Pulse Width Modulation - Lincoln Electric INVERTEC CV350-R Service Manual

E-7
(-)
2 µsec
(+)

PULSE WIDTH MODULATION

The term PULSE WIDTH MODULATION is used to
describe how much
conduction in the cycle. Changing the pulse width
is known as MODULATION.
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 possible over a 33
microsecond time period.
The shaded portion of the signal represents the
IGBT, conducting for 2 microseconds. Since only
2 microseconds of the 33 microsecond time period
is devoted to conducting, the output power is
minimized.
Theory of Operation
FIGURE E.6 – PULSE WIDTH MODULATION
MINIIMUM OUTPUT
MAXIMUM OUTPUT
time is devoted
Pulse Width
INVERTEC
31 µsec
33 µsec
31 µsec
33 µsec
MAXIMUM OUTPUT
to
By holding the gate signal on for 31 microseconds
and allowing only 2 microseconds of off time
during the 33 microseconds cycle, the output is
maximized. The darkened area under the min.
curve can be compared to the darkened area
under the max. curve. The more darkened area,
the more power is present.
TM
CV350-R
E-7