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

Accurate commutation is a key factor to ensure the ideal electrical torque performance and high motor efficiency for position sensorless brushless dc motor. In order to eliminate the commutation error, this article presents a closed-loop correction method using the hardware-based floating phase back electromotive force (EMF) integration. First, the relationship between the floating phase back-EMF integral and commutation error is analyzed. Then, based on the relationship, a closed-loop controller fed by the integral is introduced to generate the angle to correct the commutation point. But the inaccurate integral calculation resulted from insufficient sampled point at high motor speed will seriously reduce the correction accuracy. For this reason, a novel hardware configuration is designed to transform the back-EMF integral into a filtered analog voltage. In this way, the integral can be obtained precisely from sampling the analog voltage with low sampling rate. Thus, a precise commutation is achieved by the closed-loop control, especially in the high speed range. Finally, experimental results on a magnetically suspended turbo molecular pump show the effectiveness of the proposed method.