Basic Research On Propusion Motor Of Unmanned Aerial Vehicle Based On Series/Parallel Switched Windings

The permanent magnet synchronous motor(PMSM)for propulsion is one of the research hotspots of Solar unmanned aerial vehicles(SUAV).The flight environment of SUAV is changeable and the working task profile is complex.Therefore,there are different output performance requirements for propulsion motor system.For example,when climbing at low altitude,the motor output torque is required to be large and the speed is low,and when cruising at high altitude,the motor output torque is required to be small and the speed is high.Due to the limited energy capacity,the propulsion motor needs to maintain high efficiency under these working conditions.In general,PMSM only maintain high efficiency in the vicinity of rated working conditions,so it is difficult to meet the actual demand of high efficiency operation of SUAV propulsion motor system under multiple working conditions.If the high altitude cruise working point is selected to design the motor,when climbing at low altitude the motor output torque will be large and the winding current is high,as a result,the motor system loss is large,the efficiency is low,and the motor temperature is high,which has a bad effect on the SUAV.Through the series and parallel switching of motor stator windings,the phase current demand and the corresponding drive loss can be reduced at low speed,so as to improve the overall efficiency of the motor system.The purpose of this paper is to study the characteristics of the overall efficiency of the propulsion motor with series/parallel switched windings under multiple working conditions,and to summarize the optimal design method of the motor.Firstly,the airgap magnetic field of the the surface magnet synchronous motor(SPM)with fractional-slot concentrated-winding(FSCW)is analyzed and calculated,and the correctness and accuracy of the analysis are verified by FEA.According to the analytical formula of airgap magnetic field and the distribution of magnetic field lines,the analytical formula of the size of stator and rotor core of SPM is derived.Based on the analysis of no-load airgap magnetic field,the optimal design method of the size parameters of permanent magnet is given.Secondly,through the analysis of the airgap magnetic field of the motor,the parametric model of the motor under the rated working condition is established;the accuracy of the model is verified by FEA.The influences of electromagnetic load,length diameter ratio,pole and slot combination and pole structure on the effective mass and efficiency of the propulsion motor are analyzed with the model.Then,based on the dq axis mathematical model of PMSM,the paper analyzes the capacity of series/parallel switched windings to expand the range of speed and torque,the efficiency characteristics of motor and driver before and after switching,summarizes and draws the efficiency map of motor system,and quantitatively analyzes the capacity of series/ parallel switched windings to improve the efficiency of motor system.Finally,the change rule of the overall efficiency of the propulsion motor system under multiple working conditions is calculated with the parametric model.The results show that the rated working point can be further close to the cruising working area with smaller rated torque after using the series/parallel switched windings,so as to improve the overall efficiency of the motor system and reduce the mass of the motor.On the basis of the above research work,a prototype with series/parallel switched windings is designed and tested,which verifies the effectiveness of switched windings to improve the efficiency of the motor system.