Motor control device controlling synchronous motor

A motor control device that generates a q-axis current command and a d-axis current command, and uses the commands to control a synchronous motor having saliency, the motor control device comprising:

• a calculating unit calculating a speed reference value that takes an initial value when a torque command is zero, and that decreases as the torque command increases;
• a determining unit determining a magnitude relation between a speed command and the speed reference value calculated for the torque command by the calculating unit;
• a q-axis-current commanding unit that
• generates, when the determining unit determines that the speed command is smaller than the speed reference value, the q-axis current command of commanding a q-axis current to flow to the synchronous motor, on the basis of
• the torque command, and
• an inverse number of a torque constant of the synchronous motor, and
• generates, when the determining unit determines that the speed command is equal to or larger than the speed reference value, the q-axis current command of commanding the q-axis current to flow to the synchronous motor, on the basis of
• a function of which an independent variable is the speed command,
• the torque command, and
• the inverse number of the torque constant of the synchronous motor;
• a d-axis-current commanding unit generating the d-axis current command of commanding a d-axis current to flow to the synchronous motor, on the basis of the q-axis current command generated by the q-axis-current commanding unit;
• and
• an inverter configured to supply power to the synchronous motor in accordance with the q-axis-current command and the d-axis-current command,
• wherein
• the speed reference value is ωn,
• the initial value of the speed reference value when the torque command is zero is ω0,
• a change ratio of the speed reference value is k,
• the torque command is TCMD, and
• the calculating unit calculates the speed reference value ωn on the basis of the equation:
• ωn=ω0−k×TCMD.