Research On Five-phase Brushless DC Motor Control System Based On Position-sensorless

Nowadays,brushless DC motors are widely used in industrial automation,household appliances and other fields.It has many advantages like simple structure,easy maintenance and high output power density etc.But in high-performance applications,the torque ripple of traditional three-phase brushless DC motors cannot meet the requirements.Using position sensor inside of the motor will increase the cost of the system,make the structure more cumbersome,and reduce the reliability of motor especially in hard environment like extreme temperature and intense radiation.Five-phase brushless DC motor shows great application potential due to its small torque ripple and strong fault tolerance.Therefore,this thesis researches and analyzes the control system of the five-phase brushless DC motor based on the position sensorless technology,and proposes an improved linear back-EMF method,combined with the traditional linear back-EMF zero-crossing method,which acts on different speed ranges of the five-phase brushless DC motor,this control method can realize high-stable and high-precision control in the full-speed range of the motor.This thesis first analyzes the basic working principle of the five-phase brushless DC motor.In order to solve problem of the slow feedback of the traditional speed calculation method when the motor is running at low speed and the filtering circuit phase delay,this thesis analyzes and compensates for the phase delay and improves the speed calculation method to speed up the speed feedback response.Secondly,we aimed at the problem that the zero-crossing method of the line back EMF cannot be used to detect the commutation position under the motor’s low speed conditions,basing on the basic working principle of the five-phase brushless DC motor.Calculating the double line back EMFs with opposite changing trends are detected in each rotor position interval,performing arithmetic processing and obtaining processing signals to detect the commutation time.However,the logic operation of the improved method is complicated,so we still used the zero-crossing method of linear back-EMF in the high-speed area of the motor.The two methods are switched according to the speed to realize the position sensorless control of the five-phase brushless DC motor at full speed.At the same time,we used the fault-tolerant control method to improve the reliability of motor control system.Finally,we designed a five-phase brushless DC motor control experimental system on TMS320F28335 platform.And verifying with the improved non-inductive commutation strategy and speed calculation method in Matlab/Simulink software.The simulation and experimental results shew that the system ran stably and had good dynamic response performance,which to a certain extent alleviated the commutation torque pulsation existing in the traditional three-phase brushless DC motor.Adopting the improved linear back-EMF method combined with the linear back-EMF zerocrossing method to act on the low-speed and high-speed area of the motor respectively.Both methods can accurately obtain the commutation time,and switch smoothly.The speed calculation result response speed was accelerated,which improves the reliability of the closed-loop structure of the system.