A motor controller estimates an initial position of a magnetic pole of a rotor of a brushless DC motor in an inductive sensing scheme. The motor controller controls a drive circuit to apply an AC voltage to a stator winding at a first energization angle, and subsequently to apply an AC voltage to the stator winding at a second energization angle before a residual current flowing through the stator winding returns to zero. At each energization angle, the motor controller corrects a peak value of a current in the stator winding based on the residual current detected immediately before a voltage is applied to the stator winding or at a time when voltage application to the stator winding is started. Based on the corrected peak value, the control circuit estimates the initial position of the magnetic pole of the rotor.

The servo controller is provided with a command reception unit and a servo control computation unit. In a measurement mode, the command reception unit asynchronously receives with every command reception period a counter output by the control device with every command update period. The servo controller is further provided with an event detection unit configured to detect the occurrence of an event which entails variation in reception intervals of the counter in the measurement mode, a deviation calculation unit configured to calculate a deviation amount between respective clocks of the control device and the servo controller, based on an occurrence period of the event and the command reception period, in the measurement mode, and a reception period adjustment unit configured to adjust the command reception period based on the deviation amount in an operation mode.

A shift range control device switches a shift range by controlling a drive of a motor in which a rotor rotates by energizing a motor winding. An angle calculation unit calculates a motor angle based on a signal from a rotation angle sensor that detects a rotation position of the rotor. An energization control unit drives the rotor so that the motor angle becomes a target angle according to the target shift range, and stops the rotor at a position where the motor angle becomes the target angle, by controlling the energization of the motor winding. A zero point estimation unit estimates a speed 0 point, which is a timing at which a rotational speed of the vibrating rotor becomes 0 during the stop control for stopping the rotor. The energization control unit switches a current control at the estimated speed 0 point.

A method and apparatus for controlling commutation of a motor. A voltage is measured at each of a plurality of windings of a motor using an electric circuit. A controller computes an overall back electromotive force for the motor using the voltage measured at each winding in the plurality of windings. The controller generates a result having either a first value or a second value based on the overall back electromotive force. The controller adjusts the commutation phase and the commutation period of the motor using the result.