A PASSIVITY-BASED METHOD FOR INDUCTION-MOTOR CONTROL

The control of an induction motor is a difficult problem, since the dy namics of the induction motor are nonlinear, the rotor electrical stat e variables (i.e., rotor fluxes or currents) are usually unavailable f or measurement, and the motor parameters can vary significantly from t heir nominal values, The main purpose of this paper Is to develop a co ntrol algorithm that forces the induction motor to track time-varying speed, position, and flux trajectories without knowledge of the rotor electrical state variables. To achieve this, a passivity-based method is developed. The key point with this method is the identification of terms, known as workless forces, which appear in the dynamic equations of the induction motor but do not have any effect on the energy balan ce equation of the induction motor, These terms do not influence the s tability properties of the induction motor and, hence, there is no nee d to cancel them with feedback control. This leads to a simpler contro l structure and enhances the robustness of the control system, Experim ental results show that the passivity-based method provides close trac king of time-varying speed, position, and flux trajectories without kn owledge of the rotor electrical state variables.