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Defense against cyberattacks is an emerging topic related to fault-tolerant control. In order to avoid difficult mathematical modeling, model-free control (MFC) is suggested as an alternative to classical control. For illustration purpose a Load Frequency Control of multi-areas power network is considered. In the simulations, load altering attacks and Denial of Service (DoS) in the communication network are applied to the system. Our aim is to compare the impact of cyberattacks on control loops closed via respectively a classical controller in such situations and a model-free one. Computer experiments show impressive results with MFC., Comment: 5th International Conference on Control and Fault-Tolerant Systems, Saint-Rapha\"{e}l, France, September 29th - October 1st, 2021

International audience; Non-residential buildings consume a significant amount of energy which represents a wide part of energy resources. Buildings are equipped with several systems like Lightning, HVAC (Heating, Ventilation and Air conditioning) ... Nevertheless, occupants' comfort is highly influenced by HVAC reliability. Moreover, HVAC energy consumption forms a significant among of total building consumption. HVAC system often has hidden performance problems leading to energy losses. In order to guarantee an acceptable comfort, energy savings and reduce maintenance costs, a proper maintenance of HVAC system is needed. Nowadays, traditional maintenance strategies are unable to provide an effective solution. HVAC performance problems can be avoided with the help of Predictive Maintenance. This later consist of diagnostic, prognostic and decision-making processes Predictive Maintenance has the ability to anticipate HVAC problems through prognostic. Then, maintenance decision is taken in order to perform the right maintenance and the right time.

International audience; In this paper a fault diagnosis and fault tolerant control based on model predictive control approach is applied for achieving efficiency in Nearly zero energy buildings. The system, for which the MPC-FDI/FTC controller has been developed, includes a heat pump for temperature regulation and a micro-grid energy system composed of PV panels, micro wind turbine, a battery pack. The objective is to meet the balance between energy production and consumption while minimizing the total cost of the energy drawn from the main grid and maintaining the building temperature within given bounds. Constraints concerning the system operation are also considered. Potential faults that may affect the efficiency of the system have been considered and the necessary actions to deal with them have been proposed.

Synergetic control is proposed for heating, ventilating and air-conditioning (HVAC) system control. The synergetic controller is developed using the nonlinear model of the HVAC system. Occupancy information in each zone is required in the design of the controller which offers inherent comfort according to the occupancy in the zone. The stability of the building system using the proposed control is verified through the Lyapunov approach. It is also proved that the synergetic controller is robust to external disturbances. Then, synergetic theories are used to design a reconfigurable control for damper stuck failures in variable air volume (VAV) to recover the nominal performance. Simulations are provided to validate the effectiveness of the proposed controller for a three-zone building.

International audience; In this paper, a resilient synergetic control is established to compensate for parametric actuator faults. The proposed strategy is based on the synergetic approaches to compensate for the dynamics fault effects and maintain the desired performance. The main idea is to estimate fault using an adaptive observer in the first place. Afterwards, the fault estimation will be integrated in the system dynamics. Then, a resilient synergetic control is designed using the new dynamics model. Simulation results prove the effectiveness of the proposed strategy.

Published in IFAC-PapersOnLine 51(11):453-458, 2018; International audience; To guarantee a good level of facilities performance (reliability and availability), maintenance activities have to be planned and scheduled efficiently. Maintenance scheduling decides, in a tactical way, when theses maintenance activities will be carried out according to the appearance of opportunities. Numerous works on opportunistic maintenance have been proposed in order to take profit of stochastic, structural and economic dependence. In the real context, the duration of an opportunity is not known accurately. Very few papers take into account the stochastic nature of opportunities duration. In this paper, we present an opportunistic maintenance scheduling methodology considering the stochastic nature of opportunities duration in a predictive maintenance strategy. The prognostic information is used to select opportunities coming before the failure. The proposed maintenance scheduling methodology is based on an optimal stopping problem algorithm known as Bruss algorithm. The originality of this paper is to consider the stochastic nature of opportunities duration using a Monte-Carlo simulation. A numerical study is finally presented to illustrate the use and the strengths of the proposed strategy.

In computing science, resilience is the ability of system or network architecture to recover normal operation after a brutal crash. When malicious cyber act on control signals of a Networked Control System (NCS) is designed to remain undetectable from passive model-based Fault Detection and Isolation (FDI) schemes, we show that the unobservable consequence on the state variable of the plant becomes brutally observable after the disappearance of the damaging action. In order to quickly recover the nominal behavior of the Linear Quadratic Gaussian (LQG) controller, a resilient LQG controller is obtained from an active version of the Generalized Likelihood Ratio (GLR) test designed to detect the disappearance of the malicious act and to increase the tracking ability of the Kalman filter at detection time.

In this chapter, we shall present the solution to the problem of Fault-tolerant Control (FTC) by taking the behavioral system theoretic viewpoint.

This chapter reviews the current and past status of the progress made in the area of FTC research. Most of the FTC techniques depends on the type of fault occurred into the system, where the FD plays a significant role. So, the chapter starts with classifying the types of faults followed by the discussion on fault diagnosis and the analysis of various FTC schemes.

