VFD set up

[Wedoca]

guys, .....question ...this might sound very elemetry but, I had to ask


what determines the type of VFD set??(constant torque, constatnt speed, constant power)

is it set by changing the drive parameter ??? or it is determine by the type of load or the motor??

 

[Skogsgurra]

It is the type of load the motor is coupled to that determines what to select.

A load that has the same torque independent of speed is a constant torque load. A hoisting system is such a load. There are no constant speed loads (except if you are running against a synchronous motor connected to the grid). A constant power load is usually a winder where web force is constant so that torque increases and speed decreases as coil diameter grows. There are also loads where torque increases with speed - a fan and its quadratic speed/torque curve is a common example.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[MacGyverS2000]

There are no constant speed loads

My lathe...

Dan - Owner

http://www.Hi-TecDesigns.com

 

[jraef]

My lathe...

That's actually a constant torque application, with a speed follower. You set the speed, the VFD alters the V and Hz output and thus maintains the torque to make the speed remain steady. When your tool bites into a work piece, the motor slows, the slip increases and the motor draws more current to return to the commanded speed. In a Vector drive, the VFD it also looking at the error and tweaking the output even more to improve the accuracy but what the VFD is doing is still maintaining that constant torque output with relation to speed. Technically, the speed changes ever so slightly in order for this to work, but what you get is a good "average speed". The better the VFD, the less speed change in that process, but it's still really about maintaining torque.

The definition of "constant speed" in the mechatronics world is "Instantaneous Speed = Average Speed". I don't see that as possible in a VFD application given that a motor is all about torque and speed. Close, but not really there.

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