Commutation Error Closed-Loop Correction Method for Sensorless BLDC Motor Using Hardware-Based Floating Phase Back-EMF Integration

Abstract

Low pass filter (LPF) and comparator are usually adopted to obtain the commutation points in sensorless brushless DC (BLDC) motor. However, the LPF phase shift along with hardware and software delay results in the commutation error reducing the motor efficiency. In order to eliminate the commutation error, this paper presents a closed-loop correction method using the floating phase back-EMF integral. First, the relationship between the back-EMF integral and commutation error is analyzed. Then, a PI controller fed by the integral is introduced for correction. Because the inaccurate integral calculation resulting from insufficient sampling rate will seriously reduce the correction accuracy, a novel hardware configuration is proposed to convert the integral into a filtered analog voltage. By this way, the integral can be obtained precisely from sampling the analog voltage directly, which ensures a precise commutation correction. Finally, experiments on a magnetically suspended turbo molecular pump (TMP) show the effectiveness.