SCADA_Dude
Member
Just looking for some opinions on VFD PID control design. What would you consider a better design for a VFD pump controlling pressure.
1. PID: Actual pressure (PV) compared to pressure setpoint (SP), output (CV) scaled directly to VFD 4-20ma. (Optionally, Actual pump speed and commanded speed are compared to generate an alarm if deviation is too large.)
2. PID: Actual pressure (PV) compared to pressure setpoint (SP), output (CV) scaled 0-100%. This 0-100% value is sent to another PID to control actual pump speed 0-100%(PV) to speed setpoint (SP), output (CV scaled directly to VFD 4-20ma.
I like the practice of comparing actual pump speed to desired speed, but both seem to accomplish the same thing, with the first being more simple. I'm interested in hearing opinions on this.
Thanks
1. PID: Actual pressure (PV) compared to pressure setpoint (SP), output (CV) scaled directly to VFD 4-20ma. (Optionally, Actual pump speed and commanded speed are compared to generate an alarm if deviation is too large.)
2. PID: Actual pressure (PV) compared to pressure setpoint (SP), output (CV) scaled 0-100%. This 0-100% value is sent to another PID to control actual pump speed 0-100%(PV) to speed setpoint (SP), output (CV scaled directly to VFD 4-20ma.
I like the practice of comparing actual pump speed to desired speed, but both seem to accomplish the same thing, with the first being more simple. I'm interested in hearing opinions on this.
Thanks