
286 Electric Motors and Drives
low at low speeds. In the medium and low power ranges the
inverter-fed induction motor (using a standard motor) is
satisfactory, and may be cheaper than the d.c. drive. For
restricted speed ranges (say from base speed down to 75 per
cent) and particularly with fan-type loads where precision
speed control is unnecessary, the simple voltage-controlled
induction motor is likely to be the cheapest solution.
LOAD REQUIREMENTS - TORQUE-SPEED
CHARACTERISTICS
The most important things we need to know about the load
are the steady-state torque-speed characteristics, and the effec-
tive inertia as seen by the motor. In additio ...