Motor control apparatus and method of controlling motor

Abstract

When a required torque increases under the condition of high-speed rotation, the conventional technique can not detect an electrical angle or control a synchronous motor in a sensor-less manner. The direction that passes through the rotating axis of the motor and makes a magnetic flux run through a permanent magnet is defined as the d-axis, whereas the direction that is electrically perpendicular to the d-axis in the rotational plane of the motor is defined as the q-axis. The technique of the present invention applies voltages to the d-axis and the q-axis based on an estimated electrical angle and solves voltage equations with the observed electric currents. The technique then calculates a correction amount of the electrical angle according to errors of the arithmetic operations and controls the motor. The arithmetic operations are carried out by varying the inductance according to the required torque of the motor. One concrete procedure determines the inductance corresponding to a specific motor driving state by interpolation of the table that stores the inductances corresponding to a variety of motor driving states. Another concrete procedure substitutes the driving states at the respective time points into the function that represents the relationship between the inductance and the driving state, so as to determine the inductance.