Patent ID: 7375482

Claim:
A driving device of a motor comprising: a main inverter circuit which applies a pseudo three-phase alternating voltage to a motor to drive the motor; current detecting means for detecting a current which flows through the motor; and control means for executing a sensor-less vector control based on an output of this current detecting means, the driving device further comprising voltage detecting means for detecting an induced electromotive voltage of the motor, wherein the control means starts the motor by rectangular wave control, detects a magnetic pole position of a rotor based on the induced electromotive voltage of one remaining phase of the motor detected by the voltage detecting means, controls the main inverter circuit based on the detected magnetic pole position, and accelerates the motor by the rectangular wave control, and in a case where a predetermined shift revolution speed is reached, the control means shifts to vector control by the sensor-less in which the magnetic pole position detected during the rectangular wave control is used as an initial value.