Design Optimization of Dual-Redundancy PM Brushless DC Motors for Torque Enhancement

To enhance the torque of short-time duty permanent magnet (PM) dual-redundancy brushless DC motors (DR-BLDCM) and avoid the motor overheating under a fixed outer diameter and length, a design method based on the optimization of split ratio and stator magnetic density (B-m) considering thermal limitations is presented. The global thermal limitation of DR-BLDCM is set by limiting loss density. The local thermal limitation of the winding is set by limiting current density. The thermal limitations are taken as the boundary of torque enhancement design optimization. Both the cold backup and hot backup DR-BLDCM are studied in this paper. By researching the relationship between torque, split ratio, and B-m, the optimal combination of split ratio and B-m are calculated analytically. The influences of thermal limitations on the maximum torque and the optimal combination are analyzed, and the principle to determine the optimal combination is obtained. The analytically calculated results are verified by finite element simulation, and the error is less than 6.82%. A prototype is manufactured based on analytical design results. The error between the calculated and measured copper loss is 6.96%. The verification results show that the proposed optimization method can fully enhance the torque of DR-BLDCM under the condition of fixed overall dimension and thermal limitations. (c) 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.