Closed-loop compensation strategy of commutation error for sensorless brushless DC motors with nonideal asymmetric back-EMFs

This article focuses on the sensorless commutation strategy of brushless DC (BLDC) motor with three-phase nonideal asymmetric back-EMFs (NAEMFs). To improve the torque performance and reduce power consumption, this article addresses two key issues: pointing out the accurate commutation positions of the BLDC motor with NAEMFs and proposing a novel closed-loop commutation error compensation strategy to obtain the accurate commutation positions. First, the accurate commutation positions are proved from the relationship between electromagnetical torque curve and commutation error on polar coordinates. Then, the novel feedback network and sampling subsystem are utilized to sample the back-EMFs of floating phases before and after the commutation positions separately. The deviation of the sampled voltages is employed as the controlled variable. Based on the controlled variable, the parallel control loops are incorporated to correct commutation positions in real time. When the controlled variable converges to zero, the commutation error is compensated synchronously. The proposed closed-loop compensation strategy utilizes any two back-EMFs of the BLDC motor, which can compensate the commutation error from the hardware and software. Furthermore, the commutation error induced by the asymmetric back-EMFs can also be eliminated. At last, the experimental results presented in this article validate the effectiveness of the proposed strategy.