Optimal electromagnetic-thermal design of a seven-phase induction motor for high-power speed-control applications.

Induction motors were traditionally used in industrial applications ranging from a fraction of horse-power up to several Megawatts due to their substantial benfits. Induction drives with more than three phases are superior to the 3-phase induction drives in terms of overall volume, torque fluctuations, current passing each stator-winding, ohmic loss, efficiency, and reliability in the case of stator-windings open-circuit fault. These benfits are particularly more attractive in variable speed drivers due to the reduced capacity of power-electronic switches. This paper aims to develop an optimal electromagnetic-thermal design procedure of a high-power seven-phase induction motor suitable for variable-speed applications. In this multi-objective design approach, the objective function is defined aiming to increase the efficiency, power-factor, power-toweight ratio, and starting-torque as well as reduce the starting-current. Furthermore, the electrical, mechanical, dimensional, magnetic, and thermal limitations are included in this optimization study in order to ensure practical realization of the designed machine. The coupled-circuit method is employed for nonlinear electromagnetic modeling, while the current displacement phenomenon is considered in calculations of rotor parameters. A lumped-parameter-thermal model is established for calculating heat rises of different parts at each iteration of optimization study. Finally, the performance characteristics of the optimally designed 1-MW 4-pole motor are verified based on 2D FE analyses. [ABSTRACT FROM AUTHOR]