Design Research On High-speed Permanent Magnet Synchronous Machines With Fractional Slot Concentrated Windings

Owing to the maturity of high-frequency power semiconductors,such as Si C MOSFET,increasing the pole number of high speed permanent magnet synchronous machines(HSPMSMs)is becoming feasible and promising.The HSPMSMs with fractional slot concentrated windings(FSCW-HSPMSMs),commonly featured as high number of poles and short ending winding,have higher torque density than traditional integral slot distributed winding HSPMSMs(ISDW-HSPMSMs),which make them competitive candidates for increasing power density and enlarging the power-speed envelope.This paper focus on FSCWHSPMSMs of 1250 Hz fundamental frequency,and design and test of this kind of machines are researched.Firstly,the state of the art of HSPMSMs,particularly FSCW-HSPMSMs is reviewed,and the main barriers to increasing power density and enlarging the power-speed envelope are revealed.On this basis,the comparison of ISDW-HSPMSM and FSCW-HSPMSM is presented,in terms of their characteristics and design considerations.For the rotor eddy current loss,the generation mechanism,calculation methods are investigated firstly.By finite element analysis(FEA),each loss sources are accurately separated,and then,the effect of winding types on them are analyzed.The influence of typical design variables and parameters on rotor eddy current loss and other performances are analyzed by parametric FEA,in conjunction with coupled field-circuit analysis.To reduce rotor eddy current loss,the effectiveness of low-conductivity materials,and their impact on other performances are evaluated.Finally,the “loss shift” concept is proposed,and the design principles of rotor eddy current loss reduction are discussed according to analysis results.The winding coil layout deterination method for machines with larger number of slots and poles is presented,as a basis for studying the variation trend of key performances against slotpole combination.This work helps to determine the optimal combination,rather than simply multiplying basic combinations.FEA is used to separate each inductance component,and then,their proportions and variations in FSCW-HSPMSM and ISDW-HSPMSM are comparatively researched.Finally,the reason for a larger phase inductance in FSCW-HSPMSM is revealed.According to the features of FSCW-HSPMSM's windings,a new ac copper loss calculation method is proposed,considering calculating efficiency and accuracy.Using this method,each source of ac copper loss is individually calculated,then the characteristics and reduction measures of this kind of loss is discussed for ISDW-HSPMSM and FSCW-HSPMSM.The principles and usability of common iron loss calculation methods are analyzed,then the effect of iron loss on magnetic field distribution is investigated.Afterwards,iron loss of ISDWHSPMSM and FSCW-HSPMSM is comparatively researched,explaining the disproportional loss increment in the latter that has a much higher electromagnetic frequency.The two-way coupled electromagnetic and thermal analysis is performed,to calculate the temperature rise of FSCW-HSPMSM with oil-cooled housing.Firstly,the windage and bearing friction losses are analytically calculated before building the thermal FEA model.Then,model parameters,such as thermal contact resistance,orthotropic thermal properties and convective heat-transfer coefficient,are derived according to design variables.The temperature simulation result is presented,and the optimization direction of rotor heat removal is discussed based on the parameter sensitivity analysis.At last,from thermal aspect,the practicability of ceramic rotor yoke is validated.The rotor strength design of FSCW-HSPMSMs that commonly have larger stator split ratio than ISDW-HSPMSMs is presented.Firstly,the stress calculation methods of the rotor consisting of orthotropic materials are comparatively studied,then failure criteria for each rotor parts are analyzed.One-way coupled electromagnetic-structural analysis and thermal-structural analysis are performed to separate stress sources,on this basis,the rotor strength design of the FSCW-HSPMSM is evaluated.To further optimize rotor structure design,the effect of the thickness of non-conductive sleeve and the interference between the sleeve and magnets are researched with parametric FEA.In addition,the variation of rotor strength distribution when using ceramic rotor yoke is simulated and discussed.Several FSCW-HSPMSMs with different powers and speeds are introduced,and thereafter the principles and characteristics of them are summarized to establish systematic and integrated design methods for this kind of machines.Among them,the design works and fabrication of the12 k W,15kr/min,1250 Hz machine are introduced in detail.A back-to-back test rig is built to measure the parameters and performances of the prototypes,under open-circuit and on-load conditions.Measured results are compared to calculated ones and the error sources are analyzed.Preliminary tests show that,for the required power and speed,1250 Hz FSCW-HSPMSM with low-switch-frequency control scheme is feasible,the design process and calculation algorithm show high reliability and accuracy.