Frequency-Domain Analytical Prediction of PWM-Induced Current Harmonics in Slotless Surface-Mounted PM Synchronous Machines

Slotless surface-mounted permanent magnet (PM) synchronous machines with high pole numbers generally have relatively low inductance, which will lead to significant current harmonics under PWM-driven inverters. Current harmonics can cause additional losses and torque ripples, severely impacting temperature rises and mechanical vibrations. Accurate prediction of current harmonics is crucial for machine performance calculation and drive system design. This article proposes a frequency-domain analytical method to predict the current harmonics with high fidelity equivalent circuit models. The harmonic prediction method is validated experimentally under a wide range of operating conditions and improves the prediction accuracy by up to 75% compared to the existing analytical modeling methods. The prediction error using the proposed method is generally maintained below 10%, making it an effective tool for practical applications.