H∞ design of rotor flux-oriented current-controlled induction motor drives: speed control, noise attenuation and stability robustness

This study deals with the design of H_∞ controllers for speed control of rotor flux-oriented current-controlled induction motors. The mixed sensitivity problem (robust stability and performance) is initially revisited, and is shown, based on practical experiments, that when the rotor time constant is the uncertain parameter, it is necessary to deploy conflicting weighting functions, therefore invaliding its application in the design of current-fed induction motors. Two other H_∞ problems are addressed: (i) a one-block problem for speed control with tracking and transient performance objectives; and (ii) a two-block problem for speed control with tracking/transient performance and noise attenuation objectives. An important part of H_∞ design is the model of the system to be controlled. In this study, the system composed of the inverter, estimator and induction motor will be modelled as a first-order system, and experiments for the identification of the gain and the time constant are proposed. It is also suggested how to properly correct an initial estimation of the rotor time constant in order to make the actual plant (inverter-induction motor) behave as a first-order linear system. The model accuracy and the efficiency of the H_∞ controllers are validated by experiments carried out in a real system.