Pulse Width Modulation - Lincoln Electric VANTAGE SVM178-B Service Manual

E-6
sec
2

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 MODULA-
TION. 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 signal pos-
sible over a 50-microsecond time period.
THEORY OF OPERATION
FIGURE E.6 – TYPICAL IGBT OUTPUTS
MINIMUM OUTPUT
sec
48
sec
50
MAXIMUM OUTPUT
sec
48
sec
50
The positive portion of the signal represents one IGBT
group conducting for 2 microsecond.
(off time) is 48 microseconds. Since only 2 microsec-
onds of the 50-microsecond time period is devoted to
conducting, 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® 500
(Dwell or Off Time)
(Dwell or Off Time)
E-6
The dwell time