Motor magnetic-pole-position estimating apparatus

A motor magnetic-pole-position estimating apparatus comprising:

• a command voltage output device configured to output a command voltage to apply current to a motor;
• a current detector configured to detect an actual current applied to the motor and to output a detection result;
• a model-current calculator configured to calculate a model current corresponding to a voltage equation for a predetermined model of the motor based on the command voltage and the actual current, and configured to output a calculation result;
• a current-difference calculator configured to calculate a current difference between the model current and the actual current;
• first and second magnetic-pole-position-difference calculators configured to perform different operations, each of the first and second magnetic-pole-position-difference calculators being configured to calculate a magnetic-pole-position difference between an actual magnetic-pole position of the motor and an estimated or designated magnetic-pole position based on the current difference depending on whether or not a rotation speed of the motor is lower than a predetermined value;
• and
• a magnetic-pole-position calculation device configured to calculate the magnetic-pole position of the motor based on the magnetic-pole-position difference calculated by the first or second magnetic-pole-position-difference calculator.