Design And Optimization Of Direct Drive PMSM

The cannonball steering motor is used to adjust the flight direction.As an important part of the cannonball,the performance of motor has an important impact on the adjustment of the flight path.The traditional cannonball motor adopts the brushless DC motor,which transmits the power through the combination of transmission mechanism.The intermediate transmission link composed of gears,hinges and other components will inevitably produce friction and other losses,which decrease the transmission efficiency.Simultaneously,the Brushless DC motor is greatly affected by large torque ripple.By comparison,the direct drive PMSM has large power factors and better transmission efficiency,and thus observes better performance.Based on these points,a direct drive outer-rotor PMSM is proposed as the cannonball steering motor,and the electromagnetic design and mechanical structure design are completed according to the motor design requirements.Moreover,the optimization of motor torque ripple is also fully studied.First of all,this paper analyzes the calculation principle of the equivalent magnetic circuit which is commonly used in the design of permanent magnet synchronous motor,to set foundation for the design and verification of the electromagnetic design of the direct drive external-rotor PMSM.Due to the lack of relevant research on direct drive PMSM for cannonball orientation,the design method of direct drive external-rotor PMSM applied in electric vehicle,elevator traction and other fields is used for reference in this paper.According to the size limitation and performance requirements of the cannonball motor,the preliminary design of the electromagnetic scheme is completed,including the magnetic circuit structure,main dimensions,permanent magnet parameters,pole slot coordination and winding design.Then the mechanical structure of the motor is designed to meet the requirements of control panel installation and motor connection,in order to improve the reliability of the motor.Secondly,this paper introduces the mathematical model and vector control principle of PMSM,and analyzes the characteristics of d-q axis inductance and electromagnetic torque composition.The results indicate that the cogging torque optimization of this type of motor is an important way to reduce torque ripple.Subsequently,the principle of cogging torque is analyzed,and the calculation formula of cogging torque is derived from the energy variation.According to the formula of cogging torque,three factors affecting cogging torque are summarized,including pole slot coordination,permanent magnet parameters and stator slot parameters.Considering the processing difficulty and the optimization effect of torque ripple,this paper analyzes the cogging torque of the designed direct drive outer-rotor PMSM through FEM from four aspects.Finally,Taguchi method is used to optimize the rated torque,cogging torque and torque ripple,and the final design of direct drive PMSM is obtained.In conclusion,this paper takes the cannonball steering motor as the research object,adopts the direct drive outer-rotor PMSM,completes the electromagnetic design and mechanical structure of the motor,and optimizes cogging torque to reduce the motor torque ripple.