Patent ID: 7649329

Claim:
A method for controlling a motor, comprising: providing a motor, wherein the motor comprises at least three phase stator coils, each stator coil comprises a first terminal and a second terminal and the first terminals of the stator coils are coupled to a common node; providing a first power voltage; providing at least three upper-bridge switches, wherein each upper-bridge switch is respectively coupled between one of the second terminals of the above-mentioned three phase stator coils and the first power voltage; providing at least three lower-bridge switches, wherein each lower-bridge switch is respectively coupled between one of the second terminals of the above-mentioned three phase stator coils and the first end of an impedance element, wherein the second end of the impedance element is coupled to a second power voltage and the second power voltage is less than the first power voltage; among the stator coils, when there is no current flowing through a first stator coil, the upper-bridge switch coupled by the second terminal of the second stator coil is turned on and the lower-bridge switch coupled by the second terminal of the third stator coil is turned on: detecting the voltage at the second terminal of the first stator coil and defining the detected voltage as a first specific voltage; detecting the voltage drop across both ends of the impedance element and defining the detected voltage as a second specific voltage; judging whether a zero-crossing occurs by using the first power voltage, the first specific voltage and the second specific voltage; among the stator coils, when there is no current flowing through the first stator coil, the upper-bridge switch coupled by the second terminal of the second stator coil is turned off and the lower-bridge switch coupled by the second terminal of the third stator coil is turned on; and performing a proportion operation on the first specific voltage to judge whether a second zero-crossing occurs.