| A high-quality motor drive system is essential for advanced manufacturing and major national equipment,responsible for energy conversion and power drive,and its quality directly affects the level of the entire equipment system.Due to the current energy saving and emission reduction policy,strategy of sustainable development,transition to new from old economic engines,"double carbon target" and other key national policies,China’s motor industry has ushered in unprecedented development opportunities.Permanent magnet synchronous motor(PMSM)drive system is widely used in industrial servo,large equipment electric drive,new energy power generation,and other national equipment as well as electric vehicles(EVs),intelligent home appliances,and other daily life areas because of a series of advantages such as high efficiency,low loss,high power density,compact structure,small size.Especially in electric vehicles,PMSMs have been used in most of the automakers’ new energy vehicle models and occupy a large market share.However,PMSMs use permanent magnets for exciting.The constant magnetomotive force(MMF),high amplitude and complex air gap magnetic field design lead to cogging torque,large tooth harmonic back-EMF/current,and possibly significant torque ripple.This significantly reduces the reliability of the PMSM drive system and the comfort of the electric vehicle occupants and greatly limits the further improvement of the overall quality of EVs.This dissertation investigates the mitigation of torque ripple,electromagnetic vibration,torsional vibration,and acoustic noise of PMSMs for EVs.An analytical model of the cogging torque of a PMSM with variable pole arc width,taking into account the MMF of the PM and the slotting of the stator,has been developed to analyse the mapping between cogging torque/tooth harmonic back-EMF and the geometrical parameters of the rotor pole arc width of the permanent magnet motor.Based on the variation of torque density/torque pulsation under changing rotor geometrical parameters,a new semi-symmetrical rotor type of synchronous permanent magnet motor with low cost and versatility is proposed,and the unbalanced radial magnetic pull introduced by the asymmetrical magnetic circuit design is eliminated by using the rotor segment staggering method;Then an analytical calculation model of the radial exciting force wave taking into account the non-linear factors such as slotted stator and non-sinusoidal magnetic field of the PMSM is established,and the order characteristics of the exciting force wave of the conventional straight slot motor and the widely used skewing slot motor/rotor step-skewing motor in engineering are analysed,and the influence of the change of rotor pole geometry parameters on the radial exciting force characteristics of the motor is obtained.Simultaneous analysis of the modal characteristics of the stator system/whole machine of a complex-shaped PMSM,study of the effects of engineering operations such as slotting,additional windings,nested housings and slanting slots on the modal frequencies of the stator system,construction of a complete modal set of the stator and rotor system of a PMSM for EVs,providing a theoretical basis for resonance screening and avoidance;Combining the proposed semi-symmetric rotor PMSM topology with the "radial exciting force wave-rotor pole geometry parameter" mapping law,the proposed method of amplitude mitigating for the main exciting force of the 0th-order and pole-related order of the PMSM is proposed,which effectively reduces the electromagnetic vibration of the PMSM of EVs with mainly 0th-order vibration components;In addition,focusing on the new problems that may be introduced in the torque ripple and electromagnetic vibration mitigation of PMSMs,the types of torsional vibration action and generation mechanism of existing motors with structural differences along the axial direction are elucidated,the torsional force action law and order characteristics of PMSMs are analyzed,and a scheme for the elimination of wrong poles of torsional force between rotor segments is proposed;Finally,a new semi-symmetrical rotor PMSM prototype with a peak power of 20kW and the benchmark prototypes were fabricated to extensively test/compare/analyse the dynamic and static electromagnetic performance,vibration and noise response,torsional vibration characteristics and other performance parameters of the new semi-symmetrical rotor motor to verify the correctness and feasibility of the obtained theory and the proposed new topology.The main research work completed in the dissertation and the results achieved are as follows:(1)A new type of semi-symmetrical rotor PMSM with excellent force-energy quality,low cost and easy assembly line production is proposed.The focus is on the two main factors of torque ripple in a PMSM,i.e.cogging torque and tooth harmonic back-EMF:Firstly,an analytical model of cogging torque is theoretically developed to take into account the non-sinusoidal distribution of the magnetic field of the PM and the slotting effect.The"cogging torque amplitude-geometry parameter of rotor pole" mapping law is obtained,and a general calculation procedure for the low harmonic recombination of cogging torque over zero with varying rotor pole arc width is given;Then,based on the law of electromotive force induction,the phase deviation and abatement law of the armature winding back-EMF harmonic caused by the rotor MMF shift under the change of pole arc width is elucidated.Based on the electric period difference and wavelength difference between the fundamental and tooth harmonic components of the back-EMF,a rotor pole arc width design is proposed that can significantly mitigate the tooth harmonic back-EMF amplitude while maintaining a high fundamental back-EMF amplitude.Finally,the proposed method for finding and designing the parameters of the semi-symmetrical rotor motor is presented,and the finite element model is developed and extensively compared with existing motors in terms of electromagnetic performance.The results of the theoretical study and finite element analysis demonstrate the effectiveness and superiority of the proposed new semi-symmetrical rotor PMSM in terms of torque quality improvement.