International Journal of Digital Signals and Smart Systems (7 papers in press)
Fractional PID Controller design for Nonlinear Systems based on Singular Perturbation Technique.
by Mohamed Lazhar WARDI, Messaoud AMAIRI, Mohamed Naceur ABDELKRIM
Abstract: This paper deals with the output regulation of nonlinear control systems in order to guarantee desired performances in the presence of plant parameters variations and external disturbances. The proposed control law structures are based on the fractional order PI (FOPI) and PID (FOPID) control schemes. By introducing the two-time-scale notions in the closed-loop system, the presented design methodology of fractional PID control guarantees desired transients. Then, the singular perturbations technique is used to analyze the closed-loop system properties and to get explicit expressions for evaluation of the controller parameters. The tuning of the controller parameters is based on a constrained optimization algorithm. Simulation examples are presented to show the effectiveness of the proposed method.
Keywords: Fractional order controller; Nonlinear Systems; Singular Perturbations Technique; Robustness.
Actuator Fault Tolerant Control Of Disturbed Switched Hybrid Systems
by Salwa Yahia, Saida Bedoui, Kamel Abderrahim
Abstract: The present work treats the problem of actuator fault tolerant control (FTC)
for disturbed switched hybrid system. By extending the data-projection method (EDPM), the fault signal is estimated fast and properly. Then, using the unknown input observers, the unavailable state is estimated. Based on the estimated state and fault estimation information the fault tolerant control is performed to compensate the fault and to guarantee the stability of the system. In fact, the proposed FTC is designed by combined an additive control computed from the EDPM to the stabilizing control. The optimal gain matrices of the stabilizing control are computed using the Linear Matrix Inequalities (LMI) technique in order to ensure the stability of the system and to correct the effect of the fault correctly. The effectiveness of the proposed method was shown by a simulation example.
Keywords: Disturbed switched hybrid system; Actuator fault; Data-based Projection
Method; Fault tolerant control; Linear Matrix Inequalities; Unknown input observers.
Observer-based model reference control for linear fractional-order systems
by Assaad JMAL, Omar Naifar, Abdellatif Ben Makhlouf, Nabil Derbel, Mohamed Ali Hammami
Abstract: In the literature, the issue of designing model-reference controllers for integer-order systems has been extensively addressed. The extension of the existing works to the fractional-order calculus is still a fertile field of research. It is within this context that the present paper is established. Herein, a new observer-based model-reference control scheme is proposed for linear fractional-order systems. The developed methodology is based on the Caputo definition of fractional derivatives, the Lyapunov theory and the Linear Matrix Inequality (LMI) technique. Finally, a simulation study is given in order to support the theoretical findings of the paper.
Keywords: Model reference control; fractional-order systems; linear systems; observer.
Improved L2 L1 T-S Fuzzy Filtering For Discrete Stochastic Systems
by Taha Zoulagh, Bensalem Boukili, Abdelaziz Hmamed, Ahmed El Hajjjaji
Abstract: The problem of L2 L1 filtering for a class of Takagi-Sugeno (T-S)rnfuzzy stochastic systems is tackled in this paper. A new design method of fullrnorder filter is presented, that guarantees the asymptotic stability of filtering error system with a prescribed L2 L1 performance level. The filter parameters are assumed to be linearly dependent on the normalized fuzzy weighting functions.rnSufficient analysis condition is proposed in the filter analysis step where some know lemmas are applied, thereafter, the corresponding filter design is cast into a convex optimization problem. Finally, numerical example from literature is employed to demonstrate the effectiveness of the proposed method.
Keywords: L2-L1 filtering; Takagi-Sugeno (T-S)fuzzy systems; stochastic systems; slack variables; Linear matrix inequalities (LMIs).
Robust Discrete Sliding Mode Control for Non-minimum Phase Systems in Input-Output Representation
by Laila Mokhtar, Houda Ben Mansour, Ahmed Said Nouri
Abstract: This paper presents a control strategy for non-minimum phase systems using sliding mode control. As the discrete sliding mode control with input-output representation, with classical sliding function, is not applicable to non-minimum phase system, a generalized sliding surface was developed to overcome the problems of unstable zero. Then, a robustness analysis is conducted to determine the most appropriate choice of discrete sliding mode control for non-minimum phase systems. Simulation results prove the effectiveness of the proposed method.
Keywords: Non-minimum phase systems; Discrete time; Sliding mode; Control; Input-Output representation; Robustness analysis.
Cluster based Non-Local Filters for Colour Image denoising
by FARHA FATINA WAHID, SUGANDHI K, RAJU G
Abstract: Non-Local filters have evolved as an alternative to local filters for image denoising. Even though, these filters relay on the similarity of pixel neighbourhoods within a search window, there are chances that similar pixel neighbourhoods may not be present in the search window. This problem is resolved in Cluster based NLM (CNLM) a recent modification to the basic NLM. CNLM suggests an alternative method for the formation of search window. The pixels in a given image are divided into clusters. Clustering is carried out based on the similarity of neighbourhoods of pixels. A given pixel P belonging to a cluster C is modified as the weighted sum of all other pixels in C. In this paper, we have carried out an extensive study of the CNLM algorithm using colour images. Further, we experimented the cluster approach with Non-Local Euclidean Median Algorithm (NLEM) and Improved Non-Local Euclidean Median Algorithm (INLEM). The study reveals that the performance of cluster based approach is better than the respective basic algorithms for low noise densities in terms of performance evaluation measures.
Keywords: Image Filtering; NLM; CNLM; NLEM; INLEM; Clusters.
Logarithmic Cost Based Improved Constant Modulus (LCICM) Type Blind Channel Equalization Algorithm For M-QAM/M-PSK Signal
by Prakhar Priyadarshi, C.S. Rai
Abstract: In this paper, authors have proposed the blind channel equalization algorithm based on logarithmic cost function for QAM/PSK signal which is widely used in the digital communication system. CMA (Constant Modulus Algorithm) and MCMA (Modified Constant Modulus Algorithm) ,the two widely referenced algorithms for blind equalization of a QAM/PSK signal, exhibit very slow convergence rates and large steady-state mean square error. Proposed algorithm attains faster convergence speed and low steady state mean square error by incorporating the improved logarithmic cost based error function in the resilient back propagation based framework. This makes the weight adaption of equalizer simple. Simulation results show that the proposed algorithm has better convergence rate and lower steady state error in comparison to CMA and MCMA algorithms.
Keywords: Equalization; Logarithmic cost function; RPROP; CMA ;MCMA.