Abstract: In this thesis, robust controllers for autonomous hyperchaotic system in the presence of desirable factors such as additive matched unstructured uncertainty, external disturbance and nonlinear control input are designed. Hyperchaotic systems have two positive lyapunov exponents and are more complex than low dimensional chaotic systems. In practice, due to physical constrains, control signals may fail to be apply linearly so other nonlinear forms of assumed control signal are exerted to system which are called nonlinear control inputs. In such occasions, designed goals of closed loop hyperchaotic system must be achieved. Adopting sliding mode control as basic method to design robust controllers, different sliding surfaces such as estimative sliding surface and proportional integral sliding surface are defined. To overcome chattering phenomenon which suppose to be a major weak point in sliding mode controllers, a new approach is discussed through analysis as well as simulation results. This approach contains replacing sign function with functions such as saturation function and fuzzy function. Fuzzy function introduces fuzzy-sliding mode control in hyperchaotic systems. In addition to sliding mode control advantages, this method remove high frequency switching by fuzzy controllers. Next, in this thesis, sliding mode control and H∞ control are combined to reach following gaols: 1: Reduction of H∞ norm of the closed loop transfer function from disturbance to controlled output of hyperchaotic systems. 2: Ability to meet certain performance indices. LMI technique is used to solve H∞ problem. Considering each of designed controllers, stability of closed loop hyperchaotic systems is proved analytically. Initial studies of this thesis led to introduction of two new hyperchaotic systems which their properties are discussed. Design controllers are simulated to exhibit their strong performance. | 
