Optimal-time control of squirrel cage induction motors with constant load torque

Optimal time trajectories, based on the Pontriagyn's maximum principle, are deduced for a squirrel-cage induction motor with constant load torque. These trajectories are valid for acceleration and deceleration with or without the load torque and for loading or unloading the motor at constant speed and ensure the minimal time transients with the stator current limited to the previously fixed value. Moreover, the optimal trajectories places the motor, at the end of the transient, at the minimum current point, which is close to the one of maximum efficiency, thus combining the brevity of the transients with the saving of energy. An optimal time control system, that implements these trajectories is designed. The simulation results of the proposed control system are presented.