Vector control device for electric motor, electric motor, vehicle drive system, and vector control method for electric motor

A vector control device for an electric motor that controls an electric power converter that converts DC power to AC power and supplies the AC power to the electric motor, the device comprising:

• a vector control unit that computes an output voltage to be output from the electric power converter according to vector control based on a torque command and a flux command that are input, and generates a PWM signal for controlling the electric power converter based on the output voltage;
• a first flux-command generation unit that generates a flux command for an asynchronous PWM mode and, when a modulation factor becomes equal to or higher than a first threshold, executes control of increasing a rotating speed by decreasing a field flux in the electric motor;
• and
• a second flux-command generation unit that generates a flux command for a synchronous PWM mode, wherein
• when an output frequency of the electric power converter is lower than a predetermined value, which is higher than the output frequency when the modulation factor becomes the first threshold, a flux command generated by the first flux-command generation unit is input to the vector control unit, and when the modulation factor is equal to or higher than the first threshold and the output frequency of the electric power converter is equal to or higher than the predetermined value, a flux command generated by the second flux-command generation unit is input to the vector control unit.