Baldor VS1GV21-1B, Installation & Operating Manual, Page: 118 / 204

8-2 Customizing Your Application MN765
PI Controller
Both the current and rate control loops are of the Proportional plus Integral type. If “E” is defined to be the error signal,
E = Command - Feedback
then the PI controller operated on “E” as
Output = (Kp * E) + (Ki ∫ E dt)
where Kp is the proportional gain of the system and Ki is the integral gain of the system.
The transfer function (output /E) of the controller using 1/s (Laplace Operator) to denote the integral,
Output/E = Kp + Ki / s = Kp (s + Ki/Kp) /s.
The second equation shows that the ratio of Ki/Kp is a frequency in radians/sec. In the Baldor AC Vector Control, the integral
gain has been redefined to be,
KI = (Ki / Kp) / (2π) Hz,
and the transfer function is,
Output/E = Kp (s + 2πKI) / s.
The integral gain is a frequency (in Hz) and should be set to about 1/10 of the bandwidth of the control loop.
The proportional gain sets the open loop gain of the system, the bandwidth (speed of response) of the system.
If the system electrical noise is excessive, the most likely cause is that the proportional gain is set too high.