Sensorless Control For BLDCM Using An Adaptive Sliding Mode Observer

The brushless DC motor(BLDCM) has been broadly applied because of its reliability, simple structure and convenient maintenance as the AC motors, and its high efficiency, good performance of speed regulation as DC motors. Traditional BLDCM can get the exact rotor position signal to realize commutation and velocity modulation through mechanical position sensor. But the mechanical position sensor affects the reliability, cost and size of the whole system. BLDCM can not be used in some cases with the position sensor. So sensorless control for BLDCM becomes a hot academic research in recent years.Sliding mode variable structure control is characterized with disturbance adaptive capacity. It can be used in motor speed control, position control. The sliding mode observer is an observer with good performance. It can evaluate the state of uncertain object and real-time variables of the inner and outer disturbance and get the good performance of BLDCM control.In this paper, the basic principles and control methods of sensorless brushless DC motors(BLDCM)are introduced, and compared with the common rotor position detection methods. An adaptive sliding mode speed and position observer is proposed for the control of sensorless BLDCM. The sliding surface is defined based on the errors between actual and estimated currents based on the math model of BLDCM. Equivalent control and model reference adaptive arithmetic are used to obtain the rotor position and speed. Using the estimated speed value as the feedback in closed-loop control, the real speed response is good. A sensorless control system for BLDCM based on the sliding mode observer is implemented. Lyapunov function is introduced to prove the convergence of the observed parameters. Simulation result shows that the proposed method can correctly estimate the speed and position of the rotor. The observer is not influenced by both load disturbance and measurement noise which shows good robustnessAt last, a BLDCM control system is designed based on DSP TMS320F2812, which is produced by TI corp. Because of superiority and abundant external devices of TM320LF2812 control chip, it is used to design the hardware and software of the control system. And functions like BLDCM starting, current& voltage sampling, rotor position detecting, speed regulating are realized.