Research On Torque Ripple Suppression Of Permanent Magnet Brushless DC Motor

The brushless DC motor is widely used in the industrial field due to its excellent speed regulation performance,concise internal structure and high use efficiency.However,due to the structure of the motor body and the control system,the brushless DC motor has a large torque ripple,which limits its application in wider fields such as high precision.Especially in the case of low-speed direct drive,the torque ripple directly acts on the load without the deceleration mechanism,which will generate a lot of vibration and noise.This paper studies the causes of the torque ripple of the brushless DC motor.Through reading a large number of related literatures,the causes of the torque ripple of the brushless DC motor and the existing suppression strategies are discussed and analyzed.For the brushless DC motor as a whole,a certain suppression strategy alone cannot solve the problem of motor torque ripple,and often only solves one of the torque ripple problems.For this paper,the DTC which directly uses the torque of the brushless DC motor as the controlled variable is proposed.The direct torque control technology has a simple control system,fast response speed,and strong adjustment ability.The torque controller is used to achieve instantaneous torque control.DTC can effectively reduce torque ripple.This paper makes three improvements to the system to make the torque ripple suppression effect of the DTC system better.Firstly,a new state observer combined with linear and nonlinear feedback solves the inaccuracy of the traditional linear state observer back-EMF observation and results in deviations in the torque calculation process,thus making the torque ripple suppression effect of the direct torque system poor The problem.The traditional state observer has high-frequency signal interference,estimated state quantity is easy to chatter,and does not consider the current fluctuation during commutation.The linear feedback method is used to solve the problem.Then,for the problem that the controller used in the traditional direct torque control system selects the same space vector for large and small errors,resulting in poor torque ripple suppression,a fuzzy controller is proposed to replace the traditional direct torque control system.The hysteresis comparator and the switch vector table achieve the purpose of reducing torque and flux ripple.The fuzzy error is used to classify the torque error,the stator flux error and the blur angle in order to select the space vector reasonably according to the size of the error.Fuzzy logic operation is performed on the fuzzy variables to obtain a suitable space vector to control the brushless DC motor.Finally,the overall sliding mode surface is used instead of the traditional linear sliding mode surface,and the hybrid approximation ratio is used to form an improved sliding mode control,and then the PI regulator is replaced.It can reduce sliding mode chattering and achieve smooth torque when approaching quickly,which can effectively suppress torque fluctuations,while reducing system steady-state errors and improving the overall performance of the system.The simulation experiment was carried out using MATLAB / Simlinksimulation software.The results show that the improved system torque is more stable,the torque ripple suppression effect is achieved,and the overall performance of the direct torque system is improved.