Position Sensorless Control Method of Two-three Conduction Brushless DC Motor Based on Line Back EMF

According to the mathematical model and the conduction mode of the brushless DC motor (BLDCM), a method to estimate the rotor position is presented, which is based on the conduction state of the corresponding power tube obtained by the rate of change of the non-commutative phase current combined with the zero-crossing of line back EMF. It is also applied to the sensorless control of the two-three conduction BLDCM. The brushless DC motor can run in no-load or load, low speed or high speed with this method, and the system uses the current inner loop and the speed outer loop to forma double closed-loop control, so that the motor runs more smoothly. The rotor position information of BLDCM under different conduction states is located. The simulation results are consistent with the theoretical analysis, which verifies the correctness and feasibility of the method.