Sensorless Control of Polyphase Induction Machines

The basics of transformations of polyphase systems into orthogonal systems are explained. Vector models of induction machines in orthogonal planes are analysed and multiscalar models for rotor flux and main flux together with stator current are presented. A speed observer based on an extended model of the induction machine for selected variables is applied in the control system for the induction machine. On the basis of the model developed for a three phase machine, a multiscalar model for a five phase machine is presented. The control system acts on the basis of the model for the first sequence of phases achieving speed control. The model for the second sequence of phases is used to synchronize the fluxes in orthogonal planes. Near trapezoidal flux distribution in the air gap is achieved independently of the machine load. All variables used in the control system are estimated using the speed observer for the first sequence and the Luenberger observer for the second sequence. The properties of the control systems are explained using examples of transients generated by simulations.