BLDC Motor Zero-Speed Startup Position Sensorless FOC Control

This paper presents the BLDC motor BEMF observer-based position sensorless control method. Online parameter identification of the stator inductance and resistance is implemented to improve the observer accuracy. Before BLDC motor startup, the rotor is aligned to a known rotor field position using the stator phase current feedback control. Afterwards, the BLDC speed ramps up to the minimum target speed in speed open loop control. When the BEMF voltage is high enough, speed close loop control is enabled using the speed and position signals obtained from the observer. To minimize the controller state transition, the stator current vector FOC control is applied in both speed open loop control and speed close loop control. The observer is continuously initialized using the speed and position signals from the speed open loop control. The proposed control algorithm is implemented in PLECS RT box and verified in a BLDC motor 3-phase inverter hardware setup. The measurement results show that the speed and position of the observer converge quickly to the speed and position measured from the incremental encoder in the speed close loop control. The proposed BLDC sensorless control scheme can achieve smooth speed acceleration with minimal stator current and the stable steady state FOC control with small position error in wide speed operation range.