Why using PID Control on VFD?

This question is for developer or those who are master in PID control & would like to save cost in certain application. For speed control, it's no longer used PID methodology by programmer. Now PID control is integrated into variable frequency drive control. For example, if you want to stabilize the speed at 1500rpm, no matter load changed, via an advanced VFD, PID is itself tuning to keep it stable at 1500rpm.

I like the auto tuning function on rotating equipment that has high inertia, it is a good starting point when putting together a coordinated VFD system, such as a paper machine drive. The auto tune for the magnetic components is already available and quite adequate, the autotune is helpful when tuning the mechanical response, including the effects of stiction, inertia, noisy mechanical loads such as water crashing around in drying cylinders, sudden application of pure friction loads at the outer diameter of a drying cylinder, and acceleration & deceleration speed regulation.
VFD PID Control


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8/26/2016 3:14 AM
I need your brilliant idea in helping me on my requirements. I have an existing pump to be controlled by a variable speed drive, a pressure switch to be installed at the suction line of the pump and pressure transducer at the discharge side of the pump. The mode of operation of this pump is to manually start/stop through the local panel but still with PID control for the constant discharge pressure. The problem is I don't want to use an extra smart relays or expensive PLC for this since this will be just temporary while the construction of the new pumps is on-going. Still permissive for the low suction will apply to protect the pump.

These are the things that I need to address:
1. Is it possible to wired directly the pressure transducer in the VFD DP/DT inputs?
2. If yes, can you give me a schematic/wiring diagram on how the pressure transmitter, VFD and pressure switch be integrated to each other?
3. Or any solution to my requirement (without using PLC/smart relays)?
8/26/2016 3:18 AM
Yes, many VFDs do have the ability to perform PID control, like GoHz. This is a normal configuration for my company. We use the HMI on the VFD to enter a setpoint in this case a pressure setpoint. The VFD should have an analog input for the pressure transducer to be wired to. The VFD also should have a digital input that the low suction pressure switch should be wired to. In the configuration of the VFD that digital input will be programmed to be a permissive.

For pressure control with a centrifugal pump, I transform the linear PID pressure output to the VFD to square root, to make the tuning more stable over a higher flow range.