Research On The Sensorless Control Mechanism For The Brushless DC Motor

The Brushless DC Motor (BLDCM) with permanent magnet, compared with other types of motors, is used widely due to the advantages of high reliability, high efficiency and good performance, etc, growing with the development of microcomputers, new power electronic devices, control theories and low cost rare earth permanent magnet.In general, the control methods of BLDCM are divided into two categories of the sensor control and the sensorless control. The former has simple drive devices and wide speed adjusting range, but with complex connection and worse reliability. And the latter can be used widely without equipping rotor position sensors with the more advantages than the former. In this paper, a position detecting method based on the simplified RC passive band-pass filter is proposed, which make the structure of system easily to realize.Firstly, the structure and operation principle of the BLDCM are introduced and the basic equations and the mathematical model are founded based on fundamental electromagnetic laws. Secondly, according to intensive analysis of the zero-crossing detection of Back EMF, a detecting method with band-bass filter and its simplified configuration are proposed. By analyzing the reason resulting in the detecting error, the corresponding correction method and the new commutation approach are presented to improve the performance of the BLDCM. On the basis of analyzing the typical open-loop method called"3-stage startup method"in detail, the synchronous operation condition from the open-loop to the closed-loop is presented for BLDCM. Lastly, the control system for BLDCM without rotor position sensors is designed and implemented based on detecting Back EMF zero-crossings. The validity and effectiveness of the proposed control method is verified through the relative simulations and experiments.