Selection of an "AC" motor and controller for a specific application are normally based on the following criteria:

Acceleration torque is the difference between the motor output torque Mt and load torque Ml during speed acceleration from a given speed to set speed. Acceleration torque is decided by the total system inertia and acceleration time set by the controller. Ma is directly proportional to moment of inertia and inversly proportional to Acceleration time i.e. (Jdw/ dt)

Frictional torque is a torque required to compensate static/dynamic load friction

Most standard AC motors are designed to operate at a fixed rated speed. At this fixed speed the built - in cooling system (cooling fan mounted on motor shaft) will keep the motor from over heating. When operated as an adjustable speed motor, cooling action will be reduced at lower speed due to reduced cooling fan speed. This will result in overheating of motor for constant torque application.Hence deration/oversizing of motor may be needed . Alternate to overframing / derating the motor special auxiliary cooling such as a blower can be used

Motor kW ratings apply for a pure sinusoidal voltage at rated speed and frequency. When motor are driven from inverters, non-sinusoidal voltage will be applied to the motor. The harmonic currents generated in the motor due to non-sinusoidal voltage will result in extra heat loss in the motor. To compensate for the additional heat, motors are to be over framed / derated. If carrier frequency is 5khz or more,no deration is required.10%deration may be requiered if carrier frequency is less than 5khz. Alternatively to derating / overframing motor, motor with class F insulation one can proceed with the risk that motor loading will be maximum 90% of motor rated power. Starting torque (breakaway torque produced by the NEMA-D motor is greater than NEMA-B motor when motor are connected to inverters the starting torque of NEMA- B motor will be much more than the NEMA-D motors It is important to remember that a properly designed inverter with the proper current rating has the capacity to permit a NEMA-B motor to develop up to near its peak torque rating to start the torque rating to start the motor at zero speed. However for all practical purpose we will assume starting torque up to 150% of rated torque will be available from motor with vector control inverters.