Research On High Efficiency And High Torque Density Permanent Magnet Synchronous Motor Of Solar Unmanned Aerial Vehicle

With the continuous improvement of the solar unmanned aerial vehicle(SUAV),the propulsion system is gradually developing towards light weight and high efficiency,which requires that the motor of the propulsion system is high efficiency and high torque density.In this paper,a high efficiency and high torque density permanent magnet synchronous motor(PMSM)is chosen,and the electromagnetic and thermal performances of the motor are studied.A parametric model of PMSM is established,and the influences of main dimensions of PMSM on the torque and efficiency are analyzed.Based on the finite element analysis(FEA),the influences of the motor structure parameters on the torque and loss are explored.The thermal performance of the motor with heat pipe inserting into the winding is studied,and the influences of the heat dissipation by heat pipe on the torque density and efficiency of the motor are studied.An experimental prototype is built to verify the electromagnetic and thermal performance,and the reasons for the differences between the experiment and the design results are analyzed.Firstly,based on the two main dimensional parameters,‘diameter length ratio' and ‘reverse split ratio',a parametric model of PMSM is built.Based on the model,the variations of torque,efficiency,mass and heat load of the motor with the main dimensional parameters are analyzed.The selection range of the main dimensional parameters and the changing law of the torque and efficiency under the limitations of the mass and thermal load are explored.The influences of the heat load boundary condition on the torque and efficiency are analyzed.According to the analytical results,the main dimensions of the motor are preliminarily determined.Secondly,based on the main dimensions,the influences of the motor structural parameters on the torque and loss are studied by FEA.They mainly include the influence of the pole and slot combination on the torque,efficiency,mass and heat load,the influence of the slot opening size(opening width and opening height)on the cogging torque,permanent magnet eddy current loss and electromagnetic torque and the influence of the magnetic pole structure and size(pole arc coefficient of the common surface-mounted permanent magnet and pole angle ratio of the Halbach array)on the back electromotive force(EMF),torque and loss.Then,to reduce the temperature rise of the motor and improve the torque density and efficiency,the heat dissipation method of heat pipe inserting into the winding is adopted,and the thermal performance of the motor is analyzed and optimized.The thermal network of the PMSM stator is built.A thermal model of the heat dissipation system by heat pipe is established according to the thermal characteristic test of the sintered heat pipe.Then the thermal model is brought into the thermal network to calculate the temperature rise of the motor.The influences of the heat dissipation on the motor temperature rise,copper loss,torque density and efficiency are analyzed,and the position of the heat pipe in the slot is optimized.The effectiveness of the heat dissipation by heat pipe is verified by FEA.Finally,based on the above analysis,an experimental prototype is built to verify the electromagnetic and thermal performances.The friction loss,the no-load loss,the linear back EMF constant,the electromagnetic torque constant,the efficiencies of all working points and the temperature rise of the maximum overload point are measured respectively.The reasons for the differences between the experiment and design results are analyzed to further improve the motor design.