Research And Design Of Electric Outdoor Advertising System Based On Brushless DC Motor

DC motors are devices which convert electrical energy into mechanical energy, and possess many characteristics, such as:reliable operation, high efficiency, good speed regulation performance and simple structure. But At the same time, there are some shortcomings existing in the brush DC motor. For example, the mechanical brush is easy to damage due to wear and tear, so it needs frequent maintenance. Brushless DC motor, which is emerged and developed on the basis of the DC motor, is a typical electromechanical integration product. Brushless DC motors not only reserve merits from DC motor, but also successfully deal with the problems caused by mechanical commutation, so brushless DC motors have been widely used in all aspects of the modern social life. How to build a reliable and practical control system of brushless DC motor, to achieve the purpose of quick response, high precision, accurate positioning, and to be applied to other industries, that has become an important issue in the Brushless DC Motor control field and plays an important role in industry application. So the research in the control system of brushless DC motor has great economic benefit.It is introduced that the basic component, driving circuit, working principle, Commutation process and modulation mode of brushless DC motor. On the basis of mathematical model established, torque ripple occurring in commutation process, which can be suppressed effectively by using H_PWM (Pulse Width Modulation)-L_ON Modulation mode in the procession of running motor, is analyzed and calculated. In the last part of this chapter, speed control strategy of PI speed regulator is raised.In this thesis, a STM32 chip is designed as the core of control system of brushless DC motor. Hardware platform is consisted of control chip circuit, power driver circuit, detecting circuit and power circuit. The normal operation of the motor and speed control is ensured by power drive circuit, control chip circuit and the position signal detection circuit. Security is kept by Detecting voltage and current of the circuits and overload is controlled.On the method of hierarchical and modular software program design, the software completed with C language, is composed of main program and subroutines. The internal ports, program modules, interrupts, peripherals and variables of software are initialized, and subroutines needed are invoked in main system. The functions, which are completed by interrupting service routines, including position signal capture, PWM generation, electronic commutation and AD testing, are used to make the motor running. By activating modules of the STM32 chip and invoking the correlation subroutines, the functions of system standby, running on time, cycling-display, picture-positioning and communication are called.Finally, the experiments results show that the control system of Brushless DC Motor researched in this thesis achieve the anticipated effects, which provide a platform for further research in the future.