Controller for permanent magnet synchronous motor, control method, and image forming apparatus

An image forming apparatus for forming an image on paper, the apparatus comprising:

• a permanent magnet synchronous motor having a rotor using a permanent magnet, the rotor rotating by a rotating magnetic field caused by a current flowing through an armature;
• a carrier roller of which rotation is driven by the permanent magnet synchronous motor to feed the paper;
• a controller configured to control the permanent magnet synchronous motor;
• and
• a speed command portion configured to input a speed command to the controller;
• wherein
• the controller includes
• a drive portion configured to feed a current to the armature to drive the rotor,
• a speed estimating portion configured to estimate a rotational speed of the rotor based on the current flowing through the armature,
• a magnetic pole position estimating portion configured to estimate a position of magnetic poles of the rotor based on an estimated speed that is the rotational speed estimated,
• a control unit configured to control, based on an estimated angle that is an estimated value of the position of magnetic poles outputted by the magnetic pole position estimating portion, the drive portion to cause the rotating magnetic field rotating at a target speed indicated in the speed command inputted,
• a step-out presuming portion configured to presume, based on the target speed and the estimated speed, whether or not a step-out occurs, and
• a correction portion configured to correct the estimated angle when the step-out presuming portion presumes that a step-out occurs, and
• when the correction portion corrects the estimated angle, the control unit controls, based on a post-correction estimated angle that is the estimated angle corrected by the correction portion, the drive portion to cause the rotating magnetic field depending on the target speed.

A method for controlling a permanent magnet synchronous motor having a rotor using a permanent magnet, the rotor rotating by a rotating magnetic field caused by a current flowing through an armature, the method comprising:

• presuming, based on a target speed and an estimated speed that is an estimated value of a rotational speed of the rotor, whether or not a step-out occurs;
• correcting, when it is presumed that a step-out occurs, an estimated angle that is an estimated value of a position of magnetic poles of the rotor;
• and
• controlling, based on a post-correction estimated angle that is the estimated angle after the correction, a current flowing through the armature to cause the rotating magnetic field rotating at the target speed.