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The universal field-oriented (UFO) controller is used to control the induction motor torque and airgap flux independently of each other. In this work, the direct UFO control is realized by sensing the airgap flux using center taps on two machine windings. Moreover, an adaptive control scheme that accomplishes a continuous and automatic tuning of the rotor time constant of the field-oriented controller whenever the drive operates in the direct field orientation mode is proposed. In addition, at low invertor frequencies, the UFO controller switches over to the indirect field orientation mode in which the rotor time constant is frozen to the last tuned value of the previous direct field orientation mode. At steady state and elevated speeds the induction motor servo drive has no detuning errors when operating under direct field orientation, while at low speeds the indirect field orientation mode exhibits minimal errors. The latter expands the use of the high-performance induction motor drive up to standstill. The proposed field-oriented controller can be realized at minimal cost in AC servomotor drives requiring motion control or accurate speed control.>
Doncker et al. (Wed,) studied this question.