Sensorless control apparatus of synchronous motor

A rotational phase angle estimation method in a sensorless control apparatus which estimates a rotational phase angle of a rotor having electrical saliency and controls a synchronous motor by a PWM inverter, the method comprising:

• a step of setting a direction of magnetic flux of the rotor to be a d-axis and setting a direction perpendicular to the d-axis to be a q-axis, and finding a distribution of a high-frequency current in a dq-axis coordinate system which rotates in sync with rotation of the rotor;
• setting an angle to the d-axis with reference to an axis in a direction of a U-phase coil of the synchronous motor to be a rotational phase angle, setting an estimated angle of the rotational phase angle to be an estimated phase angle, setting an axis in a direction of the estimated phase angle to be a γ-axis, setting an axis perpendicular to the γ-axis to be a δ-axis, and setting an angle between the γ-axis and the d-axis to be an estimation error;
• a step of examining in advance an index proportional to the estimation error on the basis of a distribution of the high-frequency current, and acquiring a first index at 0° of the estimation error;
• a step of calculating, at each time of switching of the inverter, a high-frequency component in a γδ-axis rotational coordinate system of a current which flows in the synchronous motor;
• a step of calculating a second index, which is proportional to the estimation error, from the high-frequency component of the current;
• and
• a step of executing an estimation arithmetic operation of the rotational phase angle by using the first index and the second index.