A design methodology of an optimal torque minimizing energy loss under torque limit for an induction motor

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 torque of the motor should be discussed in order to maximize the regenerative electric energy and to minimize the required energy for acceleration. This paper proposes a design methodology of an optimal regenerative torque for a squirrel-cage induction motor (IM) to maximize the regenerative electric energy by means of the variational method when the constraint conditions of torque amplitude, operation time period, and rotating speed range are given. Similarly, an optimal torque for acceleration is derived in order to minimize the required energy to drive. The effectiveness of the proposed methods are illustrated by both simulations and experiments.