关键词: 无感无刷直流电机, 反电势, BEMF 信号, 过零检测, 自适应算法

Abstract: To address the issue of difficult back electromotive force ( BEMF) signal detection caused by weak lowspeed signals and significant high-speed delays in the BEMF zero-crossing detection method for brushless DC motors,this paper proposes a sensorless BEMF detection circuit and detection method for brushless DC motors. This design leverages the on or off characteristics of diodes to prevent the BEMF signal from being divided at low motor speeds, enabling the microcontroller to perform AD conversion and zero-crossing detection on the BEMF signal. Additionally, it eliminates the
filter circuit,allowing for accurate sampling even when the high-speed BEMF signal exhibits significant jitter. Furthermore, a speed-adaptive BEMF zero-crossing detection method was proposed to ensure precise BEMF signal detection across the full speed range of the motor. The proposed solution has been successfully applied to high-voltage and high-speed hair dryer products,where the motor speed can reach over 110,000 r / min. It enables accurate BEMF signal detection in both lowspeed and high-speed states, ensuring stable and reliable system operation. The proposed detection circuit and method effectively overcome the shortcomings of traditional schemes. It can suppress interference without the need for a filter circuit,providing a low-cost and high-performance solution for the full-speed range control of high-speed brushless motors with speeds exceeding 100,000 r / min.

Key words: sensorless brushless DC motor, back electromotive force, back electromotive force signal, zero-crossing detection,adaptive algorithm