Research On Commutation Strategy And Torque Ripple Suppression Of Brushless DC Moto

In recent years,with the vigorous development of new energy vehicles and industrial robots,brushless DC motors have been widely used in life and industrial production due to their advantages of easy speed regulation and high efficiency.The sensorless control system of brushless DC motor controls the motor to generate torque and complete the driving target.Different control systems have different application fields.Among them,square wave control and vector control are widely used in sensorless control systems.The traditional square wave control hardware cost is low and the software program is easy to implement,but the torque ripple problem is inevitable.At the same time,the phenomenon of inaccurate rotor signal capture in sensorless technology still exists.Therefore,in view of the above problems,this paper takes the square wave control of brushless DC motor as the research object,focusing on the study of rotor commutation,speed capture and torque ripple suppression.The details are as follows:Firstly,aiming at the problems of inaccurate rotor position signal capture,large speed estimation error and phase delay in sensorless technology,a commutation strategy based on terminal voltage and improved sliding mode observer is designed,and the stability of the observer is proved by Lyapunov stability theorem.The freewheeling signal is obtained by the logic judgment of the terminal voltage and the DC bus voltage,and the commutation interference component is removed by the detected freewheeling signal.In addition,the line back electromotive force is used as the state variable,eliminating the low-pass filter and phase compensation circuit,and the hyperbolic tangent function is used instead of the switching function to suppress the influence of oscillation on the system.The simulation results show that the method accurately captures the commutation signal and verifies the improvement effect.Secondly,aiming at the inherent torque ripple phenomenon of traditional six-step commutation control,a torque ripple suppression strategy based on torque current change rate is designed.Firstly,the monotonicity of the torque is judged by the positive and negative of the torque change rate during the normal conduction period.According to the comparison between the actual output torque and the given reference torque,the torque vector with monotonicity is selected.The closed-loop control is introduced to make the torque close to the reference value,and the modulation duty cycle is obtained.Then,aiming at the phenomenon that the change of back electromotive force during commutation will affect the torque and output phase current,the constraint conditions of commutation process are analyzed,the output opposite electromotive force is fitted,and the corresponding modulation duty cycle is calculated.The simulation results show that the combination of the two parts can effectively suppress the torque ripple in the whole motion process.Finally,STM32F031 is used as the control core to complete the design of hardware and software.A 750 W brushless DC motor is used as the experimental prototype to build a complete experimental platform.The commutation strategy,torque ripple suppression strategy and the operation performance of the whole machine are experimentally verified.Through the comparison of experimental waveforms,the feasibility of the strategy adopted in this paper is verified,and the overall working performance of brushless DC motor under square wave control is improved.