| The axial flux permanent magnet machines(AFPMMs)have the advantages of high power density and compact structure,having good application prospects in wind power generation,flywheel energy storage and electric vehicle field.With the development of ultra-thin low-loss soft magnetic materials,amorphous alloys are more suitable for the winding process,the research on high-frequency AFPMMs has been greatly concerned and developed rapidly.The frequency of the AFPMMs also breaks through the conventional motor frequency limit,reaching 800 Hz or even 1200 Hz or higher.Excessive frequency will increase the rotor loss and then lead to excessive temperature rise of motor rotor,which poses great challenges to the rotor heat dissipation and even the safe and reliable operation of the motor.First of all,this paper proposed an analytical model to analyze the magnet loss of axial flux permanent magnet synchronous machines with the different widths of the stator slot opening considering the magnet offset and skewing and the different slot-pole combinations.The magnetic field in the magnets is obtained by solving Maxwell equations in subdomains.The magnet eddy current loss is calculated using a resistance network.The analytical model is verified by the comparison with the finite element calculation results.Secondly,this paper proposed a rotor temperature rise suppression method for the water-cooled totally enclosed high-frequency AFPMMs by installing centrifugal fan blades on the outer surface of the rotor to improve the air turbulence intensity inside the machine.Based on the computational fluid dynamics method,the influence of the number and length of fan blades on the air friction loss and rotor temperature rise of a TE AFPMM are analyzed.In order to further improve the heat dissipation capacity,the influence of different aspect ratios of fan blades is investigated,when the area of rectangular fan blades is fixed.On this basis,the improved rotor blade structure is further presented,and the influence of two improved blade shapes on the heat dissipation performance of the motor,the suppression of the bearing temperature rise by installing the fan blades on the inside of the rotor are also analyzed.At last,the accuracy of the calculation method is verified by a temperature rise test of an AFPMM prototype.Finally,a rotor temperature rise suppression method is proposed for the water-cooled totally enclosed high-frequency AFPMMs,which is provided with fan blades outside the rotor and ventilation holes on the rotor bracket,aiming at the promotion of air turbulence intensity inside the machine.Based on the CFD method,the temperature rise suppression effect of ventilation holes and fan blades is analyzed and compared.On this basis,the influence of the ventilation hole number and the duty ratio of ventilation holes to the rotor bracket on the air friction loss and rotor temperature rise of TE AFPMMs is studied.In order to further reduce the rotor temperature rise,the effect of the number of blades and ventilation holes on the motor heat dissipation performance is analyzed.The rotor temperature rise suppression effect is remarkable.The accuracy of the analysis method is verified by a temperature rise test of an AFPMM prototype. |
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