Research On High Performance Analog Driver For Brushless DC Motor

In BLDCM,the stator magnet and rotor windings are replaced by stator windings and rotor magnet,so the brush structure is abandoned,which makes the service life of the electric motor greatly extended.The BLDCM not only has the advantages of the starting performance and speed regulation performance of DC motor,it also has the advantages of simple structure,stable operation and easy maintenance of AC motor.In recent years,with the rapid development of the BLDCM,it is widely used in the fields of electric vehicles,industrial control,automation,aerospace and so on.Firstly,the paper introduces the structure of BLDCM,deduces and establishes the mathematical model,and analyzes the working principle and control technology of BLDCM.Because the driver uses square wave to drive the BLDCM,it is inevitably affected by the torque ripple.Therefore,this paper studies the cause of the torque ripple and its suppression method.Based on the comparison of the common PWM modulation methods,a new ON-PWM-ON modulation method is proposed,which completely eliminates the non-conductive phase continuous current phenomenon during the non-commutation period and cooperates with the improved strategy of combined PWM speed control method,it effectively reduces the commutation torque ripple of the motor runtime,and improves the performance of the analog drive system.Secondly,according to the characteristics of traditional software control mode,such as slow speed and poor anti-interference ability,a set of high-performance simulator with full hardware circuit is designed.The complex programmable logic device(CPLD)model of ATMEL company is selected as the main control chip.The PI module of speed and current is the proportional integral circuit composed of operational amplifier.The RC intermittent oscillator and comparator constitute the hardware PWM generating circuit.The driver also includes sampling modulation circuit,encoder speed feedback circuit,power driving circuit,power supply and protection circuit.At last,the control logic is determined.The Hall signal in the six step trapezoid commutation determines the conduction sequence of MOS switches;the speed feedback of encoder and the current feedback of sampling module are combined with the triangle wave signal through the hardware PI circuit to generate PWM duty cycle signal,which is transmitted to the main controller CPLD to adjust the on-off time of MOS switches,thus realizing the real-time speed and current double closed-loop speed regulation.According to the control logic,the main program of CPLD is written by Verilog hardware description language.The system alarm and output protection measures are added to improve the hardware system.In order to compare the performance differences between the full hardware analog drive system and the traditional digital drive system,the driver model is built by MATLAB/ Simulink,and the start-up speed curve,sudden load speed curve and phase current fluctuation are compared by using the self-defined package hardware circuit module and the system's own digital module.The physical experiment platform is set up to analyze the driver characteristics.The simulation and experimental results show that the CPLD based high-performance simulator has faster response speed,better follow-up characteristics and better suppression of commutation torque ripple than the traditional driver,which verifies the feasibility of the high-performance simulation driver designed in this paper.