Position Sensorless Control Of Brushless DC Motor Based On Sliding Mode Observer

Brushless DC motor（BLDCM）is widely used in many fields, as it is simple instructure, easy to control.The detection of the rotor position is the most important in thecontrol of BLDCM.Sensorless control of BLDCM not only reduces the hardware cost, butalso simplifies the motor design, which can expand the application range of BLDCMgreatly.There are many methods of Sensoless Control of BLDCM, in this paper, a slidingmode observer was designed based on line back-EMF, after the analysis of thephase-to-phase back-EMF zero crossing method.The paper analyzes the strueture and work principle of BLDCM and deduces amathematic model，then introduces the basic structure and engineering design method ofthe double-loop speed control system for BLDCM. A simplified phase-to-phaseback-EMF calculation method is proposed, as the zero-crossing of phase-to-phaseback-EMF is the commutation point of BLDCM. The method can only get the accurateposition signal in the steady state, and when the speed varies the method can not track thephase-to-phase back-EMF effectly. To solve the problem, a sliding-mode observer isproposed to estimate the phase-to-phase back-EMF using the Reaching Law,and thecontrol effect of three common Reaching Laws are analyzed and compared.The slidingmode observer is simulated in Matlab/Simulink,the result shows that the sliding modeobserver can estimate the phase-to-phase back-EMF accurately in the steady-state anddynamic and get the correct position signal,and has good stability of the load change andgood robustness of resistance change.