P: Proportional Gain
I: Integral Gain
D: Derivative Gain.
Now, what really is PID and what does it matter to VFD users.
PID loops control some kind of process. There is a setpoint or target and then there is feedback showing the actual result. The most easiest one to relate is the cruise control in your automobile. You set the cruise control to 70mph. This is your setpoint. When you go up a hill, the speed starts dropping to 69, 68 mph (feedback) and the engine gets more fuel to compensate until the speed is brought back to 70mph. Go downhill and the speed hits 71, 72 and the fuel is reduced to allow the car to slow. (In a perfect process control it would even tap on the brakes to hold a tighter speed). If you want to put some P-I-D on this, then here’s what happens. The initial reaction of the accelerator is really the “P” (proportional) part of PID. You could even call it a scaled reaction. Meaning the higher the “P” is set the more the initial response of the accelerator. But let’s assume the hill is winning. Then “I” (integrator) comes into play and adds more fuel to the fire. You could say it “integrates” the amount it adds to the process. So Proportional is now, Integral is after some time has passed and the target is still not met. The D or derivative will not be discussed beyond it is for super-fast adjustments, which most times leads to an oscillation. Most users leave the D out and use the PI portion.
In the VFD world, PID can be used for a multitude of things. Keeping tension on winding paper towels, maintaining water pressure in a hotel as different faucets are turned on and off, holding a storage tank level to a certain depth, maintaining a temperature setting in a room, etc.
Does Fuji have PID control or controls? Yes, in every drive they make. They don’t skimp on this part.
Taking it a step further The ECO and Aqua Drives have multiple Process Control loops.
Special thanks to National Power Quality and
Consulting for providing these Did You Know articles.
For electrical consulting needs, NPQC can be contacted at www.natpowerquality.com