A Sensorless Drive System of BLDC Motor

To drive the PMBLDC motor, for the conventional 120-degree commutation, the winding without phase current in each conduction interval can be considered as a sensor for back-emf detection. However, in the case of 180-degree commutation, the back-emf detection cannot be realized because all the three phases conduct current in each interval and no back-emf signals are available on stator terminals, which is the reason why the 180-degree sensorless commutation has not been considered so far. In this thesis, a novel 180-degree sensorless system for a PMBLDC motor is proposed. The position and speed information are estimated based on the back-emf signals, which are estimated from the simple sensing of the stator terminal voltage and phase current signals. Each phase of the conventional 120-degree rotates only 120 degrees with current to generate torque and waits for next excitation in the other 60 degrees without torque generated. However, each phase of the proposed 180-degree sensorless system conducts current for the entire electrical period, which produces more torque. The comparison between the 120-degree and the 180-degree sensorless system is also investigated.

Boyang Hu received the B.Eng and M.Phil degrees in 2008 and 2010, respectively, from the School of Electrical and Information Engineering, The University of Sydney, where he also started his Ph.D research from 2010. His research interests include the AC motor drive, power electronics and renewable energy (wind and solar) for smart grid.