Fractional order PID controller design for autonomous navigation of agricultural machinery

Influence of time delay on stability of the agricultural vehicle steering system was discussed in this paper. Under the control of a PD controller tuned by virtue of ITAE performance index, maximum time delay was given. In this case, the agricultural vehicle steering system was marginally stable. Then, in order to attenuate the influence of time delay on system stability, parameters of the PD controller with marginal time delay were tuned based on ITAE performance index. To further improve control performance and robustness of the system, a fractional order PD controller was designed based on flat phase method. Due to the drawback of the flat phase method, the fractional order PD controller designed based on flat phase method does not work well. Therefore, an improved method was proposed to search the optimal value of the controller parameters globally. The evident difference between the method proposed in this note and the flat phase method lies in the solution procedure of the fractional order parameter. Simulation results showed that the optimal fractional order PD controller designed by the method proposed in this paper worked more effectively than the optimal integer order PD controller. Moreover, the controller parameters tuned by the improved method can make the system obtain better performance than those tuned by the flat phase method.