Classification Of Choppers


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Classification Of Choppers
• Choppers are classified as
– Class A Chopper – Class B Chopper – Class C Chopper – Class D Chopper – Class E Chopper
1
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

Class A Chopper

i0

v0

+

Chopper

L

V

O A

v0 V

FWD

D



Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

i0
2

• When chopper is ON, supply voltage V is connected across the load.
• When chopper is OFF, vO = 0 and the load current continues to flow in the same direction through the FWD.
• The average values of output voltage and current are always positive.
• Class A Chopper is a first quadrant chopper .
3
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

• Class A Chopper is a step-down chopper in which power always flows form source to load.
• It is used to control the speed of dc motor. • The output current equations obtained in step
down chopper with R-L load can be used to study the performance of Class A Chopper.
4
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

ig
i0 CH ON
v0 FWD Conducts
tON T
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

Thyristor gate pulse
t Output current
t Output voltage
t
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Class B Chopper

D i0 v0 +
R

V

L v0

Chopper

E

i0



6
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

• When chopper is ON, E drives a current through L and R in a direction opposite to that shown in figure.
• During the ON period of the chopper, the inductance L stores energy.
• When Chopper is OFF, diode D conducts, and part of the energy stored in inductor L is returned to the supply.
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Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

• Average output voltage is positive. • Average output current is negative. • Therefore Class B Chopper operates in second
quadrant. • In this chopper, power flows from load to
source. • Class B Chopper is used for regenerative
braking of dc motor. • Class B Chopper is a step-up chopper.
8
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

ig
i0 tOFF tON T
Imax Imin D
conducts Chopper conducts
v0
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

Thyristor gate pulse
t
t Output current
Output voltage
t
9

Expression for Output Current
10
Prof. T.K. Anantha Kumar, E&E Dept., MSRIT

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Classification Of Choppers