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The MFDC system is more elaborate than the Low Frequency Control
System. From a three phase power supply, the control implements
fullwave rectification. This rectified power is sustain with substantial
capacitance in order to smooth out as much line ripple as possible.
There are four IGBT switches for controlling the output to the welding
power transformer. The IGBTs are turned on and off in pairs (1 with
4, and 2 with 3). Since IGBTs are turned ON and OFF by the control
system, the algorithms for controlling the welding output are deterministic
rather than predictive. The length of time that the IGBTs are left
on (pulsewidth) determines the output to the welding transformer.
There are significant advantages for using MFDC systems.
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