Micro External-Rotor BLDC Motor and Its Control

　　Micro External-Rotor BLDC Motor and Its Control
　　BLDCMs have been widely used in the field of aeromodelling with the advantages of small size, light weight, high efficiency and reliability. BLDCMs can be divided into external rotor BLDCMs and inner rotor BLDCMs due to the different structure. This paper designs a type of External rotor BLDCM and the control system.Firstly, the external rotor BLDCM was analyzed from permanent magnet material, magnet.structure, magnetization, winding distribution Block neodymium magnet and pole-slot combinations. The parameters of the motor were calculated according to classical BLDCM design methods and formulas. Meanwhile, in order to validate the rationality of the parameters, this paper also established the finite element simulation model. Based on the finite element analysis, the characteristic and static performance of the motor were acquired, the torque and gap magnetic field were also calculated.Secondly, this paper developed a controller for the sensorless BLDCM based on the MCU Atmega88. The BLDCM control system based on BEMF method was designed. The peripheral circuits, power circuits and BEMF detection circuit of this system were introduced in detail. The whole design and the main program flowchart were expounded. A few primary flowchart such as pulse detection, self-starting, sensorless operation were also expatiated.Lastly, the external rotor BLDC motor http://www.chinamagnets.biz/Neodymium/Block-neodymium-magnet.php was carried on experiments including unloaded state, loaded state and gradually loaded state, etc. The experiment results validated that the whole system worked steadily and reliably which supplies the reference for the following research work.