Motor control device

1. A motor control device that controls an induction motor which drives a spindle of a machine tool, the motor control device comprising:

an operation control part that generates a torque command based on an operation command, and controls a rotational position and/or rotational speed of the spindle;

a current control part that generates an excitation current command to control secondary magnetic flux of the induction motor, and a torque current command to control torque of the induction motor based on the torque command, and performs vector control on the induction motor;

a change detection part that detects a change in operation command requiring increasing the secondary magnetic flux of the induction motor;

a magnetic flux amplification part that performs magnetic flux amplification to temporarily increase the excitation current command or a magnetic flux command for generating the excitation current command in the current control part, in a case of a change in the operation command being detected by the change detection part; and

a gain change part that changes gain of the operation control part when performing magnetic flux amplification by the magnetic flux amplification part,

wherein the gain change part decreases the gain of the operation control part, when performing magnetic flux amplification by the magnetic flux amplification part.

2. The motor control device according to claim 1 , wherein a time of magnetic flux amplification by the magnetic flux amplification par is determined based on a time constant related to a change in secondary magnetic flux of the induction motor.

3. The motor control device according to claim 1 , wherein the operation control part includes:

a position control part that controls rotational position of the spindle based on a position command; and

a speed control part that controls rotational speed of the spindle based on a speed command,

wherein a change in the operation command is a change in operation command from the speed command to the position command,

wherein the gain change part includes:

a position gain change part that changes a position gain of the position control part; and

a speed gain change part that changes a speed gain of the speed control part, and

changes at least one among the position gain and the speed gain.

4. The motor control device according to claim 1 , wherein the operation control part has a speed control part that controls the rotational speed of the spindle based on a speed command,

wherein the change in the operation command is an increase in the speed command, and

wherein the gain change part has a speed gain change part which changes the speed gain of the speed control part.