Analytical Calculation of Eddy Current Losses in High-Speed PM Motor Considering PWM and Core Nonlinearity

One significant challenge in high-speed motor design is the eddy current losses in permanent magnets (PMs), which primarily arises from distortions in the armature reaction field. The main causes of the distortions are slotting effects and current harmonics introduced by pulse-width modulation (PWM). In order to figure out how the armature reaction field influences the eddy current losses of PMs, this paper proposes a fast and accurate analytical method to calculate PM eddy current losses in surface-mounted permanent magnet synchronous motors (SPMSMs) based on an improved reluctance network analysis (RNA) model of the motor and equivalent electrical network model of PMs. To overcome the limitation of conventional RNA in capturing high-frequency magnetic field variations, the proposed RNA of the motor incorporates an analytical model of the armature reaction for analysis of magnetic flux density distributions. The corresponding eddy current distribution and losses in the PMs are calculated through an equivalent electrical network model. Furthermore, the impact of high-order current harmonics caused by PWM on eddy current losses is systematically investigated. The accuracy and efficiency of the proposed method are demonstrated by results from finite element analysis (FEA) and experiments. From the study results we can conclude that the high-order current harmonics caused by the PWM leads to a significant increase in PM eddy current losses, and it is necessary to consider PWM effects in losses analysis and motor design.