OPTIMAL AND ROBUST DIGITAL CURRENT CONTROLLER SYNTHESIS FOR VECTOR-CONTROLLED INDUCTION-MOTOR DRIVE SYSTEMS

The vector-controlled induction-motor drive is a multi-input multi-out put system. By using modern control techniques, all feedback loops can be closed simultaneously, in addition to obtaining optimal gains for the controllers. A systematic approach to the design of the digital cu rrent controllers is proposed. A vector-controlled induction-motor-dri ve system is usually viewed as a full-state feedback problem, where th e non-measurable states are estimated using suitable reduced-order obs ervers. Here, the induction-motor-drive system is viewed as a linear q uadratic (LQ) tracker problem with output feedback, as this approach u ses only the measurable states of the system and provides flexibility in choosing the control structure. The current controllers are designe d for the torque dynamics of the induction motor. The controller shoul d also be so designed that the whole drive system is stable for a clas s of induction motors, i.e. the whole drive system should be stable in the face of uncertainties in the parameters of the induction motor. T herefore, it becomes essential to build stability robustness into the controller design. Here, the proposed systematic approach determines t he optimal controller gains for a given performance specification unde r the constraint that the whole system has stability robustness for un certainties in the specified parameters of the induction motor. The co ncepts are illustrated by simulation.