International Journal of Control and Automation Vol. 9, No. 4 (2016), pp. 149-160 http://dx.doi.org/10.14257/ijca.2016.9.4.15 ISSN: 2005-4297 IJCA Copyrightⓒ 2016 SERSC Robust Control of Vehicle Active Suspension System Narinder Singh 1 , Himanshu Chhabra 2 and Karansher Bhangal 3 Instrumentation and Control Engineering and Computer Science and Engineering 1 BR AmbedkarNational Institute of Technology . Jalandhar, India 2 BR.Ambedkar National Institute of Technology.Jalandhar, India 3 PEC University of Tech. Chandigarh, India 1 nsbhangal@yahoo.co.in, 2 him08miet@gmail.com, 3 karansherbhangal@gmail.com Abstract In order to improve the road handling and passenger comfort of a vehicle, suspension is provided. An active suspension is considered to be better than a passive suspension. In this paper, 2 degree of freedom model of quarter car active suspension system is designed, which is subjected to road disturbance. Due to the fact that strong nonlinearity inherently exist in the spring ,damper and actuator components, therefore nonlinear effects must be taken into account in designing the controller for practical suspension systems. Since parametric uncertainty in the spring, damper and actuator has been considered, therefore robust control is used. H ∞ and μ- synthesis controllers are used to improve the ride comfort and road handling ability of the car as well as to check the robust performance of the system. The results shows that both controllers give good performance, but μ synthesis controller has superior robust performance as compared to H ∞ controller as well as settling time of body acceleration and suspension deflection is also minimum with μ synthesis controller. Keywords: Quarter Vehicle Active Suspension System (QVASS), Linear Fractional Transformation (LFT), H ∞ Controller, μ- Synthesis Controller 1. Introduction The purpose of a car is to adequately support the physical body, to maintain tire contact with the ground and to manage the compromise between passenger comfort and vehicle road handling. This is important for the safety of the ride. Suspension consists of system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Generally, there are three types of suspension systems, namely, passive, semi active and active suspensions. Passive suspension has the ability to store energy via a spring and dissipate it via a damper. Passive suspensions can only achieve good ride comfort or good road handling since these two criteria conflict each other and involve different spring and damper characteristics. Semi-active suspensions with their variable damping characteristics and low power consumption, offers a considerable improvement. A significant improvement can be achieved by using a active suspension system. The active suspension system able to inject energy into the vehicle dynamic system via actuator. The force actuator is able to add and dissipate energy from the system. This force may be function of several variables, which can be measured or sensed by sensors, so the flexibility can be greatly improved. In recent past, a study of active suspension model and various types of controllers used had been reported [1].A comparison between passive and active suspension systems had been reported [2]. The aim is to achieve small amplitude value for suspension travel, wheel deflection and car body acceleration, LQR control is found to be better. It is noted that system parametric variation, which is caused by environmental changes or worn and