Wherein the three-phase winding is connected with the neutral wire. One end of the three-phase winding of the motor stator is connected to the phase line of the three-phase power supply, which is also the input point of the three-phase winding power supply of the motor. The contact point of the other end of the three-phase winding of the motor connected to the zero line is the center point, so the neutral point of the stator is welded at the joint of the three-phase winding and the zero line.