Use of Time-Harmonic FE Analysis to Compute Rotor Eddy-Current Losses in Synchronous Machines Subject to Distorted Stator Currents

The problem of accurately computing rotor eddy-current losses in synchronous machines subject to non-sinusoidal phase currents is usually approached with Time-Stepping Finite-Element Analysis (TSFEA), where rotor motion and armature current distortion effects are naturally included. The drawbacks of TSFEA are the long computation times and the need to wait for steady-state conditions to extract results. Such features make TSFEA unsuitable for integration into automatic design optimization programs. This paper illustrates how the problem can be alternatively solved by Time-Harmonic Finite-Element Analysis (THFEA) on a set of modified machine models conceived so that rotor motion and current distortion effects can be accounted for. As an illustrative example, the proposed method is applied to a Surface Permanent-Magnet (SPM) generator whose electromagnetic design is being processed through genetic optimization algorithms. Eddy-current losses are independently computed by both TSFEA and TFFEA in different generator operating conditions and design configurations showing that results are in good accordance. Furthermore, the proposed approach takes much smaller simulation times and can be easily incorporated into the overall optimization process.