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Current regulation (Creg/ACC) is a weld control procedure for controlling
the output to the work piece. Rather than phase-shifting the SCRs
strictly on a time domain basis (example 50% of sine wave), the
control determines the phase angle based on the programmed secondary
current (Is).
On a SCR system, the welding control proceeds in the following sequence:
1) the control predicts the phase firing for the target current,
2) the control fires the SCRs at the calculated point, 3) the control
reads the resulting current for that period, then 4) the control
compares the resulting current with the target current. This sets
up a new prediction for the subsequent firing point on the next
half cycle period.
On an inverter system, the control simply turns on the IGBT until
the target current or the maximum pulse width is achieved. The inverter
system is a deterministic algorithm since it is capable of turning
off the IGBT as needed. The SCR can only be turned on leaving the
balance of current flow determined by the welding bus crossover
point of the sine wave.
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