Speed range is the ratio of the output maximum frequency/minimum frequency where the nominal torque is available.
Example: For a 50Hz motor
Altivar 71 in open loop mode, speed range is to 1...100Hz with a nominal speed motor of 50 Hz.
1- 50/100=0.5 Hz and 50/1= 50 Hz
2- The torque curve is guaranty in the speed range of 0.5 Hz to 50 Hz