Patent ID: 8269444

Claim:
A system for controlling a sensorless motor, wherein the sensorless motor comprises at least three motor coils connected to a neutral point and at least three driving transistor groups respectively connected to the motor coils, and the system comprises: a motor driver, used to drive the sensorless motor to enable a voltage of each of the motor coils to enter a blanking period when the value of the voltage of each of the motor coils is changed from negative to positive or from positive to negative, wherein the motor driver comprises: a control signal generator used to generate a pulse-width modulation signal for each of the driving transistor groups selected, so as to enable the sensorless motor to work in accordance with the pulse-width modulation signal, wherein the pulse-width modulation signal comprises a plurality of pulses having spaces there between; and a zero-crossing detector, used to detect a zero-crossing point for the sensorless motor at the time when the voltage of one of the motor coils enters the blanking period wherein the zero-crossing detector comprises: a sensor, used to detect an internal parasitic effect of inductor and capacitor (internal L-C effect) of the sensorless motor; and a detector, used to start detecting the zero-crossing point in a period when the voltage of one of the motor coils enters the blanking period, and each of the two driving transistor groups connected to the other two motor coils receives the pulse-width modulation signal, but after the internal parasitic effect of inductor and capacitor ends.