Research On The Design Of High Power Density Outer Rotor Permanent Magnet Synchronous Motor For All-electric Aircraft

With the implementation of ten key areas of made in China 2025,a broad platform has been provided for the development of all-electric aircraft(AEA).At present,some countries and research institutions have developed AEA.However,only a few successful AEAs are published at home and abroad,and the literatures about driving motor for AEA are rarely published.Therefore,the research on driving motor with high power density and high torque density is an important theoretical significance and practical applicationvalue for the development of AEA.For this topic,an outer rotor surface-mounted permanent magnet synchronous motor(SPMSM)for two-seat AEA is taken as research object,and its electromagnetic characteristic,loss distribution,cooling system design and temperature rise characteristic are discussed.In order to solve the problem that the magnetic conductivity of ferromagnetic material is infinite in the analytical modeling process of classical subdomain method,which results in a bigger analytical calculation result.A hybrid analytical model which can consider the nonlinear variation of ferromagnetic material is proposed.Firstly,for SPMSM with similar number of poles and slots,the leakage flux is bigger.Therefore,the analytical models of inter-pole and zigzag leakage flux of SPMSM are established.The distribution of magnetic permeability in different regions are obtained by interpolation operation of B-H curve of ferromagnetic material.The correction coefficient is obtained through multiple iterations,which is used to consider the influence of nonlinear variation of core reluctance on electromagnetic parameters,such as air-gap flux density,no-load back electromotive force(EMF)and electromagnetic torque.On this basis,the analytical models for chamfered pole and non-concentric pole are established based on subdomain superposition method,and the excellent parameters for PM are obtained.Finally,the accuracy of proposed analytical model is verified by 2D finite element model(FEM)and experimental test.Driving motor for AEA requires high power density and high torque density,which results in an extreme state of magnetic load and electrical load.Therefore,it is important to analyse the accurate calculation of loss and the technology of loss suppression.Firstly,in order to reduce core loss,B35A230 self-bonded silicon steel sheet is used as stator and rotor core,the magnetic property of B35A230 is tested by the method of Epstein frame and ring specimen,and the ratio-loss cruves at different frequency and different flux density are measured.According to the experimental results of ring specimen method,a loss model is adopted to improve accuracy,considering processing factor,alternating and rotating magnetization modes and harmonic magnetic field.Secondly,the influences of slot opening width and axial segment of PM on eddy current loss are analyzed to reduce loss.Finally,in order to shorten the length of winding end and reduce copper loss and weight,the processing method of single-tooth core is adopted to manufacture prototype,and the analytical model of DC copper loss is built.The influences of skin effect,proximity effect and alternating flux leakage in slot on AC copper loss are analyzed by 2D-FEM,and the increasing coefficient of DC resistance is calculated to obtain more accurate copper loss.Due to the limitation of working place,AEA has higher requirement on weight and heat dissipation for driving motor and its cooling system.The thermal problem of driving motor is more prominent,but water cooling and oil cooling will increase aircraft weight.In addition,because the loss of outer rotor SPMSM is mainly concentrated on stator core and winding coil,and the traditional forced air cooling method cannot effectively transfer heat to outside through motor housing and end cover.Therefore,a high performance cooling system based on heat pipe technology is used to solve the problem of excessive temperature rise and weight limitation.Firstly,an experimental test system is built to test the cooling capacity of proposed cooling system,and the cooling power and average convection coefficient of radiator are obtained under different cooling conditions.Secondly,based on 3D transient temperature field simulation,the influences of winding end potting heat-conducting glue,axial size of radiator,wind speed of radiator surface,thermal conductivity of cooling pipe and different radiator structures on motor temperature rise are elaborated in detail.It is great significance to solve the overheat problem of driving motor for AEA.Finally,a 22-poles and 24-slots outer rotor SPMSM for AEA is designed and manufactured,and the experiment tests about no-load characteristic,load characteristic and temperature rise under different working conditions are completed to verify relevant design technology.At the same time,the fault-tolerant performance of prototype is analyzed theoretically under the fault of one or two-phase winding.And temperature field under the fault tolerant operation is simulated to ensure that the driving motor can continue to run reliably after fault.