Adaptive decoupling circuit for universal field oriented controller operating in the airgap flux reference frame

The paper discusses modification of the decoupling circuit of a universal field oriented (UFO) controller which operates with orientation along the airgap flux, that are necessary if the decoupler is to provide self-adaptive feature with respect to main flux saturation in the induction machine. It is shown that such an adaptive decoupling circuit can easily be derived. It asks for three nonlinear functional dependencies and provides full adaptation to instantaneous main flux saturation level in the machine. Verification is provided by simulation of a current-fed indirect vector controlled induction machine operating in the torque mode. The circuit enables very good matching between commanded and actual magnetic flux and torque values for any degree of the flux command variation. Possible simplifications of the full adaptive decoupling circuit are also discussed and assessed by simulation. In particular, three different simplified structures that ask for a reduced number of nonlinear functions, are discussed. It is shown that even the simplest structure, where just one nonlinearity is retained, provides superior responses compared to the constant parameter decoupling circuit