Calculation Of Iron Losses For Vehicle-used Permanent Magnet Synchronous Machines

Renewable energy electric vehicles are developing rapidly to stimulate performances improvement of electric machines. The total losses of permanent magnet synchronous machines(PMSM), as core components in power system of new energy vehicles, directly affect their efficiency and temperature rise, resulting in limitation of the car’s mileage and working life. For such PMSM, iron losses occupy heavy weights out of the total losses. Therefore, calculation of the iron losses with high precision is the key to design PMSM.The mechanism of iron losses which are influenced by factors is complicated. Many scholars in the world have proposed different methods or models to calculate iron losses in accordance with theoretical analysis and experimental results. The worldwide used commercial software, namely Ansoft based on finite element method(FEM), is adopted to perform iron losses calculation.Mechanism of iron losses, including hysteresis, eddy current and abnormal losses is illustrated briefly, based on which the impact of rotating magnetic field density and manufacturing processes on iron losses is discussed in detail. After that the calculation method of iron losses used by Ansoft is described. The three- and two-term iron losses models are compared in fitting loss curves, i.e. the flux density versus per unit iron losses curves, so that the loss coefficients of different terms are obtained.Then the structural characteristics, method of calculating electromagnetic parameters and waveform of working current of the PMSM are presented. Based on which the sources of stator and rotor losses are analyzed, the spatial MMF waveform is decomposed with sinusoidal functions to derive the high spatial harmonics of MMF and high harmonics of MMF in time domain induced in the rotor, which provided basis to analyze the source of rotor flux density fluctuations. The key points using FEM to calculate eddy current losses in PMSM are also listed. Some nontrivial factors neglected before in iron losses calculation are further explored. On the one hand, eddy current loss is directly calculated using FEM in a 3D single silicon sheet model. On the other hand, the filtered current of the measured one is used as excitation source to check the impact of high harmonic current components on iron losses, thus the correction coefficients on iron losses are achieved.Meanwhile, a simplified iron losses calculation method is proposed by using two-term iron losses model in order to speed up the algorithm which focuses on flux density analysis in different positions of the PMSM and under different working conditions. The calculation result of the proposed method is consistent with the one of the FEM.Finally, the copper loss of the stator windings and mechanical loss of the rotor are analyzed, and their calculation formulae according to the test results are obtained. The total loss value is the sum of the results by the theoretical formulae and the core losses under sinusoidal current by FEM. There exist some errors between the theoretical value and the measured total losses. After considering the impact of higher harmonic current components and introducing correct coefficients of iron losses, the theoretical total loss are consistent with the measured one.