In this chapter, we introduce basic concepts of the behavioral approach that put the foundation to address active FTC approaches in this book. We shall see here how the behaviors are described for a dynamical system. The elementary properties (for example linearity, time/shift invariance) associated with a dynamical system are discussed taking this behavioral point of view. As we mentioned (very briefly) in the last chapter, the real essence of this approach lies in its representation-free description. However, for the brevity of explanation, we shall often utilize kernel representations. These representations consider the polynomial matrices for describing a system, which are considered more general way of representing dynamical systems since these representations can easily be translated into either external-type or internal-type of representations by Chen (Linear systsem theory and design. Oxford University Press, New York, 1999, [18, Sects. 6–7]), Polderman and Willems (Introduction to mathematical systems theory: a behavioral approach. Springer, Berlin, 1997, [84]). To motivate further use of behavioral framework, we have considered various follow-up examples.

The prime aim of a fault-tolerant control system is to maintain the system performance, defined in terms of the desired behavior, at anytime, i.e., even after an occurrence of a fault. In previous two chapters, we presented novel real-time controller reconfiguration mechanisms to deal with the aforementioned issue.

International audience; Huge maintenance costs in non-residential buildings weighted it down the overall costs allocated to HVAC (Heating, ventilation and air conditioning) system maintenance. Maintenance Management objective is to reduce or even avoid the corrective maintenance by proper planning and implementation of maintenance tasks at the right time. The aim of this paper is to early plan maintenance interventions for a multi-components system based on stoppages characteristics, system RUL (Remaining Useful Life) and components criticalities. This maintenance plan is made through a dynamic maintenance decision approach (DMDA) to help the maintenance expert in taking decision. Since combining maintenance activities is cheaper than performing maintenance on components separately, maintenance actions groupings are performed in the proposed approach by the mean of odds algorithm. This will allow optimizing system availability, reducing maintenance costs and delaying as late as possible maintenance interventions. Components criticalities are used for prioritizing components in the grouping process. Moreover, DMDA take into account predictive information such as system/components RUL, given by an existing prognostic process. At the end, a numerical example of a HVAC system with five components (Heat exchanger, filter, dampers, valve and fan) demonstrates the use and the advantages of the proposed DMDA.

This paper considers the problem of attitude sensor fault diagnosis in a quadrotor helicopter. The proposed approach is composed of two stages. The first one is the modelling of the system attitude dynamics taking into account the induced communication constraints. Then a robust fault detection and evaluation scheme is proposed using a post-filter designed under a particular design objective. This approach is compared with previous results based on the standard Kalman filter and gives better results for sensor fault diagnosis.

This paper deals with a multi-objective fault detection observer design problem in time and frequency domain for time invariant systems. Firstly, to improve the abilities of designed observer, different design criteria are proposed, which are evaluated by some suitable performance indices in time and frequency domain. Details about the relationships among different criteria are analyzed for two cases when the fault appears and disappears. With selected residual evaluation function and threshold, a formula with an envelope in time domain to realize fast fault detection is proposed for some typical faults. The designed observer considers the trade-off between fast transients of the residual for specified faults and the traditional criterion H – /H ∞ for general faults and disturbances. Compared with H – /H ∞ frequency design method, the effectiveness of the proposed method is demonstrated by the numerical simulation with a vehicle lateral dynamics system.

International audience; Variable air volume (VAV) air-conditioning system is considered an energy-efficient solution for multi-zones building, which can meet the stringent cooling and heating demands of the occupants within individual zones. The role within this system is to feed zones with varying flow of constant temperature air independently supplied by an air-handling unit. A fault appearing in the VAV damper deteriorates severely the control performance and consequently, would not only affect the energy efficiency of the overall system but also lead to occupant discomfort. To circumvent this issue, we present a novel data-driven fault-tolerant control (FTC) scheme in this paper for a VAV thermal system within a multi-zone building. The novelty of the proposed strategy is that neither the thermal dynamical model is used in real-time, nor online identification of this model is required. The design of the FTC scheme is solely based on the online data generated by the process. The effectiveness of the developed scheme is demonstrated on a case-study of two-zones in a multi-storey building.

International audience; Security of Cyber-Physical Systems (CPS) against Cyber attacks has become an important challenging research field. If false data injections on control and/or measurement signals of a Fault-Tolerant Control System (FTCS) can be treated as detectable virtual actuator or sensor faults, the FTCS can automatically accommodate false data injections by triggering the controller reconfiguration mechanism at detection time given by the mode-based Fault Detection and Isolation (FDI) algorithm. After having shown that an intelligent adversary can destabilize the non minimum phase plant of the FTCS by designing a false data injection attack on the control signal while remaining undetectable from any passive FDI algorithm, this paper proposes to transform stealthy false data injections into detectable attacks from an active FTCS based on a switching Linear Quadratic Gaussian (LQG) controller and a confining coding method able to block the attack signal on a minimum number of encoded control signals.