Control apparatus for brushless DC motor

Claim 1

A control apparatus for a brushless DC motor, comprising: a) a converter for converting AC electric power to DC electric power; b) at least one inverter being connected between the converter and an armature winding of the brushless DC motor for generating a drive current from the DC electric power generated by the converter and for supplying the drive current to the armature winding of the brushless DC motor; c) torque command value calculating means for calculating a torque command value to drive the brushless DC motor in response to a speed command; d) torque current calculating means for calculating a torque current on the basis of the calculated torque command value, the torque current being driven through the armature winding of the brushless DC motor and being in phase with an electrical angle of the brushless DC motor; e) phase advance current calculating means for calculating a phase advance current to be driven through the motor armature winding, the phase advance current having a phase advance of 90° with respect to the motor electrical angle; and f) current controlling means for calculating a target current from the calculated torque current and the calculated phase advance current, and for controlling an actual current through the motor armature winding in response to the calculated target current; wherein the phase advance current calculating means comprises: e1) upper limit calculating means for calculating an upper limit of the phase advance current on the basis of at least one of the speed command and a rotational speed of the brushless DC motor; e2) means for detecting the actual current through the motor armature winding which is controlled by the current controlling means; e3) follow-up condition determining means for determining whether or not the detected actual current through the motor armature winding follows the target current; and e4) phase advance current updating means for, when the follow-up condition determining means determines that the detected actual current through the motor armature winding follows the target current, decreasing the phase advance current within a range having a lower limit equal to zero, and for, when the follow-up condition determining means determines that the detected actual current through the motor armature winding does not follow the target current, increasing the phase advance current within a range having an upper limit equal to the upper limit calculated by the upper limit calculating means.