Motor/brake transitioning for an inverter driven a-c induction motor

Abstract

Dynamic response of an a-c induction motor control system including an adjustable frequency and adjustable magnitude power source is made more stable during the transition from a motoring to an electrical braking mode by modifying the system characteristics as a function of rate of change of motor flux and torque magnitude during electrical braking. The control system responds to a torque command signal and a torque feedback signal to generate an error signal which controls the frequency of the excitation supplied to the motor and thus the torque developed by the motor. During electrical braking this error signal is modified as a direct function of the rate of change of motor flux and as an inverse function of the magnitude of torque developed by the motor. During the transition from motoring to electrical braking, when the system tends to be unstable, the rate of change of flux is relatively high while the motor torque is at a relatively low value. Accordingly, the error signal becomes very large in magnitude and rapidly forces the control system and motor out of the transition zone into a more stable operating zone. Once stabilized, modification of the error signal becomes negligible.

Dependencies are inferred from the claim text.