 20 minutes.
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37. Cont.
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Converter
UPS

38. Any
question???
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