Distinguishing the efficiency requirements in motoring and generating operations of PM machines

The influences of stator winding resistance and dc bus voltage variations on the efficiency maps of permanent magnet machines for motoring and generating operations are discussed. A large-scale design optimization algorithm is presented in which the efficiency requirements are independently treated for motoring and generating operations over the entire torque-speed plane. The separate treatment of efficiency is especially important in machines with large per-unit stator winding resistances, or in machine-drive systems with unregulated dc bus voltage, as is the case for low-voltage hybrid vehicle systems.