Research On Torque Ripple Suppression And Rotor Initial Positioning Of Brushless DC Motor

Brushless DC motor(BLDCM)not only inherits the advantages of simple control,high efficiency,excellent speed regulation performance and high power density of DC motor,but also solves the problems of spark and noise caused by mechanical commutation.The advantages make BLDCM widely used in household appliances,electric tools,new energy vehicles and other fields.However,the discontinuous circular magnetic field formed by the stator winding of BLDCM is easy to produce large torque ripple,which is hard to be ignored in some areas with high stability requirements.At the same time,the application of position sensor also limits BLDCM in a certain extent.Therefore,it is great significance to carry out the research of BLDCM torque ripple suppression and rotor initial positioning without position sensor.This paper focuses on the above two problems and makes the following work.Firstly,the structure and operation principle of BLDCM are introduced in detail.On this basis,the mathematical model of BLDCM in three-phase stator coordinate system is established.At the same time,the coordinate system and coordinate transformation frequently used in this paper are introduced.Secondly,the principle of traditional direct torque control(DTC)algorithm is introduced,and the synthesis method of the voltage space vectors under two-phase conduction mode and the establishment process of the switching table are analyzed.At the same time,to the problems of too large sector divided and unreasonable selection of the voltage space vectors,an improved DTC algorithm based on two-phase and three-phase hybrid conduction control is proposed.The improved DTC algorithm not only subdivides the sector,but also changes the traditional sector division method,which makes the selection of the voltage space vectors more reasonable.In order to compare the effect of the two control algorithms,BLDCM control systems based on the two control algorithms are built in Matlab/Simulink,and simulation experiments are carried out.The simulation results show that the two control algorithms can make the motor show good speed tracking and dynamic response,but the torque ripple suppression ability of the improved DTC algorithm is obviously better than that of the traditional DTC algorithm,and the difference is more obvious in the high speed.Thirdly,to solve the torque ripple existing in the commutation of BLDCM under the control of DTC algorithm,a direct torque and flux control method based on space vector modulation(SVM)is proposed.In this method,SVM module is used to replace the switch table module in traditional DTC algorithm.Meanwhile,the electromagnetic torque and stator flux are decoupled to complete the separate control of them.In order to avoid the accumulated error and integral drift caused by integrator,this study chooses to calculate stator flux and electromagnetic torque in synchronous rotation orthogonal coordinate system.In this study,the BLDCM control system based on the control algorithm is built in Matlab/Simulink,and the simulation experiments are carried out.The simulation results show that the proposed control algorithm can keep the dynamic response speed of the BLDCM under the control of DTC algorithm,and effectively suppress the torque ripple during commutation.Then,in order to solve the problem that there is no rotor initial position feedback in BLDCM control system based on DTC algorithm,starting reversal or starting failure of the motor may occur due to the inability to select the appropriate voltage space vector,this paper proposes a rotor initial position method based on magnetic saturation effect,and introduces the principle and implementation steps of this method in detail.Then,to solve the problem that BLDCM is prone to start-up reversal or start failure without rotor initial position feedback,a rotor initial positioning method based on magnetic saturation effect is proposed.The principle and implementation steps of the proposed method are introduced.In addition,the method proposed is verified by simulating the magnetic saturation of the experimental prototyp in Matlab/Simulink.The simulation results show that the rotor position can be accurately located in 30° sector by the proposed method.Finally,a BLDCM control system is built to detect the initial position of the rotor,and the hardware and software parts of the system are introduced.In the hardware part,the main control circuit based on TMS320F28335 digital signal processor(DSP),the power driving circuit with PS21765 intelligent power module(IPM),the isolation circuit with HCPL-4504,the current detection circuit with the Hall current sensor and the voltage detection circuit based on resistance voltage dividing strategy are demonstrated.In the software part,the main controller program based on TMS320F28335 and the state observation window program based on Lab VIEW are demonstrated.