Sensorless Control Of Bldcm Based On Double Sliding Mode Variable-structure

Brushless DC motors (BLDCM) are widely used in every walk of life in view of its excellent qualities such as high operating efficiency, no spark during commutating, and good mechanical properties. Generally, traditional control strategy can be achieved by getting the exact commutation signal with the mechanical position sensors. However, the mechanical position sensors may restrict BLDCM's application in some areas, such as aerospace, automobile. These may hinder the development of BLDCM.To solve the above problems, a new method for sensorless control of BLDCM is designed on the basis of the characteristics of sliding-mode variable-structure control (VSC). Sliding-mode variable-structure control is the most effective control method for nonlinear or uncertain system. It takes advantage of discontinuous control showing system's invariance; it is characterized with disturbance adaptive capacity.Firstly, the principles of sensorless control methods of BLDCM are introduced, and the common rotor position detection techniques are researched. Secondly, on the basis of the analysis of the motor model and sliding-mode variable-structure principle, a sliding mode observer which can estimate electromotive force (EMF) is proposed. The sliding surface is defined based on the errors between actual and estimated currents, and then the EMF, the rotor speed and the rotor position are obtained according to the relationship between them. Using the estimated speed as the closed loop speed feedback and considering the effect of electrical parameter perturbations on the drive performance, the sliding-mode controller is constructed. The simulation illustrates that the sliding mode observer can accurately estimate the rotor speed and the rotor position. And comparing with the PI controller, the sliding-mode variable-structure controller can make the BLDCM control system with less overshoot, quick velocity response, and good robustness. And this control strategy can inhibit the torque ripple.Finally, the hardware and software of the BLDCM control system are designed based on the MSP430F149 MCU. And the voltage sampling, the speed regulating, the position detecting functions are realized.