Method of estimating magnetic pole position in motor and apparatus of controlling the motor based on the estimated position

A method of estimating a magnetic pole position of a rotor in a synchronous motor, comprising the steps of:

• providing a motor model expression for estimating the magnetic pole position from an instructed voltage determined from an instructed rotational speed of the rotor and applied to the motor, a current generated from the instructed voltage and a parameter;
• and
• calculating an estimated magnetic pole position in the motor from the instructed voltage, the generated current and the parameter according to the motor model expression, wherein the step of calculating the estimated magnetic pole position comprises:
• calculating an actual power factor angle from a difference in phase between the instructed voltage and the generated current;
• calculating a normal power factor angle from the instructed rotational speed and a torque of the rotor, the normal power factor angle being defined as a power factor angle obtained when the estimated magnetic pole position matches with a true magnetic pole position;
• correcting a value of the parameter such that the actual power factor angle substantially coincides with the normal power factor angle;
• and
• calculating an estimated magnetic pole position from the instructed voltage, the generated current and the parameter having the corrected value.

An apparatus of controlling a synchronous motor having salient poles, comprising:

• an estimating unit which estimates a magnetic pole position in the motor from an instructed voltage applied to the motor, a current generated from the instructed voltage and a parameter;
• and
• a control unit which controls the motor according to the estimated magnetic pole position,
• wherein the estimating unit has:
• an applying unit which applies, to the motor, a phase matching voltage which has a frequency higher than that of the instructed voltage and has a phase matching with the estimated magnetic pole position previously obtained;
• a detecting unit which detects a phase matching current generated from the phase matching voltage from the motor;
• a correcting unit which corrects a value of the parameter such that a difference in phase between the phase matching voltage and the phase matching current substantially becomes zero;
• and
• a calculating unit which calculates an estimated magnetic pole position from the instructed voltage, the detected current and the parameter having the corrected value, and
• the control unit controls the motor according to the estimated magnetic pole position calculated in the calculating unit.

An apparatus of controlling a synchronous motor, comprising:

• an estimating unit which estimates a magnetic pole position of a rotor in the motor from an instructed voltage determined from an instructed rotational speed of the rotor and applied to the motor, a current generated from the instructed voltage and a parameter;
• and
• a control unit which controls the motor according to the estimated magnetic pole position,
• wherein the estimating unit has:
• a first calculator which calculates an actual power factor angle from a difference in phase between the instructed voltage and the generated current;
• a second calculator which calculates a normal power factor angle from the instructed rotational speed and a torque of the rotor, the normal power factor angle being defined as a power factor angle obtained when the estimated magnetic pole position matches with a true magnetic pole position;
• a correcting unit which corrects a value of the parameter such that the actual power factor angle substantially coincides with the normal power factor angle;
• and
• a third calculator which calculates an estimated magnetic pole position from the instructed voltage, the generated current and the parameter having the corrected value.