Brushless Motor Control System Based On Phase-locked Loop

Based on the background of brushless motor drive control,using closed-loop control of PLL,as the core of MCU and Phase locked loop chip cd74hc4046 were used for a brushless motor control system based on phase locked loop is designed to realize high precision speed control of brushless motor.Firstly,this paper introduces the principle of PLL control system and describes the workflow of each link in the system.Modelling and analysis are also carried out for each part of PLL control system,such as frequency discriminator,loop filter and VCO.The structure of the loop filter is built around the operational amplifier to improve the dynamic performance of the system.Combined with the mathematical model of brushless motor,the stability of the control system is verified by Matlab simulation.Secondly,based on the model and functional requirements of the PLL control system,the hardware structure of the control system is determined,and the circuit is built around MCU and PLL chip CD74HC4046.Using CD74HC4046 to complete the function of frequency and phase discrimination;The second-order filter is built by operational amplifier to realize the loop filtering function;using MCU to generate PWM driving signal and complete the corresponding commutation logic;using special gate driver and MOSFET to build the inverter circuit of the system;building gate circuit to process the output signal of Hall sensor,etc.Then,through the MCU programming to improve the control system on the various functions,mainly including the Hall sensor output signal acquisition;generating commutation logic;output PWM control signal;sampling of bus current;protection function of the system;closed-loop control of phase-locked loop,communication between MCU and PC,etc.Software part through the MCU programming to improve the control system on the various functions,such as the Hall sensor output signal acquisition;output of PWM control signal;Sampling of current and voltage signals;control algorithm of motor,etc.Finally,the experimental platform of the control system is built to debug the hardware circuit of the system,the PWM control signal,phase voltage,phase current,speed stability and speed regulation performance of the motor are tested.Test results show that the control system has excellent speed stability and speed regulation performance.Speed accuracy can reach 0.033% when the speed is steady,and it has good tracking ability for the command signal with slope of ±5Hz/s.The control system can meet the needs of high speed precision occasions.