An Improved Method of Brushless DC Motors with Torque Constant Estimation for Home Appliances

The use of brushless dc motors is widely increasing in home appliances, military applications, and various other industries due to their high power-to-volume ratio, simple structure, high efficiency, and low cost .Comparing to the permanent-magnet synchronous machine, the BLDCM has higher power/weight and higher torque/current ratio. For proper commutation of the phase currents, the rotor position must be obtained with position devices. However, there are some constraints to installing position sensors to BLDCMs. These constraints include severe driving environments, cost burden, drive volume, and reliability. Many sensors less control algorithms have The back EMF can be easily obtained from the voltage equation of the BLDCM. The estimated back EMF decreases simultaneously with the estimated torque constant at the commutation point. By using this phenomenon, the commutation of the phase currents can be done automatically at the drop point of the estimated torque constant. Unlike conventional back-EMF-based methods, the proposed method provides highly accurate sensor less operation even under low speeds because only the drop of the torque constant is used for position detection and current commutation. Therefore, the position accuracy is not affected by the electric parameter errors of the BLDCM. Also, this algorithm does not require an additional hardware circuit for position detection.