A Sensorless Control Method for Low-voltage and High-current BLDC Based on Back-EMF

For the position sensorless drive system of low-voltage high-current brushless DC (BLDC) motor for oil pump, a three-stage start-up control strategy to improve the voltage at the back electromotive force terminal voltage is studied. The back-EMF detection circuit is built with sampling resistor and comparator. The logical relationship between the comparator output signal and the power device switch is determined. Pre-positioning is achieved by energizing any two phases in the inverter and controlling the winding current. The BLDC is steadily accelerated by increasing the commutation signal frequency of the driver. When the motor accelerates to the predetermined speed, it can accurately detect the back-EMF zero-crossing signal and switch to the self-synchronization operation state. The proposed method is verified by simulation and experiment, and the results show that the speed and current closed-loop sensorless PI control strategy has good performance.