AB Powerflex 755 drive PID control questions

Hi all,


I have a project that use 755 drive to control a induction motor(pump) to maintain certain flow rate. Flow meter is promass 100, unit is g/s.



Processor is L33ERMS, use PID control in the plc, not in 755 drive. The PID output% scaled into a value from 0 - 32767, this is the part I am not sure, should it be -32767 - 32767 or something else?


Right now, the pump is oscillating really bad, Ki is 2, Kp is 0.2. No matter how I change the value, it does not looks like it helps at all. The output% is always change from 0 to a small number and change back to 0, back and forth. It does not maintain to a specific number.



I have to increase the accel and dccel to 40s
to make it smooth.



In the drive parameters,



#545 Spd Ref A Sel is set to Port 0: port 13 Reference
#535 Accel time 1 0.8s
#537 Decel time 1 0.8s
#35 Motor Ctrl Mode Induction SV


We had a similar project uses powerflex 70 drive that does not have his issue, the settings are the same as the 755 drive except the



#40 motor type Induction
#53 motor cntl sel Sensrls Vect
#476 Scale1 in value 60

#477 Scale1 in Hi 60

#482 Scale2 in value 60

#483 Scale2 in Hi 60





Anyone have any idea?



Thank you very much!

For the PF70 you send 0-32767 for your min to max frequency.
For the PF755 you send the direct value of the frequency so for 40.0Hz you need to send 400.

Alan