An internal power angle control strategy for high-speed sensorless brushless DC motors

High-speed Brushless DC Motors (BLDCMs) usually adopt a sensorless control strategy and operate in three-phase six-state drive mode. However, the sampling errors of the rotor position and the driving method increase the Internal Power Angle (IPA), resulting in a decrease in the efficiency of the system. Conventional IPA reduction strategies are either sensitive to motor parameters, or ignore diode freewheeling during the commutation process, or require additional current sensors. In this paper, a new strategy to reduce the IPA is proposed. Firstly, a Zero-Crossing Point (ZCP) detection method for the back-EMF without filter is proposed to reduce the sampling errors of the rotor position. Secondly, the relationship between the non-energized terminal voltage and the ZCP of the corresponding back-EMF is analyzed. The non-energized terminal voltage that has completed the diode freewheeling is divided into two triangles by half of the bus voltage. When the IPA is suppressed, the areas of the two triangles are equal. Thirdly, an advanced angle for reducing the IPA is obtained through a PI regulator which can eliminate the deviation between the two areas. Finally, both a simulation model and an experimental circuit are built to verify the proposed control strategy.