Fractional-Order Control of Hydraulically Powered Actuators: Controller Design and Experimental Validation

This paper presents a model-free design procedure for the position control of hydraulic actuators. A fractional-order PID (FOPID) controller is designed by employing the Oustaloup recursive method. The controller parameters are tuned experimentally based on the iterative feedback tuning (IFT) technique. The IFT optimizes an objective function using the experimental data taken from an instrumented valve-controlled hydraulic actuator test rig. The objective function, to be minimized, includes both tracking and robust stability criteria. The efficacy of the proposed controller is examined by comparing the experimental results with those from a quantitative feedback theory (QFT) based controller. Although the QFT controller gives rise to good tracking responses, the comparisons show that the FOPID controller results in better settling time in tracking the desired response than the QFT controller. Moreover, it is much less sensitive to the effect of the hunting phenomenon, originating from the dry friction, than the QFT controller. The robustness of the FOPID controller against system uncertainties including the external load, the inertia, and friction is also demonstrated.