The Research And Design Of Sensorless Control System For Brushless DC Motor

BLDCM is widely applied in household appliance,electrocar and industry for its simple structure,superior speed control and reliable operation.Meanwhile,the BLDCM sensorless controls and omits the position sensor,which avoid,the adverse effect by the installation of position sensor and embraces wide attention.This paper takes the electro-tricycle BLDCM as the study object,and makes analysis and research of the BLDCM sensorless control system.Fi rstly,the paper conducts the research on the structure and work theory of BLDCM,and describe the stator voltage,torque and rotor equation of motion by mathematical description,then establish the mathematical model of BLDCM.At the same time,the analysis of BLDCM mechanical properties and speed regulation characteristics lays theory foundation for the research on BLDCM sensorless control system.Contrasting and analyzing the detection method of current rotor flux position of the BLDCM,and aiming at the particularity of uncertain electrocar load to research the method to improve the detection precision of rotor position.As for the phase shift caused by zero crossing under different zero crossing,the paper obtains the fitting curve of compensatory angle by theory analysis and experiment testification,then effectively improve the detection precision of rotor position by the confirmation of practical compensatory angle based on the curve and work situation.Pointing at the start trouble of sensorless control system under still or low speed sitation,this paper analysizes the application condition and defect as well as merit of the traditional start method of sensorless control system,then designs the combined starting method,which improves the precision of rotor position loctating.The use of frequency and voltage raise of software dedicates to the synchronous acceleration,then realizes the improvement of motor load start ability without rely on hardware circuit.Meanwhile,in the starting process,the current is detected in real time,and the corresponding frequency rising and boosting action is carried out,so as to avoid the damage of the system due to the high current for a long time.The detection of zero crossing signal occurs during the start process,when it is obtained continuous K times the system will change into synchronous operation automatically.The analysis of the reason of the appearance of commutation torque ripple aims to solve the problem when in operation,the busbar voltage is changed based on the features of buck-boost of Cuk convertor then restrain the commutation torque ripple to establish the system simulation model to testify the effectiveness of this method.At last,the establish of sensorless control system simulation model based on Lab VIEW testifies the practicability of system,then sets up the performance test platform of electro tricycle control system and lays solid foundation for system debug and monitor.Furthermore,sets up the electro tricycle control system platform by sensorless control system hardware circuit and software function to conduct testing experiment.It turns out the practicabilty of combined starting method and the zero crossing phase angle compensation method.