Synchronous motor control apparatus

A synchronous motor control apparatus that performs current vector control of a permanent-magnet synchronous motor based on a q-phase current command and a d-phase current command, comprising:

• a first candidate value calculating unit which, using the motor speed of said synchronous motor and a control apparatus current limit value and control apparatus voltage limit value preset in said control apparatus, calculates a first d-phase current limit candidate value and a first q-phase current limit candidate value, based on points of intersection at which a current limiting circle representing a current vector locus that said control apparatus current limit value describes on a d-q current coordinate plane intersects a voltage limiting ellipse representing a current vector locus that said control apparatus voltage limit value describes as a function of said motor speed;
• a second candidate value calculating unit which, using the motor speed of said synchronous motor and said control apparatus voltage limit value, calculates a second d-phase current limit candidate value and a second q-phase current limit candidate value, based on points of intersection at which a maximum torque/flux curve representing a current vector locus that maximizes torque for the same flux linkage on said d-q current coordinate plane intersects said voltage limiting ellipse representing the current vector locus that said control apparatus voltage limit value describes as a function of said motor speed;
• a q-phase current command unit which, when the absolute value of said first d-phase current limit candidate value is smaller than the absolute value of said second d-phase current limit candidate value, then sets said first q-phase current limit candidate value as a q-phase current limit value, but otherwise sets said second q-phase current limit candidate value as the q-phase current limit value and, when said q-phase current command created based on a torque command exceeds said q-phase current limit value, then limits said q-phase current command to said q-phase current limit value and outputs said limited q-phase current command;
• and
• a d-phase current command unit which, when the absolute value of said first d-phase current limit candidate value is smaller than the absolute value of said second d-phase current limit candidate value, then sets said first d-phase current limit candidate value as a d-phase current limit value, but otherwise sets said second d-phase current limit candidate value as the d-phase current limit value and, when said d-phase current command created based on said motor speed and said q-phase current command exceeds said d-phase current limit value, then limits said d-phase current command to said d-phase current limit value and outputs said limited d-phase current command.