Study Of A Hybrid Permanent Magnet Memory Motor

In recent years,permanent magnet synchonous motors(PMSMs)have been more and more widely used in industry,agricultrue,defense and daily life,due to their high efficiency,high power density,high control accuracy,etc.However,the air-gap flux of PMSMs is usually invariable because it is provided by permanent magnets with constant magnetic properties,which limits the operation speed range of PMSM.At present,flux-weakening control strategy is usually used to expand the operation speed range of the conventional PMSMs.The flux-weakening control strategy can effectively expand the operation speed range of the conventional PMSMs,however,some deficiencies still exist.The continuous d-axis current increases the copper loss in armature windings,which lowers the efficiency in high speed operating area.Moreover,some other schemes such as hybrid excitation and mechanical structure modification can also make the machine air-gap flux adjustable,but the fabrication and the control of these machines will be more difficult,and then the cost will be higher.Therefore,developing a kind of PMSM,in which air-gap flux can be adjusted by a simple method,is meaningful.Memory motor,which intentionally adopts low coercive force(LCF)magnet and adjusts the air-gap flux by changing the magnetization state of the LCF magnets,is a valuable option.In this dissertation,development of the memory motor is firstly introduced,and the related research is systematically review.Then hybrid permanent magnet memory motor,in which the magnetization state of the LCF magnets is adjusted by armature windings,is determined to study.The main contents of this dissertation are organized as follows:1.Analysis of utility of AlNiCo and ferrite magnets in hybrid PM memory motorA 27-slot/6-pole structure based on some existing hybrid PM memory motors is designed to investigate the application of LCF magnets.Finite element analysis(FEA)results show that the fully positive magnetization of the LCF magnets is very difficult,and the variation range of the air-gap flux is limited.On the other hand,the influence of q-axis current on the magnetization state of the LCF magnets cannot be neglected.By comparing the application of AlNiCo and ferrite magnets in the designed motor,ferrite magnets are deemed to be an valuable option for this kind of hybrid PM memory motor.2.Improvement and optimization of hybrid PM memory motorConsidering the problems in the original scheme of hybrid PM memory motor,an improvement scheme is proposed,in which magnetic barriers are added into the rotor.The positive magnetization characteristic of the ferrite magnets is improved and the influence of q-axis current on the magnetization state of the ferrite magnets is greatly weakened.For the improved motor,the choice of the numbers of magnet poles and stator slots is discussed through the analysis of torque,EMF and magnetization characteristic of ferrite magnets,etc.The influence of some important dimensional parameters on the motor performance is investigated to optimize the motor design.3.Performance analysis and experimental verification of improved motor.After optimization,a prototype is designed,and a series of FEA have been conducted.Distribution of the flux density,EMF,winding inductances,and torque are analyzed when the ferrite magnets are fully positively and negatively magnetized.The influence of the q-axis current on the magnetic properties of the ferrite magnets is considered,and the positive and negative magnetization of the ferrite magnets are investigated.Mechanical strength of the rotor is also analyzed.Finally,the prototype is fabricated and tested,and the experimental results have verified the theoretical analysis results.