A review of convex approaches for control, observation and safety of linear parameter varying and Takagi-Sugeno systems

This paper provides a review about the concept of convex systems based on Takagi-Sugeno, linear parameter varying (LPV) and quasi-LPV modeling. These paradigms are capable of hiding the nonlinearities by means of an equivalent description which uses a set of linear models interpolated by appropriately defined weighing functions. Convex systems have become very popular since they allow applying extended linear techniques based on linear matrix inequalities (LMIs) to complex nonlinear systems. This survey aims at providing the reader with a significant overview of the existing LMI-based techniques for convex systems in the fields of control, observation and safety. Firstly, a detailed review of stability, feedback, tracking and model predictive control (MPC) convex controllers is considered. Secondly, the problem of state estimation is addressed through the design of proportional, proportional-integral, unknown input and descriptor observers. Finally, safety of convex systems is discussed by describing popular techniques for fault diagnosis and fault tolerant control (FTC).Peer ReviewedPostprint (published version

A virtual actuator approach for the secure control of networked LPV systems under pulse-width modulated DoS attacks

In this paper, we formulate and analyze the problem of secure control in the context of networked linear parameter varying (LPV) systems. We consider an energy-constrained, pulse-width modulated (PWM) jammer, which corrupts the control communication channel by performing a denial-of-service (DoS) attack. In particular, the malicious attacker is able to erase the data sent to one or more actuators. In order to achieve secure control, we propose a virtual actuator technique under the assumption that the behavior of the attacker has been identified. The main advantage brought by this technique is that the existing components in the control system can be maintained without need of retuning them, since the virtual actuator will perform a reconfiguration of the plant, hiding the attack from the controller point of view. Using Lyapunov-based results that take into account the possible behavior of the attacker, design conditions for calculating the virtual actuators gains are obtained. A numerical example is used to illustrate the proposed secure control strategy.Peer ReviewedPostprint (author's final draft

Review of selection criteria for sensor and actuator configurations suitable for internal combustion engines

This literature review considers the problem of finding a suitable configuration of sensors and actuators for the control of an internal combustion engine. It takes a look at the methods, algorithms, processes, metrics, applications, research groups and patents relevant for this topic. Several formal metric have been proposed, but practical use remains limited. Maximal information criteria are theoretically optimal for selecting sensors, but hard to apply to a system as complex and nonlinear as an engine. Thus, we reviewed methods applied to neighboring fields including nonlinear systems and non-minimal phase systems. Furthermore, the closed loop nature of control means that information is not the only consideration, and speed, stability and robustness have to be considered. The optimal use of sensor information also requires the use of models, observers, state estimators or virtual sensors, and practical acceptance of these remains limited. Simple control metrics such as conditioning number are popular, mostly because they need fewer assumptions than closed-loop metrics, which require a full plant, disturbance and goal model. Overall, no clear consensus can be found on the choice of metrics to define optimal control configurations, with physical measures, linear algebra metrics and modern control metrics all being used. Genetic algorithms and multi-criterial optimisation were identified as the most widely used methods for optimal sensor selection, although addressing the dimensionality and complexity of formulating the problem remains a challenge. This review does present a number of different successful approaches for specific applications domains, some of which may be applicable to diesel engines and other automotive applications. For a thorough treatment, non-linear dynamics and uncertainties need to be considered together, which requires sophisticated (non-Gaussian) stochastic models to establish the value of a control architecture

Real-time implementation of an ISM Fault Tolerant Control scheme for LPV plants

Copyright © 2014 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper proposes a fault tolerant control scheme for linear parameter varying systems based on integral sliding modes and control allocation, and describes the implementation and evaluation of the controllers on a 6 degree-of-freedom research flight simulator called SIMONA. The fault tolerant control scheme is developed using a linear parameter varying approach to extend ideas previously developed for linear time invariant systems, in order to cover a wide range of operating conditions. The scheme benefits from the combination of the inherent robustness properties of integral sliding modes (to ensure sliding occurs throughout the simulation) and control allocation, which has the ability to redistribute control signals to all available actuators in the event of faults/failures

Decentralized and Fault-Tolerant Control of Power Systems with High Levels of Renewables

