Research On Negative-saliency Axial Flux Permanent Magnet Synchronous In-wheel Motor

The axial dimension of axial flux permanent magnet synchronous motor(AFPMSM) is short and torque density of AFPMSM is high, which make it easy to realize multiple plate structure and light weight. It has been drawing great attention by the hybrid electric drive wheeled vehicle field which has high requirements on unsprung mass and axial space. But the field-weakening range of AFPMSM is small because of its surface mounted permanent magnet structure, which makes it hard to be applied in wheel systems. The negative-saliency axial flux permanent magnet synchronous motor(NSAFPMSM) is studied to solve this problem. The relationship between component percentage of soft magnetic materials and permanent magnet materials and saliency ratio are researched to improve the field-weakening range. The main contents are as follows:Firstly, the magnetic circuit characteristics of different NSAFPMSM structures are analyzed and the influence on magnetic field distribution in motor by different pole structures is studied by FEM. The operation characteristics of different saliency motors are compared theoretically and the differences in control are also researched. Combining with the characteristics of the motor, the motor design principles of NSAFPMSM used in wheel systems are summarized. Voltage equation and torque equation of different NSAFPMSM structures are given.Secondly, based on magnetic circuit method, the inductance of fractional slot concentrated winding NSAFPMSM is theoretical deduced. D-axis inductance and q-axis inductance formula of different pole structures are provided and verified by FEM. Differences between inductance expressions of non-saturation and saturation are also analyzed. Based on FEM, inductances of fractional slot concentrated winding and integer slot distributed winding are compared.Thirdly, the influence on power output characteristics by change of inductance and flux linkage is studied and the applicable condition of motor with different saliency is pointed out. The FEM is used to compare the differences of field-weakening range and output power among different pole structures.Finally, the factor which influences the inner power factor angle under MPTA control of NSAFPMSM is researched and the composition of electromagnetic torque is analyzed. Cogging torque and ripple torque of NSAFPMSM are analyzed to be weakened. A new pole structure is proposed to get a better inhibitory effect.