In this paper, a fuzzy logic controller is designed for controlling non-linear behaviours in a rod-type plasma torch system. This system may behave chaotically when its parameters pass through critical values, and gives rise to undesirable oscillations, which degrade the performance of the system. In order to avoid such behaviours, the state feedback controller and the terminal sliding mode controller are combined into a fuzzy system to stabilize the equilibrium point of the system. The fuzzy rules include consequent parts in which state feedback control or terminal sliding mode control is utilized for different conditions. The proposed scheme provides the advantages of both methods, i.e. a decreased settling time is achieved using terminal sliding mode control, and using state feedback control, the chattering phenomenon is removed. The proposed method provides robustness against the external disturbance and uncertainty. Numerical simulations are given to verify that the proposed fuzzy control scheme can effectively control chaotic behaviour of the rod-type plasma torch system and the method provides the best performance among the other methods discussed in the paper.
This paper proposes a fuzzy predictive control scheme for controlling power output of a boiler−turbine system in the presence of disturbances and uncertainties. A new model of the boiler−turbine system is introduced based on the modeling approaches of hybrid systems, namely, the mixed logical dynamical modeling approach. Nonlinear parts of the system are linearized using the piecewise affine approach. To overcome the deficiency of the model predictive control in presence of disturbance and uncertainty, a fuzzy predictive control scheme is proposed in which a fuzzy supervisor is utilized to adjust the main predictive controller. The proposed fuzzy predictive control scheme has advantages such as simplicity and efficiency in nominal conditions and strong robustness in the presence of disturbances and uncertainties. Simulation results demonstrate the effectiveness and superiority of the method. 2 3 1 4 5(2-3)
An integral terminal sliding mode controller is proposed in order to control chaos in a rod-type plasma torch system. In this method, a new sliding surface is defined based on a combination of the conventional sliding surface in terminal sliding mode control and a nonlinear function of the integral of the system states. It is assumed that the dynamics of a chaotic system are unknown and also the system is exposed to disturbance and unstructured uncertainty. To achieve a chattering-free and high-speed response for such an unknown system, an adaptive neuro-fuzzy inference system is utilized in the next step to approximate the unknown part of the nonlinear dynamics. Then, the proposed integral terminal sliding mode controller stabilizes the approximated system based on Lyapunov's stability theory. In addition, a Bee algorithm is used to select the coefficients of integral terminal sliding mode controller to improve the performance of the proposed method. Simulation results demonstrate the improvement in the response speed, chattering rejection, transient response, and robustness against uncertainties.
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