A torque control strategy of brushless DC motor with low resolution encoder

Abstract

This paper describes a torque controller with an observer for a brushless DC (BLDC) motor. The torque control strategy needs accurate position and speed information, but the BLDC motor has a low resolution internal encoder to determine switching position. Therefore, the speed and the intermediate position are obtained from a stable estimator which would be derived from nonlinear modelling. The torque control algorithm is derived for a motor of arbitrary back-EMF waveform considering the freewheeling current. It would be possible to have accurate speed control for wide range of speed without torque ripple. The proposed system is easily implemented and computation time is reduced by new motor modelling. In the experiment, the controller is realized by a DSP TMS320C31. The effectiveness of the controller is shown by simulation and experiment.<>