Research on High Power Density Design Method of PMSM Based on the Highly Saturated Motor Core

The core flux density is empirically designed around the knee point of the material, but this article found that the conservative selection of core saturation hinders the performance of permanent magnet synchronous motor (PMSM). Conversely, by utilizing the nonlinear variations in electromagnetic loadings, the global optimum of maximum power density and efficiency can be achieved synchronously under the saturated core. First, we analyze the realization condition of optimal power density and efficiency in PMSM, and propose a three-step-design-workflow based on the constant-loss-control-strategy and nonlinear variation of electromagnetic loadings under saturated core. Second, by using the finite element method (FEM), we analyze the features of variation in losses, power, efficiency, torque ripple and overload capability of PMSM against the variation of core saturation by parameterizing the slot size and PM volume. Then, based on the performance trajectory along the variation of the PM magnetomotive force (MMF) and winding flux linkage, the saturated design and optimization method are proposed, offering an improvement of over 20% in power density and a same total loss compared with the initial unsaturated scheme. The results proves that a “suitable” saturation degree is superior to a “safe” one in PMSM. Finally, the idea and method are verified by prototype experiments.