Basic Principle of dc chopper

in this PPT i gave introductions of the dc chopper . basic principle and working of dc chopper. and all the contents are in ps bimbhra power electronics book.

1. Power Electronics - 1 (2150903)
Active Learning Assignment
on
Basic Principle And Operation of DC Chopper
Prepared By:
Patel RajalKumar H.
(160123109013)
Guided By :
Prof. Purv Mistry
Electrical Department
Batch-B3
Gandhinagar Institute of Technology 1

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Introduction
Basic principle of DC chopper
Operation of DC chopper
Conclusion
References

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Many industrial application require power from dc voltage
sources. several of these application,. however , perform better
in case these are fed from variable dc voltage sources.
Example of these like trolley buses, subway cars, battery-
operated vehicles, battery-charging etc.
There is two type of chopper
1)AC Link Chopper
2)DC Chopper

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1)AC chopper:
In the ac link chopper, dc is first converted to ac by an
inverter (dc to ac Converter). AC is then stepped-down or
stepped-up by a transformer which is than converted back to
DC by a diode Rectifier.
As the conversation is in two stages, dc to ac and then ac to
dc, ac link chopper is costly, bulky and less efficient.

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A chopper is a static device that converts fixed dc input
voltage to a variable dc output voltage directly.
A chopper may be through of as dc equivalent of an ac
transformer since they behave in an identical manner. as
chopper involve one stage conversion. these are more efficient.
The power semiconductor devices used for a chopper circuit
can be power BJT, power MOSFET, GTO or force-
commutated thyristor. These Devices, in general , can be
represented by a switch SW with an arrow as shown in fig (c).

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when the switch is off, on current can flow. when the switch is
on, current flows in the direction of arrow only.
the power semiconductor devices have on-state voltage drops
of 0.5V to 2.5V across them.
As stated above , a Chopper is dc equivalent to an ac
transformer having continuously variable turns ratio, like a
transformer, a chopper can be used to step down or step up the
fixed dc input voltage.

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A chopper is high speed on/off semiconductor switch. it is
connects sources to load and disconnects the load from source
at a fast speed. in this manner, a chopped load voltage as shown
in fig.2(b). is obtained from a constant dc supply of magnitude
V
s
Shown in fig.2(a).
Chopper is represented by a switch SW inside a dotted
rectangle, which may be turned-on or turned-off as desired. for
the sake of highlighting the principle of chopper operation, the
circuitry used for controlled on, off periods of this switch is not
shown.

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FIG. 2(a) Elementary chopper circuit

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Fig. 2(b) Output voltage and current waveforms.

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During the period T
on
, chopper is on and load voltage is equal to
source voltage V
s
. During the interval T
off
, chopper is off, load
current flows through the freewheeling diode FD. As a result, load
terminals are short circuited by FD and load voltage is therefore
zero during T
off
. in this manner, a chopped dc voltage is produced
at the load terminals. The load current as shown in Fig. 2(b) is
continuous.

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After study this Topic I understand the basic principle and
operation of chopper.
In this topic I studied the Different types of semiconductor are
use as chopper.

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Power Electronics -1
(P.S.Bimbhra)

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