Patent ID: 7723944

Claim:
A vector control device that controls driving of an induction motor via an inverter, comprising: a secondary magnetic flux command computing module that computes a secondary magnetic flux command for the induction motor by taking a maximum voltage that the inverter can generate into account on a basis of a torque command from an external source, a DC voltage to be input into the inverter, and an inverter angular frequency, which is an angular frequency of an AC voltage to be output from the inverter; a q-axis/d-axis current command generator that generates a q-axis current command and a d-axis current command on a d-q axes rotating coordinate system in reference to a secondary magnetic flux of the induction motor on a basis of the torque command and the secondary magnetic flux command; an output voltage computing module that computes an output voltage that the inverter is to output on a basis of the q-axis current command, the d-axis current command, and a circuit constant of the induction motor; and a voltage command/PWM signal generator for controlling the inverter to output the output voltage; wherein the secondary magnetic flux command computing module has: an output voltage maximum value computation portion configured to compute the maximum voltage that the inverter can generate on a basis of the DC voltage applied to the inverter; a maximum voltage secondary magnetic flux command computation portion configured to compute a maximum voltage secondary magnetic flux command, which is a secondary magnetic flux command to bring the maximum voltage that the inverter can generate and the output voltage into coincidence in magnitude; and a lower-order preference portion configured to choose and output either the maximum voltage secondary magnetic flux command or a pre-set rated secondary magnetic flux command, whichever is the smaller, as the secondary magnetic flux command.