Inter-area oscillations have been identified as a major problem faced by most power systems and stability of these oscillations are of vital concern due to the potential for equipment damage and resulting restrictions on available transmission capacity. In recent years, wide-area measurement systems (WAMSs) have been deployed that allow inter-area modes to be observed and identified.Power grids consist of interconnections of many subsystems which may interact with their neighbors and include several sensors and actuator arrays. Modern grids are spatially distributed and centralized strategies are computationally expensive and might be impractical in terms of hardware limitations such as communication speed. Hence, decentralized control strategies are more desirable.Recently, the use of HVDC links, FACTS devices and renewable sources for damping of inter-area oscillations have been discussed in the literature. However, very few such systems have been deployed in practice partly due to the high level of robustness and reliability requirements for any closed loop power system controls. For instance, weather dependent sources such as distributed winds have the ability to provide services only within a narrow range and might not always be available due to weather, maintenance or communication failures.Given this background, the motivation of this work is to ensure power grid resiliency and improve overall grid reliability. The first consideration is the design of optimal decentralized controllers where decisions are based on a subset of total information. The second consideration is to design controllers that incorporate actuator limitations to guarantee the stability and performance of the system. The third consideration is to build robust controllers to ensure resiliency to different actuator failures and availabilities. The fourth consideration is to design distributed, fault-tolerant and cooperative controllers to address above issues at the same time. Finally, stability problem of these controllers with intermittent information transmission is investigated.To validate the feasibility and demonstrate the design principles, a set of comprehensive case studies are conducted based on different power system models including 39-bus New England system and modified Western Electricity Coordinating Council (WECC) system with different operating points, renewable penetration and failures

Fault tolerant LPV control of the GTM UAV with dynamic control allocation

The aim of the paper is to present a dynamic control allocation architecture for the design and development of reconfigurable and fault-tolerant control systems in aerial vehicles. The baseline control system is designed for the nominal dynamics of the aircraft, while faults and actuator saturation limits are handled by the dynamic control allocation scheme. Coordination of these components is provided by a supervisor which re-allocates control authority based on health information, flight envelope limits and cross coupling between lateral and longitudinal motion. The monitoring components and FDI filters provide the supervisor with information about different fault operations, based on that it is able to make decisions about necessary interventions into the vehicle motions and guarantee fault-tolerant operation of the aircraft. The design of the proposed reconfigurable control algorithm is based on Linear Parameter-varying (LPV) control methods that uses a parameter dependent dynamic control allocation scheme. The design is demonstrated on the lateral axis motion of the NASA AirSTAR Flight Test Vehicle simulation model

Advanced information processing system for advanced launch system: Avionics architecture synthesis

The Advanced Information Processing System (AIPS) is a fault-tolerant distributed computer system architecture that was developed to meet the real time computational needs of advanced aerospace vehicles. One such vehicle is the Advanced Launch System (ALS) being developed jointly by NASA and the Department of Defense to launch heavy payloads into low earth orbit at one tenth the cost (per pound of payload) of the current launch vehicles. An avionics architecture that utilizes the AIPS hardware and software building blocks was synthesized for ALS. The AIPS for ALS architecture synthesis process starting with the ALS mission requirements and ending with an analysis of the candidate ALS avionics architecture is described

Active actuator fault-tolerant control of a wind turbine benchmark model

This paper describes the design of an active fault-tolerant control scheme that is applied to the actuator of a wind turbine benchmark. The methodology is based on adaptive filters obtained via the nonlinear geometric approach, which allows to obtain interesting decoupling property with respect to uncertainty affecting the wind turbine system. The controller accommodation scheme exploits the on-line estimate of the actuator fault signal generated by the adaptive filters. The nonlinearity of the wind turbine model is described by the mapping to the power conversion ratio from tip-speed ratio and blade pitch angles. This mapping represents the aerodynamic uncertainty, and usually is not known in analytical form, but in general represented by approximated two-dimensional maps (i.e. look-up tables). Therefore, this paper suggests a scheme to estimate this power conversion ratio in an analytical form by means of a two-dimensional polynomial, which is subsequently used for designing the active fault-tolerant control scheme. The wind turbine power generating unit of a grid is considered as a benchmark to show the design procedure, including the aspects of the nonlinear disturbance decoupling method, as well as the viability of the proposed approach. Extensive simulations of the benchmark process are practical tools for assessing experimentally the features of the developed actuator fault-tolerant control scheme, in the presence of modelling and measurement errors. Comparisons with different fault-tolerant schemes serve to highlight the advantages and drawbacks of the proposed methodology

