Modeling,Analyzing,and Designing For Interior Permanent Magnet Synchronous Machine

The interior permanent magnet(PM)machine has some outstanding advantages,such as wide speed range,high power density,and high overload capability,which makes it suitable for traction motor in city rail train and electric vehicle.Hence,this paper takes the interior PM machine as the research object.Establishing magnetic field model for interior PM machine is difficult due to its complex structure.Meanwhile,irreversible demagnetization easily appears in the PMs of interior PM machine due to the influence of the demagnetizing armature reaction field.In addition,the iron loss in the interior PM machine is high due to its high rotation speed.Aiming at above problems exsited in interior PM machine,this paper makes research on the modeling,analyzing and designing for interior PM machine.The boundary of interior PM machine is irregular,and significant magnetic saturation exists in the iron of machine,which makes it difficult to establish the magnetic field model of interior PM machine.Aiming at this problem,in this paper,each PM under each magnetic pole is segmented,and magnetic networks in rotor pole shoe are refined.Meanwhile,both a radial permeance unit and a tangential permeance unit are set for each refined network in the rotor pole shoe considering the flux path of the d-axis magnetic field and q-axis magnetic field.Based on the improment measures,an improved equivalent magnetic network model(EMNM)is established.Utilizing the improved EMNM,the magnetic field distribution,electromagnetic performances and working points of PMs in the machine are calculated accurately.Meanwhile,effects of some key parameters in machine on the magnetic field,electromagnetic performances and working points of PMs are analyzed.When interior PM machine operates under load condition,the armature current is ahead of back electromotive force(back-EMF).The advanced armature current produces demagnetizing field,which makes irreversible demagnetization appeared in PMs easily.Aiming at this problem,to analyze effect of demagnetizing armature reaction field on irreversible demagnetization in PMs,exponential demagnetization model of PM is established,and the flux density component of each point in PMs along the corresponding magnetization direction is derived.On this basis,a calculation model to analyze the demagnetization in PM is established.Based on the calculation model,influence and related influence machanism of armature current on irreversible demagnetization in PM are analyzed in detail.Meanwhile,several improment approaches for air flux barrier geometry in rotor are proposed to strengthen the anti-demagnetization ability of PM.Effects of variables in improved geometries on irreversible demagnetization in PM and rated electromagnetic torque are analyzed.Finally,a better improved geometry is achieved taking consideration to anti-demagnetization ability of PM and rated electromagnetic torque of machine.When interior PM machine operates under high speed,the alternative frequencies of fundamental waveform and harmonic waveforms of air-gap magnetic field are high,which makes iron loss in machine high.Aiming at this problem,a new air flux barrier geometry is proposed to improve the rotor geometry.By improving the rotor geometry,the iron loss in machine is weakened effectively.In order to make the improved rotor geometry work well in each operation stage of machine,the improved rotor geometry is optimized in some typical operation points of machine by the Taguchi method.The traction motor in electric vehicle needs a wide speed range and high overload capability.Aiming at the performance requirements of traction motor in electric vehicle,an interior PM machine is designed and manufactured in this paper.The designed machine has sinusoidal air-gap magnetic field distribution,small iron loss and low electromagnetic torque ripple.Finally,the prototype is validated by finite element method and experiment.