Vector control method for controlling a rotor speed of an induction motor

Abstract

A vector control method is provided for controlling a rotor speed of an induction motor by an inverter which provides an AC current of varying frequency to the induction motor, and a vector controller which provides control voltage Vu, Vv, Vw, in response to an excitation current command i.sub.1d*. The excitation current command is indicative of an excitation current being fed to the induction motor, a desired rotation speed command .omega..sub.r*, and a primary frequency .omega., for controlling the inverter to vary the rotor speed. The method includes the steps of detecting a primary current being fed to the induction motor, analyzing the detected primary current to obtain an excitation current i.sub.1d and a detected torque current i.sub.1q, multiplying a torque value represented by the detected torque current i.sub.1q by a predetermined motor constant K.sub.m to obtain a slip frequency .omega..sub.s, and adding the obtained slip frequency .omega..sub.s to the rotation speed command .omega..sub.r* to determine the primary frequency .omega. (.omega.=.omega..sub.r* +.omega..sub.s), calculating a deviation between the delay torque current i.sub.1q, and the detected torque current i.sub.1q and supplying the deviation to a proportional plus integral controller, the proportional plus integral controller producing as an output an updated delayed torque current i.sub.1q, as the torque value for determining the primary frequency .omega..