Describe the function of the DC choppers.
Function of the DC choppers
The function of the DC choppers is to convert fixed direct voltage into variable direct voltage.
What are the different technologies to convert fixed direct voltage into variable direct voltage?
Fixed
direct voltage in variable direct voltage
Line commutated
converters by using controlled rectifier
AC link chopper –
inverter and rectifier
DC Chopper
Describe the advantages of DC choppers over motor – generator
set.
Advantages
of the DC choppers
High efficiency
Low maintenance
Fast response
Low cost
Small size
Describe the various types of the DC chopper.
According to output
voltage
Step up chopper and
Step down chopper
According to the direction
of output voltage and current
Type A chopper
Type B chopper
Type C chopper
Type D chopper
Type E chopper
According to commutation
method
Voltage commutated
Current commutated
Load commutated
Impulse commutated
Which type of semiconductor device is used as switch in the DC
chopper circuit?
Semiconductor
device as a switch
Silicon controlled
rectifier
Power metal oxide field
effect transistor
Insulated gate bipolar
transistor
Gate turn off thyristor
MOS controlled thyristor
Explain the term : Step up chopper, Step down chopper
Step
up chopper
It is a chopper in which
the DC output voltage is more than that of the input DC voltage.
Step
down chopper
It is a chopper in which
the DC output voltage is less than that of the input DC voltage.
Define : Duty cycle
Duty
cycle
It is defined as the
ratio of the chopper on time to the chopper switching time.
K = TON / T
K = Duty cycle
TON
= Chopper turn on time
T = Chopper switching time
Which is main factor responsible for control of the output
voltage of the chopper?
Duty cycle
Describe the various methods of output voltage control in the
chopper
Method
of chopper output voltage control
Constant frequency
control ( Pulse width modulation control )
Variable frequency
control ( Frequency modulation control )
Current limit control
In which method of voltage control chopping frequency is kept
constant in the chopper?
Constant frequency
control ( Pulse width modulation control )
Describe the disadvantages of the frequency modulation voltage
control over the pulse width modulation voltage control.
Disadvantages
of the frequency modulation voltage control over the pulse width modulation
voltage control
There is a possibility of
radio interference with nearby telephone lines and other signaling. Load
becomes discontinuous if the chopper OFF time is larger than that of chopper ON
time. Filter design is difficult due to wide frequency variations.
Describe the disadvantage of current limit control in the DC
chopper.
Disadvantages
of current limit control
If there is a small
difference between maximum and minimum current, the output waveform contain ripple.
Higher switching losses due to high chopping frequency
Why higher value of inductor is preferred for step up chopper?
In order to reduce output
voltage ripple
Write the relation between input and output voltage in the step
down chopper, step up chopper and step up / down chopper
Relation
between output voltage and input voltage
Step down chopper
VO = KVIN
( K < 1)
Step up chopper
VO = VIN
/ ( 1 – K ) ( 0 < K < 1 )
Step up / down chopper
VO = [ K / ( 1
– K ) ] × VIN
Where VO =
Output voltage
VIN = Input voltage
K = Duty cycle
The chopper works as step
down chopper if 0 < K < 0.5 . The
chopper works as step up chopper if 0.5 < K < 1.
Why the operation of the chopper in the first quadrant is called
as forward drive?
The output voltage and
output current of the chopper is positive therefore the operation of the
chopper in the first quadrant is called as forward drive.
Why the type A chopper is called as step down chopper?
Type
A chopper ( Step down chopper )
As the output voltage is
less than the input voltage in the type A chopper, it is also called as step
down chopper.
Which chopper works in the second quadrant?
Type B chopper
Why the type B chopper is called as step up chopper?
Type
B chopper ( Step up chopper )
As the power flow from
load to source in type B chopper, it is also called as step up chopper.
Which chopper configuration is used in the regenerative braking?
Type B chopper
Which chopper is parallel combination of type A and type B
chopper?
Type C chopper
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