AB VFD Help on a Saturday!?

[Steve Bailey]

Does the drive's PI algorithm include a 'Bias' or 'Feedforward' parameter? If so, by adding some bias, you can reduce the influence of the proportional and integral terms. Bias is independent of error, so it is always present. The P and I terms are algebraically added to it. If you can make the bias track the setpoint, so much the better.

 

[Beryl]

Unless they are hidden somewhere (which is entirely possible) then it does not. I will ask the question.
I think I have the drive setup to where it won't drop below about 30Hz just by tuning the loop better. The pump has to run about there to maintain the desired pressure on the pipe even at no usage. The problem came about if you went from a very high flow to virtually now flow in a short period of time. The freq would drop very quickly to try and compensate. I slowed this decent down to where the pressure has time to stabilize and without causing a large spike in pressure. I'll be for buying a different drive in the future that has more bells and whistles.

 

[msinclair]

Beryl,

Have a look at parameters 150 and 250. If I am reading the manual correctly, then in PI mode all that will happen is that an alarm will be issued (so you are correct - the "Min Frequency" seems to be ignored).

As Philip said though, if you look at parameter 223 (PI Neg Limit), I think you can get the behavior that you want.

Good luck,

Marc