Modeling, simulation and implementation of a sensorless commutation method for brushless DC motors without phase shifter

This paper presents a simple method for detection of commutation instants of the extensively used low power brushless DC motors. In the proposed method the commutation signals are obtained without any phase shift circuit which is required in the conventional sensorless control methods. So the overall cost is decreased and the sensorless control is easy to be implemented. In the proposed method, instead of detecting the zero crossing points of the unexcited motor back electromotive force, which has inherently 30° phase shift with respect to the ideal commutation point, the commutation signals are extracted directly from the motor terminal voltages differences. Simulation and experimental results are presented to justify the effectiveness of the proposed method. These results show that this method, despite of its simplicity, has acceptable stability against switching noises.