Welding Current Regulation

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.