Design Of CT Direct Drive Motor And Study Of Anti-disturbance Control Strategy

At present,the advanced medical CT adopts direct-drive structure.For the elimination of the transmission links,the response and transmission efficiency is greatly improved.However,the load disturbances are directly transmitted to the motor shaft,and the torque ripple or vibration noise from the motor also act on the CT frame,affecting the speed and positioning accuracy during scanning.Therefore,this paper focused on the CT frame motor design and anti-load-disturbance control strategy,and carried out the following research:Firstly,the factors related to electromagnetic noise,torque fluctuation and loss were summarized.According to conductor vector superposition,the automatic calculation of winding coefficient was realized by programming.By analyzing the harmonic distribution of the combination of slots/poles,the reasonable combination was selected to complete the relevant electromagnetic structure design.Secondly,with the finite element model of the motor established,the distortion rate of the no-load air gap density was reduced by 4.3% with the orthogonal array method.The performance of the motor was obtained by the model to verify the rationality of the analytical design.At the same time,considering the stator manufacturing,the segmented stator structure on the motor performance was analyzed.Besides,the edge torque was reduced by optimizing the core length.Afterwards,the CT direct-drive motor system was modeled in Simulink,and the source of load disturbance was analyzed.In order to improve the robustness of the system,this paper studied the sliding mode control(SMC),and the expansion state observer(ESO)was introduced to observe the system disturbance to weaken the chattering from SMC control.At the same time,a new switching rule was used to solve the problem of over speed in the positioning process.Finally,to verify the anti disturbance ability of SMC + ESO control,a low-speed motor was manufactured and the system of d SPACE + IPM was established.In the experiment of speed control,step and eccentric load disturbance were applied to the motor,and the anti-disturbance ability of SMC+ ESO control was stronger by 30%.In the position control experiment,the improved SMC + ESO controller was verified.The racking accuracy and robustness of SMC + ESO control were better than PI control.