Controle reconfigurável de processos sujeitos a falhas em atuadores : uma abordagem baseada no MPC em duas camadas

Orientadores: Flávio Vasconcelos da Silva, Thiago Vaz da CostaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia QuímicaResumo: Plantas industriais modernas estão suscetíveis a falhas em equipamentos de processo e em instrumentos e componentes da malha de controle. Tais eventos anormais podem acarretar danos a equipamentos, degradação do desempenho do processo e até cenários extremos como a parada da planta e acidentes graves. Em vista disso, o emprego de sistemas de controle tolerante a falhas visa a elevar o grau de confiabilidade e segurança do processo por meio do tratamento e mitigação de eventos anormais, evitando que evoluam para situações críticas. Nesse sentido, este trabalho tem como objetivo desenvolver uma técnica de controle reconfigurável tolerante a falhas para processos sujeitos a falhas em atuadores. A presente proposta é baseada em abordagens por atuadores virtuais e ocultação da falha. Essas técnicas consistem no recálculo das ações de controle e na ocultação da falha do ponto de vista do controlador nominal, permitindo que o mesmo seja mantido após a reconfiguração da malha de controle. Na presente proposta, o atuador virtual é baseado na estrutura do controlador preditivo em duas camadas. Uma camada consiste no cálculo de referências para as variáveis de entrada e para o desvio previsto entre o comportamento da planta nominal e com falha. A outra camada, por sua vez, é responsável por conduzir as variáveis de processo para as referências calculadas na etapa anterior. Ambas as camadas são baseadas em problemas de programação quadrática e levam em consideração as restrições do processo, como limites de atuadores e desvios permissíveis em relação ao comportamento nominal da planta. Essa técnica possibilita a consideração de cenários de falhas nos quais não há graus de liberdade suficientes para a manutenção de variáveis controladas em valores desejados. Assim, a estimativa de perturbações permite que novas referências atingíveis sejam calculadas, ainda que haja erros de identificação do modelo pós-falha do processo. Por fim, a estrutura de controle proposta foi aplicada em simulações utilizando um processo de tanques quádruplos, bem como em experimentos conduzidos em uma planta de neutralização de pHAbstract: Modern industrial plants are susceptible to faults in process equipment and in instruments and components of the control loop. Such abnormal events can lead to equipment damage, degradation of process performance and even extreme scenarios such as plant shutdown and serious accidents. Thus, the use of fault-tolerant control systems aims to increase process reliability and safety by treating and mitigating abnormal events, preventing them from evolving to critical situations. In this sense, this work aims to develop a reconfigurable fault tolerant control technique for processes subject to actuator faults. The present proposal is based on the virtual actuator and fault hiding approaches. These techniques consist of recomputing control actions and hiding the fault from the nominal controller perspective, allowing it to be maintained after the control loop reconfiguration. We propose a virtual actuator based on the two-layer model predictive control structure. One layer consists of calculating references for input variables and for the predicted deviation between the nominal and faulty plant behaviors. The other layer, in turn, is responsible for driving process variables to the references calculated in the previous step. Both layers are based on quadratic programming problems and take into account process constraints such as actuator limits and permissible deviations from the nominal plant behavior. This technique allows the consideration of fault scenarios in which there are not enough degrees of freedom for the maintenance of controlled variables in desired values. Thus, disturbance estimation allows the calculation of new achievable references, even though there are identification errors in the post-fault model. Finally, the proposed control structure has been applied to an experimental pH neutralization plant. Finally, the proposed control structure was applied in simulations to a quadruple-tank process as well as in experiments conducted in a pH neutralization plantMestradoSistemas de Processos Quimicos e InformaticaMestre em Engenharia Química130952/2015-0CNP