Variable torque drives are used on Fans and Centrifugal Pumps, which may also be called Quadratic Torque Applications.

The torque to be supplied by the drive is proportional to the square of the motor speed.

Accordingly, the power required is the cube of the motor speed.

Schneider Electric have three ranges of drives for use in industry and the service sector respectively, as the constraints in these two sectors differ:

ATV212xxx drives are intended for use in the service sector (buildings) for HVAC (Heating Ventilation & Air Conditioning) applications.
They are designed for stand-alone use: with no braking resistor and no line choke; communication protocols commonly used in this type of application, such as LonWorks, Metasys N2, Apogee FLN and BACnet, are available as options.
As such it is a low-cost solution but is not available with a single-phase supply. It has limited energy storage capacity, which means that micro-cuts are not masked and result in an immediate loss of power.

The torque which can be delivered on start-up by the ATV212 is lower than that delivered by the ATV630

ATV630xxx drives are aimed more specifically at industrial processes for which continuity of service is extremely important.
They deliver a high starting torque.
The ATV630 has a greater storage capacity than the ATV212, allowing the temporary storage of energy so that micro-cuts are masked.
Communication protocols used in industry: Modbus, CANopen, TCP/IP, Profibus, Profinet ,  DeviceNet,  BACNet   "

The third drive is a simple drive which can be set to variable torque the ATV320xxx. This drive only goes up to 15Kw and has Modbus or CANopen built in with additiaonal options of ethernet TCP/IP , Profibus DP, Device bus , ether cat powerlink or profinet communications, but it can be used on single phase supply up to 2.2Kw but may require extra filters to achieve the objectives