Dear Colleagues,

The state of a dynamical system consists in the information that, together with the input, uniquely determines the output. In many cases, research on control theory is carried out under the supposition that the whole state is known by means of external measurements using a sensor. However, it is well known that one can use fewer sensors than there are states of systems due to economic costs or technological limitations. One of the more famous solutions to this problem is the design of algorithms of estimation or observers, i.e., dynamical systems capable of estimating internal information from measurements of the available input and output of that system. To encompass as much as possible all the properties of the system dynamics and to obtain more accurate and flexible structures, research has been conducted employing different modeling approaches using fractional calculus. Fractional calculus is a generalization of conventional integer-order calculus employing integrodifferential operators, for example, Caputo, Riemann–Liouville, Atangana–Baleanu, or Caputo–Fabrizio. Further generalizations are possible with Prabhakar fractional operators, Sonine-like generalized operators, and conformable and distributed-order derivatives.

This Special Issue addresses the newest developments in nonlinear observers’ theory of fractional-order systems modeled with different integrodifferential operators, convergence analysis utilizing the Lyapunov approach, observability properties of certain classes of nonlinear fractional-order systems, state reconstruction design by means of asymptotic and finite-time observers, observer-based controllers, separation principles in fractional systems, synchronization, and fault estimation.

Prof. Dr. Guillermo Fernández-Anaya
Dr. Oscar Martínez-Fuentes
Dr. Aldo Jonathan Muñoz-Vazquez
Guest Editors

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• nonlinear observers
• fractional differential equations
• generalized calculus
• observer theory
• fault detection
• synchronization
• observer-based controllers