Pulse Width Modulation - Lincoln Electric VANTAGE 400 Service Manual

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PULSE WIDTH MODULATION

The term PULSE WIDTH MODULATION is used to
describe how much time is devoted to conduction in the
cycle. Changing the pulse width is known as MODU-
LATION. Pulse Width Modulation (PWM) is the varying
of the pulse width over the allowed range of a cycle to
affect the output of the machine.
MINIMUM OUTPUT
By controlling the duration of the gate signal, the IGBT
is turned on and off for different durations during a
cycle. The top drawing shows the minimum output sig-
nal possible over a 50-microsecond time period.
THEORY OF OPERATION
FIGURE E.6 – TYPICAL IGBT OUTPUTS
MINIMUM OUTPUT
sec
48
50 sec
MAXIMUM OUTPUT
sec
48
50 sec
The positive portion of the signal represents one IGBT
group conducting for 2 microsecond. The dwell time (off
time) is 48 microseconds. Since only 2 microseconds of
the 50-microsecond time period is devoted to conduct-
ing, the output power is minimized.
MAXIMUM OUTPUT
By holding the gate signals on for 48 microseconds and
allowing only 2 microseconds of dwell time (off time)
during the 50-microsecond cycle, the output is maxi-
mized. The darkened area under the top curve can be
compared to the area under the bottom curve. The
more darkened area under the curve, the more power
is present.
VANTAGE® 400
(Dwell or Off Time)
(Dwell or Off Time)
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