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The principle of the universal field-oriented (UFO) controller operating in the airgap flux reference frame is applied to an induction motor with center-tapped stator windings, allowing the airgap flux to be directly sensed without additional calculations which depend on machine parameters. The resulting direct universal field-oriented (DUFO) controller is not affected by steady-state detuning and can operate in flux weakening up to the theoretical speed limit of the drive. Furthermore, due to its high degree of generality, the UFO controller is fully compatible with direct and indirect field orientation. As a consequence, it is feasible to switch over to indirect universal field-oriented (IUFO) control at low speed. The latter expands the use of the high performance induction motor drive up to standstill.>
Doncker et al. (Mon,) studied this question.