Research On Brushless DC Motor Control System Based On FPGA

Permanent magnet brushless dc motors(BLDCM)are widely used in many fields such as vehicle,household appliances,robots,aerospace and medical instruments.Using FPGA as the control core,the research focuses on the current ripple during commutation and the performance of reverse braking method in the BLDCM speed control system.Firstly,the FPGA chip SPARTAN XC3S500E of Xilinx is selected as the core of the controller and the software and hardware design of the BLDCM speed control system is carried out.Based on the PI control,this system adopts double closed-loop control,which includes the outer speed loop and the inner current loop.In FPGA hardware design,the main control circuit with FPGA as the core,IPM drive circuit,current sample circuit,A/D conversion circuit,D/A conversion circuit and other peripheral circuit design have been implemented.In FPGA software design,speed detection module,A/D conversion module,D/A conversion module,PWM module,sampling filter module,commutation module,PI control module and other specific methods have been implemented by Verilog HDL and EDA modular design.Secondly,the five commonly used PWM methods are introduced.By focusing on the PWM ON method which causes the smallest torque ripple,this paper analyzes the motor's phase current during commutation and clarifies the cause of the commutation ripple.Based on the analysis of the continuous flow path of the shut-off phase under the different modulation methods of the non-commutation phase in the commutation zone,overlapping commutation method is used to suppress the current ripple during commutation.In addition,the article also studies the braking problem of brushless DC motor for large-inertia system.Based on reverse braking method,H_PWM_L_PWM which controls impact current better is adopted.In order to apply reverse braking method to the whole process of braking,a constant braking current method is proposed.Under the premise of ensuring that the braking current is stable within a certain range,the motor can be quickly and smoothly stopped.