Research On Starting Control Method Of Sensorless BLDCM

With the change of time, the DC motor has been replaced by AC motor because the brushes and commutator limit the development of the DC motor. The AC motor contains induction motor and synchronous motor, the Synchronous motor also can be divided into brushless DC motor and permanent magnet synchronous motor according to the different back EMF, the former’s back EMF is trapezoidal wave and the latter is sine wave. Because of the BLDCM with simple structure and light weight has high efficiency and reliable operation, It has been developing in some important areas widely, such as aerospace, medical equipment, household appliances, electric vehicles and robotics. As present the scholars study the focus of Optimal control algorithm and improve performance on BLDCM.The three output signals of hall sensor guide motor commutation in the control system of position sensors. However, due to its application condition is limited, sensorless control method is applied widely. In the sensorless control system, detecting the accurate rotor position is the key to realize the right commutation and the normal operation of BLDCM. It can be detected the rotor position through the method of BEMF crossing zero, this article uses the method of detecting the voltage of the phase to get the BEMF, When the back EMF is crossing zero and then is delayed 30 electrical angle to get commutation points. Currently the sensorless control method based on EMF is constantly improved, but the problem of motor starting has been the difficult and hot topic in the field of BLDCM. In this paper, a synchronous open-loop starting device is constructed on the basis of three-start methods mainly by 120° of the trigger module, the clock timer and switch device. The simulation results show that the starting method can achieve motor starting smoothly. The main work content of the topic as follows:Firstly, analyzing body structure, working principle, the control method with sensor and sensorless of BLDCM and comparing their advantages and disadvantages. The working process of BLDCM between two-two and three-three conduction mode is given. On the basis of analyzing the BLDCM mathematical model, the algorithm of rotor position detection is improved, and the relevant mathematical models are converted into the form of the state equation to facilitate the modeling and simulation of starting control system of the sensorless BLDCM.Secondly, the starting methods of sensorless control based on back EMF are analyzed. It introduces several common starting method and studies their advantages and disadvantages. It focuses on the three stages of the three-step starting method, the traditional three-step starting method is improved according to the relevant theoretical analysis. The acceleration phase is implemented by shortening the commutation time. If the position signal is detected, it will be detected more times. When the sufficiently stable BEMF zero crossing signal is detected, the switching process will be implemented by setting the threshold in switching module. It can be switched from open-loop control to closed-loop control if the time is consistent with the threshold. Finally, according to the relevant mathematical models and state equations of BLDCM, the whole starting control system of the sensorless control is modeled and simulated in the MATLAB. The results show that the parameters waveform of BLDCM accord with theoretical analysis, and the starting control method based on back EMF is feasible and effective, so the BLDCM with sensorless control method can start reliably.Finally, the design of hardware circuit of the sensorless control system is given on experimental platform with DSP TMS320F28335, while its program is designed in CCS3.3 software development environment. Through the combination of hardware circuit and software programming, the parameters will be calculated when the whole control system is going hardware simulation. At last, the real-time changes of the parameters waveforms is shown by the oscilloscope and the dynamic analysis of the parameters is displayed to verify the starting method based on EMF to realize the reliable starting of BLDCM on DSP experiment platform.