Research On Torque Ripple Suppression Of Brushless DC Motor Based On Mixed Logic Dynamic Model

Uav spraying technology for agricultural plant protection has improved the efficiency and safety of agricultural production and promoted the development of national agricultural modernization.Brushless DC motor(BLDCM)is often used as the driving motor of unmanned aircraft due to its small size and light weight.However,the square-wave driven brushless DC motor has a large torque ripple during phase conversion which affects the working quality of plant protection unmanned aircraft.A study of this problem is conducted in this paper.The brushless DC motor drive system contains both continuous time variables such as inductance current and discrete event variables such as power switch tube turn-off,forming a hybrid system.In view of this,Mixed Logic Dynamic model(MLD)of brushless DC motor drive system is established by introducing hybrid system theory.Based on this model,a commutation torque ripple suppression method for brushless DC motor is proposed.Firstly,the basic structure and working principle of brushless DC motor are introduced,and the mathematical model of the motor is derived based on the working principle.On this basis,the causes of commutation torque ripple of brushless DC motor are analyzed.The commutation torque ripple is caused by the fluctuation of continuous conduction phase current in the process of commutation,and the commutation torque is proportional to the continuous conduction phase current.Therefore,the key problems are determined.In order to seek solutions,the performance of the traditional control strategy is analyzed,the advantages and disadvantages of the traditional control strategy are summarized,and combined with the hybrid control theory,the research objectives and technical routes of this paper are determined.Secondly,the hybrid characteristics of the brushless DC motor drive system are analyzed,and the events,modes and changes of the system are clarified.Then,the continuous time dynamic model and discrete event dynamic model of brushless DC motor are established.On this basis,the hybrid logic dynamic model is established considering the coupling characteristics between them.Based on this model,a model predictive control method was proposed to suppress torque ripple,that is,the hybrid logic dynamic model was taken as the prediction model of the continuous on-phase current during commutation,the minimum of commutation torque ripple was taken as the objective to establish a cost function for rolling optimization,and a group of optimal control inputs were found to act on the inverter to achieve the purpose of suppressing the commutation torque ripple.Since the torque ripple is small during the non-commutation period,the commutation/non-commutation control strategy is switched according to Hall signal using the PWM-ON-PWM modulation strategy during this period.Finally,in order to verify the rationality and effectiveness of the control strategy in this paper,the controller simulation model was first built in the MATLAB/Simulink environment for simulation verification,and then the motor experiment platform was built based on the RTUBOX control platform for experimental verification,to verify the torque ripple suppression effect of the motor under the control strategy in the low speed and high speed operating conditions.The results show that this method can effectively suppress the commutation torque ripple at both low speed and high speed,and the motor has good dynamic characteristics and strong robustness,which proves that the control strategy in this paper is reasonable and effective.