Computer control strategies for induction motor drives

The problem of utilizing advanced discrete control techniques for the realization of the control system of a drive using a frequency controlled induction motor as an actuator is complicated not only by motor nonlinearities and saturation of state variables but also by the constraints imposed by the online implementation of the selected control algorithm. To have satisfactory operation of the motor and to ensure a good matching of its mathematical model, it is necessary to ensure that motor flux and stator current never exceed properly assigned values. Two control strategies for computer control are formulated and their effects on the system transient performance are investigated with particular attention to the problems of online application. In the first strategy the stabilizing feedback control for the nonlinear motor model is obtained by using the second method of Lyapunov for discrete systems. The resulting control law is a linear function of the state variables with coefficients which are nonlinear functions of the value assumed by the slip angular frequency in the corresponding sampling interval. In the second strategy the control law is of the bang-bang type and is obtained by assuming that the bilinear control variable may assume only two values