Electric energy comparison of an induction motor driven by optimal torques for various operation time periods

When the motor speed is reduced by using a regenerative brake, the mechanical energy of rotation can be converted to the regenerative electric energy. In order to improve the efficiency of the motor drive systems, optimal regenerative and acceleration torques of the motor should be discussed in order to maximize the regenerative electric energy and to minimize the required energy for acceleration. On this stand point, a design methodology of an optimal torque for a squirrel-cage induction motor (IM) has been proposed by means of the variational method. This method has been extended to the case that the torque amplitude limit is given. This paper gives a simple derivation procedure of the optimal torque in order to clarify that the derived optimal torque minimizes the total loss of IM. Then the effectiveness of the optimal torques are investigated by checking the electric energy of IM for various operation time periods.