PURPOSE: To eliminate useless current consumption, to a raise the motor speed quickly and to enable high speed rotation by a method wherein splitted coil segments in Y-connection are not short-circuited when a motor is started but coil segments corresponding to respective phases in the Y-connection are short- circuited according to the rotation of the motor after start thereof thereby eliminating current limiter.

CONSTITUTION: Each coil in Y-connection is splitted into two coil segments. One coil segments LA1-LC1 for respective phases are provided with short circuits TA1-TC1. The short circuits are switched through switches SW1-SW3. Coil segments LA1-LC1 and the short circuits TA1-TC1 are switched by a switching signal S at switching terminal 2S. When a rotor is started, the coil segments LA1-LC1 are connected to input terminals 2A-2C by means of the switching signal S. When the rotation of the rotor reaches to a predetermined level, the short circuits TA1-TC1 are connected to the input terminals 2A-2C by means of the switching signal S. By such arrangement, motor speed can be raised to a high level at the start thereof and high speed rotation can be realized after start of the motor.