International Journal of Electrical and Computer Engineering (IJECE) Vol. 8, No. 4, August 2018, pp. 2148~2156 ISSN: 2088-8708, DOI: 10.11591/ijece.v8i4.2148-2156  2148 Journal homepage: http://iaescore.com/journals/index.php/IJECE Optimization of Modified Sliding Mode Controller for an Electro-hydraulic Actuator System with Mismatched Disturbance Siti Marhainis Othman 1 , M. F. Rahmat 2 , S. M. Rozali 3 , Zulfatman Has 4 , A. F. Z. Abidin 5 1,2 Department of Control and Mechatronics Engineering, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, Malaysia 1 Mechatronic Engineering Programme, School of Mechatronic Engineering, Universiti Malaysia Perlis 3,5 Department of Electrical Engineering Technology, Faculty of Engineering Technology, Universiti Teknikal Malaysia Melaka, Malaysia 4 Dept. of Electrical Engineering, University of Muhammadiyah Malang, Kota Malang, Indonesia Article Info ABSTRACT Article history: Received Aug 28, 2017 Revised Feb 14, 2018 Accepted Apr 4, 2018 This paper presents the design of the modified sliding mode controller (MSMC) for the purpose of tracking the nonlinear system with mismatched disturbance. Provided that the performance of the designed controller depends on the value of control parameters, gravitational search algorithm (GSA), and particle swarm optimization (PSO) techniques are used to optimize these parameters in order to achieve a predefined system’s performance. In respect of system’s performance, it is evaluated based on the tracking error present between reference inputs transferred to the system and the system output. This is followed by verification of the efficiency of the designed controller in simulation environment under various values, with and without the inclusion of external disturbance. It can be seen from the simulation results that the MSMC with PSO exhibits a better performance in comparison to the performance of the similar controller with GSA in terms of output response and tracking error. Keyword: Electro-hydraulic actuator Gravitational particle swarm Gravitational search algorithm Modified sliding mode control Particle swarm optimization Sum square error Copyright © 2018 Institute of Advanced Engineering and Science. All rights reserved. Corresponding Author: M. F. Rahmat, Department of Control and Mechatronics Engineering, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, Malaysia. Email: fuaad@fke.utm.my 1. INTRODUCTION Electro-Hydraulic Actuator (EHA) system is one of the important drive systems in industrial sectors and most engineering practices. However, the system is highly nonlinear due to many factors, such as leakage, friction, and especially the expression of fluid flow through the servo valve [12]. With these attributes being present, the system’s performance will be reduced significantly. In order to overcome the issue previously highlighted, the controller utilized for the system should be robust enough to overcome the entire operating range. Therefore, a suitable controller needs to be designed for a positive performance to be shown by the electro-hydraulic actuator. The raised numbers of works conducted with electro-hydraulic actuator system have been proposed over the past decades ranged from linear control, nonlinear control to intelligent control strategies such as [3]-[6] have been proposed over the past decades. Based on the literature study in [7]-[10], sliding mode control (SMC) is found to be efficient and widely applied in nonlinear systems [11]. However, it has been noticed that most of the existing results regarding the sliding surface design are more emphasized on the matched uncertainties and disturbances attenuation, provided the insensitivity of the sliding motion of