DC Chopper Voltage Control Methods
There are following methods for DC Chopper Voltage
Controls.
- Constant frequency control
- Variable frequency control
- Current limit control
DC Chopper Voltage Control: Constant Frequency Control
DC Chopper Voltage Control: Constant
frequency control ( Pulse
width modulation control )
The
chopping frequency is kept constant in this method therefore it is called as
constant frequency control. The chopper ON
time or chopper OFF time is adjusted in this method therefore it is called as
pulse width modulation control. When the chopper ON
time and OFF time is kept equal, the output voltage is equal to half the input
voltage.
When
Chopper ON time is equal to chopper OFF time
VO =
( TON / TON + TOFF ) Vdc
= ( TON / TON + TON) Vdc ( TON =
TOFF )
= 0.5Vdc
If the chopper ON time is kept ¼
times chopper OFF time, the output voltage becomes 20% of the input voltage.
VO =
( TON / TON + TOFF ) Vdc
= ( TON / TON + 4TON) Vdc
( TON = TOFF /
4)
= 0.2Vdc
= 20% Vdc
DC Chopper Voltage Control: Variable
frequency control (Frequency modulation control)
The chopping frequency is kept variable in this method and chopper ON time or OFF time is kept constant therefore it is called as frequency modulation control. The chopper OFF time is kept constant and chopper frequency is kept variable as shown in the figure B. Similarly, the chopper ON time is kept constant and chopper frequency is kept variable in the figure C.
Disadvantages of frequency modulation techniques over pulse width modulation techniques
The
design of filter circuit is difficult because the range of chopping frequency
is very large to control output voltage. The load current becomes discontinuous
if the chopper ON time is kept higher than the chopper OFF time. There is
communication interference with nearby telecommunication lines and other
digital signal.
DC Chopper Voltage Control: Current limit control
The maximum current and minimum current pass-through
chopper is determined in this method to turn on and turn off it. When the
current becomes maximum, the chopper becomes OFF. Similarly, when the current
becomes minimum, the chopper becomes ON. The chopper ON – OFF control is shown
in the figure D.
If there is small difference between maximum and
minimum current, the ripple is produced at the output waveform.
Disadvantages of current limit control
The semiconductor switching losses are higher due to high chopping frequency.
last diagram is not right.
ReplyDeletewhat is mistake?
ReplyDeleteThe last diagram lacks specification regarding to BSS 17:1896
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