Design optimization of IPM machines for efficient operation in extended speed range

Practical considerations in the design of Interior Permanent Magnet (IPM) machines are examined to identify the key objectives for large-scale design optimization of such machines over an extended speed range. The goal of the optimization is to ensure efficient operation over the entire operating range under various performance and operational constraints. First, this paper illustrates that when the non-linear and lossy nature of the machine is considered from the efficiency standpoint, congruity of the characteristic versus the rated current cannot be the ideal criterion for constant power operation. Second, a new design optimization algorithm for constant power operation is developed which pursues efficient and reliable performance in the extended speed range under the rated current and maximum voltage constraints. To include the full non-linear nature of the machine and to address the effects of copper and iron losses on the motor behavior, this study is centered on finite element (FE) method for analysis and consequently optimization of a 50 hp, 48-slot, 8-pole IPM with single-layer v-type magnets which is used in the 2004 Toyota Prius. The results can be generalized to other PM motor configurations with sinusoidal back-emf waveforms.