Based On The Third Harmonic Detection Method Of Sensorless Brushless Dc Motor Control And Design

The Brushless DC motor (BLDCM) sensorless control technology based on the third harmonic component is studied in the dissertation, and a BLDCM sensorless control system based on DSP56F807 of freescale is designed, then the availability and feasibility of the project is proved through experiments.In the dissertation, the study status of the field is introduced firstly, then, the operation principle and control methods of the BLDCM without rotor position sensor are discussed. Based on analyzing and synthesizing the existing research results, a feasible project is presented: (1) the position detection of rotor adopting the third harmonic method, that is, by detecting the zero-crossing point of the third harmonic at virtual neutral point of electromotor stator, the changing information of the phase of the stator will be obtained. The band-pass filter is employed to get the third harmonic. The negative pole voltage of DC-link is used as the reference voltage for method. (2) The startup method, a key matter for BLDCM drives open-loop method called"3-stage startup method" is analyzed in detail, the synchronous approach from the open-loop to the closed-loop is presented. (3) A commutation approach without phase shift limit is proposed based on study on commutation approaches for BLDCM drives without rotor position sensors. The performance of the BLDCM can be improved with the commutation approach and the whole system will be more stable.Lastly, the software and hardware project of the BLDCM senseless control system are proposed. The hardware of the control system includes a power supply for drive, a switching power, a third harmonic zero-crossing detecting circuit, an inverter, isolating circuits, and protecting circuits. Using the Codewarrior as the Development Platform and adopting the assembly as the Development language, the experiments are carried out with investigated methods and matters on drive. By analyzing the filtering effect of the filter at the low-speed and high-speed of motor, the simulating results of the position detecting circuit are given. At last, based on the results of the actual debug, a conclusion is proposed that the experimental results improved the availability of project.