Research On Sensorless Brushless DC Motor Controller Of Electric Scooter

In the era of increasing environmental awareness of people,traditional ways of traveling have been replaced by more and more electric vehicle.Among them,the electric scooter that had emerged in recent years has became one of the most popular means of travel for short trips because of its attractive appearance,small size,easy carrying,and simple operation.The electric scooter consists of three critical parts: driving motor,motor controller and battery.Most driving motors are brushless DC motor(BLDCM),which have the advantages of large torque,good dynamic performance,long-lifetime,ect.In this paper,BLDCM was taken as the research object to design a digital control system of BLDCM without position sensor based on STM32.Finally,the feasibility and stability of the system were verified by experiments.The dissertation mainly completed the following aspects:(1)The working principle and mathematical model of BLDCM were analyzed.On this basis,a sensorless control theory of back electromotive force(BEMF)zero-crossing detection method was studied.(2)Aiming at the case that the terminal voltage is distorted by freewheeling current from which is inactive phase in the commutation process and detection circuit output signal edges are aside from the actual BEMF zero-crossing,this paper,on the one hand,explained the cause of the freewheeling and analyzed the three-phase current expression during the commutation to obtain a method that shorten the commutation time by adjusting the electrified mode of motor winding,on the other hand,in order to eliminate effect of commutation freewheeling event to a maximum extent,a time-sharing segment sampling strategy was adopted at the same time.(3)The research on motor start-up was carried out.From the comprehensive consideration of the difficulty,the hardware requirement and the reliability,the three-stage starting method was finally selected.Beyond that,numerous issues involved in the start-up process was also illustrated in detail,including voltage and electrified time applied on stator winding in the rotor pre-setting stage,the relationship between the PWM modulation signal duty and the commutation frequency in the external synchronization acceleration stage and switching condition from the accelerated phase to self_controlled synchronous stage,ect.(4)Hardware circuit of control system was designed with STM32F103C8T6 as theMicroprocessor,which was comprised of STM32F103C8T6's peripheral circuit,power supply circuit,full-bridge inverter circuit and its drive circuit,detection circuit,etc.(5)By Hardware circuit carrier,software design of the controller was completed under IAR environment.Furthermore,the software implementation process of key technology in the system was introduced in detail.Finally,by means of software debugging and testing,the result proved that the sensorless control technique adopted in this paper could operate normally.