Design of Position Detection Circuit for Sensorless Brushless DC Motor Drives

In this paper, a back electromotive-force(EMF) detection circuit for position sensorless brushless DC motor (BLDCM) drive systems is presented, in which the second-order active Butterworth low-pass filter is used. The detecting circuit is composed of a voltage divider and an active low-pass filter. First, the voltage dividing circuit is designed, and two design principles should be followed. Second, the selections of the structure, the order and the parameters of the active filter are investigated in detail. Last, the theoretical analysis, simulation and experiment are all done with the proposed position detecting circuit. The investigation results show that designed circuit can operate well in the sensorless BLDCM drive.