Research On Sensorless Control Technology Of Brushless DC Motor

The DC motor has good speed regulation performance,and the speed changes linearly with the bus voltage,but the traditional brushed DC motor has mechanical noise when it rotates,which easily generates electric sparks,which limits its application.The brushless DC motor uses electronic commutation,which not only has the characteristics of excellent speed regulation performance,high reliability,small size and large torque of the brushed DC motor,but also overcomes the disadvantages of the brushed DC motor mechanical commutation.However,because the electronic commutation requires the use of position sensors,the application of brushless DC motors is limited.In this thesis,a square wave brushless DC motor is used as the plant,and a set of position sensorless brushless DC motor double closed-loop speed control system is designed.First,the structure and operation principle of the control system of the brushless DC motor are introduced.On this basis,the back-EMF zero-crossing detection method is used instead of the position sensor to realize the sensorless brushless DC motor control.Theoretical analysis and experiments prove its feasibility.Due to the small anti-point momentum of the static or low-speed brushless DC motor,the commutation point cannot be accurately detected.The traditional three-stage startup and inductance method are used to start.Through simulation and experimental analysis,the feasibility of the two is proved.A comparison was made.Moreover,in order to improve the performance of the control system,a fuzzy PI control algorithm is introduced in the closed-loop control part,which reduces the amount of speed overshoot when the motor is started and improves the anti-interference ability of the motor during operation.According to the design scheme of the control system,the hardware platform of the brushless DC motor position sensorless control system with STM32F103RCT6 as the core is designed,including the drive circuit,current detection circuit,back-EMF zero-crossing detection circuit,power supply circuit and STM3 2 minimum system circuit.The system software structure corresponding to the hardware circuit is shown.The experimental results obtained on the hardware platform are consistent with the theoretical analysis,verifying the feasibility of the back-EMF zero-crossing detection method,comparing the traditional three-stage startup and the inductive method startup,and finding that the traditional three-stage startup structure is simple but easy affected by the starting load,the inductive method is not easy to be affected by the starting load,the current fluctuation is small,but the structure is more complicated and the noise is larger.