Research On Sensorless Control For Brushless DC Motor

In the system of the brushless DC motor (BLDCM), the electrical commutation mode is adoptedinstead of the mechanical mode used in the traditional DC motors. The electrical mode requiresposition signals to commutate, so there should be some position sensors installed inside the motor.However, the presence of hall element position sensor does cause a lot of shortcomings, such asincreasing the size of the motor, reducing the reliability and so on. Therefore, the sensorless techniqueof the BLDCM, as the focus for the researchers at home and abroad, is of important researchsignificance and application value. To begine with traditional back electromotive force (back-EMF)method, this paper exactly researches on the aspects of rotor position detecting, speed estimation andstarting of the sesorless BLDCM. The main contects are listed below.Firstly, the paper introduces the operating principle and mathematical model of the BLDCM,reviews the basic principle of the back-EMF method, and analyzes the influence of the low-pass filter.On the basis, the paper presents a novel sesorless technique called coordinate transformation. Throughrotating the stator coordinate system for a special angle, the technique processes the three-phaseterminal voltage in the new frame, which compensates the filter phase shift and offers thecommutation signals to the control system. Meanwhile, the motor speed can be calculated using theorthogonal coordinate system. The estimation algorithm improves the real-time performance andeliminates the limitation of traditional method which relies on the commutating point. The simulationis done to verify the correctness of the sensorless technique.During starting, the method based on coordinate transformation cannot get the rotor position, soother initial rotor positon detection is required. The article does the research on the principle of theinductance method, analyzes the influence of freewheeling, and presents the countermeasures.According to the analysis above, the simulation model is built in the environment ofMATLAB/Simulink, and the simulation is finished to verify the validity of the starting method.In the end, the paper designs the software and hardware platform with the control core ofTMS320F2812. And the experiment is completed with the inductance method and the sensorlesstechnique of coordinate transformation. The experiment results show the validity of the academicanalysis.