Electromagnetic Losses Analysis In Permanent Magnet Synchronous Machines For Electric Vehicles With Considering Saturation

In recent years,permanent magnet synchronous machine(PMSM)has been widely used in automotive drive systems due to its high power density,high efficiency,etc.Because of the high power density of machine,the magnetic saturation has a great influence on the electromagnetic losses including the stator core loss,rotor eddy current loss and copper loss,especially for the electromagnetic losses under space vector pulse width modulation(SVPWM)excitation.Meanwhile,there is a conflict between calculation time and accuracy in the conventional calculation method of stator core loss,and it is difficult to iteratively calculate the multiple operating points in the initial design of the machine.Moreover,the magnetic saturation is serious when the machine operates in the low-speed and high-torque region.The higher electromagnetic losses cause the temperature rise problem,which restricts the increase of peak torque.Therefore,in order to increase the peak torque,taking the magnetic saturation into account,it is significant to analyze the efficient calculation method of stator core loss and the way to reduce the electromagnetic losses in the low-speed and high-torque region.In the paper,an external rotor in-wheel PMSM used in the China-Germany Ministry of Science and Technology cooperation project and an internal rotor PMSM used in an armored vehicle electric drive system have been chosen as the research object.Taking the magnetic saturation into account,the calculation method of stator core loss has been studied under sinusoidal current source and current harmonics caused by SVPWM.Moreover,the method for reducing the electromagnetic losses and maximum operating temperature in the low-speed and high-torque region has been investigated.At last,the test benches have been set up to verify the analytical results of electromagnetic losses.First,based on the equivalent magnetic circuit method and conformal mapping method,an analytical model for calculating the core loss of external rotor PMSM with different winding forms and pole/slot number combinations has been presented with considering the magnetic saturation.The core loss at different operating points in the region of constant torque,constant power and rated speed has been studied by using the analytical model,the accuracy of which has been verified by the finite element analysis results of core loss.Compared with the finite element analysis method,the analytical model of core loss has the higher calculation accuracy and lower computer time,and it is easily embedded into the program of machine optimization design for quick calculation.Secondly,based on the simulation data of flux-linkage in the external and internal PMSM,a core loss prediction model with piecewise variable coefficients under SVPWM excitation is proposed with considering saturation,which is applied to any type of external and internal PMSM.The stator core loss at different operating points has been investigated by using the core loss prediction model with piecewise variable coefficients.Compared with the co-simulation results,the core loss model has the higher calculation accuracy and lower simulation time.Then,according to the method for calculating electromagnetic losses under SVPWM excitation with considering saturation,the method for reducing the electromagnetic losses and maximum operating temperature of the internal PMSM in the low-speed and high-torque region has been proposed.The method for calculating the copper loss and eddy current loss of permanent magnet under SVPWM excitation has been analyzed.Then the influences of stator structure and winding parameters on the electromagnetic losses and the maximum temperature have been studied,and the method for reducing the electromagnetic losses and maximum operating temperature in the low-speed and high-torque region has been investigated.The study provides reference for the increase of peak torque.Finally,the test benches of oil-cooled external PMSM and water-cooled internal PMSM have been established to verify the analytical results of electromagnetic losses.