PID auto-tuning by a composed structure

The authors propose to reduce the excessive overshoot produced by the tuning of Ziegler-Nichols method and to obtain better rise times of the tuning Åstrom method by using a structure called composed structure and by weighting the three actions of the PID controller by three factors. These last factors F_p, F_i, F_d are determined as functions of the system parameters so as to guarantee a specified overshoot in closed-loop. The usual parameters (K,T_i,T_d) of the PID are fixed by the tuning of Ziegler-Nichols method, which provides a good rejection of the load disturbance. The auto-tuning of this method can be easily obtained by using the relay method for the determination of Ziegler-Nichols frequency model parameters