Torque limit and Control

[maypot]

Hi,

Basically why torque limit and control is not possible in V/F and open loop vector mode of control.

Thanks.

Bob

 

[Skogsgurra]

Simply because there is no torque signal in the V/f drive. A *true* vector drive should always be able to torque limit - but some may not have the limit available to the user.



Gunnar Englund

http://www.gke.org

 

[PowerfulStuff]

maypot,
I was (un)lucky enough to be run through the maths of vector drive operation. Simply put, it breaks the rotating magnetic field into two components at 90 degrees. One creates the effective flux in the stator and the other induces current in the rotor. The key is knowing where the rotor to determine where the field should be, and then create the voltages on the leads in to get there. With this in mind it is very easy to control torque by varying the second flux component. I have seen many 'sensorless' vector drives but am a little bit sceptical about how well they sense rotor position. I have seen closed loop vector drives do astounding things however- everything promised!

 

[laundry]

Hello maypot
You canot have torque control in v/f because in torque control the current demand is connected to the current PI controller giving closed loop torque/current control. the current error is passed through proportional and integral terms to give a frequency ref

Barry.

 

[jraef]

faq237-1062

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