Design of Fuzzy self-tuning PID controller for pitch control system of aircraft autopilot

Abstract

A variety of control systems have been proposed for aircraft autopilot systems. Traditional approaches such as proportional controller and conventional PID (CPID) controller are widely used. PID controller has a good static performance especially for linear and time-invariant systems, but a weak dynamic performance and discouraging function on nonlinear, time-varying, and uncertain systems. Fuzzy control theory can improve dynamic response in various conditions of system performance. This paper designs fuzzy self-tuning PID (FSPID) controller to improve disadvantages of conventional PID in aircraft autopilots. We apply proposed controller to pitch angle of aircraft then the abilities of proposed controller will be compared to the conventional PID and proportional controller. Inner feedback loop acts as oscillation damper in traditional schemes, but here is removed to compare the capabilities of Fuzzy self-tuning PID, conventional PID, and proportional controller. Based on the simulations, both of Conventional and Fuzzy self-tuning PID controllers can properly damp oscillations in lack of the inner feedback loop, but proportional controller cannot do. Then short-period approximation is assumed to assess the function of FSPID and CPID controllers in confront with abrupt and continuous disturbances, in addition to inappropriate tuning of parameters. Simulation results of short-period approximation show a better anti-disturbance function for Fuzzy self-tuning PID compare to the conventional type. Fuzzy self-tuning PID can tune the PID parameters for achieving the optimal response in view of speed, overshoot, and steady-state error in conditions of inappropriate tuning of PID parameters, based on the results of simulation in short-period approximation, the proposed controller can adaptively improve the system response by on-line setting of PID parameters.