Analytical Calculation of Maximum Mechanical Stress on the Rotor of the Interior Permanent-Magnet Synchronous Machine

Abstract

This paper investigates the analytical methods for estimating the mechanical stress on the rotor of interior permanent-magnet synchronous machines (IPMSM). By adopting the principle of stress concentration, an analytical method, which can provide an accurate calculation of the maximum mechanical stress (MMS) on the rotor of IPMSMs rather than an approximate worst-case estimation, is proposed. The case of hyperbola notches on a regular tension bar is used as an equivalent of the notches on the rotor of IPMSMs to simplify the non-local stress distribution to a localized stress concentration problem. A modified function of stress concentration factor (SCF) is developed based on the stress analysis of the IPM rotor notch using finite element analysis (FEA). The modified SCF function combined with the traditional equivalent ring method (ERM) of stress calculation provides an accurate solution of the concentrated MMS on the iron-bridge of IPMSM rotors. A 4-pole flat-type IPMSM rotor was used in this study. MMS at the iron bridges of the IPMSM were calculated for different rotating speeds and notch shapes. Analytically estimated MMS of the proposed ERM-SCF method were compared with the results obtained from the FEA and the other existing analytical methods, which showed that the proposed method has excellent accuracy for calculating the maximum stress on rotors of the IPMSM.