12-step Position Sensorless Control of High-Speed Brushless DC Motor using Enhanced Back-EMF in Discontinuous Conduction Mode

This paper proposes a 12-step position sensorless control method using the enhanced back-EMF detected in the discontinuous conduction mode for highspeed brushless DC (BLDC) motors. Along with analysis of the PWM inverter's operation by discontinuous conduction under low-speed or light-load conditions, the 3-phase terminal voltage and neutral-point voltage are analyzed mathematically and schematically. Based on the results, the terminal voltages for all cases for each operation modes in each of the 3-phase switching modes are completely summarized. A 12-step position detection method based on the enhanced back-EMF generated by discontinuous freewheeling current is proposed. The analysis and proposed method are verified through experimental results.