Sensorless position optimal control strategy of Brushless DC motor

Brushless DC motor is a high efficiency energy saving motor, requires Hall sensors for commutation. But Hall sensor can't operate in any high temperature or high noise place, so need change to sensorless drive. The sensorless drive technology becomes more and more mature, in which the most widely used technique is the direct BEMF detection. Direct BEMF detection usually use hardware low pass filter or software detecting method to filter out the noise signal, but they all need to find suitable parameters for zero-drift problems which will occur in varying speed or load conditions. In this paper, analyzing unexcited phase freewheeling current technique is proposed to overcome these drawbacks. To achieve practically applicable, a simple arithmetic calculation is devised for analyzing the freewheeling current and thus complex operations are avoided. Experimental results show that the proposed method can accurately find the shifted position and the system stability is also assured.