A novel research on detecting position of brushless DC motors

A novel phase detection method based on fundamental wave of the virtual neutral point was presented for the sensorless control system of Brushless DC(BLDC) motors. Rotor space-position information can be directly obtained by detecting the voltage difference between the open phase terminal and the virtual neutral point. In two half bridge modulation methods of H_PWM_L_ON and L_PWM_H_ON, both during PWM_ON and PWM_OFF periods, the comparing objects need not to be changed. The theoretical analysis proves the correctness of the method, and the control results are given under different duty cycles in the experiments, which confirms the validity of the proposed method.