Motor drive device and electric compressor

An electric compressor comprising:

• a multi-phase synchronous motor including a rotor having a permanent magnet and a stator having coils of different phases;
• and
• a motor drive device that drives the multi-phase synchronous motor, the motor drive device including an inverter that supplies current to the coils and a control unit that controls the inverter, wherein
• the control unit executes:
• an initial angular position calculation processing including detecting a d-axis and a q-axis of the rotor as an initial angular position of the rotor based on a current flowing in response to a voltage pulse applied to the coils of the stator;
• a rotating processing including rotating the d-axis and the q-axis of the rotor by a predetermined angle θa in a direction opposite to rotation of the rotor;
• an acceleration processing including accelerating the rotation of the rotor by rotating the rotated d-axis and the rotated q-axis in the rotating direction of the rotor and flowing through the stator the torque component current determined based on a d-axis and a q-axis;
• and
• a sensorless control processing including controlling the rotation of the rotor based on an angular position and a speed of the rotor estimated based on the voltage applied to or the current flowing through the coils after an angular velocity of the rotor has reached a predetermined speed by executing the acceleration processing, wherein
• the predetermined angle θa is determined based on an initial target of a d-axis and an initial target of a q-axis of the sensorless control processing.