(2)The main source of electromagnetic vibration and acoustic noise in PMSM for EVs,the electromagnetic exciting force wave,is investigated,and the main exciting force components mitigating method is proposed in conjunction with the proposed semi-symmetric rotor design.Firstly,the air gap magnetic field of a conventional motor is analysed,and the general expression for the "potential-permeability" of the radial exciting force wave is obtained based on the characteristics of the air gap magnetic field distribution,as well as the order and amplitude characteristics.Then the influence law of the change of motor structure on the air gap magnetomotive force and permeability of the commonly used engineering methods is analysed,revealing the limitations of the current commonly used engineering methods for radial exciting force wave mitigation in EV drive motors.Considering the positive correlation between the high amplitude complex air gap magnetic field and the high force energy output demand of EV drive motors,the 0th-order and pole number related order main exciting force wave components amplitude mitigating method of rotor pole variable structure parameters is proposed.The magnetic field distribution characteristics of the PMSM under the variation and combination of the rotor pole arc width are analysed,and the order characteristics and variation law of the radial exciting force under the variation of the rotor pole arc width are analysed.The finite element method is also used to perform validation calculations.Finally,a mapping set between the rotor pole arc width and the radial exciting force wave characteristics of the PMSM is established,which provides theoretical support for the source-side improvement of the electromagnetic vibration mitigating of the PM drive system of EVs.(3)The mechanical system consisting of parameters such as the structure of the mechanical components of the body of an EV’s PMSM,the connection method,and the position distribution between the components is the structural carrier of the electromagnetic vibration and acoustic noise of the motor.The modal properties reflect the inherent nature of the structural carrier,and the electromagnetic vibration and acoustic noise of the motor are closely related to the modal parameters of its key components.In order to overcome the resonance problem of PMSMs for EVs in a wide range of operating speeds,this dissertation uses a combination of modal analytical analysis,finite element modal analysis of complex structural components and modal experimental test analysis to effectively identify the various modal parameters of existing PMSMs and the proposed new semi-symmetric rotor motor for EVs.The influence of the variation of the outer stator geometry on the modal frequency is investigated,and the resonance preconditions of the proposed new semi-symmetrical rotor motor are obtained by combining the"motor geometry-low order modal frequency" mapping law.The electromagnetic vibration and acoustic noise of the proposed semi-symmetrical rotor motor under various common operating conditions are extensively compared,and the beneficial effects of the proposed semi-symmetrical rotor motor on vibration and acoustic noise reduction under different operating modes in the full speed range are demonstrated through finite element calculations and experimental tests.(4)In view of the structural differences along the axial direction and the asymmetrical magnetic circuit design of the proposed semi-symmetrical rotor motor,the torsional vibration problem of the shaft system and the inherent shaft voltage problem that may be aggravated by the asymmetrical magnetic circuit design of this motor and the existing skewing slot motor/rotor step-skewing motor are discussed.The mechanism and order/frequency characteristics of the torsional force generated by structural differences along the axial direction are obtained by analytical analysis.The torsional forces induced by structural differences along the axial direction of the motor are eliminated by the proposed method of in-phase misalignment of the motor rotor and the simultaneous elimination of the unbalanced magnetic pull in both the parallel and the axial directions.The effectiveness of the new semi-symmetrical rotor motor for torsional vibration suppression is confirmed by verifying and comparing the torsional vibration conditions using harmonic response analysis.In order to investigate the potential aggravation of the intrinsic shaft voltage by the asymmetric magnetic circuit design of the proposed motor,the effect of the proposed motor’s asymmetric magnetic circuit design on the intrinsic shaft voltage is revealed by means of magnetic circuit simulation and comparison.To assess the engineering feasibility of the proposed motor,the intrinsic shaft voltage of the proposed motor is calculated and compared with that of an existing conventional motor,skewing slot motor,rotor step-skewing motor and an 8-pole 36-slot fractional-slot PMSM of the same size and power class by means of the finite element method.The results verify the engineering feasibility of the proposed semi-symmetrical rotor motor.(5)The proposed semi-symmetrical rotor motor prototype and the benchmark prototype were produced with a design peak power of 20kW,and extensive experimental tests were carried out on each prototype covering dynamic/static electromagnetic performance,electromagnetic vibration noise response,torsional vibration response,etc.In the dynamic/static electromagnetic performance tests of the prototypes,the cogging torque,backEMF,torque angle characteristics,instantaneous torque at different operating conditions,current waveform,full speed domain efficiency map and other performance parameters characterizing the motor’s energy conversion quality were measured,proving that the proposed semi-symmetrical rotor motor has a significant improvement in torque quality with lower cost than the skewing slot/rotor step-skewing motor and no degradation in force energy density;In terms of electromagnetic vibration,acoustic noise and torsional vibration measurement,the parameters or performance of the key components of the motor modal and the overall system modal,vibration transient waveform,vibration order distribution,instantaneous waveform of acoustic noise,noise order distribution pattern,tangential torsional vibration transient waveform and order distribution characteristics of the shaft system were tested,and "finite element-experiment" and "experiment-experiment" results were compared to obtain the commonality between the vibration and noise characteristics of the proposed semi-symmetric rotor motor and those of existing motors.In summary,the theoretical research and simulation results of the proposed semi-symmetrical rotor PMSM torque performance,vibration and noise characteristics,shaft torsional vibration,etc.can be verified,and provide a basis for the comprehensive improvement of force-energy quality and performance parameters such as torque ripple mitigation,vibration and noise reduction and torsional vibration weakening of PMSMs for EVs. |
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