A design approach for feedback-feedforward control systems

In this paper, a general design approach is proposed to derive the feedforward control law in feedback-feedforward control systems. This design approach is based on the concept of 'Control Equilibrium Point'. In this design approach, the feedback controller generates the transient control command and the feedforward controller generates the steady state one. Using the proposed feedforward controller, for a wide class of process plants, the stability of system is guaranteed if the feedback controller is a gain with an arbitrarily high value. That is, the only limit for the feedback (transient) control command is the actuator's practical limit; however, in this approach, a mathematical model of the system is needed to derive the feedforward control law. In order to remove this drawback, in case of having significant uncertainties, an artificial neural network, independent of mathematical model of the system, is designed to play the role of feedforward (steady state) control law.