Research On Rotor Position Detection For High-Speed Permanent Brushless DC Machines

Due to their smaller size and lower mass than normal machines, high speed machines are widely used in environmental control systems, household appliances and machining process, etc. Brushless DC machines(BLDCM) are extremely suitable for high speed operation because of their high power density, simple control algorithm and low position precision required. Thus, high speed BLDCMs have been widely researching in the whole world. Rotor position signal should be implemented during BLDCM operation and higher characteristics are required for that of high speed BLDCMs.Rotor position sensors are the mostly used devices for rotor position detection. For a high speed levitating BLDCM, this paper proposed rotor position detection algorithms using single and double eddy current sensors respectively. The former one reduced the amount of sensors; while the latter compensated the detection error caused by the bias of tested metal disk. Finally, the algorithm was implemented on a 50000 rpm high speed BLDCM, which verified the validity of the algorithm.To further simplify the machine structure and improve the performance of rotor detection, “sensorless” technique is becoming research highlight in the field of high speed BLDCMs. As the most popular sensorless algorithm for BLDCM, conventional back-EMF zero crossing point(ZCP) detection method is not able to operate in heavy load. This paper proposed a novel ZCP detection method based on the comparison between current slope and threshold. By using this method, the ZCP can still be detected at heavy load even the diode conduction angle exceeds 30°. The operation range of ZCP detection can be widened if the proposed method combined with conventional ZCP detection. The simulation verified the validity of the algorithm. The influence of shapes of phase back-EMF for detection precision was also discussed.Digital controller cannot calculate current slope and detect rotor position as precise as requirement when BLDCMs operate at high speed. Hardware circuits are implemented in comparison module for current slope and threshold in this paper. By cooperating with software system, the rotor position can be detected in either light or heavy load. Finally, the experiment was implemented and the results verified the validity of the new algorithm.