Showing papers by "Tarek Ahmed-Ali published in 2017"

Exponential Stability Analysis of Sampled-Data ODE–PDE Systems and Application to Observer Design

Abstract: A small-gain approach is presented for analyzing exponential stability of a class of (dynamical) hybrid systems. The systems considered in the paper are composed of finite-dimensional dynamics, represented by a linear ordinary differential equation (ODE), and infinite-dimensional dynamics described by a parabolic partial differential equation (PDE). Exponential stability is established under conditions involving the maximum allowable sampling period (MASP). This new stability result is shown to be useful in the design of sampled-output exponentially convergent observers for linear systems that are described by an ODE–PDE cascade. The new stability result also proves to be useful in designing practical approximate observers involving no PDEs.

System identification of a class of Wiener systems with hysteretic nonlinearities

Abstract: Existing works on Wiener system identification have essentially been focused on the case where the output nonlinearity is memoryless. When memory nonlinearities have been considered, the focus has been restricted to backlash like nonlinearities. In this paper, we are considering Wiener systems where the output nonlinearity is a general hysteresis operator captured by the well-known Bouc-Wen model. The Wiener system identification problem is addressed by making use of a steady-state property, obtained in periodic regime, referred to as 'hysteretic loop assumption'. The complexity of this problem comes from the system nonlinearity as well as its unknown parameters that enter in a non-affine way in the model. It is shown that the linear part of the system is accurately identified using a frequency method. Then, the nonlinear hysteretic subsystem is identified, on the basis of a parameterized representation, using a prediction-error approach. Copyright © 2016 John Wiley & Sons, Ltd.

Observer design for triangular nonlinear systems in the presence of arbitrarily large output delay - a PDE based approach

Abstract: An observer design method is presented for a class of systems subject to sensor delay of any size. Accordingly, the delay is modelled by a first-order hyperbolic PDE, leading to an ODE-PDE cascade representation of the system. Then, a new observer is developed that relies on the full-order feedback-predictor PDE-based design and on the chain-predictor principle, so far only developed in the ODE framework. We show that the observer constructed in this manner is exponentially convergent.

An adaptive nonlinear controller for microgrid inverters

Abstract: In this paper, we propose an adaptive nonlinear controller for Voltage Source Inverters (VSI) used in microgrids. We aim to enforce the output voltage to track a given reference even if the load resistance is unknown and time variable. After the system modeling, the controller is designed using the backstepping technique and it includes an estimation of the load resistance. Many simulations have been carried out under different conditions to validate the designed controller. The simulation results show that the elaborated controller allows a perfect tracking of the reference voltage and an asymptotic stability. It is worth mentioning that the designed controller can operate in both microgrid modes: grid connected mode and islanded mode.