Australian Journal of Basic and Applied Sciences, 5(4): 207-222, 2011 ISSN 1991-8178 Intelligently Tuned Weights Based Robust H 4 Controller Design For Pneumatic Servo Actuator System With Parametric Uncertainty Hazem I. Ali, Samsul Bahari Mohd Noor, S. M. Bashi, Mohammad Hamiruce Marhaban Department of Electrical and Electronic Engineering, Faculty of Engineering, University Putra Malaysia, Malaysia Abstract: This paper presents a new method for tuning the weighing functions to design an H 4 controller. Based on a particle swarm optimization (PSO) algorithm the, weighting functions are tuned. The PSO algorithm is used to minimize the infinity norm of the transfer functions matrix of the nominal closed loop system to obtain the optimal parameters of the weighting function. This method is applied to a typical industrial pneumatic servo actuator controlled by a jet pipe valve. The pneumatic system nonlinearity and system parameters uncertainty are the main problems in the design of a desired controller for this plant. A linear model of the plant at certain operating point is derived and the structured (parametric) perturbations in the plant coeficients are taken into account. This method ensures an optimal robust stability and robust performance for the pneumatic servo actuator system. Simulation results are presented to verify the objectives of this method. Key words: Robust control, H 4 control, Pneumatic actuator, Nonlinear system, Uncertain system, PSO. INTRODUCTION A control system is robust if it remains stable and achieves certain performance criteria in the presence of possible uncertainties. The robust design is to find a controller, for a given system, such that the closed loop system is robust. The H 4 optimization approach and its related approaches, being developed in the last two decades and still an active research area, have been shown to be effective and efficient robust design methods for linear, time invariant control systems (Da-Wei et al, 2005). The goal of robust systems design is to retain assurance of system performance in spite of model inaccuracies and changes. A system is robust when it has acceptable changes in performance due to model changes or inaccuracies. A control system is robust when (i) it has low sensitivity, (ii) it is stable over the range of parameter variations and (iii) the performance continues to meet the specification in the presence of a set of changes in the system parameters (Dorf, 2001). H 4 is one of the most known techniques available nowadays for robust control. It is a method in control theory for the design of optimal controllers. Basically, it is an optimization method that takes into consideration a strong definition of the mathematical way to express the ability to include both classical and robust control concepts within a single design framework. It is known that H 4 control is an effective method for attenuating disturbances and noise that appear in the system. It has been proven to be one of the best techniques in linear control system (Alok, 2007). Robust control techniques such as modern H 4 and classical quantitative feedback theory (QFT) have received comparatively little attention in the fluid power literature, especially with regard to pneumatic systems (Mark and Nariman, 2004). High performance position control of pneumatic actuators remains a difficult task. In most industrial applications, safety requires that the pressure of the air supply be kept low, which makes it difficult to design high bandwidth systems. Moreover, low supply pressure tends to limit the achievable actuator stiffness, which affects the ability of the servomechanism to reject disturbing loads. Nonlinear control valve flows and uncertainties in the plant parameters also complicate the design of high performance pneumatic servos. On the other hand, the pneumatic actuators are widely employed in position and speed control applications when cheap, clean, simple, and safe operating conditions are required. In recent years, low cost microprocessors and pneumatic components became available in the market, which made it possible to adopt more sophisticated control strategies in pneumatic system control (Jihong et al, 2007). The pneumatic cylinders can offer a better alternative to electrical or hydraulic actuators for certain types of applications and the pneumatic actuators Corresponding Author: Hazem I. Ali, Department of Electrical and Electronic Engineering, Faculty of Engineering, University Putra Malaysia, Malaysia E-mail: hazemcontrol2001@yahoo.com 207