Rotor Structure Design Of External Rotor Generator For Range-Extender Based On Multi-field Coupling

Extended-range electric vehicles has been greatly developed for it can solve the problem of short battery life of new energy vehicles.Its core components-extended range generator has high power density,high efficiency and high reliability design requirements.At present,there is no mature generator model specially developed for the extended range project at home and abroad.The new external permanent magnet synchronous generator designed in this paper has the advantages of stable operation,compact structure and high power density,which provides a good solution for the generator with extender.However,the outer rotor is large in diameter and susceptible to centrifugal force damage during high-speed rotation.Meanwhile,the combined effect of electromagnetic field,temperature field and structural stress-strain field during rotor operation poses some challenges to the accurate design of the rotor.In this paper,we set the logistics vehicles,light commercial vehicles with external rotor permanent magnet synchronous generator rotor as the research object.In order to achieve the goal of lightweight and high reliability,the calculation model of rotor structural strength considering the electromagnetic force,thermal stress,centrifugal force and assembly stress is established.The rotor structure parameter scheme is calculated and its reliability is verified.Among them,using the 2D magnetic field finite element model to calculate the basic parameters of the magnetic field,Then,the distribution density of the magnetic field force is obtained by analytical method,which is applied to the rotor statics simulation model.Calculation of thermal stress must first find the temperature distribution of the rotor.The fluid-solid coupling finite element temperature field simulation model is established and then validated by the prototype temperature rise experiment,after that the temperature distribution of the rotor is obtained after the parameters of the generator waterway are designed.Centrifugal force and assembly stress can be directly applied in the rotor statics simulation model.The rotor structure parameters are designed under such a boundary condition that electromagnetic force,thermal stress,centrifugal force and assembly stress are applied,and the final solution is obtained.In this case,the maximum deformation of the rotor during over-speed operation is 0.4 mm.The strength calculation shows that the rotor material will not yield.Then the electromagnetic performance and rotor dynamic performance of the program are analyzed: the working area efficiency of the generator is maintained at 96%-97%;the lowest natural frequency of the generator is 102.57 Hz;and the generator will not resonate.In order to verify the calculation results,a prototype was made.The first-order natural frequency of the whole machine was measured by modal experiment at 95 Hz,which was 7.3% different from the simulation.The maximum working frequency of the rotor is 83.3 Hz,which is lower than the first-order natural frequency of the rotor and the rotor structure is safe.