Patent ID: 8120305

Claim:
A method for starting single phase induction motor, the method comprising: turning on a semiconductor switching device to flow a current in a start winding, in a single phase induction motor in which a run winding and the start winding are connected in parallel via the semiconductor switching device; detecting an induced voltage proportional to an angular velocity of a rotor from the start winding, when a current flows in the start winding; receiving the detected induced voltage to calculate a variation rate of the induced voltage proportional to an acceleration torque, and storing the calculated variation rate; comparing the stored variation rate of the induced voltage, and determining a time when the variation rate of the induced voltage is the maximum as a time when a start torque is the maximum, when the variation rate of the induced voltage increases and then decreases; and turning off the semiconductor switching device to complete start, when the variation rate of the induced voltage begins decreasing after the determination.