A Study Of Pmsm With Asymmetric Eccentric Air Gap Designed For Electric Motorcycle

To improve the power density of permanent magnet synchronous motor(PMSM)designed for electric motorcycle(EMC),the air gap length is usually minimized,which aggravates the influence of armature reaction on air gap magnetic field,resulting in severe distortion of the load air gap flux density and back-EMF.Hence,an asymmetric eccentric air gap structure is designed.The research is carried out with the application of asymmetric eccentric air gap in integral-slot distributed-winding PMSM(ISDWPMSM)and fractional-slot concentrated-winding PMSM(FSCWPMSM).The main research contents are as follows:(1)Electromagnetic Parameters of PMSM considering Cross-coupling and Saturation.The calculation method of inductance parameters based on frozen permeability method(FPM)is introduced.Based on FPM,the flux linkage and torque equations in the basic mathematical model of PMSM under (9-axis coordinate system are modified,which lays a theoretical foundation for subsequent analysis.(2)Design and Analysis of Asymmetric Eccentric Air Gap in ISDWPMSM.Because of the obvious load air gap magnetic field distortion of the designed conventional ISDWPMSM,in view of the characteristic of unidirectional driving of EMC,an asymmetric eccentric air gap structure is designed which the eccentric air gap is only utilized in each pole air gap magnetic field strengthened area.The optimization of the structure is carried out by defining the design parameter named the ratio of maximum air gap to minimum air gap.The electromagnetic characteristics of two ISDWPMSMs are compared,and the traditional flux-current method and FPM are exploited to analyze the influences of asymmetric eccentric air gap structure on the inductance,the torque is analyzed in depth based on FPM.The research shows that the asymmetric eccentric air gap structure can significantly weaken the distortion of load magnetic field,the torque ripple can be reduced by 70.75% under rated condition,and the efficiency is obviously improved under different loads at rated speed.The -axis inductance decreases as the air gap of -axis increases,while the (9-axis inductance is substantially unchanged.Compared to the conventional ISDWPMSM,the permanent magnet torque of the motor with asymmetric eccentric air gap structure is larger,as the conventional reluctance torque is relatively small.(3)Design and Analysis of Asymmetric Eccentric Air Gap in FSCWPMSM.The FSCWPMSMs with conventional and asymmetric eccentric air gap structures are designed based on the principle that the back EMF and the main dimensions of the stator and rotor are consistent,the electromagnetic characteristics of two FSCWPMSMs are compared as well.Under the conditions of ideal sinusoidal current supply and inverter power supply,the inhibition of asymmetric eccentric air gap structure on the iron loss of the motor is analyzed.The research demonstrates that FSCWPMSM is rich in magnetomotive harmonics,the magnetic field distortion is more serious,but the asymmetric eccentric air gap structure can effectively suppress it and improve the performance of the motor.The iron loss of ISDWPMSM and FSCWPMSM can be respectively reduced by 22.74% and 29.11% under rated condition,and the structure has more significant effects on eddy current loss(compared to hysteresis loss)and rotor iron loss(compared to stator iron loss).When the influence of current time harmonics are considered,the iron loss is significantly increased,but the structure can still suppress it effectively.(4)Co-simulation of PMSM based on Vector Control.In order to consider the influence of the actual control system on the performance of the motors,a JMAG-Simulink-PSPICE co-simulation platform based on vector control is established,and the four designed motors are analyzed by the platform to further verify the validity and feasibility of the asymmetric eccentric air gap structure.