Research And Design On Permanent Magnet Brushless DC Motor Direct Torque Control

The use of electronic commutation instead of the mechanical commutation of the brush in the permanent magnet brushless DC motors(PMBLDCM)makes the brushless DC motor not only has the advantages of DC motor,but also reduces the abrasion caused by the brush.PMBLDCM has many advantages,including high efficiency,saving electricity,large output torque,wide speed range,high power density,simple control method and flexible and reliable operation.Due to the PMBLDCM has many advantages,making its use of the periphery has been spread throughout the aerospace,home appliances,electric vehicles,industrial and many other areas,but also has the irreplaceable function.So,nowadays,the control of brushless motor is very important.The structure and working principle of PMBLDCM were discussed in detail.Then the mathematical model and simulation model based on the platform of PLECS were established.The principle of direct torque control of Brushless DC motor were also discussed,and then according to the principle,the voltage space vector table was developed.What's more,the initial direct torque control system simulation model was built.Through simulation and verification,the voltage space vector table was modified constantly.Based on the comparison of the direct torque control(DTC)system simulation results of the direct torque control system with the flux linkage and without the flux,the application of the brushless DC motor without flux linkage was proposed.Although it is found that the torque ripple of Brushless DC motor is suppressed by using direct torque control method,the torque ripple is still high and the switching frequency is high.In order to solve these problems,the improved direct torque control is proposed.The problem of the high frequency and the torque ripple were solved well by using the torque hysteresis loop and opening current hysteresis loop.And by choice the improved voltage vector make the PWM-ON-PWM modulation.What's more,based on simulation analysis,permanent magnet brushless DC motor direct torque control system hardware platform was built based on DSP&CPLD as the main control chip.The hardware circuit are introduced in detail,illustrating the division of labor based on DSP and CPLD,introducing the DSP and CPLD software design process,coming out the results of the experiment.Through the experimental waveforms can draw the conclusion that the improved direct torque control system not only can effectively restrain torque ripple and reduce the switch frequency of the switch tube,but also the dynamic response effect is the same with traditional direct torque control systems.