I had a bit of a problem implementing feed forward control on some flow control valves. During steady state, the control with feed forward was much better than the straight PID control. However, on startup and during setpoint changes, the time taken for the flow rate to change generally resulted in some reset windup with a small but unacceptable overshoot and a long settling time.
I overcame this on startup by disabling the integral control for the first 10 seconds, and so far the small adjustments to the setpoint by the operators haven't caused much of a problem. However, I was looking at another possible solution where for every setpoint change, I will set the integral hold function for 5 to 10 seconds.
Now the question I would like to ask is for those who use feed forward control, is this a common problem? And do you normally disable the PID control during setpoint changes? Is there another way of doing this?
Thanks in advance.
Doug
I overcame this on startup by disabling the integral control for the first 10 seconds, and so far the small adjustments to the setpoint by the operators haven't caused much of a problem. However, I was looking at another possible solution where for every setpoint change, I will set the integral hold function for 5 to 10 seconds.
Now the question I would like to ask is for those who use feed forward control, is this a common problem? And do you normally disable the PID control during setpoint changes? Is there another way of doing this?
Thanks in advance.
Doug