Sensorless high-speed BLDC machine using hardware-RFO

High-speed permanent magnet (PM) brushless dc (BLDC) motor often needs a continuous rotor position signal for dynamic phase-advancing control, whist such kind of position signal cannot be directly obtained from the conventional Hall effect sensors or via the traditional back-EMF-based sensorless control strategy. Furthermore, during high-speed operation, the inverter free-wheeling diodes may conduct for more than 30 elec-deg, obscuring the back-EMF zero- crossings. Hence, the traditional back-EMF-based sensorless control strategy becomes unworkable. To overcome these problems, a new sensorless control method is proposed in this paper. It uses full hardware to observe the flux vector which is excited by rotor magnets. Thus, it can provide the rotor position which is the same as the phase angle of the observed flux vector. The proposed sensorless control method is validated with a 2Kw, 85000rpm PM BLDC motor system.