Patent ID: 8248007

Claim:
A control apparatus for an AC motor including a rotor having a permanent magnet and a stator having a stator coil, the control apparatus capable of controlling an inverter in a pulse width modulation scheme to feed a coil current to the stator coil, the apparatus comprising: a position detecting mechanism configured to detect a rotational position of the rotor; a current detecting mechanism configured to detect the coil current; a pattern switching mechanism configured to switch a control pattern for the AC motor to a first pattern when a required output of the AC motor is smaller than a predetermined value and to a second pattern when the required output is larger than the predetermined value; a first pattern calculating mechanism configured to calculate a control signal using a parameter for the first pattern on the basis of the detected rotational position and coil current in the first pattern; a second pattern calculating mechanism configured to calculate a control signal using a parameter for the second pattern on the basis of the detected rotational position and coil current in the second pattern; an offset calculating mechanism configured to calculate a difference, as an offset amount, between a control signal obtained in an old pattern immediately before switching and a control signal obtained in a new pattern immediately after switching when the pattern switching mechanism switches a pattern, and to reflect the offset amount on the control signal of the new pattern; and a control output mechanism configured to calculate a final control output signal on the basis of the control signals which are obtained by the first pattern calculating mechanism, the second pattern calculating mechanism, and the offset calculating mechanism, and to transmit the final control output signal to the inverter via a pulse width modulation circuit.