Research On Technologies Of Sensorless Control For Brushless DC Motor In Full Speed Range

The brushless DC motor(BLDC)has the advantages of high power-density,high reliability,relatively simple structure,stable speed and convenient speed regulation.So,BLDC has been widely used in many fields,such as household appliances,industrial control,aerospace and so on.To drive brushless DC motors,the position of the rotor is usually induced by hall sensors,which is used as the feedback of the closed-loop control.However,the use of hall sensors not only increases the cost of the system,but also reduces the reliability of the system.To overcome these adverse effects brought by mechanical sensors,technologies of sensorless control of brushless dc motors in full speed range is explored in this paper.To improve the accuracy of the initial position determination and avoid the mechanical damage caused by the reverse rotation of the motor,an initial position identification method based on the magnetic-saturated saliency-effect will be studied in this paper.The current response of the voltage vector will be simulated and analyzed,and the method to shorten the minimum time interval of voltage pulse injection will be proposed.The influence of switching mode on saturation degree will be analyzed,and the optimal switching mode will be proposed.The margin required for initial position identification will be analyzed from the perspective of ripple and noise,and the influence of the margin on starting will be analyzed.Finally,the correctness of the conclusion and the feasibility of the initial position identification strategy will be verified by experiments.To realize the sensorless closed-loop starting of brushless DC motors,a low-speed operation strategy based on the magnetic-saturated saliency-effect will be proposed.To solve the problem that the speed of the algorithm is low under load,the starting algorithm will be optimized for detecting voltage.Then,to make full use of the discrete rotor position information,a sensorless low-speed operation strategy of brushless DC motors based on vector tracking observer will be studied.A vector tracking observer will be designed by analyzing the harmonic content of rotor signals,and the influence of parameter selection on the stability of the vector tracking observer will be analyzed.Finally,the proposed low-speed operation strategy will be verified by simulation and experiment.To realize sensorless operation in high speed field of brushless DC motors,this paper will study the zero crossing point of back electromotive force detection strategy based on active phase shift circuit to realize controllable phase shift.Then,by analyzing the armature reaction,the correction of the phase switching signal error will be carried out,and the weak magnetic control in high speed field will be realized.This paper will analyze and suppress the high harmonics of switching signal during low speed operation,reduce the error of phase switching signal,and realize the switch of sensorless control strategy from starting to medium and high speed field.The validity of the control strategy in the medium and high speed field and the switching strategy will be verified by experiments.