Mohamed Djemai

On the robust fault detection via a sliding mode disturbance observer

This paper deals with robust fault detection for non-linear systems. This problem is usually solved by designing an observable subsystem which is only affected by the fault and not by the control and disturbance inputs. However, such a subsystem may not exist so that the so-called fundamental problem of residual generation (FPRG) is not solvable. The aim of the present paper is to design a fault detection filter when the conditions for the existence of a solution to the non-linear FPRG are not satisfied. Our approach is made in a geometric context. Under some decoupling assumptions, the design of sliding mode observers allows us to reconstruct the disturbance inputs and then to generate an effective residual. An illustrative example is given throughout the paper.

Sliding mode observer for triangular input form

This paper discusses the problem of designing an observer for nonlinear systems. In Drakunov and Utkin (1995) a new concept of sliding observers was introduced, where the key point is that the equivalent control concept is extensively used. Moreover, in Boukhobza, Djemai, and Barbot (1996) we use a classical sliding mode observer in order to design an observer for the largest class with the so-called output injection form. Here, our purpose is to discuss the observer design for a system in a triangular input observer form. For a system in a triangular input observer form there is no problem of singular input. The second purpose of this paper is to show how to use the anti-peaking sliding method in the case of successive equivalent vectors.

Robust finite time observer design for multicellular converters

In this article, a nonlinear finite time observer is designed for multicellular converters. The aim is to estimate the capacitor voltages by taking into account the hybrid behaviour of the converter. This article extends the validity of the strong Lyapunov function, proposed in Moreno and Osorio (Moreno, J., and Osorio, M. (2008), ‘A Lyapunov Approach to Second Order Sliding Mode Controllers and Observers’, in Proceedings of the IEEE Conference on Decision and Control, New Orleans, USA, pp. 2856–2861), in order to deeply study the reaching time estimation and robustness of the homogeneous finite time observer given in Perruquetti et al. (Perruquetti, W., Floquet, T., and Moulay, E. (2008), ‘Finite Time Observers: Application to Secure Communication’, IEEE Transactions on Automatic Control, 53, 356–360). The proposed approach enables the stabilisation of the observation errors in spite of the presence of perturbations and uncertainties. Some simulations and comparisons with the super-twisting sliding mode observer highlight the efficiency of the proposed strategy.

A New Control Strategy of an Electric-Power-Assisted Steering System

The control of electric-power-assisted steering (EPAS) systems is a challenging problem due to multiple objectives and the need for several pieces of information to implement the control. The control objectives are to generate assist torque with fast responses to drivers torque commands, ensure system stability, attenuate vibrations, transmit the road information to the driver, and improve the steering wheel returnability and free-control performance. The control must also be robust to modeling errors and parameter uncertainties. To achieve these objectives, a new control strategy is introduced in this paper. A reference model is used to generate an ideal motor angle that can guarantee the desired performance, and then, a sliding-mode control is used to track the desired motor angle. This reference model is built using a dynamic mechanical EPAS model, which is driven by the driver torque, the road reaction torque, and the desired assist torque. To implement the reference model with a minimum of sensors, a sliding-mode observer with unknown inputs and robust differentiators are employed to estimate the driver torque, the road reaction torque, and the systems states. With the proposed control strategy, there is no need for different algorithms, rules for switching between these algorithms, or fine-tuning of several parameters. In addition, our strategy improves system performance and robustness and reduces costs. The simulation results show that the proposed control structure can satisfy the desired performance.

High-order sliding mode control of a DC motor drive via a switched controlled multi-cellular converter

In this article, we present a high-order sliding mode controller of a DC motor drive connected to a multi-cellular converter. More specifically, we design a second-order (super-twisting) control algorithm for the speed regulation of a DC motor. For this, a switching control for the multi-cellular converter is derived in order to supply the correct reference value for the speed regulation. A practical implementation of the controller is realised using a laboratory set-up. The performance and the validity of the controller are shown experimentally.

Sliding Mode Based Analysis and Identification of Vehicle Dynamics

Vehicles are complex mechanical systems with strong nonlinear characteristics and which can present some uncertainties due to their dynamic parameters such as masses, inertias, suspension springs, tires side slip coefficients, etc. A vehicle is composed of many parts, namely the unsprung mass, the sprung mass, the suspension which makes the link between these two masses and therefore ensures passenger comfort, and also the pneumatic which absorbs the energy coming from the road and ensures contact between the vehicle and the road. In addition to its complexity and the presence of many nonlinearities and uncertainties, the presence of some external perturbations, such as the wind and the road inputs with its own characteristics (radius of curvature, longitudinal and lateral slop, road profile and skid resistance) can cause risks not only to the vehicle but also to passengers and other road users. Many methods have been developed in order to understand the behavior of a vehicle, control it and assist the driver in order to avoid possible lane departures, rollover or jackknifing risks, to ensure a better passenger comfort by means of a suspension control and/or to estimate a safety speed and trajectory. The present book is an attempt to show how the sliding mode based observation, uncertainties identification and parameter estimation may be applied in the control of vehicle dynamics as well as for parameter and perturbations estimation. This book is the first of long series of books in the field of variable structure system in automotive application. Some other results and tools will be proposed and explained in the next publications

Nonlinear control with flux observer for a singularly perturbed induction motor

This paper provides a feedback composite control with nonlinear sliding-mode flux observer for an induction motor using singular perturbation methods. This feedback is composed of slow and fast parts. The authors prove the stability of the closed-loop system with observer. This decomposition simplifies the control scheme which is computed separately on the basis of two subsystems (slow and fast). The control of an induction motor is considered as a case study.<<ETX>>

Hybrid sliding mode observer for switched linear systems with unknown inputs

Abstract This paper addresses the state observation and unknown input estimation of a class of switched linear systems with unknown inputs. This class of systems may have modes in which the state is not fully observable. A state transformation allows implementing two suitable reduced-order observers. The first one, based on second order sliding mode techniques, is proposed to reconstruct the discrete state in the presence of unknown inputs. The second one, based on gathering partial information from individual modes of the switched system and on higher order sliding mode techniques, is introduced to estimate the continuous state. Then, the observer injection signal of the first second order sliding mode observer is used to estimate the unknown inputs. Simulation results highlight the efficiency of the proposed method.

Nonlinear Sliding Observer for Systems in Output and Output Derivative Injection Form

Abstract Necessary and sufficient conditions to obtain output and outputs derivative injection form are given. From this form, a sliding observer design is presented. The paper starts and ends with examples illustrating the proposed method.

Control of an Electric Power Assisted Steering system using reference model

This paper presents a new control strategy of Electric Power Assisted Steering (EPAS) systems to ensure several control objectives. First, a reference model is employed to generate ideal motor angle that can guarantee the control objectives, assist torque generation, fast response to drivers torque command, vibration attenuation, supplying road information to the driver, improving steering wheel returnability and free control performance. Second, a sliding mode control law is used to track the desired motor angle. Finally, a sliding mode observer with unknown inputs and robust differentiators are designed to implement the reference model. Simulation results show that the proposed control structure can satisfy the desired performance.