Parameter sensitivity of indirect universal field-oriented controllers

The universal field-oriented (UFO) controller was developed to decouple flux and torque in an arbitrary synchronous flux reference frame, realizing a high degree of generality, which makes the UFO controller compatible with all existing field-oriented controllers, including indirect and direct field orientation. This compatibility is useful to realize drives over a wide speed range using both direct UFO (DUFO) control and indirect UFO (IUFO). In this paper, generalized steady-state torque and flux expressions are derived analytically for detuned operation of the IUFO controller in an arbitrary reference frame. For a given machine (determined by its leakage factor), the expressions can be graphically represented (using only three parameters) as a function of the input command ratios. With these graphs, the steady-state performance of all indirect field-oriented controllers (controlling rotor flux, airgap flux, or stator flux) can be readily evaluated