The Universal Field Oriented (UFO) controller operating in the airgap flux reference frame is applied to a current regulated PWM induction motor drive. Inside the induction motor, voltages induced in center tapped windings are used to sense directly the airgap flux position and amplitude. Field orientation is realized without any additional calculations requiring machine parameters. In steady state, the resulting Direct Universal Field Oriented (DUFO) controller is not affected by detuning errors and can operate during flux weakening up to the theoretical limits of the drive. The DUFO drive has an excellent dynamic performance even under strongly detuned conditions.
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 Orientation (IUFO) at low speed. The latter expands the use of the high performance induction motor drive down to standstill.