Speed-torque characteristics of brushless DC motor based on average back EMF during conduction area

Speed-torque characteristics of brushless DC motor with ideal trapezoidal back electromotive force (EMF) is obtained under the analysis of the commutation and conduction region with two switches conducted and six states driven mode. The back EMF coefficient is calculated from the average value of back EMF during conduction area to speed. And torque coefficient is calculated from the ratio of average torque and average current. Then the speed-torque characteristics expression of brushless DC motor with unideal back EMF is gotten instead by the new back EMF coefficient and torque coefficient. Simulation and experimental results show this method can precisely meet the real speed-torque characteristics.