Induction machine control in presence of magnetic saturation speed regulation with optimized flux reference

The problem of induction machine speed control is considered. Most previous works considered the machine magnetic characteristic to be linear and the flux reference to be constant. Specifically, the constant flux reference is chosen in the elbow zone of the magnetic characteristic. Doing so, the machine operation mode is not optimal in presence of small loads. In the present work, a new speed control strategy is developed that accounts for the saturation feature of the magnetic characteristic making possible the generation of optimal flux references. Flux optimality guarantees satisfactory machine performances (efficiency, power factor, maximal torque,...). The obtained flux reference turns out to be a function of the machine state variables. Then, a speed controller is designed using the backstepping technique. The originality of the presented control design is twofold: (i) the magnetic characteristic nonlinearity makes the machine model highly nonlinear, (ii) the flux reference signal is state-dependent. The performances of the developed control strategy are formally analysed and their supremacy with respect to the standard control solution is illustrated through a simulation study.