Research On Characteristics Of In-wheel Permanent Magnet Synchronous Machines

In-wheel motors are the motors directly incorporated with hubs in the vehicles and drive devices.In-wheel motors eliminate intermediate mechanism,which transmits the power between motors and wheels.Due to the advantages of compact structure,high transmission efficiency,and flexible dynamic,the electrical vehicles equipped with wheel motors are known as the final development form of the electrical vehicles.Permanent magnet synchronous machines(PMSMs)with different rotor structures are widely focused on as in-wheel motors when investigating.However,when the in-wheel motor PMSMs are popularized to different type of electrical vehicles,the power density and torque density of the in-wheel PMSM become higher.Besides,the pole/slot combinations of in-wheel motors are difficult to decide;permanent magnet(PM)eddy current loss is much;constant power speed range(CPSR)is hard to realize;torque ripple of PMSMs is complex and not easy to suppress.And these problems are different from each other for different rotor types.For the point of the overall view,researching on these problems with considering the different rotor type and combination is very important.In view of the high power density requirements of the in-wheel motor,PMSMs with fractional slot concentrated winding(FSCW)structure are determined.The slot/pole combination principle and the winding coefficients of FSCWs are studied.Slot/pole scheme selection criteria and rotor structure of in-wheel PMSMs are analyzed.The magnetomotive force(MMF)of the FSCW is analyzed.Minimum modules of radial forces with different pole/slot combinations are studied.Based on the results,the scheme of the in-wheel motor is determined.Because the characteristics of the in-wheel motor constant power speed range(CPSR)is wide and difficult to achieve,constant power working points in the current phase plane are analyzed.It is deduced that the decision of magnetic flux linkage of motor and synchronous inductance.The relationship between flux,inductance and electrical machine parameters is researched.Design methods considering of CPSR are proposed for in-wheel surface-mounted PMSMs and interior PMSMs.Through prototype design process and constant power experiments,the effectiveness of constant power operating point analysis and the design method are validated.The composition of harmonic magnetomotive force(MMF)of in-wheel PMSMs is analyzed and calculated,and the relationship between harmonics of MMF and PM eddy current is studied.PM eddy current losses of in-wheel SPM motors with different pole/slot combinations are compared using analytical calculation method.The effect of splicing pole on PM eddy current loss is analyzed and compared using the numerical finite element method(FEM).PM eddy current losses of in-wheel SPM and IPM motors are compared.It is proposed for reducing PM eddy current loss to increase the PM placed depth.Eddy current loss of the experimental the prototypes validate the correctness of the calculation of eddy current loss and suppression methods.From the point of view of energy,the mathematical model of electromagnetic torque of PMSMs is derived,and is compared with other mathematical model.The results show that the modified torque model is more general.Based on the improved torque model,the causes of torque ripple in in-wheel PMSMs are analyzed.The design method of shape optimization of the rotor surface and the PM poles is proposed,which can effectively suppress the flux harmonic and torque ripple.According to the mathematical torque model,the principle of harmonics of current to suppress the torque ripple is derived.The suppression of torque ripples of the in-wheel PMSMs in different conditions is researched.The calculation method of the harmonic current are proposed,and the injected harmonic current can effectively suppress the torque ripple of the in-wheel PMSM,especially in the deep constant power operating region.