Design And Magneto-Thermal Coupling Analysis Of Outer Rotor Brushless DC Motor For Helicopter Electric Tail Rotor

Compared to traditional helicopter mechanical tail rotor,helicopter electric tail rotor abandons mechanical transmission components,reduces noise and vibration,improves its maintainability,reliability,and maneuverability,and meets the new requirements of green aviation development.It has good application prospects in future military,civilian and other fields.As one of the key technologies of the helicopter electric tail rotor system,the design of the drive motor is particularly important,requiring advantages such as high power density and high torque density.The outer rotor brushless DC motor has the above advantages and is very suitable for electric tail rotor direct drive applications.Therefore,this article designs an outer rotor brushless DC motor for helicopter electric tail rotor,and conducts relevant research on its electromagnetic characteristics,multi-objective optimization,loss characteristics,and magneto thermal coupling.According to the design requirements of the drive motor,firstly,the selection of the motor phase number,motor body mechanism,winding structure and slot pole number combination is analyzed in detail.Secondly,the permanent magnet and air gap length are designed through relevant formulas.Finally,the armature diameter,core length,stator structure and rotor structure of the motor are calculated and determined respectively,and a five phase 25 slot 24 pole outer rotor brushless DC motor is designed.A two-dimensional finite element model was established based on the design parameters of the motor,and the no-load and load characteristics were analyzed to verify the rationality of the design scheme.Using genetic algorithm for multi-objective optimization of motors,the effectiveness of optimization process was verified by comparing the efficiency,output power,loss,average torque,torque ripple,and cogging torque ripple of the motor before and after optimization.An analysis was conducted on the core loss model,and it was concluded that using the same loss coefficient for calculating core losses at different alternating frequencies would result in significant errors.A core loss calculation model considering both alternating magnetization,rotating magnetization,and harmonic magnetic field was adopted to accurately calculate the stator core loss.The effects of slot width,air gap length,radial and axial segmentation of permanent magnets on eddy current losses of permanent magnets were analyzed,and effective suppression of eddy current losses of permanent magnets was achieved.Considering the influence of temperature on the performance of copper winding materials,the DC copper loss of the armature winding was calculated and analyzed,and further divided into front-end winding copper loss,slot winding copper loss,and back-end winding copper loss.The losses of each part were distributed according to volume ratio.A magneto-thermal coupling analysis method for outer rotor brushless DC motors based on the lumped parameter thermal network(LPTN)method is proposed.Considering the different heat transfer paths between the end winding and the slot winding,the armature winding is subdivided into front-end winding,slot winding group,and back-end winding,thereby improving the accuracy of the calculation results.Due to the traditional LPTN method not considering the influence of temperature on material properties,this method considers the influence of temperature on the material properties of copper windings.The LPTN model is used for magneto-thermal coupling analysis,and the feasibility of this method is verified by comparing it with the results of Motor CAD calculations.Finally,a comparative analysis was conducted on convective ventilation,water cooling in the tank,and internal oil cooling,and convective ventilation was selected as the cooling measure for the motor.