Rotor Position Estimation Brushless DC Motor With Sensorless Control Based On Back EMF Method

With the development of digital control technology and the emergence of newkind of permanent magnetic materials such as Nd-Fe-B,the brushless DC motor with its high-efficiency,stability,low-cost characteristic features is applied widely.Since the emergence of sensorless control technology,this not only makes the volume,weight,cost advantage to continue to ascend,but also greatly increase the anti interference ability of the motor in some harsh conditions.Sensorless control technology not only further reducing the volume,weight,cost of the motor,but also enhances its anti-jamming ability with harsh conditions.In a word,sensorless control technology significantly push the application range of the brushless DC motor in the field of industrial.This paper is based on back EMF method develops a set of simple structure,convenient control of sensorless control system.Firstly,this paper introduced the development and applications of brushless DC motor and discuss the control method.Motor mathematical model,body structure and operating principle of the brushless DC motor are introduced.This paper compares the different position sensor control and sensorless control method.The mathematical theory of sensorless control is analyzed,Some position estimation method in the sensorless is compared in detail,and ultimately determine the back EMFmethod as the rotor position examination.Secondly,a kind of flux "three-stage" start method was proposed in order to solve difficult problem,compared several start methods in sensorless control.The feasibility of the selected starting mode has been verified in the simulation.The control system adopts double closed loop PI control,the outer loop is the speed loop,the inner loop is current loop.According to the simulation,the inverter on the hardware experimental platform was completed,which use the TI's TMS320F2812 as its core controller.This paper makes a detailed introduction for the hardware circuit of each module function.The system software program was completed using C language in the CCS compiler environment.It include motor main program,start program,voltage and current AD sampling program,dual closed-loop program,commutation program,systems protection program and so on.For the motor in the operation process,a circuit of a neutral point reconstruction has been introduced,because the zero crossing detection is not good,and the neutral point voltage can not be measured.In the end,the sensorless control system of brushless DC motor is proved to befeasible on the hardware experimental platform.