Current regulator circuit

In the thyristor DC drive system, the current regulator is used to maintain a constant current
. It keeps the system at the maximum current given value during the starting process to improve the starting performance and shorten the starting time.
It also has strong resistance to grid interference.
    The current regulator consists of a high-gain operational amplifier A and a proportional-integral link (R, C3) to form a PI lexicon. It has multiple input terminals to synthesize
the current given signal , current feedback signal and other signals . Its output characteristics
are shown in Figure 16-76 (b).