Optimal Shape Design of Rotor Slot in Squirrel-Cage Induction Motor Considering Torque Characteristics

Induction motors are widely used in various industrial applications with different torque-speed characteristics. Since the configuration of the rotor slot has a great impact on the electromagnetic torque-speed characteristics, a design optimization process is necessary to improve the motor performance of the induction motor. The material boundaries of the rotor slot are represented by a level set function, and a voltage driven time-harmonic field analysis is performed to estimate the characteristics of the induction motor. An optimization problem is formulated to maximize the torque at one speed either a rated or starting condition constrained by the torque at other speeds, starting currents and efficiency. A level set equation with an augmented Lagrangian method is derived to find the optimal design. Optimal results are achieved by updating the sequential changes of the material region driven by the shape derivative. The design flexibility of the proposed method is confirmed to obtain National Electrical Manufacturers Association (NEMA) designs satisfying different torque characteristics.