Research On Direct Torque Control Algorithm Of Permanent Magnet Brushless DC Motor

Due to the emergence of environmental pollution,urban traffic crowdedness and the lack of non-renewable energy,the society needs a small,high energy efficiency traffic tools,and the new energy electric vehicles meet the needs.Permanent magnet brushless dc motor(BLDCM)control system,which has large torque output and simple structure and control,can meet the power control requirements of new energy electric vehicles.Direct torque control(DTC)technology is a high performance ac speed regulation technology,it controls brushless dc motor electromagnetic torque in real-time,so that the output torque of the system can be quickly controlled,the system response should be fast.But brushless dc motor mostly uses two-phase conduction mode,which has square waveform current and trapezoidal back EMF,and itself electromagnetic interference,make BLDC produce large torque ripple.And torque ripple largely affects the control performance of BLDC control system,so it's urgent to study how to decrease the BLDC torque ripple in DTC control algorithm.Firstly,the influence factors of brushless dc motor torque ripple,the research of DTC at home and abroad,the direct torque strategy and shortcomings of the sliding mode observer are briefly introduced in the paper.The causes of the pulsation of brushless dc motor are analyzed.Then,the paper introduces two strategies of permanent brushless dc motor direct torque control,and the control strategy ignoring the control of flux are applied in this paper.Moreover,using the traditional sliding mode observer method to obtain the back electromotive force is introduced,which also can get the electromagnetic torque.The analysis from theory and simulation shows the shortcomings of traditional sliding mode observer.Secondly,a non-singular fast terminal sliding mode observer based on the error of current is proposed,which can be applied to direct torque control of brushless dc motor.Considering the chattering,high harmonic and slow convergence of the traditional sliding mode observer,a non-singular fast terminal sliding mode observer is proposed to obtain the back EMF.Subsequently,a comparative simulation analysis of the non-singular fast terminal sliding mode observer and the traditional sliding mode observer is carried out on the simulation.The simulation results show that the back EMF of non-singular sliding mode observer is more accurate,and the smaller chattering,faster approach rate and smaller torque ripple can be obtained.Then,a new non-singular fast terminal sliding mode observer based on the differential current error is proposed and applied to direct torque control of brushless dc motor.By analyzing the sliding surface of the non-singular fast terminal sliding mode observer,a new non-singular fast terminal sliding mode observer is proposed to observe the back EMF.Meanwhile,S function is used to adjust the coefficient of linear sliding mode.Then the new global fast terminal sliding mode observer is simulated on the Simulink software,compared with the traditional sliding mode observer,the results show that the new sliding mode observer has more accurate back EMF,faster approaching rate and smaller torque ripple.Finally,the experimental platform of direct torque control of brushless dc motor with dSPACE as the controller is designed.Selecting a 750 W brushless dc motor and choosing dSPACE as the controller of the algorithm,which concludes the design of platform protection circuit,three-phase inverter circuit,collection circuit,and the choice of motor and load.The BLDCM platform was built to verify the effectiveness of algorithm under the proposed DTC sliding mode observation.