Research On Improved Start-up Methods Of Sensorless Brushless DC Motor

Some start-up methods at present have some shortcomings including inaccurate location of rotor,inaccuracy of commutation time,and the unstable running of rotor when starting with heavy load etc.Which leads to the failure of BLDCM starting or the phenomenon of shaking and reversing.As a result,it is significant to design a start-up method that has greater reliability,lower cost and higher value.First of all,this paper describes the development and application of the BLDCM and further introduces sensor-less control strategies based on different methods.Furthermore,this paper introduces current research of start-up methods at home and abroad.Beside these,the working principles of sensor-less / sensor BLDCM are analyzed and then its mathematical model is built up.Secondly,in this paper,an improved start-up method has been proposed which aims to deal with difficulties such as incorrect location of rotor and inaccurate commutation time related to traditional three-stage start-up method.To start with,the combination of long and short-width-time pulse voltage vectors are used to supply electricity to windings.In this way,an accurate position of the rotor is located in the electrical angle range of °± 15.During the stage of acceleration,the closed-loop acceleration of the rotor is achieved by considering the difference between the current value and the current threshold as commutation condition.In this way,the assessment of commutation time in accelerating period is simplified.When the speed of motor increases to a certain figure,the average value method can be used to switch the status of motors smoothly,therefore ensuring the smooth switch between internal synchronization and external synchronization.In the step of internal synchronization,proper Pulse-Width Modulation way is applied and zero-crossing signal of Back-EMF can be obtained by using the gap of line voltage.Then the paper based on the Matlab/Simulink model for simulation of BLDCM improved three stage starting method is eatablished,then the simulation verification has been validated.The results prove the rationality of the improved three stage starting method.In the last phrase,throughout the design of the software and hardware of the system,then an experimental platform of control system of BLDCM is built where STM32 is used as main control chip.It helps to test the waveform which was shown during the starting-up process and the results of these tests are analyzed.It is concluded that the improved three-stage start-up method described in this paper can ensure closed-loop status of the motor from being still to stable operating state.Throughout the process,the motor works steadily,without losing step or starting failure,which proves the feasibility and effectiveness of the proposed starting method in this paper.