Research On Sliding Mode Control And Torque Ripple Suppression Of Brushless DC Motor

With the development of modern power electronics technology and the continuous improvement of permanent magnet material performance,permanent magnet brushless DC motor(BLDCM)has attracted more and more attention in the field of high performance motion control.BLDCM has the advantages of large output torque,high efficiency,fast response,long life and high reliability.It has been widely used in aerospace,precision machinery,vehicles and household appliances.In order to meet the requirements of high performance control in complex working environment,it is urgent to further improve the control performance of BLDCM so as to better solve the interference caused by various uncertainties on motor operation.In addition,the torque ripple is an important basis to measure the performance of BLDCM in high precision and high reliability situations,which makes the suppression of torque ripple become one of the main research hotspots at present.Therefore,based on the current problems and research status of BLDCM,the speed control strategy and torque ripple suppression of BLDCM are studied in depth.In this thesis,firstly,the development and research status of BLDCM are described,and its basic structure and working principle are briefly introduced.On this basis,the mathematical model and motion equation are established.In order to further improve the control performance of motor and weaken the inherent chattering in traditional sliding mode control system,a new approach law control method based on fal function is designed on the basic principle of sliding mode reaching law control.For this new reaching law,firstly,its stability is proved by using Lyapunov criterion,and its reaching time is calculated theoretically,which proves that it has faster reaching speed than the constant reaching law.In addition,the sliding mode control system based on a typical second-order system is simulated by using Matlab.The results show that the new reaching law has excellent performance in chattering suppression and reaching speed.According to the operation principle of BLDCM,the speed controller of motor is designed based on the new reaching law sliding mode control and is simulated in the environment of Matlab/Simulink.The results show that the proposed algorithm has better dynamic response and robustness to external disturbances and internal parameter perturbations than the conventional PI control and the sliding mode control with constant speed reaching law.Secondly,the electromagnetic torque of BLDCM in commutation period is analyzed in this thesis.In order to keep the change rate of commutation current consistent,a control method is proposed to compensate the DC input voltage of inverters by using the high voltage gain characteristics of switched inductance quasi-Z source network.Finally,an effective way to suppress commutation torque ripple is constructed.For the selection of the front-end circuit of inverters,the working principle and boost capability of traditional Z-source network,quasi-Z-source network and switching inductance quasi-Z-source network are mainly analyzed.The results show that the duty cycle of Switched-Inductance quasi-Z-source converter is smaller under the same boost ratio,and the capacitance in the network bears lower voltage stress.Therefore,the application scope of the system is increased to a certain extent.The suppression strategy is simulated under the environment of Matlab/Simulink.The results show that after voltage compensation,the phase current waveform of the motor winding is closer to the ideal current waveform,and the amplitude of the output electromagnetic torque decreases obviously and tends to be stable.The output torque ripple is about 4.76%of the average torque.It proves that this strategy can effectively suppress the torque ripple of BLDCM.