中文摘要：

无位置传感器无刷直流电机在高速段时反电势信号过大，容易造成检测电路无法正常T作甚至损坏，而在较低速段时，反电势信号又难以有效检测。针对反电势过零检测在极端速段的问题，提出了一种反电势过零检测新方法。在三相采样等效电路上分别并联一组三极管控制的电阻分压开关电路，参考电机转速线性调节控制信号占空比，以此控制三极管通断，从而调节电阻分压开关电路阻值，可以避免高速时反电势幅值高于检测电路供电电压的危险。同时，根据控制信号占空比切换低速区与高速区反电势采样方式，能有效改善在低速区时反电势过零检测效果。实验结果表明，提出的反电势过零检测新方法能保证电机工作于更宽的转速范围内。

英文摘要：

The（ back electromotive force BEMF） signal of brushless DC motor without position sensor is too large and beyond the detecting circuit capacity at high speed ,which causes the detecting circuit not to work, even damage the detecting circuit; however, at low speed the signal is too low and is hardly detected effectively. Aiming at the BEMF zero-crossing detection problem in extreme speed region,a novel BEMF zero-crossing detecting method is proposed in this paper. A resistance voltage dividing circuit controlled by a group of transistors is in parallel with the equivalent three-phase sample circuit. The reference rotor speed linearly adjusts the duty cycle of the transistor control signal, which switches the transistors to adjust the resistance dividing ratio of the resistance voltage divider. Therefore, the danger that the BEMF amplitude is greater than the power supply of the detecting circuit can be avoided. Moreover, switching the BEMF sampling manner between high and low speed regions according to the duty cycle of the control signal can effectively improve the BEMF zero-crossing detection effect in low speed region. Experiment result indicates that the proposed novel BEMF zero-crossing detecting method can ensure brushless DC motor operate steadily in a wider speed region.