Fourth Order Sliding Mode Control of Position for Electro-Hydraulic Actuator

A control method for the accurate tracking of position of an Electro-Hydraulic actuation system is presented in this paper. The Electro-Hydraulic state space model of the system is derived from the fundamental equations of an actuator. A second order demodulator is used to obtain the output position feedback of the system. Because of the insensitivity to parameter variations and uncertainties, the sliding mode algorithm is recognized as an effective technology for the design of robust controllers. Hence, a sliding mode technique is adopted to control the position of the system to follow the desired command signal. Since, the relative degree of the system with respect to position is four, a universal control law which is developed explicitly for SISO systems with higher relative degrees has been used known as the 4 - Sliding Mode Control. The control system developed is proposed to minimize the tracking error as the position feedback follows the reference command. The effectiveness of the proposed control algorithm is validated by simulations carried out on the system. The results are then compared with a traditional PI controller and a Lag compensator in cascade with a roll-off filter which further shows the beneficial effects of the proposed 4 - SMC.