REFERENCE TRAJECTORY GENERATION FOR SINGLE-LOOP CONTROLLERS

A controller that is well tuned with respect to load disturbances may exhibit an undesirable response when large set-point changes are made. The reason for the undesirable response, which typically contains lar ge overshoot, is often control signal saturation. If the reference inp ut is instead changed smoothly by generation of a reference trajectory , the saturation of the control signal can be avoided, and the respons e can be improved. This paper presents a method for reference trajecto ry generation for single-loop controllers. The purpose is to generate a smooth reference trajectory which both gives an improved response co mpared to a step change in the reference input, and at the same time t ransfers the process to the desired set point in minimum time. The met hod uses an available feedback controller, e.g. a PID controller, whic h is tuned for satisfactory performance with respect to load disturban ces and small changes in the reference input. The method is designed t o handle set-point changes in real time, and time delays in the contro lled process. The method has been implemented, and is evaluated by lab oratory experiments. The experimental results show that the generated reference trajectory can give significant improvement compared to step changes in the reference input. Copyright (C) 1997 Elsevier Science L td.