Apparatus and method for high slip operation of an AC electric motor at substantially zero rotation and substantially zero torque

摘要

Apparatus and method for high slip operation of an AC electric motor at substantially zero rotation and substantially zero torque in an AC electric motor drive system is disclosed. The electric motor produces a rotation in response to an outgoing signal, such as a drive current, of variable magnitude and frequency supplied by the drive system. An idle control signal is furnished when the drive system is in a substantially zero rotation and substantially zero torque state, where the frequency of the current is approximately zero. The idle control signal causes substantially simultaneously an adjustment of the magnitude of the current to a predetermined magnitude level and a rapid raising of the frequency of the current to a higher frequency value to produce per-unit slip s=(n.sub.1 -n)/n.sub.b greater than 0.1, where n.sub.1 is the synchronous rotation of the stator field of the motor, n is the rotation of the rotor of the motor, and n.sub.b is the synchronous speed of the stator field at motor rated rpm. The adjustment in the magnitude and the rapid increase in the frequency of the current causes the motor to produce substantially zero rotation and substantially zero torque because the motor is operating in the high slip region of its torque-rotation curve. The apparatus and method of the present invention allows the motor to accelerate rapidly on command from the substantially zero rotation and substantially zero torque high slip mode.