Direct Torque Control System For BLDCM Based On Optimized Sliding Mode Observer

As one of the most component of motor field,brushless DC motor is playing a great role in industrial production and social life due to its several advantages,such as the small volume,the low cost,the good torque characteristics and simple and safe maintenance.Also,it becomes a popular research topic both in scientific research and market application.But there is always a problem to be solved for the brushless DC motor driven by square wave,that is the torque ripple is much worse than the other types of motor,which limit the application in field with high precision and high dynamic performance.Thus,how to suppress the torque ripple of Brushless DC motor has been the focus and difficulty of scientific research.Firstly,we gave a detailed analysis of the mathematical model of a BLDCM.Then,The cause of commutation torque ripple is analyzed in detail.The current ripple is generated in the commutation process which attributed to the indutorwa,thereby causing the torque ripple.In order to reduce the torque ripple,direct torque control is proposed,which contains torque loop and speed loop.The required torque can be obtained through the PI controller of rotor speed control loop.In the last step of direct torque control,appropriate space voltage vector is selected by the output of torque controller.The key issue of torque calculation is the estimation of back EMF.For that this paper creatively put forward an optimized back electromotive force(back-EMF)sliding mode observer(SMO).In the basic of mathematical model of brushless DC motor,the three phase voltage and current are reconstructed,and then the accurate estimation of the back EMF can be obtained.System chattering is inevitable when traditional sliding mode observer with signum function is used,to solve this problem,an optimized sliding mode observer when arc-tangent function is proposed and hen the sliding and convergence condition is proved.In the environment of MATLAB / Simulink,the overall system of direct torque control for BLDCM based on optimized sliding mode observer is simulated.Compared with the traditional sliding mode observer,the optimized sliding mode observer is much better at weakening system chattering.Simulation results show the correctness and effectiveness of the proposed scheme.Under the condition of theory research and simulation analysis,brushless DC motor control system platform is introduced in detail.On the basis of the hardware experimental environment,the C language in CCS 3.3 is completed by the program of the control system software.Finally,the application of the sliding mode observer in the brushless DC motor is realized,as result,accurate back EMF observation waveform is obtained.Experiment results show the correctness and effectiveness of the proposed scheme.