Research On Technologies Of Sensorless Control Of Brushless DC Motors

As the fast-paced developement of the power electronics technology and application of high-energy permanent magnet materials,the BLDC motor was developed as a kind of mechatronics product.It is used in the industrial,household and consumer electronic and many other areas.Typically,the BLDC motor need hall sensors in order to rotating continually.However,the hall sensors on it cannot be used in some applications,such as high-tempperature,high-humidity.Because of that,researchers have proposed a lot of methods to solve the problem to make the motor commutate without the hall sensors.There are two main ideas.On one hand,the zero-crossing time of back-EMF can be detected and it is involved to the commutation time. On the other hand, the mathematic models of the motor are used,or combined with the modern control theorys to observe the back-EMF and the flux.The former seems to be more popular in the BLDC motors drived by the trapezidal waves.And the latter is more popular in which are drived by sine waves.This dissertation reviews the development history of brushless dc motor and control methods which are widely used.Futhermore,the basic principles and theories of brushless dc motor has carried on the thorough analysis, and the mathematical model are built, and the design of a complete control system with hall sensors is proposed with trapezidal waves.And four- quadrant control and double loops control method are developed.A benchmark is provided for the follow researches and comparations.The methods to control the BLDC motors both with and without the hall sensors drive by trapezidal waves which are widely used are introduced in this dissertation.Based on that,two different methods to detect the zero-crossing time of the BEMF are analysiced.To start the motor,a method called “Align-and-go”is studied and the method is improved.The method of directly detecting the back-EMF is studied. And the control system is simulated to verify the feasibility. The state observer is used on the sensorless control drived by the sine waves and the Quadrature phase locked loop is used. The programs are designed.The simulation test the feasibility.The three digital control methods are achived based on the micro-controller STM32F103.The experiment results are achieved and compared and analysed.