Research On The Startup Control Method Of Sensorless Brushless DC Motor

Brushless DC Motor(BLDCM)is widely used in various areas for its stable running state and good dynamic performance.As an important part of BLDCM,position sensor is used to detect the position of rotor.However,the position sensor increases the volume of motor and failure rate,which partly limits the application of BLDCM.With the development of science and technology and the progress of society,sensorless control method is coming and getting more and more attention from researchers.At present,the electromotive force(EMF)method is the most frequently used method of sensorless control technology,but it still has difficulty in detecting rotor position during the startup process.For this reason,this paper starts a research on the sensorless startup control method.Firstly,this paper studies the motor’s structure and establishs its mathematical model.After comparing various inverter bridge circuit structures,the full-bridge star connection structure is selected,and the working principle of BLDCM is illustrated by taking the three-phase six-state pairwise on-off control mode as an example,and the steady-state operation characteristics of BLDCM are also analyzed.Secondly,this paper studies the traditional "three-stage" startup method,and points out its problems: the rotor will reverse and shake in pre-location period,lose step in open-loop acceleration period and virtual neutral point needs to be constructed for the counter electromotive force detection method based on terminal voltage which made the detection accuracy low.In conclusion,this paper puts forward a new "three-stage" start control method: in pre-location stage,this paper uses a position detection method based on inductance method,which can improve the position accuracy to 60°electrical angle and the rotor will not reverse or shake;in the external synchronous acceleration stage,multiple groups of detection voltage vectors and acceleration voltage vectors are applied to the stator windings,and the rotor’s closed loop is accelerated to run smoothly without losing step.In the phase of self synchronous stage,the zero-crossing detection method of electromotive force method based on line voltage difference is adopted.It is notnecessary for it to construct a virtual neutral point,and the modulation method of H_PWM-L-PWM is selected to eliminate the interference of non-conducting phase relay current.This paper also builds a simulation model of the motor control system on the Matlab/Simulink platform.The simulation results prove that the startup control method is effective and feasible.Finally,this paper has designed a whole BLDCM control system and takes a experiment to verify the startup control method.In terms of system hardware,DSP28335 chip is selected as the main controller,and modules such as voltage conversion circuit,power inverter circuit,power drive circuit and anti-electromotive force zero-crossing detection circuit are designed.In terms of system software,CCS6.0 is used as the integrated development platform to write the motor start control program.The experimental results show that the "three-stage" startup control method proposed in this paper can make the motor start and run smoothly.