Center Post and Rib Length Optimization of a High Speed Permanent Magnet Assisted Synchronous Reluctance Motor

This paper presents the optimization of center post and rib length of a high speed permanent magnet assisted synchronous reluctance motor (PMa-SynRM) through the modeling of performance parameters. With low torque ripple, wider field weakening region and cost effective structure, PMa-SynRM can be a deserving candidate for high speed machine design. One of the most crucial factors for PMa-SynRM operating in high speed region is the mechanical stress and deformation in the rotor. To reduce these, center post and rib can be introduced in the design. But center post and rib length can lead to a reduced torque and an increased torque ripple and back emf. In this paper, apart from stress and deformation, the trend of performance parameters like average torque, torque ripple and back emf are considered for center post and rib length optimization. Through multivariate correlation and nonlinear regression analysis, the pattern of performance parameters has been captured by using initially designed high speed PMa-SynRM. The second order equation for each performance parameter was formed as a function of center post and rib length. Finally, by using fmincon optimization function with objective of stress minimization and performance parameter constraints, optimal value of center post and rib length was calculated. Simulation results in finite element analysis (FEA) shows noticeable improvement of average torque, torque ripple, stress compared to an initially designed model. This algorithm can effectively be used in high speed PMa-SynRM design to balance both mechanical and performance parameters.