Magnetic pole direction detection device

A magnetic pole direction detection device for detecting a magnetic pole direction of a rotor in a multiphase electric motor comprising the rotor which is rotated by a rotating magnetic field generated by a current flowing through multiphase coils wound around a winding portion provided on a stator, the magnetic pole direction detection device comprising:

• a detecting target magnet attached to a tip of a rotating shaft of the rotor;
• a magnetic detection unit that outputs a detection signal which changes according to a change in a magnetic field;
• a magnetic pole direction calculation unit that calculates a magnetic pole direction of the rotor before correction based on the detection signal output by the magnetic detection unit;
• a current detection unit that detects a current flowing through each of the multiphase coils;
• a rotating magnetic field vector calculation unit that calculates a vector of the rotating magnetic field based on magnitude of the current of each phase detected by the current detection unit;
• a direction correction amount calculation unit that calculates a direction correction amount based on a direction and magnitude of the rotating magnetic field calculated by the rotating magnetic field vector calculation unit;
• and
• a magnetic pole direction correction unit that corrects the magnetic pole direction before correction calculated by the magnetic pole direction calculation unit by using the direction correction amount calculated by the direction correction amount calculation unit.